Small mammal responses to moose supplementary winter feeding

Supplementary feeding of wild large herbivores is a widespread practice in North America and Europe. The presence of feeding stations may have ecological consequences through changes to animal distributions, patterns of herbivory and a net nutrient input into the ecosystem. In Fennoscandia, supplementary feeding of moose in winter (Alces alces) is increasing. Although it has been shown to affect bird communities, its effects on small mammal communities were unknown. Here, we studied the effects of moose supplementary feeding stations on plants and on abundance, reproduction, and biomass of small mammals in years with low and high vole abundance. We sampled small mammals with snap traps and conducted surveys of the field layer vegetation, at varying distances from moose supplemental feeding stations. Due to the vegetation changes induced by feeding stations, abundance of common shrews (Sorex araneus) and Microtus voles were positively affected by long-term moose winter feeding, while bank voles (Myodes glareolus) were not affected. Moose feeding stations did not affect reproduction, individual body mass, or the total biomass of small mammals. Moose winter-feeding stations have impacts on nontarget species, providing islands of preferred grass and forb habitat for Microtus spp. and common shrews, allowing them to penetrate into a matrix of less preferred forest habitat.     

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.     

Conservation opportunities in commercial plantations: The case of mammals

Enhancing the structural complexity of commercial plantations could enrich the presence of mammals within them. We tested this hypothesis through a meta-analysis in order to determine whether more complex plantations, with a dense understory, can sustain more mammal diversity and if mammals respond differently pending on its taxonomic affiliation, body size, and diet group. We recorded 71 cases of forest–plantation comparisons, and 10 cases of plantation–plantation comparisons. Both richness and abundance of native mammals were lower in plantations than in native forests, although there was no significant difference in body size, dietary group, and taxonomic affiliation between those two habitats. Complex plantations showed higher richness and abundance of native mammals, independently of the plantation type. Taxonomic affiliation, body size and diet did not significantly differ between complex and simple plantations. Structural complexity of commercial plantations may increase mammal diversity, hence, enriching the auxiliary value of forestry plantations for biological conservation. Therefore, forest plantation management ought to pursue the enhancement of structural complexity.     

An allometric model of home range formation explains the structuring of animal communities exploiting heterogeneous resources

Understanding and predicting the composition and spatial structure of communities is a central challenge in ecology. An important structural property of animal communities is the distribution of individual home ranges. Home range formation is controlled by resource heterogeneity, the physiology and behaviour of individual animals, and their intra‐ and interspecific interactions. However, a quantitative mechanistic understanding of how home range formation influences community composition is still lacking. To explore the link between home range formation and community composition in heterogeneous landscapes we combine allometric relationships for physiological properties with an algorithm that selects optimal home ranges given locomotion costs, resource depletion and competition in a spatially‐explicit individual‐based modelling framework. From a spatial distribution of resources and an input distribution of animal body mass, our model predicts the size and location of individual home ranges as well as the individual size distribution (ISD) in an animal community. For a broad range of body mass input distributions, including empirical body mass distributions of North American and Australian mammals, our model predictions agree with independent data on the body mass scaling of home range size and individual abundance in terrestrial mammals. Model predictions are also robust against variation in habitat productivity and landscape heterogeneity. The combination of allometric relationships for locomotion costs and resource needs with resource competition in an optimal foraging framework enables us to scale from individual properties to the structure of animal communities in heterogeneous landscapes. The proposed spatially‐explicit modelling concept not only allows for detailed investigation of landscape effects on animal communities, but also provides novel insights into the mechanisms by which resource competition in space shapes animal communities.     

Ecological correlates of lion social organization (Panthers, leo)

Data on lion home range size, pride size, density, group size, cub survival, litter size and adult sex ratio were extracted from studies carried out in 10 habitats. The data were compared with five measures of food supply: mean prey biomass, prey biomass during the season of greatest abundance, prey biomass during the season of least abundance, biomass of middle-sized prey species (i.e. those with mean adult live-weights between 50 and 250 kg), and the mean size of carcasses fed on by lions. The results indicated that range size is inversely correlated with the abundance of prey during the period of least abundance, but not with overall prey abundance. Range size showed no consistent variation with pride size or with minimum metabolic requirements. Pride size (measured in terms of average number of animals per pride and average number of adult females) and cub survival strongly correlated with lean season food abundance. No relationship was found between group size or litter size and any of the measures of food supply Adult sex ratio did not vary consistently with food supply or lion density, although the data did suggest that prides inhabiting small, circumscribed reserves may experience less inter-male competition and this, in turn, may affect the adult sex ratio.     

The role of size and dominance in the feeding behaviour of coexisting hummingbirds

Interspecific competition can strongly influence community structure and limit the distribution and abundance of species. One of the main factors that determine hummingbird community structure is competition for food. The temporal and spatial distribution of nectar has a strong impact on hummingbird assemblages, shaping foraging niches according to hummingbird dominance and foraging strategy. We investigated whether body size and the degree of aggressive dominance influence feeding behaviour of hummingbirds in a temperate forest in northwestern Mexico (El Palmito, Mexico) when winter migrant hummingbirds are present in the community. First, we determined the dominance status of hummingbirds and evaluated the relationship between dominance and body mass, wing disc loading and migratory status. Secondly, we determined how hummingbird species used plant species differently. Thirdly, we examined whether the most dominant hummingbird species defended floral patches with more energy and/or with a larger number of flowers. At each flower patch, hummingbird species, number of hummingbird interactions, feeding time and number of flowers present were recorded. The total number of calories available within each floral patch was also determined. Our results demonstrate that the dominance hierarchy of 13 hummingbird species (migratory and resident) was correlated with body size but not wing disc loading, and that members of the hummingbird community showed a clear separation in resource use (by plant species). Hummingbirds at the top of the dominance hierarchy defended and fed on the best flower patches, defined by the quantity of calories available. Hence, the feeding behaviour of hummingbirds at El Palmito depends on the abundance of plant species used by hummingbirds and on the amount of energy available from each flower patch. Thus, hummingbird body size, aggressive dominance and defence of quality flower patches determines niche partitioning among species.     

Quantifying Primate Food Distribution and Abundance for Socioecological Studies: An Objective Consumer-centered Method

Food abundance and distribution have played a central role in the conceptual theory of primate socioecology. This theory predicts that agonistic (contest) competition should occur when food is distributed in discrete, defensible patches; in contrast, when food sources are distributed uniformly or randomly, nonagonistic (scramble) competition is expected. Primatologists usually measure resource density and patchiness from a botanical perspective, without an explicit link to the biology of the animal being studied. Such an approach may be irrelevant to how the animals view the dispersion of resources. For studies related to feeding competition, we suggest the use of a method that provides a consumer-based index of food distribution. We then describe such an approach and apply it to understand agonistic behavior in white-faced capuchins (Cebus capucinus), at Lomas Barbudal. Instead of choosing sample plots at random, we use each actual feeding tree of a group as the center of a sample plot and we use the monkey species’ average group spread as the sampling area. This focal tree method allows us to evaluate the resource availability both within and outside of the feeding tree during a particular feeding bout. To summarize the spatial distribution of food at the level of a foraging group, we define and use an extension of Lloyd’s Dispersion Index, Lloyd’s Extended Index (LEI), designed to allow the inclusion of resources of diverse sizes and species in a single measure. We evaluate if LEI can be used to predict the frequency of aggression, if changing the area of the plot alters these results, and if calculating LEI based on fruit abundance or fruit biomass better predicts the frequency of aggression in this population of capuchins. In support of socioecological predictions, our results show that the frequency of agonism in a focal tree declines as LEI increases. This relationship is significant when LEI is calculated using a 20-m plot size and weighting tree size by fruit counts, but not when using larger plot sizes, unweighted tree counts, or weighting by fruit biomass. Our approach demonstrates the importance of carefully considering plot size and different measures of food availability when testing socioecological models relating resource distribution and quality to aggression in nonhuman primates.     

Ecological correlates of body size in gamasid mites parasitic on small mammals: abundance and niche breadth

We studied ecological correlates of body size (abundance and niche breadth) in gamasid mites parasitic on small mammals in 28 regions of the Palearctic. We predicted that smaller species would be characterized by higher abundance than larger species, all else (e.g. host species) being equal. We also predicted that host specificity of mites would decrease (that is, number of host species they use would increase) with an increase in their body size. We focused on mites collected from host bodies that include a) species that feed solely on host’s blood (obligate exclusive haematophages), b) species that feed on both host’s blood and small arthropods (obligate non‐exclusive haematophages), and c) facultative haematophages. We expected that the relationship between body size and abundance and/or host specificity would be more pronounced in obligate exclusively haematophagous mites than for obligate non‐exclusively and facultative haematophagous mites. Across all mite species across regions, mean abundance correlated negatively with body size. The same was true for obligate haematophagous species, but not for facultative haematophages. When mite communities on the same host in a location were considered, the negative body mass–abundance relationship was found in only 3 of 44 communities. Nevertheless, a meta‐analytic (across host species) estimate of the slope of this relationship appeared to be significantly negative. No significant relationship between mite body size and host specificity was found in the analyses across all mite species as well as in obligate exclusive or obligate non‐exclusive haematophages. However, the number of hosts used by facultative haematophagous mites decreased significantly with an increase in their body size. We explain the relationships between morphological (body size) and ecological (abundance and niche breadth) properties of ectoparasites by their interactions with hosts or physical environment.     

Body mass–abundance relationships are robust to cascading effects in marine food webs

Body mass has been shown to scale negatively with abundance in a wide range of habitats and ecosystems. It is believed that this relationship has important consequences for the distribution and maintenance of energy in natural communities. Some studies have shown that the relationship between body mass and abundance may be robust to major food web perturbations, fuelling the belief that natural processes may preserve the slope of this relationship and the associated cycling of energy and nutrients. Here, we use data from a long‐term experimental food web manipulation to examine this issue in a semi‐natural environment. Similar communities were developed in large experimental mesocosms over a six month period. Some of the mesocosms were then subjected to species removals, based on the mean strength of their trophic interactions in the communities. In treatments where the strongest interactors were removed, a community‐level trophic cascade occurred. The biomass density of invertebrates increased dramatically in these communities, which led to a suppression of primary production. In spite of these widespread changes in ecosystem functioning, the slope of the relationship between body mass and abundance remained unchanged. This was the case whether average species body mass and abundance or individual organism size spectra were considered. An examination of changes in species composition before and after the experimental manipulations revealed an important mechanism for maintaining the body mass–abundance relationship. The manipulated communities all had a higher species turnover than the intact communities, with the highest turnover in communities that experienced cascading effects. As some species increased in body mass and abundance, new species filled the available size–abundance niches that were created. This maintained the overall body mass–abundance relationship and provided a stabilising structure to these experimental communities.     

Age class differences in the feeding behavior of captive Japanese macaques (Macaca fuscataia) in the forested and nonvegetated enclosure groups

Age class differences in feeding behavior of primates are affected by many factors, including feeding competition, foraging skills, habitat type, food abundance and distribution, body mass, and food types. Two captive groups of Japanese macaques (Macaca fuscata), one housed in a forested enclosure and the other in a nonvegetated enclosure, were studied to examine the effect of environmental enrichment on age class differences in feeding behavior. Although there was no significant age class difference in time spent feeding on provisioned foods in either enclosure, the feeding rate (intake of unit food/minute) of adults consuming provisioned monkey chow was significantly higher than that of immatures in both enclosures, and was faster for both age groups in the nonvegetated than in the forested enclosure. Overall, feeding time was greatly extended for individuals of both age classes in the forested enclosure compared with their counterparts in the nonvegetated enclosure. Immatures in the forested enclosure utilized a significantly greater number of plant species and food items, exploiting many food items available among the terminal branches, and spent significantly more time feeding than adults. Perhaps constrained by larger body size, adults fed more often on the ground or middle height of the trees, likely reducing competition over plant food resources between adults and immatures. The natural vegetation played an important role in extending feeding time and segregating substrate use during feeding by adults and immatures. This study revealed the benefits concerning environmental enrichment of a naturally forested enclosure, which provides captive primates the opportunity to exhibit age class and species-typical feeding behaviors of importance for their dietary maintenance and general health.     

Ecology of a community of mammals in a seasonailly dry forest in Roraima, Brazilian Amazon

A community of middle-sized and larger mammals was studied in a seasonally dry forest in the far north of the Brazilian Amazon. Diurnal and nocturnal surveys were carried out through the linetransect method, in 5 different forest types along a 10-km transect. Data were collected an density, biomass, and use of the forest types, and forest strata by the mammals. The terrestrial community of mammals was more abundant than the arboreal one, with ungulates contributing to the bulk of the biomass, as a result of Maracá being highly seasonal Overall densities were lower than in other sites in the neotropics, varying from 90.2 ind/km² in mixed forest, to 159.9 ind/km² in Terra Firme forest, whereas biomass, due to the contribution of large mammals, was much higher (2613.2 kg/km² in mixed forest, and 4351.6 kg/km² in Terra Firme forest). This study confirms that the animals surviving in larger numbers in these highly seasonal forests, where food productivity may be very low during the dry season, are those that have larger home ranges and travel longer distances in search of food.     

Influence of body size on coexistence of bird species

Theory suggests that body size is an important factor in determining interspecific competition and, ultimately, in structuring ecological communities. However, there is a lack of pragmatic studies linking body size and interspecific competition to patterns in ecological communities. The objective of the present study was to determine the effect of body size (mass) on competitive interactions between bird pairs and to investigate the influence of food guilds. Point-counts were carried out in nine sites every month from November 2002 to November 2003 in the Cuetzalan Region, Mexico, and we used presence/absence and abundance data for the analyses. To calculate the strength of competition we used the Angle Frequency Method to extract form factors from 20 pairwise interactions. A prototype competition interaction and random pairs were also constructed. We used clustering techniques (PCA) to calculate the dissimilarity scores (distances, D) of each of the pairwise interactions to the prototype competition and random pairs and one-way ANOVA to test for differences between the means of the random and competitive pairs. The ratio in body mass (lnBM) for each of the interacting pairs was calculated, and the association between the lnBM ratio and the strength of competition (D) was tested using a Pearson product-moment correlation coefficient. To test for the influence of foraging guilds we used a univariate general linear model. Our results demonstrate a significant negative relationship between bird body mass ratio and competition strength – i.e. competition strength increased when the body masses of the birds became more similar. We did not find a significant influence of foraging guild on the relationship between body mass ratio and competition strength. On the basis of these results, we suggest that high variation in body sizes amongst sympatric species promotes coexistence in communities.     

Brief communication: Hair density and body mass in mammals and the evolution of human hairlessness

Humans are unusual among mammals in appearing hairless. Several hypotheses propose explanations for this phenotype, but few data are available to test these hypotheses. To elucidate the evolutionary history of human “hairlessness,” a comparative approach is needed. One previous study on primate hair density concluded that great apes have systematically less dense hair than smaller primates. While there is a negative correlation between body size and hair density, it remains unclear whether great apes have less dense hair than is expected for their body size. To revisit the scaling relationship between hair density and body size in mammals, I compiled data from the literature on 23 primates and 29 nonprimate mammals and conducted Phylogenetic Generalized Least Squares regressions. Among anthropoids, there is a significant negative correlation between hair density and body mass. Chimpanzees display the largest residuals, exhibiting less dense hair than is expected for their body size. There is a negative correlation between hair density and body mass among the broader mammalian sample, although the functional significance of this scaling relationship remains to be tested. Results indicate that all primates, and chimpanzees in particular, are relatively hairless compared to other mammals. This suggests that there may have been selective pressures acting on the ancestor of humans and chimpanzees that led to an initial reduction in hair density. To further understand the evolution of human hairlessness, a systematic study of hair density and physiology in a wide range of species is necessary. Am J Phys Anthropol 152:145–150, 2013. © 2013 Wiley Periodicals, Inc.     

Primate Group Size and Abundance in the Caatinga Dry Forest, Northeastern Brazil

The Caatinga dry forest poses a series of ecological challenges for mammals in general and primates in particular. The erratic rainfall pattern impacts on plant diversity and phenological patterns; from year to year there is marked variability in fruit production and failure to fruit is common. The harshness apparently accounts for the impoverished mammalian fauna. However, data on primate abundance, distribution, and possible environmental effects on primate density are lacking in this type of dry forest. I censused the primate community in 3 habitats of the Serra da Capivara National Park, Piaui, NE Brazil, over a total distance of 318 km. Overall, the abundance of primates in the Caatinga dry forest is very low as a consequence of low abundance of food resources both in space and time. Alouatta caraya (predominantly folivorous) occurs at extremely low density, and during the dry season are apparently confined to canyon areas, where trees retain their leaves. Callithrix jacchus has morphological feeding specializations for gum-eating, and gum is an important resource during food bottleneck periods. Nonetheless, Callithrix jacchus occurs at comparatively low densities. Group sizes for howlers and marmosets in the Caatinga are significantly smaller than in other forest types. Contrarily, Cebus apella libidinosus had an average group size within the range reported for Amazonian and Atlantic forests. Researchers consider the generalized diet of capuchins as the explanation for their similar abundance in different habitats, indicating relative independence from ecological constraints. However, I suggest that capuchin foraging style and cognitive abilities are important factors accounting for their unreduced group size and density even under extreme conditions.     

An experimental analysis of self-thinning in juvenile steelhead trout

Mobile animal populations have been proposed to decline in density according to a slope based on the allometry of metabolic requirements or space requirements. In salmonid fishes, metabolic rate and food consumption scale to body mass by the exponent 0.87 and 0.73, respectively; whereas the territory size of steelhead trout scales to body mass by the exponent 0.86. Experimental cohorts of juvenile steelhead trout ( Oncorhynchus mykiss ) were used to test the hypothesis that mobile animal populations composed of individuals with indeterminate growth decline in density as a result of self-thinning. After controlling for experimentally manipulated levels of food abundance and stocking density, cohorts of steelhead trout declined in density with increasing body size according to a slope closest to the allometry of food consumption. Densities of steelhead trout were inversely related to average mass by the exponent −0.74. Despite the similarity to the food consumption slope, a relatively wide confidence interval also precluded distinguishing the slope either the metabolic rate or territory size slopes. Data from the literature were also examined to determine if there was general support for the idea of self-thinning in natural populations of stream-dwelling salmonid fish. Although not all data suggest that populations of salmonids in streams decline as a result of density-dependent intraspecific competition, at least some appear to fit the idea of self-thinning; especially when density is above a minimum level of habitat saturation.     

Cell size is positively correlated between different tissues in passerine birds and amphibians,but not necessarily in mammals

We examined cell size correlations between tissues, and cell size to body mass relationships in passerine birds, amphibians and mammals. The size correlated highly between all cell types in birds and amphibians; mammalian tissues clustered by size correlation in three tissue groups. Erythrocyte size correlated well with the volume of other cell types in birds and amphibians, but poorly in mammals. In birds, body mass correlated positively with the size of all cell types including erythrocytes, and in mammals only with the sizes of some cell types. Size of mammalian erythrocytes correlated with body mass only within the most taxonomically uniform group of species (rodents and lagomorphs). Cell volume increased with body mass of birds and mammals to less than 0.3 power, indicating that body size evolved mostly by changes in cell number. Our evidence suggests that epigenetic mechanisms determining cell size relationships in tissues are conservative in birds and amphibians, but less stringent in mammals. The patterns of cell size to body mass relationships we obtained challenge some key assumptions of fractal and cellular models used by allometric theory to explain mass-scaling of metabolism. We suggest that the assumptions in both models are not universal, and that such models need reformulation.     

Ecological scaling laws link individual body size variation to population abundance fluctuation

Scaling research has seen remarkable progress in the past several decades. Many scaling relationships were discovered within and across individual and population levels, such as species–abundance relationship, Taylor's law, and density mass allometry. However none of these established patterns incorporate individual variation in the formulation. Individual body size variation is a key evolutionary phenomenon and closely related to ecological diversity and species adaptation. Using a macroecological approach, I test 57 Long‐Term Ecological Research data sets and show that a power‐law and a generalized power‐law function describe well the mean‐variance scaling of individual body mass. This relationship connects Taylor's law and density mass allometry, and leads to a new scaling pattern between the individual body size variation and population abundance fluctuation, which is confirmed using freshwater fish and forest tree data. Underlying mechanisms and implications of the proposed scaling relationships are discussed. This synthesis shows that integration and extension of existing ecological laws can lead to the discovery of new scaling patterns and complete our understanding of the relation between individual trait and population abundance. Synthesis Scaling relationships are useful for community ecology as they reveal ubiquitous patterns across different levels of biological organizations. This work extends and integrates two existing scaling laws: Taylor's law and density‐mass allometry, and derives a new variance allometry between individual body mass and population abundance. The result shows that diverse individual body size is associated with stable population fluctuation, reflecting the effect of individual traits on population characteristics. Confirmed by several empirical data sets, these scaling relationships suggest new ways to study the underlying mechanisms of Taylor's law and have profound implications for fisheries and other applied sciences.     

Size–abundance relationships in Florida ant communities reveal how ants break the energetic equivalence rule

1. Ants are among the most abundant terrestrial organisms, yet little is known of how ant communities divide resources because it is difficult to measure the number of individuals in colonies and the density of colonies. 2. The body size–abundance relationships of the ants of five upland ecosystems in Florida were examined. The study tested whether abundance, energy use, and total biomass were distributed among species and body sizes as predicted by Damuth's energetic equivalence rule. Estimates of average worker body size, colony size, colony mass, and field metabolic rates were used to examine the relationships among body sizes, energy use, and total biomass. 3. Analyses revealed significant variation in energy use and did not support the energetic equivalence hypothesis. Specifically, the energy use and total standing biomass of species with large workers and colonies was much greater than smaller species. 4. These results suggest that larger species with larger colonies account for a disproportionate fraction of the total abundance and biomass of ants. A general model of resource allocation in colonies provides a possible explanation for why ants do not conform to the predictions of the energetic equivalence rule and for why ants are so abundant.     

Of mice and wrens: the relation between abundance and geographic range size in British mammals and birds

We examine the relation between population size and geographic range size for British breeding birds and mammals. As for most other assemblages studied, a strong positive interspecific correlation is found in both taxa. The relation is also recovered once the phylogenetic relatedness of species has been controlled for using an evolutionary comparative method. The slope of the relation is steeper for birds than for mammals, but this is due in large part to two species of mammals that have much higher population sizes than expected from their small geographic ranges. These outlying mammal species are the only ones in Britain to be found only on small offshore islands, and so may be exhibiting density compensation effects. With them excluded, the slope of the abundance–range size relation for mammals is not significantly different to that for birds. However, the elevation of the relation is higher for mammals than for birds, indicating that mammals are approximately 30 times more abundant than birds of equivalent geographic range size. An earlier study of these assemblages showed that, for a given body mass, bats had abundances more similar to birds than to non-volant mammals, suggesting that the difference in abundance between mammals and birds might be due to constraints of flight. Our analyses show that the abundance–range size relation for bats is not different for that from other mammals, and that the anomalously low abundance of bats for their body mass may result because they have smaller than expected geographic extents for their size. Other reasons why birds and mammals might have different elevations for the relation between population size and geographic range size are discussed, together with possible reasons for why the slopes of these relations might be similar.     

Contrasting effects of habitat fragmentation,population density,and prey availability on body condition of two orb‐weaving spiders

1. Habitat fragmentation is a major threat to biodiversity because it disrupts movement between habitat patches. In addition, arthropod fitness may be reduced in fragmented habitats, e.g. due to reduced prey availability. 2. We studied the relationship of spider body condition with habitat fragmentation, population density, and prey availability. We expected that prey availability and population density of spiders would be affected by landscape composition and patch isolation. Body condition should be enhanced by high prey availability, but negatively affected by population density due to competition. 3. We sampled spiders on 30 groups of cherry trees that varied independently in the level of isolation from other woody habitats and in the percentage of woody habitat within 500 m radius. As a measure of body condition, we used residuals of the relationship between individual body mass/opisthosoma width and prosoma width of the two most common orb‐weaving spider species, Nuctenea umbratica Clerck and Araniella opisthographa Kulczynski. 4. Body condition of A. opisthographa was positively correlated with the abundance of flies, which increased with the percentage of forest in the landscape. In contrast, body condition of N. umbratica was reduced at high population densities, presumably due to intraspecific competition. In addition, body condition and population density of A. opisthographa was lower at isolated sites. 5. Our study suggests that effects of landscape fragmentation on body condition vary strongly between spider species, depending on the relative role of food limitation and intraspecific competition.