Habitat Use by the Alligator Snapping Turtle (Macrochelys Temminckii) and Eastern Snapping Turtle (Chelydra Serpentina) in Southeastern Missouri
Lescher, Timothy C., Tang-Martínez, Zuleyma, Briggler, Jeffrey T., The American Midland Naturalist
ABSTRACT.-This study addresses habitat differences of two sympatric turtle species, alligator snapping turtles (Macrochelys temminckii) and eastern snapping turdes (Chelydra serpentina) in six watersheds in southeastern Missouri. We found that alligator snapping turtle presence corresponded with higher abundance of submerged physical structures in the stream, deeper water, relatively higher levels of detritus, and warmer water temperatures. Greater amount of aquatic vegetation was important in characterizing eastern snapping turtle presence in traps. Eastern snapping turtles and alligator snapping turdes did not use the same areas spatially at either a microhabitat or macrohabitat scale, and were only trapped at the same location once in 282 trap locations. Future conservation plans for the alligator snapping turtle and eastern snapping turtle should consider the microhabitat characteristics of sites used by these turtles.
Resources may be partitioned among species by time, type, or space (Moll and Moll, 2004) . This partitioning is possible because although most species have adapted to certain optimal environmental conditions, many exhibit some degree of behavioral and/or physiological plasticity for dealing with environmental constraints or competitive pressures (Simmonds and Isaac, 2007). Such plasticity can allow coexistence and overlapping niches (Vogt, 1981).
Partitioning of habitat resources has been documented in a wide variety of organisms, including turdes (Lindeman, 2000; Moll and Moll, 2004; Luiselli, 2008). For example, the white-lipped mud turtle (Kinostemon leucostomum) eats less animal matter where it occurs in sympatry with the mollusk specialist the giant Mexican mud turde (Staurotypus triporcatus). Kinostemon leucostomum also uses shallower pools than S. triporcatus in these areas (Vogt and Guzman, 1988). Differential utilization of streams has been observed in die spiny softshell turde (Apalone spinifera) and the smooth softshell turtle (Apalone mutica), two closely related congeners that inhabit Missouri rivers and streams. Apalone spinifera occupies closed side channels and tributaries in areas of slow-moving water and high visibility, whereas A. mutica predominates in fast-moving, deep areas near die main channel (Barko and Briggler, 2006) . In the northern map turde (Graptemys geographica), Ouachita map turde (G. ouachitensis) , and false map turde (G. pseudogeographica pseudogeographica) , partitioning exists in areas where the species overlap. Graptemys geographica uses rock and gravel substrates and benthically feeds on mollusks; G ouachitensis is an omnivorous surface feeder, and uses mud, sand, and rock; and G p. pseudogeographica is an omnivorous bottom and surface feeder, and uses mud substrates (Fuselier and Edds, 1994; Vogt, 1981).
In this study we examine habitat partitioning in two species of turtles in Missouri: the alligator snapping turtle (Macrochelys temminckii) , and the eastern snapping turde (Chelydra serpentina) . These two species are the only extant representatives of the family Chelydridae in the United States, and the alligator snapping turde is considered a species of concern in Missouri because its numbers have declined throughout its range in the state. Alligator snapping turtles and eastern snapping turtles have been implicated in interspecific agonistic interactions (Shipman et al, 1994), they are closely related (Shaffer et al, 2008), and they may have similar microhabitat requirements (Riedle et al, 2009). However the alligator snapping turde is found almost exclusively in southeast Missouri (Shipman and Riedle, 2008; Santhuff, 1993), while the eastern snapping turde is widespread in Missouri (Johnson, 2000).
Previous studies diat have examined habitat use by die alligator snapping turtle suggest that the microhabitat the species occupies may vary geographically, seasonally, and as a result of die environmental context e.g., presence of odier species). …