Historical and dispersal processes drive community assembly of multiple aquatic taxa in glacierized catchments in the Qinghai-Tibet plateau.

Understanding the relative role of dispersal dynamics and niche constraints is not only a core task in community ecology, but also becomes an important prerequisite for bioassessment. Despite the recent progress in our knowledge of community assembly in space and time, patterns and processes underlying biotic communities in alpine glacierized catchments remain mostly ignored. To fill this knowledge gap, we combined the recently proposed dispersal-niche continuum index (DNCI) with traditional constrained ordinations and idealized patterns of species distributions to unravel community assembly mechanisms of different key groups of primary producers and consumers (i.e., phytoplankton, epiphytic algae, zooplankton, macroinvertebrates, and fishes) in rivers in the Qinghai-Tibet Plateau, the World's Third Pole. We tested whether organismal groups with contrasting body sizes differed in their assembly processes, and discussed their applicability in bioassessment in alpine zones. We found that community structure of alpine river biotas was always predominantly explained in terms of dispersal dynamics and historical biogeography. These patterns are most likely the result of differences in species-specific functional attributes, the stochastic colonization-extinction dynamics driven by multi-year glacier disturbances and the repeated hydrodynamic separation among alpine catchments after the rising of the Qilian mountains. Additionally, we found that the strength of dispersal dynamics and niche constraints was partially mediated by organismal body sizes, with dispersal processes being more influential for microscopic primary producers. Finding that zooplankton and macroinvertebrate communities followed clumped species replacement structures (i.e., Clementsian gradients) supports the notion that environmental filtering also contributes to the structure of high-altitude animal communities in glacierized catchments. In terms of the applied fields, we argue that freshwater bioassessment in glacierized catchments can benefit from incorporating the metacommunity perspective and applying novel approaches to (i) detect the optimal spatial scale for species sorting and (ii) identify and eliminate the species that are sensitive to dispersal-related processes.

Diversification of the widespread neotropical frog Physalaemus cuvieri in response to Neogene-Quaternary geological events and climate dynamics.

Here we reconstructed the demographical history and the dispersal dynamics of Physalemus cuvieri through the Neogene-Quaternary periods by coupling DNA regions with different mutation rates, ecological niche modelling, reconstruction of spatio-temporal lineage dispersal and coalescent simulations. Still, to test alternative diversification scenarios we used approximate Bayesian computation. Molecular phylogenetic analysis recovered four deep and strongly supported clades, which we interpret as population lineages. The ancestral location reconstruction placed the root in southcentral Amazonia, and the dispersal events indicate that spatial displacement was widespread early in the diversification of this species. The demographical scenario of "Multiple Refugia" with recent lineage admixture was the most likely hypothesis to predict the observed genetic parameters of P. cuvieri. Our results revealed that Neogene orogenic events might have played a prominent role in the early diversification of P. cuvieri. The species shows deep divergences with strong regional population structure, despite its widespread distribution. Final uplift of the central Brazilian Plateau and formation of the river basins in Central South America played an important role in the origin, diversification and the maintenance of P. cuvieri lineages.

How complex should models be? Comparing correlative and mechanistic range dynamics models.

Criticism has been levelled at climate-change-induced forecasts of species range shifts that do not account explicitly for complex population dynamics. The relative importance of such dynamics under climate change is, however, undetermined because direct tests comparing the performance of demographic models vs. simpler ecological niche models are still lacking owing to difficulties in evaluating forecasts using real-world data. We provide the first comparison of the skill of coupled ecological-niche-population models and ecological niche models in predicting documented shifts in the ranges of 20 British breeding bird species across a 40-year period. Forecasts from models calibrated with data centred on 1970 were evaluated using data centred on 2010. We found that more complex coupled ecological-niche-population models (that account for dispersal and metapopulation dynamics) tend to have higher predictive accuracy in forecasting species range shifts than structurally simpler models that only account for variation in climate. However, these better forecasts are achieved only if ecological responses to climate change are simulated without static snapshots of historic land use, taken at a single point in time. In contrast, including both static land use and dynamic climate variables in simpler ecological niche models improve forecasts of observed range shifts. Despite being less skilful at predicting range changes at the grid-cell level, ecological niche models do as well, or better, than more complex models at predicting the magnitude of relative change in range size. Therefore, ecological niche models can provide a reasonable first approximation of the magnitude of species' potential range shifts, especially when more detailed data are lacking on dispersal dynamics, demographic processes underpinning population performance, and change in land cover.

Quantifying the roles of seed dispersal, filtering, and climate on regional patterns of grassland biodiversity.

Seed dispersal and local filtering interactively govern community membership and scale up to shape regional vegetation patterns, but data revealing how and why particular species are excluded from specific communities in nature are scarce. This lack of data is a missing link between our theoretical understanding of how diversity patterns can form and how they actually form in nature, and it hampers our ability to predict community responses to climate change. Here, we compare seed, seedling, and adult plant communities at 12 grassland sites with different climates in southern Norway to examine how community membership is interactively shaped by seed dispersal and local filtering, and how this process varies with climate across sites. To do this, we divide species at each site into two groups: locally transient species, which occur as seeds but are rare or absent as adults (i.e., they arrive but are filtered out), and locally persistent species, which occur consistently as adults in annual vegetation surveys. We then ask how and why locally transient species are disfavored during community assembly. Our results led to four main conclusions: (1) the total numbers of seeds and species that arrived, but failed to establish locally persistent populations, rose with temperature, indicating an increase in the realized effects of local filtering on community assembly, as well as an increase in the number of species poised to rapidly colonize those warmer sites if local conditions change in their favor, (2) locally transient species were selectively filtered out during seedling emergence, but not during seedling establishment, (3) selective filtering was partly driven by species climate preferences, exemplified by the poor performance of seeds dispersing outside of their realized climate niches into colder and drier foreign climates, and (4) locally transient species had traits that likely made them better dispersers (i.e., smaller seeds) but poorer competitors for light (i.e., shorter statures and less persistent clonal connections) than locally persistent species, potentially explaining why these species arrived to new sites but did not establish locally persistent adult populations. Our study is the first to combine seed, seedling, and adult survey data across sites to rigorously characterize how seed dispersal and local filtering govern community membership and shape climate-associated vegetation patterns.

Spores of lichen-forming fungi in the mycoaerosol and their relationships with climate factors.

Fungal particulates are a dominant component of the bioaerosol, but aerobiological studies traditionally focused on a limited set of fungi having relevance as allergens or plant pathogens. This study first analyzes the occurrence of lichen meiospores in the mycoaerosol, quantitatively evaluating in the atmosphere of an alpine environment the occurrence of polar diblastic spores, unequivocally attributable to the lichen family Teloschistaceae. The analysis of air-samples collected one week per month for one year with a Hirst-type sampler displayed a low percentage occurrence of polar-diblastic spores (<0.1%) with respect to the whole mycoaerosol, dominated by Cladosporium. Spearman's correlation tests on aerobiological and climatic data highlighted a strong relationship between the detection of Teloschistaceae spores and rainfall events, excluding seasonal patterns or daily rhythms of dispersion. The fact that all the air-sampled spores were attributable to the species of Teloschistaceae occurring in the site, together with laboratory observations of predominant short range dispersal patterns for polar diblastic and other lichen spores, indicated that sexual reproduction is mostly involved in the local expansion of colonization, dispersal from a long distance appearing a less probable phenomenon. These findings indicated that responses of lichen communities to climate factors, usually related to physiological processes, also depend on their influence on meiospore dispersal dynamics. Spatial limitations in dispersal, however, have to be taken into account in evaluating lichen distributional shifts as indicators of environmental changes.