PARENT SESSION

HP10 New Advances in Estimating Effects of Toxicants on Populations
D135-136
1:20 PM - 5:20 PM, Thursday

() Development of population models to support ecological risk assessments.

Gleason, Timothy¹, Mitro, Mathew², Gobell, Ruth¹, Walters, Steven¹, Nacci, Diane¹, Munns, Jr, Wayne¹, Grear, Jason¹, ¹ U.S. EPA, ORD, NHEERL, Atlantic Ecology Division, Narragansett, Rhode Island, USA² Wisconsin Department of Natural Resources, Madison, Wisconsin, USA

ABSTRACT- As part of a broader research effort to develop ecological risk assessment approaches to estimate potential chemical effects on non-target populations, we describe an approach for developing simple population models to estimate the extent to which acute effects on individuals impact populations. We developed matrix population models to assess the population-level effects on four bird species. Our objectives were to: construct matrix population models for four bird species using data available in the published literature; evaluate the quality of the data available to parameterize the models and identify data needs; and analyze the matrix population models to estimate population growth rates ( ), and determine how and simulated abundances respond to perturbations in model parameters. The literature search revealed considerable information on reproductive parameters but generally little information on survival parameters. When model parameters were not well estimated, model projection uncertainty was large. Population growth rates based on literature derived parameter estimates were near 1.0, thereby implying long-term stability in the populations. However, the simulations and confidence intervals also indicated that any given realization of population growth rate could be <1 (a declining population) or >1 (an increasing population). Elasticity analyses showed that proportional changes in adult survival effected greater or approximately equal changes in population growth rate as compared to proportional changes in reproductive output and juvenile survival. Therefore, improved survival rate estimates for both juveniles and adults will be needed to complete more definitive risk assessments. Three of four species modeled were projected to have declining populations (<1) after 20% reductions in survival or reproductive success. Finding that relatively small impacts in the vital rates lead to projections of population decline in simple screening models illustrates the need to understand compensatory mechanisms for more definitive risk assessments.

Key words: elasticity, matrix model, population growth rate, avian