EcoEvoPub: Samuel Bressler and Evan Doughty
SAMUEL BRESSLER
Department of Ecology and Evolutionary Biology,
Yeh Lab, UCLA
“Shifts in nesting behavior in response to novel environments in two urban songbird populations”
Urban avian colonizers and adapters exhibit a wide range of behavioral modifications in response to an environment with artificial structures. Prior studies have demonstrated differing predation pressures in urban bird populations compared to their wildland counterparts, leading to a host of nesting adaptations in urban environments. In this study we ask how nest characteristics correlate with success in an urban environment, and if nesting preferences are plastic with regard to prior outcomes. We also compare nest characteristics between urban populations to measure behavioral convergence. To do this we monitored a population of urban Dark-eyed Juncos (Junco hyemalis) on the UCLA campus from January to August 2019. This sparrow typically nests on the ground or in low vegetation in montane forest habitat, however this species colonized urban Los Angeles in the mid-2000s and has subsequently expanded throughout much of the Los Angeles basin. Unlike their wildland counterparts, urban juncos will often nest above the ground on trees or artificial structures. Urban Juncos also breed earlier than wildland Juncos, and produce more clutches. We examined how height above ground, vegetation type the nest was concealed in, and first egg date correlated with nesting outcome. To measure convergence we compared nest characteristics in the Los Angeles population to a similar urban population in San Diego. Finally, we examined plasticity by testing whether Juncos modify nesting behaviors in response to prior outcomes, for instance adopting a “win-stay, lose-go” strategy. These results will elucidate how urban songbirds modify their behavior in response to novel environmental pressures, and if populations may respond differently to novel environments.
EVAN DOUGHTY
Department of Ecology and Evolutionary Biology,
Van Valkenburgh Lab, UCLA
“Modeling the Entrainment of Bison Cranial Material During the Missouri River Flood of 2011”
A mathematical model was developed for estimating transport and accumulation of a sub-fossil bison assemblage discovered within the Missouri River south of the Oahe Dam, SD in late September of 2011. This assemblage, considered to be a byproduct of the 2011 flood of the Missouri River, was comprised of disarticulated skeletal material dispersed within an interstream sediment bar of poorly sorted, subrounded fluvial sediments. A total of twenty-four bison skulls were measured using five parameters which were used to calculate the volume of each skull. Volume was then approximated as a sphere of equivalent volume and density as a bison skull. Flow measurement data from 1/2/2002 to 2/13/2014 were acquired from the US Army Corps of Engineers Oahe Dam office. Channel area and perimeter was determined using the sediment range at river mile 1069.68, and gauge height data from USGS hydrologic station 064440000. Flow velocity was determined for each record by dividing discharge rate by the channel area. Once determined, the flow velocity was used to calculate the Reynolds number for each skull. Reynolds number was then utilized in determining the drag and lift forces. Discharge rates required to entrain a given skull sphere, were determined by calculating the lift and drag forces against the force of gravity. Results indicated a discharge rate of 6345 m^3/s was required for the vertical component of force to overcome gravity. This indicated that no vertical entrainment was possible given measured discharge rates. However, it was determined that horizontally oriented entrainment was possible in 4 of the 3353 records used in the analysis.