On the evolutionary origins of host–microbe associations

Many microorganisms with high prevalence in host populations are beneficial to the host and maintained by specialized transmission mechanisms. Although microbial promotion of host fitness and specificity of the associations undoubtedly enhance microbial prevalence, it is an open question whether these symbiotic traits are also a prerequisite for the evolutionary origin of prevalent microbial taxa. To address this issue, we investigate how processes without positive microbial effects on host fitness or host choice can influence the prevalence of certain microbes in a host population. Specifically, we develop a theoretical model to assess the conditions under which particular microbes can become enriched in animal hosts even when they are not providing a specific benefit to a particular host. We find increased prevalence of specific microbes in a host when both show some overlap in their lifecycles, and especially when both share dispersal routes across a patchy habitat distribution. Our results emphasize that host enrichment per se is not a reliable indicator of beneficial host–microbe interactions. The resulting increase in time spent associated with a host may nevertheless give rise to new selection conditions, which can favor microbial adaptations toward a host-associated lifestyle, and, thus, it could be the foundation for subsequent evolution of mutually beneficial coevolved symbioses.

Stochastic Spatiotemporal Patterns of Metapopulation Occupancy in Dynamic Wetlandscapes

<p>Dynamic internal feedbacks and stochastic external shocks drive the spatial organization and heterogeneity of patchy habitats, and thus the temporal variability of patch suitability and accessibility. Such spatiotemporal shifts impact species dispersal among patches and metapopulation persistence. Here, we extended the widely recognized concepts of patch-occupancy and metapopulation capacity from static to dynamic patchy habitats, with isolated wetlands embedded in uplands as the case study. We present a new metapopulation modeling approach by linking a hydrological model for wetland variability with a dynamic stochastic patch-occupancy model. In two case study wetlandscapes, we evaluate (1) spatiotemporal dynamics of wetland hydrologic regimes, and patch suitability and connectivity driven by stochastic hydroclimatic forcing, and (2) spatiotemporal patterns of patch occupancy and metapopulation dispersal dynamics. Our modeling results reveal the importance of specific connected patches that serve as persistent hubs and form the backbone of dispersal corridors to support species dispersal in fragmented dynamic landscapes. Our analyses reveal that the interplay between stochastic hydroclimatic forcing and patchy habitat structure could drive species to extinction when specific thresholds are crossed.</p>

Dispersion Pattern of Native Species in Sal Forests of Chhotanagpur Plateau, India

Changes in the dispersion pattern of native tree species were studied in Sal forests of Chhotanagpur plateau by selecting 1 hectare (ha) plot at four sites, located 2 to 10 km apart from each other. Each plot was divided into 100 quadrats each of 10 m x 10 m in size. For each 10 m x 10 m quadrat, the number of species and density of adult trees (>30 cm circumference at breast height: 1.37 m) were measured and identified. The range of uniform dispersion (77-89%) was greater than clumped dispersion (6-19%) and random dispersion (4-8%) in all four sites. About 78% of the plant species were characterised by uniform dispersion indicating dominant ecological reaction (i.e. dispersion behaviour) in response to alterations in the habitat conditions. A greater part of quadrats had 1-3 species and 1-4, 5-8 and 9-12 individuals indicating a patchy habitat with poor species richness and density at each site, a characteristic of the highly disturbed Sal forests.