Host specificity and the distribution-abundance relationship in a community of parasites infecting fishes in streams of North Carolina

A positive relationship between distribution and local abundance is often observed among species in a community. The resource-breadth hypothesis suggests that this pattern is the result of differential abilities among species to utilize available resources, such that generalists are widely distributed and locally abundant, and specialists are narrowly distributed and locally sparse. This hypothesis was tested in a community consisting of 22 species or morphospecies of parasites infecting members of 18 species of fish among 14 sites in 7 small streams in the Appalachian Mountains of North Carolina. A positive relationship between distribution (fraction of sites occupied) and abundance (average local abundance) was evident among parasite species. The number of host species infected by each parasite species was positively related to both distribution and average local abundance; both relationships held after statistical removal of the distribution and abundance of the hosts, respectively. These results support the resource-breadth hypothesis as an explanation for the distribution-abundance relationship in this system.     

Abundance-occupancy dynamics in a human dominated environment: linking interspecific and intraspecific trends in British farmland and woodland birds

1. Range size, population size and body size, the key macroecological variables, vary temporally both within and across species in response to anthropogenic and natural environmental change. However, resulting temporal trends in the relationships between these variables (i.e. macroecological patterns) have received little attention. 2. Positive relationships between the local abundance and regional occupancy of species (abundance-occupancy relationships) are among the most pervasive of all macroecological patterns. In the absence of formal predictions of how abundance-occupancy relationships may vary temporally, we outline several scenarios of how changes in abundance within species might affect interspecific patterns. 3. We use data on the distribution and abundance of 73 farmland and 55 woodland bird species in Britain over a 32-year period encompassing substantial habitat modification to assess the likelihood of these scenarios. 4. In both farmland and woodland habitats, the interspecific abundance-occupancy relationship changed markedly over the period 1968-99, with a significant decline in the strength of the relationship. 5. Consideration of intraspecific dynamics shows that this has been due to a decoupling of abundance and occupancy particularly in rare and declining species. Insights into the intraspecific processes responsible for the interspecific trend are obtained by analysis of temporal trends in the distribution of individuals between sites, which show patterns consistent with habitat quality declines. 6. This study shows that a profitable approach to ascertaining the nature of human impacts is to link intra- and interspecific processes. In the case of British farmland and woodland birds, changes to the environment lead to species-specific responses in large-scale distributions. These species-specific changes are the driver of the observed changes in the form and strength of the interspecific relationship.     

长白山阔叶红松林物种多度和空间分布格局的关系

应用随机分布多度模型和聚集分布多度模型,探讨不同研究尺度下物种多度和空间分布格局的关系.结果表明,预测的物种多度不仅受物种分布面积大小的影响,还受其聚集程度的影响.物种多度和空间分布格局的关系存在着明显的尺度效应,即随着研究尺度的增加,无论是随机分布多度模型还是聚集分布多度模型,通过物种空间分布格局来预测物种多度的准确度都在下降.聚集分布多度模型预测物种多度的结果要好于随机分布多度模型,这表明该区大多数物种是聚集分布的.由于物种的空间分布格局不同,不同物种多度的预测值和真实值之间的差异也不同.因此,为了进一步提高模型预测的准确性,进一步考虑不同物种的生活史特性是必要的.     

Effects of habitat characteristics and interspecific interactions on co-occurrence patterns of saproxylic beetles breeding in tree boles after forest fire: null model analyses

It is often suggested that habitat attributes and interspecific interactions can cause non-random species co-occurrence patterns, but quantifying their contributions can be difficult. Null models that systematically exclude and include habitat effects can give information on the contribution of these factors to community assembly. In the boreal forest, saproxylic beetles are known to be attracted to recently burned forests where they breed in dead and dying trees. We examined whether species co-occurrences of saproxylic beetles that develop in, and emerge from, boles of recently burned trees show non-random patterns. We also estimated the extent to which both the post-fire habitat attributes and interspecific interactions among beetles contribute to such patterns. We sampled tree boles encompassing key attributes (tree species, tree size/dbh and burn severity) that are thought to characterize species–habitat associations of saproxylic beetles, a proposition that we tested using indicator species analysis. Two null models with no habitat constraints (“unconstrained”) indicated that a total of 29.4% of the species pairs tested had significant co-occurrence patterns. Habitat-constrained null models indicated that most of the detected species aggregations (72%) and segregations (59%) can be explained by shared and distinct species–habitat relationships, respectively. The assembly pattern was also driven by interspecific interactions, of which some were modulated by habitat; for example, predator and prey species tended to co-occur in large-sized trees (a proxy of available bark/wood food resource primarily for the prey). In addition, some species segregation suggesting antagonistic, competitive, or prey–predator interactions were evident after accounting for the species’ affinities for the same tree species. Overall, our results suggest that an intimate link between habitat and interspecific interactions can have important roles for community assembly of saproxylic assemblages even following disturbance by fire. We also show that a systematic application of null models can offer insight into the mechanisms behind the assembly of ecological communities.     

Does interspecific competition drive patterns of habitat use in desert bat communities?

Bodies of water are a key foraging habitat for insectivorous bats. Since water is a scarce and limiting resource in arid environments, bodies of open water may have a structuring effect on desert bat communities, resulting in temporal or spatial partitioning of bat activity. Using acoustic monitoring, we studied the spatial and temporal activity patterns of insectivorous bats over desert ponds, and hypothesised that sympatric bat species partition the foraging space above ponds based on interspecific competitive interactions. We used indirect measures of competition (niche overlap and competition coefficients from the regression method) and tested for differences in pond habitat selection and peak activity time over ponds. We examined the effect of changes in the activity of bat species on their potential competitors. We found that interspecific competition affects bat community structure and activity patterns. Competing species partitioned their use of ponds spatially, whereby each species was associated with different pond size and hydroperiod (the number of months a pond holds water) categories, as well as temporally, whereby their activity peaked at different hours of the night. The drying out of temporary ponds increased temporal partitioning over permanent ponds. Differences in the activity of species over ponds in response to the presence or absence of their competitors lend further support to the role of interspecific competition in structuring desert bat communities. We suggest that habitat use and night activity pattern of insectivorous bats in arid environments reflect the trade-offs between selection of preferred pond type or activity time and constraints posed by competitive interactions.     

Fine-scale structure and cross-taxon congruence of bird and beetle assemblages in an old-growth boreal forest mosaic

Aim Nestedness occurs when species present in depauperate sites are subsets of those found in species‐rich sites. The degree of congruence of site nestedness among different assemblages can inform commonalities of mechanisms structuring the assemblages. Well‐nested assemblages may still contain idiosyncratic species and sites that notably depart from the typical assemblage pattern. Idiosyncrasy can arise from multiple processes, including interspecific interactions and habitat preferences, which entail different consequences for species co‐occurrences. We investigate the influence of fine‐scale habitat variation on nestedness and idiosyncrasy patterns of beetle and bird assemblages. We examine community‐level and pairwise species co‐occurrence patterns, and highlight the potential influence of interspecific interactions for assemblage structure. Location Côte‐Nord region of Québec, Canada. Methods We sampled occurrences of ground‐dwelling beetles, flying beetles and birds at sites within old‐growth boreal forest. We examined the nestedness and idiosyncrasy of sites and sought relationships to habitat attributes. We analysed non‐random species co‐occurrence patterns at pairwise and community levels, using null model analysis and five ‘association’ indices. Results All three assemblages were significantly nested. There was limited congruence only between birds and flying beetles whose nestedness was related to canopy openness. For ground‐dwelling beetles, nestedness was related to high stand heterogeneity and sapling density, whereas site idiosyncrasy was inversely related to structural heterogeneity. For birds, site idiosyncrasy increased with canopy cover, and most idiosyncratic species were closed‐canopy specialists. In all assemblages, species idiosyncrasy was positively correlated with the frequency of negative pairwise associations. Species co‐occurrence patterns were non‐random, and for flying beetles and birds positive species pairwise associations dominated. Community‐level co‐occurrence summaries may not, however, always reflect these patterns. Main conclusions Nestedness patterns of different assemblages may not correlate, even when sampled at common locations, because of different responses to local habitat attributes. We found idiosyncrasy patterns indicating opposing habitat preferences, consistent with antagonistic interactions among species within assemblages. Analysis of such patterns can thus suggest the mechanisms generating assemblage structures, with implications for biodiversity conservation.     

An historical interpretation of habitat use by frogs in a Central Amazonian Forest

Interpretations of habitat use in tropical frog assemblages have centred on resource partitioning and stressed the influence of interspecific interaction and climatic fluctuation on numbers of species using various habitats. We used audio strip transects and visual methods to determine the species composition, reproductive modes, and habitat occupancy patterns of the entire assemblage of frog species in 1900 hectares of primary forest north of Manaus in the central Amazon. We then compared taxon, reproductive mode, and habitat of species at six analogous lowland forest sites of similar species richness (five in the Amazon and one in Southeast Asia) to determine similarity of habitat use among sites and whether habitat is strongly associated with species» systematic positions. In all lowland Amazonian faunas, most species with aquatic development use pools, many species undergo some degree of terrestrial development, and few species are riparian or develop in streams. In contrast, about half the species in Southeast Asian assemblages are riparian and develop in streams, and few species develop terrestrially. Because reproductive mode and habitat associate strongly with taxon, patterns of habitat use observed at this regional scale are better explained by historical biogeography and differential rates of speciation than by proximal selection generated by contemporary environmental conditions. This study presents an inventory of frog species in a central Amazonian terre-firme forest and measurements of habitat availability and use by an entire assemblage of frogs throughout a large area (other portions of this study were published by Gascon, 1990, 1991; Zimmerman & Rodrigues, 1990; Zimmerman, 1991). We asked whether this local pattern of habitat occupancy differed from the regional Amazonian pattern and whether local species composition could be predicted from (sub)habitat composition. Viewing the assemblage at the local level did reveal species-(sub)habitat relationships masked at the broader regional level. About half the pool-breeders at the Manaus forest study sites would not use pools that could be flooded by a permanent stream; several species distinguished between permanent and temporary ponds; and some species occupied all available breeding habitat, whereas others occurred patchily. This pattern was maintained over four breeding seasons, and species composition could be predicted from (sub)habitat composition. Phylogeny was not a predictor of subhabitat occupancy. Perhaps species are phylogenetically constrained to develop in pool, stream, riparian, or terrestrial habitats, but contemporary selection governs their narrow distribution within these major habitat types. Finally, we asked whether anuran species richness in the central Amazon differs from that of the upper or lower Amazon. One genus, Eleutherodactylus , accounts for elevated species richness at upper Amazonian sites. Dry seasons in the central and lower Amazon are unlikely to restrict the spread of eleutherodactylines, which reproduce terrestrially. There are as many non-eleutherodactylines with terrestrial development at seasonal sites as there are at continually wet sites. Colonization history and the topography of central and lower Amazonia are more likely to limit eleutherodactyline richness.     

Roe and fallow deer: are they compatible neighbours?

The analysis of the relationships between population density and habitat features is important to evaluate the ecological needs of a species, its potential impact on ecosystems and its interspecific interactions. We analysed the spatial variation of roe deer Capreolus capreolus and fallow deer Dama dama densities in a Mediterranean area in summer 2007 and winter 2007/2008. Previous research has shown that fallow deer can actively displace and exclude roe deer from natural feeding sites. Here we show that both species have the greatest densities in ecotone habitats between wood and open fields (abandoned olive groves and pastures), but with contrasting geographic patterns. The fallow deer showed the greatest densities in the central northern part of the study area near to local historical release sites. The densities of roe deer were great where fallow deer were rare and low where fallow deer were abundant. Spatial overlap was great at the habitat scale, indicating a high potential for competition, but was low at the plot scale, suggesting that partitioning of space occurred at a fine scale. Supporting great numbers of deer, the ecotone areas are crucial for the management of ecosystems. We suggest that roe deer avoid areas with great densities of fallow deer and that interspecific interference from the latter affects the density and distribution of the former both at a fine and at a large scale.     

The interplay between local and landscape scales on the density of pond-dwelling anurans in subtropical grasslands

We investigated the role of local and landscape environmental variables on anurans density classified as habitat specialists and generalists in grassland landscapes, known as South Brazilian grasslands (SBG). In this region, we surveyed 187 ponds distributed over 40 landscape sampling units. For each pond, 31 local environmental variables were measured. Each landscape sampling unit was embedded within a larger regional sampling unit with different landscape properties. For each landscape and regional sampling units, 16 landscape metrics were extracted from a land cover and use map. We recorded 35 species, eleven of which are specialists in the SBG. The specialists were affected by 11 local and 2 landscape environmental variables, while generalists were affected by 14 local and one landscape environmental variable. Thus, specialists and generalists presented different relationships with local and landscape variables, but in general local variables had a greater influence on the density of anurans than the landscape variables. However, the landscape indirectly influenced local variables because higher quality ponds were in landscapes with higher percentages of natural habitat. In conclusion, reproductive sites with higher local quality and located within landscapes with higher percentages of natural grasslands are essential to conserve anurans in this habitat. Effective conservation of such sites would benefit from further studies that assess effects of land use and biotic integrity of ponds, which can help to determine (a) the relative effects of local habitat quality of ponds and (b) the effectiveness of protecting ponds and their local surroundings for anuran conservation in SBG. Abstract in Portuguese is available with online material.     

Canopy Closure and Emigration by Juvenile Gopher Frogs

ABSTRACT Although studies have addressed effects of abrupt transitions in habitat type (e.g., forest-clear-cut or forest-field edges) on amphibian movements, little is known about effects of more subtle habitat transitions on patterns of migration and habitat use in amphibians. We used radiotelemetry to study movement patterns of juvenile gopher frogs (Rana capito) emigrating from ponds that were surrounded by longleaf pine (Pinus palustris) forest that varied in structure as a result of fire suppression. Our primary purpose was to determine if frogs emigrate directionally from their natal ponds and select habitat at random during their first month following metamorphosis. We found that frogs emigrated in nonrandom directions from ponds that were surrounded by heterogeneous habitat and selected fire-maintained habitat that was associated with an open canopy, few hardwood trees, small amounts of leaf litter, and large amounts of wiregrass (Aristida beyrichiana). Fire-maintained habitat contained higher densities of burrows excavated by gopher tortoises (Gopherus polyphemus) and small mammals, which are the priamry refuge sites for both juvenile and adult gopher frogs. Frogs moved up to 691 m from their natal ponds, frequently crossed dirt roads, and even seemed to use these roads as migration corridors. To maintain suitable terrestrial habitat for gopher frogs, including habitat used by migrating individuals, it is important to apply frequent prescribed fire to uplands surrounding breeding ponds that lead all the way to the edges of breeding ponds, as well as through ponds during periodic droughts.     

Horned grebe habitat use of constructed wetlands in Alberta,Canada

Wetland degradation has resulted in declines in populations of aquatic birds throughout North America. Horned grebe (Podiceps auritus), a migratory diving bird experiencing population decline, may benefit from wetland construction. We examined horned grebe use of borrow pits (ponds created during highway construction) in Alberta, Canada. Our goals were to document patterns of occurrence and breeding success of grebes on borrow pits and to determine if occupied and unoccupied sites differed in local habitat or landscape characteristics. In May 2003 and 2007, 330 constructed ponds were surveyed for horned grebes. We chose 100 occupied and 100 unoccupied ponds for additional surveys in 2007 and 2008, and collected habitat and landscape data for these sites. We used generalized linear mixed model and generalized linear model regression, coupled with Akaike's Information Criterion, to determine which environmental variables were most effective in explaining occurrence of horned grebes. The best model included all measured local and landscape habitat features. Horned grebes occurred on 36% of ponds in May 2003 and 2007, and chicks were produced on 74.5–81.3% of occupied ponds in 2007 and 2008. Grebes occupied larger ponds with more emergent and riparian vegetation and avoided ponds that supported beavers, contained human structures, and were primarily surrounded by forest within 1 km. On ponds with grebe pairs, chicks were produced more often on sites surrounded by more riparian vegetation. We conclude that the construction of small wetlands offers a promising means of increasing breeding habitat for horned grebes and present specific recommendations for breeding pond construction. © 2012 The Wildlife Society.     

Individual species–area relationships and spatial patterns of species diversity in a Great Basin,semi‐arid shrubland

Traditional biodiversity metrics operate at the level of a plant community but do not capture spatial variation in diversity from a ‘plant's‐eye view’ of a community. Recently‐developed statistics consider the spatial patterns of plants as well as the number and distribution of species in local plant neighborhoods to quantitatively assess multispecies spatial patterns from a ‘plant's‐eye view’. We used one such statistic, the individual species area relationship (ISAR), to assess spatial patterns of species diversity in a Great Basin (USA) semi‐arid shrubland through an analysis of a spatial dataset on shrub species and locations. In conjunction with appropriate null models, the ISAR blends species area relationships with second‐order spatial statistics to measure the expected species richness in local neighborhoods of variable size around the individuals of a focal species within a community. We found that, contrary to a previous analysis using more traditional methods, the community was well‐mixed with a typical shrub surrounded on average by 4.9 shrub neighbors of 2.1 species at a neighborhood scale of 1.0 m. We also found statistically significant fine‐scale variation in diversity patterns, such that neighborhoods of two species were more diverse than expected by a heterogeneous Poisson null model that accounted for larger‐scale habitat heterogeneity. However, this effect was caused by intraspecific aggregation of these species and was not due to positive interspecific association. Contrary to previous findings in other semi‐arid shrublands, our analysis suggests that the spatial pattern of the shrub community was not significantly structured by interspecific facilitation. This result supports growing evidence for balanced species patterns of adult plants in multispecies communities. Our approach may be used in other communities to describe complex multispecies spatial patterns, quantify species‐specific associations with diversity patterns, and to generate hypotheses regarding relationships between patterns and community‐structuring processes.     

Processes involved in species saturation of ground‐dwelling ant communities (Hymenoptera,Formicidae)

The species saturation hypothesis in ground‐dwelling ant communities was tested, the relationship between local and regional species richness was studied and the possible processes involved in this relationship were evaluated in the present paper. To describe the relationship between local and regional species richness, the ground‐dwelling ant fauna of 10 forest remnants was sampled, using 10 1 m² quadrats in each remnant. The ants were extracted from the litter by using Winkler sacs. Using regression analyses, an asymptotic pattern between local and regional species richness was detected. This saturated pattern may be related to three processes: (i) high interspecific competition; (ii) habitat species specialization; or (iii) stochastic equilibrium. It is concluded that non‐interactive processes, such as stochastic equilibrium and habitat specialization may act as factors regulating species richness in this community. The predominance of locally restricted species, in all sampled remnants, seems to indicate the occurrence of a high degree of habitat specialization by the ant species. This result is evidence for the hypothesis that community saturation has been generated by non‐interactive processes. Although ants are frequently described as highly interactive, it is possible that interspecific competition is not important in the structuring of ground‐dwelling ant communities.     

Local, among-site, and regional diversity patterns of benthic macroinvertebrates in high altitude waterbodies: do ponds differ from lakes?

In this study we aimed at comparing invertebrate diversity of high altitude lakes and ponds along hierarchical spatial scales. We compared local, among-site, and regional diversity of benthic macroinvertebrates in 25 ponds and 34 lakes in the Tatra Mountains, central Europe. The ponds showed significantly lower local diversity, higher among-site diversity and similar regional diversity than the lakes. The species–area relationships (SAR), habitat heterogeneity, and environmental harshness are assumed as drivers for the local diversity patterns. An ecological threshold separating pond and lake systems emerged at an area of 2 ha, where the SAR pattern changed significantly. Differences in species turnover between these systems were likely driven by greater environmental variability and isolation of the ponds. High altitude ponds neither significantly support greater regional diversity nor higher number of unique taxa than lakes. The higher among-site diversity of ponds relative to lakes highlights the relevance of ponds for regional diversity in mountain areas.     

Mechanical barriers to introgressive hybridization revealed by mitochondrial introgression patterns in Ohomopterus ground beetle assemblages

To reveal the role of diverged body size and genital morphology in reproductive isolation among closely related species, we examined patterns of, and factors limiting, introgressive hybridization between sympatric Ohomopterus ground beetles in central Japan using mitochondrial NADH dehydrogenase subunit 5 (ND5) gene sequences. We sampled 17 local assemblages that consisted of two to five species and estimated levels of interspecific gene flow using the genetic distance, D(A), and maximum-likelihood estimates of gene flow. Sharing of haplotypes or haplotype lineages was detected between six of seven species that occurred in the study areas, indicating mitochondrial introgression. The intensity and direction of mitochondrial gene flow were variable among species pairs. To determine the factors affecting introgression patterns, we tested the relationships between interspecific D(A) and five independent variables: difference in body size, difference in genital size, phylogenetic relatedness (nuclear gene sequence divergence), habitat difference, and species richness of the assemblage. Body and genital size differences contributed significantly to preventing gene flow. Thus, mechanical isolation mechanisms reduce the chance of introgressive hybridization between closely related species. Our results highlight the role of morphological divergence in speciation and assemblage formation processes through mechanical isolation.     

The anatomy of the interspecific abundance–range size relationship for the British avifauna: I. Spatial patterns

Data from the British Trust for Ornithology Common Birds Census and two atlases of breeding birds were used to examine the form of the interspecific abundance–range size relationship for the British avifauna. The relationship is positive for both farmland and woodland habitats and over two different periods, with some evidence of curvilinearity, using either proportion of occupied sites or numbers of occupied 10 × 10 km squares as measures of range size, and mean density at occupied sites as a measure of abundance. A log-linear plot gives the highest correlation. The relationship is stronger if based on maximum local densities than if based on average densities, but there is no relationship using minimum local densities. Relationships based on abundances at individual sites are uniformly positive for all sites, although the relationships for many sites also show evidence of curvilinearity, especially when range size is measured as the proportion of occupied sites. Species show significant concordance in their rank abundances across sites. We discuss some implications of these results.     

Metacommunity patterns in larval odonates

The growth of metacommunity ecology as a subdiscipline has increased interest in how processes at different spatial scales structure communities. However, there is still a significant knowledge gap with respect to relating the action of niche- and dispersal-assembly mechanisms to observed species distributions across gradients. Surveys of the larval dragonfly community (Odonata: Anisoptera) in 57 lakes and ponds in southeast Michigan were used to evaluate hypotheses about the processes regulating community structure in this system. We considered the roles of both niche- and dispersal-assembly processes in determining patterns of species richness and composition across a habitat gradient involving changes in the extent of habitat permanence, canopy cover, area, and top predator type. We compared observed richness patterns and species distributions in this system to patterns predicted by four general community models: species sorting related to adaptive trade-offs, a developmental constraints hypothesis, dispersal assembly, and a neutral community assemblage. Our results supported neither the developmental constraints nor the neutral-assemblage models. Observed patterns of richness and species distributions were consistent with patterns expected when adaptive tradeoffs and dispersal-assembly mechanisms affect community structure. Adaptive trade-offs appeared to be important in limiting the distributions of species which segregate across the habitat gradient. However, dispersal was important in shaping the distributions of species that utilize habitats with a broad range of hydroperiods and alternative top predator types. Our results also suggest that the relative importance of these mechanisms may change across this habitat gradient and that a metacommunity perspective which incorporates both niche- and dispersal-assembly processes is necessary to understand how communities are organized. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Implications of body size for interspecific interactions and assemblage organization among coral-reef fishes

Abstract Population size-structure is often ignored in assemblage-level studies of reef fishes, which usually rely on static and dynamic patterns of relative total abundance to infer what mechanisms organize those assemblages. However, body size has substantial effects on processes that affect competitive relationships between species: (i) small, recently recruited fish, which usually(?) suffer high mortality, can dominate total abundance and strongly influence the dynamics of the relative total abundances of different species, while having little effect on interspecific biomass relations; (ii) numeric abundance and biomass of a species can vary independently, due to habitat variation in population size-structure resulting from variation in mortality and growth, as well as habitat selection; and (iii) population size-structure affects the potential for and outcome of interspecific competition due to (a) ontogenetic change in types of resources used, (b) levels of resource needs being dependent on individual and species biomass rather than numbers, (c) advantages due to large size in behavioural contests, (d) variation in population size-structure being linked to habitat preference, which affects expression of competitive dominance, and (e) size dependency in the development of interspecific resource-sharing relationships. Assemblage-level analyses that ignore such size effects may fail to detect important effects of interspecific interactions.     

The role of local and regional processes in structuring larval dragonfly distributions across habitat gradients

Despite the importance of community-structuring processes operating at both local and regional scales, there is relatively little work examining both forces within a single system. I used a combination of observational and experimental approaches to examine the processes structuring larval dragonfly distributions in lentic habitats that encompass a gradient of both permanence and top predator type. I compared the relative vulnerability of species to predators from different portions of this gradient to assess the role of predation as a local force structuring communities. I also assessed the role of regional processes on species' distributions by examining species' propensity to disperse to and colonize artificial ponds distributed across a landscape. In both studies I contrasted habitat specialist species, which had larvae restricted to permanent lakes, with habitat generalist species, which had larvae that occur broadly across the habitat permanence and top predator transition. Results from this work suggest that dispersal and colonization behavior were critical mechanisms restricting the distributions of habitat specialist species, but that predation may act to reinforce this pattern. The habitat specialists dispersed less frequently, colonized artificial ponds less often when they did reach them, and most moved shorter distances than the habitat generalist species. Habitat specialists were also more vulnerable than habitat generalists to an invertebrate top predator with which they do not co-exist. Results from these studies suggest that species distributions can be shaped by processes operating at both regional and local spatial scales. The role of dispersal and recruitment limitation may be generally underestimated as a force shaping species distributions and community structure across habitat gradients in which there is a transition in both the biotic interactions and the disturbance interval across that gradient.     

Multiple habitat use by declining migratory birds necessitates joined‐up conservation

Many species depend on multiple habitats at different points in space and time. Their effective conservation requires an understanding of how and when each habitat is used, coupled with adequate protection. Migratory shorebirds use intertidal and supratidal wetlands, both of which are affected by coastal landscape change. Yet the extent to which shorebirds use artificial supratidal habitats, particularly at highly developed stopover sites, remains poorly understood leading to potential deficiencies in habitat management. We surveyed shorebirds on their southward migration in southern Jiangsu, a critical stopover region in the East Asian Australasian Flyway (EAAF), to measure their use of artificial supratidal habitats and assess linkages between intertidal and supratidal habitat use. To inform management, we examined how biophysical features influenced occupancy of supratidal habitats, and whether these habitats were used for roosting or foraging. We found that shorebirds at four of five sites were limited to artificial supratidal habitats at high tide for ~11–25 days per month because natural intertidal flats were completely covered by seawater. Within the supratidal landscape, at least 37 shorebird species aggregated on artificial wetlands, and shorebirds were more abundant on larger ponds with less water cover, less vegetation, at least one unvegetated bund, and fewer built structures nearby. Artificial supratidal habitats were rarely used for foraging and rarely occupied when intertidal flats were available, underscoring the complementarity between supratidal roosting habitat and intertidal foraging habitat. Joined‐up artificial supratidal management and natural intertidal habitat conservation are clearly required at our study site given the simultaneous dependence by over 35,000 migrating shorebirds on both habitats. Guided by observed patterns of habitat use, there is a clear opportunity to improve habitat condition by working with local land custodians to consider shorebird habitat requirements when managing supratidal ponds. This approach is likely applicable to shorebird sites throughout the EAAF.