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Monday, January 25 • 11:40am - 12:00pm
Estimating Population Abundance Trends Via Presence-Absence Data

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AUTHORS: Sam Rossman*; Elise Zipkin

ABSTRACT: Monitoring a species population abundances across large geographic ranges is critically important to conservation efforts but generally requires precise abundance estimates from a large number of sites, and across many years which are often difficult to obtain. Mark recapture studies provide precise estimates of abundance but are generally limited to small geographic ranges. Recently, developed N-mixture models can provide abundance estimates from counts of unmarked individuals, however, many species are predominately identified via presence-absence data (e.g., occupancy) such as those identified by call or scat analysis. We present a novel modeling framework in which we use only occupancy data to derive abundance estimates through time. This state space modeling uses an observation model in which non-detections are the conditional probability of failing to detect any individual present. This observational model provides a link between occupancy data and abundance estimation. We validate this model using simulation studies and discuss the required data. While, this approach requires a large amount of occupancy data it provides a means to monitor the abundance of species in which count data is difficult or impossible to obtain and could be particularly powerful in the analysis of citizen science data. We apply our model to examine population trends in the northern spotted owl which is threatened by the invasive barred owl in Western Oregon. Previous to our analysis population abundance monitoring was not feasible for this threatened species.

Monday January 25, 2016 11:40am - 12:00pm EST
Vandenberg B