Movement and space-use responses of a large herbivore to experimental alteration of resource availability

Resource acquisition is a key factor governing patterns of animal movement. While the link between spatio-temporal resource patterns and movement behaviour has been widely documented for migration, our understanding of home ranging behaviour in relation to resource dynamics has been limited by challenges of quantifying resource heterogeneity at fine spatio-temporal scales. In this study, we addressed this issue by analysing the movement responses of a resident large herbivore in response to an in situ manipulation of a high-quality, concentrated food resource. Specifically, we fitted roe deer (Capreolus capreolus) with GPS collars in the Eastern Italian Alps and recorded their fine-scale movement responses to an alteration of feeding site accessibility, for a total of 25 animal-years. The experiment involved identifying, for each animal, a familiar feeding site, whose accessibility was transitorily restricted (i.e., closed) while maintaining the availability of forage at alternative feeding sites. First, we tested whether individuals altered their spatial behaviour to track dynamical changes in resource availability. Experimental closure led to larger, spatially-shifted home ranges, resulting from more exploratory movements. Individual roe deer compensated the loss of their familiar feeding site by using alternative ones, and by doing so maintained their overall use of these concentrated resources. Our results demonstrate that roe deer actively track resource dynamics, and rapidly adjust their space-use and movement behaviour in response to changes in resource availability. Second, we showed that individual resource preferences mediate these behavioural adjustments: individuals characterized by a high preference for feeding sites exhibited larger space-use shifts and stronger changes in resource use in response to the resource manipulation. In contrast, sex had relatively minor influence on the observed patterns. Third, we investigated the role of site familiarity in roe deer foraging decisions. We found that space-use and resource use during the post-closure period were restored to pre-closure patterns, thereby providing evidence for the inherent benefits of site familiarity to animals maintaining a home range. Together, our results establish the connections between movement, space-use, individual preference, and the spatio-temporal pattern of resources in deer home ranging behaviour.

Eastern Italian Alps and recorded their fine-scale movement responses to an alteration of feeding 23 site accessibility, for a total of 25 animal-years. The experiment involved identifying, for each 24 animal, a familiar feeding site, whose accessibility was transitorily restricted (i.e., closed) while 25 maintaining the availability of forage at alternative feeding sites. First, we tested whether 26 individuals altered their spatial behaviour to track dynamical changes in resource availability. 27 Experimental closure led to larger, spatially-shifted home ranges, resulting from more 28 exploratory movements. Individual roe deer compensated the loss of their familiar feeding site 29 by using alternative ones, and by doing so maintained their overall use of these concentrated 30 resources. Our results demonstrate that roe deer actively track resource dynamics, and rapidly 31 adjust their space-use and movement behaviour in response to changes in resource availability. 32 Second, we showed that individual resource preferences mediate these behavioural adjustments: 33 individuals characterized by a high preference for feeding sites exhibited larger space-use shifts 34 and stronger changes in resource use in response to the resource manipulation. In contrast, sex 35 had relatively minor influence on the observed patterns. Third, we investigated the role of site 36 familiarity in roe deer foraging decisions. We found that space-use and resource use during the 37 8 with GPS-GSM radio collars programmed to acquire hourly GPS locations for a year, after 153 which they were released via a drop-off mechanism. Radio-collared roe deer moved an average 154 of 61.2 m per hour. This value of the average hourly movement distance (l) was subsequently 155 utilized in the analyses described below. 156 For all captured animals, we assumed a post-capture response in ranging behaviour. We 157 therefore considered the first re-visitation of the capture location as the sign of resettlement in 158 the original range and we used this time as the earliest possible onset of the experimental pre-159 closure phase. Although not all the individuals were manipulated at the same time, we avoided 160 interference between capture operations and FS manipulations and between co-occurring 161 different manipulation phases (i.e. ensuring that co-occurring manipulations occurred in separate 162 areas). 163 During the pre-closure phase, we assessed the use of FS by radio-collared roe deer. We To ensure meaningful comparisons between animal-years, we homogenized the durations 175 of each experimental phase to the minimum length of the closure phase (i.e., 14 days). 176 Specifically, we truncated the movement data by removing initial excess positions for the pre-177 closure and closure phases, and terminal excess positions for the post-closure phase. GPS 178 acquisition success was extremely high (99.57 % during the experiment) and we did not 179 interpolate missing fixes in the collected data. 180 The analyses of space-use and movement behaviour were based on spatially-explicit, raw 181 movement trajectories. We analysed how the experimental manipulation, and its interaction with both preference 207 for FS and sex, affected roe deer space-use, movement behaviour, and resource use. 208 Space-use: We assessed the changes of home range and core area sizes (P1.1), and of 209 space-use overlap (P1.2, P3.1) between experimental phases. We calculated utilization 210 distributions, (UD; sensu Worton 1989) for each animal-year and experimental phase using a 211 Gaussian kernel density estimation. After visual inspection, we chose to compute the UDs at a 212 spatial resolution of 10 m and with a fixed bandwidth, set to half the average hourly movement 213 distance (i.e. /2=30.6 m). 214 For home range and core area sizes, we calculated the area (in hectares) corresponding to 215 the 95% and 50% UD contours, respectively, for each experimental phase (Phase; three levels; 216 reference level: Pre-closure). We then analysed the log-transformed areas using a linear mixed-217 effect model (LMM) with five fixed effects: Phase, ℎ #$ , Sex (categorical predictor; reference 218 level: Female), and two interaction terms (Phase:ℎ #$ and Phase:Sex). We included animal-year 219 (ind) as random effect (intercept). In all analyses, interaction terms were dropped when 220 statistically non-significant (p-value>0.05). 221 For space-use patterns, we estimated the overlaps for three pairs of UDs -pre-and post-222 closure, pre-closure and closure, and closure and post-closure (Contrast; three levels; reference 223 level: Pre-/Closure) -using the volume of intersection statistic (VI; Fieberg and Kochany 2005). 224 VI ranges between 0 (no overlap) and 1 (complete overlap). We then analysed the logit-225 transformed overlaps using an LMM with Contrast, ℎ #$ , Sex, Contrast:ℎ #$ and Contrast:Sex as 226 fixed effects, and ind as random intercept. 227 Resource use: To test whether the experiment led to a transitory change in resource use 239 (P1.4a-b, P3.2), we fitted separate mixed-effect logistic regression models to the three single-240 state presence/absence time series ( <,) , =,) and >,) ) using Phase, ℎ #$ , Sex, Phase:ℎ #$ and 241 Phase:Sex as fixed effects, and ind as random intercept. The pre-closure level for Phase was 12 dropped for > to avoid circularity (ℎ #$ = 1 − @ >,) ABC6DEFGHBC ). We also included the response 243 variables measured at lags 1, 2 and 24 h (e.g., <,)65 , <,)69 , <,)69: ) as fixed effects to reduce 244 the autocorrelation of the model residuals. However, for the sake of conciseness and clarity, we 245 omit these response lags when visualizing resource use predictions. Because the model results 246 were consistent regardless of the inclusion of the response lags (Appendix S6: Table S6.

Space-use and movement responses to alteration of resource availability 261
Roe deer space-use changed significantly during the experiment: the size of both home 262 ranges (95% UD isopleth; Appendix S4: Table S4.1) and core areas (50% isopleth; Table 2) 263 increased significantly during the experimental closure ( Fig. 2 Home range and core area sizes were influenced by individual preference for FS (ℎ #$ ) 268 and there was an interaction between ℎ #$ and experimental phase: individuals with a high ℎ #$ 269 had smaller home ranges during the pre-closure and, overall, smaller core areas than those with 270 lower ℎ #$ , but stronger increases following the experimental closure ( Fig. 2; Table 2; Appendix 271 S4: Table S4.1; P2.2). There was no significant effect of sex or interactions between sex and 272 experimental phase on home range size (Appendix S4: Table S4.2; P2.1), but a marginally 273 significant interaction between sex and experimental phase on core area size (Appendix S4: 274 Table S4.3) with responses to closure tending to be slightly larger for males. Overall, the models 275 quantifying the changes in observed home range and core area sizes accounted for a high 276 proportion of the total variance (conditional coefficient of determination, cR 2 : 0.62 and 0.51, 277 respectively). 278 Alongside home range size, the spatial pattern of roe deer home ranges shifted 279 dramatically following the experimental closure (  Table 3; P2.2), with higher ℎ #$ being associated to larger space-use shifts. However, there was 284 no apparent influence of sex in the space-use patterns (Appendix S4:

Resource use responses to alteration of availability 299
The spatio-temporal dynamics of resources availability during the experiment led to 300 important shifts in FS resource use ( Fig. 4; Table 4). On average, the proportion of use of the 301 main FS (M) dropped from 31% during the pre-closure phase to 4% during closure (P1.4a), and 302 then rebounded to 19% in the post-closure phase (P3.2). This decrease in the use of M during the 303 closure phase was partially compensated by elevated use of the other FS (O) -which increased 304 from 3% to 16% following closure (P1.4b), and an increase of the use of vegetation (V) from 305 66% to 80% following closure. During the post closure, use of O and V declined to 9% and 72%, 306 respectively. The shifts in resource use were very consistent among animal-years for M and O 307 but were more variable for V (Fig. 4, top panels). 308 Roe deer preference for FS significantly influenced how animals used the three resource 309 types and, in particular, interacted with experimental phase for M and O (Fig. 4, bottom panels; 310 Table 4). Roe deer characterized by a high ℎ #$ had significantly higher use of M during pre-311 closure (by definition) and post-closure, as well as consistently lower use of V. High ℎ #$ animals 312 were associated with stronger decreases in use of M and larger increases in the use of O during 313 closure (P2.2). This compensation for O during closure was stronger for females (Table 4;  314 Appendix S6: Fig. S6.1; P2.1). However, sex did not influence the use of M or V (Appendix S6: 315 The results of this field resource manipulation experiment provide direct evidence for the 320 tight coupling between the spatio-temporal distribution of resources and consequently spatially-321 restricted movements of a large herbivore. Specifically, we show that roe deer track resource 322 dynamics ( Fig. 4; H1), which leads to changes in their space-use (Figs. 2, 3) and underpinning 323 movements (Appendix S5: Figs S5.1, S5.2), and that individual traits, especially resource 324 preference, mediate these behavioural adjustments (H2). In additional, we show that roe deer 325 exhibit a high attraction to familiar locations, a process which leads to site fidelity (H3). As far 326 as we are aware, this is the first experimental demonstration of these interdependencies in a large 327 mammalian herbivore. 328

329
Roe deer alter space-use and movement behaviour to track resources 330 The experimental alterations of food availability led to larger (Fig. 2), spatially-shifted 331 home ranges (Fig. 3), and more explorative movements by roe deer (Appendix S5: Figs S5.1, 332 S5.2), thereby directly establishing the connections between movement, space-use and the 333 spatio-temporal patterns of resources. 334 In a previous observational study, Fryxell et al. (2008) showed that elk alternated 335 between two movement modes: a low speed and high sinuosity mode thought to be within-patch 336 area-restricted search, and a high speed and low sinuosity mode between resource patches. In our 337 experimental study, we can directly link these movement modes to changing resources: the 338 exploratory movements of roe deer (high velocity and low sinuosity) observed during the closure 339 phase (P1.3) suggested that the animals were motivated to find alternative resource patches when 340 do not generally defend territories, and consequently their spatial distribution can approximate 362 that of an ideal free distribution (Walhström & Kjellander, 1995). Territorial tenure (Linnell & 363 Andersen, 1998) may explain the marginally different response of males (P2.1), specifically their 364 tendency to have larger core areas (Appendix S4: Table S4.3), more explorative movements 365 (Appendix S5: Table S5.1, S5.2) and lower resource compensation than females following 366 closure (Table 4; Appendix S6: Fig. S6.1). In fact, except for one individual (M11) showing high 367 spatial instability during its two-year monitoring, the space-use patterns of males tended to be 368 less influenced by the experimental closure than females.

Resource tracking is mediated by individual preference 377
This study moves beyond the findings of Kilpatrick and Stober (2002) by demonstrating 378 that inter-individual variation in preference for FS strongly mediated the responses of roe deer 379 movement patterns, space-use and resource use to changes in the spatio-temporal distribution of 380 resources (H2). During the closure phase, the changes in all measured variables were of larger 381 magnitude for individuals associated with a high FS preference (P2.1). The influence of FS 382 preference was particularly striking in the shifts of space-use (Fig. 3) and in the compensating 383 use of alternative FS following loss of the familiar resource (Fig. 4). 384 In this study, FS preference varied across individuals (Appendix S3: Table S3.1). These 385 inter-individual differences may be linked to either the environment the individuals were 386 winter is likely to vary between years. In addition, the dynamics in the quality and quantity of 394 natural browse -either spatial (e.g., between home ranges) and/or temporal (e.g., between years) 395 -could lead to variations in FS preference. Indeed, FS preference was higher in 2017 than in 396 2018 for all roe deer manipulated in these consecutive years (Appendix S3: Table S3.1). 397 Preference can therefore be considered a dynamic variable (Beyer et al., 2010) that we evaluated 398 at the individual level over a short period of relative stability (pre-closure phase in each winter). 399 We considered the temporal extent of our experiment (ca 6 weeks) short enough to consider FS 400 During the post-closure phase of the experiment, roe deer increased their use of familiar 424 FS (M), whose food accessibility had been restored after a transitory restriction (Fig. 4, left-hand 425 panels; P3.1), and home ranges shifted back to pre-closure patterns, as suggested by the high 426 overlap between temporally-disjointed pre-and post-closure space-use ( Fig. 3; P3.2 foraging value. Second, the FS were located in comparable environments with close proximity to 446 cover, a factor that largely influence roe deer movements and space-use (e.g., Tufto et al. 1996, 447 Bongi   Table 4. Summary of the final models for the use of the main feeding site ( <,) ), other feeding 664 sites ( =,) ) and vegetation ( >,)