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.     

Spring movements of Rüppell's Vulture Gyps rueppellii across the Strait of Gibraltar

Most of our understanding of territorial behaviour in birds comes from studies of temperate species. Territoriality and factors influencing territory size of tropical birds are still poorly studied. In this study, 11 territories of the Cinnamon-breasted Rock Bunting Emberiza tahapisi were measured in the Amurum Forest Reserve and adjoining farmlands. Factors influencing the habitat choice of this species were also studied. Territory sizes ranged from 0.1–0.3 ha with a mean territory size of 0.19 ± 0.1ha. Territory size decreased with increasing food abundance and increased with tree height and number of saplings. The birds did not show signs of territoriality in farmlands but flocked in small groups (mean group size 6.88 ± 0.89). Flock size also increased with increasing number of seeds. In the forested land, birds showed a preference for rocky outcrops, whereas in farmlands, they appeared to prefer open and newly cultivated farmlands with little or no ground cover. Understanding the influence of habitat variables on territory size and habitat selection in a locally abundant and widely distributed tropical species such as the Cinnamon-breasted Rock Bunting thus offers unique opportunities for understanding how changes in landscape caused by land-use regimes may affect populations.     

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.     

The influence of territory characteristics and food supply on the breeding performance of the Red-backed Shrike (<Emphasis Type="Italic">Lanius collurio</Emphasis>) in an extensively farmed region of eastern Poland

The breeding performance of the Red-backed Shrike (Lanius collurio) in relation to the territory characteristics was investigated. The study was conducted in an area of high agricultural land use, characterised by small field size, a more mosaic habitat and low use of mineral fertilisers in comparison to Western European countries. The influence of habitat structure and composition in the territory on the date of clutch initiation, nest predation and clutch size in the Red-backed Shrike was not found, but such an influence on the number of nestlings was shown. The minimum adequate model explained 18.3% of the variation between territories in nestling’s number. The number of fledglings was positively correlated with the area of pastures, meadows, orchards and fallows within territories, and negatively correlated with length of overhead transmission lines. The number of fledglings was correlated with food abundance within territories, based on to the results from pitfall traps. There was no correlation between territory food abundance and the size of clutch. The presence of pastures, meadows and fallows, which are foraging places, thus seems to be crucial for the protection of the Red-backed Shrike.     

Predation Risk,Resource Quality,and Reef Structural Complexity Shape Territoriality in a Coral Reef Herbivore

For many species securing territories is important for feeding and reproduction. Factors such as competition, habitat availability, and male characteristics can influence an individual’s ability to establish and maintain a territory. The risk of predation can have an important influence on feeding and reproduction; however, few have studied its effect on territoriality. We investigated territoriality in a haremic, polygynous species of coral reef herbivore, Sparisoma aurofrenatum (redband parrotfish), across eight reefs in the Florida Keys National Marine Sanctuary that were either protected or unprotected from fishing of piscivorous fishes. We examined how territory size and quality varied with reef protection status, competition, predation risk, and male size. We then determined how territory size and quality influenced harem size and female size to understand the effect of territoriality on reproductive potential. We found that protected reefs trended towards having more large predatory fishes and that territories there were smaller but had greater algal nutritional quality relative to unprotected reefs. Our data suggest that even though males in protected sites have smaller territories, which support fewer females, they may improve their reproductive potential by choosing nutritionally rich areas, which support larger females. Thus, reef protection appears to shape the trade-off that herbivorous fishes make between territory size and quality. Furthermore, we provide evidence that males in unprotected sites, which are generally less complex than protected sites, choose territories with higher structural complexity, suggesting the importance of this type of habitat for feeding and reproduction in S. aurofrenatum. Our work argues that the loss of corals and the resulting decline in structural complexity, as well as management efforts to protect reefs, could alter the territory dynamics and reproductive potential of important herbivorous fish species.     

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.     

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.     

Responses in spatial organization to manipulations of the food resource in polygynandrous alpine accentors

The alpine accentorPrunella collaris is a territorial and polygynandrous mating species. The breeding unit is a group consisting of about seven members who share a group territory which contains all the resources necessary for living. Each female holds a small territory around her own nest within the larger group territory. Supplemental food in the form of millet seed was provided for a total of 23 group territories to test the hypothesis that the abundance and distribution of food influences the size of a female's territory and her dispersion pattern which, in turn, determine the mating system. Both males and females had regular access to the feeders, but females and groups provided with feeders did not have smaller territories than those without feeders. No groups were divided into two by offering extra food. Provision of extra food resulted in an increase of group size but did not alter the sex ratio. All members, including new settlers, were sexually active and the sexual relationships among the members of a group were still multiple matings. Food addition did not prompt the fed females to choose nest sites nearer the feeder. Nest sites were restricted to particular rocky slopes and non-vegetated areas which were invariably free from snow each year due to the effects of strong winds and the topography. Females showed a nest-site fidelity for successive years. The reason why supplemental food had no effect on the territory size or dispersion of female alpine accentors is discussed.     

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.     

Density dependence,territoriality, and divisibility of resources: from optimality models to population processes

Species differ enormously in their territorial systems. Some species defend only small areas surrounded by undefended space, while others defend large contiguous territories. Using an optimization approach, we show that this variation can be explained from the density of two types of resources: divisible and nondivisible. We assume that benefits of territories are monotonously related to the defended amount of divisible resources (hereafter called food). In contrast, no benefits are obtained without a nondivisible resource (hereafter called nest site) in the territory, while more than one nest site does not further increase the benefits. The optimal territory size depends on the relative abundance of these resources. With a low density of nest sites, the optimal territory size is small and includes only the nest site. If the density of nest sites is relatively large, the optimal territory size is high, and territories are contiguous. Competition for these different resources yields contrasting patterns of how populations are regulated. If there is mainly competition for nest sites, we expect density-dependent exclusion through territoriality and no density-dependent reproduction. When competition is mainly for food, we expect density-dependent reproduction because optimal territory size will be compressed at higher densities, resulting in lower reproductive success. These predicted patterns indeed are observed in some well-studied passerine species for which both the territorial system and the occurrence of density dependence is known.     

The effect of food abundance on territory size and population density of juvenile steelhead trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

Optimal territory size models predict a decrease in territory size with increasing food abundance. However, most of these models may not be applicable to juvenile salmonids in streams, because they defend contiguous territories at high densities. The optimal size of a contiguous territory is predicted to (1) be independent of food abundance when food is rare and (2) decrease only when food abundance is high enough to induce a reduction in territory size below the contiguous optimum. To test these predictions, we raised equal densities of juvenile steelhead trout in outdoor stream channels over a 32-fold range of food abundance in the absence of emigration for 25 days. Increasing competition for scarce food resulted in increasing mortality, higher willingness to emigrate, higher variance in body mass, lower growth, lower population density and lower biomass. The size of territories decreased with increasing local population density, and increased with increasing body size. However, territory size did not change with food abundance, a result consistent with the prediction of a contiguous territory size model. On average, total salmonid biomass increased 5.7 times in response to the 32-fold increase in food abundance. Our data provide strong support for an earlier quantitative relationship between the abundance of stream salmonids and their food.     

Patterns of territory size and defence level in rural and urban tawny owl (Strix aluco) populations

The effect of different variables on the territory size and defence level of tawny owl ( Strix aluco L.) populations was studied in two habitats: mixed farmland (1976–1978) and town (1986–1988). Territory size was determined by plotting the position of territorial challenges (hoots) of males which were individually recognizable in most cases. No differences were found in size, defence, number of competitors and biomass between territories in farmland and in town, but territories in town were more fragmented and showed a larger nearest neighbour distance. Size of rural territories was adequately predicted both by some structural habitat features and food supplies, while size of urban territories was affected only by habitat structure and by years of territory occupancy. No effect on territory size by competing neighbours was found in either habitat, thus confirming that behavioural interactions between the owners of territories and potential settlers prevent a decrease of territory size.
Defence level of urban territories was affected by 'social'variables (nearest neighbour distance and years of occupancy), structural variables (percentage of poplar grove and diversity), and food supply, while in rural territories only structural variables (fragmentation or natural vegetation) and food supplies affected defence level.
This was due to different settlement tactics in the two areas, depending on the extent and quality of suitable habitat.     

Effect of competitor abundance on feeding territoriality in a grazing fish,the ayuPlecoglossus altivelis

The grazing fish, ayu,Plecoglossus altivelis Temminck & Schlegel, establishes feeding territorialiry during the young stage. The population density fluctuates from year to year by more than a hundredfold, but the determinant of territory size is less well known. The feeding territoriality of ayu was examined under simulated habitat conditions where fish density was manipulated and food resources were renewable. Fish competed for algae attached to the substrata and were divided into residents with territories, and floaters without territories. By experimental alteration of fish density the number of residents increased with density and rerritory size decreased with density. Floaters intruded into territories in a school to feed on algae, which induced overt aggression of the resident and reduced the productivity of algae growing there. Both the intruding frequency of floaters over territorial areas and their feeding pressure on algae increased at higher floater density. Floaters functioned to shift cost-benefit relationships for various territory sizes. They acted as food competitors to restrict territory size below a maximum through competitive interference. Although the growth rate of residents was inversely related to fish density, residents grew faster than floaters in each group. Under a given set of competitor abundances, economic defensibility determined territory size.     

Determining habitat quality for the cooperatively breeding Rufous Treecreeper,Climacteris rufa

Abstract The theory of habitat selection predicts that organisms should use habitat that maximizes their fitness. The cooperatively breeding Rufous Treecreeper, Climacteris rufa, exhibits non‐random habitat use at a number of spatial scales. By assessing correlative relationships between nest‐site use and nest success, and territory use and reproductive success and survival, it was determined whether non‐random use of habitat yields fitness benefits. It was also determined whether breeding group size contributed significantly to fitness once differences in territory quality had been considered. Structural characteristics of nest sites that were positively correlated with the probability of a site being used had no relationship with nest success. This result probably reflects the relatively unrestricted access to an abundance of suitable nest sites in the study area. Habitat traits that predicted territory use by treecreepers were positively correlated with a number of fitness measures. They were also positively correlated with breeding group size and provisioning rate to nestlings, which in turn were correlated with fitness. However, group size was not significantly related to any measure of fitness, except primary male survival, once territory quality had been considered. The quality of territories occupied by Rufous Treecreepers appeared to be a significant factor for breeding group fitness.     

Comparative dynamics of small mammal populations in treefall gaps and surrounding understorey within Amazonian rainforest

Variation in food resource availability can have profound effects on habitat selection and dynamics of populations. Previous studies reported higher food resource availability and fruit removal in treefall gaps than in the understorey. Therefore, gaps have been considered "keystone habitat" for Neotropical frugivore birds. Here we test if this prediction would also hold for terrestrial small mammals. In the Amazon, we quantified food resource availability in eleven treefall gaps and paired understorey habitats and used feeding experiments to test if two common terrestrial rodents ( Oryzomys megacephalus and Proechimys spp.) would perceive differences between habitats. We live-trapped small mammals in eleven gaps and understorey sites for two years, and compared abundance, fitness components (survival and per capita recruitment) and dispersal of these two rodent species across gaps and understorey and seasons (rainy and dry). Our data indicated no differences in resource availability and consumption rate between habitats. Treefall gaps may represent a sink habitat for Oryzomys where individuals had lower fitness, apparently because of habitat-specific ant predation on early life stages, than in the understorey, the source habitat. Conversely, gaps may be source habitat for Proechimys where individuals had higher fitness, than in the understorey, the sink habitat. Our results suggest the presence of source-sink dynamics in a tropical gap-understorey landscape, where two rodent species perceive habitats differently. This may be a mechanism for their coexistence in a heterogeneous and species-diverse system.     

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.     

Correlation between male size and territory quality: consequence of male competition or predation susceptibility?

Territory characteristics correlate with male characteristics in several species. This can result from male competition for the best territories, or from males varying in their ability to pay other costs of territoriality, such as predation risk costs. In a population of threespine sticklebacks, Gasterosteus aculeatus , we found the biggest males to defend the biggest territories with a low structural complexity and a high female encounter rate. By experimentally manipulating competition intensity and habitat structure, we show that both male competition and predation exposure influenced the distribution of territories among males. Males increased the size of their territory when a neighbouring male was removed, whereas they reduced their territory when habitat complexity and cover from predators were reduced, with large males reducing their territory size less than smaller males. This suggests that large males occupy large, open territories both because of their superior competitive ability and because of their either lower predation susceptibility or higher risk-taking. Large, open territories were beneficial in mate attraction and male competition and predation exposure therefore biased mating opportunities towards large males. This suggests that cost of territoriality to males may reduce mate choice costs to females by securing that large males are encountered more often than small males, and by providing an additional cue, territory quality, which indicates which males are worth inspecting.     

Food and density limitations of the Seychelles Magpie Robin,Copsychus sechellarum,on Cousine Island

The critically endangered Seychelles Magpie Robin, Copsychus sechellarum, is one of the rarest birds in the world. At the end of December 1999, there were 88 individuals distributed on four small granite islands: Fregate, Aride, Cousin and Cousine. Little is known of Magpie Robin ecology in its natural habitat. Studies carried out on Aride, Cousin and Cousine are therefore valuable as each island is dominated by native woodland. The composition of Magpie Robin diet was compared between Fregate and Cousine. An exotic species of cockroach, Pycnoscelus indicus, and dropped fish were found to be considerably more important prey items on Cousine. Observations of chick food provisioning indicated habitat quality differences between the territories. Invertebrate and vertebrate food resources available to the Magpie Robin were sampled on Cousine between 1997 and 1998. Fourteen sites were sampled for invertebrates and fifty-two species from fifteen taxa were identified. There were significant differences between the mean number of species recorded per site and the mean number of animals found at each site. Skink density was estimated at between 1219-1516/ha and 354-538/ha for Mabuya sechellensis and Mabuya wrightii respectively. Invertebrate diversity and abundance was greatest in areas dominated by closed-canopy woodland on or near the coastal plain. These results explained the current distribution of Magpie Robin territories. The invertebrate abundance data were used to estimate the carrying capacity of the island for the Magpie Robin. Cousine could theoretically support up to six breeding pairs but it is questionable that a population of this size could be self-sustaining in the long-term.     

Spatial and Temporal Variability in Territoriality of a Tropical Benthic Damselfish on a Coral Reef (Réunion Island)

The relationship between length of individual Stegastes nigricans and size of the territory that they defend, and both the spatial and temporal variation in territoriality were investigated monthly on a fringing coral reef of Réunion Island over the course of one year. Length of individual S. nigricans was correlated positively with size of the territory. Most small individuals were found separate from adults, in areas with low algal turf cover. This is probably due to strong intra-specific competition for access to algal food resources and shelter availability, and/or differences in habitat preference. Both abundance of individuals and surface defended showed seasonal fluctuations. Densities were slightly higher in austral summer than in winter, and the surface defended by individuals larger than 8cm increased in winter. A permanent redistribution of territories also occured between individuals over time.     

Temporal partitioning of a floral resource by territorial hummingbirds

Most studies of territoriality in hummingbirds have focused on intraspecific competition for resources and the consequences for the spatial distribution of individuals within a habitat. As a result, we know little of the effects of interspecific competition for resources and less still of temporal resource partitioning. Here I describe the interactions of four species of tropical hummingbird which defended the same territory at different stages in the flowering period and at different times of the day. The pattern of territory defence was greatly influenced by the dominance hierarchy between species and the costs and benefits of territory ownership. I used a simple economic model to calculate the predicted territory size based on four potential strategies. Hummingbirds appeared to be defending territories of the smallest economical size, agreeing with two hypotheses: (1) that hummingbirds minimize the cost of territory ownership and (2) that hummingbirds maximize the time spent sitting. The model predicted accurately the observed pattern of territory acquisition; hummingbirds initiated defence as soon as the territory contained sufficient resources and were either displaced by a larger species or replaced by a smaller one as the value of the territory changed.