Species richness correlates of raw and standardized co‐occurrence metrics

Measuring β‐diversity and changes in species composition across multiple sites and environments is a major research focus in macroecology, and a variety of metrics have been proposed to quantify species co‐occurrence patterns in a species × site occurrence matrix. However, indices of β‐diversity and species co‐occurrence are often statistically dependent on the number of species in an assemblage. We compared the results of several common co‐occurrence metrics with patterns generated by a spatially explicit neutral model simulation. We found that all measures of co‐occurrence and β‐diversity, whether raw, rescaled or standardized by a null model expectation, were highly correlated with the total species richness of the landscape. The one important exception were the effect sizes of the fixed–fixed null model algorithm, which preserves row and column sums of the original matrix during matrix randomization. Our results call for a careful interpretation of meta‐analyses of assemblages that differ widely in species richness. At a minimum, observed species richness should be used as a statistical covariate in regression analyses, and results of the fixed–fixed algorithm should be compared carefully with the results of other randomization tests.     

Land use types influenced avian assemblage structure in a forest–agriculture landscape in Ghana

The conservation of biodiversity within tropical forest regions does not lie only in the maintenance of natural forest areas, but on conservation strategies directed toward agricultural land types within which they are embedded. This study investigated variations in bird assemblages of different functional groups of forest‐dependent birds in three agricultural land types, relative to distance from the interior of 34 tropical forest patches of varying sizes. Point counts were used to sample birds at each study site visited. Data from counts were used to estimate species richness, species evenness, and Simpson's diversity of birds. Mean species richness, evenness, and diversity were modeled as responses and as a function of agricultural land type, distance from the forest interior and three site‐scale vegetation covariates (density of large trees, fruiting trees, and patch size) using generalized linear mixed‐effect models. Mean observed species richness of birds varied significantly within habitat types. Mean observed species richness was highest in forest interior sites while sites located in farm centers recorded the lowest mean species richness. Species richness of forest specialists was strongly influenced by the type of agricultural land use. Fallow lands, density of large trees, and patch size strongly positively influenced forest specialists. Insectivorous and frugivorous birds were more species‐rich in fallow lands while monoculture plantations favored nectarivorous birds. Our results suggest that poor agricultural practices can lead to population declines of forest‐dependent birds particularly specialist species. Conservation actions should include proper land use management that ensures heterogeneity through retention of native tree species on farms in tropical forest‐agriculture landscapes.     

Landscape context affects the relationship between local and landscape species richness of butterflies in semi‐natural habitats

Local species richness of butterflies can be expected to benefit from both local habitat properties as well as the availability of suitable habitats and source populations in the surrounding landscape. Whether local species richness is dependent on local or landscape factors can be assessed by examining the relationship between local and landscape species richness. Here we studied how local species richness is related to landscape‐level species richness in landscapes differing in agricultural intensity. The relationship was linear for field boundaries in intensively cultivated landscapes and non‐linear in less‐intensively cultivated landscapes. In landscapes containing semi‐natural grasslands (on average 4% of overall land‐use), the relationship was non‐linear for field boundaries, but linear when considering local species richness of the grasslands themselves. These results show that local factors are more important than landscape factors in determining local species richness in landscapes which contained semi‐natural grasslands. Local species richness was limited by landscape factors in intensively cultivated landscapes. This interpretation was supported by the relationship between local species richness and landscape‐scale average mobility and generalist percentage of butterfly assemblages. We conclude that the management of field boundary habitat quality for butterflies is expected to be most effective in landscapes with semi‐natural grasslands, the species composition of which in turn is dependent on the regional occurrence of grasslands. Based on our results, managing non‐crop habitats for the conservation of habitat specialists and species with poor mobility will be most efficient in regions where patches of semi‐natural grasslands occur.     

Co‐declining mammal–dung beetle faunas throughout the Atlantic Forest biome of South America

The millennial–scale evolutionary relationships between mammals and dung beetles have been eroded due to several drivers of contemporary biodiversity loss. Although some evidence of co‐decline has been shown for mammals and dung beetles at some Neotropical sites, a biome‐scale analysis for the entire Atlantic Forest of South America would strengthen our understanding of how relictual sets of mammal species can affect dung beetle co‐occurrences and co‐declines. We therefore collated hundreds of assemblages of both dung beetles and medium‐ to large‐bodied mammals throughout the world's longest tropical forest latitudinal gradient to examine to what extent mammal assemblages may exert a positive influence on dung beetle species composition and functional assembly, and whether this relationship is scale dependent. We also collated several climatic and other environmental variables to examine the degree to which they shape mammal–dung beetle relationships. The relationships between local mammal and dung beetle faunas were examined using regression models, variation partitioning, dissimilarity indices and ecological networks. We found a clear positive relationship between mammal and dung beetle species richness across this forest biome, indicating an ongoing process of mammal–dung beetle niche‐mediated co‐decline. We found a strong relationship between the species composition of both taxa, in which dung beetle species dissimilarity apparently track changes in mammalian dissimilarity, typically in 80% of all cases. Co‐variables such as phytomass and climatic variables also influenced mammal–dung beetle patterns of co‐decline along the Atlantic Forest. We conclude that dung beetle diversity and community assembly are shaped by the remaining co‐occurring mammal assemblages and their functional traits, and both groups were governed by environmental features. We emphasize that ecosystem‐wide effects of mammal population declines remain poorly understood both quantitatively and qualitatively, and curbing large vertebrate defaunation will ensure the persistence of co‐dependent species.     

Even the Smallest Non-Crop Habitat Islands Could Be Beneficial: Distribution of Carabid Beetles and Spiders in Agricultural Landscape

Carabid beetles and ground-dwelling spiders inhabiting agroecosystems are beneficial organisms with a potential to control pest species. Intensification of agricultural management and reduction of areas covered by non-crop vegetation during recent decades in some areas has led to many potentially serious environmental problems including a decline in the diversity and abundance of beneficial arthropods in agricultural landscapes. This study investigated carabid beetle and spider assemblages in non-crop habitat islands of various sizes (50 to 18,000 square metres) within one large field, as well as the arable land within the field, using pitfall traps in two consecutive sampling periods (spring to early summer and peak summer). The non-crop habitat islands situated inside arable land hosted many unique ground-dwelling arthropod species that were not present within the surrounding arable land. Even the smallest non-crop habitat islands with areas of tens of square metres were inhabited by assemblages substantially different from these inhabiting arable land and thus enhanced the biodiversity of agricultural landscapes. The non-crop habitat area substantially affected the activity density, recorded species richness and recorded species composition of carabid and ground-dwelling spider assemblages; however, the effects were weakened when species specialised to non-crop habitats species were analysed separately. Interestingly, recorded species richness of spiders increased with non-crop habitat area, whereas recorded species richness of carabid beetles exhibited an opposite trend. There was substantial temporal variation in the spatial distribution of ground-dwelling arthropods, and contrasting patterns were observed for particular taxa (carabid beetles and spiders). In general, local environmental conditions (i.e., non-crop habitat island tree cover, shrub cover, grass cover and litter depth) were better determinants of arthropod assemblages than non-crop habitat island size, indicating that the creation of quite small but diversified (e.g., differing in vegetation cover) non-crop habitat islands could be the most efficient tool for the maintenance and enhancement of diversity of ground-dwelling carabids and spiders in agricultural landscapes.     

Biodiversity of leaf-litter ants in fragmented tropical rainforests of Borneo: the value of publically and privately managed forest fragments

In view of the rapid rate of expansion of agriculture in tropical regions, attention has focused on the potential for privately-managed rainforest patches within agricultural land to contribute to biodiversity conservation. However, these sites generally differ in their history of forest disturbance and management compared with other forest fragments, and more information is required on the biodiversity value of these privately-managed sites, particularly in oil-palm dominated landscapes of SE Asia. Here we address this issue, using tropical leaf-litter ants in rainforest fragments surrounded by mature oil palm plantations in Sabah, Borneo as a model system. We compare the species richness and composition of ant assemblages in privately-managed forest fragments (‘high conservation value’ fragments; HCVs) with those in publically-managed fragments of forest (virgin jungle reserves; VJRs) and control sites in extensive tracts of primary forest. In this way, we test the hypothesis that privately-managed and publically-managed forest fragments differ in their species richness and composition as a result of differences in history and management and hence in habitat quality. In support of this hypothesis, we found that HCVs had much poorer habitat quality than VJRs, including lower sizes and densities of trees, less canopy cover, fewer dipterocarp trees and shallower leaf litter. Consequently, HCVs supported only half the species richness of ants in VJRs, which in turn supported 70 % of the species richness of control sites, with vegetation structure and composition explaining 77 % of the variation among forest fragments in ant species richness. HCVs were also much smaller than VJRs but there was only a weak relationship between fragment size and habitat quality, and species richness was not related to fragment size. VJRs supported 78 % of the 156 species found in extensive tracts of forest whereas HCVs supported only 22 %, which was only slightly higher than the proportion previously recorded in oil palm (19 %). These data support previous findings that publically-managed VJR fragments can make an important contribution to biodiversity conservation within agricultural landscapes. However, we suggest that for these HCVs to be effective as reservoirs of biodiversity, management is required to restore vegetation structure and habitat quality, for instance through enrichment planting with native tree species.     

Butterfly community structure and landscape composition in agricultural landscapes of the central United States

Agricultural landscapes worldwide are under increased pressure to provide food, feed, fiber, and fuel for a growing human population. These demands are leading to changes in agricultural landscapes and subsequent declines in biodiversity. We used citizen science data from the North American Butterfly Association and remotely-sensed land cover data from the US Department of Agriculture to study relationships between agricultural landscape composition and butterfly community structure in the Midwestern US. Landscape-level butterfly species richness (based on rarefaction estimates) was highest in agricultural landscapes with relatively low amounts of cropland, relatively high amounts of woodland, and intermediate amounts of grassland and wetland. Rarefied richness generally declined with the dominance of any of these land cover types. Unlike other land cover types, urban development had a consistent negative effect on rarefied richness. Butterfly community structure (based on relative abundance) was also significantly related to the amount of cropland, woodland, grassland, and wetland in the landscape. The rarest butterfly species were associated with woodland-, grassland-, and wetland-dominated landscapes, likely due to their association with plant species occurring in savannahs, prairies, and marshes, respectively. Assuming that variation across space reflects changes over time, our results support conclusions from previous studies that removal of natural and seminatural habitats alters butterfly community structure and decreases species diversity in agricultural landscapes.     

Comparative effects of urban and agricultural land transformation on Odonata assemblages in a biodiversity hotspot

Rivers of the Cape Floristic Region (CFR) biodiversity hotspot are threatened by land transformation. This region is a centre of endemism for many taxa, including Odonata. These insects are highly sensitive to changes in physical habitat structure, which makes them good bioindicators, and this led to the development of the Dragonfly Biotic Index (DBI). We investigated the effects of local agricultural and urban land transformations on Odonata species richness, assemblage composition and DBI scores in three CFR rivers. A total of 48 sites were selected and categorized as natural, agricultural or urban land use. Adult male Odonata and four environmental variables were recorded over two seasons. Land transformation significantly influenced Odonata assemblage composition but did not always significantly reduce species richness. Average vegetation height also affected Odonata assemblage composition and decreased species richness. Agricultural and urban sites had Odonata assemblages differing from those in the natural areas. Agricultural and urban local land use types reduced opportunities for some endemic species but provided for the persistence and establishment of widespread, generalist species, as indicated by great changes in DBI scores. Mitigating the adverse influences of land transformation through establishment of protected areas is essential for the conservation of rare taxa, particularly in an area with a high number of endemic species.     

Diversity and community composition of butterflies and odonates in an ENSO-induced fire affected habitat mosaic: a case study from East Kalimantan, Indonesia

Little is known about the diversity of tropical animal communities in recently fire‐affected environments. Here we assessed species richness, evenness, and community similarity of butterflies and odonates in landscapes located in unburned isolates and burned areas in a habitat mosaic that was severely affected by the 1997/98 ENSO (El Niño Southern Oscillation) event in east Kalimantan, Indonesian Borneo. In addition related community similarity to variation in geographic distance between sampling sites and the habitat/vegetation structure Species richness and evenness differed significantly among landscapes but there was no congruence between both taxa. The species richness of butterflies was, for example, highest in sites located in a very large unburned isolate whereas odonate species richness was highest in sites located in a small unburned isolate and once‐burned forest. We also found substantial variation in the habitat/vegetation structure among landscapes but this was mainly due to variation between unburned and burned landscapes and variation among burned landscapes. Both distance and environment (habitat/vegetation) contributed substantially to explaining variation in the community similarity (beta diversity) of both taxa. The contribution of the environment was, however, mainly due to variation between unburned and burned landscapes, which contained very different assemblages of both taxa. Sites located in the burned forest contained assemblages that were intermediate between assemblages from sites in unburned forest and sites from a highly degraded slash‐and‐burn area indicating that the burned forest was probably recolonised by species from these disparate environments. We, furthermore, note that in contrast to species richness (alpha diversity) the patterns of community similarity (beta diversity) were highly congruent between both taxa. These results indicate that community‐wide multivariate measures of beta diversity are more consistent among taxa and more reliable indicators of disturbance, such as ENSO‐induced burning, than univariate measures.     

Assembly rules are rare in SE Australian bird communities,but sometimes apply in fragmented agricultural landscapes

Assembly rules have been difficult to observe partly because species interactions vary with resource availability, the amount of disturbance, and species richness. Using bird survey data from two years in five regions of SE Australia (463 sites), we tested six predictions from assembly rules theory. We developed generalised linear models for all pair‐wise species comparisons within a region, after first taking vegetation differences among sites into account. We found: 1) that disturbed and fragmented agricultural landscapes had more negative relationships because aggressive honeyeaters monopolised patches; 2) differences between wet and dry years (high and low resources) were attributed to emigration, immigration, and reduced intensity of negative interactions in the dry year, and not to more intense competition; 3) although negative correlations were expected among ecologically‐similar species, we observed the opposite pattern with significant positive associations in fragmented landscapes; 4) relationships involving aggressive honeyeaters led to more negative relationships as predicted; however, this was only observed in fragmented landscapes and was not significant in every year; 5) in two agricultural landscapes, there were fewer negative relationships in low species‐richness sites, probably because one species from each pair had low abundance. This enabled us to suggest dominance relationships among species pairs; 6) there was evidence of more negative relationships in low‐disturbance sites in agricultural landscapes as predicted. However, instead of the mechanism predicted by theory (reduced disruption allowing assembly processes to approach equilibrium), we suggest that sites with low disturbance represent resources worthy of defence by dominant species. We conclude that bird communities in SE Australia are rarely limited by negative species interactions, although aggressive honeyeaters are a feature of fragmented landscapes. However, diverse mechanisms underlie the temporal and spatial variation in species interactions when they do occur, meaning that simple statements of assembly rules may not be useful in these systems.     

Wasp community responses to habitat complexity in Sydney sandstone forests

Abstract Habitat structure and complexity affect the diversity and composition of fauna in a number of systems. We investigated patterns in wasp species richness, abundance and composition and also their associations with habitat complexity in Sydney sandstone forests, Australia. Pitfall and flight‐intercept traps collected dissimilar wasp assemblages. High complexity habitats supported greater abundance and species richness and a dissimilar composition of pitfall‐trapped wasps to low complexity habitats. Soil moisture, tree canopy cover, ground herb cover and shrub canopy cover all had significant positive associations with the species richness of pitfall‐trapped wasps. Although the five most abundant families of wasps we trapped are endoparasitoids of other arthropods, they showed a variety of preferences for habitat variables. The mechanisms driving associations between habitat complexity and patterns in wasp communities may also provide a basis for understanding factors influencing the regulation of arthropod assemblages by wasps in agricultural and natural landscapes.     

Forest bees are replaced in agricultural and urban landscapes by native species with different phenologies and life‐history traits

Anthropogenic landscapes are associated with biodiversity loss and large shifts in species composition and traits. These changes predict the identities of winners and losers of future global change, and also reveal which environmental variables drive a taxon's response to land use change. We explored how the biodiversity of native bee species changes across forested, agricultural, and urban landscapes. We collected bee community data from 36 sites across a 75,000 km² region, and analyzed bee abundance, species richness, composition, and life‐history traits. Season‐long bee abundance and richness were not detectably different between natural and anthropogenic landscapes, but community phenologies differed strongly, with an early spring peak followed by decline in forests, and a more extended summer season in agricultural and urban habitats. Bee community composition differed significantly between all three land use types, as did phylogenetic composition. Anthropogenic land use had negative effects on the persistence of several life‐history strategies, including early spring flight season and brood parasitism, which may indicate adaptation to conditions in forest habitat. Overall, anthropogenic communities are not diminished subsets of contemporary natural communities. Rather, forest species do not persist in anthropogenic habitats, but are replaced by different native species and phylogenetic lineages preadapted to open habitats. Characterizing compositional and functional differences is crucial for understanding land use as a global change driver across large regional scales.     

Agricultural intensification alters bat assemblage composition and abundance in a dynamic Neotropical landscape

The recent trend of agricultural intensification in tropical landscapes poses a new threat to biodiversity conservation. Conversion of previously heterogeneous agricultural landscapes to intensive plantation agriculture simplifies and homogenizes the landscape, reducing availability, and connectivity of natural habitat for native species. To assess the impact of agricultural intensification on bats, we characterized the bat assemblage in the Sarapiquí region of Costa Rica, where heterogeneous land uses are being converted to intensive, large‐scale pineapple plantations. In 2012 and 2013, we sampled bats in 20 remnant forest patches surrounded by varying proportions of pasture, mature forest, and pineapple and captured 1821 individual bats representing 39 species. We used ordination analyses to evaluate changes in species composition, where pineapple is the main component of the agricultural matrix. We identified landscape metrics specifically correlated with pineapple and used multiple linear regression to test their effects on bat species richness, diversity, and guild‐specific relative abundance. Results suggest pineapple expansion is driving changes in assemblage composition in remnant forest patches, resulting in new assemblages with higher proportions of frugivorous bats and lower proportions of insectivorous bats than in continuous mature forests. In addition, while pineapple does not diminish total bat species richness and diversity, the reduced forest cover and increased distance between forest patches in pineapple plantations has a significant negative impact on the relative abundance of insectivores. We also identify a potential threshold effect whereby patches surrounded by more than 50 percent forest can retain assemblage composition similar to that found in continuous mature forest.     

Using biodiversity deconstruction to disentangle assembly and diversity dynamics of understorey plants along post‐fire succession in boreal forest

Aim The study aims to decipher the co‐occurrence of understorey plant assemblages and, accordingly, to identify a set of species groups (diversity deconstruction) to better understand the multiple causal processes underlying post‐fire succession and diversity patterns in boreal forest. Location North‐eastern Canadian boreal forest (49°07′–51°44′ N; 70°13′–65°15′ W). Methods Data on understorey plant communities and habitat factors were collected from 1097 plots. Species co‐occurrence was analysed using null model analysis. We derive species groups (i.e. biodiversity deconstruction) using the strength of pairwise species co‐occurrences after accounting for random expectation under a null model and cluster analyses. We examine the influence of a set of spatiotemporal environmental variables (overstorey composition, time‐since‐fire, spatial location and topography) on richness of species groups using Bayesian model averaging, and their relative influence through hierarchical partitioning of variance. Results Understorey plant assemblages were highly structured, with co‐occurrence‐based classification providing species groups that were coherently aggregated within, but variably segregated between, species groups. Group richness models indicate both common and distinct responses to factors affecting plant succession. For example, Group 2 (e.g. Rhododendron groenlandicum and Cladina rangiferina) showed concurrent contrasting responses to overstorey composition and was strongly segregated from Groups 3 (e.g. Clintonia borealis and Maianthenum canadense) and 4 (e.g. Epilobium angustifolium and Alnus rugosa). Groups 3 and 4 showed partial similarity, but they differed in their response to time‐since‐fire, drainage and latitude, which were more important for Group 1 (e.g. Ptilium crista‐castrensis and Empetrum nigrum). A single successional model based on total richness masked crucial group‐level relationships with factors that we examined, such as latitude. Main conclusions By demonstrating the co‐occurrence structure and linking to causal factors, the results from this study characterize both common and distinct responses of understorey plants to biophysical attributes of sites, and potential interspecific interactions, behind non‐random assemblage structure during post‐fire succession. A biodiversity deconstruction approach could offer a concise and explicit framework to gain a better understanding of the complex assembly of ecological communities during succession.     

Revisitation of sites surveyed 19 years ago reveals impoverishment of longhorned beetles in natural and planted forests

As planted forests expand in area, they are beginning to dominate landscapes as a matrix and cause the fragmentation of remaining natural forests. To understand and predict the responses of biological assemblages to maturing planted landscapes, examining the effects of forest type (natural vs planted) and forest age on such assemblages is particularly important. Therefore, to document the effects of forest type and age on longhorned beetle assemblages, in 2008 we collected beetles in broad‐leaved natural and cedar planted forests where beetles had also been collected in 1989. Beetle species composition differed greatly between the two forest types in 1989, whereas this difference was less pronounced in 2008. Species richness and total abundance were higher in natural forests than in planted forests in 1989. In 2008, species richness had decreased in both forest types, but the difference between the two forest types had been maintained. Total abundance was also markedly lower in 2008, and the difference between forest types was much smaller. Although larval host plants were not associated with the responses of species to year (forest age or maturation), beetle species whose larvae fed on either broad‐leaved or coniferous trees (or both) exhibited slight preferences for natural forests. These results suggest that longhorned beetle assemblages become impoverished in planted landscapes as the planted matrix matures. Changes in species composition with forest maturation may be difficult to predict based on larval host plants. However, consideration of larval host plants may enable the prediction of changes in species composition caused by the replacement of natural forests by planted forests.     

Plant functional group composition and large‐scale species richness in European agricultural landscapes

Question: Which are the plant functional groups responding most clearly to agricultural disturbances? Which are the relative roles of habitat availability, landscape configuration and agricultural land use intensity in affecting the functional composition and diversity of vascular plants in agricultural landscapes? Location: 25 agricultural landscape areas in seven European countries. Methods: We examined the plant species richness and abundance in 4 km × 4 km landscape study sites. The plant functional group classification was derived from the BIOLFLOR database. Factorial decomposition of functional groups was applied. Results: Natural habitat availability and low land use intensity supported the abundance and richness of perennials, sedges, pteridophytes and high nature quality indicator species. The abundance of clonal species, C and S strategists was also correlated with habitat area. An increasing density of field edges explained a decrease in richness of high nature quality species and an increase in richness of annual graminoids. Intensive agriculture enhanced the richness of annuals and low nature quality species. Conclusions: Habitat patch availability and habitat quality are the main drivers of functional group composition and plant species richness in European agricultural landscapes. Linear elements do not compensate for the loss of habitats, as they mostly support disturbance tolerant generalist species. In order to conserve vascular plant species diversity in agricultural landscapes, the protection and enlargement of existing patches of (semi‐) natural habitats appears to be more effective than relying on the rescue effect of linear elements. This should be done in combination with appropriate agricultural management techniques to limit the effect of agrochemicals to the fields.     

Land‐use history,historical connectivity,and land management interact to determine longleaf pine woodland understory richness and composition

Restoration and management activities targeted at recovering biodiversity can lead to unexpected results. In part, this is due to a lack of understanding of how site‐level characteristics, landscape factors, and land‐use history interact with restoration and management practices to determine patterns of diversity. For plants, such factors may be particularly important since plant populations often exhibit lagged responses to habitat loss and degradation. Here, we assess the importance of site‐level, landscape, and historical effects for understory plant species richness and composition across a set of 40 longleaf pine Pinus palustris woodlands undergoing restoration for the federally endangered red‐cockaded woodpecker in the southeastern United States. Land‐use history had an overarching effect on richness and composition. Relative to historically forested sites, sites with agricultural histories (i.e. former pastures or cultivated fields) supported lower species richness and an altered species composition due to fewer upland longleaf pine woodland community members. Landscape effects did not influence the total number of species in either historically forested or post‐agricultural sites; however, understory species composition was affected by historical connectivity, but only for post‐agricultural sites. The influences of management and restoration activities were only apparent once land‐use history was accounted for. Prescribed burning and mechanical overstory thinning were key drivers of understory composition and promoted understory richness in post‐agricultural sites. In historically forested sites these activities had no impact on richness and only prescribed fire influenced composition. Our findings reveal complex interplays between site‐level, landscape, and historical effects, suggest fundamentally different controls over plant communities in longleaf pine woodlands with varying land‐use history, and underscore the importance of considering land‐use history and landscape effects during restoration.     

Altitudinal variation of dung beetle (Scarabaeidae: Scarabaeinae) assemblages in the Colombian Andes

Aim We describe the changes in species richness, rarity and composition with altitude, and explore whether the differences in Scarabaeinae dung beetle composition along five altitudinal transects of the same mountain range are related to altitude or if there are interregional differences in these altitudinal gradients. Location Field work was carried out on the eastern slope of the eastern Cordillera, Colombian Andes, between Tamá Peak to the north, in the Tamá National Park (07°23′ N, 72°23′ W) and the San Miguel River (00°28′ N, 77°17′ W) to the south. Methods Sampling was carried out between February 1997 and November 1999 in five regions spanning elevation gradients. In each gradient, six sites were chosen at 250 m intervals between 1000 and 2250 m a.s.l. Results We found a curvilinear relationship between altitude and mean species richness, with a peak in richness at middle elevations. However, the diversity of dung beetle assemblages does not seem to be related to the interregional differences in environmental conditions. The number of geographically restricted species is negatively and significantly related to altitude, with geographically restricted species more frequent at low altitude sites. Ordination delimited the two main groups according to altitude: one with all the highest sites (1750–2250 m a.s.l.) and a second group with the remaining sites (< 1750 m a.s.l.). Analysis of species co‐occurrence shows that these dung beetle assemblages seem to be spatially structured when all sites have the same probability of being chosen. In contrast, the spatial structure of species assemblages seems to be random when the probability of choosing any site is proportional to its altitude. Main conclusions The altitude of sites is the main factor that influences the diversity of these dung beetle assemblages. The peak in species richness at middle elevations, the higher number of geographically restricted species at lower altitudinal levels, and the compositional differences along these mountain gradients seem to result from the mixing at these altitudes of dung beetle assemblages that have different environmental adaptations and, probably, different origins. The relevance of altitude in these assemblages is related to the limited role of these Neotropical high altitude environments as centres of refuge and vicariance for a monophyletic group of warm‐adapted species, for which the vertical colonization of these high mountain environments by lineages distributed at lower altitudes would have been very difficult.     

Changes in rain forest butterfly diversity following major ENSO-induced fires in Borneo

Aims Throughout South‐East Asia, droughts associated with ENSO (El Niño Southern Oscillation) events have resulted in large‐scale fires affecting millions of hectares of rain forest. However, the long‐term impacts of these fires on the rain forest faunas are only poorly understood. Our aim was to study the recovery of rain forest butterfly assemblages following the 1997–98 ENSO event, which resulted in the largest‐scale fires in the recorded history of the region. Location A 420‐km² area in the Balikpapan‐Samarinda region of East Kalimantan, Indonesian Borneo. Methods Four landscapes were assessed after the 1997–98 ENSO event, including one landscape that was assessed prior to the event. Comparisons of species richness, species composition and guild abundance were made among landscapes and years. The relative importance of environment, geographical distance between sampling sites, and time between sampling years was quantified during the succession phase using a variance partitioning technique. Results The fires dramatically altered the butterfly community and resulted in a major decline in observed species richness within the landscape surveyed prior to the ENSO event. Following fires in 1998, butterfly assemblages in all landscapes were dominated by large‐winged generalist species. During 1999 and 2000, assemblages became increasingly dominated by smaller specialist species. Species endemic to Borneo that were present before fires were absent in 2000, despite intensive sampling over enhanced spatial and environmental scales. Community similarity was significantly dependent upon local environmental variables, geographical distance between sampling sites, and time between sampling years. Together, these explained over 52% of the observed variation in samples. Conclusions The importance of geographical distance between sampling sites indicates that recovery was dependent upon colonization from proximate habitats. Despite an apparent trend of return to pre‐ENSO community structure, low species richness throughout the survey area indicates that full recovery had not taken place by 2000.     

Host species composition influences infection severity among amphibians in the absence of spillover transmission

Wildlife epidemiological outcomes can depend strongly on the composition of an ecological community, particularly when multiple host species are affected by the same pathogen. However, the relationship between host species richness and disease risk can vary with community context and with the degree of spillover transmission that occurs among co‐occurring host species. We examined the degree to which host species composition influences infection by Batrachochytrium dendrobatidis (Bd), a widespread fungal pathogen associated with amphibian population declines around the world, and whether transmission occurs from one highly susceptible host species to other co‐occurring host species. By manipulating larval assemblages of three sympatric amphibian species in the laboratory, we characterized the relationship between host species richness and infection severity, whether infection mediates growth and survivorship differently across various combinations of host species, and whether Bd is transmitted from experimentally inoculated tadpoles to uninfected tadpoles. We found evidence of a dilution effect where Bd infection severity was dramatically reduced in the most susceptible of the three host species (Anaxyrus boreas). Infection also mediated survival and growth of all three host species such that the presence of multiple host species had both positive (e.g., infection reduction) and negative (e.g., mortality) effects on focal species. However, we found no evidence that Bd infection is transmitted by this species. While these results demonstrate that host species richness as well as species identity underpin infection dynamics in this system, dilution is not the product of reduced transmission via fewer infectious individuals of a susceptible host species. We discuss various mechanisms, including encounter reduction and antagonistic interactions such as competition and opportunistic cannibalism that may act in concert to mediate patterns of infection severity, growth, and mortality observed in multihost communities.