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POPULATION DYNAMICS AND SURVIVAL OF AN ENDANGERED WALLABY: A COMPARISON OF FOUR METHODS
Author(s) -
Fisher Diana O.,
Hoyle Simon D.,
Blomberg Simon P.
Publication year - 2000
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.1890/1051-0761(2000)010[0901:pdasoa]2.0.co;2
Subject(s) - population , biology , endangered species , ecology , leslie matrix , mark and recapture , vital rates , abundance (ecology) , population size , population model , habitat , critically endangered , vegetation (pathology) , transect , demography , population growth , sociology , medicine , pathology
The bridled nailtail wallaby Onychogalea fraenata is a critically endangered marsupial, now restricted to a single locality in central Queensland, eastern Australia. Its small size and its nocturnal, solitary, and cryptic behavior present problems for monitoring of population dynamics. The population apparently declined during a major drought between 1991 and 1995, when juvenile survival was low. We carried out a detailed demographic analysis from 1994 to 1997 in order to estimate survival and abundance in two different habitats, using mark–recapture, mark–resight, radio‐tagging, and line‐transect methods. The finite rate of increase (λ) and its sensitivity to changes in survival and reproduction of each age class were also calculated using a matrix population projection model. We then assessed biases and the value of each method for management. For data other than those based on radio‐tagging data, population size and survival estimates were negatively biased and had large confidence limits. Line‐transect estimates were likely to be the least biased. The reasons were that probabilities of capture and sighting varied among sexes, sites, and times; habitat use varied according to vegetation conditions; and the populations were small. Despite this, all methods indicated an increasing population size. The projected value of λ based on radio‐tagging data was most sensitive to adult survival. Vegetation conditions improved throughout the study after an initial drought, and the mean projected intrinsic rate of increase was 28% per year. We conclude that management should aim to increase adult survival via predator control and that line‐transect estimation is the most appropriate long‐term monitoring method.