Geology topics

David L. Garshelis

Publications and source records attributed to David L. Garshelis.

7 recordsLinked to original sources

USGS2022

The occupancy-abundance relationship and sampling designs using occupancy to monitor populations of Asian bears

Designing a population monitoring program for Asian bears presents challenges associated with their low densities and detectability, generally large home ranges, and logistical or resource constraints. The use of an occupancy-based method to monitor bear populations can be appropriate under certain conditions given the mechanistic relationship between occupancy and abundance. The form of the occupancy–abundance relationship is dependent on species-specific characteristics such as home range size and population density, as well as study area size. To assess the statistical power of tests to detect population change of Asian bears, we conducted a study using a range of scenarios by simulating spatially explicit individual-based capture-recapture data from a demographically open model. Simulations assessed the power to detect changes in population density via changes in site-level occupancy or abundance through time, estimated using a standard occupancy model or a Royle-Nichols model, both with point detectors (representing camera traps). We used IUCN Red List criteria as a guide in selection of two population decline scenarios (20% and 50%), but we chose a shorter time horizon (10 years = 1 bear generation), meaning that declines were steeper than used for IUCN criteria (3 generations). Our simulations detected population declines of 50% with high power (>0.80) and low false positive rates (FPR: incorrectly detecting a decline) (<0.10) when detectors were spaced at > 0.67 times the home range diameter (home-range spacing ratio: HRSR, a measure of spatial correlation), such that bears would tend to overlap no more than two detectors. There was high (0.85) correlation between realized occupancy and N in these scenarios. The FPR increased as the HRSR decreased because of spatial correlation in the occupancy process induced when individual home ranges overlap multiple detectors. The mean statistical power to detect more gradual population declines (20% in 10 years) with HRSR > 0.67 was low for occupancy models 0.22 (maximum power 0.67) and Royle-Nichols models (0.24; maximum power 0.67), suggesting that declines of this magnitude may not be described reliably with 10 years of monitoring. Our results demonstrated that under many realistic scenarios that we explored, false positive rates were unacceptably high. We highlight that when designing occupancy studies, the spacing between point detectors be at least 0.67 times the diameter of the home range size of the larger sex (e.g., males) when the assumptions of the spatial capture-recapture model used for simulation are met.

Global Ecology and Conservation↗

USGS2022

Review of field methods for monitoring Asian bears

Efficient and effective monitoring methods are required to assess population status and gauge efficacy of conservation actions for threatened species. Here we review the spectrum of field methods useful for monitoring distribution, occupancy, abundance, and population trend for the five species of Asian terrestrial bears. Methods reviewed include expert opinion, local knowledge, bear sign, visual observations, camera traps, DNA-based methods (hair and scat derived), and radio telemetry. We examine the application of each method in terms of realizing specific monitoring objectives, their assumptions, challenges, and advantages. Our goal is to assist researchers in matching appropriate field methods with sought-after project objectives and to highlight shortfalls and trade-offs. Methods vary greatly in terms of cost, logistics, required number and expertise of staff, and the reliability of the data they provide. Many Asian bear population assessments have relied on expert opinion, local interviews, and sign surveys to provide estimates of distribution, abundance, and trend, in part because these are inexpensive and relatively easy to employ. However, increasing use of camera traps and DNA-based methods now allow for better monitoring via occupancy or rigorous capture–recapture population estimation, with the caveat that these methods may be restricted by inadequate budgets or logistical constraints. For distribution monitoring, camera traps and DNA yield the most definitive records of presence, but in low density bear populations, sign and local knowledge may be more effective. For occupancy, camera traps and DNA are advantageous in providing definitive detections in known time periods. For abundance/density or population trend monitoring in relatively small areas (<10,000 km 2 ), bears must be individually identified and used in a mark-recapture design. This requires DNA from collections of hair or scat, or a camera-based survey in which natural chest marks are clearly visible and individually distinguishable. DNA-methods or camera traps within individual identification is best for population trend when sufficient funding is available. Alternatively, careful use of local knowledge or expert opinion may be viable options, but come with greater uncertainty. For the foreseeable future, we believe that expert opinion will likely continue to play a large part in monitoring Asian bears, but these opinions should be informed by more rigorous data from the other methods we discuss.

Global Ecology and Conservation↗

USGS2022

The need to step-up monitoring of Asian bears

Many wildlife species are threatened in Asia, including the five species of terrestrial bears (Asiatic black, Ursus thibetanus ; brown, U. arctos ; sloth, Melursus ursinus ; sun, Helarctos malayanus ; giant panda, Ailuropoda melanoleuca ): many populations of these bears are thought to be declining or imperiled by small population size. Here our aim is to document how population assessments have been conducted for bears in Asia. We searched the literature and identified 102 studies published during 1999–2021 that investigated the status of an Asian bear population; these occurred in 24 of the 32 bear range countries in Asia. At the most basic level, 11% of studies verified presence of bears in places where they were not known to exist. The most common objective (53% of papers) was a distribution map, often derived from presence locations in a habitat-based model. Occupancy studies (15%) used temporal (time stamps on images from cameras) or spatial (transect segments) replicates, but tended to focus on “use”, so detector spacing was sometimes not appropriate for occupancy. Purported population indices, such as sign density or camera trap encounter rates, were reported in 16% of studies. One third of studies provided a population estimate, but only 10 studies in two decades used a rigorous method (e.g., mark–recapture). Sign surveys and interviews were the most common methods for determining bear presence, and local interviews were heavily relied upon for assessing population trend. Camera trapping has become increasingly prevalent, but only one study obtained a population estimate using photographs to distinguish natural individual markings. Only three studies used hair traps to obtain DNA-based population estimates, and three other studies obtained population estimates from DNA in scats. Just three studies quantitatively measured change in population size or occupancy over time, and none of these showed a decline. Unique rangewide sign surveys of giant pandas showed significant geographic expansion. The opinions of experts and local people, now heavily relied upon for population assessments, are not reliable or sensitive enough for monitoring. Quantitative population assessments are desirable to direct conservation actions toward the most perilous situations, and provide a means to gauge the effectiveness of conservation actions. This paper demonstrates the paucity of rigorous monitoring of Asian bears, and leads off a series of papers that propose improved methods for assessing distribution, occupancy, and density

Global Ecology and Conservation↗

USGS2018

Genetic diversity, effective population size, and structure among black bear populations in the Lower Mississippi Alluvial Valley, USA

Multiple small populations of American black bears Ursus americanus , including the recently delisted Louisiana black bear subspecies U. a. luteolus , occupy a fragmented landscape in the Lower Mississippi Alluvial Valley, USA (LMAV). Populations include bears native to the LMAV, bears translocated from Minnesota during the 1960s, and recently reintroduced and colonizing populations sourced from within the LMAV. We estimated population structure, gene flow, and genetic parameters important to conservation of small populations using genotypes at 23 microsatellite markers for 265 bears from seven populations. We inferred five genetic clusters corresponding to the following populations: White River and western Mississippi, Tensas River and Three Rivers, Upper Atchafalaya, Lower Atchafalaya, and Minnesota. Upper Atchafalaya was suggested as the product of Minnesota-sourced translocations, but those populations have since diverged, likely because of a founder effect followed by genetic drift and isolation. An admixture zone recently developed in northeastern Louisiana and western Mississippi between migrants from White River and Tensas River, resulting in a Wahlund effect. However, gene flow among most populations has been limited and considerable genetic differentiation accumulated (global F ST = 0.22), particularly among the three Louisiana black bear populations that existed when federal listing occurred. Consistent with previous bottlenecks, founder effects, and persisting isolation, all LMAV bear populations had low genetic diversity ( A R = 2.08–4.81; H E = 0.36–0.63) or small effective population size ( N E = 3–49). Translocating bears among populations as part of a regional genetic restoration program may help improve genetic diversity and increase effective population sizes.

Lower Mississippi Alluvial Valley↗

USGS2014

Polar bears from space: Assessing satellite imagery as a tool to track Arctic wildlife

Development of efficient techniques for monitoring wildlife is a priority in the Arctic, where the impacts of climate change are acute and remoteness and logistical constraints hinder access. We evaluated high resolution satellite imagery as a tool to track the distribution and abundance of polar bears. We examined satellite images of a small island in Foxe Basin, Canada, occupied by a high density of bears during the summer ice-free season. Bears were distinguished from other light-colored spots by comparing images collected on different dates. A sample of ground-truthed points demonstrated that we accurately classified bears. Independent observers reviewed images and a population estimate was obtained using mark- recapture models. This estimate (N: 94; 95% Confidence Interval: 92-105) was remarkably similar to an abundance estimate derived from a line transect aerial survey conducted a few days earlier (N: 102; 95% CI: 69-152). Our findings suggest that satellite imagery is a promising tool for monitoring polar bears on land, with implications for use with other Arctic wildlife. Large scale applications may require development of automated detection processes to expedite review and analysis. Future research should assess the utility of multi-spectral imagery and examine sites with different environmental characteristics.

PLoS ONE↗

USGS2010

The impact of conservation on the status of the world's vertebrates

Using data for 25,780 species categorized on the International Union for Conservation of Nature Red List, we present an assessment of the status of the world's vertebrates. One-fifth of species are classified as Threatened, and we show that this figure is increasing: On average, 52 species of mammals, birds, and amphibians move one category closer to extinction each year. However, this overall pattern conceals the impact of conservation successes, and we show that the rate of deterioration would have been at least one-fifth again as much in the absence of these. Nonetheless, current conservation efforts remain insufficient to offset the main drivers of biodiversity loss in these groups: agricultural expansion, logging, overexploitation, and invasive alien species.

Science↗

USGS2006

Sea otter mortality from the Exxon Valdez spill: Evaluation of an estimate from boat-based surveys

The Exxon Valadez oil spill killed large numbers of sea otters ( Enhydra lutris ) in Prince William Sound (PWS), Alaska, where the spill originated, as well as within the oil’s path along the coasts of the Kenai Peninsula and Kodiak Island. Sea otters attracted particular attention after the spill due to their public appeal (Batten 1990) and known vulnerability to oil (Costa and Kooyman 1982, Siniff et al. 1982, Davis et al. 1988, Williams et al. 1988). Extensive efforts were made to rescue and rehabilitate oiled otters at a resulting cost of ca. $80,000 per animal (Estes 1991). The argument that otters lost in the spill should be similarly valued made the estimate of mortality a matter of substantial concern to those involved in spill-related litigation or out-of-court settlements.

Alaska↗