Seasonal Variation in Space Use and Territoriality in an Invasive Large Mammal (Sus Scrofa)


 An individual’s spatial behavior is shaped by social and environmental factors and provides critical information about population processes to inform conservation and management actions. Heterogeneity in spatial overlap among conspecifics can be evaluated using estimates of home ranges and core areas and used to understand factors influencing space use and territoriality. To understand and test predictions about spatial behavior in an invasive large mammal, the wild pig (Sus scrofa), we examined variation in space use between sexes and seasons. We predicted that if animals were territorial that there would be a reduction in space-use overlap when comparing overlap of home ranges (HR-HR), to home ranges and core areas (HR-CA), and in-turn to core areas (CA-CA). Home ranges and core areas were estimated for 54 wild pigs at Buck Island Ranch, FL from GPS telemetry data. Overlap indices were calculated to estimate the strength (space-use overlap) and number of potential interactions within three wet seasons (June-October) and two dry seasons (December-April). Across all seasons, males exhibited larger home ranges compared to females (M = 10.36±0.79 km² (±SE), F = 3.21±0.16 km²) and interacted with a greater number of individuals than females. Home range size and strength of interactions did not vary between wet and dry seasons. Consistent with our predictions, wild pigs appeared to exhibit territorial behavior, where strength of overlap decreased when comparing HR-HR to HR-CA and HR-CA to CA-CA. Strength of overlap varied by sex, which was lowest between females, intermediate between females and males, and greatest between males. Our framework can be used to understand patterns of space use and territoriality in populations, which has important implications in understanding population processes and how pathogens and parasites might spread within and among populations.


Introduction
Spatial behavior through time can be characterized by an individual's home range and territory. Home ranges are selected by animals to maximize their survival and reproduction, with territories traditionally de ned as a reduced portion of the home range that is actively defended or exclusively used 1,2,3,4 . Spatial overlap of individuals in uences intraspeci c interactions, which can drive population processes such as disease transmission 5 , survival 6,7 , competition 8 , and reproduction 9 . The relationship between the spatial organization of a species and dynamic interaction among individuals is expected to vary based on both behavioral and environmental factors.
Variation in spatial interactions among animals can identify the selective pressures that shape spatial behavior. Differences between males and females in spatial behavior are related to differing reproductive strategies and spatial requirements allometrically scaling with body size 10,11,12 , which can in uence home range size 13 and habitat use 14 . Seasonal changes in behavioral and environmental in uences can also modify spatial behavior and in uence overlap and association of conspeci cs 13,15,16,17 . Isolating factors that in uence heterogeneity in spatial overlap can improve management and conservation decisions by identifying important time periods for disease transmission 19 , intraspeci c competition 8 , and management actions 19 . Despite the growing evidence that spatial relationships affect a diverse range of socio-ecological processes 20 , variation in spatial overlap patterns between sexes and seasons is poorly understood for many species and is dependent on the individual's spatial organization.
Territorial behavior can increase an individual's tness by excluding conspeci cs from areas containing limiting resources, including food, cover, and mates. There is considerable variation, however, in how territories are de ned and interpreted 3,4 and they are often approximated by estimating core areas (i.e., areas of high probability of use within an animal's home range 21,22,23 . Although the identi cation of core areas can be subjective, territoriality can be identi ed by examining overlap between adjacent individual's home range and core areas 24,25,26 . Non-territorial species are expected to overlap with conspeci cs at random which would result in overlap with a similar number of individuals in home ranges and core areas (Fig. 1). Conversely, territorial behavior creates spatial heterogeneity in the number and strength of conspeci c interactions, leading to reduced overlap of core areas compared to home ranges (Fig. 1). In the paradigm proposed by Burt (1943) 1 and Schoener (1968) 2 , territorial species overlap in their home ranges but have exclusive core areas and thus home ranges do not overlap core areas between neighboring individuals ( Fig. 1; Fig. 2). Other studies have de ned territoriality as occurring when core areas are mutually exclusive between animals, but home ranges overlap with core areas of adjacent individuals 24,27,26,23,28 (Fig. 1; Fig. 2). It is predicted that if animals are territorial that there will be a reduction in spatial overlap when comparing overlap of home ranges (HR-HR), home ranges and core areas (HR-CA), and core areas (CA-CA) (Fig. 1). If animals are not territorial and spatial overlap among individuals is random, then it would be predicted that overlap would be similar when comparing HR-HR, HR-CA, and CA-CA (Fig. 1). Spatial overlap patterns could be used to quantify territoriality in many species and across a range of different social structures, but this approach could be particularly useful for species that exhibit heterogeneity in space use yet lack conspicuous territorial behaviors or exclusive core areas.
Wild pigs, Sus scrofa, are a large-bodied, gregarious species with an expansive native and invasive range, ecological role as an ecosystem engineer, and complex socio-spatial behavior 29,30,31,32 . Seasonal wild pig home ranges can vary inversely with forage availability 33,34,35,36,37,38 , which could in uence spatial overlap 39,40 and territorial patterns 8, 40 . Although territorial patterns have been predicted for wild pigs 41 , previous studies have provided con icting evidence. Female groups are argued to be territorial with other female groups where groups overlap in their home ranges, but exhibit mutually exclusive core areas 27,42,43 . This pattern, however, is not detected in other systems 35,44,45 , and the role of territoriality in wild pig social structure is unclear. Males are reported to be less territorial than females (but see Boitani et al.1994 35 ), with males exhibiting larger home ranges that overlap with both sexes 46 . How home range size, spatial overlap, and territoriality vary across seasons has not been widely evaluated for wild pigs and it is unclear how different behavioral and environmental factors in uence space-use overlap.
Here we examined variation in the spatial behavior of wild pigs and used this information to understand patterns of territoriality. Our rst objective was to examine variation in home range size and spatial overlap between sexes within a single season. We expected that males would 1) exhibit larger home ranges, 2) interact with a greater number of conspeci cs within their home ranges, and 3) exhibit increased intra-sexual space-use overlap compared to females 46,47 . Our second objective was to evaluate how home range size and space-use overlap varied seasonally. Assuming forage availability to be lower during the dry season than the wet season 48, 49 , we predicted that home range size and space-use overlap would be greater during dry seasons because animals would use larger areas to acquire su cient resources 38 . Conversely, if resources are more concentrated and limiting during the dry season, then wild pigs might exhibit less space-use overlap during this season. Our third objective was to use measures of spatial overlap to evaluate territoriality in wild pigs among years and between wet and dry seasons. If wild pigs exhibited territoriality, we expected that spatial overlap among individuals would be greatest for home range to home range (HR-HR) interactions, reduced for home range to core area (HR-CA) interactions, and lowest for core area to core area (CA-CA) interactions (Fig. 1). We predicted that males and females would differ in their spatial overlap, with females exhibiting more exclusive core areas.
Territoriality was expected to be strongest during the dry season as resources are assumed to be more limiting.

Results
Spatial data from 54 individuals was used to create 80 seasonal wild pig home ranges across 5 seasons, with the number of monitored individuals and sex ratio varying by season (Table 1). Following predictions, males and females differed in home range size and space use metrics within seasons (Table 1). Females had smaller home ranges than males in all seasons (Table 1; p < 0.001), but home ranges did not differ in size seasonally within sexes (Table 1; Female: p = 0.86, Male: p = 0.99). Between males and females, degree did not differ in any season (p-values ranged from 0.12-0.89), although males overlapped with a greater number of individuals than females in all seasons (Table 2). Similarly, interacting males exhibited greater UDOI values than interacting females in all seasons except the Wet 2017 season (Figs. 3a and S1) where one dyad of females overlapped extensively in their home ranges (UDOI = 0.567). Interactions among males did not differ from interactions among females in any season (p values ranged from = 0.17-0.61). Across all seasons, space-use overlap of interacting male home ranges averaged 0.212 (± 0.045 S.E.) and interacting female home ranges averaged 0.099 (± 0.029). We did not detect differences in UDOI between seasons when evaluating HR-HR interactions of all individuals (p = 0.21).  Table 2 Seasonal estimates of degree (number of animals an individual overlapped with in space use) for female (F) and male (M) wild pigs at Buck Island Ranch, Florida. We estimated degree among home ranges (HR-HR), between home ranges and the individual's core area (HR-CA), and among core areas (CA-CA Wild pigs exhibited territoriality behavior, which was consistent with our predictions ( Fig. 1 and Fig. 3a). The top model included the variable "level" (HR-HR, HR-CA, or CA-CA interactions) for both comparisons, and these top models accounted for the majority of model weights (Table 3a and Figure S1). Seasonal effects were not included in any top models and exhibited minimal model weight (Table 3a and 3b). Table 3 Results of generalized mixed-effects linear-regression models evaluating variation in spatial overlap of wild pigs at Buck Island Ranch, FL. Spatial overlap was measured by utilization distribution of overlap index (UDOI, a. and b.) and degree (c. and d.). Models include sex (Sex), level (home range-home range (HR-HR), home range -core area (HR-CA), and core area -core area (CA-CA) overlap, and season. For UDOI, sex indicates the sex of the two interacting individuals (two females, female and male, and two males). For degree, sex is the sex of the individual used to determine degree. Model output includes the number of parameters (K), AIC values, ΔAIC values, AIC weights (w i ), and residual deviance (Dev. We also detected territorial patterns in degree which were explained by a three-way interaction between level, sex of the individual, and season (Table 3c and Fig. 3b and Figure S2). Males consistently overlapped with a greater number of individuals than females in all seasons ( Table 2, Fig. 3b and Figure S2). Season was also included in the top model with beta coe cients positively correlated with the number of individuals monitored, suggesting that seasonal effects were at least partially due to differences in sampling intensity.

Discussion
Consistent with our predictions, wild pigs exhibited territoriality congruent with proposed patterns of strength and number of interactions. Female's expression of territoriality was more robust than males, with less space-use overlap between females in both home ranges and in core areas. This decreased strength of overlap by females compared to males supports that females appear to exhibit greater territoriality with neighboring females compared to associated males 47 Interactions within shared space may also be limited due to temporal partitioning via avoidance, site speci c dominance, or priority of access to resources 3 (Kaufman 1983). Evaluating how wild pigs interact in both time and space, particularly under contrasting resource availability could identify how spatial behavior varies with ecological conditions.
Although males and females exhibited varying sized home ranges and spatial behavior, seasonal variation in home range size and spatial overlap were not detected in wild pigs in this study. The absence of seasonal differences in spatial overlap may re ect more consistent forage availability in subtropical climates, which can stabilize spatial segregation patterns 39 (McLoughlin et al. 2000). Conversely, wild pigs are often foraging below the soil surface by rooting, and utilization of these sub-surface resources may mitigate the reductions in above ground productivity during the dry season 48 (Singh and Yadava 1974 (Keuling et al. 2008) can in uence seasonal space use by wild pigs but these factors were not present in this study, potentially limiting seasonal changes in uencing space-use. Although environmental or behavioral factors may have eliminated the need for seasonal changes in spatial overlap, territorial patterns were consistently detected from the spatial behavior of wild pigs.
The conceptual framework that we presented (Fig. 1)  Sex ratios and the number of individuals collared varied among seasons. Therefore, we evaluated variation in home range size and degree between males and females within seasons using t-tests. To evaluate differences in intra-sexual interactions, we compared UDOI values for all male-male and femalefemale home range interactions using t-tests. Seasonal patterns in home range size and space-use overlap of home ranges were evaluated using ANOVAs. Home range sizes were evaluated separately for males and females and UDOI values were pooled across sexes. We applied a Bonferroni correction to all results to minimize the risk of Type I error.
To evaluate patterns of territoriality, we used generalized mixed-effects regression models 80  , season, and the interaction between level and sex. We calculated degree within seasons per individual for each space use level. Random effects included individual animal, and xed effects included space use level, sex, season, the interaction between level and sex, and the threeway interaction between level, sex, and season. A negative binomial distribution was used to model degree because counts were overdispersed. For both UDOI and degree, 12 a priori models were identi ed that included the null model and all combinations of level, sex, season, and two interaction terms (Table 3). We ranked models using Akaike Information Criterion 82 (Akaike 1973). We validated each Predicted relationships evaluating territoriality among animals based on spatial overlap in home ranges (HR) and core areas (CA). Interactions can occur between two individual's home ranges (HR-HR), between one individual's home range and another individual's core area (HR-CA), or between two individual's core areas (CA-CA). If animals are not territorial, spatial overlap is expected to be the same across HR-HR, HR-CA, and CA-CA comparisons (solid line). If animals are territorial, it is expected that spatial overlap will decrease between HR-HR and HR-CA comparisons (dashed line; consistent with Burt (1943) and Schoener   Space-use overlap (measured by utilization distribution of overlap index (UDOI)); a) and degree (number of individuals overlapped); b) estimates with associated 95% con dence intervals for wild pigs at Buck Island Ranch, FL in the Dry 2016 season. Estimates were created for home range to home range (HR-HR), home range to core area (HR-CA) and core area to core area (CA-CA) overlap. UDOI was estimated for