Antoine Gardarin
email: antoine.gardarin@inra.fr

Manuel Plantegenest

Armin Bischoff

Muriel Valantin-Morison

Understanding plant-arthropod interactions in multitrophic communities to improve conservation biological control: useful traits and metrics

Keywords: entomophagous arthropods, flower strip, functional diversity, functional trait, interaction trait, natural enemy

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Introduction

There is increasing evidence that semi-natural habitats provide a wide range of services (Wratten et al. 2012) dependent on ecosystem functioning and on its interactions with the management of these habitats. The role of biodiversity in ecosystem service provisioning is increasingly being studied by trait-based functional approaches investigating the relationships between environmental variables, including habitat management, and ecosystem functioning, community assembly and structure. Traitbased approaches are widely used in plant ecology (e.g. Lavorel et al. 2011) and have been extended to studies of other taxonomic groups, such as soil invertebrates (Birkhofer et al. 2017;Pey et al. 2014), but studies connecting different trophic levels on the basis of their traits remain rare [START_REF] Boukal | Trait-and size-based descriptions of trophic links in freshwater food webs: current status and perspectives[END_REF]; but see Moretti et al. 2013).

Several ecosystem services, such as herbivore regulation, pollination and biogeochemical cycles, are dependent on multitrophic interactions, and there is an urgent need to improve our understanding of the relationships between plant and animal communities (Wood et al. 2015). The functioning of species-rich assemblages involved in interaction networks has been little studied to date and the mechanisms underlying the functioning of such assemblages remain poorly understood and quantified (Violle et al. 2014). Correlations have recently been found between the functional composition of vegetation and the abundance of phytophagous invertebrates in agroecosystems (Storkey et al. 2013) and natural habitats [START_REF] Frenette-Dussault | Linking plant and insect traits to understand multitrophic community structure in arid steppes[END_REF]. Here, we extend the trait-based framework of Lavorel et al. (2013), which focused on trophic interactions, to non-trophic interactions, and we explain how it applies to conservation biological control in agroecosystems.

Our understanding of interactions between plant and animal communities and their effect on the biological control of pests remains limited. Conservation biological control aims to increase the abundance, diversity and efficacy of natural enemies through environmental management and the adoption of particular agricultural practices. Species-rich habitats, such as linear field margins between crop fields, support populations of the natural enemies of pests, and therefore help to improve the biological control of crop herbivores (Bischoff et al. 2016). Their effects are thought to be mediated by plant species composition (Haaland et al. 2011). The plant species found in these habitats provide functions not supplied by crop plants. This is obvious in natural enemies of crop herbivores that depend on specific plant resources at particular stages of their life cycle, such as hoverflies and parasitic wasps do. The role of plant species composition is less obvious for groups of natural enemies that do not feed on plants. For ground beetles, spiders and ground-dwelling arthropods, vegetation cover via structure-mediated effects is as important, or more, than resource-mediated effects (Balzan et al. 2016;[START_REF] Diehl | Arable weeds in organically managed wheat fields foster carabid beetles by resource-and structure-mediated effects[END_REF].

If the implementation or the management of habitats to enhance functional biodiversity increases natural enemy populations, this does not necessarily result in a significant reduction of crop herbivores. The performance of these populations, in terms of biological control, depends on many other factors and interactions (Jonsson et al. 2008), and we are often unable to understand why some plant species mixtures perform better than other ones. There is also currently no methodology for knowledge transfer concerning the biological control efficiency of a given plant mixture to facilitate the choice of new sets of species adapted to other agronomic and climatic situations. Previous studies on trophic and non-trophic interactions within and between plant and animal communities focused principally on analyses of biological diversity through taxonomic approaches or on the global relationship between species diversity and community functioning (Snyder et al. 2006). Their results depended strongly on the species composition of the plant community studied (Wilby et al. 2013). A functional description of plant and arthropod communities is therefore required, to render findings more general and for the development of predictive agroecology.

Here, we review and discuss the contribution of a trait-based approach to improving our understanding of plant-arthropod interactions in agroecosystems, focusing on both trophic (e.g. arthropods feeding on plants, predators feeding on alternative prey) and non-trophic interactions. We address the following questions: (1) What characteristics of entomophagous arthropod communities are related to the regulation of crop herbivore populations? (2) Which functions and plants traits are involved in plantarthropod interactions? (3) How could the effects of plants on arthropod assemblages at community and landscape levels be scaled up, and what issues would this raise?

For the preparation of this review, we searched the Web of Science literature database (http://apps.webofknowledge.com) with two search strings in the "topic" search field. The first was [(arthropod* or insect* or pest* or prey* or "natural ennem*" or predator* or parasitoid*) and ("biological control" or biocontrol) and diversity and communit*], to target scientific articles investigating the role of arthropod community structure in biological control. The second search string was [("food web*" or "trophic network*" or "interaction network*") and (multitrophic or interaction*) and (trait* or morpholog* or characteristic*) and (plant* or arthropod* or insect* or flower*)], to target articles identifying traits involved in plant-arthropod interactions. Limiting our search to articles published between 2005 and 2017 (last updated 29 th November 2017), the two search strings identified 507 and 528 articles, respectively. This first set of articles was analysed, and additional relevant articles cited by these articles were added to the working set, whereas articles considered to be outside the scope of the study were removed. We retained 515 articles for the final analysis (Online Resource 1).

The role of natural enemy diversity in controlling crop herbivore communities

The main properties of biological control and their relationship to the characteristics of entomophagous arthropod communities emerging from the selected studies are summarized in Fig. 1 (first two columns). Crops harbour many herbivore species differing in terms of their taxonomic identity and relative importance between years and between crop species. Interannual pest dynamics and crop rotations make it necessary to consider interactions of herbivores and natural enemies at community level. In general, control efficiency, for a large range of herbivore species, increases with the diversity of natural enemies (Jonsson et al. 2017). Studies on predator and prey communities in mesocosms have shown that the niche complementarity of predators is the principal mechanism underlying the higher levels of predation in more diverse predator communities (Northfield et al. 2010;Wilby et al. 2005). The number and complementarity of functional groups of natural enemies, rather than their taxonomic richness, thus appears to be the major determinant of the effect of diversity, when it exists.

By contrast, the stability of biological control for multispecies herbivore communities requires functional diversity (i.e. diversity in the functions provided) and redundancy of natural enemies, which should include both specialists and generalists (Gontijo et al. 2015), with no antagonistic interactions (Fig. 1). Most relationships between community structure and functioning have been inferred from experiments carried out in mesocosms, and their extrapolation to more complex communities under field conditions is problematic. In croplands, habitat management is often used as a tool to support beneficial insects (conservation biological control). It has been suggested that high levels of plant diversity in non-crop habitats favour the amount of natural enemies, leading to a decrease in herbivore abundance (Letourneau et al. 2011). However, little is known about the plant traits favouring effective biological control and their interactions with arthropod communities. Below, we will review and discuss current knowledge.

A trait-based approach to understanding plant-arthropod interactions

What functions must plant communities provide to promote herbivore regulation within arthropod communities?

Plant community management to improve the efficiency of herbivore control by natural enemy communities should have several objectives (third column in Fig. 1). Here, we focus on the case of the neighbouring environment of the field, but our analysis also applies to within-field plant diversity. The surrounding non-crop vegetation fulfils two main functions for the natural enemies of pests (detailed in Fig. 1): it provides both trophic resources and shelter (Griffiths et al. 2008).

The abundance of several insect groups (e.g. Heteroptera, Syrphidae: Pfiffner and Wyss 2004) increases with the total amount of resources available, whereas other groups of insects also respond to the diversity of these resources (Carabidae, Harwood et al. 2009). The resources supplied by plant communities and required for completion of the life cycles of several natural enemies include nectar and pollen for adults herbivores (hoverflies, parasitoids), and alternative prey for larval or adult predators. The provision of trophic resources, such as floral nectar, increases the fecundity of some parasitoids and, thus, the parasitism rates (Heimpel and Jervis 2005). Food resources must be abundant, but also accessible and available at different times. Accessibility, such as the matching of nectar depth in the corolla to the size of arthropod mouthparts, can be used as a criterion for targeting specific arthropod natural enemies (Baggen et al. 1999). Plant communities could be designed to improve the regulation of a large range of herbivores through the support of diverse groups of natural enemies. The duration of the resource provisioning period is also crucial for both the maintenance of entomophagous communities throughout the year, and to increase the growth rates of specialists during pest outbreaks [START_REF] Welch | Temporal dynamics of natural enemy-pest interactions in a changing environment[END_REF].

The role of vegetation in providing shelter has been little studied. Perennial plant communities, such as beetle banks, provide refuges to protect populations of natural enemies against disturbances in the vicinity of cropped habitats (MacLeod et al. 2004;[START_REF] Porcel | The effect of resident vegetation cover on abundance and diversity of green lacewings (Neuroptera: Chrysopidae) on olive trees[END_REF]. The density and complexity of vegetation architecture and litter are important drivers of microclimate affecting vulnerable stages in the life cycles of arthropods (oviposition, estivation, hivernation, Griffiths et al. 2008). Vegetation provides attachment points for spider webs (MacLeod et al. 2004). Vegetation structure also determines habitat complexity, thereby modifying interactions between natural enemies. It may reduce intraguild predation by providing refuges and shelter, and reduce competition between natural enemies from the same guild [START_REF] Finke | Spatial refuge from intraguild predation: implications for prey suppression and trophic cascades[END_REF]Wilby et al. 2013). However, studies investigating resource-and structure-mediated effects have suggested that the provision of shelter and a favourable microclimate affect the activity-density of arthropod generalist predators indirectly, by increasing weed-borne resources or alternative prey (Birkhofer et al. 2008;[START_REF] Diehl | Arable weeds in organically managed wheat fields foster carabid beetles by resource-and structure-mediated effects[END_REF].

Increases in the quantity and diversity of trophic resources may also affect crop pests, as demonstrated for several lepidopteran herbivores (Balzan et al. 2016;Winkler et al. 2010). Plant communities designed to enhance natural enemies should provide these populations with specific resources and other habitat features not favourable to crop herbivores.

Overall, plant communities can promote herbivore regulation by supplying diversified trophic resources accessible to various arthropod species with mouthparts of different shapes and sizes. These trophic resources should be available over a long period and should not be exploitable by unwanted herbivores (Fig. 1). Many studies have been performed to investigate the provision, by plants, of floral resources for parasitoids (e.g. Sivinski et al. 2011;Winkler et al. 2009) andhoverflies (van Rijn andWäckers 2010), and of overwintering habitats (Bürki and Hausammann 1992). A few of these studies have shown that arthropod groups tend to be associated with particular functional traits of plant resources (e.g. Wäckers and van Rijn 2012). Most of the studies cited above focused specifically on particular species, and their results cannot be directly extrapolated to other plant-arthropod pairs. Given the large number of possible interactions within and between arthropod communities, alternative approaches are required to predict the functioning of these communities.

Use of interaction traits to analyse relationships between plant and arthropod communities

The mechanisms underlying community assembly processes involve morphological, physiological, phenological and behavioural traits (sensu Pey et al. 2014;Violle et al. 2007). A role for morphological traits has been demonstrated in several plant-insect studies. For instance, pollination depends on the existence of a good match between insect proboscis length and the nectar holder depth of the corolla (Ibanez 2012;Stang et al. 2006). Grasshopper herbivory is mediated by a match between the toughness of plant leaves and insect mandibular strength (Ibanez et al. 2013).

Pairs of response-and-effect traits must be identified, to improve resource provisioning to beneficial arthropods (Lavorel et al. 2013): plants modify arthropod performance via their effect traits, and the response of arthropods to the vegetation depends on their response traits. We will use the term "interaction traits" to denote all traits mediating interactions between plants and animals.

Interaction traits include not only trophic (Lavorel et al. 2013), but also non-trophic interactions, such as shelter functions, with all of them having an effect on overall performance. Non-trophic interactions can modify feeding parameters (escape from predation), non-feeding parameters (mortality, reproduction) and dispersal. A well-known example of a non-trophic interaction is the presence of domatia in some plant species, providing specific habitats for arthropods, such as ants, to increase predation on herbivores and enhance plant defences [START_REF] Agrawal | Domatia mediate plant-arthropod mutualism[END_REF].

A trait-based approach, such as that recently used to predict the effect of various flower strips on hoverflies (van Rijn and Wäckers 2016), might improve the understanding and prediction of assemblages of invertebrate communities as a function of plant community composition (weed communities, semi-natural habitats, flower strips). Many studies have assessed the attractiveness of individual plant species to insects, but the identification of plant and animal interaction traits would make it possible to extrapolate findings to untested plant species. Despite the known effects of traits in mediating interactions, most ecological networks are still built on a taxonomic basis. Improvements in our understanding of interaction traits should facilitate the prediction of the role of these traits in structuring ecological networks and communities (Kissling and Schleuning 2015).

The mechanisms by which invertebrates affect other components of the ecosystem involve several interaction traits (Moretti et al. 2013). This is of great practical importance when the studied organisms are predators or parasitoids of agricultural pests. The relevant effect traits may be related to diet, foraging behaviour, dispersal ability, shelter requirement and longevity.

What are the key plant traits involved in plant-arthropod interactions?

We will focus here on some key arthropod functional groups involved in biological control (soil dwellers, nectar and pollen feeders, leaf feeders, vegetation dwelling and flying predators).

Plant traits associated with trophic interactions

Studies on plant-herbivore and plant-pollinator interactions have identified several plant traits implied in these interactions related to resource type, attractiveness, accessibility, quality and availability (Fig.

2).

Resource type: Plants provide various food resources, such as leaves, stems, roots, fruits and seeds, sap, floral and extrafloral nectar and pollen. They also indirectly provide honeydew and alternative hosts and prey. Nectar and pollen have been studied mostly as resources for parasitoids, but these resources are also consumed by various other insects and spiders [START_REF] Chen | A survey of nectar feeding by spiders in three different habitats[END_REF]. The availability over time, quality and quantity of these resources constitute interaction traits that vary broadly among plant species (Kühn et al. 2004). The carbohydrate and protein resources provided by plants increase the longevity, reproduction and dispersal of their consumers (Wäckers et al. 2005). Fitness effects vary considerably with the diet, sex and stage in the lifecycle of the arthropod consumer (Wäckers et al. 2007). Plants may act as occasional and supplementary food sources, but the resources they supply may also be of crucial importance, in synovigenic species of parasitoids for instance (Jervis et al. 2004), with nectar and pollen proteins have strong effects on adult performance and egg maturation.

Attractiveness of the resource:

The presence of trophic resources does not necessarily imply that they are consumed. Olfactory, gustatory and visual signals facilitate the recognition and detection of resources, but may also be repellent, depending on the preferences of arthropod groups. Flowers emit olfactory signals and different species are not equally attractive to parasitoids (Belz et al. 2013).

Visual signals, such as plant height, flower height, inflorescence size and colour, are involved in resource detection and a high degree of visual attractiveness increases the abundance of natural enemies [START_REF] Fiedler | Plant characteristics associated with natural enemy abundance at Michigan native plants[END_REF].

For phytophagous insects feeding on plant tissues, secondary metabolites have a deterrent effect, defending the plant against attack. In the Brassicaceae, glucosinolates act as defence compounds against generalist herbivores, but may attract specialists [START_REF] Fahey | The chemical diversity and distribution of glucosinolates and isothiocyanates among plants[END_REF]. This attractiveness to specialists increases with specific glucosinolate content (Kos et al. 2014). Chemical traits are often used to predict the relative attractiveness or repellent effects of plant species and genotypes, although the effect of secondary metabolites on phytophagous insects varies considerably, and their role as defence compounds has been called into question [START_REF] Carmona | Plant traits that predict resistance to herbivores[END_REF].

Resource accessibility: Flower morphology, including corolla shape in particular, plays a crucial role in determining the accessibility of floral nectar and pollen (Heimpel and Jervis 2005). In flowervisiting arthropods, head or body size may physically restrict access to floral resources in flowers with a small corolla diameter. In such cases, the plant-arthropod interaction depends on the length of the mouthparts. A correlation between nectar holder depth and the proboscis length of the flower visitor has been observed in several insect groups, especially in pollinators. Short corolla flowers favour hoverflies, whereas bumblebees prefer long corollas (Campbell et al. 2012). As a result, flower size is one of the most important variables determining the abundance and diversity of flower visitors and their size (Ibanez 2012;Stang et al. 2006;van Rijn and Wäckers 2016). By contrast, extrafloral nectar is generally produced on exposed nectaries, with no size constraints on its accessibility. However, extrafloral nectar has a higher sugar content than floral nectar, rendering it more viscous. This high viscosity facilitates the feeding of hymenopteran parasitoids, which have adapted mouthparts, but limits the accessibility of this resource to lepidopterans, which feed only on dilute nectar (Géneau et al. 2012).

In the herbivores serving as alternative prey for the natural enemies of pests, resource provisioning is dependent on plant palatability, which in turn depends on various morphological (e.g. presence of trichomes, [START_REF] Carmona | Plant traits that predict resistance to herbivores[END_REF], biomechanical and chemical traits (e.g. silica content, Massey et al. 2006). Plant resistance to chewing insects is positively related to leaf punch strength, work to shear and work to tear (Peeters et al. 2007). The incisor strength of insect mandibles is thus related to the traits of the leaves consumed (like leaf dry matter content and carbon:nitrogen ratio, [START_REF] Deraison | Functional trait diversity across trophic levels determines herbivore impact on plant community biomass[END_REF]. Biomechanical properties are associated with several leaf structure traits, such as cuticle thickness, lignin content, specific leaf area and leaf dry matter content (Pérez-Harguindeguy et al. 2003;Schädler et al. 2003). However, the effect of biomechanical properties may be partly confounded with leaf nutrient quality (nitrogen content, carbon:nitrogen ratio, assimilate content), which is negatively correlated with mechanical resistance (Peeters et al. 2007).

Nutritional characteristics of the resource: Floral nectar, extrafloral nectar and honeydew are composed of sugars, whereas pollen is a source of proteins and free amino acids. The sugar, protein and amino acid composition of these resources varies considerably between plant species (Heimpel and Jervis 2005). Floral nectar contains mostly sucrose, fructose and glucose (Baker and Baker 1983).

The sugar composition of nectar affects pollinator preferences. Parasitoids prefer floral nectar composed predominantly of sucrose (Vattala et al. 2006), partly due to a gustatory response [START_REF] Cocco | Not all sugars are created equal: some mask aversive tastes better than others in an herbivorous insect[END_REF]. Extrafloral nectar generally has a higher sugar concentration, whereas honeydew has a lower nutritional quality than nectar (Lee et al. 2004).

Temporal availability of resources:

The synchrony between the plant and arthropod cycles determines the likelihood of interaction [START_REF] Welch | Temporal dynamics of natural enemy-pest interactions in a changing environment[END_REF]. The circadian rhythm of nectar production must coincide with the timing of flower and extrafloral nectaries visitors. The seasonal availability of resources depends on plant phenology. The phenological match between flowering period and arthropod floral resource requirements is crucial for completion of the life cycles of both herbivores and their natural enemies.

A number of trophic interaction traits have, thus, been clearly identified (Fig. 2), and several traits must be considered simultaneously in the evaluation of trophic interactions between plants and arthropods.

Plant traits associated with the non-resource functions of the habitat

Plants have a number of other effects on invertebrates in addition to providing food (Fig. 2): physical habitat provision, microclimate modification and habitat provision for all life stages, including the most critical, such as reproduction.

The structural properties of non-crop vegetation, such as density, height and litter quantity, are known to influence the distribution of soil-dwelling arthropods (Griffiths et al. 2008). Plant structural traits, such as growth form, height, architecture (density and orientation of branches and leaves, leaf morphology) and the presence of domatia shape arthropod habitats (Parolin et al. 2012). For example, plant morphology influences small-scale invertebrate distribution: plants with a complex morphology have higher invertebrate abundances and biomasses than plants with a simple morphology (Hansen et al. 2010). At a smaller scale, the properties of plant surfaces, such as leaf toughness, epicuticular waxes, pubescence and trichomes, affect the attachment and movement of arthropods, with contrasting effects on herbivores and predators, either enhancing or impairing biological control [START_REF] Mitchell | Plant defense against herbivorous pests: exploiting resistance and tolerance traits for sustainable crop protection[END_REF]Petersen 2016).

Plants also provide epigeic invertebrates with shelter, particularly during the periods outside the crop growing season. The plant canopy maintains a moist microclimate and reduces wind speed (Norris and Kogan 2005), protecting invertebrates from desiccation and providing favourable sites for aestivation.

Conversely, relatively dry sites with little temperature variation, such as grass tussocks, are favourable sites for the overwintering of ground beetles (MacLeod et al. 2004). The role of plants in providing suitable overwintering sites has been evaluated for a large range of plant and soil invertebrate species (Bürki and Hausammann 1992), but the corresponding traits have yet to be identified, making it difficult to draw general conclusions.

Habitat provision for reproduction, such as the choice of oviposition sites, has been analysed principally in relation to adult and larval food distribution in the framework of optimal oviposition theory (Wäckers et al. 2007). The olfactory stimuli emitted by plants, such as kairomones and allomones, seem to predominate in the long-distance attraction or repulsion of gravid female herbivores, whereas visual stimuli drive the choice of specific oviposition sites, limiting oviposition on non-host plants (Hooks and Johnson 2003). Plants associated with higher egg survival rates are suitable oviposition sites for phytophagous and predatory insects, and may be different from the plants on which these insects feed (Norris and Kogan 2005). The physical characteristics of the plant are also important. For example, hollow tree and shrub stems are selected as nesting sites for sphecid wasps (Bitsch and Leclercq 1993). Nentwig (1992) recorded the oviposition preferences of lacewings on a large range of plant species and found that oviposition rates were particularly high on plants of the Papaveraceae and Boraginaceae species, possibly due to the pilosity of these species. However, it remains unclear how plant traits, such as architecture or surface features (wax, pilosity etc.) affect the oviposition behaviour of arthropods.

Scaling up to the community and landscape levels

Overcoming the limitations of single-species approaches

Most studies on conservation biological control have focused on one or a few plant species and their role in the regulation of one or a few herbivore groups by one or a few natural enemies (e.g. Langoya and van Rijn 2008;Laubertie et al. 2012). Several of these studies have involved the screening of plants in controlled conditions to identify the most appropriate species for increasing the biocontrol performance of a particular natural enemy. The most frequently tested species are Phacelia tanacetifolia, Fagopyrum esculentum Moench and Lobularia maritima (L.) Desv.

However, crops are generally susceptible to attacks from several herbivore species. Moreover, in arable fields used for the cultivation of annual crops in rotation, a diverse community of natural enemies is required to regulate the associated communities of herbivores. The surrounding non-crop vegetation must, therefore, also consist of a mixture of plant species if it is to support a diverse community of natural enemies. However, plant effects on arthropod behaviour have been analysed mostly in pure stands, and little is known about the effect of plant assemblages (Pontin et al. 2006). In plant communities, attractive plant species may divert herbivores from less attractive species, resulting in lower visiting rates than for single-species stands. Interactions may also occur within arthropod communities, such as competition between an aggressive species and a less aggressive species (bee vs. hoverflies, Hogg et al. 2011). A greater diversity of plant resources and plant habitats may result in lower levels of competition and other negative interactions between arthropods, promoting a greater diversity of arthropods than would be expected from experimental results obtained for single-species stands. The occurrence of interactions makes it necessary to develop community-level approaches, to identify the characteristics of plant communities most likely to improve conservation biological control. Most studies to date have focused on a particular mixture (e.g. Gillespie et al. 2011;Pfiffner et al. 2009), but a small proportion of studies have compared different mixtures (eight studies out of 40 synthesized in Haaland et al. 2011).

However, there is strong evidence for functional relationships between plant and arthropod communities. The abundance of phytophagous invertebrates is positively correlated with plant traits related to resistance to community-level disturbances (e.g. low leaf dry matter content), suggesting a functional link between the two communities (Storkey et al. 2013). In addition to the mean trait values for plant communities, trait diversity may also be important. Potts et al. (2004) showed that the diversity of nectar resources was positively related to bee species richness.

Which metrics provide information about the effects of plant community structure on arthropod assemblages, and what are their limitations?

In this section, we review the characteristics of plant communities relating to arthropod assemblages and their functioning in terms of herbivore regulation.

Several descriptors can be used to characterise communities. The first is species identity. This approach assumes that each species has an idiosyncratic role and that the functioning of the community depends on the particular species it contains. This view may reflect insufficient knowledge or an inadequate description of the mechanisms underlying the processes studied.

The second type of descriptor is based on the functional composition of the community. According to the biomass-ratio hypothesis, 'the extent to which the traits of a species affect ecosystem properties is likely to be strongly related to the contributions of the species [...]' to community biomass (Grime 1998). This suggests that the effects of plants on ecosystem functions are determined primarily by mean trait values at community level, weighted by the relative importance of each species. For example, in subalpine grasslands, the mean body mass of grasshoppers responds to the community weighted mean of leaf dry matter content (Moretti et al. 2013). The abundance of nectar-and pollenfeeding arthropods would be expected to increase with the amount of accessible resources provided by the whole plant community, possibly modulated by their nutritional value.

However, interactions between the functional components of the community may result in a community functioning that could not be inferred simply by adding together the effects of individual species. The ecosystem impact of organisms from higher trophic levels may be less related to abundance or biomass (Grime 1998) as in plants. Non-additive diversity effects can result from functional complementarity, which facilitates niche partitioning, or from synergistic or antagonistic interactions. Functional diversity is often measured as the diversity of functional traits and can be described by functional trait richness, evenness and divergence [START_REF] Dias | An experimental framework to identify community functional components driving ecosystem processes and services delivery[END_REF]. In plant-invertebrate communities, a high diversity of plant resources and microhabitats would be expected to support a high diversity of invertebrates. Podgaiski et al. (2013) found a positive correlation between functional diversity in plant communities (in terms of size and architecture) and functional diversity in spiders (morphology and web-building type). However, this finding was not supported by those of other recent studies analysing the effects of the functional diversity of flower resources on natural enemies (Balzan et al. 2014;Uyttenbroeck et al. 2017). Due to the long generation times of several natural enemies, particularly for generalists, the temporal diversity of resource provisioning (e.g. flowering date and duration) may play an important role than the instantaneous diversity of flower resources.

There is no consensus concerning the relative importance of community species composition and functional structure [START_REF] Costanzo | Functional agrobiodiversity and agroecosystem services in sustainable wheat production[END_REF], and the contribution of functional diversity effects to ecosystem functioning remains unclear [START_REF] Gagic | Functional identity and diversity of animals predict ecosystem functioning better than speciesbased indices[END_REF][START_REF] Garibaldi | Trait matching of flower visitors and crops predicts fruit set better than trait diversity[END_REF][START_REF] Garnier | Plant functional diversity[END_REF].

Recent meta-analyses have provided evidence that plant species diversity and functional diversity favour generalist predators [START_REF] Dassou | Response of pest control by generalist predators to local-scale plant diversity: a metaanalysis[END_REF], thereby increasing herbivore regulation by natural enemies (Iverson et al. 2014). Several unanswered questions remain concerning the type of functional diversity (i.e. which traits?) and the degree of diversity optimising herbivore regulation.

How is plant functional diversity related to herbivore regulation?

It is not easy to determine the level of functional diversity required to optimise herbivore control at community level. The biological control of a single herbivore species might be expected to depend principally on the amounts of trophic resources and habitats supporting its main natural enemies (dominance effects). The plants traits supporting the natural enemies of additional herbivore species may differ, resulting in a need for diverse plant functions to support the entire natural enemy community required to regulate a community of herbivores. As shown by Isbell et al. (2011), the larger the number of ecosystem services required of plant communities, the larger the number of plants with different functions is needed to provide those services. However, in a plant community of fixed size, plant functional diversity cannot be increased in isolation, without modifying other community properties.

First, the generally hump-shaped relationship between the community weighted mean of traits (CWM) and functional diversity [START_REF] Dias | An experimental framework to identify community functional components driving ecosystem processes and services delivery[END_REF] implies that, for any given trait, functional diversity tends to be lowest at extreme values of CWM. Thus, depending on the plant trait values related to biological control, this interdependence may constrain increases in functional diversity.

Second, evenness, which is a component of functional diversity, reduces dominance effects by diluting the relative contribution of dominant species within the community. For example, combining plant species according to their flowering period, so as to ensure that nectar and pollen are supplied throughout the year, decreases the density of plants flowering at the same time. At peak flowering, more resources are available in communities with a homogeneous phenology than in communities with a heterogeneous phenology, resulting in a trade-off between the diversity of resources and their instantaneous availability. Thus, increasing the diversity of plant traits to increase the diversity of arthropods may result in a lower density of each type of arthropod. This trade-off between evenness and dominance effects suggests that the functional diversitybiological control relationship may not be monotonous. Provided that plant functional diversity promotes complementarity and positive interactions with natural enemies, this should counterbalance the decrease in plant dominance effects. Thus, the functional diversity-herbivore regulation relationship may not always be positive, and may reach a plateau or an optimum value, depending on the strength of the synergistic interactions at high levels of plant functional diversity. The deciphering of this relationship will require experiments in which the functional composition and diversity of plant communities are varied, for the simultaneous testing of the two effects, and for quantitative analyses of the relationships between functional trait diversity, composition and ecosystem functions.

Several traits (Fig. 2) and metrics have been proposed to account for the interactions between species or between restricted taxonomic groups. The next step is the identification of combinations of plant community metrics accounting for the effects of the plant community on arthropod communities, and taking into account the effects of functional composition, functional diversity and species identity (when effects cannot be related to functional traits). The level of functional redundancy is another important aspect.

Taking interactions with surrounding landscapes into account

The management of a given habitat for conservation biological control must be adapted to the characteristics of the neighbouring habitats, such as crop fields and other non-crop structures (Tscharntke et al. 2016). The creation of a new habitat, such as a wildflower strip, provides additional resources and habitats. Plant community management or establishment should therefore be based on i) assessments of the requirements of natural enemies and ii) assessments of the resources already provided in the surroundings, in locally limiting resources or habitats. For instance, the effect of wildflower strips on pollinators depends strongly on their complementarity with the resources already available at landscape scale (Scheper et al. 2015), particularly as concerns synchrony between flowering period and pollinator requirements. Plant traits must be adapted to abiotic conditions, such as climate and soil conditions. In arid climates, arthropods may search for moist shelters protecting them from drought stress (tussocks and creeping plants providing shade and higher levels of humidity), whereas, in humid climates, open habitats with rapid warming may result in higher levels of arthropod activity. A functional characterisation of the surrounding landscape (functional landscape ecology) is therefore required, with an improvement of the metrics of landscape description beyond land use [START_REF] Vialatte | Landscape potential for pollen provisioning for beneficial insects favours biological control in crop fields[END_REF]; landscape ecology). Simplified vegetation relevés, stratified by habitat type, can be used to calculate the landscape-wide floral resource availability (Scheper 2015). This approach could be extended to other plant properties, including habitat-related traits, and other metrics, such as the spatial diversity of plant trait values. In the future, such descriptions of the properties of plant communities at the landscape scale should make it possible to adapt habitat creation and management, to improve spatial functional supplementation and complementation rather than making use of standardised greening infrastructures.

Conclusions and implications for conservation biological control

A trait-based approach opens up exciting new possibilities for improving our understanding of the relationships between plant assemblages and conservation biological control. The well-known influence of morphological and biochemical traits on the interaction between plants and pollinators (Stang et al. 2009) suggests that this approach may also be useful for dealing with other biotic interactions.

We also need to identify the characteristics of arthropod communities associated with efficient biological control. Despite the general finding that the stable biological control of multispecies herbivore communities requires functional diversity and a redundancy of natural enemies, the development of appropriate management practices remains limited by our poor understanding of the functioning of arthropod communities, and of their trophic interaction network, in particular.

We also propose the identification of "interaction traits" specifically involved in plant-arthropod interactions, including the effect traits of plants (traits with an impact on arthropods) and the response traits of arthropods (traits associated with the arthropod response to plants). Interaction traits are correlated with plant features relating to the provision of trophic resources (amount of resource, phenology of production, corolla shape etc.) and habitat (plant architecture) affecting arthropods (Fig. 2). Important interaction traits, such as nectar composition, extrafloral nectar availability, presence of domatia and plant pilosity, are currently poorly documented in botanical databases. The use of such traits would improve our mechanistic understanding of interactions at community level. It might also make it possible to quantify the diversity and redundancy of interaction traits in plant communities and to determine their relationship to the abundance of natural enemies or herbivore regulation.

We need to scale up our knowledge of plant-arthropod interactions, from the population to the community level. The extent to which arthropod communities are affected by plant traits at community level remains largely unexplored. An intermediate level of plant functional diversity might be expected to maximise the service of herbivore regulation, but experimental designs facilitating the comparison of contrasting plant communities (such as Hatt et al. 2017) will be useful for disentangling the respective roles of plant functional composition and diversity.

The identification of relevant community characteristics should not be limited to additive species traits. It should also take into account the structure of the interaction network, species complementarity and the generalist/specialist ratio.

Over and above the identification of relevant plant traits, the high specificity of certain plant-insect and insect-insect interactions may weaken the trait-based approach. Aphid-parasitoid and plant-aphid interactions are usually species-specific. Consequently, aphid regulation often requires the targeting of a particular aphid species by promoting a particular parasitoid species. Trade-offs may occur between the positive effects of plant traits on one group of natural enemies and negative effects on another. It therefore seems likely that some sets of traits are related to herbivore regulation in general, but we cannot exclude the possibility that these combinations are highly specific and that a trait-based approach is not necessarily more straightforward than a species-based approach. We do not, therefore, recommend the exclusive use of trait-based approaches, and advances in food-web ecology will undoubtedly also improve the understanding and management of trophic interactions. If interactions are idiosyncratic or poorly understood, and if trait attributes are phylogenetically conserved, then phylogenetic parameters may be better predictors of ecosystem functioning than functional traits or groups (Cadotte et al. 2008). However, interaction specificity usually includes a single dimension of a niche, and a trait-based approach may still be straightforward for the other dimensions. For generalist predators, a trait-based approach would remain relevant, but difficulties may arise due to the number of traits and their interactions to be considered in each situation to predict their functioning. If patterns become too complex and difficult to generalize, then the trait-based approach may be impractical.

In practice, interaction traits may be used to decide on the combinations of plant properties required to guide the formulation of seed mixtures for creating or restoring semi-natural habitats, rather than using standard species lists applied to several biogeographical zones. The identification of plant species from the local flora with the desired trait criteria would make it possible to design seed mixtures with similar functional characteristics based on species adapted to local climatic conditions.

The use of functional traits as proxies for community and ecosystem functioning should not completely supplant other drivers of plant arthropod interactions, such as environmental conditions and habitat management. In addition, the use of plant communities to support biological control must also take into account a diversity of ecological, technical and socio-economic criteria, such as a potential loss of diversity during plant succession.

Problematic weed species cannot be included in the mixtures sown, even if they present ideal trait combinations. Plant species of local origin should be preferred whenever possible, to select locally adapted populations and to prevent genetic pollution. Finally, trade-offs with other ecosystem services should be considered from a multifunctional standpoint, including pollination, species conservation and landscape aesthetics.

Conflict of interest: The authors have no conflict of interest to declare.

Figures and online resource

  [START_REF] Carmona | Plant traits that predict resistance to herbivores[END_REF] Plant traits that predict resistance to herbivores FunctEcol 25:358-367 doi:10.1111Ecol 25:358-367 doi:10. /j.1365Ecol 25:358-367 doi:10. -2435Ecol 25:358-367 doi:10. .2010.01794.x .01794.x Chen XQ, Chen YC, Wu LB, Peng Y, Chen JA, Liu FX (2010) A survey of nectar feeding by spiders in three different habitats Bull Insectol 63:203-208 Cocco N, Glendinning JI (2012) Not all sugars are created equal: some mask aversive tastes better than others in an herbivorous insect J Exp Biol 215:1412-1421 doi:10.1242/jeb.059832 Costanzo A, Barberi P (2014) Functional agrobiodiversity and agroecosystem services in sustainable wheat production. A review Agronomy for Sustainable Development 34:327-348 doi:10.1007/s13593-013-0178-1 Dassou AG, Tixier P (2016) Response of pest control by generalist predators to local-scale plant diversity: a meta-analysis Ecology and Evolution 6:1143-1153 doi:10.1002/ece3.1917 Deraison H, Badenhausser I, Loeuille N, Scherber C, Gross N (2015) Functional trait diversity across trophic levels determines herbivore impact on plant community biomass Ecology Letters 18:1346-1355 doi:10.1111/ele.12529 Dias ATC, Berg MP, de Bello F, Van Oosten AR, Bílá K, Moretti M (2013) An experimental framework to identify community functional components driving ecosystem processes and services delivery J Ecol 101:29-37 doi:10.1111/1365-2745.12024 Diehl E, Wolters V, Birkhofer K (2012) Arable weeds in organically managed wheat fields foster carabid beetles by resource-and structure-mediated effects Arthropod-Plant Interactions 6:75-82 doi:10.1007/s11829-011-9153-4 Fahey JW, Zalcmann AT, Talalay P (2001) The chemical diversity and distribution of glucosinolates and isothiocyanates among plants Phytochemistry 56:5-51 doi:10.1016/s0031-9422(00)00316-2 Fiedler AK, Landis DA (2007) Plant characteristics associated with natural enemy abundance 36[878:pcawne]2.0.co;2 Finke DL, Denno RF (2006) Spatial refuge from intraguild predation: implications for prey suppression and trophic cascades Oecologia 149:265-275 doi:10.1007/s00442-006-0443-y Frenette-Dussault C, Shipley B, Hingrat Y (2013) Linking plant and insect traits to understand multitrophic community structure in arid steppes Funct Ecol 27:786-792 doi:10.1111/1365-2435.12075 Gagic V et al. (2015) Functional identity and diversity of animals predict ecosystem functioning better than species-based indices Proc R Soc B 282:sous presse doi:10.1098/rspb.2014.2620 Garibaldi LA et al. (2015) Trait matching of flower visitors and crops predicts fruit set better than trait diversity J Appl Ecol 52:1436-1444 doi:10.1111/1365-2664.12530 Garnier É, Navas M-L, Grigulis K (2016) Plant functional diversity. Oxford University Press, United Kingdom,

Fig. 1

 1 Fig. 1 Outline of the main objectives targeted for efficient conservation biological control (first

Fig. 2

 2 Fig.2Overview of the main plant-arthropod interaction traits recorded in published studies and

Figure 1

 1 Figure 1

Acknowledgements

This work was partly supported by the Agence Nationale de la Recherche PEERLESS project (ANR-12-AGRO-0006). We thank the reviewers for their helpful comments on the manuscript.


M Pouget

S Youssef
email: sami.youssef@hotmail.com

P. -J Dumas

T Baumberger
email: teddy.baumberger@yahoo.fr

A San Roman

F Torre

Laurence Affre
email: laurence.affre@imbe.fr

F Médail

Alex Baumel
email: alex.baumel@imbe.fr

P.-J Dumas

Spatial mismatches between plant biodiversity facets and evolutionary legacy in the

Keywords:

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Introduction

Conservation biology aims to conserve all components of biodiversity as well as the ecological and evolutionary processes that sustain them [START_REF] Moritz | Strategies to protect biological diversity and the evolutionary processes that sustain it[END_REF]Lankau et al., 2011). To date, conservation strategies have largely focused on taxonomic diversity to protect species or areas at various scales. Evolutionary assessments of biodiversity may reveal serious weaknesses in the network of protected areas, especially where areas with high species richness are not cradles of diversification [START_REF] Becerra | Sources and sinks of diversification and conservation priorities for the Mexican tropical dry forest[END_REF] or hotspots of genetic diversity or uniqueness [START_REF] Taberlet | Genetic diversity in widespread species is not congruent with species richness in alpine plant communities[END_REF]. For example, [START_REF] Davis | The California Hotspots Project: identifying regions of rapid diversification of mammals[END_REF], who investigated mammal diversity, and [START_REF] Kraft | Range size, taxon age and hotspots of neoendemism in the California flora[END_REF], who focused on plant diversity, demonstrate some spatial discrepancies between simple counts of endemic species richness and ongoing diversification within the California biodiversity hotspot. Other recent studies report robust links between the genetic and specific components of biodiversity (e.g., [START_REF] He | Covariation species between intraspecific genetic diversity within a plant functional diversity group[END_REF][START_REF] Papadopoulou | Testing the species-genetic diversity correlation in the Aegean archipelago: toward a haplotype-based macroecology?[END_REF][START_REF] Lamy | Variation in habitat connectivity generates positive correlations between species and genetic diversity in a metacommunity[END_REF] and support the existence of surrogates of genetic diversity under certain conditions and scales. These results emphasise that, for system-based conservation planning [START_REF] Whittaker | Conservation Biogeography: assessment and prospect[END_REF][START_REF] Rodrigues | Shortcuts for biodiversity conservation planning: the effectiveness of surrogates[END_REF], and to better understand the future of biodiversity under global change [START_REF] Lee | Future battlegrounds for conservation under global change[END_REF], we need to improve our knowledge of the relevance and consistency of putative links between the different components of biodiversity. These links question the existence and value of biological and ecological surrogates.

The inclusion of the evolutionary history of populations in conservation planning is an important issue for long-term management of biodiversity [START_REF] Moritz | Strategies to protect biological diversity and the evolutionary processes that sustain it[END_REF][START_REF] Sechrest | Hotspots and the conservation of evolutionary history[END_REF][START_REF] Tucker | Incorporation geographical and evolutionary rarity into conservation prioritization[END_REF][START_REF] Moritz | The importance of an evolutionary perspective in conservation policy planning[END_REF]. Historically isolated sets of populations are likely to have distinct evolutionary potential [START_REF] Moritz | Defining 'evolutionarily significant units' for conservation[END_REF]: their existence is the consequence of past evolutionary processes that occurred within populations, shaping genome diversity and structuring genetic variation as well as a response to selection in case of environmental change (Lankau et al., 2011). The evolutionary legacy of populations is mostly examined through phylogeographical studies [START_REF] Avise | Phylogeography: retrospect and prospect[END_REF] and concerns the structure of distinct evolutionary lineages at the intraspecific level or between closely related species. Their recognition led to the adoption of a dynamic view of biodiversity constituting continuously evolving lineages (e.g., [START_REF] Sgro | Building evolutionary resilience for conserving biodiversity under climate change[END_REF][START_REF] Hoffmann | A framework for incorporating evolutionary genomics into biodiversity conservation and management[END_REF] sustaining the potential of future evolution to face environmental changes. As such, giving priority to areas that maximise only species-level diversity may have detrimental consequences for future biodiversity due to the inability to recognise the evolutionary legacy of population histories.

Dealing with pattern and history, biogeography has attached great importance to macrorefugia and microrefugia [START_REF] Avise | Phylogeography: retrospect and prospect[END_REF][START_REF] Mosblech | On metapopulations and microrefugia: palaeoecological insights[END_REF][START_REF] Hampe | Climate relicts: past, present, future[END_REF][START_REF] Keppel | Refugia: identifying and understanding safe havens for biodiversity under climate change[END_REF][START_REF] Mee | The ecological and evolutionary implications of microrefugia[END_REF] because of their role in the persistence of the genetic and specific components of biodiversity, notably species endemism [START_REF] Sandel | The influence of late quaternary climate-change velocity on species endemism[END_REF]. In the Mediterranean region, a positive association has been observed between hotspots of plant endemism and phylogeographically defined refugia, designating them as areas requiring special attention for conservation [START_REF] Médail | Glacial refugia influence plant diversity patterns in the Mediterranean Basin[END_REF]. More recently several studies have focused on the geographical congruence between the different facets of biodiversity and analysed it at coarse spatial scales (e.g., [START_REF] Kraft | Range size, taxon age and hotspots of neoendemism in the California flora[END_REF][START_REF] Devictor | Spatial mismatch and congruence between taxonomic, phylogenetic and functional diversity: the need for integrative conservation strategies in a changing world[END_REF][START_REF] Mouquet | Ecophylogenetics: advances and perspectives[END_REF][START_REF] Taberlet | Genetic diversity in widespread species is not congruent with species richness in alpine plant communities[END_REF][START_REF] Zupan | Spatial mismatch of phylogenetic diversity across three vertebrate groups and protected areas in Europe[END_REF]. For example, [START_REF] Devictor | Spatial mismatch and congruence between taxonomic, phylogenetic and functional diversity: the need for integrative conservation strategies in a changing world[END_REF] found for bird biodiversity that high taxonomic diversity is better represented in French protected areas than phylogenetic or functional diversities. However, conservation strategies need to consider multiple scales, and assessment of biodiversity components at smaller scales deserves more attention because it represents the practical scale for efficient conservation planning [START_REF] Schwartz | Choosing the appropriate scale of reserve for conservation[END_REF]. Conservation strategies have to deal with human settlement issues and give attention to places where people live [START_REF] Miller | Conservation where people live and work[END_REF]. Even small protected areas can be impacted by human activities such as mass tourism which can have strong effect on endangered species [START_REF] Ballantyne | Tourism and recreation: a common threat to IUCN red-listed vascular plants in Europe[END_REF]. Biodiversity studies focusing on large scale (e.g., [START_REF] Devictor | Spatial mismatch and congruence between taxonomic, phylogenetic and functional diversity: the need for integrative conservation strategies in a changing world[END_REF][START_REF] Zupan | Spatial mismatch of phylogenetic diversity across three vertebrate groups and protected areas in Europe[END_REF] are therefore not sufficient to deal with the difficult issue of conservation planning.

To address the issue of congruence among different components of biodiversity, including evolutionary legacy, at a practical scale for conservation planning, we have used an extensive vegetation survey coupled with phylogeographic knowledge of a Mediterranean narrow endemic threatened plant, Arenaria provincialis Chater & Hallid. (Caryophyllaceae). A. provincialis occurs on limestone outcrops in Provence (south-eastern France) surrounding the big city of Marseille, and its habitats are threatened by severe urban sprawl, recreation and trampling leading to habitat degradation. Like many other endemic species of the Mediterranean region, A. provincialis is high in conservation priorities [START_REF] Thompson | Ecological differentiation of Mediterranean endemic plants[END_REF][START_REF] Hobohm | The increasing importance of endemism: responsibility, the media and education[END_REF], but seriously threatened by human activities [START_REF] Hoekstra | Confronting a biome crisis: global disparities of habitat loss and protection[END_REF][START_REF] Underwood | Threats and biodiversity in the mediterranean biome[END_REF] and particularly by urban sprawl along Mediterranean coastlines in the vicinity of major cities [START_REF] Médail | Biodiversité végétale méditerranéenne et anthropisation: approches macro et micro-régionales[END_REF][START_REF] Vimal | Detecting threatened biodiversity by urbanization at regional and local scales using an urban sprawl simulation approach: application on the French Mediterranean region[END_REF].

Previous studies [START_REF] Youssef | Factors underlying the narrow distribution of the mediterranean annual plant Arenaria provincialis (Caryophyllaceae)[END_REF][START_REF] Imbert | Do endemic species always have a low competitive ability? A test for two Mediterranean plant species under controlled conditions[END_REF][START_REF] Pouget | Phylogeography sheds light on the central-marginal hypothesis in a Mediterranean narrow endemic plant[END_REF] have demonstrated that A. provincialis evolved throughout the Pleistocene, acquiring very specific adaptations to persist in its highly stressful habitats. A recent phylogeographical study demonstrated highly structured genetic diversity from the centre towards the margins of its distribution and a high distinctness of its populations at the genetic and ecological levels [START_REF] Pouget | Phylogeography sheds light on the central-marginal hypothesis in a Mediterranean narrow endemic plant[END_REF]. One of the main striking points of the phylogeography of A. provincialis, revealed by the study of [START_REF] Pouget | Phylogeography sheds light on the central-marginal hypothesis in a Mediterranean narrow endemic plant[END_REF], is that the core area of its distribution has the highest level of genetic diversity. Any efficient conservation planning of A. provincialis should, at least, target this core area. Here, we use our knowledge on A. provincialis as a natural experiment to test the efficiency of various biodiversity components as indicators for conservation planning. The theoretical threshold of 17% of areas to be designated as protected areas (proposed by the "2020" goal of the Convention for Biological Diversity, CBD, 2012), was used to compare the capacity of the various components of biodiversity and environmental heterogeneity to be surrogates of the evolutionary legacy of A. provincialis.

Our aims were: (i) to examine the congruencies between different components of plant biodiversity (species and phylogenetic diversity), and the evolutionary legacy of A. provincialis. (ii) To compare the relevance of the various components of biodiversity to be surrogates of the evolutionary legacy of A. provincialis and to recognise the core area of the distribution of A. provincialis as a prime conservation goal.

Materials and methods

Study area, ecological and floristic data

The study area is located in Southern Provence (South-East of France: see Fig. 1) with a strongly seasonal Mediterranean climate, in an area characterised by several limestone outcrops (up to 1150 m above sea level). The landscapes of these outcrops are characterised by a mosaic of low matorrals ("garrigues") mainly dominated by Quercus coccifera with open rocky spaces and a low vegetation cover formed by herbaceous plants. Along with an increase in the human population density occurring in Mediterranean lowlands near the coast, the naturally open habitats of Provence are affected by a combination of urban sprawl, habitat fragmentation, trampling and direct or indirect pollution [START_REF] Barbero | Changes and disturbances of forest ecosystems caused by human activities in the western part of the Mediterranean Basin[END_REF][START_REF] Médail | Organisation de la richesse et de la composition floristiques d' îles de la Méditerranée occidentale (sud-est de la France)[END_REF][START_REF] Tatoni | The impact of changes in land use on ecological pattern in Provence (Mediterranean France)[END_REF][START_REF] Dumas | Mediterranean urban-forest interface classification (MUFIC): a quantitative method combining SPOT5 imagery and landscape ecology indices[END_REF][START_REF] Baumberger | Plant community changes as ecological indicator of seabird colonies' impacts on Mediterranean Islands[END_REF][START_REF] Vimal | Detecting threatened biodiversity by urbanization at regional and local scales using an urban sprawl simulation approach: application on the French Mediterranean region[END_REF]. In parallel, the rocky habitats of Southern Provence shelter many rare or endemic plant taxa that make this area a priority for biodiversity conservation assessment and management. Since 2012, the southern part of the focus area and the islands between Marseille and La Ciotat have been included into the National Park of Calanques (NPCal: see Fig. 1). This study focused on the rocky open habitats of these outcrops situated at the periphery of Marseille, which also encompasses the small islands and islets situated less than five kilometres off the coast (Fig. 1).

Assessment of the different components of biodiversity

Assessment of species taxonomic and phylogenetic diversity

The study area has been surveyed by the Mediterranean Institute for Biodiversity and Ecology (IMBE), resulting in a database of 1132 floristic and mesologic relevés established for 100 m 2 circular areas. This method is relevant when comparing the ecology of plants inhabiting rocky habitats in southern Provence [START_REF] Youssef | Distribution, habitat and population size variation of Genista lobelii (Fabaceae) from the calcareous mountains of Basse Provence (S-E France)[END_REF][START_REF] Youssef | Factors underlying the narrow distribution of the mediterranean annual plant Arenaria provincialis (Caryophyllaceae)[END_REF][START_REF] Baumberger | Plant community changes as ecological indicator of seabird colonies' impacts on Mediterranean Islands[END_REF]. Plant diversity was measured at the taxonomic and phylogenetic levels. Five indices of biodiversity were computed: the alpha species diversity (ASD), the beta species diversity (BSD), the floristic dissimilarity between relevés (FD), the gamma species diversity (GSD) and the phylogenetic species diversity (PSD). ASD, BSD and GSD were computed according to [START_REF] Jost | Partitioning diversity into independent alpha and beta components[END_REF] using the "H" function of the "vegetarian" package in R (R Development Core Team, 2012). The floristic dissimilarity (FD) was measured according to the Jaccard distance ("dist.binary" function and "ade4" package in R).

The phylogeny of the 565 plant species encountered inside the 1132 relevés was constructed in two steps. A preliminary phylogeny was established on a subset of species (ca 40%) using nucleotide sequence data for the rbcL gene extracted from the Gen-Bank database. This phylogeny was obtained using the BEAST 1.7 software [START_REF] Drummond | Bayesian phylogenetics with BEAUti and the BEAST 1.7[END_REF] after alignment of the sequences in Mega 5.1 [START_REF] Tamura | MEGA5: Molecular Evolutionary Genetics Analysis using maximum likelihood, evolutionary distance, and maximum parsimony methods[END_REF]. This first tree was compared according to APG3 to check for misidentification in published sequences. The missing taxa, i.e., having no GenBank accession for rbcL gene, were then positioned into the phylogeny with respect to published molecular phylogenies of other markers. They have been added manually using Treegraph2 software [START_REF] Stöver | TreeGraph 2: combining and visualizing evidence from different phylogenetic analyses[END_REF]. When no molecular information was available, taxa have been positioned at the node of their genus, creating a polytomy that was resolved by the R function "multi2di". It only concerned recent nodes and did not affect the results of the phylogenetic diversity measures. After corrections, the final tree was converted to a chronogram with branch lengths calibrated to millions of years (Ma) by the penalised likelihood semi-parametric method [START_REF] Sanderson | Estimating absolute rates of molecular evolution and divergence times: a penalized likelihood approach[END_REF] using the R function "chronopl" and 26 node ages for time calibration. The phylogeny tree is provided in the supplementary material as a chronogram in newick format (Appendix 1a) with the literature used to calibrate the node ages (Appendix 1b).

The phylogenetic species diversity was calculated as the mean phylogenetic distance among all pairs of species in a relevé or a set of relevés (mean PSD, "mpd" function, "picante" package, R; [START_REF] Webb | Phylogenies and community ecology[END_REF]. Mean PSD represents the mean distance between two randomly chosen species in a community; this is an estimate of the phylogenetic information occurring in a community but is independent of the number of species in the community.

Assessment of environmental heterogeneity

Environmental heterogeneity was also considered in these analyses because it is also often suggested as a crucial factor for biodiversity persistence in the context of metapopulation and microrefugia theories [START_REF] Tamme | Environmental heterogeneity, species diversity and co-existence at different spatial scales[END_REF][START_REF] Rull | On microrefugia and cryptic refugia[END_REF][START_REF] Dobrowski | A climatic basis for microrefugia: the influence of terrain on climate[END_REF]. The mesologic relevés were scored using 14 variables: altitude, slope, exposition, cover percentage of high and low shrubs, high and low trees, herbaceous plants and total plant cover, and the proportions of bare ground, litter, rocks, pebbles and gravel. The measurement of the environmental heterogeneity was based on the two main axes obtained through a Principal Components Analysis (PCA, 1132 relevés × 14 variables table, "dudi.pca" function, package "ade4", R), which accounted for 36% of the environmental variance. The results of the PCA of environmental variables are provided in the supplementary material (Appendix 2). According to the table of inertia ("inertia.dudi" function), the environmental heterogeneity (EH) is mainly represented by a gradient of the vegetation cover (first PCA axis), which ranges from a highly open habitat with a significant slope to a habitat with more trees and shrubs, and a second gradient (second PCA axis) that ranges from southern exposure to northern exposure with a more herbaceous plant cover. The environmental distance between the relevés was calculated through the Euclidean distance based on the coordinates (latitudinal and longitudinal position) of each relevé based on the two PCA axes (function "dist", package "stats", R). In the correlation analyses introduced below, the environmental heterogeneity (EH) is either the pairwise distance between the relevés or determined by the mean pairwise distance within a set of relevés. A high value of EH indicates important distances within the environmental space defined by the two PCA axes between the relevés.

Assessment of evolutionary legacy

The results reported by [START_REF] Pouget | Phylogeography sheds light on the central-marginal hypothesis in a Mediterranean narrow endemic plant[END_REF] were used to compute the evolutionary legacy (EL) of A. provincialis for each of its occurrences. The EL was computed from the haplotypic diversity of four chloroplast loci (internal part of matK gene, trnK intron plus 5 part of matK, tnrL-trnF spacer and trnT-trnL spacer). This haplotypic diversity was demonstrated to be geographically costructured with the genomic multi-locus variation estimated by Amplified Fragment Length Polymorphism as well as the ecological distinctness of the populations [START_REF] Pouget | Phylogeography sheds light on the central-marginal hypothesis in a Mediterranean narrow endemic plant[END_REF], and therefore we considered it a relevant indicator of the EL of A. provincialis.

EL was not computed directly from nucleotidic variation but from phylogenetic relationships of cpDNA haplotypes. First, a chronogram was created using the BEAST software to approximate the ages of divergence among haplotypes of A. provincialis (details of the methods are presented by [START_REF] Pouget | Phylogeography sheds light on the central-marginal hypothesis in a Mediterranean narrow endemic plant[END_REF]). This chronogram was used to calculate a distance matrix between the haplotypes using the function "distTips" (package "adephylo", R). The mean pairwise distance between a precise population and all other locations was calculated for each population using this distance matrix and the "divc" function (package "ade4", R). Second, this mean pairwise distance was collected per population (40 populations) to produce an interpolation map using the ArcGIS software version 9.1 (ESRI, Inc., Redlands, CA, USA) with the "krigage" function and an exponential variogram. Finally, the map allowed us to obtain the value of EL for all 174 populations of A. provincialis.

Congruency analysis between components of plant biodiversity

To set analysis of congruency we clustered all the relevés per zones computed after spatial autocorrelation analysis. The objective was to obtain several zones to compare and to map the different components of biodiversity analysed here. The spatial autocorrelations of FD, PSD and EH were evaluated by a mantelogram analysis of the correlation between each variable and the spatial distance (1000 permutations, function "mantel", "ecodist" package, R); these analyses are provided in supplementary material (Appendix 3). According to results we decided to cluster all the relevés in zones consisting of relevés separated by a maximal distance of 2000 m. This class of distance was the best trade-off to reduce the spatial autocorrelation of the data and retain enough samples of the biodiversity components for correlation analysis. The clustering ("hclust" function, method "average", package "stats", R) revealed 94 local neighbourhoods named "2000 m-zones". All 2000 m-zones with less than three relevés were removed to obtain a final number of 72 zones. The analyses (not shown) performed at the 500-m and 4000-m class distances revealed the same trends.

Pairwise correlations between the ASD, BSD, GSD, mean PSD and mean EH were analysed according to the correlation coefficient of Kendall (tau, function "cor.test", method "kendall", stats package, R) and a simple regression analysis (function "lm", "stats" package, R). The five variables computed within the 2000 m-zones (ASD, BSD, GSD, PSD, EH), as well as EL, were mapped.

Surrogacy assessment based on the 17% threshold optimisation groups

The theoretical threshold of 17% of protected areas proposed by the "2020" goal of the CBD was used in this study to examine the implications of choosing a precise component of plant diversity as a conservation target for the other components, specifically, in this study, the evolutionary legacy of A. provincialis. After application to the dataset, the 17% threshold corresponds to a subset of 192 relevés. We chose the 192 relevés presenting the highest ASD and the highest PSD, and the 192 relevés representing at best EH range. To determine the subset representing the full EH range, we applied a k-means clustering method (function "kmeans", R) on the two PCA axes of the environmental variables to obtain 192 groups of relevés. We then randomly sampled one relevé in each group for a total of 192 relevés representing at best the EH.

For each of these three sets of relevés, which were denoted conservation optimisation groups, we calculated the different indices: ASD, BSD, GSD, mean PSD, mean EH (using the distance matrix), and mean EL (calculated only for the relevés with A. provincialis). The differences in the mean EL according to the three conservation optimisation groups was analysed using ANOVA ("aov" function, "stats" package, R).

Results

Assessment of plant biodiversity

The total plant richness of the 1132 relevés included 565 species from 75 families and 33 orders with a majority of Asteraceae and Poaceae. The most frequent species was Brachypodium retusum followed by Rosmarinus officinalis. Among the tree and shrub species, Q. coccifera and Pinus halepensis were present at the highest frequencies. A. provincialis was ranked 54th, occurring 174 times in the dataset. The majority of the species (301) were present in less than 1% of the relevés, and 101 species were found in only one relevé. The dataset contributes to the knowledge of several rare and protected plant species, with 79 species considered rare at a regional level and 34 species protected under French laws.

The species diversity ranged from three to 68 species per relevé, with an alpha diversity (ASD) of 24.1 species per relevé. The overall species turnover between relevés, i.e., beta species diversity (BSD) was 23.5, and the overall number of species (GSD) was 565. The phylogenetic species diversity (PSD) per relevé ranged from 153.8 to 422.8 mean pairwise distances with a mean of 284.6. High values of phylogenetic diversity represent relevés with few species but highly divergent species, particularly when both ferns and angiosperms are present, whereas low values are due to the presence of angiosperms belonging to closely related families. As a comparison example, the relevé with the maximum PSD (in the north of the area) has six species, including a fern, a monocotyledon and four eudicotyledons (rosids and asterids), and the relevé with the minimum PSD (in the southwest of the area) has five species, all from the Caryophyllales order.

Congruency analysis between the different components of diversity

The values of the six indices of diversity were mapped within 2000 m-zones: ASD, BSD, GSD, mean PSD, mean EH and mean EL (Fig. 2). These maps highlight a strong spatial structure for ASD, BSD, GSD and EL and a less structured pattern for PSD and EH. As previously reported by [START_REF] Pouget | Phylogeography sheds light on the central-marginal hypothesis in a Mediterranean narrow endemic plant[END_REF], the EL of A. provincialis is higher in the core area. The relationships between the five indices (ASD, BSD, GSD, mean PSD, and mean EH) computed in 2000 m-zones are displayed on the PCA (Fig. 3a) and on the simple linear regressions (Fig. 3b). It revealed both significant positive and negative correlations with three particular patterns of note. First, when the mean EH is increasing, the ASD is decreasing (tau = -0.19, p < 0.001; R 2 = 0.25, p < 0.001), and the BSD is increasing (tau = 0.36, p < 0.001; R 2 = 0.16 p < 0.001). Second, the strongest positive correlation was observed between BSD and GSD (tau = 0.56, p < 0.001; R 2 = 0.68, p < 0.001). The correlation between ASD and GSD was weak. Then, in decreasing order of correlation magnitude, the overall species diversity (GSD) in a 2000 m-zone was mainly correlated to the changes in the composition between relevés (BSD), which is itself positively correlated to the mean environmental heterogeneity of this zone (mean EH). It is worth noting that the mean EH has a negative effect on ASD. Finally, the mean PSD is not correlated with the mean EH, ASD or BSD and is weakly and negatively correlated to GSD (tau = -0.23, p = 0.004; R 2 = 0.09, p = 0.006). As observed previously, PSD is less geographically structured but exhibits important variations (Figs. 2 and3b). In fact, PSD appeared to not be associated with the local species diversity or environmental heterogeneity (Fig. 3b).

Can the various components of diversity be surrogate of the A. provincialis evolutionary legacy?

The theoretical threshold of 17% of areas applied to the whole dataset corresponds to 192 relevés. Only eight relevés are common to the three groups of optimisation. In addition, 31 are common to ASD-17% and EH-17% only, 24 are common to ASD-17% and PSD-17%, and 27 are common to EH-17% and PSD-17%. This lack of overlap is consistent with the analyses presented above and explains that one criterion never optimises more than two targets (Table 1). There is no single optimisation criterion that matches all of the targets, i.e., rejecting the existence of a single surrogate for all components of biodiversity. The evolutionary legacy of A. provincialis is best optimised by the PSD-17% criterion (Table 1) because it selects more relevés situated centrally (Fig. 2) with a high level of EL (Figs. 2 and4), therefore raising the mean EL. The worse optimisation was obtained for the EH-17% criterion, which picked relevés with low values of EL. However, these results have to be nuanced by the low capacity of the three criteria to include A. provincialis; 13, 37 and 36 of 174 relevés were selected by one of the three criteria, namely ASD-17%, PSD-17%, and EH-17%, respectively.

Discussion

To the best of our knowledge, our sampling effort and analyses of diversity is the first significant study of its kind realised at a scale relevant for conservation actions in areas neighbouring a large Mediterranean city affected by the threat of mass tourism and urban sprawl. Important insights emerge from our results and involve several implications for conservation planning for the evolutionary legacy and the different components of biodiversity.

Spatial mismatch between different components of diversity

The general picture of our study is the lack of congruence between components of plant biodiversity (e.g., Figs. 2 and3b) and associated spatial mismatches (Fig. 4). Various processes are confounded in the determination of the composition and richness of plant communities [START_REF] Lortie | Rethinking plant community theory[END_REF] and the lack of congruence between components of plant biodiversity revealed here suggest that different factors control the different components. Significant correlations between species and genetic diversity are more frequently observed in discrete habitats [START_REF] Vellend | Drawing ecological inferences from coincident patterns of population-and communitylevel biodiversity[END_REF]; in the study area the sampling units were not isolated from similar habitats, rejecting any likely effect of patch size or isolation on diversity. Moreover, Mediterranean landscapes are also impacted by a long history of human induced disturbances (e.g., recurring fires) that may have broken the co-structures between the various components of diversity.

None of the three criteria that designate optimisation groups can match all of the conservation targets (Table 1). Contrary to the observation of [START_REF] Rodrigues | Shortcuts for biodiversity conservation planning: the effectiveness of surrogates[END_REF] that review a positive surrogacy power, our key result rejects the hypothesis of a single surrogate. The spatial mismatches among biodiversity facets involve the necessity of conservation planning considering several targets in order to protect the various components of biodiversity [START_REF] Margules | Systematic conservation planning[END_REF][START_REF] Devictor | Spatial mismatch and congruence between taxonomic, phylogenetic and functional diversity: the need for integrative conservation strategies in a changing world[END_REF][START_REF] Mouquet | Spatial mismatch of phylogenetic diversity across three vertebrate groups and protected areas in Europe[END_REF][START_REF] Zupan | Spatial mismatch of phylogenetic diversity across three vertebrate groups and protected areas in Europe[END_REF]. [START_REF] Zupan | Spatial mismatch of phylogenetic diversity across three vertebrate groups and protected areas in Europe[END_REF] demonstrate that patterns of diversity including taxonomic, phylogenetic and functional diversity of terrestrial vertebrates strongly diverge and that evolutionary history is unequally protected. Areas with a high phylogenetic diversity are likely to harbour a great evolutionary history, which is by itself a crucial aspect of biodiversity [START_REF] Faith | Conservation evaluation and phylogenetic diversity[END_REF][START_REF] Webb | Phylogenies and community ecology[END_REF][START_REF] Mace | Preserving the tree of life[END_REF][START_REF] Mace | Evolutionary biology and practical conservation: bridging a widening gap[END_REF][START_REF] Cadotte | Rarest of the rare: advances in combining evolutionary distinctiveness and scarcity to inform conservation at biogeographical scales[END_REF]. In this study the phylogenetic species diversity, measured by mean phylogenetic pairwise distance methods (mean PSD), is less spatially structured than the other indices (Fig. 2). Reinforcing overall observation of spatial mismatches among biodiversity facets, our analyses revealed that phylogenetic species diversity (mean PSD) was poorly correlated to the taxonomic species diversities (ASD, BSD and GSD) and to the environmental heterogeneity (EH) (Fig. 3b). The mean PSD highlighted zones with the widest phylogenetic composition among vascular plants, e.g., deep phylogenetic divergence within angiosperms. Maximising protection of phylogenetic diversity may aid protecting ecosystem function [START_REF] Smith | Prescriptive evolution to conserve and manage biodiversity[END_REF].

Species biodiversity components are not effective surrogate of evolutionary legacy

This study represents the first assessment of the congruence between plant biodiversity and evolutionary legacy of an endemic taxon. The inclusion of intra-specific genetic diversity in conservation planning is key for evolutionary resilience over the long-term [START_REF] Sgro | Building evolutionary resilience for conserving biodiversity under climate change[END_REF].

At the fine scale of the analyses conducted in this study, neither the taxonomic species diversity, i.e., alpha, gamma or beta diversity, nor the mean environmental heterogeneity are able to target the core area of the distribution of A. provincialis (Fig. 2). This core area is sheltering the highest level of genetic diversity of A. provincialis and has been at the origin of westward and eastward expansions that led to the current distribution of the species [START_REF] Pouget | Phylogeography sheds light on the central-marginal hypothesis in a Mediterranean narrow endemic plant[END_REF].

Contrary to the congruent biogeographical patterns observed at the coarser scale in the Mediterranean area [START_REF] Médail | Glacial refugia influence plant diversity patterns in the Mediterranean Basin[END_REF], our analysis supports the lack of congruency between the evolutionary legacy of a narrow endemic plant and the floristic diversity of the vegetation surrounding its habitat. Giving priority to the plant taxonomic species diversity criterion does not optimise and would not protect the overall population distinctness of A. provincialis. The species is represented by two major phylogeographic lineages, occurring in two well-differentiated parts of the ecological niche [START_REF] Pouget | Phylogeography sheds light on the central-marginal hypothesis in a Mediterranean narrow endemic plant[END_REF]: the alpha species diversity (ASD) level is high in the northeast lineage of A. provincialis, whereas the beta species diversity (BSD) level is high in the southwest lineage. Similarly, the environmental heterogeneity will especially target the southwest lineage. As a result, prioritising the taxonomic diversity (alpha or beta) or environmental heterogeneity will not optimise the conservation of the evolutionary legacy of A. provincialis (Table 1 and Fig. 4a andc). High levels of phylogenetic species diversity (mean PSD, Fig. 2) result in a better sampling of the evolutionary legacy of A. provincialis (EL) because of relevés with a high mean PSD within the core area where molecular variation of A. provincialis is highest. As a result, mean PSD is the "least bad" criteria among the three criteria compared (Table 1 and Fig. 4b) to target the evolutionary legacy of A. provincialis but we cannot exclude the possibility that this result was due to a random effect linked to the absence of spatial correlation among the mean PSD values.

As previously shown by [START_REF] Lamy | Variation in habitat connectivity generates positive correlations between species and genetic diversity in a metacommunity[END_REF] correlations analyses between species and genetic diversities should be conducted at the relevant spatial and temporal scales. Our results are demonstrating that coarse scale studies of biodiversity will overlook evolutionary legacy as well as crucial areas for long-term persistence. To our knowledge and in the current state of our analysis of biodiversity in the study area, no component of biodiversity was able to predict the area sheltering the highest evolutionary legacy of A. provincialis. Perspectives will be to generalise these findings to specialist plant species living with A. provincialis in lapiaz (e.g., Linaria supina or Pimpinella tragium) or in steep screes (e.g., Laserpitium gallicum) to restrict the range of processes [START_REF] Manel | Ten years of landscape genetics[END_REF].

Applied implications for conservation planning

Our analyses, conducted at a finer scale than recent studies of spatial congruency (e.g., references cited above), raise a concern regarding the difficulty of maximising the efficient use of limited conservation resources to protect all components of biodiversity [START_REF] Bottrill | Is conservation triage just smart decision making?[END_REF]. Especially, it rejects the possibility of a single surrogate of biodiversity.

For example, A. provincialis is protected under European Habitat Directive (annexe 2) and French laws, and therefore, its presence could have a beneficial effect on the conservation of the whole flora and surrounding habitats. However, the presence of A. provincialis is rarely associated with the area of strongest species richness (ASD or BSD) and this species is not a good surrogate for the preservation of floristic diversity. Furthermore, the focus area is also partially protected from urban sprawl by the recent establishment of the National Park of Calanques (NPCal, Fig. 1), which was created in 2012. NPCal protects a large number (425 species) of the 565 species within the study area and shelters several nationally protected plant species (25 species), mostly on islands and coastal plant communities. Yet, NPCal covers only partially the evolutionary legacy of A. provincialis and the ecological distinctness of its populations (Figs. 1 and2). This fact is true for the evolutionary legacy of A. provincialis but also for the other components of biodiversity measured in this study. Indeed, the highest values of phylogenetic diversity (mean PSD) or species richness (ASD) fall outside the perimeter of the NPCal (Fig. 2), and this result should be considered for any future planning of protected areas near Marseille. The spatially mismatched and unequally protected biodiversity facets studied here are an example of the high singularity of Mediterranean biotas that have already been reported at higher scales (e.g., Nieto Feliner, 2011;[START_REF] Aparicio | Fragmentation and comparative genetic structure of four Mediterranean woody species: complex interactions between life history traits and the landscape context[END_REF]. Our results strengthen the need for higher consideration of the complexity of Mediterranean biodiversity in conservation planning, with more focus on intra-specific diversity, which may be high and vulnerable in the surroundings of urban areas [START_REF] Araújo | The coincidence of people and biodiversity in Europe[END_REF][START_REF] Luck | A review of the relationships between human population density and biodiversity[END_REF].

Since [START_REF] Avise | Intraspecific phylogeography: the mitochondrial DNA bridge between population genetics and systematics[END_REF], the repeated discovery of phylogeographic lineages within species has challenged the perspectives of conservation biology. The importance of intra-specific diversity for ecosystem functioning and for preserving the evolutionary potential of species demands that genetic diversity should not be neglected when designing conservation strategies [START_REF] Bonin | Population adaptive index: a new method to help measure intraspecific genetic diversity and prioritize populations for conservation[END_REF][START_REF] Lankau | Newly rare or newly common: evolutionary feedbacks through changes in population density and relative species abundance, and their management implications[END_REF][START_REF] D'amen | Conservation of phylogeographic lineages under climate change[END_REF][START_REF] Smith | Prescriptive evolution to conserve and manage biodiversity[END_REF] even when time and money are lacking [START_REF] Ponce-Reyes | Geographical surrogates of genetic variation for selecting island populations for conservation[END_REF]. The strong phylogeographical structure of A. provincialis affords an excellent opportunity to relate the evolutionary legacy of long-term persistence to current environment and species diversity patterns. Our study highlights the crucial role of phylogeography in the evaluation of current protected areas and as a necessary criterion for future conservation planning.

Fig. 1 .

 1 Fig. 1. Geographical distribution in south-eastern France (southern Provence) of the 1132 relevés, the limits of the National Park of Calanques (NPCal, green) and pictures of typical calcareous outcrops. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of the article.)

Fig. 2 .

 2 Fig. 2. Map of the alpha, beta and gamma species diversity (ASD, BSD, and GSD), mean phylogenetic diversity (PSD), mean evolutionary legacy of A. provincialis (EL) and mean environmental heterogeneity (EH) computed within seventy-two 2000 m-zones. The blue colours depict low values, whereas the red colours depict high values. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of the article.)

Fig. 3 .

 3 Fig. 3. (a) Principal component analysis of the relationships between the five indices of biodiversity computed for the 2000 m-zones (with more than two relevés, i.e., 72) in southern Provence. (b) Plots and linear regression results of the relationships between the five indices (Kendall tau values and p-value of this test, R-squared value of the linear regression and p-value). ASD, BSD, GSD, mean PSD and mean EH are alpha, beta, gamma species diversity, mean phylogenetic diversity and mean environmental heterogeneity respectively, all indices were computed for the 72 zones.

Fig. 4 .

 4 Fig. 4. Arenaria provincialis evolutionary legacy distribution as a function of the frequency of sites per class of EL value (white area). The grey areas represent the value for (a) the set of sites with the highest species diversity (ASD), (b) the set of sites with the highest phylogenetic species diversity (PSD), and (c) the set of sites with the highest environmental heterogeneity (EH). The overall mean value of EL is represented with a black line in (a)-(c), and the mean value of EL for each criterion is indicated by a grey line.

Table 1

 1 Comparison among the three criteria of surrogate capacity for different targets of biodiversity and evolutionary legacy of A. provincialis. Exponents a , b and c represent the results of the ANOVA test, and the presence of the same letter indicates no significant difference, and different letters indicate that the values are significantly different.

		Target
		␥ diversity	␤ diversity	␣ diversity (ASD)	Mean PSD	Mean HE	Mean EL
	Criteria
	Highest ASD 17%	462	11.8	39.8	288.45	1.92	0.6 a,b
	Highest PSD 17%	314	14.8	21.22	320.51	2.98	0.78 a
	Highest HE 17%	346	17.7	19.59	293.29	3.87	0.42 b

Acknowledgements

We thank the Ministère de l'Ecologie (DREAL/DDTM) for allowing us to collect Arenaria provincialis material. We are grateful to Daniel Pavon for his help in the field and with the botanical assessment. The English language was edited and improved by Elsevier English editing service and by kindly review of Alan Forrest. This research was funded by the CNRS, the French National Office of Forests (ONF) and the General Council of Bouches du Rhône district (CG13). Marine Pouget and Pierre-Jean Dumas were supported by the Provence-Alpes-Côte d'Azur region (PACA).

Appendix A. Supplementary data

Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.ecolind.2015. 07.017.