Sarah Nasser

Anne Moreau

Romain Jeantet

Alain Hédoux

Guillaume Delaplace
email: guillaume.delaplace@inra.fr

Influence of storage conditions on the functional properties of micellar casein powder

Keywords: milk protein concentrate, MC: micellar casein, P1: powder 1, P2: powder 2 Casein micellar, powder, storage, rehydration

Highlights

 Solubility and fragmentation time are shown to be strongly correlated with rehydration times  Ageing itineraries of MC powder can be defined from accelerated ageing tests  Knowledge of ageing itinerary allow to predict the rehydration time of aged sample

Comment citer ce document : Nasser, S., Moreau, A., Jeantet, R., Hédoux, A., Delaplace, G. (2017). Influence of storage conditions on the functional properties of micellar casein powder. Food and Bioproducts Processing, 106, 181-192. , DOI : 10.1016/j.fbp.2017.09.004

For the two MC powders tested, it was shown that the two characteristic times and the browning index increased with storage duration and temperature applied during ageing, whereas solubility decreased. For each MC powder studied, it was shown that i)there is a correlation (ageing curves) between the rehydration time (the target variable) and the indicator parameters (fragmentation time, browning index and solubility) and (ii)the shape of each ageing curve is independent of the ageing conditions but dependent on the MC powder studied.

These results clearly suggest the i)possibility to obtain reference ageing curves for each indicator, linking total rehydration time and the following indicators: fragmentation time, browning index and solubility ii)possibility to identify several ageing similarities between severe and moderate storage conditions iii)feasibility of applying accelerated ageing conditions to rapidly establish the shape of the reference ageing curves for a given MC powder, and iv)possibility of predicting the rehydration time of the MC powder studied using reference ageing curves through the measurement of one indicator (fragmentation time, browning index and solubility). This predicting ability of the proposed approach has been ascertained by comparing experimental and predicted values of rehydration time for aged samples having undergone storage accidents.

Introduction

Milk protein concentrate (MPC) powders are produced from skimmed milk by spray drying after ultrafiltration [START_REF] Haque | Protein Conformational Modifications and Kinetics of Water-Protein Interactions in Milk Protein Concentrate Powder upon Aging: Effect on Solubility[END_REF]. These dairy-derived powders have a high protein content, with the dry matter content ranging from 40 to 90 % [START_REF] Castro-Morel | Basic functionality of commercial milk protein concentrates[END_REF]. The casein to whey protein ratio of MPC is identical to that of skimmed milk.

Due to their high nutritional value and favourable functional properties (e.g. foaming, emulsifying, gelling, etc.), MPC powders are incorporated as an ingredient into a wide range of applications in downstream food industries (Selomulya & Fang, 2013). For example, they can be used to standardise the protein content of milk and are used as ingredients in many food applications including raising the protein content of cheese and yoghurt.

For most applications, a prior dissolution of MPC powder in water is mandatory in order to allow the powder to fully express its functional properties (Gaiani, Scher, et al., 2007) Consequently, rehydration and solubility are important end-use properties for MPC powders and require accurate assessment.

Unfortunately, several studies have reported that MPC powders are characterised by poor rehydration properties (Gaiani, Schuck, Scher, Desobry, & Banon, 2007;[START_REF] Richard | Towards a better control of dairy powder rehydration processes[END_REF][START_REF] Richard | Ultrasound tests in a stirred vessel to evaluate the reconstitution ability of dairy powders[END_REF]P. Schuck et al., 2007). This is even truer for micellar casein (MC) powder, whether freshly prepared or stored. MC powder is a high-protein dairy powder obtained from milk microfiltration retentate. The objective is to eliminate almost all of the whey proteins, lactose and minerals (Schuck et al., 1994) and to concentrate the casein micelles while preserving their native structure. Due to the enriched micellar casein content, MC powder is an attractive material for the food industry, as it can enhance the structure, texture and consistency of various foodstuffs [START_REF] Paracha | Characterisation of the rehydration of milk protein concentrates in the presence of sugar[END_REF]Singh, 2002). For powder enriched in micellar casein, it was i) shown that the total rehydration process required more than 3 hours at 25 °C under stirring at 900 rpm, and ii) observed that despite the Comment citer ce document : Nasser, S., Moreau, A., Jeantet, R., Hédoux, A., Delaplace, G. (2017). Influence of storage conditions on the functional properties of micellar casein powder. Food and Bioproducts Processing, 106, 181-192. , DOI : 10.1016/j.fbp.2017.09.004 aforementioned treatment, some undissolved material remained, which is generally referred to as the 'insoluble fraction' [START_REF] Richard | Towards a better control of dairy powder rehydration processes[END_REF].

The impact of storage on the properties of MPC has been extensively studied [START_REF] Anema | Effects of storage temperature on the solubility of milk protein concentrate (MPC85)[END_REF][START_REF] Fang | On quantifying the dissolution behaviour of milk protein concentrate[END_REF][START_REF] Gazi | Influence of protein content and storage conditions on the solubility of caseins and whey proteins in milk protein concentrates[END_REF][START_REF] Haque | Change in molecular structure and dynamics of protein in milk protein concentrate powder upon ageing by solid-state carbon NMR[END_REF][START_REF] Haque | Kinetics of enthalpy relaxation of milk protein concentrate powder upon ageing and its effect on solubility[END_REF][START_REF] Havea | Protein interactions in milk protein concentrate powders[END_REF][START_REF] Hunter | Effect of storage time and temperature of milk protein concentrate (MPC85) on the renneting properties of skim milk fortified with MPC85[END_REF][START_REF] Jimenezflores | Properties of ultrafiltered skim milk retentate powders[END_REF]Le, Bhandari, & Deeth, 2011;[START_REF] Marella | Manufacture of modified milk protein concentrate utilizing injection of carbon dioxide[END_REF]Mimouni, Deeth, Whittaker, Gidley, & Bhandari, 2010a[START_REF] Mimouni | Rehydration of high-protein-containing dairy powder: Slow-and fast-dissolving components and storage effects[END_REF]Sikand, Tong, Walker, Wang, & Rodriguez-Saona, 2016;Udabage, Puvanenthiran, Yoo, Versteeg, & Augustin, 2012), with particular focus on the gradual loss of solubility during storage [START_REF] Anema | Effects of storage temperature on the solubility of milk protein concentrate (MPC85)[END_REF][START_REF] Fyfe | Storage induced changes to high protein powders: influence on surface properties and solubility[END_REF][START_REF] Haque | Kinetics of enthalpy relaxation of milk protein concentrate powder upon ageing and its effect on solubility[END_REF][START_REF] Mimouni | Rehydration of high-protein-containing dairy powder: Slow-and fast-dissolving components and storage effects[END_REF]. These studies have shown that the solubility and rehydration properties of MPC were negatively impacted by severe ageing conditions (temperature, humidity and storage time). Poor reconstitution properties, and hence poor functionality of high-micellar casein powders can prevent them from achieving full market potential [START_REF] Castro-Morel | Basic functionality of commercial milk protein concentrates[END_REF]. Thus, various studies have investigated ways of preventing insolubility of a powder, either by attempting to adjust adequate process parameters during filtration and spray drying operations (namely the drying inlet temperature conditions for example (Schuck et al., 1994), or by adapting the initial retentate formulation. It was found that adding monovalent salts to the ultrafiltered retentate prior to drying may improve solubility while increasing the calcium/total mineral ratio decreases the solubility of MPC [START_REF] Carr | Monovalent salt enhances solubility of milk protein concentrate[END_REF].

At present, protein destabilisation due to conformational changes [START_REF] Fyfe | Storage induced changes to high protein powders: influence on surface properties and solubility[END_REF][START_REF] Haque | Protein Conformational Modifications and Kinetics of Water-Protein Interactions in Milk Protein Concentrate Powder upon Aging: Effect on Solubility[END_REF][START_REF] Haque | Ageing-induced solubility loss in milk protein concentrate powder: effect of protein conformational modifications and interactions with water[END_REF][START_REF] Haque | Change in molecular structure and dynamics of protein in milk protein concentrate powder upon ageing by solid-state carbon NMR[END_REF][START_REF] Haque | Kinetics of enthalpy relaxation of milk protein concentrate powder upon ageing and its effect on solubility[END_REF][START_REF] Kher | FTIR investigation of spray-dried milk protein concentrate powders[END_REF] and Maillard reactions in the presence of lactose [START_REF] Haque | Protein Conformational Modifications and Kinetics of Water-Protein Interactions in Milk Protein Concentrate Powder upon Aging: Effect on Solubility[END_REF][START_REF] Haque | Ageing-induced solubility loss in milk protein concentrate powder: effect of protein conformational modifications and interactions with water[END_REF][START_REF] Haque | Change in molecular structure and dynamics of protein in milk protein concentrate powder upon ageing by solid-state carbon NMR[END_REF] From analysis of state of the art, it also appears that the colorimetric change in MC powder with ageing (browning index) has been poorly documented.

Further work is thus needed to establish the influence of storage temperature and time on the ageing of MC powders and to illustrate the link between rehydration time and other ageing indicators (solubility, fragmentation time and browning index). Providing experimental data addressing this issue is the main aim of this study rather than to investigate MC at molecular scale or to establish a relationship between structural modifications and changes in rehydration/browning properties. At present, protein instability in its dry form (conformational modifications and water-protein interaction) and Maillard reaction due to the non limiting lactose content are the most frequently cited causes to explain the loss of MPC rehydration properties [START_REF] Haque | Protein Conformational Modifications and Kinetics of Water-Protein Interactions in Milk Protein Concentrate Powder upon Aging: Effect on Solubility[END_REF][START_REF] Haque | Ageing-induced solubility loss in milk protein concentrate powder: effect of protein conformational modifications and interactions with water[END_REF][START_REF] Haque | Change in molecular structure and dynamics of protein in milk protein concentrate powder upon ageing by solid-state carbon NMR[END_REF].

Materials and methods

2.1. Dairy powders manufacture: physicochemical analysis at inlet and outlet of the spray drying tower and process parameters MC concentrates were obtained through microfiltration (pore size = 0.1 μm) of skimmed milk from Ingredia (Arras, France).

Powders were obtained by spray drying an MC concentrate in a pilot workshop (GEA, Niro Atomizer, St Quentin en Yvelines, France) at Bionov (Rennes, France). The same operating conditions as described by [START_REF] Pierre | Native micellar casein separation through cross flow membrane microfiltration[END_REF] and Schuck et al. (1994) were used for the spray drying. The inlet temperature was 180 °C ± 10 °C and the outlet temperature was 65 ± 5 °C.

Two batches of MC powder were prepared (P1 and P2). Various physico-chemical analyses were performed on the initial microfiltration retentates and the resulting dairy powders. The nitrogen contents (total nitrogen, non-casein nitrogen, non-protein nitrogen) of initial statefresh powder were determined as described by Schuck et al., (2012). The total nitrogen content, non-casein nitrogen content corresponding to the soluble fraction at pH 4.6, and nonprotein nitrogen content corresponding to the insoluble fraction after their precipitation were determined by the Kjeldhal method. Nitrogen contents were converted into protein contents using 6.38 as multiplying factor. These analyses are reported in Table 1. MC powders were packed into individual 380 g tin cans after manufacture. The powders were stored at controlled temperatures of 4 °C (referred to as "reference powder"), 20 °C, 40 °C and 60 °C for various durations to a maximum of 12 months.

Determination of solubility

To determine solubility, aqueous solutions of 5 % (w/w) MC powder were firstly prepared in distilled water at room temperature for 1 hour under stirring. Then, 50 ml of the MC solution was transferred into 50 ml centrifugation tubes and centrifuged using a Sigma 6K15 refrigerated centrifuge (Sigma, Labozentrifugen GmbH, Osterode am Harz, Germany) at 700 × g at 20 °C for 20 min. The supernatant was placed in a preweighed moisture dish and weighed. After that, the moisture dish (filled with the supernatant) was dried for 24 h in an oven at 105 °C before being cooled down to room temperature in a desiccator containing dry silica gel to avoid condensation and then reweighed. The percentage of soluble material (σ) of the MC powder was calculated using the following equation [START_REF] Anema | Effects of storage temperature on the solubility of milk protein concentrate (MPC85)[END_REF]:

σ =
Weight of dry material weight of solution × 100

Eq. ( 1)

It represents the solids in the ultracentrifugal supernatant, expressed as a percentage of total soluble solids in the whole solution. The σ values of aged powder samples were compared to that of the reference powder, and this σ(aged)/σ(reference) ratio in percentage was used to study the solubility evolution during ageing.

Colour measurement of MC powder and browning index determination

The colour measurements were carried out during storage Eq. ( 2)

With x = (a * +1.750×L * ) (5.645×L * +a * -3.012×b * )
Eq. ( 3)

Rehydration tests

The equipment used for performing rehydration tests has been previously described by [START_REF] Richard | Towards a better control of dairy powder rehydration processes[END_REF]2012).

MC powders were reconstituted at 8 % (w/w) dry matter content. This concentration is commonly used in dairy applications at industrial scale. The dairy powder was added manually to the free liquid surface. The powder rehydration protocol was described in a previous publication [START_REF] Jeantet | The influence of stirring speed, temperature and solid concentration on the rehydration time of micellar casein powder[END_REF]. The rehydration protocol and sampling site were kept constant throughout all the experiments.

After the addition of powder to the liquid surface (at a stirring rate of 900 rpm), the impeller rotational speed of the agitator N was set at 1,200 rpm for 45 seconds to ensure that the powder was fully incorporated into the liquid. Then, N was set at a constant speed of 900 rpm until the end of the rehydration test. It should be noted that a turbulent flow regime and full suspension of powder particles were achieved at this N value.

Granulomorphometer measurements and determination of fragmentation time

Comment citer ce document : Nasser, S., Moreau, A., Jeantet, R., Hédoux, A., Delaplace, G. ( 2017). Influence of storage conditions on the functional properties of micellar casein powder. Food and Bioproducts Processing, 106, 181-192. , DOI : 10.1016/j.fbp.2017.09.004

Digital images of powder particles during the course of the rehydration tests were obtained using the Flow-Cell272 200 S-M (Occhio, Angleur, Belgium) granulomorphometer. This microscopy technique makes it possible to analyse samples, diluted or not, of the MC suspension pumped into the vessel of the rehydration test. The principle of this granulomorphometer was described in a previous publication [START_REF] Richard | Ultrasound tests in a stirred vessel to evaluate the reconstitution ability of dairy powders[END_REF]. Readers can refer to this article for more details.

As previously described by [START_REF] Richard | Ultrasound tests in a stirred vessel to evaluate the reconstitution ability of dairy powders[END_REF], the fragmentation time has been defined as the time required to reach the maximum number of particles during the rehydration test.

Static light scattering and determination of total rehydration time

As described by [START_REF] Richard | Ultrasound tests in a stirred vessel to evaluate the reconstitution ability of dairy powders[END_REF], particle size distribution, measured by SLS (Static Light Scattering, Mastersizer 2000, Malvern Instruments Ltd, England) was used to determine the total rehydration time for each test. Sampling was done as follows: 0.5 mL of the powder suspension was withdrawn with a 16-mm-diameter syringe from the rehydration vessel.

Samples were diluted in the Malvern cell (volume: 100 mL) with distilled water to reach appropriate obscuration (25 %). The solvent and particle refractive indices were set at 1.33 and 1.3, respectively, for particle size distribution measurements. The absorption index was set at 0.1. The class size limits were 0.02-2,000 μm. Particle size distribution was measured every 5 minutes until the fragmentation time was complete, and then approximately every 30 minutes as long as the size of the particles was larger than 15 µm and finally every 5 minutes until the end of the experiment when reaching the total rehydration time. According to [START_REF] Richard | Ultrasound tests in a stirred vessel to evaluate the reconstitution ability of dairy powders[END_REF], the total rehydration time was defined as the time required for Dv50, medium value of the particle size distributions, to reach 0.2 μm after the addition of powder.

The mean standard deviation of total rehydration time results was equal to 11.4%. Similar values of standard deviation for different powders were obtained by [START_REF] Jeantet | The influence of stirring speed, temperature and solid concentration on the rehydration time of micellar casein powder[END_REF].

Comment citer ce document : Nasser, S., Moreau, A., Jeantet, R., Hédoux, A., Delaplace, G. ( 2017). Influence of storage conditions on the functional properties of micellar casein powder. Food and Bioproducts Processing, 106, 181-192. , DOI : 10.1016/j.fbp.2017.09.004

Statistical analysis

Student's t-tests with a 0.05 level of significance were used to measure the significance of the differences between samples stored and reference powder none stored. As widely known, the differences are statistically nonsignificant when p > 0.05 and statistically significant when p < 0.05

Results & discussion

Firstly, experimental data collected for MC P1 for the 4 different storage temperatures are presented and discussed.

Browning index evolution with ageing conditions

The change of colour visually observed for the MC P1 as a function of storage time for different storage temperatures is illustrated in Figure 1A. As expected, it clearly appears that browning is strongly influenced by the storage temperature set. Browning occurred faster when the storage temperature increased. At a storage temperature of 60 °C, the increase of the brown coloration of the powder is so significant that it is clearly detectable even by naked eyes.

The a slope equal to 0.46) (p<0.05). Then for the storage period from 60 to 360 days, the increasing rate of BI decreased down to nearly 0 and a plateau was observed (p>0.05).

In the literature, it is often suggested that the presence of small quantities of lactose is sufficient to trigger a Maillard reaction. Indeed, interactions between lactose and lysine can occur, leading to food properties evolution like colour, flavour and nutritional value [START_REF] Martins | A review of Maillard reaction in food and implications to kinetic modelling[END_REF].

Typically, both the temperature and the storage time have been proven to impact the Maillard reaction. For the MC P1 investigated, it is highly probable that such phenomena were also involved in the browning process.

Solubility evolution with ageing conditions

The solubility of MC P1 stored at different temperatures is plotted as a function of time in The MC P1 stored at 20 °C showed little change in solubility over a storage time of 180 days.

It could be observed that the solubility slightly and linearly decreased from 100 % to ~80 % over that period of storage.

A different solubility evolution upon ageing is observed when storage temperature increases.

Indeed, the solubility of MC P1 stored at 40 °C drastically decreased in the first days of ageing, then after 60 days of storage at this temperature a plateau was reached and the solubility became constant at around 25 % of the initial value. This drastic decrease of solubility at the first instant of storage at a higher storage temperature was amplified when ageing occurred at 60 °C. It could be noticed that the solubility of the MC P1 stored at 60°C decreased dramatically after 8 h of storage and reached an asymptotic value of ~15 % at 60 days of storage. For these two most severe storage conditions tested, the solubility was first subjected to an exponential decay then reached an asymptotic value.

The loss of solubility observed for MC P1 at higher storage temperatures was in agreement with both the expected trend (increase in quantity of insoluble material with time and storage temperature) and previous studies of high-protein dairy powder [START_REF] Anema | Effects of storage temperature on the solubility of milk protein concentrate (MPC85)[END_REF][START_REF] Gazi | Influence of protein content and storage conditions on the solubility of caseins and whey proteins in milk protein concentrates[END_REF]Le, Bhandari, & Deeth, 2011;[START_REF] Le | Maillard Reaction and Protein Cross-Linking in Relation to the Solubility of Milk Powders[END_REF] From further analysis of the experimental data, it appeared that solubility and browning index didn't follow the same evolution with storage time: decay with time is observed for solubility whereas a growth is noticed for BI. For a given storage temperature, the monotonicity and rates of change of these two indicators vary differently with storage time. Indeed, for a storage temperature fixed at 40 °C, the change in solubility followed an exponential decrease contrary to the change in BI, which followed a linear growth at this temperature (Figure 1). Similarly, the BI values did not change with time during storage at 20 °C, whereas solubility decreased by 23 %. This kinetic difference clearly indicates that loss of solubility and increase in browning during storage are not induced by the same phenomena and consequently the evolution of these two indicators are unlikely to be governed by the apparition of the same chemical species at molecular level. To our knowledge, there is yet no study reported on fragmentation time evolution upon ageing. We are the first group to report this indicator evolution with storage time for various storage temperatures. Consequently, it is difficult to do further discussion and comparison on the experimental data obtained. Nevertheless, the change in fragmentation time should be regarded as an indicator which quantifies the ease of dissolution of the solid bridges between cross-linked micellar caseins. Consequently, the increase of fragmentation time with the severity of ageing that we observed is actually in agreement with the work of [START_REF] Anema | Effects of storage temperature on the solubility of milk protein concentrate (MPC85)[END_REF], who have reported a cross-linking increase with storage time and temperature. Indeed, the increase of protein cross-linking during storage makes it more difficult to fragment and dissolve the particles.

Fragmentation time evolution with ageing conditions

Rehydration time evolution with ageing conditions

The rehydration time of MC P1 is plotted against storage time in Figure 4. Again, temperature was observed to have a major impact on the evolution of total rehydration time upon ageing.

The total rehydration time, after 12 months of storage, increased from ~3.5 h to ~5 h for the powder stored at 4 °C (p<0.05) and from ~3.5 h to ~7 h (p<0.05) for the powder stored at 20 °C. It is worth re-mentioning that a 23 % decrease in solubility was observed after 6 months of storage for the powder stored at 20 °C (Figure 2). The change in rehydration time of MC P1 stored at 60 °C was even more drastic. Its value has more than doubled after only 24 h of storage (p<0.05) and reached ~35 h after only 5 days of storage (p<0.05). These results indicate that basically insolubility developed under all storage conditions, but at different rates depending on the storage temperature.

It seemed that the storage-temperature dependent rehydration time and solubility changes are intimately linked; the lower the solubility, the longer the rehydration time. This is in agreement with several works that have previously referred to this trend for MPC powder [START_REF] Anema | Effects of storage temperature on the solubility of milk protein concentrate (MPC85)[END_REF][START_REF] Gazi | Influence of protein content and storage conditions on the solubility of caseins and whey proteins in milk protein concentrates[END_REF].

As suggested by [START_REF] Fyfe | Storage induced changes to high protein powders: influence on surface properties and solubility[END_REF] and Mimouni et al., (2011;2010a) insolubility can be caused by the formation of a network of cross-linked proteins at the surface of the powder.

These surface cross-links act as a barrier to the transport of water which inhibits the hydration of the particles, their subsequent disruption and dissolution, leading to the increase of both fragmentation time and total rehydration time. The increase in the degree of cross-linking with increasing storage time and temperature reported by [START_REF] Anema | Effects of storage temperature on the solubility of milk protein concentrate (MPC85)[END_REF] is consistent with this interpretation.

The greater the severity of storage conditions, the more the indicators change. However, it is still difficult at this stage to assess whether indicator parameters (fragmentation time, solubility loss and browning index) could be used to rapidly predict the increase in rehydration times due to ageing. The objective of the next section is to address this issue. follows a reference ageing curve, which could be described using a linear function independent of the storage time and temperature set during ageing. The fitting functions are given by Equation 4(A&B) for Figure 5A and by Equation 5(A&B) for Figure 5B.

Rehydration time = -0.08 × solubility + 12.13 with R 2 = 0.96 if solubility > 33 % Eq. ( 4A) In a second time, the rehydration time versus browning index was plotted (Figure 5C).

Similarly, the analysis of this figure also reveals the existence of an ageing curve independent of the storage time and temperature for this indicator (Equation 6).

Rehydration time = 0.0004 × Browning Index 4.4 with R 2 = 0.90 Eq. ( 6) The existence of these reference ageing curves and fitting functions (Equations 4-5-6) are of interest. The time-consuming and tedious-experimental-protocol requiring rehydration time determination process could be simplified since the rehydration time could be rapidly predicted through the determination of fragmentation time or solubility. This is to say that it would be sufficient to carry out fragmentation time or solubility measurements, which are among the easiest tests, to rapidly estimate the rehydration time for the solid-liquid suspension. Based on this method, process parameters (for example rotational impeller speed, N for rehydration in agitated vessel equipped with vertical agitator centrally mounted) can be easily adjusted to achieve the desired product quality and functionality [START_REF] Jeantet | The influence of stirring speed, temperature and solid concentration on the rehydration time of micellar casein powder[END_REF][START_REF] Richard | Towards a better control of dairy powder rehydration processes[END_REF].

The discovery that reference ageing curves exist and gather all the aged samples of the MC P1 studied is of interest. Indeed, this fact suggests that changes occurred at the highest temperatures over a short storage period could mimic changes occurred under milder temperature conditions over a longer period of time. Therefore, it can be envisaged to establish, under accelerated ageing conditions, the ageing curves for MC P1 which are also valid for less severe conditions. For example, the approximate rehydration time / solubility ageing curve of MC P1 can be plotted using 3 experimental points: initial state and after 2 and 5 days of storage at 60 °C. Ces 3 points ont été choisi car couvre l'ensemble des données experimental. Evidemment,plus le nombre de points à vieillissement accéléré est important, plus la precision de la courbe approximé sera importante.

Linear regression of the 2 straight lines obtained by connecting the three experimental points leads to the following equations (Equations 7-8-9) :

Rehydration time = -0.11 × solubility + 14.84 with R 2 = 1 if solubility > 29.21 % Eq. ( 7A) Rehydration time = 3.44 × fragmentation time + 2.86 with R 2 = 1 if fragmentation time < 2.52

Eq. ( 8A)

Rehydration time = 6.16 × fragmentation time -3.99 with R 2 = 1 if fragmentation time > 2.52

Eq. ( 8B)

Rehydration time = 3.17 × Browning Index -21.90 with R 2 = 0.93 if IB < 10.8 Eq. ( 9A)

Rehydration time = 7.40 × Browning Index -68.43 with R 2 = 1 if IB > 10.8 Eq. ( 9B)

It could be noticed on figure 5 that "the approximated ageing curves", established using only 3 accelerated ageing points (dotted line) are not far away from the reference ageing curves

(obtained with all the data points tested, in solid line). In this demonstration, only 3 points were used to obtain the approximated ageing curve, because they are sufficient to cover all the experimental data. Obviously, the greater the number of accelerated ageing points used, the more accurate the approximated ageing curve will be.

Confirmation of the existence of reference ageing curves and possibility to establish ageing curves using accelerated ageing conditions for MC P2

To confirm the existence of reference ageing curves independent of temperature and storage aged MC P2 powder is lower than that of the aged MC P1 powder. Moreover, it turned out that rehydration properties of the two aged powders are markedly different after 5 days of storage at 60 °C: a total rehydration is achieved more quickly for powder 2 compared to powder 1.

Firstly, since lactose is responsible for the brown colour of the powders (via the Maillard reaction), the lower lactose content of MC P2 explains its lower browning index.

Secondly, the dry matter compositions of the two retentates are comparable. The lower dry extract of MC P2 implies hence a lower viscosity of retentate 2 [START_REF] Devilder | The continous measurement of the viscosity of the concentrate during the production of milk powder[END_REF]P. Schuck, Mejean, Dolivet, Beaucher, & Famelart, 2005;Snoeren, Dammam, & Klok, 1982) explaining the smaller particle size of the powder produced by spray drying [START_REF] Baldwin | The effect of concentrate viscosity on the properties of spray-dried skim milk powder[END_REF][START_REF] Masters | Spray Drying in Practice[END_REF], as shown in Table 1. When the viscosity of the feed liquid increases, more energy is dissipated in the spray tower nozzle to overcome viscous forces. Thus the energy available for breaking up the droplets is reduced, resulting in larger droplets. Therefore, smaller droplets are formed for a less viscous liquid.

Finally, it is widely recognised since the pioneer work of Noyes-Whitney, (1897) that the dissolution rate of chemical particles is faster for smaller ones because the specific surface area increases when particle size decreases. The review of [START_REF] Dokoumetzidis | A century of dissolution research: From Noyes and Whitney to the Biopharmaceutics Classification System[END_REF] and the work of Gaiani et al. (2007) have also confirmed this physical law respectively for biopowders and for milk derivative powders. It is evidenced that the dispersion step (corresponding to the dispersion of single particles throughout the water) is favoured when particle size decreases. As dispersion is known to be the limiting step of MC powder rehydration (Gaiani, Schuck, et al., 2007), it is logical to consider the smaller particle size of MC P2, resulting from viscosity difference in the drying operation, to be responsible for its faster rehydration.

Comment citer ce document : Nasser, S., Moreau, A., Jeantet, R., Hédoux, A., Delaplace, G. ( 2017). Influence of storage conditions on the functional properties of micellar casein powder. Food and Bioproducts Processing, 106, 181-192. , DOI : 10.1016/j.fbp.2017.09.004

The relationships between the different indicators and the rehydration times were plotted for MC P2. The reference ageing curves obtained for this second batch MC P2 are presented in Figure 6. The corresponding fitting functions are as follows (Equations 10 to 12):

Rehydration time = 8834.2 × solubility -2.2 with R 2 = 0.98 Eq. ( 10)

Rehydration time = -0.1 × fragmentation time 2 + 2.2 × fragmentation time + 0.3 with R 2 = 0.94 Eq. ( 11)

Rehydration time = 0.5 × Browning Index ² + 11.1 × Browning Index -55 with R 2 = 0.94 Eq. ( 12)

Unsurprisingly, the shape of reference ageing curves and type of mathematical equations for MC P2 were very different from MC P1. But this new set of results confirmed again anyway the possibility of obtaining reference ageing curves that link the rehydration time with each individual indicator (fragmentation time, browning index and solubility), regardless of the ageing conditions adopted during storage. Experimental data obtained for MC P2 also corroborate the idea that applying accelerated ageing conditions is an interesting way to predict the changes that would occur under milder conditions (lower temperatures). As for previous MC P1 investigated, three conditions of storage seem particularly interesting to examine the predictive trajectory of ageing curves: initial state and after 2 and 5 days' storage at 60 °C.

The equations for the ageing curves of MC P2 established on these three ageing points using a linear regression per interval are as follows:

Rehydration time = -0.09 × solubility + 9.67 with R 2 = 1 if solubility > 27 % Eq. Eq. (14B)

Again, it could be remarked on figure 6 that the ageing curves established using these 3 accelerated ageing conditions (dotted line) give good approximation of reference ageing curves obtained using all experimental data points (solid line).

Further observations of the reference ageing curves (Figures 5 &6) made it possible to identify and confirm several ageing similarities between severe and moderate ageing conditions. For example, ageing after a period of 8 hours at 60 °C was approximately equivalent to ageing after a period of 12 months at 20 °C, the condition commonly encountered during powder storage and delivery. In the same way, ageing after a 24 hour period at 60 °C is equivalent to that after 1 month period at 40 °C. These equivalences are outlined in blue bold in Figure 5 & 6. These [storage time; storage temperature] concordances are of great help to rapidly predict property changes of the powder during storage. In previous section, it has been suggested to rapidly identify the shapes of reference ageing curves for the MC powder studied (by using accelerated ageing conditions). It is then necessary to assess the accuracy of predicted rehydration times. The objective of the next section 3.6. is to address this issue. A reverse engineering approach is proposed based on the approximate ageing curves obtained and the measurements of indicators.

Comparison between experimental and predicted rehydration time

In order to assess the feasibility of predicting the rehydration time for aged samples, experimental and predicted values have been compared for the two MC powders studied. The 4-step procedure used to determine the predicted rehydration time is as follows:

Step 1. Indicator (solubility, fragmentation time or BI) and rehydration time values of the powder studied are measured for three particular ageing conditions (initial state-fresh powder and two accelerated ageing conditions -2 and 5 days of storage at 60 °C)

Step 2. The three experimental points obtained [indicator; rehydration time] are plotted to obtain a first approximated ageing curve

Step 3. The equations of the approximate ageing curve are obtained through linear regression of the 2 straight lines connecting the 3 points.

Step temperatures close to 60 °C). Note that this kind of storage accidents are episodes that a powder is proved to undergo during its ship expedition [START_REF] Leinberger | Temperature and humidity in ocean containers[END_REF]. Consequently, predicting the effect on powder properties of such short exposure to high temperature is of great interest for both industries and consumers.

6 different accidents of storage were imposed for the 6 aged samples and measurements of indicator parameters and rehydration times were carried out. The ageing conditions of these additional samples and the exact instantaneous time for storage accident are presented in detail Figure 8. Sample 1 has been stored for 5 months at 20 °C with no storage accident.

Samples 2, 5 and 6 have been stored for 5 months at 20 °C including one storage accident (a rise in temperature to 60 °C and then maintained at 60 °C for 8 h after the temperature rise) at different storage times. Sample 5 and 6 have been stored for 5 months at 20 °C including respectively two and three storage accidents. (Figure S1).

Predicted rehydration time values of these additional samples subjected to storage accidents have been obtained using the procedure described above. Again, the experimental and predicted values of rehydration time for these additional samples are in good agreement. This further validates our rehydration time prediction procedure based on the determination of indicator parameters and corresponding ageing curves (which could be established by imposing accelerated ageing conditions).

Conclusion

To conclude, it has been shown that the characteristic rehydration times (total rehydration time and fragmentation time) as well as the browning index increased with storage time and temperature, whereas solubility decreased for both MC powders studied.

  However and more specifically, (Nasser et al., 2017) recently showed that the lipid migration towards the particle surface and the surface densification of micellar particles were responsible for major changes in MC rehydration dynamics during storage. In order to provide such temperature-time correspondences upon ageing, MC was stored at temperatures ranging from 4 to 60°C for periods up to 12 months. The evolution of various indicators (evolution of browning index, change in solubility, fragmentation time and total rehydration time) upon ageing was evaluated. The first part of this article consists in analyzing the indicators' evolution with time and to assess for any MC the temperature-time Comment citer ce document : Nasser, S., Moreau, A., Jeantet, R., Hédoux, A., Delaplace, G. (2017

  on 3 different points on the surface of the receptacle. The browning index (BI), used to assess the intensity of the brown colour of the samples, was calculated from formula combining the L*a*b*[START_REF] Oliveira | Evaluation of MAP engineering design parameters on quality of fresh-sliced mushrooms[END_REF]:

Figure 2 .

 2 Figure 2. Like what was observed for BI, evolution of solubility with storage time also

Figure 3

 3 Figure 3 shows the change in fragmentation time of MC P1 stored at various temperatures for

  These changes in total rehydration time over storage period are relatively mild when compared to storage at 40 °C and 60 °C. Indeed, the rehydration time doubled for MC P1 stored at 40 °C after 15 days (p<0.05) and reached ~29 h after 2 months of storage (p<0.05). Comment citer ce document : Nasser, S., Moreau, A., Jeantet, R., Hédoux, A., Delaplace, G. (2017). Influence of storage conditions on the functional properties of micellar casein powder. Food and Bioproducts Processing, 106, 181-192. , DOI : 10.1016/j.fbp.2017.09.004

3. 5 .

 5 Correlation between indicators (fragmentation times, solubility and Browning Index) and rehydration time for MC P1 Firstly, rehydration time versus solubility (Figure 5A) and rehydration time versus fragmentation time were plotted (Figure 5B). These two indicators (fragmentation times and Comment citer ce document : Nasser, S., Moreau, A., Jeantet, R., Hédoux, A., Delaplace, G. (2017). Influence of storage conditions on the functional properties of micellar casein powder. Food and Bioproducts Processing, 106, 181-192. , DOI : 10.1016/j.fbp.2017.09.004 solubility) were analysed first rather than browning index since the underlying phenomena involved in the evolution of these two indicators are expected to be the same as those governing the rehydration time evolution during ageing. As evoked previously, it is not so evident that the BI change is closely connected to rehydration properties evolution. Indeed, browning and insoluble formation are not necessarily induced by the same chemical modification pathway. Analysis of Figures 5A and 5B reveals that each pair of indicators ([solubility; rehydration time] and [fragmentation time; rehydration time] respectively)

  Comment citer ce document : Nasser, S., Moreau, A.,[START_REF] Nasser | Influence of storage conditions on the functional properties of micellar casein powder[END_REF]. Influence of storage conditions on the functional properties of micellar casein powder. Food and Bioproducts Processing, 106, 181-192. , DOI : 10.1016/j.fbp.2017.09.004 Rehydration time = -0.63 × solubility + 24.05 with R 2 = 1 if solubility < 27 % Eq. (12B) Rehydration time = 3.71 × fragmentaion time + 0.16 with R 2 = 1 if fragmentation time < 1.87 Eq. (13A) Rehydration time = 0.61 × fragmentation time + 5.98 with R 2 = 1 if fragmentation time > 1.87 Eq. (13B) Rehydration time = 5.14 × browning index -34.78 with R 2 = 1 if browning index < 8.15 Eq. (14A) Rehydration time = 1.85 × browning index -7.96 with R 2 = 1 if browning index > 8.15

  4. The indicator is measured for an arbitrary aged sample and the corresponding rehydration time value is evaluated using the set of equations obtained at step 3 by inverse engineering approach Comparisons between experimental and predicted values of rehydration time for MC powders P1 and P2 are presented in Figure 7. Namely, Figures 7A, 7B and 7C give the comparisons based respectively on different indicators (solubility, fragmentation and browning index). Comment citer ce document : Nasser, S., Moreau, A., Jeantet, R., Hédoux, A., Delaplace, G. (2017). Influence of storage conditions on the functional properties of micellar casein powder. Food and Bioproducts Processing, 106, 181-192. , DOI : 10.1016/j.fbp.2017.09.004

  Figure 1. (A) Pictures of MC P1 and visualisation of browning of powder during storage (B) Browning index as a function of storage time for MC P1 stored at different temperatures

Figure 2 .

 2 Figure 2. Change in solubility as a function of storage time for MC P1 stored at different temperatures

Figure 3 .

 3 Figure 3. Fragmentation time as a function of storage time for MC P1 stored at different temperatures

Figure 4 .

 4 Figure 4. Rehydration time as a function of storage time for MC P1 stored at different temperatures

Figure 5 .

 5 Figure 5. Rehydration time as a function of (A) solubility (B) fragmentation time (C) browning index, of MC P1 stored at 4°C (circle), 20 °C (square), 40 °C (triangle) and 60°C (diamond shape); For the legend, the darker the inner colour of the symbol, the longer the storage time.Reference ageing curves using all ageing points tested are in solid lines, approximate ageing curves established with 3 ageing points (surrounded in red) are in dotted line. Ageing similarities between severe storage and moderate storage are outlined in blue.

Figure 6 .

 6 Figure 6. Rehydration time as a function of (A) solubility (B) fragmentation time (C) browning index, of MC P2 stored at 4°C (circle), 20 °C (square), 40 °C (triangle) and 60°C (diamond shape); ); For the legend, the darker the inner colour of the symbol, the longer the storage time.Ageing curves using whole ageing points are in solid lines, ageing curves established with 3 ageing points (surrounded in red) are in dotted line. Ageing similarities between severe storage and moderate storage are outlined in blue

Figure 7 .

 7 Figure 7. Comparison between rehydration times experimentally measured and predicted using approximate ageing curves based on the measurements of (A) solubility (B) fragmentation time (C) browning index . Measurements for MC P1 are in dark, measurements for MC P2 are in grey, measurements for samples going through storage accidents are represented by red cross. Dotted line represent percentage error.

  Development of insolubility of the two high-micelle-casein-content powders, MC and MPC, is believed to share similar mechanisms, nevertheless MC has been less studied and the exact relationship between storage and changes in rehydration properties is not yet precisely known.

; Le, Comment citer ce document : Nasser, S., Moreau, A., Jeantet, R., Hédoux, A., Delaplace, G. (2017). Influence of storage conditions on the functional properties of micellar casein powder. Food and Bioproducts Processing, 106, 181-192. , DOI : 10.1016/j.fbp.2017.09.004 Bhandari, & Deeth, 2011; Le, Bhandari, Holland, & Deeth, 2011; Le, Holland, Bhandari, Alewood, & Deeth, 2013) are the most frequently cited causes for the loss of rehydration properties at molecular level.

  The second part of this paper is devoted to ascertaining whether or not relevant master curves exist between these indicators. If established, these curves will help identify indicators which could be used to rapidly quantify and predict MPC powder's loss of rehydration capacity with ageing.

). Influence of storage conditions on the functional properties of micellar casein powder. Food and Bioproducts Processing, 106, 181-192. , DOI : 10.1016/j.fbp.2017.09.004 correspondences upon ageing.

  The BI of the MC P1 stored at 4 °C and 20 °C evolves slightly from

	8.34 to 8.43 and 8.72, respectively, after 365 days of storage (p<0.05). However, the BI
	indicator of the MC P1 stored at 40 °C showed a significant slight linear evolution (p<0.05)
	over the whole range of storage time studied (360 days). At 60 °C, the evolution of BI with
	storage time for MC P1 was so drastic that an increase of 50 % was achieved after only 5 days

evolution of the BI for MC P1 stored at different temperatures as a function of time is illustrated in Figure 1B. of storage. In fact, the change in BI over time at 60 °C is characterised by a two-step mechanism: During the first 60 days of storage, BI increased linearly with storage time (with Comment citer ce document : Nasser, S., Moreau, A., Jeantet, R., Hédoux, A., Delaplace, G. (2017). Influence of storage conditions on the functional properties of micellar casein powder. Food and Bioproducts Processing, 106, 181-192. , DOI : 10.1016/j.fbp.2017.09.004

  Comment citer ce document : Nasser, S., Moreau, A., Jeantet, R., Hédoux, A., Delaplace, G. (2017). Influence of storage conditions on the functional properties of micellar casein powder. Food and Bioproducts Processing, 106, 181-192. , DOI : 10.1016/j.fbp.2017.09.004

  Comment citer ce document : Nasser, S., Moreau, A., Jeantet, R., Hédoux, A., Delaplace, G. (2017). Influence of storage Ageing curves were plotted for each indicator, linking total rehydration time with fragmentation time, browning index and solubility. Several ageing similarities between severe storage and moderate storage have been demonstrated. The shape of each ageing curve depends only on the MC powder, not on ageing conditions.

	It has then been shown that applying accelerated ageing conditions made it possible to
	visualize the reference ageing curves of the MC powders to be characterised. 3 samples
	subjected to three particular ageing conditions (initial state-fresh powder and two accelerated
	ageing conditions -2 and 5 days of storage at 60 °C) were used for this purpose.
	With the approximate ageing curves, the rehydration time can be rapidly predicted by
	measuring one indicator.

conditions on the functional properties of micellar casein powder. Food and Bioproducts Processing, 106, 181-192. , DOI : 10.1016/j.fbp.2017.09.004 Finally, feasibility of obtaining predicted values of rehydration times was also demonstrated for a MC powder having undergone storage accidents (one or more temperature rises to 60 °C in the course of 5 months of storage).

Comment citer ce document : Nasser, S., Moreau, A., Jeantet, R., Hédoux, A., Delaplace, G. (2017). Influence of storage conditions on the functional properties of micellar casein powder. Food and Bioproducts Processing, 106, 181-192. , DOI : 10.1016/j.fbp.2017.09.004 Comment citer ce document : Nasser, S., Moreau, A., Jeantet, R., Hédoux, A., Delaplace, G. (2017). Influence of storage conditions on the functional properties of micellar casein powder. Food and Bioproducts Processing, 106, 181-192. , DOI : 10.1016/j.fbp.2017.09.004

Table 1 .

 1 Physico chemical properties of MC retentates and powders

	Total dry matter (g.kg -1 )	Total nitrogen (% N x 6.38)	Non Protein Nitrogen (% N x 6.38)	Non Casein Nitrogen (% N x 6.38)	Ash (g.kg -1 )	Lactose (g.kg -1 )	Particle size (µm) Dv50	Water activity
			Batch 1
	Retentate 1 137.60	11.9	0.01	1.16	11.00
	Powder 1 944.40	81.55	1.02	7.43	81.49	25.50	53.51	0.25
			Batch 2
	Retentate 2 125.00	11.10	0.01	1.03	10.00
	Powder 2 935.00	83.60	0.97	7.05	75.20	11.30	39.01	0.29

Comment citer ce document : Nasser, S., Moreau, A., Jeantet, R., Hédoux, A., Delaplace, G. (2017). Influence of storage conditions on the functional properties of micellar casein powder. Food and Bioproducts Processing, 106, 181-192. , DOI : 10.1016/j.fbp.2017.09.004

Table 2 .

 2 Functional properties of the two powders studied at reference state (storage at 4°C) and after 5 days' storage at 60 °C

			Powder 1		Powder 2
		Reference	Powder stored 5 days	Reference	Powder stored 5 days at
		powder	at 60 °C	powder	60 °C
	Browning index	8.34	13.97	6.82	11.86
	Solubility (%)	100.00	24.00	100.00	16.10
	Fragmentation time (Hours)	0.19	6.33	0.04	13.10
	Rehydration time (Hours)	3.51	35.00	0.29	14.00

Acknowledgements

This work was carried out within the framework of a CNIEL research program and deal issues of the ALIBIOTECH research project. Consequently, the authors would like to acknowledge the CNIEL and also thank the Haut de France region and FEDER for their financial support.

Comment citer ce document : Nasser, S., Moreau, A., Jeantet, R., Hédoux, A., Delaplace, G. (2017) deviations between predicted and experimental values. In this case, the equations of the approximate ageing curves will become similar to that describing the reference ageing curves (Equations 7-9 and 10-12, depending on the MC powder studied and the indicators considered). In this context, it is obvious that a compromise between the accuracy of predicted values and experimental time consumed to build ageing curves should be chosen.

Nevertheless, from a practical aspect, the feasibility to apply the proposed procedure for fast prediction of rehydration time has been demonstrated for the two powders studied.

To go further, it was decided to check the procedure with an independent series of data. 6 additional samples of aged powder were studied for this purpose. The independent series of data was obtained by subjecting MC P1 powder to storage accidents (short exposure to high


A Guerbois

Alexandre Caron

B Loveridge

Hugo Valls-Fox
email: hugo.valls.fox@normalesup.org

Simon Chamaillé-Jammes

Michel De Garine-Wichatitsky

Arthur Perrotton

Nicolas Courbin

Eve Miguel

Chloé Guerbois

Andrew Loveridge

Brent Stapelkamp

Martin Muzamba

Hervé Fritz

Surface water availability and cattle herding practices shape the human-wildlife interface at the edge of a protected area

Keywords: coexistence, conflict, habitat selection, livestock, temporal shift, resource partitioning, wildlife/livestock interface

published or not. The documents may come     Copyright Water and cattle shape habitat selection by wild herbivores at the edge of a protected area

4. During the rainy and cold dry season, buffalo successfully avoid cattle at the home-range scale and at the scale of foraging bouts. By the end of the dry season, buffalo herds, which are restricted in their movement to the vicinity of water, still avoid using areas used by cattle but tolerate higher overlap with cattle and cannot afford to avoid them as strongly at fine scales.

5. Elephant home ranges overlap extensively with cattle throughout the year but elephant avoid cattle by staying away from the boundary during the day and getting closer at night. As the dry season advances, elephant bulls range closer to the boundary especially at night and may even make excursions into the communal land in their search for forage.

6. Synthesis and applications: Wild herbivores strongly avoid livestock and people as long as their foraging and drinking resources allow. During the rainy season, when resources are abundant, cattle herding create a buffer zone between wildlife areas and human settlements.

When resources are scarce (during a drought) long term planning of artificial water provisioning is essential to maintain spatial segregation and mitigate conflicts such as disease transmission or crop-raiding.

Introduction

To date, setting aside land for conservation remains one of the core conservation strategies [START_REF] Palomo | Incorporating the social-ecological approach in protected areas in the anthropocene[END_REF]). Yet, protected areas only cover 15% of the land surface worldwide [START_REF] Juffe-Bignoli | Protected Planet Report 2014[END_REF] and their implementation has not been sufficient to curtail the decline of large mammal populations [START_REF] Craigie | Large mammal population declines in Africa's protected areas[END_REF]. Land sharing in addition to land sparing is increasingly being considered as a necessary and effective option to maintain biodiversity [START_REF] Fischer | Conservation: Limits of Land Sparing[END_REF]. However, the effectiveness of conservation within these multiple use areas depends on how wildlife responds to human activities [START_REF] Fynn | Strategic management of livestock to improve biodiversity conservation in African savannahs: A conceptual basis for wildlife-livestock co-existence[END_REF].

Despite increasing population densities and encroachment by agriculture [START_REF] Newmark | Isolation of African protected areas[END_REF], livestock husbandry and subsistence agro-pastoralism remain the primary land-uses around wildlife areas in semi-arid rangeland ecosystems, particularly near African protected savannas [START_REF] Caron | Relationship between burden of infection in ungulate populations and wildlife/livestock interfaces[END_REF]. The partitioning of rangelands into different land-uses, including protected areas, commercial ranching or communal agro-pastoralism, has often been accompanied by the establishment of fences to hinder the movement of wildlife, livestock and people (Somers & Hayward 2011). However, many areas have remained unfenced or have seen their fences decommissioned over the past decades [START_REF] Cumming | Beyond Fences : Wildlife , Livestock and Land Use in Southern Africa. One health: The theory and practice of integrated health approaches[END_REF]. In the absence of fences, livestock and wildlife ranges may overlap. Current land-tenure implies that this overlap can generate conservation conflicts (sensu [START_REF] Redpath | Understanding and managing conservation conflicts[END_REF] resulting from cattle incursions into protected areas [START_REF] Hibert | Spatial avoidance of invading pastoral cattle by wild ungulates: insights from using point process statistics[END_REF][START_REF] Butt | Coping with Uncertainty and Variability: The Influence of Protected Areas on Pastoral Herding Strategies in East Africa[END_REF] or wildlife excursions outside of protected areas [START_REF] Graham | The movement of African elephants in a human-dominated land-use mosaic[END_REF].

Comment citer ce document : Valls-Fox, H., Chamaillé-Jammes, S., de Garine-Wichatitsky, M., Perrotton, A., Courbin Access to resources, such as dry season forage for herbivores, is a key determinant for both wildlife population dynamics [START_REF] Illius | Resource heterogeneity and ungulate population dynamics[END_REF] and the livelihoods of people living at the edge of protected areas [START_REF] Murwira | Resource gradients and movement accross the edge of transfrontier parks. Transfrontier conservation areas: people living on the edge[END_REF]. Ecological theory predicts that one of the conditions for sustainable coexistence between species is resource partitioning [START_REF] Roughgarden | Resource partitioning among competing species--a coevolutionary approach[END_REF]). Wild and domestic herbivores provide a good model to study spatiotemporal partitioning because they have similar resource requirements implying they can share the same habitat or compete for its resources [START_REF] Butt | Coping with Uncertainty and Variability: The Influence of Protected Areas on Pastoral Herding Strategies in East Africa[END_REF][START_REF] Odadi | African wild ungulates compete with or facilitate cattle depending on season[END_REF][START_REF] Fynn | Strategic management of livestock to improve biodiversity conservation in African savannahs: A conceptual basis for wildlife-livestock co-existence[END_REF].

Whether wild or domestic, the distribution of water-dependent herbivores is primarily driven by surface water availability [START_REF] De Leeuw | Distribution and diversity of wildlife in northern Kenya in relation to livestock and permanent water points[END_REF][START_REF] Ogutu | Large herbivore responses to surface water and land use in an East African savanna: implications for conservation and human-wildlife conflicts[END_REF]. At large scales, pastoralists [START_REF] Adriansen | Going where the grass is greener: on the study of pastoral mobility in Ferlo, Senegal[END_REF] and migratory herbivores [START_REF] Hopcraft | Competition, predation, and migration: individual choice patterns of Serengeti migrants captured by hierarchical models[END_REF] distribute themselves according to foraging opportunities during the rainy season when they are not constrained by access to water. However, they congregate around the remaining water sources during the dry season and are forced to make the best of areas within commuting distance of water [START_REF] Butt | Pastoral resource access and utilization: Quantifying the spatial and temporal relationships between livestock mobility, density and biomass availability in southern Kenya[END_REF][START_REF] Cornélis | Spatiotemporal dynamics of forage and water resources shape space use of West African savanna buffaloes[END_REF][START_REF] Chamaillé-Jammes | African elephants adjust speed in response to surface-water constraint on foraging during the dry-season[END_REF] Wildlife populations in protected areas in savanna ecosystems are particularly vulnerable to droughts [START_REF] Walker | To Cull or Not to Cull : Lessons from a Southern African Drought[END_REF]. In southern Africa, droughts have worsened over the past decades (Chamaillé-Jammes, Fritz & Murindagomo 2007) and recent climatic scenarios predict decreasing rainfall and increasing temperatures during the 21 st century [START_REF] Giannini | A global perspective on African climate[END_REF]. During a drought, one might expect hot dry season conditions to prevail earlier in the season and persist longer in the case of delayed rains. Cattle will likely range even further inside the protected area [START_REF] Butt | the Political Ecology of 'Incursions': Livestock, Protected Areas and Socio-Ecological Dynamics in the Mara Region of Kenya[END_REF]) and wildlife will aggregate in larger numbers around the remaining water pans. As a result, human-wildlife conflicts such as disease transmission [START_REF] Miguel | Contacts and foot and mouth disease transmission from wild to domestic bovines in Africa[END_REF], livestock depredation [START_REF] Kuiper | Seasonal herding practices influence predation on domestic stock by African lions along a protected area boundary[END_REF] or raiding by elephants [START_REF] Guerbois | Combining multi-scale socio-ecological approaches to understand the susceptibility of subsistence farmers to elephant crop raiding on the edge of a protected area[END_REF] are likely to increase.

Comment citer ce document : Valls-Fox, H., Chamaillé-Jammes, S., de Garine-Wichatitsky, M., Perrotton, A., Courbin protected area in North-Western Zimbabwe (Fig. 1). All three of the studied species are water-dependent [START_REF] Hempson | A continent-wide assessment of the form and intensity of large mammal herbivory in Africa-supp-material[END_REF]. Unlike inside the protected areas where elephant are the dominant herbivore species at waterholes [START_REF] Valeix | Interference competition and temporal niche shifts: elephants and herbivore communities at waterholes[END_REF], the association of cattle with people implies they may effectively exclude wild herbivores from waterholes when they come to drink or forage in close proximity [START_REF] Western | Water availability and its influence on the structure and dynamics of a savannah large mammal community[END_REF][START_REF] Sitters | Herded cattle and wild grazers partition water but share forage resources during dry years in East African savannas[END_REF][START_REF] Ogutu | Large herbivore responses to surface water and land use in an East African savanna: implications for conservation and human-wildlife conflicts[END_REF]. In response to cattle presence, wild herbivores could operate a temporal niche shift towards nocturnal activity to continue using the same

water sources yet avoid the disturbances caused by cattle and people.

Segregation between cattle and wildlife may also result from competition for forage. Evidence for exploitation competition is scarce [START_REF] Kartzinel | DNA metabarcoding illuminates dietary niche partitioning by African large herbivores[END_REF]. We hypothesize exploitation competition may occur throughout the year for buffalo and cattle that are both grazers, whereas it is more likely to be limited to the rainy season for elephant that essentially browse during the dry season [START_REF] Williamson | The condition and nutrition of elephant in Wankie National Park[END_REF]. Exploitation competition is expected to be strongest during the dry season when forage is limiting and may be negligible or even outweighed by facilitation during the rainy season [START_REF] Odadi | African wild ungulates compete with or facilitate cattle depending on season[END_REF]). However, competition can be asymmetrical: Cattle have been reported to compensate for forage depletion by wildlife whereas wild herbivores do not [START_REF] Young | Competition and compensation among cattle, zebras, and elephants in a semi-arid savanna in Laikipia, Kenya[END_REF]. As a result, buffalo are expected to strongly avoid areas that are heavily grazed by cattle throughout the year whereas elephant may still find browse in these areas and attempt to exploit them when cattle are absent.

Comment citer ce document : Valls-Fox, H., Chamaillé-Jammes, S., de Garine-Wichatitsky, M., Perrotton, A., Courbin

Methods

Study area

We conducted the study in an area covering 190 km 2 of Sikumi Forestry Commission land (26.9°E, 18.6°S) on the boundary of Hwange National Park, Zimbabwe. There is currently no fence between the Communal Land, Sikumi, Hwange National Park and adjacent photographic or trophy hunting safari areas (Fig. 1). Homesteads and fields are located immediately across the boundary or a few hundred meters away [START_REF] Guerbois | Combining multi-scale socio-ecological approaches to understand the susceptibility of subsistence farmers to elephant crop raiding on the edge of a protected area[END_REF]. A veterinary fence had been erected between Sikumi and the communal land in the 1960's. After the 1992 drought, gates were installed along the fence to allow cattle to enter.

The fence rapidly became ineffective due to lack of maintenance during the economic crisis and was finally dismantled after the year 2000. only be found at 13 artificial waterholes in which groundwater is continuously pumped.

Human presence inside

Surface water availability for each season was determined following the systematic monitoring of 78 natural water pans in the area throughout the 2013 and 2014 dry seasons (Fig. 1).

Vegetation is typical of dystrophic semi-arid savanna dominated by the trees Baikiaea plurijuga, Colophospermum mopane, Kirkia acuminata and Bauhinia petersiana. Herbivore aggregations around water pans create piospheres due to repeated grazing and trampling.

Vegetation in Sikumi is similar to Hwange National Park, woody cover generally increases with distance from water pans (Chamaillé-Jammes, Fritz & Madzikanda 2009). A simplified vegetation map was adapted from Courbin et al. (2016). Four classes were defined according to the proportion of woody cover: Open Grasslands (0.8%) only found within 500m of water pans, Bushed Grasslands (16.6%) and Bushland (26.8%) both found within 2km of water and Bushed Woodland (55.8%) that predominantly occupies the areas farthest from water (Fig. S1). Communal land consists of dispersed homesteads in a matrix of fields and native vegetation, however tree cover is much reduced.

Modelling cattle incursions

Cattle owners usually keep their cattle in kraals located close to their homesteads overnight to protect livestock from predators and thieves. For each one of the three seasons, we modelled the probability of cattle presence inside Sikumi as an Inhomogeneous Poisson Point process (IPP) using GPS locations [START_REF] Johnson | Estimating animal resource selection from telemetry data using point process models[END_REF]. Independent variables included vegetation structure, distance to water, distance to the kraal, distance to the boundary and distance between the kraal and boundary.

Model predictions were computed for each one of the 321 kraals within 2km of the boundary (Fig. 1) and summed to produce a map of cattle intensity of use covering the entire study area for each season. The area used by cattle was defined by drawing the 95th percentile of the summed utilization distributions. A detailed description of model design, validation and predictions is given in Appendix S2.

Modelling buffalo distribution and habitat selection

Sikumi harbours a single herd of approximately 500 buffalo. Five adult females were tracked with GPS collars between November 2012 and August 2014. Collars recorded 1 location per hour. We calculated seasonal occupancy by summing the individual Utilization Distributions (UD) calculated with biased random bridges [START_REF] Cornélis | Spatiotemporal dynamics of forage and water resources shape space use of West African savanna buffaloes[END_REF]. Spatial overlap was defined as the percentage of the buffalo UD that was within the 95 th percentile of the cattle

Comment citer ce document : Valls-Fox, H., Chamaillé-Jammes, S., de Garine-Wichatitsky, M., Perrotton, A., Courbin [START_REF] Sinclair | The African Buffalo A Study of Ressource Limitation of Populations[END_REF]. We restricted our analyses to foraging periods by removing steps that were shorter than 30m. To account for spatio-temporal correlation between our GPS data we identified three foraging bouts: morning (4am-12pm), evening (12pm-8pm) and night (8pm-4am) (Appendix S3).

Step Selection Functions were estimated independently for each foraging bout, predictor variables included vegetation, distance to water, distance to the boundary and cattle density. The home-range scale: buffalo avoid cattle but elephants do not.

Modelling elephant distribution and habitat selection

Buffalo remain within the boundaries of Sikumi and their home range is delimited by the extent of cattle excursions as long as water is widely distributed. During the rainy season, buffalo only spend 2.5% of their time within the areas used by cattle (Fig. 3a). During the cold dry season, buffalo spend twice as much time within 3km of the boundary (from 7% to 13%, Fig. 3b). However, cattle incursions are shorter, briefer and less frequent so the overlap remains minimal (2.5%). During the hot dry season, buffalo contract their home range around the remaining water pans and stay further away from the boundary. However, cattle range further inside Sikumi as well. As a result, buffalo spend 11% of their time in the area used by cattle. Cattle and buffalo home ranges particularly around permanent waterholes or corridors between them (Fig. 3c).

Conversely, the home ranges of elephant bulls extend up to the Sikumi boundary, overlapping the area occupied by cattle (Fig. 3) albeit with considerable variation between individuals and seasons (15% to 68% UD overlap).

Comment citer ce document : Valls-Fox, H., Chamaillé-Jammes, S., de Garine-Wichatitsky, M., Perrotton, A., Courbin The foraging scale: daytime avoidance and night-time opportunism.

Both buffalo and elephant prefer foraging further away from the boundary and are strongly deterred by the presence of cattle whenever they come closer, as shown by the difference between the full line and the dashed line in Figs. 4 &5. Both species prefer areas with less woody cover throughout the year. However, buffalo select these areas more strongly when they are closer to the boundary (Appendix S3).

During the rainy and cold dry seasons, encounters between cattle and buffalo are even less likely since buffalo select areas away from water during the morning bout and only return towards water during the evening bout when cattle are no longer present (Fig. 4). Similarly, elephant bulls prefer areas further away from water during the day than during the night (Fig. 5). Interestingly, distance to water no longer appears to be a decisive criterion during the day or during the night when elephant bulls forage close to the boundary and particularly in areas where cattle are present (Fig. 5). Overall, both species range closer to the boundary during the cold dry season than the rainy season. Buffalo select area closer to the Sikumi boundary during the evening and night (~4km) than during the morning but strongly avoid areas used by cattle within 2km of the boundary. Elephant bulls prefer areas between 3km and 4km from the boundary.

Unlike previous seasons, buffalo select areas close to water during both the morning and evening bouts during the hot dry season (Fig. 4) suggesting they drink twice a day, increasing the likelihood of contact with cattle at waterholes. Buffalo stay away from the boundary but hardly respond to cattle presence suggesting the main driver of their movement is access to water. Elephant bulls range closer to the boundary in the hot dry season (3-4km) and take advantage of the night to forage in areas that cattle use during the daytime (Fig. 5).

Occasionally, elephant bulls make nightly excursions into the communal land. Over the study

Comment citer ce document : Valls-Fox, H., Chamaillé-Jammes, S., de Garine-Wichatitsky, M., Perrotton, A., Courbin

Discussion

Cattle, elephant and buffalo share a preference for open grassland habitats found close to water in Sikumi but have different constraints resulting from their relationship to humans.

Cattle incursions are strongly constrained by the central place effect of their home kraal that keeps them from wandering beyond a few kilometres from the boundary. Buffalo and elephant avoid cattle by staying away from the boundary at large scales but can also fine-tune their diel behaviour to exploit the area close to the boundary at night. These patterns are consistent with avoidance of cattle by wild herbivores in African [START_REF] Hibert | Spatial avoidance of invading pastoral cattle by wild ungulates: insights from using point process statistics[END_REF][START_REF] Ogutu | Large herbivore responses to surface water and land use in an East African savanna: implications for conservation and human-wildlife conflicts[END_REF]) and North-American [START_REF] Stewart | Temporospatial Distributions of Elk, Mule Deer, and Cattle: Resource Partitioning and Competitive Displacement[END_REF] rangelands.

Buffalo predominantly rely on avoidance at the home range scale (Fig. 3) whereas elephant appear to favour temporal niche shift, by avoiding direct encounters with cattle (or people)

during the day but coming closer to the boundary and to water at night (Fig. 5). This difference could result from competitive exclusion of buffalo by cattle (both species being grazers) whereas elephant bulls have access to a broader niche being mixed feeders [START_REF] Kartzinel | DNA metabarcoding illuminates dietary niche partitioning by African large herbivores[END_REF]. Alternatively, solitary elephant bulls are more likely to adopt a cryptic behaviour allowing a more flexible and adaptive foraging strategy, whereas buffalo splinter groups usually include at least a few dozen or even several hundred individuals [START_REF] Cross | Disentangling association patterns in fission-fusion societies using African buffalo as an example[END_REF], reducing their ability to remain inconspicuous during the daytime. Seasonal changes suggest access to key resources is one of the key drivers of cattle-wildlife interactions

Comment citer ce document : Valls-Fox, H., Chamaillé-Jammes, S., de Garine-Wichatitsky, M., Perrotton, A., Courbin, Miguel, E., Guerbois, C., Caron, Loveridge, A., Stapelkamp, Muzamba, Fritz, H. ( 2018). Water and cattle shape habitat selection by wild herbivores at the edge of a protected area. Animal Conservation, 21 (5), 365-375. , DOI : 10.1111/acv.12403 [START_REF] Zengeya | Spatial overlap between sympatric wild and domestic herbivores links to resource gradients[END_REF]) but ecological differences between species lead to different behavioural responses.

Seasonal changes drive cattle-wildlife interactions

During the rainy season, herd boys drive cattle into Sikumi daily to keep their livestock out of fields and to exploit the pastures around waterholes. Widespread distribution of water pans allows buffalo and elephant to successfully avoid cattle. Although waterholes still constitute key habitats for all species, buffalo shift their home range at large scales to exploit the open areas around water pans further inside Sikumi whereas elephant only visit waterholes at night when they range closer to the boundary.

During the dry season, cattle are no longer herded, they initially spend most of their time in the communal land feeding on crop residues, but eventually return to Sikumi and gradually travel further away from the boundary and from water suggesting that intraspecific competition [START_REF] Young | Competition and compensation among cattle, zebras, and elephants in a semi-arid savanna in Laikipia, Kenya[END_REF][START_REF] Odadi | African wild ungulates compete with or facilitate cattle depending on season[END_REF]) is stronger than the risk of encountering predators [START_REF] Kuiper | Seasonal herding practices influence predation on domestic stock by African lions along a protected area boundary[END_REF] or than competition with wild herbivores.

As the dry season advances, buffalo water dependence takes precedence over avoidance of cattle. They strongly contract their home-range around waterholes [START_REF] Cornélis | Spatiotemporal dynamics of forage and water resources shape space use of West African savanna buffaloes[END_REF]) and only venture further away from water during their nocturnal foraging bout (Fig. 4). Buffalo and cattle home-range overlap increases fivefold, heightening the likelihood of contacts between both species and the risk of disease transmission [START_REF] Miguel | Contacts and foot and mouth disease transmission from wild to domestic bovines in Africa[END_REF].

As resources dwindle, elephant bulls select areas closer and closer to the boundary at night, suggesting that they avoid intraspecific competition as well by foraging in areas with lower browser densities when forage becomes most limiting rather than the attractiveness of crops.

Comment citer ce document : Valls-Fox, H., Chamaillé-Jammes, S., de Garine-Wichatitsky, M., Perrotton, A., Courbin Can surface water management mitigate the effects drought?

In Sikumi, the 1992 drought was a turning point when traditional authorities and the Forestry Commission came to an informal agreement to tolerate cattle incursions within the first few kilometres to mitigate a massive die-off in domestic livestock due to forage and water shortages. Current water management is already a key determinant of human-wildlife coexistence. The spatial overlaps between buffalo and cattle reflect the distribution of water pans pumped by safari operators (Fig. 3) and cattle owners can manipulate the behaviour of their livestock by providing water from boreholes (pers. obs.).

Local stakeholders may reduce conflicts by shifting artificial waterholes further away from unfenced protected area boundaries and increasing access to boreholes for cattle in the communal lands. Such policies might also reduce livestock depredation as predators will select for areas with higher wild prey densities and remain close to permanent waterholes [START_REF] Valeix | How key habitat features influence large terrestrial carnivore movements: waterholes and African lions in a semi-arid savanna of north-western Zimbabwe[END_REF].

Avoidance of cattle or avoidance of people?

Whereas cattle and buffalo hardly overlap and almost never meet in Sikumi, up to 60% of elephant bull's seasonal home-range can be found within the area utilized by cattle. In other ecosystems, livestock can displace other herbivore species completely [START_REF] Stewart | Temporospatial Distributions of Elk, Mule Deer, and Cattle: Resource Partitioning and Competitive Displacement[END_REF][START_REF] Hibert | Spatial avoidance of invading pastoral cattle by wild ungulates: insights from using point process statistics[END_REF], they may overlap in space but not in time [START_REF] Cooper | Distribution and interaction of white-tailed deer and cattle in a semi-arid grazing system[END_REF][START_REF] Atickem | Livestock-wildlife conflicts in the Ethiopian highlands: Assessing the dietary and spatial overlap between mountain nyala and cattle[END_REF] or even co-mingle [START_REF] Dohna | Wildlifelivestock interactions in a western rangeland setting: Quantifying disease-relevant contacts[END_REF]. Moreover, buffalo strongly avoid cattle in Sikumi whereas their range overlap extensively with cattle around the Greater Limpopo Transfrontier Conservation Area [START_REF] Miguel | Contacts and foot and mouth disease transmission from wild to domestic bovines in Africa[END_REF].

Rather than avoiding cattle per se, buffalo and elephants might in fact be avoiding humans. are not systematically accompanied by people, the association may be sufficiently strong for wildlife to consider them as cues for human presence.

Free ranging cattle can displace wild herbivores even in the absence of humans [START_REF] Stewart | Temporospatial Distributions of Elk, Mule Deer, and Cattle: Resource Partitioning and Competitive Displacement[END_REF][START_REF] Cooper | Distribution and interaction of white-tailed deer and cattle in a semi-arid grazing system[END_REF]) and the presence of cattle herders does not necessarily imply a greater displacement of wild herbivores. In East-African savannas, sedentarisation of nomadic pastoral communities resulted in a decline in herbivore abundance attributed to displacement from key grazing resources by resident livestock [START_REF] Western | The impact of subdivision and sedentarization of pastoral lands on wildlife in an African savanna ecosystem[END_REF]. The decline neither resulted from increased offtake nor from higher cattle densities. A neighbouring nomadic community with similar human and livestock population growth witnessed an increase in wildlife abundance over the same period. In southern Kenya, Maasai pastoralists preferentially take their cattle to forage far from water during dry periods and commute large distances between their pastures and water. Such practices ease coexistence with wild herbivores that select foraging grounds along the distance to water gradient according to their water dependency [START_REF] Sitters | Herded cattle and wild grazers partition water but share forage resources during dry years in East African savannas[END_REF]

Conclusion

Cattle are ubiquitous and highly valued in most agro-pastoral societies that live around protected areas worldwide. However, cattle incursions into protected areas are often perceived as "unnatural" and considered as a threat to wildlife via overgrazing [START_REF] Butt | the Political Ecology of 'Incursions': Livestock, Protected Areas and Socio-Ecological Dynamics in the Mara Region of Kenya[END_REF].

Displacement of wildlife on the boundary of protected areas over a distance of a few kilometers does not entail substantial habitat loss, however it can promote coexistence by delimiting a buffer zone that protects people from wildlife (e.g. livestock predation, crop destruction, zoonosis transmission). The implementation of such buffering strategies are particularly relevant for large conservation areas such as the Kavango-Zambezi TFCA that encompasses multiple protected areas as well as communal land.

In order to maintain the integrity of protected area boundaries, two mechanisms may be mobilized: fear of humans and resource availability. In arid lands, water provisioning may be designed to allow for the segregation of livestock and wildlife in order to minimise conflict.

However, in more mesic landscapes or situations, such as savannas during the rainy season, the relation between cattle and wildlife may be one of facilitation rather than competition [START_REF] Fynn | Strategic management of livestock to improve biodiversity conservation in African savannahs: A conceptual basis for wildlife-livestock co-existence[END_REF]. Nonetheless, cattle may only be perceived as cues for human presence, thus traditional herding practices, that often rely on people accompanying cattle, may be paramount to maintaining segregation between cattle and wildlife.

Comment citer ce document : Valls-Fox, H., Chamaillé-Jammes, S., de Garine-Wichatitsky, M., Perrotton, A., Courbin

  Sikumi mainly consists in game viewing from 4x4 vehicles and patrols by Forestry Commission scouts and anti-poaching units. People living on the edge of Sikumi also enter within the first few kilometres of the boundary. Their main activity is cattle herding although they regularly collect natural resources such as firewood and thatching grass. The exact distance cattle are allowed to enter is unclear and remains a bone of contention between cattle owners and the Forestry Commission. Mean annual precipitation is 600mm with large variations between years (Chamaillé-Jammes, Fritz & Murindagomo 2006). Climate is characterized by a rainy season that extends from November to April followed by the dry season which can be subdivided in a cold dry season (May-August) and a hot dry season (September-November). There are no perennial rivers in the study area, natural depressions and dams fill up with water during the rainy season but gradually dry up throughout the dry season. By the end of the dry season, surface water can Comment citer ce document : Valls-Fox, H., Chamaillé-Jammes, S., de Garine-Wichatitsky, M., Perrotton, A., Courbin, Miguel, E., Guerbois, C., Caron, Loveridge, A., Stapelkamp, Muzamba, Fritz, H. (2018). Water and cattle shape habitat selection by wild herbivores at the edge of a protected area. Animal Conservation, 21 (5), 365-375. , DOI : 10.1111/acv.12403

  Elephant bulls are responsible for most of the crop-raiding incidents[START_REF] Guerbois | Combining multi-scale socio-ecological approaches to understand the susceptibility of subsistence farmers to elephant crop raiding on the edge of a protected area[END_REF]. Ten individuals were equipped with GPS collars recording 1 location per hour between December 2010 and February 2013. Unfortunately, only 6 provided sufficiently long datasets within the study area for us to conduct statistical analyses. We measured elephant's spatial overlap with cattle and resource selection using the same methods than the ones used for buffalo. However, elephants being monogastric herbivores, they do not have the clear-cut foraging bouts (Fig.S5, Appendix S4). Since cattle enter the Forest area during the daytime and elephant excursions into Communal land generally occur at night, day-time and nighttime Step Selection Functions were estimated separately for each season. Comment citer ce document : Valls-Fox, H., Chamaillé-Jammes, S., de Garine-Wichatitsky, M., Perrotton, A., Courbin, Miguel, E., Guerbois, C., Caron, Loveridge, A., Stapelkamp, Muzamba, Fritz, H. (2018). Water and cattle shape habitat selection by wild herbivores at the edge of a protected area. Animal Conservation, 21 (5), 365-375. , DOI : 10.1111/acv.12403 Results Cattle use of Sikumi Forest. Cattle habitat selection patterns reflect the strong central place effect of their home kraal; as shown by the strong decrease in probability of selection as distance to the boundary increases, regardless of distance to water and habitat type (Fig. 2, Appendix S2). Cattle also select areas close to water pans during the rainy season. The pattern dampens in the cold dry season and is actually reversed when the pans are dry in the hot dry season. Unsurprisingly, cattle select the most open habitats, especially near water pans. However, as the dry season advances, the difference between habitats decreases and cattle distribution becomes less predictable.

  Comment citer ce document : Valls-Fox, H., Chamaillé-Jammes, S., de Garine-Wichatitsky, M., Perrotton, A.,Courbin, Miguel, E., Guerbois, C., Caron, Loveridge, A., Stapelkamp, Muzamba, Fritz, H. (2018). Water and cattle shape habitat selection by wild herbivores at the edge of a protected area. Animal Conservation, 21 (5), 365-375. , DOI : 10.1111/acv.12403

  Kraals act as central places from which cattle depart in the morning and return to before sundown. Cattle from 11 different kraals were They range about 1.6km from the boundary but may reach up to 5.4km and spend on average 4.3h per day inside. During the cold dry season, cattle are no longer herded and roam freely in the villages, feeding on communal pastures and crops residues left in the fields. They enter the Sikumi less than one day out of five. Some herds are briefly driven into Sikumi to drink but

	most drink at boreholes inside the communal area. Incursions are briefer (mean=1.8h) and
	closer to the boundary (mean=0.8km, max=3.8km). As for the hot dry season, cattle enter
	Sikumi to graze on their own more often (one day out of three), stay longer (mean=3.1h) and
	travel further (mean=1.4 km, max=6.0 km). Herders only enter to collect them in the late
	afternoon (Valls-Fox & Perrotton unpublished data).
	equipped with GPS collars recording 1 location every hour. Five cows were tracked in 2010-
	2011 and 9 in 2012-2014.

Cattle incursions in Sikumi follow the seasonal changes in herding strategies, water availability and forage abundance. During the rainy season, cattle are driven into Sikumi nearly every single day, mainly to prevent them from destroying crops in adjacent fields.

Comment citer ce document : Valls-Fox, H., Chamaillé-Jammes, S., de Garine-Wichatitsky, M., Perrotton, A.,

Courbin

, Miguel, E., Guerbois, C., Caron, Loveridge, A., Stapelkamp, Muzamba, Fritz, H. (2018). Water and cattle shape habitat selection by wild herbivores at the edge of a protected area. Animal Conservation, 21 (5), 365-375. , DOI : 10.1111/acv.12403

  To understand how buffalo foraging decisions are influenced by the presence of cattle we used Step Selection Functions (Thurfjell, Ciuti & Boyce 2014). Resource selection was estimated by pairing each one hour step with 10 random controls having a different direction and length. At fine scales, buffalo alternate foraging bouts lasting a few hours with periods of resting and ruminating

, Miguel, E., Guerbois, C., Caron, Loveridge, A., Stapelkamp, Muzamba, Fritz, H. (2018). Water and cattle shape habitat selection by wild herbivores at the edge of a protected area. Animal Conservation, 21 (5), 365-375. , DOI : 10.1111/acv.12403 UD.

  , we recorded only 79 excursions out of the 1960 nights spent by the six collared bulls in the study area (226 -334 nights per individual). Half of the excursions occurred during the hot dry season and 25% at the end of the cropping season between March and May.

, Miguel, E., Guerbois, C., Caron, Loveridge, A., Stapelkamp, Muzamba, Fritz, H. (2018). Water and cattle shape habitat selection by wild herbivores at the edge of a protected area. Animal Conservation, 21 (5), 365-375. , DOI : 10.1111/acv.12403 period

  During the rainy season, herd boys drive cattle into Sikumi and stay with them all day. During dry season, cattle range freely and often enter unaccompanied. Unfortunately, seasonal changes in cattle movement are confounded with changing herding practices, and we cannot tell whether elephant and buffalo's usage of areas closer to the boundary result from the absence of herd boys or from shorter and less frequent cattle incursions. Even though cattle

Comment citer ce document : Valls-Fox, H., Chamaillé-Jammes, S., de Garine-Wichatitsky, M., Perrotton, A.,

Courbin

, Miguel, E., Guerbois, C., Caron, Loveridge, A., Stapelkamp, Muzamba, Fritz, H. (2018). Water and cattle shape habitat selection by wild herbivores at the edge of a protected area. Animal Conservation, 21 (5), 365-375. , DOI : 10.1111/acv.12403 the

  . Herding practices in Sikumi consist in repeated incursions by sedentary livestock to the same areas close to water. Unlike patterns reported by[START_REF] Sitters | Herded cattle and wild grazers partition water but share forage resources during dry years in East African savannas[END_REF] and as suggested by[START_REF] Western | The impact of subdivision and sedentarization of pastoral lands on wildlife in an African savanna ecosystem[END_REF] in Kenya, herding practices in Sikumi may effectively exclude wild herbivores from the vicinity of the Forest boundary.Edge effects at an unfenced interfaceDespite the absence of any physical barrier to movement, buffalo never cross into the communal land and elephant bulls make rare excursions during the rainy and hot dry seasons.Both species avoid Sikumi boundary but bunch up against a virtual fence[START_REF] Jachowski | Good virtual fences make good Version preprint Comment citer ce document[END_REF] corresponding to the contour of the area used by cattle. The boundary of Sikumi has edge effects on wildlife that are comparable to effects of real barriers[START_REF] Loarie | Fences and artificial water affect African savannah elephant movement patterns[END_REF]. However, our study focuses on elephant bulls and adult female buffalo, individuals from different sex and age classes could perceive the boundary differently as has been recently demonstrated for sub-adult buffalo in the Greater Limpopo TFCA(Caron et al.

	2016).

Comment citer ce document : Valls-Fox, H., Chamaillé-Jammes, S., de Garine-Wichatitsky, M., Perrotton, A.,

Courbin

, Miguel, E., Guerbois, C., Caron, Loveridge, A., Stapelkamp, Muzamba, Fritz, H. (2018). Water and cattle shape habitat selection by wild herbivores at the edge of a protected area. Animal Conservation, 21 (5), 365-375. , DOI : 10.1111/acv.12403

Acknowledgments

We are grateful to the cattle owners and Forestry scouts for their time and their trust. This research was authorized by the Research Council of Zimbabwe, the Forestry Commission, the Zimbabwe Parks and Wildlife Management Authority, the Hwange District Administrator and chief Nelukoba. Funding was provided by the grant ANR-11-CEPS-003 of the French 'Agence National de la Recherche' and a PhD fellowship from the Ecole Normale Supérieure & Université de Montpellier. This work was conducted within the framework of the Research Platform "Production and Conservation in Partnership" (www.rp-pcp.org) and the FSP-RenCaRe project (FSP n°2011-36).

Authors' Contributions

HVF, SCJ, MDGW & HF conceived the ideas and designed methodology; HFV, AP, BS, MM, and EM collected the data; HVF analysed the data with guidance from NC and SCJ; HVF led the writing of the manuscript. All authors contributed critically to the drafts and gave final approval for publication.