Resource Dispersion Hypothesis Research Articles

Population density and ranging behaviour of a generalist carnivore varies with human population.

Canid species are highly adaptable, including to urban and peri-urban areas, where they can come into close contact with people. Understanding the mechanisms of wild canid population persistence in these areas is key to managing any negative impacts. The resource dispersion hypothesis predicts that animal density increases and home range size decreases as resource concentration increases, and may help to explain how canids are distributed in environments with an urban-natural gradient. In Australia, dingoes have adapted to human presence, sometimes living in close proximity to towns. Using a targeted camera trap survey and spatial capture-recapture models, we estimated spatial variation in the population density and detection rates of dingoes on Worimi Country in the Great Lakes region of the NSW coast. We tested whether dingo home range and population densities varied across a gradient of human population density, in a mixed-use landscape including, urban, peri-urban, and National Park environs. We found human population density to be a strong driver of dingo density (ranging from 0.025 to 0.433 dingoes/km2 across the natural-urban gradient), and to have a negative effect on dingo home range size. The spatial scale parameter changed depending on survey period, being smaller in the peak tourism period, when human population increases in the area, than in adjacent survey periods, potentially indicating reduced home range size when additional resources are available. Our study highlights the potential value of managing anthropogenic resource availability to manage carnivore densities and potential risk of human-carnivore interactions.

Resources and predation: drivers of sociality in a cyclic mesopredator

In socially flexible species, the tendency to live in groups is expected to vary through a trade-off between costs and benefits, determined by ecological conditions. The Resource Dispersion Hypothesis predicts that group size changes in response to patterns in resource availability. An additional dimension is described in Hersteinsson’s model positing that sociality is further affected by a cost–benefit trade-off related to predation pressure. In the arctic fox (Vulpes lagopus), group-living follows a regional trade-off in resources’ availability and intra-guild predation pressure. However, the effect of local fluctuations is poorly known, but offers an unusual opportunity to test predictions that differ between the two hypotheses in systems where prey availability is linked to intra-guild predation. Based on 17-year monitoring of arctic fox and cyclic rodent prey populations, we addressed the Resource Dispersion Hypothesis and discuss the results in relation to the impact of predation in Hersteinsson’s model. Group-living increased with prey density, from 7.7% (low density) to 28% (high density). However, it remained high (44%) despite a rodent crash and this could be explained by increased benefits from cooperative defence against prey switching by top predators. We conclude that both resource abundance and predation pressure are factors underpinning the formation of social groups in fluctuating ecosystems.

Variable intraspecific space use supports optimality in an apex predator

Within optimality theory, an animal’s home range can be considered a fitness-driven attempt to obtain resources for survival and reproduction while minimizing costs. We assessed whether brown bears (Ursus arctos) in two island populations maximized resource patches within home ranges (Resource Dispersion Hypothesis [RDH]) or occupied only areas necessary to meet their biological requirements (Temporal Resource Variability Hypothesis [TRVH]) at annual and seasonal scales. We further examined how intrinsic factors (age, reproductive status) affected optimal choices. We found dynamic patterns of space use between populations, with support for RDH and TRVH at both scales. The RDH was likely supported seasonally as a result of bears maximizing space use to obtain a mix of nutritional resources for weight gain. Annually, support for RDH likely reflected changing abundances and distributions of foods within different timber stand classes. TRVH was supported at both scales, with bears minimizing space use when food resources were temporally concentrated. Range sizes and optimal strategies varied among sex and reproductive classes, with males occupying larger ranges, supporting mate seeking behavior and increased metabolic demands of larger body sizes. This work emphasizes the importance of scale when examining animal movement ecology, as optimal behavioral decisions are scale dependent.

Spatial Aspects of Gardens Drive Ranging in Urban Foxes (Vulpes vulpes): The Resource Dispersion Hypothesis Revisited.

Red foxes are a well-established species of urban ecosystems in the UK and worldwide. Understanding the spatial ecology of foxes in urban landscapes is important for enhancement of urban biodiversity and effective disease management. The Resource Dispersion Hypothesis (RDH) holds that territory (home range) size is linked to distribution and richness of habitat patches such that aggregation of rich resources should be negatively associated with range size. Here, we tested the RDH on a sample of 20 red foxes (Vulpes vulpes) in the city of Brighton and Hove. We focused on residential garden areas, as foxes were associated with these in previous studies. We equipped 12 male and 8 female foxes with GPS collars recording at 15 min intervals during discrete seasons over four years. We regressed fox core area size against garden size, number of garden patches, and edge density within and between patches as extracted from GIS in a series of bivariate linear mixed models. We found that foxes used smaller core areas where gardens were large and well-connected and larger core areas where numerous, smaller gardens were fragmented by internal barriers (e.g., fences, walls) or bisected by other habitats such as managed grassland or built-up areas. Our findings confirm the RDH and help to inform future urban planning for wildlife.

Spatial partitioning by a subordinate carnivore is mediated by conspecific overlap.

There are several hypotheses that could explain territory size in mammals, including the resource dispersion hypothesis (RDH), the intruder pressure hypothesis (IPH), and the intraguild predation hypothesis (IGPH). In this study, we tested predictions of these three hypotheses regarding territories of 19 packs of endangered African wild dogs (Lycaon pictus) over 2years in the Kruger National Park, South Africa. If territory size was supported by the RDH, then we would observe (1) wild dog territories would be larger when resource patches were more dispersed, (2) pack sizes would be larger when resource patches were rich, and (3) pack size would not affect territory size. If supported by the IPH, then we would observe (4) larger territories would experience less intrusions, and (5) there would be an increase in territory overlap in areas of low resource dispersion. Finally, if supported by the IGPH, we would observe (6) territories would be larger in areas of higher lion (Panthera leo) density, as evidence of a spatial avoidance strategy. We found that the IGPH was fully supported (6), the IPH half supported (5), and the RDH partially supported (1 and 3), where we found spatial partitioning of wild dogs with lions, potentially mediated by resources and territory overlap with conspecifics. Ultimately, our results show that subordinate carnivores must balance a trade-off between dominant interspecific competitors and conspecifics to successfully coexist in areas with dominant carnivores.

Breeding Behavior of Mara [Dolichotis patagonum (Zimmermann, 1780)] in the Monte-Chaco Ecotone of Argentina

Phylogenetic constraints and ecological factors have been suggested as alternative key factors in the evolution of animal sociality. The mara (Dolichotis patagonum) is a cavid rodent endemic to Argentina that has the particularity of being monogamous with a communal breeding system. Researches on reproductive behavior of mara in its natural habitat have been restricted to Peninsula de Valdes (PV). In this work, we studied the breeding behavior of the mara in Sierra de las Quijadas National Park (SQNP). A census to locate mara's dens in 230 ha, was conducted through adjacent line transects of five meters width. After locating the dens, we followed their reproductive activity using camera traps. A density of 4.34 randomly distributed dens/ha was found. No communal breeding was observed. Breeding season extended from October to June. Estimated density was from 0.16 to 0.24 reproductive adults/ha. The survival rate of juveniles was 31.3%. These observations differ from those reported for the species. Resource dispersion hypothesis could explain both reproductive strategies prevailing in the extremes of its distribution, SQNP (solitary breeding) and PV (communal breeding). The intraspecific variability registered enhances the importance of ecological factors in determining sociality traits for the mara.

Applying the resource dispersion hypothesis to a fission-fusion society: A case study of the African lion (Panthera leo).

The relationship between the spatiotemporal distribution of resources and patterns of sociality is widely discussed. While the resource dispersion hypothesis (RDH) was formulated to explain why animals sometimes live in groups from which they derive no obvious benefits, it has also been successfully applied to species that benefit from group living. Some empirical tests have supported the RDH, but others have not, so conclusions remain equivocal and further research is required to determine the extent to which RDH predictions hold in natural systems. Here, we test four predictions of the RDH in an African lion population in the context of their fission–fusion society. We analyzed data on group composition of GPS‐collared lions and patterns of prey availability. Our results supported the first and second predictions of the RDH: Home range size (a) was independent of group size and (b) increased with distance between encounters with prey herds. Nonetheless, the third and fourth RDH predictions were not supported: (c) The measure of resource heterogeneity and (d) resource patch richness measured through prey herd size and body size had no significant effect on lion group size. However, regarding the fourth prediction, we added an adaptation to account for dynamics of fission–fusion society and found that the frequency of pride fission increased as group size increased. Our data set restricted us from going on to explore the effect of fission–fusion dynamics on the relationship between group size and patch richness. However, this should be investigated in future studies as including fission–fusion dynamics provides a more nuanced, realistic appreciation of lion society. Our study emphasizes the importance of understanding the complexity of a species' behavioral ecology within the framework of resource dispersion. Whatever larger theoretical framework may emerge to explain lion society, incorporating fission–fusion dynamics should allow the RDH to be refined and improved.

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.

Association with humans and seasonality interact to reverse predictions for animal space use

BackgroundVariation in animal space use reflects fitness trade-offs associated with ecological constraints. Associated theories such as the metabolic theory of ecology and the resource dispersion hypothesis generate predictions about what drives variation in animal space use. But, metabolic theory is usually tested in macro-ecological studies and is seldom invoked explicitly in within-species studies. Full evaluation of the resource dispersion hypothesis requires testing in more species. Neither have been evaluated in the context of anthropogenic landscape change.MethodsIn this study, we used data for banded mongooses (Mungos mungo) in northeastern Botswana, along a gradient of association with humans, to test for effects of space use drivers predicted by these theories. We used Bayesian parameter estimation and inference from linear models to test for seasonal differences in space use metrics and to model seasonal effects of space use drivers.ResultsResults suggest that space use is strongly associated with variation in the level of overlap that mongoose groups have with humans. Seasonality influences this association, reversing seasonal space use predictions historically-accepted by ecologists. We found support for predictions of the metabolic theory when moderated by seasonality, by association with humans and by their interaction. Space use of mongooses living in association with humans was more concentrated in the dry season than the wet season, when historically-accepted ecological theory predicted more dispersed space use. Resource richness factors such as building density were associated with space use only during the dry season. We found negligible support for predictions of the resource dispersion hypothesis in general or for metabolic theory where seasonality and association with humans were not included. For mongooses living in association with humans, space use was not associated with patch dispersion or group size over both seasons.ConclusionsIn our study, living in association with humans influenced space use patterns that diverged from historically-accepted predictions. There is growing need to explicitly incorporate human–animal interactions into ecological theory and research. Our results and methodology may contribute to understanding effects of anthropogenic landscape change on wildlife populations.

Social interactions in a solitary carnivore.

In total, 177 of 245 terrestrial carnivores are described as solitary, and much of carnivore ecology is built on the assumptions that interactions between adult solitary carnivores are rare. We employed Global Positioning System (GPS) technology and motion-triggered cameras to test predictions of land-tenure territoriality and the resource dispersion hypothesis in a territorial carnivore, the puma Puma concolor. We documented 89 independent GPS interactions, 60% of which occurred at puma kills (n = 53), 59 camera interactions, 11 (17%) of which captured courtship behaviors, and 5 other interactions (1 F-F, 3 M-F, and 1 M-M). Mean minimum weekly contact rates were 5.5 times higher in winter, the season when elk Cervus elaphus were aggregated at lower elevations and during which puma courtship primarily occurred. In winter, contacts rates were 0.6 ± 0.3 (standard deviation (SD)) interactions/week vs. 0.1 ± 0.1 (SD) interactions/week during summer. The preponderance of interactions at food sources supported the resource dispersion hypothesis, which predicts that resource fluxes can explain temporary social behaviors that do not result in any apparent benefits for the individuals involved. Conspecific tolerance is logical when a prey is so large that the predator that killed it cannot consume it entirely, and thus, the costs of tolerating a conspecific sharing the kill are less than the potential costs associated with defending it and being injured. Puma aggregations at kills numbered as high as 9, emphasizing the need for future research on what explains tolerance among solitary carnivores.

Spatial overlap in a solitary carnivore: support for the land tenure, kinship or resource dispersion hypotheses?

There are several alternative hypotheses about the effects of territoriality, kinship and prey availability on individual carnivore distributions within populations. The first is the land-tenure hypothesis, which predicts that carnivores regulate their density through territoriality and temporal avoidance. The second is the kinship hypothesis, which predicts related individuals will be clumped within populations, and the third is the resource dispersion hypothesis, which suggests that resource richness may explain variable sociality, spatial overlap or temporary aggregations of conspecifics. Research on the socio-spatial organization of animals is essential in understanding territoriality, intra- and interspecific competition, and contact rates that influence diverse ecology, including disease transmission between conspecifics and courtship behaviours. We explored these hypotheses with data collected on a solitary carnivore, the cougar (Puma concolor), from 2005 to 2012 in the Southern Yellowstone Ecosystem, Wyoming, USA. We employed 27 annual home ranges for 13 cougars to test whether home range overlap was better explained by land tenure, kinship, resource dispersion or some combination of the three. We found support for both the land tenure and resource dispersion hypotheses, but not for kinship. Cougar sex was the primary driver explaining variation in home range overlap. Males overlapped significantly with females, whereas the remaining dyads (F-F, M-M) overlapped significantly less. In support for the resource dispersion hypothesis, hunting opportunity (the probability of a cougar killing prey in a given location) was often higher in overlapping than in non-overlapping portions of cougar home ranges. In particular, winter hunt opportunity rather than summer hunt opportunity was higher in overlapping portions of female-female and male-female home ranges. Our results may indicate that solitary carnivores are more tolerant of sharing key resources with unrelated conspecifics than previously believed, or at least during periods of high resource availability. Further, our results suggest that the resource dispersion hypothesis, which is typically applied to social species, is applicable in describing the spatial organization of solitary carnivores.

The interplay between clumped resources, social aggregation, and genetic relatedness in the raccoon

The extent to which individuals within a population live in groups is often variable, as group formation is most likely to occur when the benefits of group-living outweigh the costs. The distribution of resources can underpin the likelihood of group formation by altering costs associated with individuals aggregating. By influencing the extent of group-living, resources may also influence relatedness patterns. To address this, we examined relatedness in raccoons (Procyon lotor) by combining spatial and genetic data in an experimental framework wherein resources were manipulated. We tested for differences in patterns of genetic relatedness among 12 sites subject to three treatments: no supplemental food; supplemental food added in a dispersed, non-predictable fashion; and clumped, predictable food supplements resulting in aggregations. We measured mean relatedness for >500 raccoons using blood and hair samples genotyped at 14 nuclear microsatellites and tested for differences between sites and sexes. For two sites, we radio-tracked raccoons and calculated volume of intersection (VI) values, which measure the probability of co-occurrence between individuals’ home ranges, and calculated the relationship between VI and relatedness. Telemetry data indicated that raccoons exposed to clumped food shifted their home ranges, in turn perturbing patterns of relatedness between individuals, especially among females. This was exhibited through a positive association between VI and relatedness for females at the site with dispersed food, which was not observed among males or at the site with clumped food. At the landscape level, sites differed significantly in mean relatedness, but there were no clear patterns that corresponded to treatments. Overall, our observations support expectations of the resource dispersion hypothesis, wherein individuals modify ranges to include clumped resources if the costs of tolerating other individuals are low.

Patchwork planet: the resource dispersion hypothesis, society, and the ecology of life

AbstractVirtually nothing in nature is uniform. Observed at the right scale, most entities are clustered rather than evenly distributed, spatially and temporally, and this applies across domains from the distribution of matter in the universe, to habitats across theEarth's surface, and to energy in the landscape. Patchiness means organisms cannot carve out even territories. Instead, their shape and size depends on the dispersion of materials needed for survival and reproduction. This fundamental feature of life is intrinsically understood in ecology, for example, in the ideal free distribution and optimal foraging theory, and is represented in the anatomy as well as behaviour of organisms via the structures and strategies for moving, finding and capturing these patchy resources. But perhaps most striking of all is the role of patchiness in facilitating the formation of social groups – of societies. The resource dispersion hypothesis (RDH) suggests that where resources are dispersed and rich enough, multiple individuals can collapse into groups that share the same space at little cost to each other. Cooperation may be absent, but sociality is favoured nevertheless. Thirty years after the origin of the hypothesis, we review the accumulating models, critiques, evidence and experiments, concluding thatRDHis a pervasive feature of animal spacing patterns across a wide range of species, taxonomic groups and ecosystems. In the spirit of the original objective of theHuxleyReviews to ‘suggest and inspire research that will improve our knowledge in the future’, we also take the opportunity to consider wider implications of theRDH. If we live and evolved on a patchwork planet, then we should expect broader effects. Indeed, we suggest that theRDHhas played an important role in the evolution of cooperation, biodiversity, behaviour and, not least, in the social organization of humans in our evolutionary past and today.

Group size correlates with territory size in European badgers: implications for the resource dispersion hypothesis?

The resource dispersion hypothesis (RDH) predicts that resource heterogeneity can act as a passive cause of group-living in social carnivores and potentially many other species. One central prediction of the RDH is that territory size and group size are not related, as they are determined by resource dispersion and quality, respectively. In this study we investigated the relationship between territory size, group size and group composition in the European badger, a non-cooperative social mustelid whose behavioural ecology was central to the development of the RDH. Using data from a long-term study in the UK, we found that territory size and group size were positively related, contradicting a core prediction of the RDH. Furthermore, territory size was more strongly correlated with the number of adult males in the group than to the number of females or total group size. This result suggests that male badgers may have a more important role in territoriality and receive greater benefits from territory enlargement. These findings are consistent with the predictions of the anti-kleptogamy hypothesis, and suggest that badger territorial and social behaviour is not purely driven by resource dispersion, but may also be associated with breeding behaviour, as in other mustelids.

Effects of spatiotemporal resource heterogeneity on home range size of American beaver

AbstractHome range size of terrestrial animals may be influenced by spatiotemporal dynamics of resources. However, little is known regarding the effects of spatiotemporal resource availability on semi‐aquatic central place foragers such as the American beaver Castor canadensis. From January 2011 to April 2012, 26 beavers at 11 wetlands at Redstone Arsenal in north‐central Alabama, USA, were captured and radio‐tracked using radio telemetry. The objectives of this study were to test the predictions of three hypotheses: (1) the resource dispersion hypothesis: more spatially dispersed resources throughout a landscape increase home range sizes; (2) the temporal resource variability hypothesis: more temporally variable resources result in decreases in home range sizes; (3) the habitat productivity hypothesis: increases in habitat productivity lead to decreases in home range sizes. Twenty‐three of 26 radio‐tagged beavers had well‐bounded home ranges, and their home range sizes were positively related to the diversity of land cover within home ranges as predicted by the resource dispersion hypothesis. Furthermore, home range sizes of 26 beavers, including three seasonally dispersing beavers, decreased with increasing seasonal variability of within‐home‐range normalized difference vegetation index (NDVI), supporting the prediction of the resource heterogeneity hypothesis. Home range sizes of American beavers increased with increasing total NDVI and proportions of woody plant cover within home ranges probably to avoid overexploitation of woody plants. Our results suggest that the combination of resource quantity, spatial distribution and seasonal variation of resources influences movements and home ranges of central place foragers.

Home range, activity and sociality of a top predator, the dingo: a test of the Resource Dispersion Hypothesis

The idea that groups of individuals may develop around resource patches led to the formulation of the Resource Dispersion Hypothesis (RDH). We tested the predictions of the RDH, within a quasi‐experimental framework, using Australia’s largest terrestrial predator, the dingo Canis lupus dingo. Average dingo group sizes were higher in areas with abundant focal food sources around two mine sites compared with those in more distant areas. This supports the notion that resource richness favours larger group size, consistent with the RDH. Irrespective of season or sex, average home range estimates and daily activity for dingoes around the mine sites were significantly less than for dingoes that lived well away. Assuming that a territory is the defended part of the home range and that territory size is correlated with home range size, consistent with the RDH, the spatial dispersion of food patches therefore determined territory size for dingoes in our study. However, although sample size was small, some dingoes that accessed the supplementary food resource at the mines also spent a large proportion of their time away, suggesting a breakdown of territorial defence around the focal food resource. This, in combination with the large variation in home range size among dingoes that accessed the same supplementary food resource, limits the predictive capabilities of the RDH for this species. We hypothesize that constraints on exclusive home range occupancy will arise if a surfeit of food resources (in excess of requirements for homeostasis) is available in a small area, and that this will have further effects on access to mates and social structure. We present a conceptual model of facultative territorial defence where focal resources are available to demonstrate our findings.

Influence of prey dispersion on territory and group size of African lions: a test of the resource dispersion hypothesis

Empirical tests of the resource dispersion hypothesis (RDH), a theory to explain group living based on resource heterogeneity, have been complicated by the fact that resource patch dispersion and richness have proved difficult to define and measure in natural systems. Here, we studied the ecology of African lions Panthera leo in Hwange National Park, Zimbabwe, where waterholes are prey hotspots, and where dispersion of water sources and abundance of prey at these water sources are quantifiable. We combined a 10-year data set from GPS-collared lions for which information of group composition was available concurrently with data for herbivore abundance at waterholes. The distance between two neighboring waterholes was a strong determinant of lion home range size, which provides strong support for the RDH prediction that territory size increases as resource patches are more dispersed in the landscape. The mean number of herbivore herds using a waterhole, a good proxy of patch richness, determined the maximum lion group biomass an area can support. This finding suggests that patch richness sets a maximum ceiling on lion group size. This study demonstrates that landscape ecology is a major driver of ranging behavior and suggests that aspects of resource dispersion limit group sizes.

Effects of resource dispersion and site familiarity on movements of translocated wild turkeys on fragmented landscapes

Animals in unfamiliar environments may increase exploratory movements, which may result in predation mortalities (the site familiarity hypothesis). Furthermore, increases in resource dispersion may reduce animal foraging time in small patches, and increase movements and home ranges of animals to acquire sufficient resources (the resource dispersion hypothesis). Little is known regarding effects of site familiarity on translocated birds in fragmented landscapes. We translocated 130 eastern wild turkeys (Meleagris gallapovo silvestris) in a sex ratio of one male to 4 females to 2 study sites that differed in forest fragmentation in MS, USA. Turkeys were captured from sites throughout Mississippi during springs 2009 and 2010. We monitored movements of translocated wild turkeys using radio telemetry. Movement distances and home ranges in 2010 did not differ among birds released in different years, inconsistent with the site familiarity hypothesis. However, movement distances and home ranges of translocated turkeys were greater at the more fragmented site than at the less fragmented site, supporting the resource dispersion hypothesis. Moreover, home range sizes were related positively to within-home-range variability in vegetative greenness measured by the normalized difference vegetation index. Effects of resource dispersion may override effects of site familiarity concerning translocated wild turkeys.

Territory quality determines social group composition in Ethiopian wolves Canis simensis

1. We contrast the value of four different models to predict variation in territory size as follows: resource density (the ideal free distribution), population density, group size and intruder pressure (relative resource-holding potential). In the framework of the resource dispersion hypothesis, we test the effect of resource abundance and spatial variation in resource distribution on the age/sex composition of social groups. 2. We explore these drivers of territory size and group size/composition in Ethiopian wolves Canis simensis in the Bale Mountains, Ethiopia, using fine-scale distribution maps of their major prey species based on satellite-derived vegetation maps. 3. The number of adult males is correlated with territory size, while prey density, wolf population density and intruder pressure are not associated with territory size. On average, each additional adult male increases territory size by 1.18 km(2). 4. Prey abundance increases with territory size (average biomass accumulation of 6.5 kg km(-2)), and larger territories provide greater per capita access to prime foraging habitat and prey. 5. The age/sex composition of wolf packs is more closely related to territory quality than territory size. Subordinate adult females are more likely to be present in territories with greater proportions of prime giant molerat Tachyoryctes macrocephalus habitat (i.e. >80% of Web Valley territories and >20% in Sanetti/Morebawa), and more yearlings (aged 12-23 months) occur in territories with greater overall prey biomass. 6. Wolf packs with restricted access to good foraging habitat tend to defend more exclusive territories, having a lower degree of overlap with neighbouring packs. 7. The greater per capita access to prey in large groups suggests a strong evolutionary advantage of collaborative territorial defence in this species, although the relative costs of territorial expansion vs. exclusion depend upon the spatial distribution of resources. We propose a model whereby territory size is determined by the number of adult males, with the presence of subordinate females and yearlings dependent on the quality of habitat, and the abundance and distribution of prey, incorporated within territory boundaries.

Abrupt spatial and numerical responses of overabundant foxes to a reduction in anthropogenic resources

Summary 1. Carnivore overabundance that results from exploitation of human derived resources can have numerous detrimental effects on local human populations and ecological communities. Experimental studies on the responses of overabundant carnivores to reductions of such resources are necessary to understand the effectiveness and impacts of resource reduction. 2. We conducted controlled experiments in two villages in which we drastically reduced the availability of anthropogenic food sources in half of each village. Spatial and numerical responses of radio‐collared red foxes Vulpes vulpes were recorded and contrasted with those of radio‐collared foxes in three similar untreated villages and pristine areas in the region. In total, we looked at survival rates of 134 foxes. 3. Prior to the resource manipulation, home range sizes (0·47 and 0·56 km2) and population densities (30 and 36 foxes km−2) in the two villages were comparable to documented low and high‐end values, respectively. 4. Fast and distinct spatial responses were observed in response to the resource manipulation, and were manifested in either increased home range size or home range shifts. In one village, foxes exposed to reduced resource availability more than doubled their home range size. 5. Survival rates of individuals in the treated areas were drastically reduced. Actual fox mortality in the two treated areas reached 100% and 64% within 12 months of the onset of resource manipulation. Estimated monthly survival in the two treated areas declined from 0·96–0·98 and 0·98–0·99 (∼0·69 and 0·78 derived annual survival) before treatment to 0·80–0·83 and 0·92–0·94 (∼<0·01 and 0·42 derived annual survival) after treatment, respectively. By contrast, average monthly survivorship in pristine areas was nearly 0·97 (∼0·69 annual survival) and in the untreated areas and other non‐treated villages was 0·95–0·99 (∼0·54–0·89 annual survival). 6. Synthesis and applications. This study demonstrates that sound waste disposal measures are very effective in controlling populations of overabundant carnivores. Contrary to common notion, the response of foxes to reduced resources was fast, manifested more by reduced survival than by successful dispersal into adjacent pristine areas. The results offer support to the Resource Dispersion Hypothesis regarding both home range size and density (suggested by the sharp decrease in survival) as a function of the spatial and temporal dispersion of resource.