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

2017 ◽  
Vol 8 (2) ◽  
pp. 377-386 ◽  
Author(s):  
Jonathan M. Stober ◽  
Rocio Prieto-Gonzalez ◽  
Lora L. Smith ◽  
Tiago A. Marques ◽  
Len Thomas
Keyword(s):  
Habitat Management ◽  
Distance Sampling ◽  
Probability Of Detection ◽  
Line Transect ◽  
Efficient Design ◽  
Gopher Tortoise ◽  
Gopherus Polyphemus ◽  
Line Transect Survey ◽  
Estimate Population Size ◽  
Survey Designs

Abstract 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 ± 0.011 burrows/ha (CV = 12.6%, 95% CI = 0.071–0.116), with 25% of burrows occupied by a tortoise (CV = 14.4%), yielding a tortoise density of 0.023 ± 0.004 tortoise/ha (CV = 19.0%, 95% CI = 0.016–0.033) and a population estimate of 297 tortoises (95% CI = 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.

scholarly journals Added Value: Gopher Tortoise Surveys Provide Estimates of Gopher Frog Abundance in Tortoise Burrows

2020 ◽  
Author(s):  
Lora L Smith ◽  
Jennifer M. Howze ◽  
Jennifer S. Staiger ◽  
Eric R. Sievers ◽  
Deborah Burr ◽  
...  
Keyword(s):  
Environmental Variability ◽  
Distance Sampling ◽  
Added Value ◽  
Line Transect ◽  
Gopher Tortoise ◽  
Gopherus Polyphemus ◽  
Abundance Estimates ◽  
Mean Width ◽  
The Status ◽  
Terrestrial Life

The gopher frog Lithobates capito is one of the most terrestrial frogs in the southeastern U.S. and often inhabits gopher tortoise burrows Gopherus polyphemus outside of the breeding season. Gopher frog populations have declined, and the species is under review for listing as threatened or endangered under the U.S. Endangered Species Act. Much of our knowledge on the status of gopher frogs is based on detections of larvae at breeding wetlands, which can be challenging due to environmental variability and provides no information on the terrestrial life stages of the species. Therefore, an alternative method is called for. We recorded observations of gopher frogs during gopher tortoise surveys at four conservation lands in Florida and used line transect distance sampling to estimate frog abundance. We also recorded burrow size, incidence of frog co-occupancy with tortoises, and distance from frog-occupied burrows to breeding wetlands. We observed 274 gopher frogs in 1,097 tortoise burrows at the four sites. The proportion of burrows occupied by gopher frogs among sites ranged from 0.17 to 0.25. Gopher frog abundance in tortoise burrows was 742 (512–1,076 95% CL) at Etoniah Creek State Forest, 465 (352–615) at Ft. White Wildlife Environmental Area, 411(283–595) at Mike Roess Gold Head Branch State Park, and 134 (97–186) at Watermelon Pond Wildlife Environmental Area. We observed up to four frogs in a single burrow. The proportion of frogs detected in burrows occupied by a gopher tortoise ranged from 0.46 to 0.79 among sites, and overall, gopher frogs preferred burrows occupied by tortoises over unoccupied burrows (χ 2 = 15.875, df=3, p = 0.001). Gopher frogs used burrows from 7 to 43 cm in width; mean width of frog-occupied burrows did not differ from that of unoccupied burrows ( F 1,3 = 0.0492, p = 0.8245). Distance from frog-occupied tortoise burrows to the nearest breeding wetland ranged from 141 to 3,402 m. Our data on gopher frogs collected in conjunction with gopher tortoise monitoring efforts using line transect distance sampling and burrow cameras provided novel information on frog abundance in their terrestrial habitat and required no additional effort. However, the extent to which frogs use tortoise burrows relative to other available refuges (small mammal burrows, stumps, or other structures) is unknown, thus our estimates should be considered conservative. We suggest that terrestrial abundance estimates for gopher frogs can complement efforts to monitor breeding activity to provide a more comprehensive means of monitoring population trends in this cryptic species.

scholarly journals Aerial line transect survey to estimate abundance of marsh deer (Blastocerus dichotomus) (Illiger, 1815)

2005 ◽  
Vol 48 (5) ◽  
pp. 807-814 ◽  
Author(s):  
Artur Andriolo ◽  
Ubiratan Piovezan ◽  
Mateus José Rodrigues Paranhos da Costa ◽  
Jeff Laake ◽  
José Maurício Barbanti Duarte
Keyword(s):  
Population Size ◽  
River Basin ◽  
Distance Sampling ◽  
Aerial Survey ◽  
Line Transect ◽  
Sampling Methodology ◽  
Future Analysis ◽  
Line Transect Survey ◽  
Blastocerus Dichotomus ◽  
The Impact

The objective was to estimate abundance of marsh deer in the Paraná River basin of this work. The results provided information to support further analysis of the impact of the Porto Primavera flooding lake over population. Sixty-nine animals were recorded by aerial survey using distance sampling methodology. Animals were widely distributed throughout the study area. The uncorrected data resulted in a estimate density of 0.0035 ind/ha and a population size of 636 individuals. Correcting the g for the animals that could be missed the calculated abundance was 896 (CV=0.27) individuals. This methodology was applied with success to survey marsh deer. The result was important to evaluate the marsh deer status in the area, and for future analysis of the impact of the flooding dam.

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

2015 ◽  
Vol 39 (4) ◽  
pp. 804-812 ◽  
Author(s):  
Traci D. Castellón ◽  
Betsie B. Rothermel ◽  
Saif Z. Nomani
Keyword(s):  
Sampling Methods ◽  
Distance Sampling ◽  
Line Transect ◽  
Population Densities ◽  
Gopher Tortoise

scholarly journals A Survey of Gopherus polyphemus Intestinal Parasites in South Florida

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Jessica N. Huffman ◽  
Kent S. Haizlett ◽  
Dana K. Elhassani ◽  
Brian T. Cooney ◽  
Evelyn M. Frazier
Keyword(s):  
Disease Transmission ◽  
Habitat Management ◽  
Parasite Species ◽  
Intestinal Parasites ◽  
Habitat Type ◽  
Parasite Prevalence ◽  
South Florida ◽  
Gopher Tortoise ◽  
Gopherus Polyphemus ◽  
Significant Health

Gopherus polyphemus populations are diminishing throughout their range due to urbanization, fragmentation, and poor habitat management. Increased population densities, poor habitat quality, and lack of fire may influence disease transmission. Parasite roles within wild tortoise populations are largely unknown; despite evidence these pathogens may pose significant health risks. This study provides a baseline of gopher tortoise intestinal parasites across South Florida and reports on how varying environmental and tortoise characteristics may affect intestinal parasite species prevalence and approximate loads. Tortoise fecal samples were taken from six tortoise populations across five South Florida sites. Seven species of intestinal parasites were discovered from 123 tortoises. Identified parasites include endohelminths such as cyathostomes, pinworms, ascarids, flukes, and protozoans including Eimeria, Cryptosporidium, and Amoeba species. Significant differences in parasite prevalence and loads were seen between sites, while parasitism among sex, size class, and habitat type remained relatively ubiquitous.

scholarly journals Variance Propagation for Density Surface Models

2021 ◽  
Author(s):  
Mark V. Bravington ◽  
David L. Miller ◽  
Sharon L. Hedley
Keyword(s):  
Random Effect ◽  
Distance Sampling ◽  
Line Transect ◽  
Line Transect Survey ◽  
Surface Models ◽  
On Line ◽  
Density Surface ◽  
Two Stages ◽  
Variance Estimates ◽  
Spatially Varying

AbstractSpatially explicit estimates of population density, together with appropriate estimates of uncertainty, are required in many management contexts. Density surface models (DSMs) are a two-stage approach for estimating spatially varying density from distance sampling data. First, detection probabilities—perhaps depending on covariates—are estimated based on details of individual encounters; next, local densities are estimated using a GAM, by fitting local encounter rates to location and/or spatially varying covariates while allowing for the estimated detectabilities. One criticism of DSMs has been that uncertainty from the two stages is not usually propagated correctly into the final variance estimates. We show how to reformulate a DSM so that the uncertainty in detection probability from the distance sampling stage (regardless of its complexity) is captured as an extra random effect in the GAM stage. In effect, we refit an approximation to the detection function model at the same time as fitting the spatial model. This allows straightforward computation of the overall variance via exactly the same software already needed to fit the GAM. A further extension allows for spatial variation in group size, which can be an important covariate for detectability as well as directly affecting abundance. We illustrate these models using point transect survey data of Island Scrub-Jays on Santa Cruz Island, CA, and harbour porpoise from the SCANS-II line transect survey of European waters. Supplementary materials accompanying this paper appear on-line.

scholarly journals Detection of Gopher Tortoise Burrows Before and After a Prescribed Fire: Implications for Surveys

2018 ◽  
Vol 10 (1) ◽  
pp. 62-68 ◽  
Author(s):  
Jennifer M. Howze ◽  
Lora L. Smith
Keyword(s):  
Habitat Structure ◽  
Survey Methodology ◽  
Distance Sampling ◽  
Population Estimates ◽  
Line Transect ◽  
Past Century ◽  
Prescribed Burn ◽  
Gopher Tortoise ◽  
Imperfect Detection ◽  
Abundance Estimate

Abstract Gopher tortoise Gopherus polyphemus populations have declined by as much as 80% over the past century, primarily as a result of habitat loss. In 2006, the eastern population of the gopher tortoise was petitioned for federal listing as threatened. In response, a Candidate Conservation Agreement was developed for the gopher tortoise. A Candidate Conservation Agreement is a voluntary agreement between the U.S. Fish and Wildlife Service and other interested parties to address the conservation needs of a species before it becomes federally listed and to enact measures to preclude the need to list the species. The gopher tortoise Candidate Conservation Agreement identified an assessment of the status of populations on protected lands as a priority and line transect distance sampling (LTDS) was adopted as the standardized survey methodology. Surveys with LTDS rely on detection of gopher tortoise burrows because tortoises are fossorial. However, gopher tortoise burrows vary greatly in size and small burrows of juveniles are rarely detected. Although LTDS is statistically robust and allows for imperfect detection, few studies have examined how detection varies with tortoise burrow size and whether habitat structure may influence detection of gopher tortoise burrows. Both factors could affect the accuracy of population estimates using LTDS and interpretation of demographic parameters needed for the Candidate Conservation Agreement. Therefore, we conducted surveys for burrows using LTDS before (28 March–13 April 2016) and after (9–18 May 2016) a prescribed burn, which reduced vegetation cover. We detected significantly more burrows (P < 0.001, n = 651) of all sizes after the burn, and the burrow abundance estimate was 64% higher postburn. Our study showed that conducting gopher tortoise surveys after a prescribed burn increased detections and provided a more accurate population estimate. We therefore recommend conducting surveys immediately after a burn. However, varying burn cycles on large sites may make it difficult to survey following a prescribed burn and because the effects of a burn on habitat structure may vary within a site, methods to account for variation in detection due to habitat structure are needed. Population estimates for gopher tortoises using LTDS that do not account for variation in detection due to habitat structure likely underestimate population size.

Double-observer evaluation of pronghorn aerial line-transect surveys

2016 ◽  
Vol 43 (6) ◽  
pp. 474 ◽  
Author(s):  
Timothy J. Smyser ◽  
Richard J. Guenzel ◽  
Christopher N. Jacques ◽  
Edward O. Garton
Keyword(s):  
Cluster Size ◽  
Distance Sampling ◽  
Landscape Composition ◽  
Probability Of Detection ◽  
Line Transect ◽  
Front Seat ◽  
Density Estimates ◽  
Seat Position ◽  
Analysis Techniques ◽  
Double Observer

Context Distance sampling is used to estimate abundance for several taxa, including pronghorn (Antilocapra americana). Comparisons between population estimates derived from quadrat sampling and distance sampling suggest that distance sampling underestimates pronghorn density, likely owing to violations of the critical assumption of distance sampling that all pronghorn within the innermost distance band (A band; nearest to the aircraft) are detected. Aims We sought to rigorously test the assumption that all pronghorn clusters are detected within the innermost distance band by applying a double-observer approach to an established pronghorn aerial-survey protocol. Additionally, we evaluated potential effects of cluster size, landscape composition and seat position (front seat versus rear) on the probability of detection. Methods We conducted aerial line-transect distance-sampling surveys using independent, paired observers and modelled the probability of detection with mark–recapture distance-sampling (MRDS) analysis techniques that explicitly estimate the probability of detection for pronghorn clusters in the innermost distance band. We compared density estimates produced by the MRDS analysis with those produced by multiple-covariate distance sampling (MCDS), a method that assumes complete detection for clusters on the transect line. Key results We identified violations of the assumption that all clusters within the innermost distance band were detected, which would contribute to proportional biases in density estimates for analysis techniques that assume complete detection. The frequency of missed clusters was modest from the front-seat position, with 45 of the 47 (96%) clusters in the A band detected. In contrast, the frequency of missed clusters was more substantial for the rear position, from which 37 of 47 (79%) clusters in the A band were detected. Further, our analysis showed that cluster size and landscape composition were important factors for pronghorn sightability. Conclusions When implementing standard survey methodologies, pronghorn aerial-line transect surveys underestimated population densities. A double-observer survey configuration allowed us to quantify and correct for the bias caused by the failure of observers to detect all pronghorn clusters within the innermost distance band. Implications Population monitoring programs should incorporate double-observer validation trials to quantify the extent of bias owing to undetected clusters within the innermost distance band realised under typical survey conditions. Wildlife managers can improve the precision of pronghorn aerial line-transect surveys by incorporating cluster size and measures of landscape composition and complexity into detection models without incurring additional survey costs.

PROFIL KERAGAMAN VEGETASI EKOSISTEM MANGROVE DI DESA TAMUKU KABUPATEN LUWU UTARA

2019 ◽  
Vol 5 ◽  
pp. 104
Author(s):  
Suhendra Purnawan ◽  
Subari Yanto ◽  
Ernawati S.Kaseng
Keyword(s):  
Survey Methods ◽  
Mangrove Ecosystem ◽  
Line Transect ◽  
Mangrove Forests ◽  
Vegetation Diversity ◽  
Line Transect Survey ◽  
Analysis Technique ◽  
Mangrove Vegetation ◽  
Data Collection Technique ◽  
The Impact

This study aims to describe the profile of vegetation diversity in the mangrove ecosystem in Tamuku Village, Bone-Bone-Bone District, North Luwu Regency. This research is a qualitative research using survey methods. The data collection technique uses the Quadrant Line Transect Survey technique. The data analysis technique uses the thinking flow which is divided into three stages, namely describing phenomena, classifying them, and seeing how the concepts that emerge are related to each other. The results of this study are the profile of mangrove vegetation in Tamuku Village, which is still found 16 varieties of true mangrove vegetation and 7 varieties of mangrove vegetation joined in the coastal area of Tamuku Village, Bone-Bone District, North Luwu Regency, South Sulawesi. The condition of mangrove vegetation in Tamuku Village is currently very worrying due to human activities that cause damage such as the project of normalization of flow, opening of new farms, disposal of garbage, water pollution due to chemicals, and exploitation of mangrove forests for living needs. The impact is ecosystem damage and reduced vegetation area as a place to grow and develop mangroves.

scholarly journals Getting the Most From Surveys: How Method Selection and Method Modification Impact Butterfly Survey Data

2021 ◽  
Author(s):  
Katherine C Kral-O’Brien ◽  
Adrienne K Antonsen ◽  
Torre J Hovick ◽  
Ryan F Limb ◽  
Jason P Harmon
Keyword(s):  
Species Richness ◽  
New Species ◽  
Count Data ◽  
Distance Sampling ◽  
Line Transect ◽  
Similar Species ◽  
Method Selection ◽  
M 10 ◽  
Sampling Procedures

Abstract Many methods are used to survey butterfly populations, with line transect and area surveys being prominent. Observers are typically limited to search within 5 or 10 m from the line, while observers are unrestricted in larger specified search regions in area surveys. Although methods differ slightly, the selection is often based on producing defendable data for conservation, maximizing data quality, and minimizing effort. To guide method selection, we compared butterfly surveys using 1) line versus area methods and 2) varying width transects (5 m, 10 m, or unrestricted) using count data from surveys in North Dakota from 2015 to 2018. Between line and area surveys, we detected more individuals with area surveys, even when accounting for effort. However, both methods accumulated new species at similar rates. When comparing transect methodology, we detected nearly 60% more individuals and nine more species when transect width increased from 5 m to unrestricted, despite similar effort across methodology. Overall, we found line surveys slightly less efficient at detecting individuals, but they collected similar species richness to area surveys when accounting for effort. Additionally, line surveys allow the use of unrestricted-width transects with distance sampling procedures, which were more effective at detecting species and individuals while providing a means to correct count data over the same transect length. Methods that reduce effort and accurately depict communities are especially important for conservation when long-term datasets are unavailable.

scholarly journals Comprehensive health assessment and blood analyte reference intervals of gopher tortoises (Gopherus polyphemus) in southeastern FL, USA

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Annie Page-Karjian ◽  
Kathleen Rafferty ◽  
Clerson Xavier ◽  
Nicole I Stacy ◽  
Jon A Moore ◽  
...  
Keyword(s):  
Plasma Protein ◽  
Health Assessment ◽  
Clinical Signs ◽  
Keystone Species ◽  
Reference Intervals ◽  
Upper Respiratory Tract ◽  
Gopher Tortoise ◽  
Gopherus Polyphemus ◽  
Baseline Information ◽  
Mycoplasma Spp

Abstract The gopher tortoise (Gopherus polyphemus), a keystone species, is declining throughout its geographic range. Lack of knowledge with respect to the potential infectious diseases present within wild populations creates a dilemma for wildlife biologists, conservationists and public policy makers. The objective of this study was to conduct a health assessment of two previously unstudied gopher tortoise aggregations located at two sites in southeastern FL. Samples were collected from 91 tortoises (48 adults, 35 juveniles, 8 hatchlings) captured at Florida Atlantic University’s Harbor Branch Oceanographic Institute, in Fort Pierce, FL, USA in 2019, and Loggerhead Park in Juno Beach, FL, USA, during 2018–2019. Samples of blood, nasal swabs and oral/cloacal swabs were analyzed for hematology, plasma protein electrophoretic profiles and infectious disease testing including Mycoplasma spp. serology and polymerase chain reaction (PCR) assays for Ranavirus, Herpesvirus and Anaplasma spp. Hematological and plasma protein electrophoresis reference intervals are presented for adult and juvenile tortoises from both sites combined. Clinical signs consistent with upper respiratory tract disease (URTD) were observed in 18/91 (20%) tortoises, and antibodies to Mycoplasma agassizii were detected in 33/77 (42.9%) tortoises. Adult tortoises were significantly more likely than juveniles to have URTD clinical signs, and statistically significant, positive relationships were observed between the presence of antibodies to Mycoplasma spp. and carapace length, packed cell volume and plasma globulin concentrations. Anaplasma spp. inclusions were observed in 8/82 (10%) tortoises, but PCR detected Anaplasma sp. in 21/83 (25%) tortoises. Herpesvirus and Ranavirus were not detected in any blood or swab samples. This work contributes important baseline information on the health of gopher tortoises toward the southern end of the species’ range.

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