Understanding why some species coexist and others do not remains one of the fundamental challenges of ecology. While several lines of evidence suggest that closely related species are unlikely to occupy the same habitat because of competitive exclusion, there are many cases where closely related species do co-occur. Research comparing sympatric and allopatric populations of co-occurring species provides a framework to understand the role of phenotypic diversification in species coexistence. In this study I focus on the livebearing fish Poeciliopsis baenschi and ask if differences in phenotypic traits among populations can be explained by the presence or absence of the congeneric species P. turneri. I focus on phenotypic divergence in life history traits and in body shape, two sets of integrated traits likely to respond to variation in competition. Additionally, I compare explore the effects of sympatry and allopatry on sexual dimorphism. I take advantage of a natural experiment in western Mexico where P. baenschi co-occur with P. turneri in some locations (sympatric populations) but also exist in isolation in other locations (allopatric populations). My results show that sympatric populations of P. baenschi differed significantly in life history traits and body shape when compared to their allopatric counterparts. Additionally, the amount of sexual dimorphism differed between sympatric and allopatric populations of P. baenschi, suggesting different constraints might exist in sympatry and allopatry for sexual dimorphism. Lastly, I explore my results in the context of trait evolution as it relates to species coexistence.



College and Department

Life Sciences; Biology



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geometric morphometrics, life history theory, Poeciliidae, resource competition, sexual dimorphism, sympatry

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Biology Commons