Integrating small population effects on both detection and persistence probabilities in the design and interpretation of presence/absence surveys.

Abstract

Determining whether or not a species has been extirpated from part of its range is one of the most important yet difficult challenges facing ecologists.  Presence/absence surveys are a primary method to determine local extinction, but negative results are difficult to interpret, particularly when informal sightings appear to support local persistence of elusive species.  Such conflicts are particularly likely for rare species, which are the most difficult to detect during a presence/absence survey due to small population size.  However, integrating small population effects on both detection and extinction probabilities resolves such conflicts by reframing occupancy questions from present to near future terms.  We developed methods for integrating the simultaneous effects of survey effort and population size on detection and extinction probabilities in the design and interpretation of presence/absence surveys.  We applied these methods to the design and interpretation of a wolverine survey in Sequoia-Kings Canyon National Parks, California, USA, to address questions about the appropriateness of translocations from other populations.  Ecological applications that can benefit from this type of analysis, simultaneously incorporating small population effects on both detection and population processes, include management of charismatic, yet elusive species, management of disease risk in translocations, and management of nonnative pests.