Ranging behavior and the potential for territoriality in pair-living titi monkeys (Plecturocebus discolor)

Patterns of ranging behavior and space use are key for evaluating current ideas about the evolution and maintenance of pair-living and sexual monogamy as they provide insights into the dispersion of females, the potential for territoriality, and whether males are limited to defending an area that can support only one female and her offspring. We examined ranging behavior and space use to evaluate the potential for territoriality in five groups of red titi monkeys (Plecturocebus discolor) during a 10-year study in Ecuadorian Amazonia. Mean home range size, calculated using a time-sensitive local convex hull estimation procedure, was 4.0 ± 1.4 ha. Annual home ranges of neighboring groups overlapped, on average, 0%-7%. Mean daily path length was 670 ± 194 m, resulting in defendability indices of 2.2-3.6 across groups. Groups visited, on average, 4 of 12 sections of their home range border area per day, but that was not more often than would be expected by chance, and intergroup encounters were infrequent. We did not find evidence of active monitoring for intruders in border areas, in that groups did not travel either faster or slower when at the border than when in central areas of their range. The absence of overt monitoring might be compensated for by engaging in loud calls, which the study groups did throughout their home ranges; these calls may serve as an advertisement of occupancy and a deterrent to intruding conspecifics. Our finding that red titis have a high potential for territoriality is consistent with several of the main hypotheses proposed to explain pair-living in mammals.

Are fission-fusion dynamics consistent among populations? A large-scale study with Cape buffalo

Fission-fusion dynamics allow animals to manage costs and benefits of group living by adjusting group size. The degree of intraspecific variation in fission-fusion dynamics across the geographical range is poorly known. During 2008-2016, 38 adult female Cape buffalo were equipped with GPS collars in three populations located in different protected areas (Gonarezhou National Park and Hwange National Park, Zimbabwe; Kruger National Park, South Africa) to investigate the patterns and environmental drivers of fission-fusion dynamics among populations. We estimated home range overlap and fission and fusion events between Cape buffalo dyads. We investigated the temporal dynamics of both events at daily and seasonal scales and examined the influence of habitat and distance to water on event location. Fission-fusion dynamics were generally consistent across populations: Fission and fusion periods lasted on average between less than one day and three days. However, we found seasonal differences in the underlying patterns of fission and fusion, which point out the likely influence of resource availability and distribution in time on group dynamics: During the wet season, Cape buffalo split and associated more frequently and were in the same or in a different subgroup for shorter periods. Cape buffalo subgroups were more likely to merge than to split in open areas located near water, but overall vegetation and distance to water were very poor predictors of where fission and fusion events occurred. This study is one of the first to quantify fission-fusion dynamics in a single species across several populations with a common methodology, thus robustly questioning the behavioral flexibility of fission-fusion dynamics among environments.

Space use and social association in a gregarious ungulate: Testing the conspecific attraction and resource dispersion hypotheses

Animals use a variety of proximate cues to assess habitat quality when resources vary spatiotemporally. Two nonmutually exclusive strategies to assess habitat quality involve either direct assessment of landscape features or observation of social cues from conspecifics as a form of information transfer about forage resources. The conspecific attraction hypothesis proposes that individual space use is dependent on the distribution of conspecifics rather than the location of resource patches, whereas the resource dispersion hypothesis proposes that individual space use and social association are driven by the abundance and distribution of resources. We tested the conspecific attraction and the resource dispersion hypotheses as two nonmutually exclusive hypotheses explaining social association and of adult female caribou (Rangifer tarandus). We used location data from GPS collars to estimate interannual site fidelity and networks representing home range overlap and social associations among individual caribou. We found that home range overlap and social associations were correlated with resource distribution in summer and conspecific attraction in winter. In summer, when resources were distributed relatively homogeneously, interannual site fidelity was high and home range overlap and social associations were low. Conversely, in winter when resources were distributed relatively heterogeneously, interannual site fidelity was low and home range overlap and social associations were high. As access to resources changes across seasons, caribou appear to alter social behavior and space use. In summer, caribou may use cues associated with the distribution of forage, and in winter caribou may use cues from conspecifics to access forage. Our results have broad implications for our understanding of caribou socioecology, suggesting that caribou use season-specific strategies to locate forage. Caribou populations continue to decline globally, and our finding that conspecific attraction is likely related to access to forage suggests that further fragmentation of caribou habitat could limit social association among caribou, particularly in winter when access to resources may be limited.

Space partitioning in wild, non-territorial mountain gorillas: the impact of food and neighbours

In territorial species, the distribution of neighbours and food abundance play a crucial role in space use patterns but less is known about how and when neighbours use shared areas in non-territorial species. We investigated space partitioning in 10 groups of wild, non-territorial mountain gorillas (Gorilla beringei beringei). Using location data, we examined factors influencing daily movement decisions and calculated the per cent overlap of annual kernel home ranges and core areas among neighbours. We found that the probability that a group chose an area was positively influenced by both food availability and the previous use of that area by the group. Additionally, groups reduced their overall utilization of areas previously used by neighbouring groups. Lastly, groups used their core areas more exclusively than their home ranges. In sum, our results show that both foraging needs and avoidance of competition with neighbours determined the gorillas' daily movement decisions, which presumably lead to largely mutually exclusive core areas. Our research suggests that non-territorial species actively avoid neighbours to maintain core area exclusivity. Together, these findings contribute to our understanding of the costs and benefits of non-territoriality.

Noninvasive genetic sampling reveals intrasex territoriality in wolverines

Due to its conspicuous manifestations and its capacity to shape the configuration and dynamics of wild populations, territorial behavior has long intrigued ecologists. Territoriality and other animal interactions in situ have traditionally been studied via direct observations and telemetry. Here, we explore whether noninvasive genetic sampling, which is increasingly supplementing traditional field methods in ecological research, can reveal territorial behavior in an elusive carnivore, the wolverine (Gulo gulo). Using the locations of genotyped wolverine scat samples collected annually over a period of 12 years in central Norway, we test three predictions: (1) male home ranges constructed from noninvasive genetic sampling data are larger than those of females, (2) individuals avoid areas used by other conspecifics of the same sex (intrasexual territoriality), and (3) avoidance of same‐sex territories diminishes or disappears after the territory owner's death. Each of these predictions is substantiated by our results: sex‐specific differences in home range size and intrasexual territoriality in wolverine are patently reflected in the spatial and temporal configuration of noninvasively collected genetic samples. Our study confirms that wildlife monitoring programs can utilize the spatial information in noninvasive genetic sampling data to detect and quantify home ranges and social organization.

Social structure and space use of Amur tigers (Panthera tigris altaica) in Southern Russian Far East based on GPS telemetry data

To better understand the spatial structure of Amur tigers (Panthera tigris altaica) at the southern edge of their range we fitted 14 tigers (6♀♀ and 8♂♂) with 15 GPS-Argos collars between 2008 and 2011 in 2 study sites: the Ussuriskii Reserve of southern Sikhote-Alin and the Land of the Leopard National Park in southwest Primorye, Russian Far East. Fixed kernel estimates of male home ranges were larger than those of female home ranges (P < 0.05 [mean 95% fixed kernel(♀) = 401 ± 205 km(2) ; mean 95% fixed kernel(♂) = 778 ± 267 km(2)]). The home range size of females varied greatly, but on average was similar to estimates derived from earlier work further north. Low overlap of adjacent home ranges suggested that females retained exclusive territories. Real core areas of females overlapped only slightly, and remained stable over multiple years. The home ranges of adult males were smaller than those of males to the north, and in contrast to previous studies, high overlap among males indicated the absence of territoriality. Nonetheless, real core areas of males did not overlap, suggesting some spatial separation. In comparison to other tiger populations and other areas of the Russian Far East, the sex ratio in our 2 study areas was highly skewed towards males. We believe this skewed sex ratio resulted in the dissolution of territoriality of males due to an inability to defend individual females, with males resorting to scramble competition for mates. Continued monitoring of these sites to determine whether shifts in the sex ratio might result in a return to male territoriality would provide confirmation of our tentative hypothesis.

Home range overlap as a driver of intelligence in primates

Various socioecological factors have been suggested to influence cognitive capacity in primates, including challenges associated with foraging and dealing with the complexities of social life. Alexander [Alexander, 1989]. Evolution of the human psyche. In: Mellars P, Stringer C, editors. The human revolution: Behavioural and biological perspectives on the origins of modern humans. Princeton: Princeton University Press. p 455-513] proposed an integrative model for the evolution of human cognitive abilities and complex sociality that incorporates competition among coalitions of conspecifics (inter-group conflict) as a major selective pressure. However, one of the premises of this model, i.e., that when confronted with inter-group conflict selection should favor enhanced cognition, has remained empirically untested. Using a comparative approach on species data, I aimed to test the prediction that primate species (n = 104) that face greater inter-group conflict have higher cognitive abilities (indexed by endocranial volume). The degree of inter-group conflict/complexity was approximated via the variable home range overlap among groups. I found a significant relationship between home range overlap and endocranial volume, even after controlling for other predictor variables and covariates such as group size and body mass. I conclude that brain size evolution cannot be attributed exclusively to social factors such as group size, but likely reflects a variety of social and ecological determinants including inter-group conflict which poses cognitive demands on monitoring both the wider social milieu as well as spatial attributes of the habitat.

No effect of inter-group conflict on within-group harmony in non-human primates

It has been a longstanding assumption that the threat of extra-group conflict can promote the expression of socio-positive behavior and cohesion within animal groups. I conducted a comparative analysis on the effect of inter-group conflict (indexed by home range overlap) on within-group affiliation levels (indexed by time engaged in allogrooming) in a sample of 48 primate species. There was no association between the 2 variables in a phylogenetic generalized least squares regression. I conclude that inter-group conflict may at best elicit short-term immediate changes in affiliation levels, but permanently elevated cohesion appears unique to humans with their large-scale social integration and scaled up inter-group conflict.

When good neighbors don't need fences: Temporal landscape partitioning among baboon social groups

Intraspecific competition is a key factor shaping space-use strategies and movement decisions in many species, yet how and when neighbors utilize shared areas while exhibiting active avoidance of one another is largely unknown. Here we investigated temporal landscape partitioning in a population of wild baboons (Papio cynocephalus). We used global positioning system (GPS) collars to synchronously record the hourly locations of 5 baboon social groups for ~900 days, and we used behavioral, demographic, and life history data to measure factors affecting use of overlap areas. Annual home ranges of neighboring groups overlapped substantially, as predicted (baboons are considered non-territorial), but home ranges overlapped less when space use was assessed over shorter time scales. Moreover, neighboring groups were in close spatial proximity to one another on fewer days than predicted by a null model, suggesting an avoidance-based spacing pattern. At all time scales examined (monthly, biweekly, and weekly), time spent in overlap areas was greater during time periods when groups fed on evenly dispersed, low-quality foods. The percent of fertile females in social groups was negatively correlated with time spent in overlap areas only during weekly time intervals. This suggests that broad temporal changes in ecological resources are a major predictor of how intensively overlap areas are used, and groups modify these ecologically driven spacing patterns at short time scales based on female reproductive status. Together these findings offer insight into the economics of territoriality by highlighting the dynamics of spacing patterns at differing time scales.