Food Shortage Disrupts Social Organization: The Case of Red Squirrels in Conifer Forests

A recent conceptual model of spatial organization in vertebrates, based upon changes in home range overlap with habitat quality, ‘the space-use model’, predicts large and strongly overlapping home ranges and absence of territorial behaviour in habitats with poor food availability. We investigated whether the model can be extended to predict intra-population variation in space-use in a habitat with strong temporal variation in resource abundance. We studied space use of Eurasian red squirrels (Sciurus vulgaris) in subalpine conifer forests over 4 years with strong fluctuations in seed production. Norway spruce dominated forests are resource limited habitats for squirrels, and tree seed availability is gradually depleted in the year following a poor seed-crop. Male and female squirrels responded to spruce seed-crop failure in 2000 by strongly increasing their home ranges and core-areas in the following year (mean MCP ± SE in summer and autumn, respectively: 2001, 122.9±14.1 ha and 84.3±9.4 ha, against 43.0±6.4 ha and 20.8±3.8 ha in 2002, and 22.7±1.5 ha and 21.4±2.0 ha in 2003). In 2001, half of the animals, those with the poorest quality pre-dispersal home ranges, emigrated to areas with more larch. Residents had multi-nuclear core-areas. Also, intra-sexual core-area overlap (males by males, females by females) was higher in 2001 and summer 2002, than in autumn 2002 and in 2003 (means ± SE in summer and autumn, respectively: males by males, 2001, 52±8 and 44±7%, 2002, 80±30 and 15±11%, 2003, 37±19 and 26±14%; females by females 2001, 52±10 and 112±32%, 2002, 55±27 and 0±0%, 2003, 12±8 and 0.1±0%). Red squirrels responded to food shortage by moving to patches with other food resources and abandoned the spacing pattern of reduced core-area overlap among males and nearly exclusive core-areas among females, found in less variable habitats. After richer seed-crops in 2001 and 2002, it took squirrels about a year to reduce the size of their home ranges and core-areas and return to a spacing pattern of stable home ranges and intra-sexual territoriality of adult females. These results are consistent with the space-use model and show that spacing behaviour in red squirrels is a plastic, conditional strategy with individuals adapting the size and/or location of their home ranges in relation to local distribution and abundance of food resources.Co-ordinating editor: R. Härdling     

Exclusive core areas and intrasexual territoriality in Eurasian red squirrels (<Emphasis Type="Italic">Sciurus vulgaris</Emphasis>) revealed by incremental cluster polygon analysis

When animal home ranges overlap extensively in species lacking overt territorial behaviours, identifying exclusive core areas within individual ranges can be difficult. By analysing the size and overlap of successively smaller core areas among individual Eurasian red squirrels (Sciurus vulgaris), we determined exclusive areas within the home ranges of resident males and females. Possible effects of habitat composition and food supplies were explored by monitoring squirrels in different conifer forests and during years with low and high tree seed production. Using outlier-exclusive cores (OEC) revealed that the total ranges consisted of large sally zones (on average, 35% of the total minimum convex polygon [MCP] range) around home ranges with multi-nucleate cores. The mean OEC home range size did not differ between the sexes but was larger with poor food availability. Home ranges (99% incremental cluster polygons [ICP]) overlapped extensively between sexes (average overlap high food–low food: males by females 21–40%, females by males 43–45%) and among males (males by males 26–44%), while intrasexual overlap among females was low (9–10%). The overlap of inner cores among females rapidly approached zero, suggesting the intrasexual territoriality of 75% core areas. This was not the case among male squirrels, for which intrasexual overlap averaged only 4% at 50% but 18% at 75% core areas. Even the smallest inner cores had some degree of intersexual overlap, indicating that complete territoriality did not occur in this species. Female home ranges were more strongly affected by annual fluctuations in food supplies than male ranges. Females reduced the size of their food-based intrasexual territories when food availability increases. Males probably benefit from using larger home ranges and core areas, which overlap with the ranges of several females, by increasing their probability of successful mating.     

Variation in home range size along an elevational gradient in the iguanid lizard Sceloporus merriami

Summary Variation in home range size among three populations of the saxicolous iguanid lizard Sceloporus merriami was studied in relation to density, food availability, behavioral patterns, and daily activity periods. These populations, separated by a maximum distance of 50 km, occur along an elevational gradient which spans the elevational range of the species in west Texas. The population with the smallest home ranges had the highest density, the lowest food availability, and the most restricted daily activity period. Within populations, males consistently had larger home ranges than females. No significant between-year variation in home range size was noted within a given area or sex. Intraspecific variation in home range size is not explained by any single factor, such as food availability or density, but appears to be complexly determined by the interaction of energetic, breeding, and activity constraints.     

Ecology and social life of the red acouchy, Myoprocta exilis; comparison with the orange-rumped agouti, Dasyprocta leporina

Red acouchies were observed in French Guiana, and compared with agoutis. Acouchies frequent all forest habitats except disturbed areas. Strictly diurnal, they show most activity in early morning. Males prefer open forests, females closed habitats. The size of home ranges and the level of activity decrease in the dry season when food resources are at a minimum. The social unit is the family, one male and one female with juveniles. Family units are separated from each other. Each individual occupies a small home range which has several much-frequented areas and many resting places, often located in hollow logs and consisting of one nest in use and several old leafheaps. There are no food reserves in the nest: fruits are buried over the whole home range. Within each social unit, every individual mainly lives alone and home ranges have little overlap. The percentage of males decreases from the juvenile to the adult stage. Populations show large year to year density variations. The red acouchy is not similar to the agouti, but instead represents an unique adaptation among the terrestrial forest herbivores.     

Habitat selection and home range size of field voles<Emphasis Type="Italic">Microtus agrestis</Emphasis> in Słowiński National Park,Poland

Habitat preference, home range size and intra-specific overlap were investigated in summer 1998 among field volesMicrotus agrestis (Linnaeus, 1761) in Słowiński National Park (N Poland). Eight individuals (2 females, 6 males) were radio-tracked for one week in August. Field voles were shown to exhibit a marked preference for meadow and the ecotone between grassland and habitats with common reed, while avoiding alder forest and proper reedbeds. No significant differences between night and day in habitat-use of voles were noted. The results suggest that, at the end of the breeding season, it was food resources, rather than the risk of predation, played an important role in the voles’ utilisation of space. The home ranges of males were larger and more diverse than those of females; their sizes being correlated with body mass, such that heavier males had larger home ranges. This further suggests that intra-sexual competition exists between males for females. The low number of females influenced their spatial behaviour, as females had completely exclusive home ranges. Four males (out of six) had overlapping home ranges with other males; three of the overlaps were of less than 20%. Attributes of promiscuity (such as a 3.5:1 operational sex ratio of males to females, intra-sexual competition between males and the territorial exclusivity of females) influenced the social system. However, the period of radio-tracking during this study was too short to define accurately the social system in the field vole population.     

Living in the suburbs: Space use by vervet monkeys (Chlorocebus pygerythrus) in an eco‐estate,South Africa

We examined vervet monkey (Chlorocebus pygerythrus) space use using GPS/UHF telemetry data from 10 vervet monkeys across six troops over 9 months within a 420 ha suburban eco‐estate. We documented a mean home range of 0.99 km² (95% MCP) and 1.07 km² (95% KDE) for females (n = 6), 1 km² (95% MCP) and 1.50 km² (95% KDE) for males (n = 4) and 0.87 km² (95% MCP) and 1.12 km² (95% KDE) for troops (n = 6), respectively, indicating that males and larger troops had larger home ranges. These relatively small home ranges included shared territorial boundaries and high home range overlap. Vervet monkey movements indicated higher morning activity levels, and habitat selection indicated significantly more use of golf course, urban residential and forest, thicket and woodland areas, and avoidance of wetland, grassland and shrub, and urban built‐up areas. Our results suggest that modified habitat use by vervet monkeys is a consequence of behavioural facilitation to access highly available food resources, thereby facilitating their persistence in green spaces in urban areas of South Africa. Conflict management is dependent on the conservation of sufficient natural habitats and food resources, to minimise their dependence on anthropogenic supplementary food resources and consequently reduce human–monkey conflict.     

Habitat selection and home range in the Blanford's fox,Vulpes cana: compatibility with the resource dispersion hypothesis

Summary This paper presents analyses of habitat-use and home range size in the Blanford's fox. We predicted, from the resource dispersion hypothesis (RDH), that home ranges would encompass similar areas of combined fruitful habitats, but widely different areas of useless habitats, and thus that home ranges would be larger where such fruitful patches are fragmented and widely dispersed. Home range estimates of 0.5–2.0 km² were calculated for 16 adult Blanford's foxes, using three different methods. There were no significant differences in home range size between sexes or study sites. One habitat, dry creekbed, was the most frequently visited in all home ranges. Dry creekbed provided abundant prey for the foxes and only sparse cover for their predators. Both the available area of creekbed in each range, and the area of creekbed patches that was used by the foxes, were independent of home range size. However, the variance in home range size was explained by the mean distance between the main denning area and the most frequently used patches of creekbed. These results are in accord with some predictions of the resource dispersion hypothesis.     

Exclusive core areas in overlapping ranges of the sleepy lizard, Tiliqua rugosa

Where animal home ranges overlap extensively, objectively identifyingexclusive areas within individual ranges has been difficult,particularly in species lacking overt territorial behaviors.By analyzing the overlap between successively smaller core areasamong individuals in a population of the long-lived Australianskink, the sleepy lizard (Tiliqua rugosa), we objectively determinedexclusive areas within animal ranges. Using 4-year radio trackingdata, we found that ranges consisted of relatively large sallyzones (mean 66–80% total range), around home ranges withmultinucleate cores strongly associated with key refuge sites.Total range and home range area varied significantly among years,being smaller in a drought year. Total ranges overlapped extensivelybetween and within sexes, but for both sexes, intrasexual overlapof inner range cores rapidly approached zero, suggesting intrasexualterritoriality. Intersexual inner core overlap reflected thisspecies socially monogamous mating system. But, male overlapof female ranges and inner cores was consistently higher thanfemale-male overlap. Refuges and/or mates may be defended resourceswithin these core areas, although aggressive behavioral interactionswere rarely observed. In the extensively overlapping sally zones,males shared space with females other than their principal partner.In productive years, with larger home ranges and more extensiveoverlap, some lizards associated with extra partners, suggestingthat males opportunistically use sally zones for polygyny. Consequently,we suggest that benefits to females from male association maychange with environmental quality, such that if food resourcesare low, monogamy may be favored if females increase foragingefficiency as a consequence of male vigilance during pairing.     

Interindividual interactions of Molina’s hog-nosed skunksConepatus chinga in the Pampas grassland of Argentina

During one year, we radiotracked two female and two male Molina’s hog-nosed skunksConepatus chinga (Molina, 1782), a little studied mephitid, in the Pampas of central Argentina, to analyze the static and dynamic interactions between individuals. Mean home range overlap was large (44.5%), but males shared a smaller proportion of their home ranges than females. The average percentage of localizations in the overlap area (39.3%) indicates that these areas were not marginal sections of individual home ranges, but this value was greater for individuals of different genders than intrasexual dyads. The Coefficient of Spatial Association confirmed that the distances between individuals of different sexes were smaller than between animals of the same sex. During simultaneous locations, females were closer than males, but reciprocal distances between individuals varied over the time. These patterns are congruent with those described as typical for mustelids and mephitids. Our results confirm that an analysis of home range overlap should not be considered complete without the study of dynamic interactions among individuals and their temporal variations, which are necessary to overcome the limitations of spatial overlap analysis.     

Social organization and space use in California voles: seasonal,sexual, and age-specific strategies

We intensively monitored space use and movement in Microtus californicus over a 2-year period that included 1 year of high density (maximum 618/ha) and one of low (minimum 5/ha); historically this population has exhibited cycles of 2 or 4 years. Adults of both sexes dispersed at the start of the breeding season, culminating in the establishment of intrasexually exclusive territories. In females, these territories persisted throughout life, except that many young females recruiting during the breeding season established contiguous, overlapping, or adjacent home ranges with their mothers. This female philopatry explains the conclusion of previous workers that females of this species are non-territorial. In the dry (non-breeding) season, females had smaller ranges that often overlapped and were clustered. Adult males moved breeding territories at a modal interval of 6 weeks; this is consistent with their avoidance of inbreeding with philopatric daughters. Ranges overlapped 1–4 adult females at any one time, and a cohort of 7 long-lived males overlapped an average of 16.4 females during their tenure on the grid. The period of maximum overlap with adult females varied among individual males, and did not correlate with the time of maximum body weight. Ranges of males in the dry season overlapped extensively, with persistent associations among some individuals. In the lowdensity year, ranges of some adults failed to overlap intersexually. Juvenile males dispersed gradually between 3 and 13 weeks of age (half before 9 weeks), with some leaving after reaching sexual maturity; a few remained philopatric. Of juvenile females, 47% remained philopatric with the rest disappearing before 9 weeks of age. New understanding of vole social behavior, dispersal, and space use is achieved by focusing on the seasonal dynamics of spatial relationships among individuals with respect to age, sex, and relatedness.     

The cost of migratory prey: seasonal changes in semi‐domestic reindeer distribution influences breeding success of Eurasian lynx in northern Norway

Migratory prey is a widespread phenomenon that has implications for predator–prey interactions. By creating large temporal variation in resource availability between seasons it becomes challenging for carnivores to secure a regular year‐round supply of food. Some predators may respond by following their migratory prey, however, most predators are sedentary and experience strong seasonal variation in resource availability. Increased predation on alternative prey may dampen such seasonal resource fluctuations, but reduced reproduction rates in predators is a predicted consequence of migratory primary prey behavior that has received little empirical attention. We used data from 23 GPS collared Eurasian lynx Lynx lynx monitored during 2007–2013 in northern Norway, to examine how spatio‐temporal variation in the migratory behavior of semi‐domestic reindeer Rangifer tarandus influences lynx spatial organization and reproductive success using estimates of seasonal home range overlap and breeding success. We found that lynx of both sexes maintained seasonally stable home ranges and exhibited site fidelity across years, independent of whether they had access to reindeer throughout the year or experienced a scarcity of reindeer in winter due to migration. However, lynx without access to reindeer in winter showed a decreased probability of reproducing and a tendency for lowered kitten survival into their first winter, when compared to female lynx with reindeer available year around. This supports the hypothesis that sedentary predators experience demographic costs in systems with migratory primary prey. Changes in the migratory behavior of ungulates, including disrupted migrations, is therefore likely to have bottom–up effects on the population dynamics of sedentary predators as well as the previously documented consequences for ungulate population dynamics.     

The ecology of asociality in Namibian leopards

Data on the ecology of leopards ( Panthera pardus ) from north-eastern Namibia are presented and discussed in terms of the possible costs and benefits of solitary behaviour. In an area of low leopard density, where individuals lived alone, both males and females occupied large home ranges,(♂= 210-1164km², ♀= 183-194km²). Despite resource and reproductive advantages in maintaining exclusive ranges, the degree of range overlap both between and within sexes was substantial. Average overlap between males was 46% and between females 35%. The cost of dispersal appeared high as all three marked sub-adults died, and most recorded mortalities were of sub-adults. Females with dependent young showed a significant increase in per capita food intake compared to single females and males. Higher foraging success by females with cubs was revealed through two energy expenditure parameters (kg/km travelled/day and kg/hunt/day). Differential food intake between females with cubs, single females and males can be explained partly by differences in day ranges, body size and costs of parental care. Females shared 27% of their food with cubs and the costs of sharing food does not appear as high as previously suggested. Inter-specific competition over food and the defence of carcasses is suggested as an important cost to group living. Leopard kills were visited by other large carnivores (12%) but food loss was minimal (2%). Leopards successfully avoided conflict with inter-specific competitors by dragging and hiding kills in thick vegetation. We argue that solitary and secretive behaviour enables leopards to avoid the costs of defending carcasses against larger and gregarious carnivores.     

Space use of common genets<Emphasis Type="Italic">Genetta genetta</Emphasis> in a Mediterranean habitat of northeastern Spain: differences between sexes and seasons

The seasonal home range size and spatial relationships of 16 adult genetsGenetta genetta Linnaeus, 1758 (6 males and 10 females) were estimated in a Mediterranean habitat of northeastern Spain. Genets minimum density was estimated as 0.98/km². Mean annual home range was 113.1 ha in males and of 72.0 ha in females. Males had larger home ranges than females in all seasons, but differences were only significant in winter. Home range size changed seasonally and showed a similar pattern in both sexes, with lower values in summer (males — 41.2 ha, females — 29.0 ha) and maximum ones in spring (males — 78.8 ha, females — 56.1 ha). Animals displayed spatial fidelity throughout the year. Core areas (MCP50) represented 27% and 19% of total home range size for males and females, respectively. Resting home ranges (based on locations of inactive animals) were 9 times lower than overall home range size. Individuals of the same sex overlapped less than individuals of different sexes, especially with regard to core areas, which showed almost no overlap. The results obtained suggest that (1) different factors are likely to affect the space use of genets, such as body mass, food abundance and reproductive cycle; (2) genets use space in a heterogeneous way, with areas of greater activity than others within their home range; (3) there was intrasexual segregation with regard to space use.     

Habitat selection and activity patterns in Alpine mountain hare (Lepus timidus varronis)

We investigated activity patterns and habitat use of 34 radio-tracked mountain hares (Lepus timidus) in the Italian Alps. We first showed that hares were nocturnal and that activity patterns changed seasonally in parallel with circadian rhythms. We predicted that day home ranges will include suitable resting (shelter) habitats, and night home ranges will primarily include suitable foraging habitats. A hare's night-range was larger than its day-range. On average, night and day ranges overlapped by 36%, suggesting that selective pressures affecting space use were, at least partly, different at night than day. Dwarf mountain-pine was the most preferred habitat in all seasons and was selected both for active behaviour (night) and resting (day) and hares avoided the most open habitats. Exploring the effects of season, time of day (day vs. night) and site, we found that habitat use by mountain hares did not differ between seasons or between the active (night) and resting (day) period of circadian cycle. Also, we found no effects of differences in landscape structure (habitat patchiness and heterogeneity) on the patterns of habitat selection. Hares always preferred the dense, forested habitats, which seemed to provide food resources as well as shelter from predators throughout the year.     

Dispersal,inbreeding avoidance and reproductive success in white-footed mice

The dispersion pattern of 360 juvenile white-footed mice, Peromyscus leucopus, from 158 matings was monitored to determine whether dispersal was sufficient to prevent close inbreeding. Dispersal was male-biased with 20% of the daughters remaining in their natal home ranges. Dispersal of sons was not ‘forced’ by adult males, but may have been influenced by the presence of their mothers. One mother-son and five father-daughter pairs had overlapping home ranges during the breeding season, but the maximum number of matings among close relatives was three of 135 (2·2%). Dispersal of juvenile males was sufficient to keep close inbreeding at a minimum. Dispersal did not result from reproductive competition. Pregnant and post-lactating females frequently moved to new home ranges. The reproductive success of immigrants was the same as that of natal residents.     

The ecology of 3-D space use in a sexually dimorphic mammal

The distribution of animals is the result of habitat selection according to sex, reproductive status and resource availability. Little is known about how marine predators investigate their 3-dimensional space along both the horizontal and vertical axes and how temporal variation affects space use. In this study, we assessed the spatio-temporal movement of a sexually dimorphic marine mammal, the grey seal Halichoerus grypus by 1) determining seasonal home range size, 2) testing whether space use of seals was affected by water depth, and 3) investigating the vertical movement of seals according to the maximum depth of each dive. Between 1993 and 2005, we fitted 49 grey seals in the Gulf of St. Lawrence with satellite transmitters. We estimated seasonal 95% fixed-kernel home ranges for each individual. For each seal, we tested for selectivity and preference for 4 water depth classes at the home range scale and within the home range. We also evaluated the proportional number of dives made in each water depth classes according to the maximum depth of each dive. Home ranges were 10 times larger in winter than in summer. Seals generally selected habitats <50 m deep. They also mainly dove to depths of 40 m or less. At both scales of selection, preference for shallow areas decreased in winter. We also observed that adults used shallow habitats more than juveniles to establish their home range. A spatial segregation based on sex also occurred at the finer scale of selection where females were more concentrated in the shallowest parts of their home range than males. Segregation in space use according to age and sex classes occurred at both the horizontal and vertical scales. Our results emphasise the importance of studying habitat selection of marine predators in 3-dimensional space, in addition to the temporal scale.     

Do fences constrain predator movements on an evolutionary scale? Home range, food intake and movement patterns of large predators reintroduced to Addo Elephant National Park, South Africa

Fencing conservation areas is ubiquitous in South Africa, however, the impact of these on predator ecology has not been tested. We used relationships between prey abundance and predator space use to create equations to predict the home range size of lions Panthera leo and leopards Panthera pardus. We then successfully tested these predictions using published data (Phinda, Makalali) and home range estimates from radio collared individuals reintroduced to Addo Elephant National Park. Spotted hyaena Crocuta crocuta ranges also seem food dependent. Lion home ranges in Addo (114 ± 5 km²) required 180 fixes to be accurately estimated, spotted hyaena ranges (91 ± 10 km²) required 200 fixes, and the solitary leopard had 295 fixes for a range of 38 km². There were no sexual differences in home range sizes of lions or hyaenas. The daily food intake rate of lions, measured during continuous follows, was 9.8 kg per female equivalent unit. Dominant male lions (14.3 km for 8.3 kg) traveled furthest but obtained the least amount of food per day compared to subordinate males (8.9 km for 16.0 kg) and females (5.8 km for 17.9 kg). Subordinate males traveled the fastest and during the day, to avoid competition and harassment from the dominant males. From an evolutionary viewpoint, the use of fences for conservation has not affected the natural behaviour of the predators as they still conform to predictions derived from unfenced reserves; that is, prey abundance is the key factor in determining space use of large predators.     

Spatial structuring and dispersal in a high density population of the California vole Microtus californicus

Space use patterns of California voles are described from intensive live-trapping data obtained during the late breeding season in a peak density year. Operational sex ratios were strongly female biased. Breeding males had mutually exclusive home ranges that overlapped the home ranges of one to several females. The average male home range was larger than the average female home range and tended to encompass female home ranges in their entirety. Breeding females had home ranges that often overlapped extensively with the home ranges of other breeding females. The degree of overlap, however, tended to be either very high or very low, indicating that groups of females may act territorially among themselves. Family groups that may include members of sequential litters formed at high density. Males on experimental removal grids had larger home ranges than males on the high density grids and some became wanderers while most females had home ranges comparable to those on the high density grids.
Dispersers onto low density grids were not a random sample of the high density population; large breeding adults and small juveniles were under-represented. No sex differences in dispersal were noted. Immigration into the high density populations was probably negligible.     

Philopatry and within-colony movements in Columbian ground squirrels

Philopatry and dispersal result in selection of habitat locations that may differ in resources and social environment and thus should influence fitness components like survival and reproduction. We examined short-distance movements of young and adult females from natal or previous nesting sites within a colony of Columbian ground squirrels (Urocitellus columbianus) in the Rocky Mountains of Alberta, Canada, over a 17-year period. Females of all ages were strongly philopatric, yet a few (10-15%) exhibited movements that took them to new home ranges. We tested three hypotheses to explain the pattern of female natal and breeding movements: (1) that movements of philopatric females promote proximity to close kin; (2) that range shifts favour close kin via bequeathal of territory and (3) that dispersers move to lower density areas where competition for resources is lower. Tests of these three hypotheses revealed that: (1) philopatry and movements of young and older philopatric females led to proximity to mothers and local presence of close kin; (2) breeding dispersal did not result in bequeathal of home range to daughters, but movements of philopatric females suggested that they shared space with close kin and (3) adult females moved to new ranges with lower local densities, though dispersing females also left ranges where local density was significantly lower than for philopatric females. Natal and breeding movements among years produced two opportunities for territorial females: close spatial proximity to close kin via short philopatric movements, and habitats with fewer competitors via longer dispersal movements.     

Within-group cannibalism by adult male chimpanzees

In the Mahale Mountains National Park, Tanzania, a young adult male chimpanzee was observed to feed on a 3-month-old male infant of the same unit-group. Four other adult males and an adult female shared the carcass. The mother of the victim had immigrated from a neighboring unit-group four years previously. Circumstantial evidence strongly suggests that the first-observed cannibal male also killed the infant. The adult male and the mother of the victim had been familiar socially and sexually with each other since the female immigrated. Since the mother of the victim had usually been ranging in the peripheral part of the unit-group's range, i.e., the overlapping area of the two unit-group's ranges during pregnancy and soon after birth, the infanticidal male might have had reason to suspect the paternity of her infant. Four such cases of within-group cannibalism by adult males suggest that the female range and association pattern before and after parturition are key factors allowing an infant to survive. The possibility of male-biased infanticide is also discussed.