Section of Integrative Biology, University of Texas at Austin, TX 78712, USA.
Proc Biol Sci. 2010 Jun 22;277(1689):1789-97. doi: 10.1098/rspb.2010.0018. Epub 2010 Feb 17.
A species's niche width reflects a balance between the diversifying effects of intraspecific competition and the constraining effects of interspecific competition. This balance shifts when a species from a competitive environment invades a depauperate habitat where interspecific competition is reduced. The resulting ecological release permits population niche expansion, via increased individual niche widths and/or increased among-individual variation. We report an experimental test of the theory of ecological release in three-spine stickleback (Gasterosteus aculeatus). We factorially manipulated the presence or absence of two interspecific competitors: juvenile cut-throat trout (Oncorhynchus clarki) and prickly sculpin (Cottus asper). Consistent with the classic niche variation hypothesis, release from trout competition increased stickleback population niche width via increased among-individual variation, while individual niche widths remained unchanged. In contrast, release from sculpin competition had no effect on population niche width, because increased individual niche widths were offset by decreased between-individual variation. Our results confirm that ecological release from interspecific competition can lead to increases in niche width, and that these changes can occur on behavioural time scales. Importantly, we find that changes in population niche width are decoupled from changes in the niche widths of individuals within the population.
物种的生态位宽度反映了种内竞争的多样化效应与种间竞争的约束效应之间的平衡。当来自竞争环境的物种入侵种间竞争减少的贫瘠生境时，这种平衡会发生变化。由此产生的生态释放允许通过增加个体生态位宽度和/或增加个体间变异来扩大种群生态位。我们在三种棘鱼（Gasterosteus aculeatus）中报告了生态释放理论的实验测试。我们通过人为因素控制两种种间竞争者的存在与否：幼年的虹鳟（Oncorhynchus clarki）和棘胸鱼（Cottus asper）。与经典的生态位变异假说一致，来自虹鳟竞争的释放通过增加个体间变异来增加棘鱼的种群生态位宽度，而个体生态位宽度保持不变。相比之下，来自棘胸鱼竞争的释放对种群生态位宽度没有影响，因为个体生态位宽度的增加被个体间变异的减少所抵消。我们的结果证实，种间竞争的生态释放可以导致生态位宽度的增加，并且这些变化可以在行为时间尺度上发生。重要的是，我们发现种群生态位宽度的变化与种群内个体的生态位宽度的变化是脱钩的。
