November 20 2014

5:00 pm BSRB 154

EcoEvoPub Series

Graduate Student Presentations


Department of Biology
California State University, Northridge

“Relative Effect of Exploitative and Interference Competition Varies with Population Density”


Holdridge, EM. And C.P. terHorst
-California State University, Northridge

Intraspecific competition is a major factor influencing population dynamics. Competition can occur via an exploitative mechanism, where individuals compete indirectly through depletion of a shared limiting resource, or an interference mechanism, in which directly inhibit one another’s ability to access resources either aggressively or passively. Although exploitative competition is inherently dependent upon resource levels, interference competition can potentially decrease population growth rates independent of resource availability. Interference competition is common in most systems, but it is still unclear whether interference competition is common in most systems, but it is still unclear whether interference increases in intensity with population density. Using experimental microcosms and maximum likelihood models, we tested the hypothesis that strength of intraspecific interference competition increases as a function of population density. Interestingly, we found that at low densities, resource availability drove differences in population growth rates between low and high resource experimental groups, while at high densities we found no effect of resource level. To test whether this pattern was due to a shift from exploitation to interference competition, we used maximum likelihood to estimate the intensity of interference within the system. We found that as density increases, populations shifted from a more exploitation-based system to a more interference-based system. Our results show that interference competition increases with density, driving interesting patterns in population dynamics and density-dependence

Department of Human Genetics

“The genetic basis of Phalacrocorax harrisi loss of flight”

The Galapagos Cormorant, Phalacrocorax harrisi, is unique in that is the only cormorant that has lost the ability to fly due to the miniaturization of its wings. Also, it is the only Cormorant species that inhabits the Galapagos Islands (Livezey, 1991). Environmental changes often eliminate or weaken selective pressures that were previously important for the maintenance of traits and such instances are known as ‘relaxed selection’ (Lahti et al, 2009). The lack of natural predators and the constant supply of food in Galapagos have been proposed as important factors leading to Phalacrocorax harrisi distinctive phenotype. Despite the high prevalence of cases of ‘relaxed selection’ in nature, the genetic and molecular basis of such evolutionary processes are poorly understood. A deeper study of these phenomena is thus necessary to better understand evolutionary forces and dynamics of speciation, as well as the evolution of shape and form of limbs. We have undertaken a comparative genomics approach in order to find the mutation or mutations responsible for P. harrisi loss of flight, which has led to de novo assembly the genomes of P. harrisi and its close relatives. Here we report our progress.















































































































































































































































































































































































































































































































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