Mesocosm Experiments on Habitat Choice by an Endemic Lizard: Implications for Timber Management

Abstract

We investigated the impacts of various logging practices on habitat choice by the endemic Florida scrub lizard (Sceloporus woodi) in the Florida scrub of Ocala National Forest (ONF). We used large outdoor mesocosms as a novel means to evaluate lizard preferences for habitats with different structural features produced by standard forestry practices. Captive lizards were offered a choice between two adjoin- ing habitats (= sides of a mesocosm) created using one of two substratum treatments (SAND = 75% open sand; WOOD = 75% coarse woody debris (CWD)) coupled with one of two insolation treatments (LIGHT = ambient sunlight; DARK = 45% ambient sunlight). The mesocosms proved to be an effective technique for evaluating lizard habitat preferences. Lizards were easily observed and remained active and healthy throughout the experiment Sighting frequencies differed significantly among the four mesocosm sides, yielding an overall preference ranking of DARK SAND > LIGHT SAND > DARK WOOD - LIGHT WOOD. Analysis of sighting frequencies by treatment factors (substratum and insolation) and of dissimilarity ma- trices both indicated that habitat choice was based primarily on substratum composition and only weakly determined by insolation level. In addition, size- and gender-specific preferences suggest that social inter- actions may help shape patterns of habitat used in conjunction with individual preferences. We conclude that the least favored mesocosm side (LIGHT WOOD) represents a habitat type that could potentially serve as a population sink for scrub lizards and recommend several methods to reduce the accumulation of CWD or to ameliorate its potential thermal stress on lizards. In addition, the most favored mesocosm side (DARK SAND) represents a shaded sandy habitat type not currently found in ONF timber stands. We present several alternative harvesting and site preparation methods that could produce such habitats and recommend further research on their potential value for enhancing populations of scrub lizards and other open-habitat scrub