Skelly David K
Department of Zoology, NJ-15, University of Washington, 98195, Seattle, WA, USA.
Oecologia. 1995 Aug;103(2):203-207. doi: 10.1007/BF00329081.
Studies of tadpole distributions have shown that despite overlapping affinities for semipermanent and permanent ponds, distributions of the spring peeper (Pseudacris crucifer) and the green frog (Rana clamitans) tend to be nonoverlapping. Because spring peepers are believed to be poor competitors, I hypothesized that competition from green frog larvae limits the distribution of spring peeper larvae. I stocked field enclosures with a constant density of spring peeper larvae, and one of four densities of green frog larvae (a "target-neighbor" design). Increased green frog density had a small effect on metamorphic size and no effects on survivorship, larval period or growth rates of spring peepers. In contrast to these small interspecific effects, green frogs had a large effect on their own performance. Intraspecific competition resulted in a 50% decline in growth rate and an 11% decline in metamorphic size. These results suggest that the species are segregated in resource use, or that compared with green frogs, spring peepers are better able to cope with depressed resource densities. In either case, this field experiment provides no evidence that interspecific competition from green frogs limits distributions of spring peepers. Other factors such as predation and breeding site choice by adults may contribute to the absence of spring peeper larvae from many semipermanent and permanent ponds.
对蝌蚪分布的研究表明，尽管春季角蛙（Pseudacris crucifer）和绿蛙（Rana clamitans）对半永久性和永久性池塘的偏好存在重叠，但它们的分布往往并不重叠。由于春季角蛙被认为是竞争力较弱的物种，我推测绿蛙幼体的竞争限制了春季角蛙幼体的分布。我在野外围栏中放入恒定密度的春季角蛙幼体，并设置了四种绿蛙幼体密度之一（一种“目标-邻居”设计）。绿蛙密度的增加对春季角蛙的变态大小影响较小，对其存活率、幼体期或生长速率没有影响。与这些较小的种间效应形成对比的是，绿蛙对自身的表现有很大影响。种内竞争导致生长速率下降50%，变态大小下降11%。这些结果表明，这两个物种在资源利用上是分离的，或者与绿蛙相比，春季角蛙更能应对资源密度降低的情况。无论哪种情况，这个野外实验都没有提供证据表明绿蛙的种间竞争限制了春季角蛙的分布。其他因素，如成年个体的捕食和繁殖地点选择，可能导致许多半永久性和永久性池塘中没有春季角蛙幼体。
