| The effects
of off-highway vehicles on the flat-tailed horned lizard and improvements
in lizard density estimation.
Principal Investigator: Paul Doherty
Graduate Student: Tyler Grant
Project Start Date: 09/03
Expected Completion Date: 12/05
Funding Agency: USGS, RWO 73
Objectives: 1) Evaluate the effectiveness of distance sampling and mark-recapture in estimating flat-tailed horned lizard density. To date estimation of flat-tailed horned lizards has been based on indices. In a pilot study we demonstrated that estimation based upon mark-recapture was a viable alternative. We will expand the number of mark-recapture plots as well as incorporate a distance sampling procedure to further refine our methodology.
2) Improve the estimation of lizard density by incorporating model averaging and mixture models into the estimation procedures. To date we have focused on the use of Program Capture and the basic closed-capture models in Program Mark. We will investigate the use of mixture models to account for heterogeneity in our abundance estimates. We will also utilize a model averaging approach to obtain better abundance estimates. We will attempt to combine information from our distance sampling data and mark-recapture data using a model averaging approach.
3) Evaluate the effects of off-highway vehicles on the density of flat-tailed horned lizards. We will evaluate the effects of off-highway vehicles in two ways. First we will conduct a correlative study by correlating the amount of off-highway vehicle tracks per plot with lizard abundance. Secondly, we will conduct a manipulative experiment in which we estimate the number of lizards in treatment and control plots, apply an off-highway vehicle treatment, and then assess any differences in lizard abundance due to the treatment.
Progress: Tyler Grant finished his coursework and passed
his Comprehensive Exams last spring. He completed field work in February,
2005. He is now writing his thesis.