Data from: Realised niche changes in a native herbivore assemblage associated with the presence of livestock

Habitat partitioning is a common ecological mechanism to avoid competition among coexisting species, and the introduction of new species into existing assemblages can increase competitive pressures. However, situations of species in allopatry and sympatry only differing in species presence but not in environmental conditions are scarce. Thus, discerning whether niche segregation arises from competition or from different habitat preferences is usually unfeasible. Here, we analyse species' habitat niches in an assemblage of native and introduced herbivores in southern Patagonia. We test if niche overlap is higher between native and domestic herbivores than among natives as expected from the relatively short time of coexistence, and we evaluate the effect of intra- and interspecific competition on niche breadth. We use a probabilistic multidimensional approach and null models to evaluate overlap and changes in niche dimensions. Overlap among native species is low as expected for species coexisting in evolutionary time. In native-domestic species pairs, niche overlap was higher than among natives, although showing some niche segregation indicating niche differentiation in ecological time. Moreover, the presence of domestic species was associated with niche narrowing of both native and introduced species, revealing interspecific density-dependent effects on their habitat niche during resource shortage periods.生境分区（habitat partitioning）是共存物种间规避竞争的常见生态学机制，将新物种引入现有物种集合会加剧竞争压力。然而，仅存在物种有无差异、环境条件一致的异域分布（allopatry）与同域分布（sympatry）物种的情况极为罕见。因此，通常难以分辨生态位分隔究竟源于物种间竞争，还是源于不同的生境偏好。 本研究聚焦巴塔哥尼亚南部本土与外来植食性动物的物种集合，分析各物种的生境生态位（habitat niche）。我们将验证：鉴于二者共存时间相对较短，本土与家养植食动物间的生态位重叠（niche overlap）是否高于本土物种间的重叠；同时评估种内与种间竞争对生态位宽度（niche breadth）的影响。本研究采用概率多维分析方法与零模型（null model），对生态位重叠及生态位维度变化进行量化评估。 进化尺度上共存的本土物种间生态位重叠较低，符合学界预期。而本土-家养物种对的生态位重叠高于本土物种间的重叠，尽管二者仍存在一定的生态位分隔，体现出生态尺度上的生态位分化。此外，家养物种的存在会导致本土与外来物种的生态位均出现收窄，这揭示了资源匮乏时期种间密度依赖效应对它们生境生态位的影响。