Modeling aspects of the ecological and evolutionary dynamics of the endangered Houston toad

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Title: Modeling aspects of the ecological and evolutionary dynamics of the endangered Houston toad
Author: Swannack, Todd Michael
Abstract: The goal of my dissertation was to describe the dynamics of a group of Houston toads located at the Griffith League Ranch (GLR ) , Bastrop County , Texas . My research included using statistical modeling to predict activity and abundance , mark -recapture techniques to estimate survivorship , and simulation modeling to explore the impacts of the difference in age at first reproduction and to project the future dynamics of the population at the GLR . From 2001 ? 2005 , 225 individual Houston toads (199 M : 26 F ) were captured using two methods : breeding pond surveys and drift fences . Houston toads were neither caught equally among capture methods , nor across years . Toad activity was mostly confined within their breeding season , and activity was not continuous . A logistic regression indicated activity depended on time of year , mean precipitation , mean minimum daily temperature , and mean percent lunation as well as two -way interactions with moon -phase and other variables . Abundance depended on time of year , current precipitation , minimum temperature , and two -way interactions between time of year and the other two variables . Twenty -one of the 199 males (10 .5 % ) and no females were recaptured among years . The probability of male survival was estimated using program MARK . Eight of 16 candidate models were supported and all but one contained precipitation as a covariate , indicating precipitation is important for Houston toad survival . Survivorship estimates varied from 0 .1 to 0 .41 . The sex ratio was significantly male -biased . The odds of catching females in traps were 3 .5 greater than capturing females in a pond , while the odds of capturing males in a trap were 0 .28 compared to ponds . Results from a simulation model indicated the sex ratio is biased because of the difference in maturation times between males and females , coupled with high juvenile mortality . Results from an individual -based , spatially -explicit , stochastic simulation model , indicated a relatively low probability ( ~ 0 .013 ) of B . houstonensis going extinct at the GLR within the next 10 years . Emergent properties of the model were similar to results observed in the field or reported in the literature . The model also identified that dispersal of Houston toads should be a future research priority .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1641
Date: 2009-05-15

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Modeling aspects of the ecological and evolutionary dynamics of the endangered Houston toad. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -1641 .

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