Species morphological changes can be mutually influenced by environmental or biotic factors, such as competition. South American canids represent a quite recent radiation of taxa that evolved forms very disparate in phenotype, ecology and behaviour. Today, in the central part of South America there is one dominant large species (the maned wolf, Chrysocyon brachyurus) that directly influence sympatric smaller taxa via interspecific killing. Further south, three species of similar sized foxes (Lycalopex spp.) share the same habitats. Such unique combination of taxa and geographic distribution makes South American dogs an ideal group to test for the simultaneous impact of climate and competition on phenotypic variation. Using geometric morphometrics, we quantified skull size and shape of 431 specimens belonging to the eight extant South American canid species: Atelocynus microtis, Cerdocyon thous, Ch. brachyurus, Lycalopex culpaeus, L. griseus, L. gymnocercus, L. vetulus and Speothos venaticus. South American canids are significantly different in both skull size and shape. The hypercarnivorous bush dog is mostly distinct in shape from all the other taxa while a degree of overlap in shape—but not size—occurs between species of the genus Lycalopex. Both climate and competition impacts interspecific morphological variation. We identified climatic adaptations as the main driving force of diversification for the South American canids. Competition has a lower degree of impact on their skull morphology although it might have played a role in the past, when canid community was richer in morphotypes.

中文翻译：

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南美洲犬科动物头骨形状的生态地理变化：是非生物过程还是生物过程？

物种的形态变化会受到环境或生物因素（例如竞争）的相互影响。南美犬科动物代表了最近的分类单元辐射，其进化形式在表型，生态和行为上截然不同。如今，在南美中部，有一种优势大种（鬃狼，Chrysocyon brachyurus）通过种间杀灭直接影响同胞较小的类群。再往南走，三种大小相似的狐狸（Lycalopexspp。）共享相同的栖息地。这种分类单元和地理分布的独特组合使南美犬成为测试气候和竞争对表型变异的同时影响的理想组。使用几何形态计量学，我们量化了431种标本的头骨尺寸和形状，这些标本属于八个现存的南美犬科动物：小食蚁兽（Atelocynus microtis），西多（Cerdocyon thous），中华绒螯蟹（Ch。brachyurus，Lycalopex culpaeus，L.灰色链霉菌，属gymnocercus，L. vetulus和Speothos venaticus。南美犬科动物的头骨大小和形状都明显不同。肉食性的布什犬在形状上与其他所有种类几乎都不同，而在Lycalopex属的物种之间却出现了一定程度的重叠（但大小没有重叠）。气候和竞争都会影响种间形态变化。我们确定气候适应是南美犬科动物多样化的主要驱动力。竞争对他们的头骨形态的影响程度较低，尽管在过去当犬科动物的形态类型较丰富时，竞争可能发挥了作用。