Data from: Explaining ecological shifts: the roles of temperature and primary production in the long-term dynamics of benthic faunal composition

Predicting the ecological consequences of environmental change requires that we can identify the drivers of long-term ecological variation. Biological assemblages can exhibit abrupt deviations from temporal trends, potentially resulting in irreversible shifts in species composition over short periods of time. Such dynamics are hypothesised to occur as gradual forcing eventually causes biological thresholds to be crossed, but could also be explained by biota simply tracking abrupt changes to their environment. Here, we modelled temporal variation in a North Sea benthic faunal assemblage over a 40-year period (1972–2012) to test for changes to temporal trends of biota and determine whether they could be explained by underlying patterns in sea temperature and primary production. These extrinsic factors were postulated to influence community dynamics through their roles in determining and sustaining the metabolic demands of organisms, respectively. A subset of mainly large and long-lived taxa (those loaded on the first principal component of taxa densities) exhibited two significant changes to their temporal trends, which culminated in a shift in assemblage composition. These changes were explained by an increase in pelagic primary production, and hence detrital food input to the seabed, but were unrelated to variation in sea temperature. A second subset of mainly small and short-lived taxa (those loaded on the second principal component) did not experience any significant changes to their temporal trends, as enhanced pelagic primary production appeared to mitigate the impact of warming on these organisms. Our results suggest that abrupt ecological shifts can occur as biota track underlying variation in extrinsic factors, in this case primary production. Changes to the structure of ecosystems may therefore be predictable based on environmental change projections.

预测环境变化的生态效应，需先明确长期生态变异的驱动因子。生物群落可能偏离其固有时间序列趋势发生突变，进而可能在短时间内引发物种组成的不可逆转变。现有假说认为，这类动态的发生要么是因为渐进式环境胁迫最终突破生物阈值，要么可简单归因于生物群落追踪环境的突变变化。本研究针对1972年至2012年这40年间的北海底栖动物群落（benthic faunal assemblage）的时间变异开展建模，以检验生物群落时间趋势的变化，并判断其是否可由海水温度与初级生产的潜在模式所解释。上述外源因子分别通过决定与维持生物体代谢需求的作用，影响群落动态。对应类群密度第一主成分载荷的类群子集（以大型、长寿命类群为主）的时间趋势出现两处显著变化，最终促成群落组成发生转变。此类变化可由浮游初级生产（pelagic primary production）的提升，亦即向海底输入的碎屑食物量增加所解释，但与海水温度的变异无关。对应类群密度第二主成分载荷的第二类群子集（以小型、短寿命类群为主）的时间趋势未出现任何显著变化，这是因为增强的浮游初级生产似乎缓解了海洋变暖对这类生物的影响。本研究结果表明，当生物群落追踪外源因子的潜在变异时，可能会出现突发的生态转变——本次研究中的外源因子即为初级生产。据此，基于环境变化的预测结果，生态系统结构的改变或可被提前预判。