Scale dependent niche evolution
Ecological niche is an important concept for investigating core ecological problems such as species coexistence, community assembly rules. Understanding how niche divergence (evolving) will be beneficial for theoretical study to species coexistence mechanism and make predications for species distribution and community structure, give hints for future conservation. Previous studies have provided evidences supporting niche conservatism. For example, based on field experiments with 32 plant species, Burns & Strauss (2011) proposed that more closely related species are more ecologically similar. Culumber & Tobler (2016) found that closely related species in the two swordtail clades exhibited higher levels of niche overlap than expected given environmental background similarity indicative of niche conservatism. Hadly et al. (2009) suggested niche conservatism above species level (genera and families) of North American mammals.
However, counter evidences were also provided by some authors. After comparing geographical parameters with molecular phylogenetic distances, Knouft et al. (2006) found that no general relationship exists between phylogenetic similarity and niche similarity, with some examples in which closely related species display niche conservatism and some in which they exhibit highly divergent niches. Losos et al. (2003) also suggested niche lability in the evolution of a Caribbean lizard community. Pearman et al. (2014) proposed no evidence for past phylogenetic niche conservatism of a European avian assemblage in climatic, habitat and trophic niches.
For these controversial results, Crisp & Cook (2012) stressed that phylogenetic niche conservatism is a pattern, not a process, and is found only in some traits and some lineages. Wang et al. (2015) also mentioned that different dimensions of ecological niche may display different evolutionary patterns.
According to our present results, we propose that niche evolution could be dependent not only on niche dimensions, but also on scales. On a large scale, niche may exhibit conservatism; while on a small scale, especially when the species co-exist in one local area, competitive exclusion principle may work, and the very closely related species may exhibit larger niche divergence. It is interesting to note that some very distantly related species showed trophic niche convergence in the present study. We guess that these distantly related species could have evolved differences in different niche dimensions, so they could share similar trophic niche. In overall, we believe that our findings will contribute to future theoretical and empirical niche explorations.
ACKNOWLEDGMENTS. We sincerely thank Qiaoling Deng, Xianglong Jiang, Huaming Hu for collection of samples. Thanks are also given to Shufan yang, Qiang Qin for their laboratory assistance. This study was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB31000000), National Key R and D Program of China (2018YFD0900806) and National Natural Science Foundation of China (31872234).