Allan Raffard
email: allan.raffard@uclouvain.be

Elvire Bestion

Julien Cote

Bart Haegeman

Nicolas Schtickzelle

Staffan Jacob

Dispersal syndromes can link intraspecific trait variability and meta-ecosystem functioning

Keywords: Dispersal syndrome, phenotypic variability, animal movement, ecosystem functioning

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Role of dispersal in meta-communities and meta-ecosystems

The rise of trait-based ecology (see Glossary) has emphasised the importance of individual trait variability for community structure and ecosystem functioning [START_REF] Mcgill | Rebuilding community ecology from functional traits[END_REF][START_REF] Violle | Let the concept of trait be functional![END_REF]. Key frameworks have been elaborated to forecast ecosystem functioning from individual traits, such as the metabolic theory of ecology and ecological stoichiometry [START_REF] Brown | Toward a metabolic theory of ecology[END_REF][START_REF] Leal | The ecology and evolution of stoichiometric phenotypes[END_REF]. Functional traits (particularly functional effect traits, sensu [START_REF] Violle | Let the concept of trait be functional![END_REF]) indeed allow inferring causal mechanisms (e.g., body size alters resource partitioning) that help understanding key ecosystem properties such as the biodiversity-ecosystem functioning relationships. By determining biotic interactions in communities, the variability of functional traits affects species coexistence and matter fluxes (i.e. chemical elements, including nutrients) in food webs, ultimately altering ecosystem processes [START_REF] Díaz | Functional traits, the phylogeny of function, and ecosystem service vulnerability[END_REF].

Nonetheless, research on the effects of individual trait variability on ecosystems still rarely considers the spatial structure of the environment [START_REF] Loreau | Meta-ecosystems: a theoretical framework for a spatial ecosystem ecology[END_REF][START_REF] Massol | Linking community and ecosystem dynamics through spatial ecology: An integrative approach to spatial food webs[END_REF][START_REF] Gonzalez | Scaling-up biodiversity-ecosystem functioning research[END_REF]. Food webs in local communities can indeed be connected by spatial flows of organisms forming a food web meta-community [START_REF] Massol | Linking community and ecosystem dynamics through spatial ecology: An integrative approach to spatial food webs[END_REF]. Dispersal can affect biotic interactions (e.g., predation) in food web meta-communities, modifying species coexistence within communities [START_REF] Loreau | Biodiversity as spatial insurance in heterogeneous landscapes[END_REF][START_REF] Thompson | Dispersal governs the reorganization of ecological networks under environmental change[END_REF]. These exchanges of organisms between local communities can modify nutrient fluxes within the landscape that, added to abiotic energy and materials fluxes between and within local ecosystems, form meta-ecosystems. Dispersal of organisms is a key process linking populations and communities, and the resulting fluxes of nutrients sequestered in organisms among habitats form a central part of meta-ecosystem dynamics as they affect primary production, consumption and decomposition [START_REF] Lundberg | Mobile link organisms and ecosystem functioning: implications for ecosystem resilience and management[END_REF][START_REF] Gravel | Source and sink dynamics in meta-ecosystems[END_REF][START_REF] Gravel | Patch dynamics, persistence, and species coexistence in metaecosystems[END_REF].

While dispersal was mostly considered as a rate in meta-community and meta-ecosystem literature, it is now widely acknowledged to be a non-random process resulting from several environmental factors, phenotypic traits and their interactions [START_REF] Clobert | Informed dispersal, heterogeneity in animal dispersal syndromes and the dynamics of spatially structured populations[END_REF]. For instance, niche breadth and life-history traits are correlated with dispersal variability among species [START_REF] Stevens | A comparative analysis of dispersal syndromes in terrestrial and semi-terrestrial animals[END_REF]. Within species, dispersal decision of individuals can also depend upon their phenotype, involving morphological, physiological or behavioural characteristics correlated with dispersal. For instance, in rodents, dispersers are often more active, bolder and explore more than residents [START_REF] Galliard | Patterns and processes of dispersal behaviour in arvicoline rodents: dispersal mechanisms in microtine rodents[END_REF]. Similarly, polymorphism (e.g. wing length of insects) is often associated with dispersal distance [START_REF] Zera | Physiology and ecology of dispersal polymorphism in insects[END_REF]. Such correlation or co-occurrence between a suite of phenotypic traits and dispersal forms a dispersal syndrome [START_REF] Clobert | Informed dispersal, heterogeneity in animal dispersal syndromes and the dynamics of spatially structured populations[END_REF][START_REF] Galliard | Patterns and processes of dispersal behaviour in arvicoline rodents: dispersal mechanisms in microtine rodents[END_REF][START_REF] Sih | Behavioral syndromes: an integrative overview[END_REF][START_REF] Cote | Evolution of dispersal strategies and dispersal syndromes in fragmented landscapes[END_REF], that may result from multiple ecological and evolutionary processes (Box 1).

Dispersal syndromes are known to affect the spatial heterogeneity of functional traits and in turn mediate intra/interspecific interactions and meta-community dynamics [START_REF] Jacob | Habitat matching and spatial heterogeneity of phenotypes: implications for metapopulation and metacommunity functioning[END_REF][START_REF] Jacob | Variability in dispersal syndromes is a key driver of metapopulation dynamics in experimental microcosms[END_REF][START_REF] Massol | How life-history traits affect ecosystem properties: effects of dispersal in meta-ecosystems[END_REF]. However, whether this variability in the movements of organisms and their phenotypic traits in landscapes can in turn modify the flows of energy and materials and affect food web metacommunity and meta-ecosystem functioning is rarely studied theoretically or empirically.

Here, we build upon empirical evidence on vertebrates, arthropods and microorganisms to highlight that traits classically integrated into trait-based ecology and known for their role in ecosystem functioning can be linked to dispersal propensity. Based on this evidence for dispersal syndromes as a linkage between trait-based ecology and ecosystem functioning, we point out potential implications of these dispersal syndromes for meta-ecosystem functioning (Figure 1). We explore the consequences of dispersal syndromes and their evolution for the spatial heterogeneity of ecosystem functions.

On the ecosystem importance of dispersal-related traits

The phenotypic structure of populations has received strong consideration from ecologists, and the description of functional effect traits has allowed a mechanistic understanding of the effects of individuals on ecosystems [START_REF] Violle | Let the concept of trait be functional![END_REF][START_REF] Matthews | Toward an integration of evolutionary biology and ecosystem science[END_REF]. The variability of functional traits within a species can be large [START_REF] Siefert | A global meta-analysis of the relative extent of intraspecific trait variation in plant communities[END_REF], and can modify the strength of trophic and non-trophic interactions, such as nutrient recycling within an ecosystem [START_REF] Raffard | The community and ecosystem consequences of intraspecific diversity: a meta-analysis[END_REF]. For example, consistent differences in foraging behaviour in pale chubs (Zacco platypus) alter trophic cascades [START_REF] Katano | Effects of individual differences in foraging of pale chub on algal biomass through trophic cascades[END_REF]; morphology of mandible in shredders (Gammarus fossarum) drives decomposition rate [START_REF] Rota | Phenotypic determinants of inter-individual variability of litter consumption rate in a detritivore population[END_REF]. Functional traits and their intraspecific variability have hence consequences for species coexistence, community structure, and subsequently drive the flows of energy and materials within and among ecosystems. Key functional traits have been found to be related to individual dispersal propensity:

in Table 1, we provide a list of relationships within the same species between dispersal and phenotypic traits on the one hand, and between these phenotypic traits and functional effect traits (sometimes even ecosystem functions) on the other hand. As such, in a freshwater fish (Salmo trutta), higher dispersal propensities are associated with larger body sizes [START_REF] Vøllestad | Small-scale dispersal and population structure in streamliving brown trout ( Salmo trutta ) inferred by mark-recapture, pedigree reconstruction, and population genetics[END_REF], a trait correlated in this species with nutrient excretion rate [START_REF] Villéger | Intra-and interspecific differences in nutrient recycling by European freshwater fish[END_REF] and known as key for ecosystem functioning [START_REF] Schmitz | Predator control of ecosystem nutrient dynamics[END_REF]. Moreover, movements of dispersers can be associated with higher metabolic costs compared to residents [START_REF] Bonte | Costs of dispersal[END_REF] -metabolism is a key trait for ecosystem functioning [START_REF] Brown | Toward a metabolic theory of ecology[END_REF] which can induce higher consumption rates to counterbalance the energetic expenditure (as found in the butterfly Melitaea cinxia. [START_REF] Niitepõld | Flight metabolic rate and Pgi genotype influence butterfly dispersal rate in the field[END_REF][START_REF] Niitepõld | Effects of flight and food stress on energetics, reproduction, and lifespan in the butterfly Melitaea cinxia[END_REF]). Finally, dispersal is often part of a general behavioural syndrome involving multiple behavioral traits [START_REF] Reale | Personality and the emergence of the pace-of-life syndrome concept at the population level[END_REF]. In the signal crayfish (Pacifastacus leniusculus), individuals staying in core populations (i.e., residents) of an invasion front are more aggressive [START_REF] Hudina | Differences in aggressive behaviour along the expanding range of an invasive crayfish: an important component of invasion dynamics[END_REF], which can alter multiple dimensions of ecosystems such as trophic interactions in food webs [START_REF] Toscano | Personality, foraging behavior and specialization: integrating behavioral and food web ecology at the individual level[END_REF]37].

Because of dispersal syndromes, individuals moving within a landscape can carry different functional traits from individuals staying locally, and spatially heterogeneous distribution of environmental conditions (e.g., environmental gradients, source-sink systems) can make the fluxes of individual phenotypes asymmetric. Therefore, spatial variability of functional traits can be generated among landscapes, potentially modifying the interactions within meta-communities and in turn material and energy fluxes in meta-ecosystems. These altered fluxes can affect two essential and intertwined dimensions of ecosystems: the strength of trophic interactions and nutrient recycling. Especially, trophic interactions govern food web structure in meta-communities, with subsequent effects on biomass production that are key for meta-ecosystems functioning. First, dispersal syndromes can modify the spatial heterogeneity of traits linked to energy and nutritional needs of organisms, consequently modifying trophic interactions [START_REF] Brown | Toward a metabolic theory of ecology[END_REF][START_REF] Toscano | Personality, foraging behavior and specialization: integrating behavioral and food web ecology at the individual level[END_REF][START_REF] Mccauley | Foraging rates of larval dragonfly colonists are positively related to habitat isolation: results from a landscape-level experiment[END_REF]. For instance, in decomposer species, dispersers may display higher litter consumption, hence affecting the decomposition rate of organic matter, although this effect varies among species [START_REF] Little | Dispersal syndromes can impact ecosystem functioning in spatially structured freshwater populations[END_REF]. In mosquitofish (Gambusia affinis), dispersers are less sociable than residents, which affects prey biomass because sociability is correlated with food intake [START_REF] Cote | Non-random dispersal mediates invader impacts on the invertebrate community[END_REF]. Dispersal-related morphological traits can also be important for ecosystem functioning. In pygmy grasshoppers (Tetrix subatala), a morphological specialisation for dispersal (i.e., fully developed wings) is associated with a different diet compared to wingless individuals [START_REF] Karpestam | Stable isotopes reveal dietary divergence between dispersal phenotypes in Tetrix subulata pygmy grasshoppers (Orthoptera: Tetrigidae)[END_REF]. This can potentially affect the recipient ecosystem through altered trophic interactions. These examples show that dispersal syndromes can affect material fluxes in food webs and thus ecosystem functions, such as decomposition of organic matter, through changes in trophic interactions (Table 1) [START_REF] Schmid | Rapid divergence of predator functional traits affects prey composition in aquatic communities[END_REF].

Second, dispersal syndromes can produce nutrient-mediated effects, modifying nutrient and detritus influxes in ecosystems, both qualitatively and quantitatively [START_REF] Massol | How life-history traits affect ecosystem properties: effects of dispersal in meta-ecosystems[END_REF]. In a freshwater fish (Salmo trutta), larger individuals disperse farther than smaller individuals [START_REF] Vøllestad | Small-scale dispersal and population structure in streamliving brown trout ( Salmo trutta ) inferred by mark-recapture, pedigree reconstruction, and population genetics[END_REF] and display higher nutrient excretion rates (i.e., N and P) [START_REF] Villéger | Intra-and interspecific differences in nutrient recycling by European freshwater fish[END_REF]. Such intraspecific variability in nutrient excretion rate, resulting from catabolic and homeostatic mechanisms, is large enough to generate functional differences among ecosystems, notably concerning primary production [START_REF] Schmitz | Predator control of ecosystem nutrient dynamics[END_REF][START_REF] Bassar | Local adaptation in Trinidadian guppies alters ecosystem processes[END_REF]. Differences between residents and dispersers may affect the spatial variability of productivity in meta-ecosystems. For example, in phosphorus-limited habitats, individuals with a higher phosphorus excretion rate cause an increased biomass of primary producers [START_REF] Evangelista | Resource composition mediates the effects of intraspecific variability in nutrient recycling on ecosystem processes[END_REF]. Organic material recycling might also be altered by differential mortality between residents and dispersers induced by the costs of dispersal. For instance, dispersers can have a higher parasite load than residents [START_REF] Clobert | Dispersal[END_REF], which may increase mortality and thus alter the stocks of dead organic matter. Moreover, the stoichiometry of organisms is an important factor governing ecosystem functions [START_REF] Leal | The ecology and evolution of stoichiometric phenotypes[END_REF], and has recently been discussed as a key parameter linking dispersal to meta-ecosystems [START_REF] Massol | How life-history traits affect ecosystem properties: effects of dispersal in meta-ecosystems[END_REF]. Intraspecific variability of stoichiometry has been documented [START_REF] Leal | The ecology and evolution of stoichiometric phenotypes[END_REF], and several studies suggest that differences between residents and dispersers are likely. For instance, differences in chemical composition (e.g., lipid, triglyceride reserves) between residents and dispersers have been found in marine fish [START_REF] Shima | Consequences of variable larval dispersal pathways and resulting phenotypic mixtures to the dynamics of marine metapopulations[END_REF] and insects [START_REF] Zera | Lipid, carbohydrate and nitrogen content of long-and shortwinged Gryllus firmus: Implications for the physiological cost of flight capability[END_REF]. Since chemical compounds within organisms consist of different proportions of the basic elements, differences in molecular traits (e.g., RNA content) and key physiological functions are expected to be associated with variability in organisms' stoichiometry [START_REF] Gillooly | The metabolic basis of whole-organism RNA and phosphorus content[END_REF][START_REF] Jeyasingh | Fundamental links between genes and elements: evolutionary implications of ecological stoichiometry[END_REF]. The potential for dispersal syndromes to include stoichiometric variability might thus result in altered nutrient flows among local ecosystems. Studying the three-way association between dispersal, stoichiometry and ecosystem functioning is an important future challenge [START_REF] Massol | How life-history traits affect ecosystem properties: effects of dispersal in meta-ecosystems[END_REF], especially since dispersal can couple distant (but often similar) ecosystems, while resource flows mostly occur locally [START_REF] Gounand | Meta-ecosystems 2.0: rooting the theory into the field[END_REF].

Implications of dispersal syndromes for meta-ecosystem functioning

Meta-community research has emphasized the central role of dispersal as a process linking biotic interactions, and global rates of material flows (through both abiotic and biotic fluxes) among local ecosystems are core to meta-ecosystem theory [START_REF] Thompson | Dispersal governs the reorganization of ecological networks under environmental change[END_REF][START_REF] Thompson | A process-based metacommunity framework linking local and regional scale community ecology[END_REF]. However, dispersal can be differenciated from abiotic fluxes as it can alter spatial distribution of organisms, mediating directly biotic interactions, in addition to modify nutrient fluxes. For instance, increasing dispersal rate tends to homogenize food webs and functions across space in a nonlinear manner, above a certain threshold [START_REF] Loreau | Biodiversity as spatial insurance in heterogeneous landscapes[END_REF][START_REF] Thompson | Dispersal governs the reorganization of ecological networks under environmental change[END_REF][START_REF] Thompson | A process-based metacommunity framework linking local and regional scale community ecology[END_REF] (though increasing consumer dispersal can also generate spatial heterogeneity, e.g., [START_REF] Gounand | The Paradox of Enrichment in Metaecosystems[END_REF]). Yet, dispersal is more than just movement rate or distance, it also includes the phenotypic characteristics of resident and disperser individuals, and therefore a potential different package of flowed nutrients (i.e., dispersing individuals). However, the potential for differences between dispersers and residents in multiple functional traits is currently not integrated in meta-ecosystem theory.

As highlighted above, dispersal syndromes often involve functional traits of major importance for ecosystem functioning (Table 1). The heterogeneity of phenotypic distributions resulting from dispersal syndromes, i.e., when dispersers have different phenotypes than residents in heterogeneous landscapes, may thus generate spatial differentiation in ecosystem functioning. For instance, the establishment of individuals or species in novel habitats as occurring during recolonization or range shifts may be associated with a non-random subset of traits, such as body mass or diet. This generates spatial heterogeneity in functional trait distribution [START_REF] Messager | Phenotypic variability of rusty crayfish ( Faxonius rusticus ) at the leading edge of its riverine invasion[END_REF] and in turn affecting resource fluxes and thus ecosystem biomass. Therefore, any biased flow of functional traits carried by dispersers in heterogeneous landscapes may modify the spatial heterogeneity of meta-ecosystems, whose importance could depend upon nutrient flows (Box 2).

The effects of dispersal on meta-ecosystems are known to depend on the rate of dispersal in classic theory. With dispersal syndromes, since dispersers differ from residents, differences in dispersal rate do not only change the total flow of organisms within metaecosystems, but also mediate the spatial distribution of functional trait values (Box 2). For instance, in a scenario where dispersers consume more resources than residents (as found in [START_REF] Little | Dispersal syndromes can impact ecosystem functioning in spatially structured freshwater populations[END_REF]), intermediate dispersal rates would alter the heterogeneity of biomass consumption at the meta-ecosystem scale compared to a scenario in which individuals disperse regardless of their phenotype. Thus the heterogeneity in resource standing stock can be modified (Box 2). Therefore, developing an integrative framework including dispersal syndromes in a metaecosystem might benefit our understanding of spatially structured environments.

Importantly, dispersal syndromes can differ among populations or species [START_REF] Clobert | Informed dispersal, heterogeneity in animal dispersal syndromes and the dynamics of spatially structured populations[END_REF][START_REF] Stevens | A comparative analysis of dispersal syndromes in terrestrial and semi-terrestrial animals[END_REF][START_REF] Galliard | Patterns and processes of dispersal behaviour in arvicoline rodents: dispersal mechanisms in microtine rodents[END_REF].

Environmental conditions and evolutionary processes can strongly shape dispersal syndromes [START_REF] Cote | Evolution of dispersal strategies and dispersal syndromes in fragmented landscapes[END_REF]. The direction and the strength of covariations as well as the traits involved in dispersal syndromes are the result of an evolutionary history where biotic interactions and landscape configuration play a key role (e.g., [START_REF] Cote | Evolution of dispersal strategies and dispersal syndromes in fragmented landscapes[END_REF][START_REF] Legrand | Ranking the ecological causes of dispersal in a butterfly[END_REF], Box 1). The resulting variability in dispersal syndromes and thus of flows of functional traits might alter meta-ecosystem dynamics through trophic interactions and nutrient-mediated effects. For instance, when dispersal is associated with high competitive abilities (e.g., due to higher aggressiveness as found in bluebirds [START_REF] Duckworth | Coupling of dispersal and aggression facilitates the rapid range expansion of a passerine bird[END_REF]), an increased dispersal rate would lead to an increase in competition strength in colonized habitats. On the contrary, dispersers can often be poorer competitors (e.g., competition-colonisation trade-off, costs of dispersal, local exclusion of poorer competitors) [START_REF] Bonte | Costs of dispersal[END_REF][START_REF] Cadotte | On testing the competition-colonization trade-off in a multispecies assemblage[END_REF]. If competitive interactions drive community composition, the consequences of dispersal for community composition, and subsequently the level and stability of ecosystem functions are likely to depend on the form of dispersal syndromes and thus on their ecological and evolutionary drivers.

The role of evolutionary processes for ecosystem functioning has been studied at the local scale [START_REF] Matthews | Toward an integration of evolutionary biology and ecosystem science[END_REF]. At the meta-community level, Urban & Skelly [START_REF] Urban | Evolving metacommunities: toward an evolutionary perspective on metacommunities[END_REF] have drawn a framework integrating the evolution of intraspecific trait variation in meta-communities. They emphasized that genetically based trait variation might be a major component of metacommunity structure affecting species coexistence. Therefore, by extending this concept, dispersal syndromes can have two main roles in the evolutionary dynamics of meta-communities and meta-ecosystems: eco-evolutionary dynamics and local adaptations. First, since the evolution of intraspecific variability of dispersal and its associations with phenotypic variability depend on biotic and abiotic conditions, the existence and form of dispersal syndromes are likely to vary in space and time [START_REF] Cote | Evolution of dispersal strategies and dispersal syndromes in fragmented landscapes[END_REF]. Therefore, eco-evolutionary feedbacks between dispersal and meta-ecosystem functioning can arise because of environmental fluctuations, due to the dependency of dispersal syndromes on abiotic conditions and its effect on ecosystem functions. The consequences of dispersal for metaecosystems are expected to differ depending on the nature of the syndrome (above and Box 2). Therefore, integrating the evolutionary dynamics of dispersal-related traits into metaecosystem theories should help understand how ecosystem functioning varies in the face of environmental changes.

Second, dispersal is generally expected to slow down adaptation by homogenizing local gene pools, at least over a certain threshold. Nonetheless, theoretical and experimental studies showed that it may instead promote local adaptation and thus population phenotypic differentiation when individuals choose to disperse and settle in habitats that better suit their phenotype [START_REF] Edelaar | Matching habitat choice causes directed gene flow: a neglected dimension in evolution and ecology[END_REF]. Since dispersal syndromes are also expected to generate spatial heterogeneity of phenotypic traits, the interaction between dispersal syndromes and habitat choice might alter the dynamics of trait variation within and between populations. Whether dispersal syndromes are fixed at the scale of population or species or depend on environmental conditions (Box 1) might generate dynamic phenotypic flows in meta-ecosystems according to evolutionary dynamics (e.g., local adaptation) and ecological context. By modifying trait dynamics within and among populations, dispersal syndromes might hence alter functional divergences among food webs and ecosystems across generations. Indeed, functional traits linked to dispersal propensity may be inherited across generations and so may be the consequences of these traits for ecosystem functioning [START_REF] Whitham | A framework for community and ecosystem genetics: from genes to ecosystems[END_REF]. Investigating the potential for such eco-evolutionary dynamics of dispersal to affect biotic interactions and as a result food webs and ecosystems is of particular importance.

Concluding remarks

Dispersal syndromes mediate phenotypic distributions and hence interaction strength and nutrient release in ecological networks and thus may play a major role in meta-ecosystem functioning. We especially pointed out that links between dispersal and traits of key importance for ecosystem functioning can modify trophic interactions and material fluxes. For example, dispersal syndromes can make dispersal increase spatial heterogeneity in ecosystem functioning relative to cases without dispersal syndromes. Predictions regarding spatial dynamics of meta-ecosystems may hence benefit from the integration of dispersal syndromes.

Yet, dispersal syndromes can greatly vary across species in both direction and traits involved, which might affect the consequences for meta-ecosystems as illustrated in Box 2. Improving our understanding of the role of dispersal for the spatial dynamics of meta-ecosystems will thus require further effort in integrating dispersal syndromes in meta-ecosystem theoretical frameworks, but also increased investigation of the ecological and evolutionary drivers of dispersal syndromes.

Modelling approaches can be a powerful method to evaluate the role of phenotypicdependent dispersal for meta-ecosystem functioning. For instance, existing models (see for example [START_REF] Massol | How life-history traits affect ecosystem properties: effects of dispersal in meta-ecosystems[END_REF][START_REF] Gounand | The Paradox of Enrichment in Metaecosystems[END_REF]) can be modified to implement dispersal syndromes. It would allow to determine whether the phenotypic differences between dispersing and non-dispersing individuals might result in an increased complexity in ecological interactions, potentially quantitatively or qualitatively altering meta-ecosystems functioning and stability (e.g., [START_REF] Gravel | Stability and complexity in model meta-ecosystems[END_REF]).

Such models should further allow assessing whether and how the evolution of dispersal syndromes alter meta-ecosystem dynamics. The evolution of dispersal syndromes is important to account for since anthropogenic pressures change the environmental conditions that are known to shape dispersal syndromes (e.g., habitat fragmentation).

Transposing those predictions to nature is challenging due to the inherent large scale of meta-ecosystem frameworks [START_REF] Gonzalez | Scaling-up biodiversity-ecosystem functioning research[END_REF], but correlative approaches in the field coupled with adequate statistics (e.g., structural equation modelling) can bring insights on the relationships between dispersal syndromes, spatially structured diversity and ecosystem patterns. A further necessary step to identify whether dispersal syndromes directly or indirectly affect metaecosystems will be to take advantage of the increasingly used micro/mesocosm experiments.

Manipulating dispersal syndromes (i.e., shape and variance) and key characteristics of the environment (e.g., abiotic conditions, habitat fragmentation) in simplified meta-ecosystems is an essential step forward for our comprehension of the effects of dispersal syndromes on biodiversity, biomass production and stability of meta-ecosystems. Understanding the role of variability of dispersal for meta-ecosystem functioning is an exciting and challenging topic for years to come (see Outstanding Questions). In a world where human activities are constantly shaping landscape structure, considering those issues might also help design ecological applications, such as conservation strategies.

innovation programme (grant agreement No 817779). This paper is contribution BRCXXX of the Biodiversity Research Center at UCLouvain.

Glossary

Dispersal: Any movement of individuals from one population to another that can potentially lead to gene flow. Dispersal must not be confounded with migration, i.e., a back-and-forth movement (often seasonal but not only) between a reproduction site and a site where other parts of the life cycle are spent.

Dispersal syndrome: Suite of phenotypic traits correlated with dispersal (i.e., differentiating dispersers from residents or along dispersal rate or distance).

Ecosystem functioning: Set of processes (or functions) describing changes in energy and matter dynamics due to biological, physical or geochemical factors.

Functional effect trait: Individual characteristics affecting community or ecosystem processes (also referred to as functional traits in the text). Can be differentiated from functional response traits allowing organisms to cope with environmental variability.

Individual trait variability (= intraspecific trait variability): Variability of trophic, physiological, behavioral or morphological features displayed by individuals within a species.

Meta-community:

Set of local communities linked by the dispersal of organisms. Multiple theoretical meta-communities have been studied, such as food web meta-communities or competitive metacommunities.

Meta-ecosystem:

Set of local ecosystems connected by flows of energy, matter, and organisms.

Nutrient-mediated effects: Modification of the dynamics of nutrient elements independently of consumptive effects, for instance through excretion of nitrogen, phosphorus, or carbon.

Trait-based ecology: Study of the interactions between organisms' phenotype and their environment.

Trophic interactions: Interactions linked to the feeding habits and the consumption of organisms and describing vertical matter fluxes. Figure 1. Overview of the potential linkage between dispersal syndromes and metaecosystem functioning through covariations with functional effect traits. (a) Dispersal syndromes consist of dispersers (white circles) with different phenotypes than residents (black circles), potentially leading to a spatial heterogeneity in the distribution of phenotypic traits. Grey arrows represent abiotic fluxes (nutrients and material) which may interact with dispersal in shaping meta-ecosystem functioning. (b) Dispersal syndromes can involve multiple phenotypic traits, such as morphology (e.g., leg size) or physiology (e.g., hormones levels). These traits are known to be linked to key functional effect traits important for ecosystem functions such as consumption rate, nitrogen excretion, and nutrient recycling. The figure illustrates an example where dispersers are more active explorers and consume more resource than residents, but other relationships can exist (Table 1). (c) Dispersal syndromes can therefore make local ecosystems differ in key properties such as biomass production, consumption rate, and nutrient recycling, hence increasing spatial heterogeneity of metaecosystem functioning.

Box 1. Processes generating dispersal syndromes and their consequences for metaecosystems.

Dispersal is part of large association among suites of phenotypic traits (e.g., pace-of-life framework [START_REF] Reale | Personality and the emergence of the pace-of-life syndrome concept at the population level[END_REF]) whose respective evolution can greatly influence each other. Multiple processes can explain these covariations between phenotype and dispersal [START_REF] Clobert | Informed dispersal, heterogeneity in animal dispersal syndromes and the dynamics of spatially structured populations[END_REF][START_REF] Cote | Evolution of dispersal strategies and dispersal syndromes in fragmented landscapes[END_REF][START_REF] Massol | How life-history traits affect ecosystem properties: effects of dispersal in meta-ecosystems[END_REF], which may generate variability of dispersal syndromes within and between species. First, trade-offs may result in negative correlations between dispersal and other traits, as when allocation of time and energy to dispersal limits investment in other biological functions (e.g., foraging, immunity). Second, syndromes can emerge from structural links between dispersal and other traits, including gene pleiotropy or allometric scaling. Finally, dispersal syndromes can result from selection, when the environment favors both dispersal and other traits (co-selection) or when selection on dispersal affects the evolution of other traits or the reverse (joint-selection). In addition, both dispersal and related phenotypic traits can be determined by both genetic and environmental factors [START_REF] Cote | Evolution of dispersal strategies and dispersal syndromes in fragmented landscapes[END_REF], which can generate different levels of spatial and temporal variability in dispersal syndromes. The level of heritability of traits involved in dispersal syndromes can modify the strength, direction, and variance of correlations between traits and dispersal across generations. Furthermore, plasticity in dispersal and related traits along environmental conditions can result in important and rapid changes in traits and their covariations, potentially generating high variability in dispersal syndromes. Depending on the relative importance of processes generating dispersal syndromes and their variation across time and space, the extent of intraspecific variation and direction of correlations between dispersal and functional traits might change among localities. Investigating how much dispersal syndromes vary among localities is thus crucial to better understand their importance for example on meta-population dynamics [START_REF] Jacob | Variability in dispersal syndromes is a key driver of metapopulation dynamics in experimental microcosms[END_REF], species range distribution [START_REF] Shine | An evolutionary process that assembles phenotypes through space rather than through time[END_REF], or the diversity and stability of meta-ecosystems [START_REF] Gravel | Stability and complexity in model meta-ecosystems[END_REF]. For instance, landscape fragmentation usually increases dispersal costs and might exacerbate dispersal syndromes that result from trade-offs [START_REF] Cote | Evolution of dispersal strategies and dispersal syndromes in fragmented landscapes[END_REF], ultimately potentially increasing the consequences for the spatial heterogeneity of meta-ecosystems. Furthermore, environmental changes can generate different levels of intra-and interspecific variability of dispersal syndromes when dispersal and related traits are plastic [START_REF] Jacob | Phenotypic plasticity can reverse the relative extent of intra-and interspecific variability across a thermal gradient[END_REF]. We might expect the resulting variability of dispersal syndromes to determine the strength and type of species interactions, thereby modifying patterns of diversity within communities and potentially meta-ecosystem stability and resilience. Identifying which mechanisms underlie variability of dispersal syndromes is thus one of the key challenges to better understand their effects on meta-ecosystem functioning.

504 Box 2. A mathematical illustration of the potential effects of dispersal syndromes on a key component of meta-ecosystems: consumption rate.

We investigated the consequences of dispersal for the spatial variability of consumption rate, a key component of meta-ecosystems, when dispersal is correlated positively or negatively to this functional trait, as found in many species (see for instance Table 1). To do so, we constructed a meta-population model with dispersal of a consumer in a landscape consisting of a 10-habitat patch network. Local environmental conditions varied randomly and temporally, leading to random local extinctions. We drew multiple scenarios involving dispersal syndromes (see Supplementary information). In a scenario of absence of a dispersal syndrome (i.e., residents and dispersers display equal consumption rates; yellow lines), increasing dispersal rate is expected to increase total resource consumption (left panel), and decrease its spatial heterogeneity (non-linearly; right panel) in meta-ecosystems. We then considered dispersal syndromes, with dispersers showing either higher (competitive advantage) or lower (competition-colonization trade-off) consumption rate compared to residents, while setting the mean consumption rate constant across different dispersal probabilities. In the case of a positive association of consumption rate and dispersal (blue lines), we observed a slight increase in total resource consumption at intermediate dispersal rates (Figure Ia), resulting from increased abundance of the disperser phenotype following recolonization of extinct patches. Although the effects on resource consumption at the landscape scale (left panel) are weak, they create an important spatial heterogeneity of resource consumption in the meta-ecosystem (Figure Ib). While increasing dispersal always has a homogenizing effect above a certain threshold, the inclusion of a dispersal syndrome where dispersers are weaker consumers than residents (red curve) could strongly moderate this effect resulting in higher heterogeneity than previously predicted. On the contrary, higher consumption in dispersers (blue curve) results in a decrease of spatial heterogeneity of ecosystem function and alleviates the effect of dispersal rate. The integration of abiotic nutrient fluxes will be an important next step since they may affect species persistence and interactions. Therefore, further studies should investigate whether abiotic fluxes interact with or blur the effects of dispersal syndromes on local biomass and nutrient recycling. This simple model highlights the potential for dispersal syndromes to significantly affect the spatial variability in ecosystem function, with direction of effects that depends on the type of dispersal syndrome considered, pointing out the potential for further investigation of the integration of dispersal syndromes in meta-ecosystem theory. 1. Some of the patches become extinct. For each patch an extinction occurs with probability p E = 0.2. This means that a patch undergoes extinction on average every five generations.

2. For each individual the dispersal phenotype is determined with probability p D a disperser, or else a resident. Then the dispersers redistribute over the metapopulation. The dispersal process is assumed to be spatially uniform: for each disperser its new patch is randomly drawn from the set of M = 10 patches.

3. Individuals reproduce in a density-dependent way. For each parent the number of off-spring is Poisson distributed with mean , where N is the number of individuals (both dispersers and residents) in the patch. After reproduction the parent individuals die. Hence, the new number of individuals in the patch is on average . This formula implies that the population is expected to double for a small population (N ≪ K) and to remain constant for a population close to carrying capacity K = 100, as it should.

After this last step the simulation continues at step 1 for the next generation.

The resource consumption of an individual is assumed to be proportional to its number of offspring. Hence, denoting by N D and N R the number of offspring produced in a patch by dispersers and residents, respectively, the total resource consumption in that patch is given by c D N D + c R N R . Note that resource consumption does not affect the meta-population dynamics, so that the same simulations can be used to study different combinations c D and c R (i.e., different types of dispersal syndrome).

In each simulation we monitor the resource consumption during 1000 generations.

Using these monitored values (M = 10 patches × 1000 generations), we compute the (spatio-temporal) mean resource consumption per patch and the (temporal) mean standard deviation of resource consumption between patches. We obtain similar results when considering the temporal rather than spatial variation of resource consumption. We repeat this procedure 10 times for each value of dispersal probability p D ranging from 0 to 1 in steps of 0.05. The figure of Box 2 shows results averaged over the 10 replicates.

Figure I .

 I Figure I. Hypothetical examples of consequences of dispersal syndromes for resource consumption in the meta-ecosystem, concerning both its average value (a) and its spatial heterogeneity of resource consumption (b).

Acknowledgements AR is supported by a F.R.S.-FNRS research project (PDR T.0211.19) awarded to NS in collaboration with SJ. NS is Senior Research Associate of the F.R.S.-FNRS and supported by an Action de Recherche Concertée grant (ARC 18/23-095). SJ, EB, BH and JC are part of TULIP (Laboratory of Excellence Grant ANR-10 LABX-41), SJ is supported by the Agence Nationale de la Recherche for the project CHOOSE (ANR-19-CE02-0016), and JC by the European Research Council (ERC) under the European Union's Horizon 2020 research and

Table 1. Traits involved in dispersal syndromes are often linked with functional traits of key importance for ecosystem dynamics. We draw a non-exhaustive list of empirical examples where a trait in a given species is involved in dispersal syndromes and where the same trait (or dispersal directly) is linked to a functional effect trait, therefore potentially sustaining dispersal syndrome effects on meta-ecosystems. Positive and negative correlations are denoted by a (-) and a (+), respectively. Wing length (+) [START_REF] Zera | Physiology and ecology of dispersal polymorphism in insects[END_REF][START_REF] Berggren | Spatial sorting may explain evolutionary dynamics of wing polymorphism in pygmy grasshoppers[END_REF] Diet (+) [START_REF] Karpestam | Stable isotopes reveal dietary divergence between dispersal phenotypes in Tetrix subulata pygmy grasshoppers (Orthoptera: Tetrigidae)[END_REF] Dispersal is positively correlated with trophic position

Brown trout (Salmo trutta, fish)

Body length (-) [START_REF] Vøllestad | Small-scale dispersal and population structure in streamliving brown trout ( Salmo trutta ) inferred by mark-recapture, pedigree reconstruction, and population genetics[END_REF] Diet/ Excretion rate (+) [START_REF] Cucherousset | Stable isotope evidence of trophic interactions between introduced brook trout Salvelinus fontinalis and native brown trout Salmo trutta in a mountain stream of south-west France[END_REF] , [START_REF] Villéger | Intra-and interspecific differences in nutrient recycling by European freshwater fish[END_REF] Dispersal is negatively correlated with Nexcretion rate and trophic position Threespine stickleback (Gasterosteus aculeatus, fish) Stream morphology (+) [START_REF] Bolnick | Phenotype-dependent native habitat preference facilitates divergence between parapatric lake and stream stickleback[END_REF] Prey biomass (-) [START_REF] Matthews | Experimental evidence of an eco-evolutionary feedback during adaptive divergence[END_REF] Dispersal reduces prey biomass Behaviour Mosquitofish (Gambusia affinis, fish) Sociability (-) [START_REF] Cote | Non-random dispersal mediates invader impacts on the invertebrate community[END_REF] Prey biomass (+) [START_REF] Cote | Non-random dispersal mediates invader impacts on the invertebrate community[END_REF] Dispersal reduces prey density Signal crayfish (Pasifastacus lenisculus, arthropod) Aggressiveness (-) [START_REF] Hudina | Differences in aggressive behaviour along the expanding range of an invasive crayfish: an important component of invasion dynamics[END_REF] Food consumption (+) [37] Dispersal is negatively correlated with prey consumption Great tit (Parus major, bird) Exploration (+) [START_REF] Dingemanse | Natal dispersal and personalities in great tits ( Parus major )[END_REF] Competitive dominance (+) [START_REF] Dingemanse | The relation between dominance and exploratory behavior is context-dependent in wild great tits[END_REF] Dispersal is positively correlated with competitiveness Bank vole (Myodes glareolus, mammal) Activity (+) [START_REF] Ebenhard | High activity in bank voles in relation to colonization ability[END_REF] Food consumption (+) [START_REF] Ebenhard | High activity in bank voles in relation to colonization ability[END_REF] Dispersal is positively correlated with consumption rate Dragonfly (Libellula spp., arthropod) Colonization distance (+) [START_REF] Mccauley | Foraging rates of larval dragonfly colonists are positively related to habitat isolation: results from a landscape-level experiment[END_REF] Food consumption (+) [START_REF] Mccauley | Foraging rates of larval dragonfly colonists are positively related to habitat isolation: results from a landscape-level experiment[END_REF] Dispersal is positively correlated with consumption rate Physiology Sand field cricket (Gryllus firmus, arthropod)

Lipid and amino acid metabolism (+) [START_REF] Zera | Physiology and ecology of dispersal polymorphism in insects[END_REF][START_REF] Zera | Intermediary metabolism and life-history trade-offs: differential metabolism of amino acids underlies the dispersal-reproduction trade-off in a wing-polymorphic cricket[END_REF] Nutrient content (+) [START_REF] Zera | Lipid, carbohydrate and nitrogen content of long-and shortwinged Gryllus firmus: Implications for the physiological cost of flight capability[END_REF] Dispersal is positively correlated with lipid and triglyceride contend Common lizard (Lacerta vivipara, squamate)

Corticosterone (-) [START_REF] De Fraipont | Increased pre-natal maternal corticosterone promotes philopatry of offspring in common lizards Lacerta vivipara[END_REF][START_REF] Meylan | Stress and body condition as prenatal and postnatal determinants of dispersal in the common lizard (Lacerta vivipara)[END_REF] Food consumption (+) [START_REF] Cote | Experimental enhancement of corticosterone levels positively affects subsequent male survival[END_REF][START_REF] Cote | Food deprivation modifies corticosterone-dependent behavioural shifts in the common lizard[END_REF] Dispersal is negatively correlated with food intake

Glanville fritillary (Melitaea cinxia, arthropod)

Metabolic rate (+) [START_REF] Niitepõld | Flight metabolic rate and Pgi genotype influence butterfly dispersal rate in the field[END_REF] Food consumption (+) [START_REF] Niitepõld | Effects of flight and food stress on energetics, reproduction, and lifespan in the butterfly Melitaea cinxia[END_REF] Dispersal is positively correlated with food intake

Life history

Common triplefin (Forsterygion lapillum, fish)

Growth rate (-) [START_REF] Shima | Consequences of variable larval dispersal pathways and resulting phenotypic mixtures to the dynamics of marine metapopulations[END_REF] Nutrient content (-) [START_REF] Shima | Consequences of variable larval dispersal pathways and resulting phenotypic mixtures to the dynamics of marine metapopulations[END_REF] Dispersal is negatively correlated with lipid concentration

Outstanding questions.

Can landscape configuration and anthropogenic modifications of landscapes (e.g. fragmentation) mediate dispersal syndromes effects on meta-ecosystems? How do different regimes of spatial and temporal variability in environmental conditions affect dispersal syndromes and their ecosystem consequences?

Marine, freshwater and terrestrial ecosystems often differ in their environmental variability and constrains on dispersal movements. Do the evolution of dispersal syndromes and consequences for meta-ecosystems differ across biomes?

In what ways do the mechanisms underlying dispersal syndromes (plastic or genetic) determine the nature and timing of meta-ecosystem consequences? Do meta-ecosystem dynamics affect in turn the evolution of dispersal syndromes? Do eco-evolutionary feedbacks between dispersal syndromes evolution and ecosystem dynamics exist and how do they drive long-term dynamics of ecosystem functioning? How do differences of mechanisms underlying syndromes and the relative importance of intra-and inter-specific variability affect meta-ecosystem dynamics? How to integrate such variability within and among species in meta-ecosystem theoretical framework?

Invasion dynamics and range expansions of populations are currently occurring worldwide. Does integration of dispersal syndromes in these theories help predict future impacts on ecosystems?

How to decipher the effects of population density from that of phenotypic differentiation in natural systems?

May dispersal syndromes change qualitatively or quantitatively the effects of dispersal for spatial and temporal stability (including resilience and resistance) of meta-ecosystems?

What are the species characteristics (trophic level, functional role, passive or active dispersal, dispersal distance) that make dispersal syndrome more or less important at the metacommunity and meta-ecosystem scales?

Supplementary information

Model description (Box 2)

We model a meta-population consisting of M = 10 identical patches. Each patch can maintain a population of K = 100 individuals. The populations are composed of two types of individuals, residents and dispersers, which can differ in their resource consumption. In the case of a positive (negative) dispersal syndrome, dispersers consume more (less) resource than residents, while in the absence of a dispersal syndrome, dispersers and residents consume the same amount of resource.

We subject this meta-population to a random sequence of local extinctions, with p E = 0.2 the extinction probability per patch and per generation. We study the response of the meta-population to these perturbations, in particular the spatial (and temporal) variation of resource consumption per patch. We are interested in how these quantities depend on the dispersal probability p D (i.e., the fraction of dispersers) and on the type of dispersal syndrome (no syndrome, positive and negative).