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.

要预测环境变化所引发的生态效应，需先明确长期生态变异的驱动因素。生物群落（biological assemblage）在时间序列上可出现突变式偏离，进而可能在短时间内造成物种组成的不可逆转变。此类动态被提出假说认为：当渐进式胁迫最终突破生物阈值（biological threshold）时便会发生；但也可通过生物群落仅追踪环境的突变变化来解释。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，以检验生物群落在时间趋势上的变化，并判断这些变化是否可由海水温度与初级生产力（primary production）的潜在格局所解释。研究假说认为，这两类外在因子分别通过调控与维持生物体的代谢需求（metabolic demands），进而影响群落动态。以大型、长寿命分类群（taxon，复数为taxa）为主的子集（即在分类群密度第一主成分（first principal component）上载荷较高的类群）在时间趋势上出现了两处显著变化，最终引发了群落组成的转变。此类变化可由浮游初级生产力（pelagic primary production）提升（进而向海底输入更多碎屑食物（detrital food input））得到解释，但与海水温度的变异无关。以小型、短寿命分类群为主的第二子集（即在分类群密度第二主成分上载荷较高的类群）的时间趋势未出现任何显著变化，这是因为提升的浮游初级生产力似乎缓解了变暖对这类生物的影响。本研究结果表明，当生物群落追踪外在因子（本研究中为初级生产力）的潜在变异时，可能会出现突变式生态转变。因此，基于环境变化预测模型，生态系统结构的变化或可被预测。