Gopher Tortoise (Gopherus polyphemus) Burrow Densities in Scrub and Flatwoods Habitats of Peninsular Florida

Castellón, Traci D.; Rothermel, Betsie B.; Nomani, Saif Z.

doi:10.2744/ccb-0972.1

Cited by 13 publications

(6 citation statements)

References 15 publications

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“…B. Rothermel, unpublished data), which are more typical of inland scrub habitats in peninsular Florida (1.3–3.0 tortoises/ha; Castellón et al . ).…”

Section: Methodsmentioning

confidence: 97%

Kinship, inbreeding and fine‐scale spatial structure influence gut microbiota in a hindgut‐fermenting tortoise

et al. 2015

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Herbivorous vertebrates rely on complex communities of mutualistic gut bacteria to facilitate the digestion of celluloses and hemicelluloses. Gut microbes are often convergent based on diet and gut morphology across a phylogenetically diverse group of mammals. However, little is known about microbial communities of herbivorous hindgut-fermenting reptiles. Here, we investigate how factors at the individual level might constrain the composition of gut microbes in an obligate herbivorous reptile. Using multiplexed 16S rRNA gene sequencing, we characterized the faecal microbial community of a population of gopher tortoises (Gopherus polyphemus) and examined how age, genetic diversity, spatial structure and kinship influence differences among individuals. We recovered phylotypes associated with known cellulolytic function, including candidate phylum Termite Group 3, suggesting their importance for gopher tortoise digestion. Although host genetic structure did not explain variation in microbial composition and community structure, we found that fine-scale spatial structure, inbreeding, degree of relatedness and possibly ontogeny shaped patterns of diversity in faecal microbiomes of gopher tortoises. Our findings corroborate widespread convergence of faecal-associated microbes based on gut morphology and diet and demonstrate the role of spatial and demographic structure in driving differentiation of gut microbiota in natural populations.

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“…B. Rothermel, unpublished data), which are more typical of inland scrub habitats in peninsular Florida (1.3–3.0 tortoises/ha; Castellón et al . ).…”

Section: Methodsmentioning

confidence: 97%

Kinship, inbreeding and fine‐scale spatial structure influence gut microbiota in a hindgut‐fermenting tortoise

et al. 2015

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“…We implemented a stratified LTDS survey (Buckland et al ) of scrub and flatwoods habitats from April through October 2009 (Castellón et al ), under Florida scientific collecting permit LSSC‐10‐00043. Pilot survey results suggested a need to survey ≥50 km of transects in scrub and ≥88 km in flatwoods to generate estimates with CV ≤20%.…”

Section: Methodsmentioning

confidence: 99%

“…We accomplished this by collecting LTDS data in a way that was consistent with each approach, allowing us to generate alternative estimates that could be evaluated based on model assumptions, statistical precision, and levels of effort required in the field. For simplicity, we describe density estimation for the scrub habitat only, where densities were greatest (Castellón et al ). However, we also discuss important factors influencing occupancy determination in scrub versus the more mesic flatwoods.…”

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confidence: 99%

A comparison of line-transect distance sampling methods for estimating gopher tortoise population densities

2015

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Line-transect distance sampling (LTDS) is increasingly used to estimate gopher tortoise (Gopherus polyphemus) densities. The process requires detecting tortoise burrows, and then determining occupancy. We compared 3 LTDS approaches that differ in how burrow detection and occupancy data are integrated, and 2 search strategies. Surveys were conducted at Avon Park Air Force Range in South-central Florida, USA, from April through October 2009. These include 1) LTDS using data from occupied burrows only; 2) LTDS with burrows treated as "clusters" of size 1 or 0 depending on occupancy; 3) LTDS to estimate burrow densities, with occupancy modeling to estimate occupancy rates; and 4) 2 search strategies: standard versus expanded searches. The LTDS method produced reliable burrow density estimates, and tortoise densities were estimated most precisely and with least effort using data from occupied burrows only. However, any method could be biased if burrow occupancy is uncertain. Indeed, in the Florida scrub and pine flatwoods habitats, video-camera scoping was hindered by groundwater or obstructions, resulting in undetermined occupancy for 45% of burrows. Improving scope technologies and surveying during the dry season has improved subsequent results for xeric habitats; however, research is needed to improve detectability of tortoises in mesic habitats with flooded burrows. If occupancy is uncertain, we recommend collecting data on all burrows, irrespective of occupancy, so that burrow densities can be estimated even if occupancy cannot. We do not recommend expanding the search area with sigmoid search paths adjacent to transects owing to potential violations of assumptions, nor use of occupancy modeling, because model requirements may lead to unacceptable exclusion of data. Ó 2015 The Wildlife Society.

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“…In these circumstances, there is a need for new approaches for LTDS surveys. This is particularly true for tortoise populations on large tracts of habitat because of the important role these may play in the overall recovery of the species, whereby these populations may harbor genetic diversity or serve as potential mitigation sites (Smith et al 2009;Castellón et al 2012).…”

Section: Introductionmentioning

confidence: 99%

“…At least 60-80 observations are recommended to model the detection function reliably (Buckland et al 2001). Gopher tortoises can occur in naturally low densities in suboptimal habitat (Breininger et al 1994;Castellón et al 2012;Legleu 2012) or may persist at low densities because of past exploitation for food or inadequate habitat management (Hermann et al 2002). Surveys of low-density populations require considerable effort in terms of total transect length, and small sample size can reduce precision (Smith et al 2009;Castellón et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Techniques for Estimating the Size of Low-Density Gopher Tortoise Populations

Stober

Prieto-Gonzalez

Smith

et al. 2017

Journal of Fish and Wildlife Management

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Gopher tortoises (Gopherus polyphemus) are candidates for range-wide listing as threatened under the U.S. Endangered Species Act. Reliable population estimates are important to inform policy and management for recovery of the species. Line transect distance sampling has been adopted as the preferred method to estimate population size. However, when tortoise density is low, it can be challenging to obtain enough tortoise observations to reliably estimate the probability of detection, a vital component of the method. We suggest a modification to the method based on counting usable tortoise burrows (more abundant than tortoises) and separately accounting for the proportion of burrows occupied by tortoises. The increased sample size of burrows can outweigh the additional uncertainty induced by the need to account for the proportion of burrows occupied. We demonstrate the method using surveys conducted within a 13,118-ha portion of the Gopher Tortoise Habitat Management Unit at Fort Gordon Army Installation, Georgia. We used a systematic random design to obtain more precise estimates, using a newly developed systematic variance estimator. Individual transects had a spatially efficient design (pseudocircuits), which greatly improved sampling efficiency on this large site. Estimated burrow density was 0.091 6 0.011 burrows/ha (CV ¼ 12.6%, 95% CI ¼ 0.071-0.116), with 25% of burrows occupied by a tortoise (CV ¼ 14.4%), yielding a tortoise density of 0.023 6 0.004 tortoise/ha (CV ¼ 19.0%, 95% CI ¼ 0.016-0.033) and a population estimate of 297 tortoises (95% CI ¼ 210-433). These techniques are applicable to other studies and species. Surveying burrows or nests, rather than animals, can produce more reliable estimates when it leads to a significantly larger sample of detections and when the occupancy status can reliably be ascertained. Systematic line transect survey designs give better precision and are practical to implement and analyze.

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Gopher Tortoise (Gopherus polyphemus) Burrow Densities in Scrub and Flatwoods Habitats of Peninsular Florida

Cited by 13 publications

References 15 publications

Kinship, inbreeding and fine‐scale spatial structure influence gut microbiota in a hindgut‐fermenting tortoise

Kinship, inbreeding and fine‐scale spatial structure influence gut microbiota in a hindgut‐fermenting tortoise

A comparison of line-transect distance sampling methods for estimating gopher tortoise population densities

Techniques for Estimating the Size of Low-Density Gopher Tortoise Populations

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