Depth and temperature drive patterns of spatial overlap among fish thermal guilds in lakes across Ontario,Canada

Aim

The spatial distribution of ectotherms is strongly dependent on the temperature of their environments. In temperate lakes, fishes with different thermal optima can become spatially segregated during summer stratification. This habitat partitioning, or niche complementarity, may play a role in the coexistence of trophically similar species; however, the extent of partitioning is dependent on the resources available within each habitat. Although habitat partitioning of fish thermal guilds has been studied in individual lakes, broad-scale patterns of spatial overlap and segregation are not yet understood. In this study, we explore the patterns and drivers of spatial overlap among thermal guilds (cold-, cool-, and warm-water) at a broad scale.

Location

Ontario, Canada.

Methods

We built a multivariate regression tree to explore patterns and environmental drivers of spatial overlap in freshwater fishes across three thermal guilds from 438 lakes.

Results

We identified five clusters of lakes exhibiting different patterns of spatial overlap among the three thermal guilds. Temperature (growing degree days) and maximum lake depth were strong drivers of the spatial overlap patterns.

Main Conclusions

These findings provide a better understanding of broad-scale patterns of spatial overlap and allow us to predict how spatial overlap, and ultimately species interactions and competition, may change under a warming climate.     

Interannual variation in reproductive phenology in a riverine fish assemblage: implications for predicting the effects of climate change and altered flow regimes

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Dung burial strategies in some South African coprine and onitine dung beetles (Scarabaeidae: Scarabaeinae)

ABSTRACT.

• 1 The dung colonization and dung burial behaviour of twelve crepuscular/nocturnal tunnelling (paracoprid) species of beetles were examined in order to identify mechanisms which might facilitate resource (dung) partitioning. The species were selected from a diverse assemblage of dung beetles, the members of which coexist in the sandy-soil regions of Natal, South Africa.
• 2 The pattern of dung colonization in relation to dung age was examined in the field using baited pitfall traps. Some species, e.g. Onitis deceptor Peringuey, Catharsius tricornutus De Geer and Copris elphenor Klug, showed a marked preference for fresh dung (1–2 days old) whereas other species, e.g. O. viridulus Boheman and Copris fallaciosus Gillet, preferred older dung (3–7 days old).
• 3 Two distinct patterns of dung burial were recognized. In the Coprini, dung burial was complete within 24–48h of pad colonization, and the level of dung burial was similar in the laboratory and in the field. In the Onitini, dung burial occurred progressively over a 12-day period, although the timing of initiation of dung burial varied between species: in O. deceptor nearly all individuals had begun burial within 2 days of pad colonization, whereas only 20% of O. viridulus had commenced dung burial by that time. However, nearly all O. viridulus had buried substantial quantities of dung by day 12.
• 4 The mass of dung buried per pair by the larger coprine beetles (100–300 g) and onitine beetles (400–1000 g) suggests that there is potential for inter- and intraspecific competition, even in pads colonized by relatively few beetles. The colonization and use of dung of different ages are discussed as means of resource partitioning in relation to the relative abilities of species to compete for dung.

     

Community structure of a Neotropical bat fauna as revealed by stable isotope analysis: Not all species fit neatly into predicted guilds

Neotropical bat communities are among the most diverse mammal communities in the world, and a better understanding of these assemblages may permit inferences about how so many species coexist. While broad trophic guilds (e.g., frugivore, insectivore) of bats are recognized, details of diet and similarities among species remain largely unknown. We used stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) to characterize the community structure of a diverse Neotropical bat fauna from Belize to test predictions of niche theory and the competitive exclusion principle. We predicted that (1) interspecific variation in isotopic overlap would be greater within guilds than between guilds, and (2) no two sympatric populations would have isotopic niches that overlap completely, unless there is variation along some other axis (e.g., temporal, spatial). We additionally tested body size as an explanatory metric of potential overlap and predicted that larger‐bodied animals would have greater niche breadths. Results suggest that while guild‐level characterizations of communities are at least somewhat informative, there are multiple examples of intra‐ and inter‐guild species pairs with significantly overlapping isotopic niches, suggesting that, counter to predictions, they may compete for resources. Understanding the trophic structure of animal communities is fundamental to conservation and management of endangered species and ecosystems and important for evolutionary studies, and stable isotope analyses can provide key insights as well as informing hypotheses of the diet of species that are not well known. Abstract in Spanish is available with online material.     

Temporal and spatial metabolic rate variation in the Antarctic springtail Gomphiocephalus hodgsoni

Spatial and temporal environmental variation in terrestrial Antarctic ecosystems are known to impact species strongly at a local scale, but the ways in which organisms respond (e.g. physiologically, behaviourally) to such variation are poorly understood. Further, very few studies have attempted to assess inter-annual variability of such responses.Building on previous work demonstrating intra-seasonal variation in standard metabolic rate in the springtail Gomphiocephalushodgsoni, we investigated variation in metabolic activity of G. hodgsoni across two austral summer periods at Cape Bird, Ross Island. We also examined the influence of spatial variation by comparing metabolic rates of G. hodgsoni at Cape Bird with those from two other isolated continental locations within Victoria Land (Garwood and Taylor Valleys).We found significant differences between metabolic rates across the 2 years of measurement at Cape Bird. In addition, standard metabolic rates of G. hodgsoni obtained from Garwood and Taylor Valleys were significantly higher than those at Cape Bird where habitats are comparable, but environmental characteristics differ (e.g. microclimatic temperatures are higher).We discuss potential underlying causes of these metabolic rate variation patterns, including those related to differences among individuals (e.g. physiological and genetic differences), locations (e.g. habitat quality and microclimatic regime differences) and populations (e.g. acclimation differences among G. hodgsoni populations in the form of metabolic cold adaptation (MCA)).     

Competition and coexistence in a small carnivore guild

The potential for strong competition among small sympatric carnivores results in a need for coexistence strategies whereby competitors partition along spatial, temporal and dietary axes as a means to reduce ecological overlaps. We determined spatial and temporal partitioning patterns of a guild of small African carnivores: the African wildcat Felis silvestris lybica, grey mongoose Galerella pulverulenta, small-spotted genet Genetta genetta, striped polecat Ictonyx striatus, and the yellow mongoose Cynictis penicillata. We quantified the degree of spatial and temporal co-occurrence of the small carnivores using camera trap data over a year-long period. Carnivores separated into two temporal groups: nocturnal species (wildcat, polecat and genet) and diurnal species (mongooses). In addition, carnivores within the same temporal group had strong patterns of reduced spatial co-occurrence. The smaller bodied carnivores showed lower co-occurrence with the larger bodied African wildcat than expected by chance, supporting the idea of dominant competitor avoidance. Thus, small carnivores likely minimise competitive interactions through spatio-temporal habitat partitioning.     

Detecting signatures of competition from observational data: a combined approach using DNA barcoding,diversity partitioning and checkerboards at small spatial scales

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Dung beetles in continuous forest, forest fragments and in an agricultural mosaic habitat island at Los Tuxtlas, Mexico

With the aim of determining what kind of landscape mosaics might sustainmaximum diversity and minimum species loss, dung beetles were sampled withbaited pitfall traps to compare species richness and species composition in atract of continuous forest, forest fragments and a habitat island consisting ofa mosaic of forest and arboreal crops in Los Tuxtlas, southern Mexico. Wecaptured 7332 dung beetles representing 33 species. Similar numbers of specieswere captured in the three habitats. However, 56% of individuals were capturedin the continuous forest, 29% in the mosaic habitat and 15% in the forestfragments. Eight species (Canthon femoralis,Copris laeviceps, Canthidium centrale,Onthophagus batesi, Deltochilumpseudoparile, O. rhinolophus, Canthonviridis vazquezae and Dichotomius satanus) accounted for 90% of thecaptures, but their relative dominance varied among habitats. A clear trend wasevident in the number of dung beetles captured in the dung processing guilds(rollers/tunnelers) as well as in the diurnal and nocturnal guilds, withcaptures decreasing from the continuous forest to the mosaic habitat to theforest fragments. A similar trend was detected in detection rates for medium andsmall size dung producing mammals. Species richness of forest fragments andmosaic habitat did not differ from that found in the continuous forest, butthese habitats differ significantly in species richness from isolated shaded andunshaded plantations, linear strips of vegetation, the forest–pasture edge andpastures according to rarefaction analysis. The co-occurrence of the continuousforest, the mosaic habitat and the cluster of forest fragments in closeproximity seems to be preserving a diverse assemblage of dung beetle species inthe local landscape.     

Spatial and temporal distribution of tadpole assemblages (Amphibia,Anura) in a seasonal dry tropical forest of southeastern Brazil

We determined spatial and temporal distribution of tadpoles in 11 breeding habitats from Morro do Diabo State Park (MDSP), southeastern Brazil. Breeding habitats occupancy by tadpoles was tested to be different from a null model of random placement of species. We also tested whether tadpole occupancy in a given breeding habitat is organized according to different ecomorphological guilds, and we analyzed spatial partitioning of tadpoles among breeding habitats through similarity analysis. For temporal analysis we analyzed temporal partitioning of tadpole monthly occurrence also using similarity analysis, and assessed what climatic variable better predicts tadpole temporal occurrence in the MDSP, through regression analysis. Among tadpoles from 19 anuran species, distribution was different from a null model, but co-occurrence patterns among the breeding habitats did not differ among different guilds. However, breeding habitats with similar hydroperiods had similar species composition, which may be related to the reproduction patterns of species. Among the three climatic variables analyzed (rainfall, temperature, and photoperiod), temporal occurrence of monthly tadpole richness and abundance was correlated with temperature and rainfall. Most species were found only during the rainy season months, and overlap occurred within three groups of species. Thus, temporal distribution does not seem to be an important mechanism in species segregation at the MDSP, where the dry season is pronounced. In this case, spatial partitioning tends to be more important for species coexistence.     

Negative Density Dependence Regulates Two Tree Species at Later Life Stage in a Temperate Forest

Numerous studies have demonstrated that tree survival is influenced by negative density dependence (NDD) and differences among species in shade tolerance could enhance coexistence via resource partitioning, but it is still unclear how NDD affects tree species with different shade-tolerance guilds at later life stages. In this study, we analyzed the spatial patterns for trees with dbh (diameter at breast height) ≥2 cm using the pair-correlation g(r) function to test for NDD in a temperate forest in South Korea after removing the effects of habitat heterogeneity. The analyses were implemented for the most abundant shade-tolerant (Chamaecyparis obtusa) and shade-intolerant (Quercus serrata) species. We found NDD existed for both species at later life stages. We also found Quercus serrata experienced greater NDD compared with Chamaecyparis obtusa. This study indicates that NDD regulates the two abundant tree species at later life stages and it is important to consider variation in species'' shade tolerance in NDD study.     

Dung beetle persistence in human-modified landscapes: Combining indicator species with anthropogenic land use and fragmentation-related effects

Identifying and making use of ecological indicators becomes an essential task in the conservation of tropical systems, mainly in fragmented landscapes where land use intensification and habitat loss are confounding factors in the detection of species’ responses to human-caused disturbance. We aimed to analyze the importance of anthropogenic land use and fragmentation-related effects on dung beetle (Coleoptera: Scarabaeinae) persistence according to the interior–exterior non-linear gradient (forest + matrix) in a fragmented Atlantic Forest landscape used to sugar cane production and cattle ranching/farming. We offer scores for a comprehensive set of community-level attributes, from beetle abundance to taxonomic and ecological composition (i.e. species body size), including a list of indicator species of different forest habitats and adjacent matrix. Dung beetles were surveyed by traps across forest interiors (i.e. core forest areas) and edges of a primary forest, small fragments, sugar cane fields and pastures in a total of 60 sites. Indicator analyses were conducted across the landscape, using two well-established methods (IndVal and SIMPER). Our results suggest that (1) cross-habitat taxonomic distinctness is associated with the presence of indicator species, (2) some species benefit or are dependent of open habitats created by human-disturbances, such as forest edges (e.g. Canthon nigripennis) and matrices (e.g. Canthon aff. piluliformis, Dichotomius nisus and Trichilum externepunctatum), (3) although landscape habitats exhibit reduced beta diversity, dung beetle assemblages are spatially organized in response to the presence of both forest habitats and matrix and fragment area, (4) forest interior supports beetle assemblages biased toward large-bodied species, (5) accordingly forest interior, forest edges and matrix support taxonomically distinct assemblages, both contributing to the bulk of species richness at landscape level, (6) the response of dung beetles to the interior–exterior non-linear gradient (i.e. forest edge + matrix) reveals a similar pattern regardless of the nature of the matrix, and (7) there is no within-habitat variation in beetle abundance and species richness associated with distance from forest edge. Given that there is a high number of forest-dependent or forest-interior specialist species (e.g. Aphengium aff. sordidum, Ateuchus aff. alipioi, Dichotomius mormon, Ontherus aff. erosus and Onthophagus aff. clypeatus) dung beetle persistence in human-modified landscape is highly dependent on the presence of core areas, although edge-affected and matrix habitats may be complementary. This information is essential to permit a better prospect for dung beetle persistence in human-modified landscapes as they continue to move toward edge-dominated landscapes with intensively managed matrices.     

Scale-Dependence of Processes Structuring Dung Beetle Metacommunities Using Functional Diversity and Community Deconstruction Approaches

Community structure is driven by mechanisms linked to environmental, spatial and temporal processes, which have been successfully addressed using metacommunity framework. The relative importance of processes shaping community structure can be identified using several different approaches. Two approaches that are increasingly being used are functional diversity and community deconstruction. Functional diversity is measured using various indices that incorporate distinct community attributes. Community deconstruction is a way to disentangle species responses to ecological processes by grouping species with similar traits. We used these two approaches to determine whether they are improvements over traditional measures (e.g., species composition, abundance, biomass) for identification of the main processes driving dung beetle (Scarabaeinae) community structure in a fragmented mainland-island landscape in southern Brazilian Atlantic Forest. We sampled five sites in each of four large forest areas, two on the mainland and two on the island. Sampling was performed in 2012 and 2013. We collected abundance and biomass data from 100 sampling points distributed over 20 sampling sites. We studied environmental, spatial and temporal effects on dung beetle community across three spatial scales, i.e., between sites, between areas and mainland-island. The γ-diversity based on species abundance was mainly attributed to β-diversity as a consequence of the increase in mean α- and β-diversity between areas. Variation partitioning on abundance, biomass and functional diversity showed scale-dependence of processes structuring dung beetle metacommunities. We identified two major groups of responses among 17 functional groups. In general, environmental filters were important at both local and regional scales. Spatial factors were important at the intermediate scale. Our study supports the notion of scale-dependence of environmental, spatial and temporal processes in the distribution and functional organization of Scarabaeinae beetles. We conclude that functional diversity may be used as a complementary approach to traditional measures, and that community deconstruction allows sufficient disentangling of responses of different trait-based groups.     

Do vegetation patch spatial patterns disrupt the spatial organization of plant species?

The mechanisms that structure plant diversity and generate long-range correlated spatial patterns have important implications for the conservation of fragmented landscapes. The ability to disperse and persist influences a plant species’ capacity for spatial organization, which can play a critical role in structuring plant diversity in metacommunities. This study examined the spatial patterns of species diversity within a network of patches in Cabo de Gata Natural Park, southeastern Spain. The objectives were to understand how the spatial heterogeneity of species composition (beta diversity) varies in a structured landscape, and how the long-range spatial autocorrelation of plant species is affected by the spatial configuration of patches.The mechanisms underlying the spatial distribution of plants acted at two scales. Between patches, spatial variation in species distributions was greater than that expected based on spatial randomization, which indicated that movement among patches was restricted. Within patches, diffusion processes reduced spatial variability in species distributions, and the effect was more prominent in large patches. Small patch size negatively influenced the long-range spatial autocorrelation of characteristic species, whereas inter-patch distance had a stronger effect on species frequency than it had on the disruption of spatial organized patterns.The long-range spatial autocorrelation was evaluated based on the dispersal abilities of the species. Among the 106 species evaluated, 39% of the woody species, 17% of the forbs, and 12% of the grasses exhibited disrupted long-range spatial autocorrelation where patches were small. The species that are more vulnerable to the effects of fragmentation tended to be those that have restricted dispersal, such as those that have short-range dispersal (atelechoric), e.g., Phlomis purpurea, Cistus albidus, Teucrium pseudochamaepytis, Brachypodium retusum, and the ballistic species, Genista spartioides. Helianthemum almeriense is another vulnerable species that has actively restricted dispersal (antitelechory), which is common in arid regions. Wind dispersers such as Launaea lanifera were less vulnerable to the effects of fragmentation. Long-distance dispersers whose persistence depends on facilitative interactions with other individuals, e.g., allogamous species such as Thymus hyemalis, Ballota hirsuta, and Anthyllis cytisoides, exhibit disrupted long-range spatial autocorrelation when patch size is reduced.     

Oribatid mites reveal that competition for resources and trophic structure combine to regulate the assembly of diverse soil animal communities

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The effect of the dung pad fauna on the emergence ofMusca tempestiva [Dipt.: Muscidae] from dung pads in southern France

The emergence ofMusca tempestiva Fallèn, from cow pads in southern France was reduced by a mean of 98% and 96% respectively in nine experiments concluded in 1979 and 1981, by the action of the complete dung fauna. Fauna emerging from dung pads and captured in simultaneous trapping using dung baited pitfall traps consisted of 13 Dipterous species (9 Muscidae, 2 Sepsidae and 2 Sphaeroceridae), 25 Coleopterous species (7 Scarabaeidae, 1 Geotrupidae, 2 Aphodiidae, 3 Hydrophilidae, 12 Staphylinidae), 3 Hymenopterous parasites and 1 species of macrochelid and 2 species of parasitoid mites carried phoretically by the dung beetles. The total number of insects and mites per trap was usually small. The Staphylinidae which included 4Aleochara species of whichAleochara tristits Gravenhorst andA. bipustulata (L.) are known parasitoids of Diptera pupae, and 6 predatory species, were the most abundant insects present. Whilst the overall abundance of insects and mites trapped was relatively low it is probable that the most important factor in the control ofM. tempestiva was the combined influence of the different elements making up the dung pad fauna.     

Large-scale spatial ecology of dung beetles

Recent modelling work shows that the composition of local communities can be influenced by the configuration of the surrounding landscape, but many of these models assume that all community members display the same type of extinction‐colonization dynamics. I use Aphodius dung beetles to test the hypothesis that interspecific differences in habitat selection and dispersal capacity may translate into differences in spatial population dynamics, even among closely related species coexisting on the same resource. If this is true, then groups of species with different characteristics would show different responses to landscape configuration. I first divided the area of Finland into a grid, and used collection records to describe regional variation in the Aphodius fauna of open cattle pastures. I then sampled dung beetles on 131 cattle farms, to examine whether the subset of species found on each farm was related to the density of pastures in the surrounding grid square. Finally, I used historical records to analyze changes in dung beetle communities during the last century, when there was great loss of pasture. Overall, I found no relationship between landscape characteristics and the total proportion of the regional species pool that was found on each farm. However, the distribution of species among guilds with different habitat specificity did relate to the configuration of the landscape, and the pattern was most pronounced in a specialists species with limited dispersal. Associations between community structure and landscape configuration were superimposed on two much larger and stronger patterns: a large‐scale latitudinal gradient in regional species richness, and a decelerating gain of species to local communities with an increasing regional species pool. I conclude that ecological variation among community members is a crucial factor in the analysis of local community composition, and that local species richness should always be conditioned on regional richness.     

Wood Specific Gravity Variations and Biomass of Central African Tree Species: The Simple Choice of the Outer Wood

Context

Wood specific gravity is a key element in tropical forest ecology. It integrates many aspects of tree mechanical properties and functioning and is an important predictor of tree biomass. Wood specific gravity varies widely among and within species and also within individual trees. Notably, contrasted patterns of radial variation of wood specific gravity have been demonstrated and related to regeneration guilds (light demanding vs. shade-bearing). However, although being repeatedly invoked as a potential source of error when estimating the biomass of trees, both intraspecific and radial variations remain little studied. In this study we characterized detailed pith-to-bark wood specific gravity profiles among contrasted species prominently contributing to the biomass of the forest, i.e., the dominant species, and we quantified the consequences of such variations on the biomass.

Methods

Radial profiles of wood density at 8% moisture content were compiled for 14 dominant species in the Democratic Republic of Congo, adapting a unique 3D X-ray scanning technique at very high spatial resolution on core samples. Mean wood density estimates were validated by water displacement measurements. Wood density profiles were converted to wood specific gravity and linear mixed models were used to decompose the radial variance. Potential errors in biomass estimation were assessed by comparing the biomass estimated from the wood specific gravity measured from pith-to-bark profiles, from global repositories, and from partial information (outer wood or inner wood).

Results

Wood specific gravity profiles from pith-to-bark presented positive, neutral and negative trends. Positive trends mainly characterized light-demanding species, increasing up to 1.8 g.cm^-3 per meter for Piptadeniastrum africanum, and negative trends characterized shade-bearing species, decreasing up to 1 g.cm^-3 per meter for Strombosia pustulata. The linear mixed model showed the greater part of wood specific gravity variance was explained by species only (45%) followed by a redundant part between species and regeneration guilds (36%). Despite substantial variation in wood specific gravity profiles among species and regeneration guilds, we found that values from the outer wood were strongly correlated to values from the whole profile, without any significant bias. In addition, we found that wood specific gravity from the DRYAD global repository may strongly differ depending on the species (up to 40% for Dialium pachyphyllum).

Main Conclusion

Therefore, when estimating forest biomass in specific sites, we recommend the systematic collection of outer wood samples on dominant species. This should prevent the main errors in biomass estimations resulting from wood specific gravity and allow for the collection of new information to explore the intraspecific variation of mechanical properties of trees.     

The finely defined shift work schedule of dung beetles and their eye morphology

In nature, nothing is wasted, not even waste. Dung, composed of metabolic trash and leftovers of food, is a high‐quality resource and the object of fierce competition. Over 800 dung beetle species (Scarabaeinae) compete in the South African dung habitat and more than 100 species can colonize a single dung pat. To coexist in the same space, using the same food, beetles divide the day between them. However, detailed diel activity periods and associated morphological adaptations have been largely overlooked in these dung‐loving insects. To address this, we used a high‐frequency trapping design to establish the diel activity period of 44 dung beetle species in their South Africa communities. This allowed us to conclude that the dung beetles show a highly refined temporal partitioning strategy, with differences in peak of activity even within the diurnal, crepuscular, and nocturnal guilds, independent of nesting behavior and taxonomic classification. We further analyzed differences in eye and body size of our 44 model species and describe their variability in external eye morphology. In general, nocturnal species are bigger than crepuscular and diurnal species, and as expected, the absolute and relative eye size is greatest in nocturnal species, followed by crepuscular and then diurnal species. A more surprising finding was that corneal structure (smooth or facetted) is influenced by the activity period of the species, appearing flat in the nocturnal species and highly curved in the diurnal species. The role of the canthus—a cuticular structure that partially or completely divides the dung beetle eye into dorsal and ventral parts—remains a mystery, but the large number of species investigated in this study nevertheless allowed us to reject any correlation between its presence and the nesting behavior or time of activity of the beetles.     

Niche Partitioning of Feather Mites within a Seabird Host, Calonectris borealis

According to classic niche theory, species can coexist in heterogeneous environments by reducing interspecific competition via niche partitioning, e.g. trophic or spatial partitioning. However, support for the role of competition on niche partitioning remains controversial. Here, we tested for spatial and trophic partitioning in feather mites, a diverse and abundant group of arthropods. We focused on the two dominant mite species, Microspalax brevipes and Zachvatkinia ovata, inhabiting flight feathers of the Cory’s shearwater, Calonectris borealis. We performed mite counts across and within primary and tail feathers on free-living shearwaters breeding on an oceanic island (Gran Canaria, Canary Islands). We then investigated trophic relationships between the two mite species and the host using stable isotope analyses of carbon and nitrogen on mite tissues and potential host food sources. The distribution of the two mite species showed clear spatial segregation among feathers; M. brevipes showed high preference for the central wing primary feathers, whereas Z. ovata was restricted to the two outermost primaries. Morphological differences between M. brevipes and Z. ovata support an adaptive basis for the spatial segregation of the two mite species. However, the two mites overlap in some central primaries and statistical modeling showed that Z. ovata tends to outcompete M. brevipes. Isotopic analyses indicated similar isotopic values for the two mite species and a strong correlation in carbon signatures between mites inhabiting the same individual host suggesting that diet is mainly based on shared host-associated resources. Among the four candidate tissues examined (blood, feather remains, skin remains and preen gland oil), we conclude that the diet is most likely dominated by preen gland oil, while the contribution of exogenous material to mite diets is less marked. Our results indicate that ongoing competition for space and resources plays a central role in structuring feather mite communities. They also illustrate that symbiotic infracommunities are excellent model systems to study trophic ecology, and can improve our understanding of mechanisms of niche differentiation and species coexistence.