Females go where the food is: does the socio-ecological model explain variation in social organisation of solitary foragers?

The socio-ecological model (SEM) links ecological factors with characteristics of social systems and allows predictions about the relationships between resource distribution, type of competition and social organisation. It has been mainly applied to group-living species but ought to explain variation in social organisation of solitary species as well. The aim of this study was to test basic predictions of the SEM in two solitary primates, which differ in two characteristics of female association patterns: (1) spatial ranging and (2) sleeping associations. Beginning in August 2002, we regularly (re-)captured and marked individuals of sympatric populations of Madame Berthe's and grey mouse lemurs (Microcebus berthae, Microcebus murinus) in Kirindy Forest (Madagascar). We recorded data on spatial patterns, feeding and social behaviour by means of direct observation of radio-collared females. The major food sources of M. berthae occurred in small dispersed patches leading to strong within-group scramble competition and over-dispersed females with a low potential for female associations. In contrast, M. murinus additionally used patchily distributed, high-quality (large) resources facilitating within-group contest competition. The combined influence of less strong within-group scramble and contest as well as between-group contest over non-food resources allowed females of this species to cluster in space. Additionally, we experimentally manipulated the spatial distribution of food sources and found that females adjusted their spatial patterns to food resource distribution. Thus, our results support basic predictions of the SEM and demonstrated that it can also explain variation in social organisation of solitary foragers.     

Economic aspects of natural resource exploitation

Low entropy accumulations of matter and energy are more economic for humans to exploit as natural resources. This accumulation of a resource takes place over time and the most concentrated resources, such as fossil fuels, are created over geological ages. As the most concentrated resources become depleted it may be possible for technology to enable the exploitation of less concentrated resources, such as low-grade metal ores or thinly populated fishing grounds. Analysis of the timescales necessary to create different types of natural resource reveals three distinct groups. Further consideration of economic characteristics of resources, including ownership and access, and rate of consumption relative to rate of supply confirms the grouping of resources into the three distinct groups. Rate of change of entropy as a resource is exploited is an indicator of its impact on the environment. Consideration of this again suggests three distinct groups of resources, and this paper identifies them as: continuous natural resources (CNR), such as solar power and wind power; potentially renewable resources (PRR), such as fish and forests; and non-renewable resources (NRR), such as fossil fuels and metals.     

Gunnison’s prairie dog (<Emphasis Type="Italic">Cynomys gunnisoni</Emphasis>): testing the resource dispersion hypothesis

Few studies have experimentally tested the resource dispersion hypothesis (RDH). In this study, I tested whether space use and social organization of Gunnison’s prairie dog responded to changes in the dispersion and abundance of resources. Food manipulations were carried out during the reproductive and nonreproductive seasons across 2 years. Gunnison’s prairie dog adults responded to the experiments by decreasing territory size as food became patchier in space and time. Both males and females modified their home ranges, with no detectable difference between sexes, either prior to or during the experiments. As food became patchier in space and time, the spatial overlap of adults increased, whereas it decreased as food became more evenly dispersed. The average size of a group, defined as those individuals occupying the same territory, did not change significantly as a result of the experiments. Where changes in the composition and size of groups did occur, there was no indication that such changes were sex specific. Results from this study support critical components of the RDH and strongly suggest that patterns of space use and social structure in Gunnison’s prairie dogs are the result of individual responses to resource abundance and distribution.     

When females should contest for food – testing hypotheses about resource density, distribution, size, and quality with Hanuman langurs (Presbytis entellus)

Predictions of ecological models on female social relationships (van Schaik 1989) and their links with food distribution and the potential competitive regime are used to analyze the feeding and spatial behavior, and resource density, size, distribution, and quality in a forest population of Hanuman langurs (Presbytis entellus). In contrast to other populations, and assumptions on folivorous primates, the females of this population exhibit a linear dominance hierarchy. The langurs concentrated their feeding on three key resources with a low density and clumped distribution. Two out of the three key resources contained significantly higher levels of extractable protein and soluble sugar than other food plants, indicating high spatial variability of food quality. Even the mature leaves of the most preferred food plant were about twice as nutritious as those from other food plants. Group spread was small and only a single high-quality resource was used at a time. Finally, even rich resources could accommodate only a subset of a group. These findings fit predictions made for the prevalence of within-group contest competition. Given the observed food distribution and phytochemical heterogeneity of mature foliage, even females of folivorous species should contest for food. The effect of female dominance rank on size and composition of feeding parties also agrees with this prediction. A comparison with data from another forest population, where female dominance relations are weakly developed, revealed a clear-cut difference in the use and abundance of resources. It is argued that between-population differences in female social relationships within a species may be viewed as adaptive responses to local habitat conditions. Received: 1 August 1997 / Accepted after revision: 7 December 1997     

Zooplankton biodiversity and lake trophic state: explanations invoking resource abundance and distribution

While empirical studies linking biodiversity to local environmental gradients have emphasized the importance of lake trophic status (related to primary productivity), theoretical studies have implicated resource spatial heterogeneity and resource relative ratios as mechanisms behind these biodiversity patterns. To test the feasibility of these mechanisms in natural aquatic systems, the biodiversity of crustacean zooplankton communities along gradients of total phosphorus (TP) as well as the vertical heterogeneity and relative abundance of their phytoplankton resources were assessed in 18 lakes in Quebec, Canada. Zooplankton community richness was regressed against TP, the spatial distribution of phytoplankton spectral groups, and the relative biomass of spectral groups. Since species richness does not adequately capture ecological function and life history of different taxa, features which are important for mechanistic theories, relationships between zooplankton functional diversity (FD) and resource conditions were examined. Zooplankton species richness showed the previously established tendency to a unimodal relationship with TP, but functional diversity declined linearly over the same gradient. Changes in zooplankton functional diversity could be attributed to changes in both the spatial distribution and type of phytoplankton resource. In the studied lakes, spatial heterogeneity of phytoplankton groups declined with TP, even while biomass of all groups increased. Zooplankton functional diversity was positively related to increased heterogeneity in cyanobacteria spatial distribution. However, a smaller amount of variation in functional diversity was also positively related to the ratio of biomass in diatoms/chrysophytes to cyanobacteria. In all observed relationships, a greater variation of functional diversity than species richness measures was explained by measured factors, suggesting that functional measures of zooplankton communities will benefit ecological research attempting to identify mechanisms behind environmental gradients affecting diversity.     

Effects of human activities (raking,scraping, off-road vehicles) and natural resource protections on the spatial distribution of beach vegetation and related shoreline features in New Jersey

This study examined the relative impacts of different human activities and natural resource protections on the spatial distribution of beach vegetation and related habitat features (wrack, dune succession) in New Jersey (USA). Field surveys of the 209-km shoreline categorized beach segments according to vegetation cover classes, human activities, protection measures (exclosures, beach management plans, access restrictions) and ownership status (federal, state, etc.). A partition model (classification tree) was used to confirm the relative dominance hierarchy of human actions on the distribution of beach vegetation observed, and quantitative comparisons of dominant activities were conducted using vegetation data collected on 218 transects. The spatial extent of beach vegetation was found to be severely restricted by human activities when unconstrained by resource protections. The greatest reductions were found to result from mechanical raking (?99 %), scraping (?91 %) and all-year recreational ORV use (?86 %), which were dominant on nearly 70 % of the state shoreline. Beaches containing larger areas of vegetation (>5 m) were concentrated in areas with resource protections of various kinds (99 %), and on federal or other public parklands (68 %). Exclosures resulted in the greatest coverage of vegetation (48 % of beach surface) compared to public access restricted areas (41 %), beach management plans (31 %), government-only ORV use (31 %), and off-season recreational ORVs (15 %). Greater protection and recovery of beach vegetation and habitat is needed for species conservation and erosion protection in New Jersey and other coastal environments where these activities occur.     

Spatial position and feeding success in ring-tailed coatis

The location of an animal within a social group has important effects on feeding success. When animals consume quickly eaten food items, individuals located at the front edge of a group typically have greater foraging success. When groups feed at large clumped resources, dominant individuals can often monopolize the resource, leading to higher feeding success in the center of the group. In order to test these predictions, behavioral data relating foraging success to within-group spatial position were recorded from two habituated groups of ring-tailed coatis (Nasua nasua) in Iguazu, Argentina. Foraging success did not fit expected patterns. When feeding on small ground litter invertebrates, coatis had the same foraging success at all spatial positions. This pattern likely resulted from an abundance of invertebrates in the ground litter. When feeding on fruit, individuals in the front of the group had greater feeding success, which was driven by the relatively quick depletion of fruit trees. Dominant juveniles were often located in the front of the group which led to increased access to food. This resulted in higher feeding success on fruits but simultaneously increased their risk of predation. Although groups typically became more elongated and traveled faster when feeding on fruit, it did not appear that the coatis were drastically changing their spacing strategies when switching between the two food types. Paradoxically, spatial position preferences during invertebrate foraging appeared to be driven by fruit trees. Because fruit trees were encountered so frequently, juveniles ranging at the front edge of the group during invertebrate foraging were the first to arrive at fruit trees and thus had higher foraging success. This study demonstrates the importance of how food patch size and depletion rate affect the spatial preferences of individuals.     

Effects of sex-associated competitive asymmetries on foraging group structure and despotic distribution in Andean condors

Phenotype-limited interference models assume competitive asymmetries among conspecifics and unequal sharing of resources. Their main prediction is a correlation between dominance status and patch quality: dominant individuals should preferentially exploit better-quality habitats. We tested assumptions and predictions of the phenotype-limited interference model in Andean condors (Vultur gryphus), a New World vulture with strong sexual size dimorphism (males are 30–40% heavier than females). We recorded searching birds in habitats differing in quality: mountains and plains. We also observed scavenging behaviour at 20 sheep carcasses, and videotaped 5 of them. Intraspecific hierarchy at carcasses was based on size: males dominated females and, within each sex, older birds dominated younger ones. Adult males and juvenile females occupied extreme positions in the feeding hierarchy. Aggression was directed at those individuals belonging to lower hierarchical levels. In high-quality areas (mountains), more condors arrived at carcasses. Juvenile females were more often observed searching in low-quality areas (plains), far from breeding areas and main roost sites. GLM analyses of individual behaviour showed that the hierarchy did not influence time of arrival, but low-ranking individuals spent more time at carcasses, especially if the number of condors at arrival was high. Additionally, low-ranking condors spent less time feeding at carcasses when individuals of higher hierarchical levels were present. On the other hand, the number of condors present had a positive effect on feeding rates of dominant individuals, probably because of a reduction in individual vigilance. These results support most of the assumptions and predictions of the phenotype-limited distribution model, although a spatial truncated distribution between phenotypes was not observed. Asymmetric feeding pay-off, unequal parental roles and sexual selection constraints could favour sexual divergence in body size in Andean condors. Received: 6 April 1998 / Accepted after revision: 11 July 1998     

Social facilitation of selective mortality

Territorial defense by breeders influences access to resources near defended nest sites by intruder species and may have indirect effects on other species within the territory, leading to local patchiness in distribution patterns. The present study demonstrates that adult males of a damselfish, Pomacentrus amboinensis, indirectly facilitate the increased survival of conspecific juveniles through the territorial defense of their nesting site from potential egg predators. Moreover, male territoriality results in a shift in the selectivity of predation on newly settled juveniles. We monitored the fate of pairs of predator-naive, newly settled P. amboinensis placed inside and outside nesting territories. Individuals within a pair differed in size by approximately 1 mm and were tagged for individual identification. Away from male territories larger juveniles had greater survival, while within territories, larger juveniles suffered higher mortality. Behavioral observations indicated that the moonwrasse Thalassoma lunare, a predator of benthic eggs and small fishes, had reduced access to juveniles within male territories, while another predator on small fishes, the dottyback Pseudochromis fuscus, had unobstructed access to male territories. Experimental removal of P. fuscus indicated that the shift in the direction of phenotypic selection on newly settled juveniles was the indirect effect of aggression by nest-guarding male damselfish, which resulted in differential access to male territories by these two predators of small fishes. Evidence suggests that behavioral interactions between the resident community and intruders will influence patchiness in selective pressures imposed on benthic prey by influencing both the composition of predator types that can access the prey resource and their relative abundance. How this spatial and temporal patchiness in predator pressure interacts with spatial patchiness of recruiting prey will have a major influence on the resulting distribution of juveniles and their phenotypic traits.     

Population and individual consequences of breeding resource availability in the European bitterling (Rhodeus amarus)

Resource availability may affect both individual fitness and population demography and the effects can interact. We used two experiments to test how breeding resource abundance and its spatial distribution, combined with female abundance, affected male reproductive behavior, population spawning rate, and embryo development and recruitment in the European bitterling (Rhodeus amarus), a small cyprinid fish that lays its eggs in living unionid mussels. In the first experiment, we found that at the population level the abundance of breeding resources (freshwater mussels) was more important for bitterling recruitment than resource spatial distribution (clumped or regular). In contrast at the individual level, (variability in reproductive success) the spatial distribution of resources was more important, but only when resource abundance was not limiting. Territorial males obtained almost exclusive access to fertilizations when resources were abundant and distributed regularly, but were unable to defend large clusters of resources (when rival abundance was always high) and abandoned territoriality. Surprisingly, territorial males remained aggressive and successfully defended their territories when resources were grouped into a single cluster, but at a low abundance. In the second experiment, more rapid embryo development and larger juvenile body size at the end of the growing season was detected at high resource abundance and low female abundance, indicating that early hatched juveniles survived better and hence investment in offspring production early in the season yields a higher fitness pay-offs. The abundance of females in spawning condition was the best overall predictor of the intensity of male reproductive behavior in both experiments.     

Site fidelity of male Galápagos sea lions: a lifetime perspective

Knowledge about the distribution of resources can lead to the development of spatial preferences and long-term site fidelity. Individuals are expected to choose sites that best suit their needs. However, dominant individuals restrict movements of less competitive ones. Accordingly, one may expect spatial preferences to differ with regard to individual characteristics and to change over time. We investigated lifetime changes of site fidelity patterns with regard to reproductive success in male Galápagos sea lions (Zalophus wollebaeki). Showing a high degree of natal philopatry in the first 2 years of life, non-territorial males pass through a stage of fidelity to their natal colony where they develop preferences for areas outside prime breeding areas. Variation in the degree of spatial preferences was not associated with age or size, characteristics linked to an individual’s dominance status. For non-territorial males, roaming proved to be an adequate strategy to gain reproductive success. Only the most competitive males established territories in areas preferentially visited by females. They had a high probability to return to breeding areas where they successfully reproduced in previous seasons. Overall, the results reveal lifetime changes in site fidelity with regard to male status. The degree of site fidelity observed within the colony suggests familiarity and thus a high degree of tolerance among individuals using the same areas. This seems to facilitate attendance in the colony and thus the possibility to prospect for oestrus females.     

Feeding and non-feeding aggression can be induced in invasive shore crabs by altering food distribution

Human activity can have a large impact on surrounding ecosystems. For example, humans alter resource distributions for other species, potentially modifying these species competitive dynamics. These changes in local competitive processes are frequently associated with species invasions. Here, we investigate how differences in resource distribution affect competitive behaviour using the highly invasive European shore crab (Carcinus maenas). Using a controlled laboratory experiment in combination with behaviour assays and social network analysis, we show that individuals feeding in habitats with clumped food distributions are more aggressive than individuals feeding in habitats where food is evenly dispersed, and this aggression is present even on days where crabs are not feeding. Additionally, this persistent aggression can be induced, suggesting that individuals of this invasive species possess the flexibility to modify their competitive behaviours in response to differences in food distributions. Furthermore, we show how these individual responses can lead to changes in overall organisation of aggressive interactions within a population. We discuss these results in relation to how human impacts can have long-term effects on competitive behavioural strategies, and how behavioural flexibility can allow invasive species to colonise and persist in highly impacted sites such as urban ecosystems.     

Measuring values for environmental resources under uncertainty

The relationship between conventional Hicksian measures of the benefits from changes in environmental amenities under certainty, and corresponding measures of valuation when the conditions of access to an uncertain environmental resource are changed, is considered. The analysis utilizes a contingent commodity framework with the assumption of state-dependent preferences. The findings suggest that the valuation of these changes will depend upon the availability of fair markets for diversifying risk. Moreover, conventional measures of compensating or equivalent surplus will not necessarily bound the individual's valuation of a change in access to an uncertain environmental resource.     

Modeling resource selection using polytomous logistic regression and kernel density estimates

Wildlife resource selection studies typically compare used to available resources; selection or avoidance occurs when use is disproportionately greater or less than availability. Comparing used to available resources is problematic because results are often greatly influenced by what is considered available to the animal. Moreover, placing relocation points within resource units is often difficult due to radiotelemetry and mapping errors. Given these problems, we suggest that an animal’s resource use be summarized at the scale of the home range (i.e., the spatial distribution of all point locations of an animal) rather than by individual points that are considered used or available. To account for differences in use-intensity throughout an animal’s home range, we model resource selection using kernel density estimates and polytomous logistic regression. We present a case study of elk (Cervus elaphus) resource selection in South Dakota to illustrate the procedure. There are several advantages of our proposed approach. First, resource availability goes undefined by the investigator, which is a difficult and often arbitrary decision. Instead, the technique compares the intensity of animal use throughout the home range. This technique also avoids problems with classifying locations rigidly as used or unused. Second, location coordinates do not need to be placed within mapped resource units, which is problematic given mapping and telemetry error. Finally, resource use is considered at an appropriate scale for management because most wildlife resource decisions are made at the level of the patch. Despite the advantages of this use-intensity procedure, future research should address spatial autocorrelation and develop spatial models for ordered categorical variables.     

Exploitative compensation by subordinate age-sex classes of migrant rufous hummingbirds

Summary The three age-sex classes of rufous hummingbirds (Selasphorus rufus) that directly interact on southward migratory stopovers in our California study system differ in territorial ability and resource use. Immature males are behaviorally dominant to adult and immature females and defend the richest territories. Here, we test the hypothesis that the territorially subordinate age-sex classes compensate exploitatively for their exclusion from rich resources. Our results show that females were able to accumulate energy stores at rates comparable to males despite their subordinate territorial status. Territorial females gained body mass at the same rate and in the same pattern as males, and resumed migration at the same body masses. Moreover, during periods when birds were nonterritorial and used dispersed resources, adult and immature females maintained or gained body mass, whereas immature males lost mass. We suggest that females may be energetically compensated by (1) lower costs of flight incurred during foraging and defense, resulting from their lower wing disc loading, and (2) greater success at robbing nectar from rich male territories, resulting from duller coloration (immature females), experience (adult females), and, possibly, hormonal differences. In the future, experiments will be necessary to distinguish the various hypotheses about the mechanisms involved in compensation. Correspondence to: F.L. Carpenter     

Climate change,risk management and the end of Nomadic pastoralism

Mobility has been argued to be the single factor explaining why some pastoralists do relatively well during extreme climatic events, while others do not, because mobility works by taking advantage of the spatial and temporal structure of resource failure by moving away from scarcity towards abundance. In spite of this, a common governmental management strategy is to resettle pastoral populations and thereby significantly reduce mobility. By revealing the underlying logic of mobility for Tibetan pastoralists, this paper questions official policy that aims at privatizing communally owned rangelands since it reduces pastoral flexibility and access to key resources. This is especially pertinent in the face of climate change. While little is known as to the specifics of how climate change will affect nomadic pastoralists, environmental variability is likely to increase. Consequently, policies resulting in decreased mobility may exacerbate the negative effects of climate change because of a positive feedback between climate and negative density dependence.     

Kriging插值法在植物物种地理分布空间格局研究中的应用

Kriging插值法是一种定量化描述地理空间分布格局的方法,主要应用于空间采样以及相关的一些空间格局分析。而物种的地理空间分布是物种在自然及人类活动共同作用下的结果。物种分布的研究目前主要从气候的角度来探讨其与气候之间的关系,并取得了很好的结果,但是仅从气候考虑又有局限性,而且很难真实地反映出物种地理空间的分布格局。因此,将Kriging插值法引进到物种分布的研究中,并以我国广泛分布的物种——栓皮栎为例,探讨其可行性。结果表明：Kriging插值法能很好地拟合物种地理空间分布的实际情况,其误差程度较小。该研究的结果可为物种资源的开发利用和物种的引种栽培提供理论依据。     

Movement ecology: size-specific behavioral response of an invasive snail to food availability

Immigration, emigration, migration, and redistribution describe processes that involve movement of individuals. These movements are an essential part of contemporary ecological models, and understanding how movement is affected by biotic and abiotic factors is important for effectively modeling ecological processes that depend on movement. We asked how phenotypic heterogeneity (body size) and environmental heterogeneity (food resource level) affect the movement behavior of an aquatic snail (Tarebia granifera), and whether including these phenotypic and environmental effects improves advection-diffusion models of movement. We postulated various elaborations of the basic advection diffusion model as a priori working hypotheses. To test our hypotheses we measured individual snail movements in experimental streams at high- and low-food resource treatments. Using these experimental movement data, we examined the dependency of model selection on resource level and body size using Akaike's Information Criterion (AIC). At low resources, large individuals moved faster than small individuals, producing a platykurtic movement distribution; including size dependency in the model improved model performance. In stark contrast, at high resources, individuals moved upstream together as a wave, and body size differences largely disappeared. The model selection exercise indicated that population heterogeneity is best described by the advection component of movement for this species, because the top-ranked model included size dependency in advection, but not diffusion. Also, all probable models included resource dependency. Thus population and environmental heterogeneities both influence individual movement behaviors and the population-level distribution kernels, and their interaction may drive variation in movement behaviors in terms of both advection rates and diffusion rates. A behaviorally informed modeling framework will integrate the sentient response of individuals in terms of movement and enhance our ability to accurately model ecological processes that depend on animal movement.     

Dominance in feeding territories relates to foraging success and offspring growth in brown skuas <Emphasis Type="Italic">Catharacta antarctica lonnbergi</Emphasis>

Territoriality should lead to strict dominance, as territory holders typically control access to resources and exclude others from their use. In feeding territories, dominance should be reflected in foraging success and ultimately in reproduction differences; however, these successive links have rarely been made explicit. Therefore, we investigated a population of brown skuas Catharacta antarctica lonnbergi, in which only part of the breeding population occupied feeding territories within penguin colonies. We identified the dominance hierarchy and determined the foraging success of the participants in fights for access to penguin carcasses within the territories. Furthermore, we monitored offspring growth from parents with and without feeding territories. Our results indicated a clear dominance hierarchy with territorial birds in their own territory dominating over territorial breeders from other territories, non-territorial breeders and non-breeding birds. However, territory owners could not completely exclude others from access to food. Foraging success was positively related to dominance scores: The dominant territory owners received 63% of a carcass, whereas non-territorial pairs could get less than 10%. The link between foraging success and offspring development was less clear: Although male chicks of non-territorial parents suffered from lower growth rates and, thus, delayed fledging, there were no such differences in female chicks. Territoriality in skuas did not imply a complete occupation of food, but guaranteed optimal growth conditions for offspring. Non-territorial individuals were forced to search for alternative resources, and the restricted access to the preferred food resulted in inferior conditions for offspring development, making this foraging strategy less rewarding.     

Correlations of food distribution and patch size with agonistic interactions in female vervets (Chlorocebus aethiops) and patas monkeys (Erythrocebus patas) living in simple habitats

Food distribution is hypothesized to be important in determining the nature of female relationships within social groups of primates. When food limits female reproductive success, spatially clumped foods are expected to produce strong, linear dominance hierarchies within groups, whereas more spatially dispersed foods are expected to produce weaker or non-existent dominance hierarchies. The association between food distribution and competitive relationships presumably occurs because clumped foods are usurpable but dispersed foods are not. We examined the spatial distribution of food patches (trees) and patch size relative to feeding behavior and agonistic interactions in vervets and patas monkeys, two closely related and sympatric species that nonetheless differ in the strength of the female dominance hierarchy. Food patches of both patas monkeys and vervets were small in size and randomly distributed in Acacia drepanolobium habitat. In contrast, in A. xanthophloea woodland, the habitat type that was exclusively used by vervets, food patches were larger and more spatially clumped. These similarities and differences between and within species were correlated with similarities and differences in the strength and linearity of their dominance hierarchies. Patas monkeys and vervets in A. drepanolobium habitat had dominance hierarchies that were weakly defined because there were relatively few agonistic interactions between females. By contrast, in A. xanthophloea habitat, vervets had a stronger, linear dominance hierarchy characterized by a higher rate of agonistic interactions over food. The covariation of agonistic interactions with patch size is discussed in relation to depletion time, another characteristic that may covary with food distribution, and resource renewal rate, an important determinant of agonistic interactions in insectivorous birds, fishes, insects, and mammals. Received: 18 February 2000 / Revised: 5 September 2000 / Accepted: 26 September 2000