Final thermal conditions override the effects of temperature history and dispersal in experimental communities

Predicting the effect of climate change on biodiversity is a multifactorial problem that is complicated by potentially interactive effects with habitat properties and altered species interactions. In a microcosm experiment with communities of microalgae, we analysed whether the effect of rising temperature on diversity depended on the initial or the final temperature of the habitat, on the rate of change, on dispersal and on landscape heterogeneity. We also tested whether the response of species to temperature measured in monoculture allowed prediction of the composition of communities under rising temperature. We found that the final temperature of the habitat was the primary driver of diversity in our experimental communities. Species richness declined faster at higher temperatures. The negative effect of warming was not alleviated by a slower rate of warming or by dispersal among habitats and did not depend on the initial temperature. The response of evenness, however, did depend on the rate of change and on the initial temperature. Community composition was not predictable from monoculture assays, but higher fitness inequality (as seen by larger variance in growth rate among species in monoculture at higher temperatures) explained the faster loss of biodiversity with rising temperature.

预测气候变化对生物多样性的影响是一项多因子难题，生境属性与物种互作改变之间潜在的交互效应进一步提升了其研究复杂度。我们以微藻群落为研究对象开展微宇宙实验（microcosm experiment），分析了升温对生物多样性的影响是否取决于生境初始温度、终末温度、温度变化速率、生物扩散以及景观异质性。本研究同时验证了：仅通过单种培养（monoculture）体系中测得的物种温度响应，能否预测升温条件下的群落组成。
研究结果显示，生境终末温度是调控本实验群落生物多样性的核心驱动因子；温度越高，物种丰富度的下降速率越快。升温产生的负面影响并未因升温速率放缓或生境间的生物扩散而得到缓解，且不受生境初始温度的影响。但物种均匀度的响应则同时受温度变化速率与初始温度的调控。仅通过单种培养测定无法预测群落组成，但更高的适合度不平等（表现为高温下单种培养体系中物种间生长速率的更大变异）能够解释升温下生物多样性更快丧失的现象。