Mordecai Erin A, Jaramillo Alejandra G, Ashford Jacob E, Hechinger Ryan F, Lafferty Kevin D
Ecology. 2016 Jun;97(6):1484-96.
Competition - colonization tradeoffs occur in many systems, and theory predicts that they can strongly promote species coexistence. However, there is little empirical evidence that observed competition - colonization tradeoffs are strong enough to maintain diversity in natural systems. This is due in part to a mismatch between theoretical assumptions and biological reality in some systems. We tested whether a competition - colonization tradeoff explains how a diverse trematode guild coexists in California horn snail populations, a system that meets the requisite criteria for the tradeoff to promote coexistence. A field experiment showed that subordinate trematode species tended to have higher colonization rates than dominant species. This tradeoff promoted coexistence in parameterized models but did not fully explain trematode diversity and abundance, suggesting a role of additional diversity maintenance mechanisms. Spatial heterogeneity is an alternative way to promote coexistence if it isolates competing species. We used scale transition theory to expand the competition - colonization tradeoff model to include spatial variation. The parameterized model showed that spatial variation in trematode prevalence did not isolate most species sufficiently to explain the overall high diversity, but could benefit some rare species. Together, the results suggest that several mechanisms combine to maintain diversity, even when a competition - colonization tradeoff occurs.
竞争 - 定殖权衡在许多系统中都会出现，理论预测它们能够有力地促进物种共存。然而，几乎没有实证证据表明观察到的竞争 - 定殖权衡强大到足以维持自然系统中的多样性。部分原因在于某些系统中理论假设与生物学现实之间存在不匹配。我们测试了竞争 - 定殖权衡是否能解释多种吸虫类群如何在加州角螺种群中共存，该系统满足权衡促进共存的必要标准。一项野外实验表明，从属吸虫物种的定殖率往往高于优势物种。这种权衡在参数化模型中促进了共存，但并未完全解释吸虫的多样性和丰度，这表明还存在其他多样性维持机制。如果空间异质性能够隔离竞争物种，那么它是促进共存的另一种方式。我们运用尺度转换理论扩展竞争 - 定殖权衡模型以纳入空间变异。参数化模型表明，吸虫流行率的空间变异并未充分隔离大多数物种以解释整体的高多样性，但可能使一些稀有物种受益。总之，结果表明即使存在竞争 - 定殖权衡，多种机制也会共同作用以维持多样性。
