A lineage colonizing a geographic region with no competitors may exhibit rapid diversification due to greater ecological opportunity. The resultant species diversity of this primary-colonizing (incumbent) clade may limit subsequent lineages' ability to persist unless these non-incumbent lineages are ecologically distinct. We compare the diversity in diet-related mandibular morphology of two sympatric murid rodent clades endemic to Luzon Island, Philippines—incumbent Phloeomyini and secondary-colonizing Chrotomyini—to the mandibular morphological diversity of Sahul Hydromyini, the sister clade of Chrotomyini and the incumbent murid lineage on the supercontinent of Sahul. This three-clade comparison allows us to test the hypothesis that incumbent lineages can force persistent ecological distinction of subsequent colonists at the time of colonization and throughout the subsequent history of the two sympatric clades. We find that Chrotomyini forms a subset of the diversity of their clade plus Sahul Hydromyini that minimizes overlap with Phloeomyini. We also infer that this differentiation extends to the stem ancestor of Chrotomyini and Sahul Hydromyini, consistent with a biotic filter imposed by Phloeomyini. Our work illustrates that incumbency has the potential to have a profound influence on the ecomorphological diversity of colonizing lineages at the island scale even when the traits in question are evolving at similar rates among independently colonizing clades.
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Passerine sister clade comparisons reveal variable macroevolutionary outcomes of interhemispheric dispersal
Dispersal events offer a unique window into macroevolutionary processes, especially with respect to the effects of competition on diversification. Empirical studies testing alternative predictions of competitive effects are often limited in either geographic or phylogenetic scale. Here, we tested some of these hypotheses by comparing an assemblage of 16 oscine passerine clades, representing independent dispersal events into the Western Hemisphere, to their sister clades in the Eastern Hemisphere. We also compared the diversity of this assemblage of clades to an older, incumbent passerine clade in the Western Hemisphere, the suboscines. Specifically, we tested for ecological opportunity and incumbency-mediated constraints by analysis of clade-specific morphological disparities and rates of evolution relative to dispersal history. While there was no consistent outcome of oscine dispersal and macroevolution in the Western Hemisphere relative to their Eastern Hemisphere sister groups, most clades supported a role for ecological opportunity or incumbency effects, and such effects were better explained by differences in species accumulation than by differences in rates of trait evolution or colonization timing. This general pattern was not evident when comparing the entire oscine assemblage of the Western Hemisphere to the incumbent suboscine radiation; oscines and suboscines occupy comparable regions of functional trait diversity and, despite higher rates of trait evolution in oscines, these observations were consistent with simulated null expectations. This result suggests that oscine and suboscine assemblages may have evolved in relative isolation for a significant fraction of their history.
more » « less- NSF-PAR ID:
- 10481897
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Journal of Evolutionary Biology
- ISSN:
- 1420-9101
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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