Inferences for Animal Populations: Basics of Capture-recapture and Occupancy Modeling

Presented by Drawing inferences about animal populations is complicated by 2 major issues: (1) inability to survey the entire area inhabited by a population and (2) inability to detect all animals present in locations that are surveyed. This workshop provides information on approaches for dealing with both issues, with an emphasis on detection probability (issue 2). Studies of specific, localized populations are typically directed at population size or density and the vital rates that drive changes in these state variables: rates of reproductive recruitment, survival and movement in and out of the population. Capture-recapture modeling is based on the detection histories of individually marked animals and provides inferences about both state variables and vital rates. We will discuss models for both closed (short time horizon; no changes in identities of animals over the course of sampling) and open (changes in animal identities and numbers likely to occur between sampling occasions) populations. Such detailed studies of individual animals are frequently not practical over large geographic scales, motivating the need for occupancy models. The state variable of these models is the proportion of either total land area or some set of discrete habitat patches that contain the focal species. Repeat visits to sample units (specified units of land area) permit inferences about occupancy itself, as well as the vital rates responsible for its dynamics, local rates of colonization and extinction. By analogy with capture-recapture, models have been developed for sampling over short time frames (closed models) or longer time frames over which extinction and colonization are expected. Both capture-recapture and occupancy models include detection probability parameters in order to deal with the issue of imperfect detection.   What will the student get from this workshop? An understanding of the importance of dealing with spatial sampling and detection probability when studying animal populations and communities. A basic understanding of capture-recapture and occupancy modeling for both closed and open populations. Basic understanding of one program, MARK, that can be used to fit these models to actual field data. Knowledge of the existence of specific extensions of these basic models that deal with various complications and assumptions.    Workshop organisers:James D. Nichols