McDevitt-Galles Travis, Johnson Pieter T J
Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, 80309, USA.
Freshw Biol. 2018 Nov;63(11):1457-1468. doi: 10.1111/fwb.13173. Epub 2018 Sep 10.
Identifying ecological niche filters that shape species community composition is a critical first step in understanding the relative contributions of deterministic and stochastic processes in structuring communities. Systems with harsh ecological filters often have a more deterministic basis to community structure. Although these filters are often treated as static, investigations into their stability through time are rare, particularly in combination with extreme forms of environmental change such as drought.We examined the richness and composition of aquatic macroinvertebrate communities from 36 ponds over four years during the onset of a megadrought to answer the following questions: (1) what are the relative influences of non-native fish presence and pond permanence in structuring communities? And (2) how do the magnitudes of such filters vary through time?As predicted, fish presence had a strong, negative effect on both alpha and gamma diversity, lowering average invertebrate richness in pond communities by 23%. However, fish presence and sample year interacted to determine both richness and taxa composition: as drought conditions intensified, the effects of fish weakened such that there were no differences in the richness or composition between fish and fishless ponds by the later sampling years. Moreover, large-bodied invertebrate groups - often considered highly vulnerable to fish predation - were detected within fish-occupied sites by the final year of the study.This pattern was associated with progressive decreases in precipitation due to a severe drought in California, emphasizing the importance of exogenous, regional factors in moderating the strength of biotic niche filters on local community structure over time. Given that all detected fish species were non-native, these results also have application to understanding and forecasting changes in the diversity of native insects and other aquatic invertebrates.
识别塑造物种群落组成的生态位筛选因素是理解确定性和随机性过程在构建群落中的相对贡献的关键第一步。具有严苛生态筛选因素的系统通常在群落结构上有更确定的基础。尽管这些筛选因素常被视为静态的，但很少有对其随时间稳定性的研究，特别是与干旱等极端形式的环境变化相结合的情况。我们在一场特大干旱开始的四年间，对36个池塘的水生大型无脊椎动物群落的丰富度和组成进行了研究，以回答以下问题：（1）非本地鱼类的存在和池塘的永久性在构建群落中各自有怎样的相对影响？以及（2）这些筛选因素的强度如何随时间变化？正如预测的那样，鱼类的存在对α多样性和γ多样性都有强烈的负面影响，使池塘群落中无脊椎动物的平均丰富度降低了23%。然而，鱼类的存在和采样年份相互作用，共同决定了丰富度和分类群组成：随着干旱状况加剧，鱼类的影响减弱，以至于到后期采样年份，有鱼池塘和无鱼池塘在丰富度或组成上没有差异。此外，在研究的最后一年，在有鱼的地点检测到了通常被认为极易受到鱼类捕食的大型无脊椎动物类群。这种模式与加利福尼亚州严重干旱导致的降水量逐渐减少有关，强调了外部区域因素在随着时间推移调节生物生态位筛选对当地群落结构强度方面的重要性。鉴于所有检测到的鱼类物种都是非本地的，这些结果也适用于理解和预测本地昆虫及其他水生无脊椎动物多样性的变化。
