October 10, 2019

5:00 1100 TLSB

EcoEvoPub Series

"Graduate Student Presentations"

MARY VAN DYKE
Department of Ecology and Evolutionary Biology,
Kraft Lab, UCLA

“Changes in Precipitation Alter Plant Coexistence and Competitive Interactions in an Annual Grassland”

As greenhouse gas emissions continue to rise, understanding how ecological communities will respond to future climate change is critical. In southern California precipitation volatility is predicted to increase with more extreme dry and wet seasons expected in the future. The composition of communities may change as these more extreme patterns favor some species over others. For a species to persist on the landscape, however, it must not only survive the direct effects of precipitation changes but also the indirect effects of altered densities and identities of competitors. Using the annual grassland community at Sedgwick Reserve, I explored how changes in precipitation alter competitive dynamics between species. I used temporary rainout shelters to grow six annual species including two grasses and four forbs, in different competitive backgrounds under an amplified and reduced precipitation treatment. I then quantified the strength of competition between species under both treatments using an annual plant demographic model that accounts for germination, fecundity and neighbor density. While finding little direct responses to the precipitation treatments in their seed production, there were changes in competitive abilities and competitive outcomes between species. These findings indicate that small direct effects can amplify to community wide changes through altered competitive dynamics.

MARK JUHN
Department of Ecology and Evolutionary Biology,
Van Valkenburgh Lab and Alfaro Lab, UCLA

“Evaluating the Permoance of the Log Rate, Log Interval (LRI) Method on Phylogenetic Trait Data”

Accurately calculating the rate at which morphology changes is critical in answering key questions in evolutionary biology. However, traditional rate metrics have a strong dependence on interval length and the tempo of evolution apart from the mode can be misleading. One method developed to explore the tempo and mode of phenotypic evolution from the fossil record is the log-rate, log-interval (LRI) method. The LRI method allows for the simultaneous determination of mode as well as the tempo of phenotypic evolution by computing all possible rates from an evolutionary sequence. A recent study applies the LRI method to phylogenetic trait data. The author found phylogenetic independent contrasts return abnormally high rates of phenotypic evolution compared to the rate calculated from pairwise differences of tips. However, the behavior of the LRI method on phylogenetic trait data is not well understood. Here we systematically explore the behavior of the LRI method under various evolutionary scenarios. We found the LRI method is only able to distinguish between evolutionary mode under extreme parameter values. Additionally, rates of phenotypic evolution calculated from independent contrasts were not significantly elevated compared to those calculated from tip differences. These results suggest the LRI method should not be applied to phylogenetic trait data.