Palaeontology., adaptation and community ecology: A response to Walter and Pater son (1994)

Abstract This paper challenges Walter and Paterson's (1994) assertion that the community concept ought to be abandoned because of recent palaeontological evidence pointing to the ‘individualistic’ nature of biological communities. The ‘individualistic’ versus ‘superorganismic’ community concepts might provide good grist for the philosophical mill, but have little practical relevance to contemporary community ecology. Ecologists define communities in terms of current species distributions and interactions, and seek to integrate the roles of both biotic and abiotic factors influencing species distributions. There is no assumption of tight co-evolution among component species; Walter and Paterson confuse ‘organization’ with ‘co-adaptation’. Nor, contrary to the authors’ claims, is there an implicit assumption that all community patterns are caused by competition. For most ecologists, the ‘competition debate’ ended a decade ago. Walter and Paterson's view that competition is rarely, if ever, important in structuring communities is not even held by the main protaganists of the ‘competition is not so important’ school of the 1980s, and is in direct contradiction of the extensive, more recent literature on the subject. It entirely ignores plant ecology. Many of Walter and Paterson's misunderstandings appear to arise from the false premise that explanation of adaptation should be the ultimate goal of any ecological discipline. The authors are hostile to community ecology because, if communities are individualistic, then little light can be shed on species adaptations. Fortunately, most ecologists are not so preoccupied with adaptation.     

Evolution mediates the effects of apex predation on aquatic food webs

Ecological and evolutionary mechanisms are increasingly thought to shape local community dynamics. Here, I evaluate if the local adaptation of a meso-predator to an apex predator alters local food webs. The marbled salamander (Ambystoma opacum) is an apex predator that consumes both the spotted salamander (Ambystoma maculatum) and shared zooplankton prey. Common garden experiments reveal that spotted salamander populations which co-occur with marbled salamanders forage more intensely than those that face other predator species. These foraging differences, in turn, alter the diversity, abundance and composition of zooplankton communities in common garden experiments and natural ponds. Locally adapted spotted salamanders exacerbate prey biomass declines associated with apex predation, but dampen the top-down effects of apex predation on prey diversity. Countergradient selection on foraging explains why locally adapted spotted salamanders exacerbate prey biomass declines. The two salamander species prefer different prey species, which explains why adapted spotted salamanders buffer changes in prey composition owing to apex predation. Results suggest that local adaptation can strongly mediate effects from apex predation on local food webs. Community ecologists might often need to consider the evolutionary history of populations to understand local diversity patterns, food web dynamics, resource gradients and their responses to disturbance.     

Parallel changes in the taxonomical structure of bacterial communities exposed to a similar environmental disturbance

Bacterial communities play a central role in ecosystems, by regulating biogeochemical fluxes. Therefore, understanding how multiple functional interactions between species face environmental perturbations is a major concern in conservation biology. Because bacteria can use several strategies, including horizontal gene transfers (HGT), to cope with rapidly changing environmental conditions, potential decoupling between function and taxonomy makes the use of a given species as a general bioindicator problematic. The present work is a first step to characterize the impact of a recent polymetallic gradient over the taxonomical networks of five lacustrine bacterial communities. Given that evolutionary convergence represents one of the best illustration of natural selection, we focused on a system composed of two pairs of impacted and clean lakes in order to test whether similar perturbation exerts a comparable impact on the taxonomical networks of independent bacterial communities. First, we showed that similar environmental stress drove parallel structural changes at the taxonomic level on two independent bacterial communities. Second, we showed that a long-term exposure to contaminant gradients drove significant taxonomic structure changes within three interconnected bacterial communities. Thus, this model lake system is relevant to characterize the strategies, namely acclimation and/or adaptation, of bacterial communities facing environmental perturbations, such as metal contamination.