Title

The American crocodile (Crocodylus acutus) in Florida: Conservation issues and population modeling

Date of Award

2003

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

Donald L. DeAngelis, Committee Chair

Abstract

To investigate how the American crocodile's (Crocodylus acutus ) population will respond to alterations in Everglades hydrology, I developed a stage-structured population model to examine which life history stages are important to population growth, a spatially explicit individual based model to examine the effect of changes in hydrology on the South Florida crocodile population, and empirically examined the effect of salinity and translocation.The stage-structured model was constructed using published data and biologically reasonable estimates. The model yields a population growth rate lambda d of 1.006, consistent with observations that the C. acutus population is slowly increasing in Florida. Elasticities of lambda d indicate that annual survivorship of sub-adults (1 m--2.25 m total length) has the greatest proportional effect on population growth. Simulated management scenarios further demonstrate the degree to which sub-adult annual survivorship can affect population growth.The spatially-explicit individual-based model was designed to relate water levels, salinities, and dominant vegetation to crocodile distribution, abundance, population growth, individual growth, survival, nesting effort, and nesting success. The model was examined with sensitivity analyses and a factorial manipulation of model salinities to evaluate the effects of salinity changes on population size, nest number, and survival of young of the year crocodiles. The model was sensitive to changes in annual survivorship of large individuals, which indicates that research should focus on improving estimates of these parameters. Similarly, conservation priority should be placed on reducing anthropogenic impacts such as road mortality on large individuals. Everglades restoration, through its effects on water flow to estuaries, is unlikely to affect large crocodiles directly. However, restoration may benefit crocodile populations if increased freshwater flow reduces the chances that regional salinity levels exceed levels at which small individuals lose mass.My empirical work on hatchling crocodiles found no effect of translocation on growth or movement. I also did not find an effect of salinity on growth. Management of C. acutus continues to emphasize salinity when it seems that the long term recovery of the Florida population would be improved by management focused on survivorship of large individuals.

Keywords

Biology, Ecology

Link to Full Text

http://access.library.miami.edu/login?url=http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3081304