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Dispersal evolution diminishes the negative density dependence in dispersal

In many organisms, dispersal varies with the local population density. Such patterns of density-dependent dispersal (DDD) are expected to shape the dynamics, spatial spread and invasiveness of populations. Despite their ecological importance, empirical evidence for the evolution of DDD patterns remains extremely scarce. This is especially relevant because rapid evolution of dispersal traits has now been empirically confirmed in several taxa. Changes in DDD of dispersing populations could help clarify not only the role of DDD in dispersal evolution, but also the possible pattern of subsequent range expansion. Here, we investigate the relationship between dispersal evolution and DDD using a long-term experimental evolution study on Drosophila melanogaster. We compared the DDD patterns of four dispersal-selected populations and their non-selected controls. The control populations showed negative DDD, which was stronger in females than in males. In contrast, the dispersal-selected populations showed density-independent dispersal, where neither males nor females exhibited DDD. We compare our results with previous evolutionary predictions that focused largely on positive DDD, and highlight how the direction of evolutionary change depends on the initial DDD pattern of a population. Finally, we discuss the implications of DDD evolution for spatial ecology and evolution.

Data from: Asymmetric contributions of seed and pollen to gene dispersal in the marsh orchid Dactylorhiza umbrosa in Asia Minor

Orchids differ from other plants in their extremely small and partly air-filled seeds that can be transported long distances by wind. Seed dispersal in orchids is expected to contribute strongly to overall gene flow, and orchids generally express low levels of genetic differentiation between populations and low pollen to seed flow ratios. However, studies in orchids distributed in northern Europe have often found a poor geographic structuring of genetic variation. Here, we studied geographic differentiation in the marsh orchid Dactylorhiza umbrosa, which is widely distributed in upland regions from Asia Minor to Central Asia. These areas were less affected by Pleistocene ice ages than northern Europe and the orchid should have been able to survive the last ice age in local refugia. In the plastid genome, which is dispersed by seeds, populations at close distance were clearly divergent, but the differentiation still increased with geographic distance, and a significant phylogeographic structure had developed. In the nuclear genome, which is dispersed by both seeds and pollen, populations showed an even stronger correlation between genetic and geographic distance, but average levels of differentiation were lower than in the plastid genome, and no phylogeographic structure was evident. Combining plastid and nuclear data, we found that the ratio of pollen to seed dispersal (mp/ms) decreases with physical distance. Comparison with orchids that grow in parts of Europe that were glaciated during the last ice suggests that a balanced structure of genetic diversity develops only slowly in many terrestrial orchids, despite of efficient seed dispersal.

Data from: Contrasting scales of local persistence between monsoonal and arid biomes in closely related, low-dispersal vertebrates

Aim: Focussing on pairs of sister species across three genera of scincid lizards, we use genomic evidence to test for larger-scale, late-Pleistocene changes in distributions of lizards in the Australian Arid Zone (AZ) than in the adjacent Monsoonal Tropics (MT). Location: Northern and central Australia. Taxon: Scincidae: Squamata. Methods: We sequenced ~ 2000 nuclear exons and one mitochondrial gene across the distributions of species with primarily MT or AZ distributions from three genera of lizards. Using phylogenetic analysis and population structure analyses we identified major phylogeographic lineages and then compared the spatial scale of structuring and tested for recent demographic expansions. Results: Two genera in particular, Proablepharus and Morethia, showed deeper and more geographically localised phylogeographic diversity in the MT than the AZ. In the MT, localised diversity was prevalent in the relatively mesic regions. By contrast, the AZ was characterised by widespread and often genetically uniform lineages and a higher proportion of these had signals of recent population expansion. Main conclusions: Consistent with other recent, but mostly less genetically extensive studies, our results point to deeper and more localised diversity in MT compared to AZ. In turn, this suggests higher local persistence in more mesic and topographically diverse biome through the late Quaternary climate fluctuations. For the AZ, geographically extensive range expansions have likely contributed to the low spatial turnover of this exceptionally rich lizard fauna.

Model output data for "Negative density-dependent dispersal emerges from the joint evolution of density- and body condition-dependent dispersal strategies"

Empirical studies have documented both positive and negative density-dependent dispersal, yet most theoretical models predict positive density dependence as a mechanism to avoid competition. Several hypotheses have been proposed to explain the occurrence of negative density-dependent dispersal, but few of these have been formally modeled. Here, we developed an individual based model of the evolution of density-dependent dispersal. This model is novel in that it considers the effects of density on dispersal directly, and indirectly through effects on individual condition. Body condition is determined mechanistically, by having juveniles compete for resources in their natal patch. We found that the evolved dispersal strategy was a steep, increasing function of both density and condition. Interestingly, although populations evolved a positive density-dependent dispersal strategy, the simulated metapopulations exhibited negative density-dependent dispersal. This occurred because of the negative relationship between density and body condition: high density sites produced low condition individuals that lacked the resources required for dispersal. Our model therefore generates the novel hypothesis that observed negative density-dependent dispersal can occur when high density limits the ability of organisms to disperse. We suggest that future studies consider how phenotype is linked to the environment when investigating the evolution of dispersal.

Data from: Tandem host-parasite dispersal inferred from similarities in phylogeographic patterns among little penguins and their 'terrestrial' ectoparasites

Aim Organisms with poor intrinsic dispersal capacity, such as parasites, often rely entirely on transport with host species that have a greater dispersal capacity. Penguins, for example, are exploited by terrestrial ectoparasites when they come ashore to breed. Recent research indicates that little penguin (Eudyptula minor and E. novaehollandiae) hard ticks (Ixodes eudyptidis and I. kohlsi) may be capable of surviving short periods (days) at sea with their hosts, but their capacity to survive longer voyages (weeks) is not known. We here aimed to assess whether phylogeographic patterns in little penguins and their ticks indicate that the terrestrial ectoparasites are able to disperse long distances at sea with their swimming hosts. Location Southern Australia and New Zealand. Taxon Ixodes eudyptidis and I. kohlsi ticks. Methods We conducted a broad-scale genomic assessment of little penguin ticks from across their hosts' ranges in Australia and New Zealand. Using Genotyping by Sequencing (GBS), we generated SNP data sets from ticks from 14 penguin colonies, and analysed phylogeographic structure. We included ticks from some sympatric flighted seabirds to verify host-specificity. Results We resolved two distinct lineages of Ixodes from little penguins, with one restricted to Australia, and the other found throughout New Zealand and in low numbers at some eastern Australian sites. Both lineages exhibited phylogeographic structure consistent with patterns observed in their hosts, with some evidence of occasional oceanic dispersal, including across the Tasman Sea between Australia and New Zealand. Ticks from sympatric short-tailed shearwaters (Ardenna tenuirostris), which disperse aerially, were genetically distinct from those collected from little penguins, supporting prior evidence of host-specificity in seabird ticks. Main conclusions The most parsimonious explanation for our results is that ticks can travel at sea with little penguins. We infer that some terrestrial ectoparasites associated with aquatically-dispersing hosts have evolved the capacity to survive oceanic voyages.

Non-continuous reproductive phenology of animal-dispersed species in young forest restoration plantings

Tree species that produce resources for fauna are recommended for forest restoration plantings to attract pollinators and seed dispersers; however, information regarding the flowering and fruiting of these species during early growth stages is scarce. We evaluated the reproductive phenology of animal-dispersed tree species widely used in Atlantic Forest restoration. We marked 16 animal-dispersed tree species in 3- to 8-year-old forest restoration plantings in Itu-São Paulo, southeast Brazil. We noted the age of the first reproductive event, flowering and fruiting seasonality, percentage of trees that reached reproductive stages, and intensity of bud, flower, and fruit production for each species. Flowering and fruiting are seasonal for most species; only two, Cecropia pachystachya and Ficus guaranitica, exhibited continuous flowering and fruiting throughout the year; we also identified Schinus terebinthifolia and Dendropanax cuneatus fruiting in the dry season during resource scarcity. Therefore, we recommend all as framework species, that is, species that are animal-dispersed with early flowering and fruiting potential, for forest restoration. Further, we recommend identifying and planting similar animal-dispersed tree species that produce fruits constantly or in the dry season to maximize fauna resource availability throughout the year in tropical forest restoration plantings.

Structure of small tropical islands freshwater fish and crustacean communities: a niche- or dispersal-based process?

Determining the relative importance of niche- and dispersal-based processes in the structuring of animal communities is central in ecology. Freshwater fish and crustacean communities of small tropical islands can bring new insights for understanding these processes as all their species present a pelagic larval stage which gives them important dispersal capacities. Consequently, we hypothesized that dispersal-based process maybe preponderant for structuring these communities from the regional- to the local, i.e. survey site, scales. Gradient forest analyses allowed us to model the effect of 12 environmental variables on freshwater taxa abundances in two southwestern Indian Ocean islands: Mayotte (26 taxa) and Reunion (21). A total of 153 surveys in Mayotte and 266 in Reunion were used for building the models. Despite the strong heterogeneity of environmental conditions between the two islands, the main factors structuring freshwater fish and crustacean communities in both islands were the elevation and the slope of the sites. The observed structure appeared more pronounced for predatory species than for primary consumers and omnivores. As predators generally have limited locomotor capacities, it is concluded that dispersal-based process structures these communities not only at large geographical scales but also at the intra-watershed scale, by limiting the inland penetration (or dispersion) of species in relation to their locomotor capacities. However, more knowledge concerning ecological traits and taxonomic status of many species is needed to confirm this assumption.

opencc-zeroSep 2020View details →

Parentage analyses identify local dispersal events and sibling aggregations in a natural population of Millepora hydrocorals, a free-spawning marine invertebrate

Dispersal is a critical process for the persistence and productivity of marine populations. For many reef species, there is increasing evidence that local demography and self-recruitment have major consequences on their genetic diversity and adaptation to environmental change. Yet empirical data of dispersal patterns in reef-building species remain scarce. Here, we document the first genetic estimates of self-recruitment and dispersal distances in a free-spawning marine invertebrate, the hydrocoral Millepora platyphylla. Using twelve microsatellite markers, we gathered genotypic information from 3,160 georeferenced colonies collected over 9,000 m2 of a single reef in three adjacent habitats in Moorea, French Polynesia; the mid slope, upper slope, and back reef. Although the adult population was predominantly clonal (85% were clones), our parentage analysis revealed a moderate self-recruitment rate with 8 to 37% of sexual propagules produced locally. Assigned offspring often settled at less than 10 meters from their parents and dispersal events decrease with increasing geographic distance. There were no discrepancies between the dispersal distances of offspring assigned to parents belonging to clonal versus non-clonal genotypes. Inter-habitat dispersal events via cross-reef transport were also detected for sexual and asexual propagules. Sibship analysis showed that full siblings recruit together on the reef (more than 40% settled at < 30 m), resulting in sibling aggregations. Our findings highlight the importance of self-recruitment together with clonality in stabilizing population dynamics, which may ultimately enhance local sustainability and resilience to disturbance.

opencc-zeroSep 2020View details →

Data from: Phylotranscriptomics resolves interspecific relationships and indicates multiple historical out-of-North America dispersals through the Bering Land Bridge for the genus Picea (Pinaceae)

A robust phylogeny is prerequisite to understand the evolution and biogeography of organisms. However, ancient and recent evolutionary radiations occurred in many plant lineages, which pose great challenges for phylogenetic analysis, especially for conifers characterized by large effective population sizes and long generation times. Picea is an important component of the dark coniferous forests in the Northern Hemisphere. Previous studies improved our understanding of its evolutionary history, but its interspecific relationships and biogeographic history remain largely unresolved. In the present study, we reconstructed a well-resolved phylogeny of Picea by comparative transcriptomic analysis based on a complete species sampling. The phylogenetic analysis, together with molecular dating and ancestral area reconstruction, further supports the North American origin hypothesis for Picea, and indicates that this genus experienced multiple out-of-North America dispersals by the Bering Land Bridge. We also found that spruces in the Japanese Archipelago have multiple origins, and P. morrisonicola from the Taiwan Island has a close relationship with species from the Qinghai-Tibetan Plateau and adjacent regions. Our study provides the first complete phylogeny of Picea at the genomic level, which is important for future studies of this genus.

House mouse Mus musculus dispersal in East Eurasia inferred from 98 newly determined complete mitochondrial genome sequences

<div> The Eurasianhouse mouse Mus musculusis useful for tracing prehistorical human movement related to the spread of farming. We determined whole mitochondrial DNA (mtDNA) sequences (ca. 16,000 bp) of 98 wild-derived individuals of two subspecies, M. m. musculus (MUS) and M. m. castaneus (CAS). We revealed directional dispersals reaching as far asthe Japanese Archipelagofrom their homelands. Our phylogenetic analysis indicated that the eastward movement of MUS was characterised by five step-wise regional extension events: 1) broad spatial expansion into eastern Europe and the western part of western China, 2) dispersal to the eastern part of western China, 3) dispersal tonorthern China, 4) dispersal to the Korean Peninsula and 5) colonisation and expansion in the Japanese Archipelago. These events were estimated to have occurred during the last 2,000–18,000 years. The dispersal of CAS was characterised by three events: initial divergences(ca. 7,000–9,000 years ago) of haplogroups in northern most China and the eastern coast of India, followed by two population expansion events that likely originated from the Yangtze River basinto broad areas of South and Southeast Asia, including Sri Lanka, Bangladesh and Indonesia (ca. 4,000–6,000 years ago) and to Yunnan, southern China and the Japanese Archipelago (ca. 2,000–3,500). This study provides a solid framework for the spatiotemporal movementof the human-associated organisms in Holocene Eastern Eurasia using whole mtDNA sequences, reliable evolutionary rates and accurate branching patterns. The information obtained here contributes to the analysis of a variety of animals and plants associated with prehistoric human migration. </div>

opencc-zeroOct 2020View details →

Intraspecific competition drives dispersal of an endangered ibis data

Although dispersal drives population dynamics and species distribution, we still know little about how it affects the dynamic of endangered and restricted-range species. After 1981, when the last seven wild individuals of Crested Ibis were discovered in China, the species remained confined to a single location ('original nesting area') until 2000 (< 24 breeding pairs). Then, the breeding population began a significant spatial and numerical expansion (toward the 'secondary nesting area'). Our analyses of long-term (1993–2017) individual-based data (n = 193) show that: (i) natal, but not breeding dispersal, was common (≈77% and ≈2.1%); (ii) as predicted by the intraspecific competition hypothesis, the probability of natal dispersal from the original nesting area increased with increasing and decreasing density at the birthplace and the first breeding site, respectively; nonetheless, (iii) in the secondary nesting area, birth dispersal was density-independent, but (iv) from here they were more likely to disperse, pointing to weak competition at these breeding areas and, since they were all born to dispersing parents, to a role for individual personality; (v) the Weibull distribution provided the best fit to the observed dispersal distances, indicating the presence of long-distance dispersers. We expect the Crested Ibis to continue to spread throughout the region if the protection programs cover a wide range to allow long-distance dispersal. Overall, our study suggests that intraspecific competition can cause dispersal in a population of few individuals confined to a small area and, therefore, be critical for the recovery and expansion of an endangered species.

opencc-zeroOct 2020View details →

Data from: Invasive lumbricid earthworms in North America – different life-histories but common dispersal?

Aim Lumbricid earthworms are invasive across northern North America, causing notable changes in forest ecosystems. During their range expansion, they encountered harsher climatic conditions compared to their native ranges in short time (~400 years). This study investigated if (1) dispersal barriers, (2) climatic selection, or (3) anthropogenic activities, i.e. fishing bait disposal, structure the dispersal of free-living earthworm populations. Location North America, forest habitats along former Wisconsinan glaciation line Taxon Lumbricus terrestris, L. rubellus Methods Lumbricus terrestris and L. rubellus co-occur in the same habitats but differ in ecology and use as fishing bait. Both species were sampled in five transects ranging from the east to the west coast of northern North America, including major dispersal barriers, three different climate zones, and bait shops near sampling locations. Genetic diversity and structure were compared between the two species, and the presence of free-living bait shop genotypes was assessed using four markers (COI, 16S rDNA, 12S rDNA, H3). Results Populations of both species were genetically diverse with some geographic structure, which was more pronounced in L. terrestris than in L. rubellus. Common haplotypes were present in all regions, but locally restricted haplotypes also occurred. Further, two distinct genetic clades of L. terrestris co-occurred only in the two most distant transects (Alberta and Minnesota). Genotypes identical to bait individuals were omnipresent in field populations of L. terrestris. Main conclusions Genetic diversity was high in both species, and invasive populations represented a genetic subset of European earthworms. Geographic and climatic dispersal barriers affected the less mobile species, L. rubellus, resulting in differences in genetic structure between the two species. Our results indicate common long-distance dispersal vectors and vectors affecting only L. terrestris. The roles of climate and anthropogenic activities are discussed, providing additional explanations of dispersal and new insights into establishment of invasive earthworm populations. Keywords biological invasion, colonisation, genetic clades, agriculture, climate, dispersal barriers

opencc-zeroOct 2020View details →

Evaluating the boundaries of marine biogeographic regions of the Southwestern Atlantic using halacarid mites (Halacaridae), meiobenthic organisms with a low dispersal potential

Aim We evaluated traditional biogeographic boundaries of coastal marine regions in SW Atlantic using DNA sequence data from common, rocky-shore inhabiting, marine mites of the genera Agauopsis and Rhombognathus, family Halacaridae. Methods We investigated geographic population genetic structure using CO1 gene sequences, estimated divergence times using a multigene dataset and absolute time-calibrated molecular clock analyses, and performed environmental niche modeling (ENM) of common marine mite species. Results Agauopsis legionium has a shallow history (2.01 Ma) with four geographically differentiated groups. Two of them corresponded to the traditional Amazonian and Northeastern ecoregions, but the boundary between the two other groups was inferred at the Abrolhos Plateau, not Cabo Frio. Rhombognathus levigatoides s. lat. was represented by two cryptic species that diverged 7.22 (multilocus data) or 10.01 Ma (CO1-only analyses), with their boundary, again at the Abrolhos Plateau. ENM showed that A. legionium has suitable habitats scattered along the coast, while the two R. levigatoides cryptic species differ considerably in their niches, especially in parameters related to upwelling. This indicates that genetic isolation associated with the Abrolhos Plateau occurred in both lineages, but for the R. levigatoides species complex, ecological niche specialization was also an important factor. Main conclusions Our study suggests that the major biogeographic boundary in the Southwestern Atlantic lies not at Cabo Frio but at the Abrolhos Plateau. There, two biogeographically relevant factors meet: (i) changes in current directions (which limit dispersal) and (ii) abrupt changes in environmental parameters associated with the South Atlantic Central Waters (SACW) upwelling (offering distinct ecological niches). We suggest that our result represents a general biogeographic pattern because a barrier at the Abrolhos Plateau was found previously for the fish genus Macrodon (phylogeographic data), prosobranch mollusks, ascidians, and reef fishes (community-level data).

opencc-zeroSep 2021View details →

Modelling mycorrhizal fungi dispersal by the mycophagous swamp wallaby (Wallabia bicolor)

Despite the importance of mammal-fungal interactions, tools to estimate the mammal-assisted dispersal distances of fungi are lacking. Many mammals actively consume fungal fruiting bodies, the spores of which remain viable after passage through their digestive tract. Many of these fungi form symbiotic relationships with trees and provide an array of other key ecosystem functions. We present a flexible, general model to predict the distance a mycophagous mammal would disperse fungal spores. We modelled the probability of spore dispersal by combining animal movement data from GPS-telemetry with data on spore gut-retention time. We test this model using an exemplar generalist mycophagist, the swamp wallaby (Wallabia bicolor). We show that swamp wallabies disperse fungal spores hundreds of metres—and occasionally up to 1265 m—from the point of consumption, distances that are ecologically significant for many mycorrhizal fungi. In addition to highlighting the ecological importance of swamp wallabies as dispersers of mycorrhizal fungi in eastern Australia, our simple modelling approach provides a novel and effective way of empirically describing spore dispersal by a mycophagous animal. This approach is applicable to the study of other animal-fungi interactions in other ecosystems.

Bacterial dispersal and drift drive microbiome diversity patterns within a population of feral hindgut fermenters

Studies of microbiome variation in wildlife often emphasize host physiology and diet as proximate selective pressures acting on host-associated microbiota. In contrast, microbial dispersal and ecological drift are more rarely considered. Using amplicon sequencing, we characterized the bacterial microbiome of adult female (n = 86) Sable Island horses (Nova Scotia, Canada) as part of a detailed individual-based study of this feral population. Using data on sampling date, horse location, age, parental status, and local habitat variables, we contrasted the ability of spatiotemporal, life history, and environmental factors to explain microbiome diversity among Sable Island horses. We extended inferences made from these analyses with both phylogeny-informed and phylogeny-independent null modeling approaches to identify deviations from stochastic expectations. Phylogeny-informed diversity measures were correlated with spatial and local habitat variables, but null modelling results suggested that heterogeneity in ecological drift, rather than differential selective pressures acting on the microbiome, was responsible for these correlations. Conversely, phylogeny-independent diversity measures were best explained by host spatial and social structure, suggesting that taxonomic composition of the microbiome was shaped most strongly by bacterial dispersal. Parental status was important but correlated with measures of β-dispersion rather than β-diversity (mares without foals had lower alpha diversity and more variable microbiomes than mares with foals). Our results suggest that between host microbiome variation within the Sable Island horse population is driven more strongly by bacterial dispersal and ecological drift than by differential selective pressures. These results emphasize the need to consider alternative ecological processes in the study of microbiomes.

Data and R Code for publication: Should dispersers be fast learners? Modelling the role of cognition in dispersal

Both cognitive abilities and dispersal tendencies can vary strongly between individuals. Since cognitive abilities may help dealing with unknown circumstances it is conceivable that dispersers may rely more heavily on learning abilities than residents. However, cognitive abilities are costly and leaving a familiar place might result in losing the advantage of having learned to deal with local conditions. Thus, individuals which invested in learning to cope with local conditions may be more reluctant to leave their natal place. In order to disentangle the complex relationship between dispersal and learning abilities we implemented individual-based simulations. By allowing for developmental plasticity, individuals could either develop a "resident" or "dispersal" cognitive phenotype. In line with our expectations, the correlation between learning abilities and dispersal could take any direction, depending how much time individuals had to recoup their investment in cognition. Both, longevity and the timing of dispersal within lifecycles determine the time individuals have to recoup that investment and thus crucially influence this correlation. We therefore suggest that species' life-history will strongly impact the expected cognitive abilities of dispersers, relative to their resident conspecifics, and that cognitive abilities might be an integral part of dispersal syndromes.

Data from: Strong dispersal limitation in post-fire regeneration of Baker cypress, a rare serotinous conifer

PREMISE: Dispersal capacity primarily determines the spatial establishment patterns that drive range expansions and contractions in tree species. For Baker cypress (Hesperocyparis bakeri [(Jeps.) Bartel]), seedling establishment relies predominantly on fire events due to its cone serotiny, shade intolerance, and small seeds requiring the optimal conditions of fire-exposed, mineral soil seedbeds. METHODS: This study quantified the density and spatial distribution of post-disturbance seedlings following the 2014 Eiler fire in northern California and compared the observed recruitment to predictions from a mechanistic seed dispersal model. RESULTS: Post-fire recruitment was dense, averaging 11 seedling/m 2 , and occurred primarily in the first year after fire. We estimated the mean descent velocity of the wingless seeds as around 4 m/sec, the highest value reported for any putatively wind-dispersed tree species. The rapid seed decent contributed to markedly constrained recruitment in space. Most seedlings (~81%) established within 5 m of the parent tree, and 94% established within 10 m. The maximum observed dispersal distance was 48.5 m, and scaled linearly with canopy height. Distributions of modeled seed dispersal distance and observed seedling establishment in Baker cypress did not differ, demonstrating that wind disperses seeds a short distance due to the lack of a wing, and secondary dispersal appeared to be minimal at this recently burned site. CONCLUSIONS: If seed dispersal is solely reliant on wind, migration in response to rapid climate change will be impeded and potentially present difficulties in sustaining populations of this and other obligate seeder species with equally constrained dispersal.

Livestock grazing is associated with seasonal reduction in pollinator biodiversity and functional dispersion but cheatgrass invasion is not: variation in bee assemblages in a multi-use shortgrass prairie

Livestock grazing and non-native plant species affect rangeland habitats globally. These factors may have important effects on ecosystem services including pollination, yet, interactions between pollinators, grazing, and invasive plants are poorly understood. To address this, we tested the hypothesis that cattle grazing and site colonization by cheatgrass (Bromus tectorum) impact bee foraging and nesting habitats, and the biodiversity of wild bee communities, in a shortgrass prairie system. Bee nesting habitats (litter and wood cover) were marginally improved in non-grazed sites with low cheatgrass cover, though foraging habitat (floral cover and richness, bare soil) did not differ among cattle-grazed sites or non-grazed sites with low or high cheatgrass cover. However, floral cover was a good predictor of bee abundance and functional dispersion. Mean bee abundance, richness, diversity and functional diversity were significantly lower in cattle-grazed habitats than in non-grazed habitats. Differences in bee diversity among habitats were pronounced early in the growing season (May) but by late-season (August) these differences eroded as Melissodes spp. and Bombus spp. became more abundant at study sites. Fourth-corner analysis revealed that sites with high floral cover tended to support large, social, polylectic bees; sites with high grass cover tended to support oligolectic solitary bees. Both cattle-grazed sites and sites with high cheatgrass cover were associated with lower abundances of above-ground nesting bees but higher abundance of below-ground nesters than non-grazed sites with low cheatgrass cover. We conclude that high cheatgrass cover is not associated with reduced bee biodiversity or abundance, but cattle grazing was negatively associated with bee abundances and altered species composition. Although floral cover is an important predictor of bee assemblages, this was not impacted by cattle grazing and our study suggests that cattle likely impact bee communities through effects other than those mediated by forbs, including soil disturbance or nest destruction. Efforts aimed at pollinator conservation in prairie habitats should focus on managing cattle impacts early in the growing season to benefit sensitive bee species.

opencc-zeroDec 2020View details →

Data from: Infection dynamics, dispersal, and adaptation: understanding the lack of recovery in a remnant frog population following a disease outbreak

Emerging infectious diseases can cause dramatic declines in wildlife populations. Sometimes these declines are followed by recovery, but many populations do not recover. Studying differential recovery patterns may yield important information for managing disease-afflicted populations and facilitating population recoveries. In the late1980s, a chytridiomycosis outbreak caused multiple frog species in Australia's Wet Tropics to decline. Populations of some species (e.g., Litoria nannotis) subsequently recovered, while others (e.g., Litoria dayi) did not. We examined the population genetics and current infection status of L. dayi, to test several hypotheses regarding the failure of its populations to recover: 1) a lack of individual dispersal abilities has prevented recolonization of previously occupied locations, 2) a loss of genetic variation has resulted in limited adaptive potential, and 3) L. dayi is currently adapting to chytridiomycosis. We found moderate to hig h levels of gene flow and diversity (Fst range: <0.01–0.15; minor allele frequency: 0.192–0.245), which were similar to previously published levels for recovered L. nannotis populations. This suggests that dispersal ability and genetic diversity do not limit the ability of L dayi to recolonize upland sites. Further, infection intensity and prevalence increased with elevation, suggesting that chytridiomycosis is still limiting the elevational range of L. dayi. Outlier tests comparing infected and uninfected individuals consistently identified 18 markers as putatively under selection, and several of those markers matched genes that were previously implicated in infection. This suggests that L. dayi has genetic variation for genes that affect infection dynamics and may be undergoing adaptation.