Abundant and rare species may invoke different assembly processes in response to climate extremes: Implications for biodiversity conservation

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Climate change is expected to increase the magnitude and frequency of extreme climate events. Accurate predictions of the effects of these events on communities and designing scientific recovery and management programs for biodiversity require an understanding of the mechanisms underlying differentially-abundant taxa responses. Here, we assessed an arboreal mangrove mollusk community before and after an extreme cold event (ECE) to determine the effects of the ECE on deterministic and stochastic processes, as well as succession, in abundant and rare taxa. We found that the ECE caused increasingly divergent succession of mollusks, as reflected by changes in species richness and species turnover; these changes more strongly affected the abundant taxa than the rare taxa. The relative importance of stochastic and deterministic processes in shaping mollusk communities was also altered after the ECE, although the effects differed between the abundant and rare species assemblages. That is, in response to the ECE, the abundant assemblage maintained a consistent level of mutualism while significantly increasing divergent succession by reducing ecological drift, decreasing niche breadths, weakening interspecific competition, promoting environmental selection, and increasing dispersal limitations. In contrast, the rare assemblage maintained high levels of divergent succession by increasing ecological drift, improving environmental filtering, decreasing niche breadths, weakening both interspecific competition and mutualism, and eroding spatial limits. Thus, species richness, species turnover, abundant species, and rare taxa should be the recommended indicators for the ECE; deterministic and stochastic processes should be mechanistic indexes for community coping with the ECE and also be theoretical indicators for biodiversity conservation and restoration after the ECE. More broadly, our results highlight that mechanistic indexes (deterministic and stochastic processes) and community structure indicators (species richness and species turnover) should be considered in differently-abundant taxa (abundant and rare taxa) in order to more accurately predict the effects of climate change on communities and devise targeted management and conservation strategies for the world's biodiversity.