PARENT SESSION
Oral Session #69: Conservation: Biodiversity assessment and reserve design.
Presiding: T. Norton
Wednesday, August 7. 1:00 PM to 4:45 PM. Grand Ballroom Central, Radisson.
Detecting population changes using presence-absence data.
Pollock, Jacob*,1, Shahani, Priya2, 1 University of California, Santa Cruz, Santa Cruz, CA2 University of California, Santa Cruz, Santa Cruz, CA
ABSTRACT- Determining whether a population is stable, increasing or declining is critical to the preservation of species. However, with large conservation areas, numerous species of concern and limited funds, there is a trade-off between obtaining detailed demographic or abundance data for one species and understanding the condition of many more species in less detail. Presence-absence data are easier and more affordable to gather than other kinds of data and may give enough information to determine the condition of a population if used correctly. Using models parameterized with data from field studies, we compare a presence-absence analysis of population change with a detailed abundance analysis. We evaluate the power of presence-absence analysis to detect population trends, and explore various ways of improving the power of presence-absence tests, as well as how to decide if a population is amenable to presence-absence analysis. In particular, we ask how detection-time data can be used in conjunction with stochastic modeling approaches to improve power and whether incorporating variable search times into survey methods will allow us to obtain more reliable results. We then test our model results using abundance and encounter rate data for several other real populations and create a spatial model to test the effect of spatial patterns of perturbation on our ability to detect population declines. Using a cost-benefit analysis, we show that presence-absence data can be powerfully used in some circumstances to detect population declines.
KEY WORDS: presence-absence data, species conservation, monitoring population trends, power analysis