Morphological convergence and coexistence in three sympatric North American species of Microtus (Rodentia: Arvicolinae)

Niche theory predicts that ecologically identical species cannot stably coexist in local communities. My aim was to investigate morphological diversity as a possible factor enabling the coexistence of a species-rich Microtus (Rodentia: Arvicolinae) fauna in a hotspot of North American mammalian diversity, the Greater Yellowstone Ecosystem (GYE). LOCATION: The Greater Yellowstone Ecosystem, North America. METHODS: Using in-hand morphological measurements of size and shape, I compared the morphologies of three North American vole species (Microtus spp.), in sympatry in the GYE and in allopatry across their ranges, in order to examine: (1) whether morphologies are fixed or plastic and (2) the degree of morphological character displacement or convergence in sympatric species. RESULTS: Support was found for plasticity of morphology for all three vole species: M. longicaudus, M. montanus and M. pennsylvanicus. However, Microtus individuals of all species from the GYE area of sympatry were more similar to each other than to allopatric individuals of the same species. MAIN CONCLUSIONS: Competition among these congeners is not manifested in morphological overdispersion. The response of these congeneric species to the same local ecological conditions is convergent. The relative strength of environmental conditions appears to be stronger than the strength of competitive interactions among the study species.

生态位理论（Niche theory）预测，生态位等同的物种无法在本地群落中稳定共存。本研究旨在探究形态多样性作为潜在驱动因子，助力物种丰富的田鼠属（Microtus，啮齿目：田鼠亚科）类群在北美哺乳动物多样性热点区域——大黄石生态系统（Greater Yellowstone Ecosystem，GYE）中实现共存。
研究区域：北美大黄石生态系统。
研究方法：通过体型与形状的实地形态测量，本研究对比了大黄石生态系统内同域分布（sympatry）的3种北美田鼠（田鼠属物种）及其分布范围内异域分布（allopatry）种群的形态特征，以考察两大科学问题：（1）田鼠的形态是固定不变还是具有可塑性（plasticity）；（2）同域分布物种间的形态特征替换或趋同（convergence）程度。
研究结果：本研究发现，3种田鼠——长尾田鼠（M. longicaudus）、山地田鼠（M. montanus）与宾夕法尼亚田鼠（M. pennsylvanicus）——均存在形态可塑性。然而，大黄石生态系统同域分布区域内的各田鼠个体间形态相似度，高于同种异域分布个体间的相似度。
主要结论：本研究中的同属物种（congeners）间的竞争并未表现为形态离散（morphological overdispersion）。这些同属物种对相同本地生态条件的响应呈现趋同性。相较于研究物种间的种间竞争强度，环境条件的相对作用更强。