The effect of prey abundance and foraging tactics on the population dynamics of a social, territorial carnivore, the spotted hyena

We used naturally occurring spatial and temporal changes in prey abundance to investigate whether the foraging behavior of a social, territorial carnivore, the spotted hyena ( Crocuta crocuta ), conformed to predictions derived from the ideal free distribution. We demonstrate that hyenas in the Ngorongoro Crater, Tanzania, redistributed themselves from less profitable to more profitable areas, even when this required them to undertake foraging trips to areas beyond their clan territory boundary, or required normally philopatric females to emigrate. As expected for a system with rank related access to food resources in the territory, females of low social status foraged more often outside their territory and were more likely to emigrate than dominant females. Probably because Crater hyenas regularly foraged outside their territories, there was no correlation between clan size and prey density within territories, suggesting that clan sizes may have exceeded the carrying capacity of territories. A substantial decline of the hyena population in the Crater from 385 adults in the mid 1960s to 117 in 1996 was most likely due to a substantial decline of their main prey. The decline in the hyena population was associated with a decline in the size of clans but not in the number of clans. The number of clans probably remained constant due to emigration by females from large clans into vacant areas or clans with no adult females, and because hyenas regularly fed in areas containing concentrations of prey beyond their territory boundary. Between 1996 and 2003 annual recruitment rates of Crater hyenas consistently exceeded annual mortality rates, resulting in an almost doubling of the adult population. This increase was most likely due to an increase in prey abundance, a relatively low level of predation on hyenas by lions ( Panthera leo ), and an absence of high levels of disease related mortality.     

Determinants of territory size in the pomacentrid reef fish,Parma victoriae

Summary Factors governing the size of territories defended by the pomacentrid reef fish, Parma victoriae, were investigated, prompted by contradictory predictions in the literature concerning the effects of food supply and competitors. Observations were carried out over the non-breeding period (March–October) on a medium density population in which territories were partially contiguous. The territory size of adult fish varied between 3 and 26 m², and was inversely correlated with local densities of conspecifics. The same range in territory size was found for both males and females, which did not differ in the time they spent on territory defence and foraging activities. No correlation existed between territory size and the abundance of algal food, body size, age or time spent on territory defence. Also, there was little variation in territory size over time, despite seasonal changes in the abundance of food algae.Experimental reduction of food supplies on isolated territories of males and females had no effect on territory size. In a higher density habitat an experiment was carried out in which population density and food abundance were simultaneously manipulated. This showed that territory size was primarily determined by intraspecific interactions, as territories exhibited considerable increases in size upon removal of neighbours. No changes in the size of defended areas resulted from either artificial increases or decreases of food levels. There were also no changes in the time spent on defence of territories, foraging time or feeding rates associated with food manipulations or territory expansion, which suggested that food was not a limited resource. This conflicted with current theories proposed to explain territory defence and expansion. It is hypothesized that intraspecific interactions constrain territory size well below the optimum in terms of the abundance of preferred food algal species.     

Patterns of territorial space use by Shining Sunbeams (Aglaeactis cupripennis), tropical montane hummingbirds

For many territorial hummingbirds, habitat use is influenced primarily by the interaction between resource acquisition and non-foraging behaviors such as territory advertisement and defense. Previous research has highlighted the importance of foraging-associated habitat features like resource density and distribution in determining the space-use patterns of hummingbirds. Less is known, however, about how habitat selection associated with non-foraging behaviors influences space use by territorial species. We used radio telemetry to examine patterns of territorial space use by Shining Sunbeams (Aglaeactis cupripennis) in high Andean montane forests near Manu National Park, Peru, and Bosque Comunal “El Carmen” near Chordeleg, Ecuador. We quantified within-territory habitat characteristics related to resource acquisition and non-foraging behaviors such as territory advertisement and defense. We found that Shining Sunbeams showed high use of core areas in territories where foraging effort was relatively low. We found no relationship, however, between the position of core areas and habitat characteristics associated with territory defense, predator avoidance, or other non-foraging behaviors. We also found no relationship between use of non-core areas and habitat use based on resource acquisition. Thus, patterns of territorial space use by Shining Sunbeams may be characterized by core areas not determined by foraging behavior. Further studies examining territorial behaviors and the influence of intrusion pressure will help identify the underlying determinants of territory space use by this and other species of Andean hummingbirds.     

Territory size of wolves Canis lupus: linking local (Białowieża Primeval Forest, Poland) and Holarctic-scale patterns

Factors affecting territory size in wolves Canis lupus were studied at 2 scales, the local population (Bia?owie?a Primeval Forest (BPF), eastern Poland) and the geographic range of species (literature review from 14 localities in the Holarctic). Four packs of wolves were studied by radio‐tracking in BPF from 1994 to 1999. The annual territories of packs (Minimum convex polygons with 95% of locations) averaged 201 km² (SD 63, range 116–310). Core areas of territories (50% MCP) covered from 14 to 78 km² (mean 35). Territory sizes and core areas both were negatively correlated to the encounter rates of ungulates (mean number of ungulates seen per unit time spent in the forest by human observers). Pack size (3–8 wolves) did not influence territory size. Home ranges of individual wolves from the same pack varied with season as well as the age, sex, and reproductive status of the wolf. Review of literature from North America and Europe (42–66^oN), showed that latitude and prey biomass were essential factors shaping the biogeographic variation in wolf territory size. Territories increased with latitude and declined with growing biomass of prey. The analysis showed that latitude acted partly independently of the south–north gradient in prey abundance. At similar standing crop of ungulate biomass (100 kg km^?2), wolf territories would average 140 km² at 40^oN, 370 km² at 50^oN, and 950 km² at 60^oN. Pack size was larger at northern latitudes, but the increase did not keep pace with enlargement of territories. Within‐territory density of wolves declined from 2.5–3 wolves 100 km^?2 at 40–45^oN to 0.7 wolves 100 km^?2 at 60^oN. Our analyses documented similarities regarding the role of prey resources in shaping wolf territoriality at the different scales. Furthermore, a macroecological approach revealed additional factors affecting wolf territory size that were not emergent from knowledge of local population.     

Predicting occurrence of wolf territories in Scandinavia

We used logistic regression to compare a set of habitat features inside known Scandinavian wolf Canis lupus territories with the same habitat features in areas outside known territories, but still close enough to be available for wolf colonization. In addition, we analysed changes in habitat variables over time within wolf territories. Wolf territories had lower densities of roads, built-up areas and open land than areas outside wolf territories, but there was no difference in the density of the wolves' main prey, elk Alces alces . The logistic regression model classified 79% of Scandinavia outside the reindeer husbandry area as suitable wolf habitat, that is with a probability of wolf occurrence >0.5. The proportion of built-up areas within the wolf territory decreased as the 'borders' of the wolf territory changed over time. Our model had a reasonably high predictive power, with correct classification in 90% (18 of 20) of the observed wolf territories in the study area. Polygons, randomly distributed outside the observed wolf territories, were correctly classified as not being occupied by wolves in 85% of the cases (17 of 20). This allows a more effective use of resources to, for example, prevent wolf depredation on livestock and dogs.     

Territory surveillance and prey management: Wolves keep track of space and time

Identifying behavioral mechanisms that underlie observed movement patterns is difficult when animals employ sophisticated cognitive‐based strategies. Such strategies may arise when timing of return visits is important, for instance to allow for resource renewal or territorial patrolling. We fitted spatially explicit random‐walk models to GPS movement data of six wolves (Canis lupus; Linnaeus, 1758) from Alberta, Canada to investigate the importance of the following: (1) territorial surveillance likely related to renewal of scent marks along territorial edges, to reduce intraspecific risk among packs, and (2) delay in return to recently hunted areas, which may be related to anti‐predator responses of prey under varying prey densities. The movement models incorporated the spatiotemporal variable “time since last visit,” which acts as a wolf's memory index of its travel history and is integrated into the movement decision along with its position in relation to territory boundaries and information on local prey densities. We used a model selection framework to test hypotheses about the combined importance of these variables in wolf movement strategies. Time‐dependent movement for territory surveillance was supported by all wolf movement tracks. Wolves generally avoided territory edges, but this avoidance was reduced as time since last visit increased. Time‐dependent prey management was weak except in one wolf. This wolf selected locations with longer time since last visit and lower prey density, which led to a longer delay in revisiting high prey density sites. Our study shows that we can use spatially explicit random walks to identify behavioral strategies that merge environmental information and explicit spatiotemporal information on past movements (i.e., “when” and “where”) to make movement decisions. The approach allows us to better understand cognition‐based movement in relation to dynamic environments and resources.     

Prey availability affects territory size,but not territorial display behavior,in green anole lizards

The availability of food resources can affect the size and shape of territories, as well as the behaviors used to defend territories, in a variety of animal taxa. However, individuals within a population may respond differently to variation in food availability if the benefits of territoriality vary among those individuals. For example, benefits to territoriality may differ for animals of differing sizes, because larger individuals may require greater territory size to acquire required resources, or territorial behavior may differ between the sexes if males and females defend different resources in their territories. In this study, we tested whether arthropod abundance and biomass were associated with natural variation in territory size and defense in insectivorous green anole lizards, Anolis carolinensis. Our results showed that both male and female lizards had smaller territories in a habitat with greater prey biomass than lizards in habitats with less available prey, but the rates of aggressive behaviors used to defend territories did not differ among these habitats. Further, we did not find a relationship between body size and territory size, and the sexes did not differ in their relationships between food availability and territory size or behavioral defense. Together, these results suggest that differences in food availability influenced male and female territorial strategies similarly, and that territory size may be more strongly associated with variation in food resources than social display behavior. Thus, anole investment in the behavioral defense of a territory may not vary with territory quality.     

Causes and consequences of individual variation in territory size in the American red squirrel

For most territorial species that defend food or other resources, territory size is inversely related to resource density. However, in some food-based territorial species, larger territories are known to contain greater absolute resource availability. For these latter species, both the specific determinants of territory size, and the relationship between territory size and fitness, remain unclear. We predicted that in American red squirrels ( Tamiasciurus hudsonicus ), where larger territories tend to hold increased food resources, survival should be correlated positively with territory size and that both individual (body mass, sex, duration of territory ownership) and habitat-specific (population density) attributes would contribute to variation in territory size. We monitored survival and territory size of 58 squirrels during a two-year period using live-trapping and radio-telemetry. Survival and territory size were correlated positively, with each 0.1 ha decrease in territory size typically resulting in a 16.6% increase in mortality risk; mortality risk for squirrels with the smallest versus largest territories differed by up to 23-fold. Territory size was negatively related to local population density, but not to any attributes of individual squirrels, implying that, in this species, territory size may not be influenced strongly by individual quality. We conclude that while larger territories may confer a survival advantage to squirrels, territory size is unrelated to individual physical attributes, likely because costs associated with the acquisition of a larger or richer territory outweigh potential benefits of increased food access.     

Territory quality, survival and reproductive success in southern emu-wrens Stipiturus malachurus

Multi-factor analyses of territory quality in relation to fitness components of adults are rare, especially in non-migratory species. I studied the influence of multiple attributes of territory quality (habitat type and the abundance of food and predators) on the reproductive success and survival of a threatened Australian passerine, the southern emu-wren Stipiturus malachurus . The abundance of frequently-selected prey types (lepidoptera, diptera, hemiptera and larvae) varied significantly across territories according to habitat type. Reproductive success (number of offspring fledged) was highest in territories containing a greater proportion of tall shrubland, which had the highest insect abundance of any habitat. Closed heathland and sedge/rushland also had high food abundance compared to other habitat types, but higher fledging success occurred only within closed heathland, possibly because predator density was lower in this habitat type. High snake density was associated with reduced adult survival during the breeding season and a lower probability of nest success. In sedge/rushland, any benefits of prey abundance may therefore be offset by a high density of predators. Emu-wren age and size were unrelated to breeding output of pairs, suggesting that ecological factors may swamp effects of individual quality on emu-wren fitness components. Preservation of tall shrubland and closed heathland habitats appear to be of key conservation priority for emu-wrens.     

Access to mates in a territorial ungulate is determined by the size of a male's territory, but not by its habitat quality

1. Territoriality is commonly associated with resource defence polygyny, where males are expected to gain access to females by anticipating how resources will influence female distribution and competing for resource-rich sites to establish their zone of dominance. 2. We tested this hypothesis in European roe deer (Capreolus capreolus) by simultaneously assessing the influence of resources on female distribution and the influence of female distribution on male distribution and breeding success using paternity analyses. 3. Females did not fully distribute themselves among male territories in relation to resources. As a result, relative female abundance in a male's territory depended on territory size, but not on its habitat quality. In turn, relative female abundance in a male's territory determined, at least partially, his breeding success. 4. Interestingly, male territory size, and hence access to females, was partly determined by male body mass (all males) and by residual antler size (subadults only). The latter result suggests that large antlers may be important to young males for establishing their first territory, which is then usually retained for all subsequent reproductive seasons. 5. To conclude, although territoriality of male roe deer has certainly evolved as a tactic for ensuring access to mates, our results suggest that it does not really conform to a conventional resource defence polygyny strategy, as males seem to gain no obvious benefit from defending a territory in an area of high habitat quality in terms of enhanced access to mates. 6. This may explain the stability of male territories between years, suggesting that male territoriality conforms to an 'always stay' and 'low risk-low gain' mating strategy in roe deer.     

The relative importance of prey availability and intruder pressure in feeding territory size regulation by harriers,Circus cyaneus

Summary The relative importance of prey availability and intruder pressure in the regulation of harrier (Circus cyaneus) territory size was investigated over two years using analytical methods chosen to permit comparison with Myers et al. (1979) study of sanderlings (Calidris alba). Relationships between territory area and two variables, prey type (mice; large, medium, and small birds) and intruder type (conspecific neighbors, conspecific floaters, and heterospecific floaters), and the consistency of these relationships between years, also were examined. Individual harrier territory areas were highly variable, ranging from 7.8 to 1249 ha in 1984/1985, and 3.9 to 71.3 ha in 1985/1986. Of the prey variables, only mouse availability was significantly inversely correlated with territory area in both years, and slopes resulting from correlations between the logarithms of these two variables did not differ significantly from — 1, the expected result if harriers were adjusting mouse availabilities. The abundance of mice in conjunction with their greater ease of capture relative to birds made them functionally more available, and hence harriers' primary prey. This may explain why mice, rather than birds, were apparently the defended resource. Of the intruder variables, neighbor variables were most strongly inversely cortelatd with territory area. Partial correlation analyses to determine the relative importance of intruder pressure and prey availability in regulating territory size revealed that in 1984/1985, mouse availability and intruder pressure were relatively independent and each explained some variation in territory area, whereas in 1985/1986, mouse availability, rather than intruder pressure, significantly explained all variation in territory area. Possible explanations for why territory sizes of harriers appear to be regulated more closely by food density, whereas territory sizes of sanderlings appear to be regulated more closely by intruder pressure, are based upon differences in 1) neighbor effects, 2) environmental ronmental variability, and 3) accuracy of resource assessment by intruders. The variation in intruder rates and prey availabilities observed between years suggests the need to conduct studies over several years in order to assess accurately the relative importance of these variables in territory-size regulation.     

Foraging costs,hunting success and its implications for African wild dog (Lycaon pictus) conservation inside and outside a protected area

When selecting a habitat, animals utilize habitat in which they yield the highest rate of energy. Differences in foraging costs and hunting success are therefore likely to affect habitat choice. In a previous study, we showed that African wild dog (Lycaon pictus) packs with territories inside Hwange National Park (HNP), over the course of several years, moved their territories into the buffer zone outside HNP, where reproductive success was higher but anthropogenic mortality exceeded natality. In this study, based on long‐term radio‐telemetry data from 22 African wild dog packs, we analysed whether differences in foraging costs and hunting success could have contributed to this territorial drift. Taking seasonality and pack size into account, we determined foraging costs (foraging distance and chase distance) and hunting success (successful or failed chase) inside and outside HNP. Although we observed no difference in foraging costs, hunting success was higher outside HNP, which is likely to have contributed to the territorial drift into the buffer zone outside the protected area. This study shows the importance of taking factors affecting hunting success into account in the conservation strategy of African wild dogs.     

The influence of food abundance,food dispersion and habitat structure on territory selection and size of an Afrotropical terrestrial insectivore

Most tropical insectivorous birds, unlike their temperate counterparts, hold and defend a feeding and breeding territory year-around. However, our understanding of ecological factors influencing territory selection and size in tropical insectivores is limited. Here we examine three prominent hypotheses relating food abundance, food dispersion (spatial arrangement of food items), and habitat structure to territoriality in the Usambara Thrush Turdus roehli. We first compared leaf-litter macro-invertebrate abundance and dispersion, and habitat structure between territories and random sites. We then examined the relation between these same ecological factors and territory size. Invertebrate abundance and dispersion were sparsely and evenly distributed across our study system and did not vary between territories and random sites. In contrast, habitat structure did vary between territories and random sites indicating the Usambara Thrush selects territories with open understorey and closed overstorey habitat. Invertebrate abundance and dispersion within territories of the Usambara Thrush were not associated with habitat structure. We believe the most likely explanation for the Usambara Thrush’s preference for open understorey and closed overstorey habitat relates to foraging behavior. Using information-theoretic model selection we found that invertebrate abundance was the highest-ranked predictor of territory size and was inversely related, consistent with food value theory of territoriality.     

Habitat requirements of the Seychelles Black Paradise Flycatcher Terpsiphone corvina: a re-evaluation of translocation priorities

The critically endangered Seychelles Black Paradise Flycatcher Terpsiphone corvina was once found on at least five of the inner (granitic) islands in the Seychelles archipelago, western Indian Ocean. Currently, it is only found on two islands, with c. 98% of the world population (c. 150–200 individuals) occurring on the 10‐km² island of La Digue. Creation of additional island populations is therefore considered crucial in improving its conservation status. The presence of native broad‐leaved plateau forest in proximity to wetland areas is proposed as an important selection criterion when considering the suitability of other islands for translocation, due to the presumed importance of insect prey (dependent on water) in the diet. We quantified habitat use, territory composition, the effect of water on invertebrate abundance, and foraging and breeding success to determine the importance of native broad‐leaved woodland and wetland areas for Flycatchers. Flycatcher territories contained significantly more native broad‐leaved woodland (88%) than its availability on the plateau (43%); Flycatchers used native tree species significantly more for both foraging (81%) and nesting (95%) than their availability within territories (71%); and territory size varied inversely with the density of native broad‐leaved tree species. Native broad‐leaved forest was associated with semipermanent and permanent water bodies and availability of native forest habitat was a good predictor of territory distribution. The number of aerial insects trapped was higher close to water, but there was no effect of the proximity to water on the number of insects counted on foliage. The majority of identified prey species in adult diet were not dependent on water: Orthoptera and Lepidoptera were the most common prey groups, comprising 66% of identified prey items. There was no effect of proximity to water on foraging or breeding success (c. 35%): depredation was the major factor determining breeding success, and accounted for the majority of nest failures. The importance of wetland areas to Flycatchers therefore appears to have been over‐emphasized. The implications for translocation and conservation of the Flycatcher are discussed.     

Habitat-related heterogeneity in breeding in a metapopulation of the Iberian lynx

Identifying attributes associated with good breeding habitat is critical for understanding animal population dynamics. However, the association between environmental heterogeneity and breeding probability has been often overlooked in habitat analyses. We evaluated habitat quality in a metapopulation of the endangered Iberian lynx Lynx pardinus by analyzing spatiotemporal patterns in breeding records. Data summarizing successful production of litters after emergence from dens over four years within 13 lynx territories were examined. We designed a set of generalized linear mixed models representing different hypotheses regarding how patterns in breeding records relate to environmental heterogeneity. Environmental heterogeneity was described by two characteristics: 1) a landscape index measured in lynx territories indicative of time‐averaged prey availability and 2) yearly variability in prey abundance not captured with this index. By including the random effect of the lynx territory we also accounted for other territory‐specific effects on reproduction. We found significant differences in yearly prey density dynamics among lynx territories. However, temporal variation in prey density contributed poorly to explaining lynx breeding. The most parsimonious model included the landscape structure as the only effect explaining breeding patterns. A multinomial‐model‐representation of the landscape hypothesis explained nearly 50% of variability in breeding records. Results pointed to the existence of a habitat quality gradient associated with particular landscape structures influencing lynx habitat selection and breeding performance. Underlying this gradient was time‐averaged prey availability. Probably as a result of long‐term fitness strategies in long‐lived territorial species, the short‐term fluctuations in prey availability had a minor influence. Our results illustrate how habitat inferences can be enhanced by incorporating the link between spatiotemporal patterns in reproduction and environmental heterogeneity.     

Territory quality affects the relative importance of habitat heterogeneity and interference competition in a long‐lived territorial songbird

Density‐dependent reproduction is commonly explained by either the habitat heterogeneity (HHH) or individual adjustment (IAH) hypothesis. Under the HHH, high quality territories are assumed to be occupied first. At higher density, occupation of low‐quality territories increases due to lower availability of high‐quality territories, which reduces mean reproductive success. Alternatively, the IAH assumes that increased competition at higher densities reduces reproductive success in all territories. For birds of prey, HHH plays an important role in territorial species, and IAH in socially breeding species. To test the generality of this hypothesis, we studied the mechanism behind density dependence in raven Corvus corax, a long‐lived passerine bird, using long‐term population data from a large number of territories. Population density decreased reproduction, which was explained by increased usage of low quality territories at higher density, supporting the HHH. Density reduced reproduction in low quality territories, but not in high and intermediate quality territories. We additionally compared the explanatory power of different models describing brood size, representing IAH, HHH, or a combination of both. The best model represented a combination of both hypotheses, in which the effect of density depended on territory quality. Our conclusion that both IAH and HHH are supported can be explained by the biology of ravens, where territorial adults not only experience interference competition with other territorial adults, but also with social groups of juveniles and floaters. We conclude that the relative importance of IAH and HHH may depend on variation in territory quality and social structure.     

On the Regulation of Pack Size in Wolves

Wolves live in territorial packs of up to 20 animals. To gain insight into the regulation of wolf populations it is necessary to understand the regulation of pack size. Based on a long-time study of the social behaviour of a wolf pack in a large enclosure, a model of the regulation of pack size is constructed. Ecological factors such as prey size and prey biomass have an influence on wolf mortality, as well as on aggressive, sexual and spatial behaviour within the pack.     

Home range size variation in a recovering wolf population: evaluating the effect of environmental, demographic, and social factors

Home range size in mammals is a key ecological trait and an important parameter in conservation planning, and has been shown to be influenced by ecological, demographic and social factors in animal populations. Information on space requirements is especially important for carnivore species which range over very large areas and often come into direct conflict with human interest. We used long-term telemetry-location data from a recovering wolf population in Scandinavia to investigate variation in home range size in relation to environmental and social characteristics of the different packs. Wolves showed considerable variation in home range size, which ranged from 259 to 1,676 km². Although wolf density increased fourfold during the study period, we found no evidence that intraspecific competition influenced range size. Local variation in moose density, which was the main prey for most packs, did not influence wolf home range size. Home ranges increased with latitude and elevation and decreased with increased roe deer density. Although prey biomass alone did not influence range size, our data suggest that there is a correlation between habitat characteristics, choice of prey species and possible hunting success, which currently combine to shape home range size in Scandinavian wolves.     

The territorial system of the kob antelope (Kobus kob kob) in the Comoé National Park, Côte d'Ivoire

The territorial system of kob antelopes in the Comoé National Park, Côte d'Ivoire, was studied from March 1993 until April 1997. Whereas size and shape of territories remained constant between 1993 and 1994, the number of territories decreased from 1994 onwards. A decline of the population density probably led to the decline in territory numbers and also to variations in size and shape of the remaining territories. The decline of kob numbers is the result of heavy poaching in the study area. Whereas a lekking system was present in the study area prior to 1975 when the population density was approximately 14.4 kobs/km², males switched to the resource defence territorial system present today after the population density decreased to 12.5/km² in 1993 and finally to 2.3/km² in 1997. Compared to other research areas with higher population densities, territories in the Comoé National Park are larger, almost all adult males are capable to defend a territory, fights over territories are rare and loss of territory tenureship is almost exclusively due to the death of the territorial male. We suggest that those differences can all be related to the low population density in the study area.     

Interspecific territoriality in gibbons (Hylobates lar and H. pileatus) and its effects on the dynamics of interspecies contact zones

We investigated the ecology and interspecific interactions of the two gibbon species (Hylobates lar and H. pileatus) that overlap in distribution within a narrow zone of contact in the headwaters of the Takhong River at Khao Yai National Park in central Thailand. The zone is about 10-km wide, with phenotypic hybrids comprising 6.5% of the adult population. We compared species with respect to diet, territory size, intra- and interspecific group encounters, and territory quality. The two gibbon species exploited the same types of resources within their territories despite variation in the relative abundance of food-plant species between territories. The gibbons were interspecifically territorial, and males of both species displayed aggressive behaviors at both intraspecific and interspecific territorial boundaries. There was no marked difference in the amount of overlap between territories of conspecific and heterospecific pairs of groups. Although the habitat was not homogeneous, territory quality did not vary significantly between species. The species have not diverged in habitat preference or in diet. Neither species dominated in interspecific encounters, and both were reproducing well in the contact zone. We analyzed the potential consequences of several types of interspecific interactions on individual dispersal options and on the structure of the contact zone. Interference competition through interspecific territoriality affects the dispersal of individuals into the range of the other species. In general, territorial competition coupled with limited hybridization leads to predictions of a narrow contact zone or parapatry between species; thus, behavioral and ecological interactions between species need to be considered as potential factors in explaining range borders of primate species.