Đang chuẩn bị liên kết để tải về tài liệu:
Research Techniques in Animal Ecology - Chapter 7

Chapter 7 Monitoring Populations Assessing changes in local populations is the key to understanding the temporal dynamics of animal populations, evaluating management effectiveness for harvested or endangered species, documenting compliance with regulatory requirements, and detecting incipient change. | Chapter 7 Monitoring Populations James P. Gibbs Assessing changes in local populations is the key to understanding the temporal dynamics of animal populations evaluating management effectiveness for harvested or endangered species documenting compliance with regulatory requirements and detecting incipient change. For these reasons population monitoring plays a critical role in animal ecology and wildlife conservation. Changes in abundance are the typical focus although changes in reproductive or survival rates that are the characteristics of individuals or other population parameters also are monitored. Consequently many researchers and managers devote considerable effort and resources to population monitoring. In doing so they generally assume that systematic surveys in different years will detect the same proportion of a population in every year and changes in the survey numbers will reflect changes in population size. Unfortunately these assumptions are often violated. In particular the following two questions are pertinent to any animal ecologist involved in population monitoring. First is the index of population abundance used valid That is does variation in for example track densities of mammals amphibian captures in sweep nets or counts of singing birds reliably reflect changes in local populations of these organisms Second does the design of a monitoring program permit a reasonable statistical probability of detecting trends that might occur in the population index In other words are estimates of population indices obtained across a representative sampling of habitats and with sufficient intensity over time to capture the trends that might occur in the population being monitored Failure to address these questions often results in costly monitoring programs that lack sufficient power to detect population trends Gibbs et al. 1998 . 214 JAMES P. GIBBS The purpose of this chapter is to assess key assumptions made by animal ecologists attempting to identify .