Mark C. Belk

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We document a strong association between predation environment and life-history phenotypes in the Costa Rican livebearing fish Brachyrhaphis rhabdophora. Populations that co-occurred with piscine predators attained maturity at a smaller size, and produced more, smaller offspring relative to populations from predator-free environments. These differences(More)
The threat-sensitivity hypothesis predicts that prey individuals will increase antipredator behaviors as apparent predator risk increases. An implicit assumption of the threat-sensitivity hypothesis is that predator risk is additive. In other words, all characteristics of a predator that indicate risk should contribute in an additive way to determine the(More)
We evaluate the cost-of-reproduction hypothesis in the burying beetle Nicrophorus orbicollis and examine how the importance of this trade-off changes as females age (i.e., the terminal-investment hypothesis). These beetles breed on small vertebrate carcasses, which serve as a food resource for them and their offspring. Consistent with the(More)
River environments are characterized by extreme spatial and temporal variation in the physical environment. The relationship of fish assemblages to environmental variation is poorly understood in many systems. In Chile zonation patterns of fish assemblages have been documented in several Andean river drainages. Coastal river drainages are comparatively(More)
We suggest that the ultimate outcome of interactions between native species and invasive species (extinction or coexistence) depends on the number of simultaneous negative interactions (competition and predation), which depends on relative body sizes of the species. Multiple simultaneous interactions may constrain the ability of native species to trade(More)
Conservation biologists rely heavily on taxonomy to set the scope for biological monitoring and recovery planning of rare or threatened species. Yet, taxonomic boundaries are seldom evaluated as falsifiable hypotheses that can be statistically tested. Here, we examine species boundaries in leatherside chub (Teleostei, Cyprinidae), an imperiled desert fish(More)
Natural selection often results in profound differences in body shape among populations from divergent selective environments. Predation is a well-studied driver of divergence, with predators having a strong effect on the evolution of prey body shape, especially for traits related to escape behavior. Comparative studies, both at the population level and(More)
Predation can cause morphological divergence among populations, while ontogeny and sex often determine much of morphological diversity among individuals. We used geometric morphometrics to characterize body shape in the livebearing fish Brachyrhaphis rhabdophora to test for interactions between these three major shape-determining factors. We assessed shape(More)
Previous studies suggested that differences in age at maturity among populations of bluegill sunfish (Lepomis macrochirus) were not genetically based, but rather were a phenotypic response to the presence of predators. I conducted two experiments to determine if the presence of largemouth bass affected age at maturity in bluegill sunfish. Bluegills from(More)