Academic journal article The American Midland Naturalist

Disruptive Influences of Drought on the Activity of a Freshwater Turtle

Academic journal article The American Midland Naturalist

Disruptive Influences of Drought on the Activity of a Freshwater Turtle

Article excerpt

Abstract. -

Drought is an ecological challenge for turtle species worldwide and can be exacerbated by habitat fragmentation and loss, especially for small populations. We studied the activity of 16 Blanding's turtles Emydoidea blandingii using radio-telemetry from 2005-2006 during consecutive drought and normal hydrological years at a fragmented preserve in northeastern Illinois, U.S.A. The preserve experienced drought conditions during 2005 with precipitation levels 20% below the 60 y average. Fine scale measures of activity (i.e., mean water depth at locations, proportion of unique locations, and proportion of locations in dry habitat) differed between years, whereas broad scale measures of activity (i.e., home range, movement distance) did not. On average only 41.3% of 2005 home ranges overlapped with 2006 home ranges suggesting space use shifted between years. Although most proportional habitat use remained unchanged between years, several individuals increased their use of riverine habitats when other wetland habitat dried. Our study underscores the need to examine the risks of severe environmental events on vulnerable populations.

Introduction

Although environmental variation is necessary for preserving ecological processes (Everard, 1996), extreme environmental stochasticity is detrimental to population persistence because of reduced population growth or carrying capacity (Lande, 1993; Lande et al., 2003). Large fluctuations in environmental factors such as precipitation and temperature alter resource distributions and often disrupt survival and fecundity as well as the composition, abundance, and population structure of animal species (Blair, 1957; Gibbons et al., 1983; Stiles, 1992; Dunham, 1994; Dodd and Dreslik, 2008; Sperry and Weatherhead, 2008; Winne et al., 2010). During extreme stochasticity, resources such as water, food, mates, and refugia become limited and can create ecological challenges; thus compelling individuals to adjust their behavior (Sapolsky, 1986).

Drought and dry season conditions are common ecological challenges for many turtle species (Georges and Kennett, 1989; Peterson, 1996; Roe and Georges, 2008; Hensley et a?, 2010). During drought conditions, freshwater turtle species either immigrate to other aquatic habitats (Gibbons et ai, 1983; Christiansen and Bickham, 1989; Kennett and Georges, 1990; Buhlmann and Gibbons, 2001; Roe and Georges, 2008; Rees et ai, 2009) or estivate in drying pockets of wetland or terrestrial refugia (Cagle, 1944; Gibbons et ai, 1983; Christiansen and Bickham, 1989; Buhlmann and Gibbons, 2001;Joyal et al, 2001; Ligón and Stone, 2003; Roe and Georges, 2008; Buhlmann et ai, 2009; Rees et ai, 2009). Response to drought conditions depends largely on whether a species evolved in an arid or a humid environment; species with arid climate evolutionary histories have behavioral adaptations, such as estivation, to cope with dry conditions, whereas those that did not evolve in an arid or xeric climate must emigrate (Gibbons et ai, 1983; Christiansen and Bickham, 1989). In addition populations of long lived species, such as turtles, may also learn to adjust behavior during dry periods from repeated exposure to drought conditions.

Drought can be detrimental to turtle populations (Kennett and Georges, 1990) and to aquatic species not adapted to arid or dry season climates (Christiansen and Bickham, 1989). Wetland drying exposes turtles to increased prédation (Breeden and Breeden, 1982; Lindeman and Rabe, 1990; Hall and Cuthbert, 2000), winterkill from freezing, and hypoxia during low water levels and cold temperatures (Christiansen and Bickham, 1989; Hall and Cuthbert, 2000) . The lack of resources during drought can also suppress individual growth (Lindeman and Rabe, 1990), reduce body condition (Kennett and Georges, 1990), decrease reproductive output (Gibbons et ai, 1983), and inflict suffocation, dehydration, and starvation (Acuña-Mesén, 1990). Further, emigration from drying habitats can cause increased stress levels (Cash and Holberton, 2005), and mortality during drought can alter the diversity and abundance of turtles occupying a wetland post drought (Cagle, 1944; Christiansen and Bickham, 1989). …

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