By Daniel Martinez

Faculty Mentor: Dr. Bradley Lamphere

Abstract

Invasive species living with closely related relatives pose an interesting question for community ecology: How do these species coexist? Typically, in nature, when two closely related species evolve together, they will segregate their niches to reduce competition. We can observe how species reduce competition in sympatric versus allopatric populations by examining character displacement between populations. Character displacement is when species living together in sympatry; morphology, behavior, niche, or physiology shift away from their allopatric state, where they live separately. My project examined how L. cyanellus (green sunfish), an invasive species, lives in sympatry with L. auritus (redbreast sunfish) vs in allopatry in Virginia streams. Both species share a similar niche as opportunistic omnivores, and I hypothesized that sympatric populations would show character displacement due to competition from overlapping niches. To achieve my goal, I collected samples from allopatric and sympatric populations from the Potomac, Rappahannock, and York drainages. I then photographed each fish and plotted landmarks to assess changes in morphology. Afterwards, I extracted their digestive tract to record their diet. From the data collected, I was able to conduct a Principal Component Analysis (PCA) to assess changes in morphology and diet caused by competition. My study found significant diet overlap between both species, regardless of population type and drainage. The morphology PCAs showed evidence of character displacement for L. cyanellus in the Potomac and L. auritus York drainages, but not the Rappahannock or the total population. Neither the diet nor the total population PCAs supported my hypothesis that one species is applying pressure on the other to change. This result suggests that each drainage is evolutionarily isolated from the others, and competition for food is not altering morphology. Environmental factors may be controlling morphology in the Potomac and York drainages, while competition in the Rappahannock displaces a different trait.