Department of Life and Environmental Sciences, Bournemouth University, Poole, UK.
Departmento de Zoología y Antropología Física, Universidad de Murcia, Murcia, Spain.
J Anim Ecol. 2019 Jul;88(7):1066-1078. doi: 10.1111/1365-2656.12996. Epub 2019 May 10.
Ecological theory on the trophic impacts of invasive fauna on native competitors is equivocal. Whilst increased interspecific competition can result in coexisting species having constricted and diverged trophic niches, the competing species might instead increase their niche sizes to maintain energy intakes. Empirical experiments can test invasion theory on competitive interactions and niche sizes across different spatial scales and complexity. The consequences of increased interspecific competition from a model alien fish Leuciscus idus were tested on two taxonomically and trophically similar native fishes, Squalius cephalus and Barbus barbus. Competitive interactions were tested in tank aquaria using comparative functional responses (CFRs) and cohabitation trials. The consequences of these competitive interactions for the trophic niche sizes and positions of the fishes were tested in pond mesocosms. Comparative functional responses revealed that compared to B. barbus, L. idus had significantly higher attack and consumption rates; cohabitation trials revealed B. barbus growth rates were depressed in sympatry with L. idus. For L. idus and S. cephalus, differences in their functional response parameters and growth rates were not significant. Pond mesocosms used stable isotope metrics to quantify shifts in the trophic niche sizes of the fishes between allopatry and sympatry using a substitutive experimental design. Isotopic niches were smaller and more divergent in sympatric paired species than predicted by their allopatric treatments, suggesting trophic impacts from interspecific competition. However, an all-species sympatric treatment revealed similar niche sizes with allopatry. This maintenance of niche sizes in the presence of all species potentially resulted from the buffering of direct competitive effects of the species pairs by indirect effects. Experimental predictions from tank aquaria assisted the interpretation of the constricted and diverged trophic niches detected in the paired-species sympatric treatments of the pond mesocosms. However, the all-species sympatric treatment of this experiment revealed greater complexity in the outcomes of the competitive interactions within and between the species. These results have important implications for understanding how alien species integrate into food webs and influence the trophic relationships between native species.
关于入侵动物对本地竞争者的营养影响的生态理论存在分歧。虽然种间竞争的加剧可能导致共存物种的营养生态位变窄和发散，但竞争物种可能会扩大其生态位大小以维持能量摄入。实证实验可以在不同的空间尺度和复杂性上测试关于竞争相互作用和生态位大小的入侵理论。使用比较功能响应 (CFR) 和共居试验在水箱水族馆中测试了模型外来鱼类 Leuciscus idus 对两种分类和营养上相似的本地鱼类 Squalius cephalus 和 Barbus barbus 的种间竞争的影响。在池塘中型中测试了这些竞争相互作用对鱼类营养生态位大小和位置的影响。比较功能响应表明，与 B. barbus 相比，L. idus 的攻击和消耗率明显更高；共居试验表明，B. barbus 的生长速度在与 L. idus 同域时受到抑制。对于 L. idus 和 S. cephalus，它们的功能响应参数和生长速度的差异不显著。池塘中型使用稳定同位素指标，通过替代实验设计，在异地和同域之间量化鱼类营养生态位大小的变化。同域配对物种的同位素生态位比异地处理预测的更小且更发散，这表明种间竞争存在营养影响。然而，所有物种的同域处理显示出与异地处理相似的生态位大小。在所有物种存在的情况下，这种生态位大小的维持可能是由于物种对的直接竞争效应被间接效应缓冲所致。水箱水族馆的实验预测有助于解释池塘中型配对物种同域处理中检测到的受限和发散的营养生态位。然而，本实验的所有物种同域处理揭示了物种间和物种内竞争相互作用的结果更加复杂。这些结果对于理解外来物种如何融入食物网以及影响本地物种之间的营养关系具有重要意义。
