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Selection of available post-fire substrate by the ground skink, Scincella lateralis (squamata: scincidae).
Article Type:
Report
Subject:
Substrates (Biochemistry) (Environmental aspects)
Author:
Watson, Charles M.
Pub Date:
08/01/2009
Publication:
Name: The Texas Journal of Science Publisher: Texas Academy of Science Audience: Academic; General Format: Magazine/Journal Subject: Science and technology Copyright: COPYRIGHT 2009 Texas Academy of Science ISSN: 0040-4403
Issue:
Date: August, 2009 Source Volume: 61 Source Issue: 3
Geographic:
Geographic Scope: Texas Geographic Code: 1U7TX Texas

Accession Number:
236012403
Full Text:
Abstract.-Burning of the forest floor alters the structural components that constitute the organic substrate. Many small animal species inhabit this layer, which typically consists of leaf litter from surrounding trees. The availability of a species' preferred substrate can be a factor in the rate of recolonization following a fire. Using pair-wise choice trials within a controlled environment, preference of substrate typically available after a burn by Scincella lateralis was determined. These skinks primarily select hardwood leaf litter and secondarily choose pine needle litter and pine bark slough. Bare ground was usually avoided. These findings indicate that S. lateralis may not be able to completely recolonize a site until after the first seasonal leaf fall following a fire.

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The effects of fire on populations of various reptiles have been well documented (Wilgers & Home 2006; Brown 2001; Granberry et al. 1994). Braithewaite (1987) found that varied fire regimes affect lizard populations differently, depending on such factors as fire intensity, duration, and seasonality. Kahn (1960) determined that the presence of unaltered refuge sites can buffer the effects of fire on certain lizard populations. For many temperate leaf-litter dwelling species, fire leaves behind limited and sparse refuge (Watson 2004). The present study determines the selectivity of the ground skink, Scincella lateralis, to four substrate components that are available at varying degrees after a fire in a mixed hardwood/pine forest. Scincella lateralis makes a sound experimental subject due to the species' abundance, small size, and limited vagility. This animal is found in temperate wooded areas where there is sufficient water, cover, and food (Brooks 1967). However, the leaf-litter layer within the forest, or at forest's edge, is considered typical habitat for this species (Fitch & von Achen 1977).

The ground skink depends on leaf litter and other structural organic components of the forest floor for refuge (Brooks 1967). The complete destruction of decaying leaf material may dramatically affect recovery of this species within burned sites. Conversely, if the ground skink will utilize pine needle litter or pine bark slough, both of which are relatively abundant following a fire, it may be able to persist and recolonize burned sites more rapidly. This experiment aims to determine the selection of individual ground skinks to four prominent substrate types found after a burn in a mixed hardwood/pine forest ecosystem in eastern Texas.

METHODS & MATERIALS

Six experimental chambers were used, each measuring 32 cm by 77 cm at the base, providing 2464 [cm.sup.2] of area. This area was uniformly covered by approximately 3 cm of sifted topsoil. Individual chambers contained two of the four treatments for habitat preference, each making up half of the surface area. Substrate treatments, with the exception of bare ground, were loosely arranged aggregates of the treatment substrate approximately 5 cm thick. These six chambers cover all of the possible comparisons for these treatments. The four treatments are as follows:

Hardwood leaf litter.-Whole broad leaves, predominantly from Quercus sp. This substrate type is generally destroyed in a burn and will not be present until the following fall. The leaves that make up this layer are broad and can serve as cover for S. lateralis.

Pine leaf litter.-Needles from Pinus taeda. This substrate type will be present shortly after a burn and will continue to accumulate throughout the year. This is due to the fact that the needles of pine trees are persistent, and their leaf fall is not seasonnaly limited (Vines 1990). The needles that make up this layer are thin and can only serve as refuge in aggregate.

Pine slough.-Thin pieces of scorched pine bark that accumulate at the base of the tree in the months following a burn. The bark pieces that make up this layer structurally resemble hardwood leaves, providing broad areas of cover and structure. However, these units are more dense than comparably sized leaves.

Bare ground.-No large organic substrate present. This represents the majority of a site's substrate immediately following a burn.

A total of 10 animals of unknown sex (five adults, snout-to-vent length of 42-51mm; five juveniles, snout-to-vent length of 29-34mm) were obtained from natural populations in Smith and Dallas counties, Texas. The organic substrates were collected from sites within Tyler State Park and heated to temperatures in excess of 65[degrees]C. The elevated temperatures ensured the elimination of prey items from the material. This was verified by observation of subsamples of this substrate under a stereomicroscope. No live invertebrates were noted.

Trials were performed under fluorescent lighting at 27[degrees]C. Individuals were each transferred to the center of the chamber, with a treatment to either side of six experimental chambers. The animal was then allowed a 10-min period of acclimation to the chamber. After this period, the investigator approached the chamber and marked which substrate type that the animal was in at time of initial detection. The skink typically was visible when the chamber was approached, and immediately retreated to cover. Each trial was repeated 20 times for each animal.

Data were analyzed as recommended by Cherry (1998). Confidence intervals were determined for the mean number of times that a specimen was observed in each substrate, given equal opportunity to choose between substrates. There were no significant differences noted between age groups for any of the treatments. Therefore, the values of both age classes were combined into one sample to increase power. Significance was determined between substrates if no values were shared within the constructed 95% confidence intervals (Figure 1).

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RESULTS & DISCUSSION

Bare ground exhibited the lowest mean frequency ([bar.x] = 1.0, 95% CI: [0.3, 1.7]), and a significant preference was exhibited for hardwood leaf litter over all three other treatments ([bar.x] = 47.6 95% CI : [43.2, 52.0]). Pine slough ([bar.x] = 34.3, 95% CI : [30.6, 38.0]) and pine needle litter ([bar.x] = 37.5, 95% CI : [33.8, 41.2]) exhibited overlap of the constructed confidence intervals, thereby exhibiting no significant selection between these treatments.

The top layer of substrate on the forest floor is typically comprised of dead and decaying organic material. Fire dramatically alters the makeup of this substrate layer, thereby altering the primary habitat of S. lateralis. Watson (2004) found, from data gathered in Smith County, Texas, that the presence of structural organic material is reduced by over 75% following a fire. Preference for those substrates that are most decimated by fire may prove to be a limiting factor in recolonization by this species.

The preference of hardwood leaf litter for cover is consistent with literature regarding other skink species (Fitch 1954). However, the three other substrates are the most commonly available in the period immediately following a burn and preceding the annual leaf fall (Watson 2004). Potential costs to this animal as related to these substrates may be a factor into substrate selection. The probability of detection of the ground skink by avian predators is increased in the absence of refugia (Smith 1997). Pine needle litter does not provide effective cover unless it is present in aggregate and the density of the pine slough may not allow for free movement of the lizard when it is arranged in a compact manner at the base of a tree. Further reasons for the substrate preferences may be dependant on the availability of prey. There is little doubt that the acquisition of prey and the ability to hide from predators play heavily in microhabitat selection.

The preferred microhabitat type for the ground skink is that which is in shortest supply following a fire. Other factors, such as prey availability and proximity to undisturbed habitat, may also affect the recovery of this species following a fire. Invertebrate communities, which constitute the prey of S. lateralis, are often initially eradicated with the burning of leaf litter, further tying the recovery of this species to the return of the leaf litter layer and associated fauna (Abbot et al. 2002; Bird 1997). Therefore, ground skinks may not be able to recolonize an area completely until hardwood leaf litter is present in pre-bum amounts, which may take over three years (Watson 2004). Furthermore, the community structure of the leaf litter layer may not reach the pre-burn state for many years afterwards, potentially limiting the full recovery of S. lateralis populations. The recovery of this species following a burn is nevertheless basically tied to substrate availability and its timeline for recovery may be delayed for months following the event, beginning with the first leaf fall and the associated accumulation of hardwood leaf litter.

ACKNOWLEDGMENTS

I would like to thank Daniel Formanowicz and Laura Gough for their input and encouragement over the duration of this project as well as Jessie Meik, Brian Fontenot, and Rebbekah Watson for their pre-submission editorial expertise.

LITERATURE CITED

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Brown, G. W. 2001. The influences of habitat disturbance on reptiles in a Box-Ironbark eucalypt forest of southeastern Australia. Biodiversity and Conservation, 10(2):161-176.

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Fitch, H. S. & P. L. von Achen. 1977. Spatial relationships and seasonality in the skinks Eumeces fasciatus and Scincella laterale in Northeastern Kansas. Herpetologica, 33(3):303-313.

Granberry, C. H., D. G. Neary & L. D. Harris. 1994. Effects of high-intensity wildfire and silvicultural treatments on reptile communities in Sand-Pine Scrub. Conservat. Biol., 8(4):1047-1057.

Kahn, W. C. 1960. Observations on the effect of a burn on a population of Sceloporus occidentalis. Ecology, 41(2):358-359

Smith, D. G. 1997. Ecological factors influencing the antipredator behaviors of the ground skink, Scincella lateralis, Behav. Ecol., 8(6):622-629.

Vines, R. A. 1990. Trees, Shrubs, and Woody Vines of the Southeast. Univ. of Texas Press, Austin, TX, 1104pp

Watson, C. M. 2004. The Effects of Controlled Burning on Ground Skink Populations in a Mixed Pine-Hardwood Habitat of East Texas. Unpublished M.S. Thesis., Univ. of Texas at Arlington. 47pp.

Wilgers, D. J. & E. A. Horne. 2006. Effects of different burn regimes on Tallgrass Prairie herpetofaunal species diversity and community composition in the Flint Hills, Kansas. J. Herpetol., 40(1):73-84.

Charles M. Watson

Department of Biology, The University of Texas at Arlington Arlington, Texas 76019

CMW at: cwatson@uta.edu
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