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November 19, 2020

5:00pm Zoom

EcoEvoPub Seminar Series
Department of Ecology and Evolutionary Biology, UCLA

" Graduate Student Presentations "

Kenji Hayashi

Department of Ecology and Evolutionary Biology, UCLA, Kraft Lab


 “Quantifying the effect of competitive interactions on the landscape-scale distributions of annual plant species in a California grassland”


As environmental change continues to drive shifts in species’ abundances and distributions, it is becoming more urgent now than ever to understand the various processes shaping species’ distributions. While much research has focused on the abiotic determinants of individual species’ distributions, in nature these species exist within ecological communities wherein biotic interactions such as resource competition can impact their realized distributions. Scaling local competitive interactions to landscape- and geographic-scale distributional patterns thus remains a key challenge in robustly predicting and responding to changes in species’ distributions. Here, I will present preliminary results from a field experiment designed to quantify the demographic performance of eight annual plant species in spatially variable edaphic and competitive environments in a California grassland, with the aim of empirically evaluating how competitive interactions shape plant species’ distributions in this natural landscape. Preliminary analyses suggest that (i) key demographic rates (germination, fecundity) are often significantly altered by both edaphic conditions and the presence of competitors, and (ii) competitive interactions appear to have a discernable impact on the realized distributional patterns of the study species on this landscape. Future directions, including relating plant species’ functional traits to the experimentally obtained responses to the abiotic and biotic environment, will be discussed.


Shalanda Grier

Department of Ecology and Evolutionary Biology, UCLA, Fong Lab


 “Sediment, light, and interspecific interactions have strong yet independent species-specific effects on 2 dominant coral reef macroalgae


Storminess is predicted to increase in the South Pacific and will affect abiotic conditions in fringing reef communities possibly resulting in reductions in light availability and increases in sediment due to runoff. Understanding macroalgal species-specific responses to these environmental changes will be imperative as macroalgae are traditionally studied as functional groups; however, recent research has strongly suggested macroalgae characteristics are not consistent across functional groups. As such species may matter.    In this study, we evaluate the species-specific growth and structural responses (calcification and thallus toughness) of two dominant brown macroalgae, Padina boryana and Sargassum mangarevense, to short term sediment and light disturbances in the South Pacific. We repeated a fully crossed caged field experiment manipulating sediment and light for both macroalgal species over a 6-7-day period. In monospecific assemblages each macroalgal species had varied responses to light and sediment disturbances wherein light negatively affected Padina growth resulting in a 67.7% growth reduction. Conversely, sediment additions significantly increased Sargassum growth by 40.4%. Light reductions diminished Padina carbonate content while sediment additions resulted in a 1.5-2.8% daily increase in carbonate content.  In interspecific assemblages Padina grew more in reduced light conditions with Sargassum while Sargassum grew less in the same conditions with Padina suggesting there may be an interaction between the two species. However, these experiments were not run concurrently so further investigation is needed to identify possible species interactions among the algae in light and sediment disturbances. Our study suggests Padina and Sargassum have species- specific growth and structural responses to light and sediment manipulations. Additionally, responses are likely influenced by environmental conditions and possibly species assemblages.