Progress 10/01/09 to 09/30/14
Outputs
Target Audience:
Nothing Reported
Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
The feasibility of monitoring the black bear population in Great Smoky Mountains National Park was testedby replacing the bait-station surveys with DNA sampling to track population growth.
Publications
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Progress 01/01/13 to 09/30/13
Outputs
Target Audience: State and federal wildlife biologists and managers. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
We systematically reduced the number of those samples used in the analysis to evaluate the effect that changes in capture probabilities may have on parameter estimates. Model-averaged N for females and males were 162 (95% CI = 115–273) and 100 (95% CI = 75–167), respectively (pooled N = 262, 95% CI = 193–419), and the average weekly capture probability was 0.09 for females and 0.12 for males. When we reduced the number of samples of the empirical data, support for heterogeneity models decreased. For the simulation analysis, we generated capture data with individual heterogeneity covering a range of sampling conditions commonly encountered in DNA-based capture-mark-recapture studies and examined the relationships between those conditions and accuracy (i.e., the probability of obtaining an estimated N that is within 20% of true N), coverage (i.e., probability that 95% confidence interval includes true N), and precision (i.e., probability of obtaining a coefficient of variation ≤20%) of estimates using logistic regression. The capture probability for the larger of 2 mixture proportions of the population (i.e., pA or pB) was most important for predicting accuracy and precision, whereas capture probabilities of both mixture proportions (pA and pB) were important to explain variation in coverage. Based on sampling conditions similar to parameter estimates from the empirical dataset (pA = 0.30, pB = 0.05, N = 250, π = 0.15, and k = 10), predicted accuracy and precision were low (60% and 53%, respectively), whereas coverage was high (94%). Increasing pB, the capture probability for the predominate but most difficult to capture proportion of the population, was most effective to improve accuracy under those conditions. However, manipulation of other parameters may be more effective under different conditions. In general, the probabilities of obtaining accurate and precise estimates were best when ≥ 0.2. Our regression models can be used by managers to evaluate specific sampling scenarios and guide development of sampling frameworks or to assess reliability of DNA-based capture-mark-recapture studies.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Laufenberg, J. S., F. T. van Manen, and J. D. Clark. Effects of sampling conditions on DNA-based estimates of black bear abundance. Journal of Wildlife Management 77:10101020
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Progress 01/01/12 to 12/31/12
Outputs
OUTPUTS: Mark-recapture methods based on DNA extracted from hair samples have received widespread use in recent years for estimating population size. However, insufficient sampling and capture biases can lead to erroneous or imprecise estimates of population parameters. Because microsatellite analysis is expensive, it is important to better understand sampling issues and study design before a range-wide study is attempted. We are investigating the relationships between sampling conditions (i.e., true abundance [N], capture probability of heterogeneity mixtures A and B [pA and pB, respectively], the proportion of each mixture [π], and number of capture occasions [k]) and the probability of obtaining reliable estimates of N using empirical and simulated capture data. Results from this work can be used by managers to examine the adequacy of potential sampling designs or to evaluate the reliability of estimates from DNA-based capture-mark-recapture studies. PARTICIPANTS: Lisa I. Muller, Associate Professor, University of Tennessee Frank T. van Manen, Adjunct Professor, University of Tennessee Joseph D. Clark, Adjunct Professor, University of Tennessee Partner Organizations: Tennessee Wildlife Resources Agency and National Park Service TARGET AUDIENCES: State and federal wildlife biologists and managers. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
DNA-based capture-mark-recapture techniques are commonly used to estimate American black bear (Ursus americanus) population abundance (N). Although the technique is well established, many questions remain regarding study design. In particular, relationships among N, capture probability of heterogeneity mixtures A and B (pA and pB, respectively, or , collectively), the proportion of each mixture (π), number of capture occasions (k), and probability of obtaining reliable estimates of N are not fully understood. We investigated these relationships using 1) an empirical dataset of DNA samples for which true N was unknown and 2) simulated datasets with known properties that represented a broader array of sampling conditions. For the empirical data analysis, we used the full closed population with heterogeneity data type in Program MARK to estimate N for a black bear population in Great Smoky Mountains National Park, Tennessee. We systematically reduced the number of those samples used in the analysis to evaluate the effect that changes in capture probabilities may have on parameter estimates. Model-averaged N for females and males were 162 (95% CI = 115-273) and 100 (95% CI = 75-167), respectively (pooled N = 262, 95% CI = 193-419), and the average weekly was 0.09 for females and 0.12 for males. When we reduced the number of samples of the empirical data, support for heterogeneity models decreased. For the simulation analysis, we generated capture data with individual heterogeneity covering a range of sampling conditions commonly encountered in DNA-based capture-mark-recapture studies and examined the relationships between those conditions and accuracy (i.e., the probability of obtaining an estimated N that is within 20% of true N), coverage (i.e., probability that 95% confidence interval includes true N), and precision (i.e., probability of obtaining a coefficient of variation ≤20%) of estimates using logistic regression. The capture probability for the larger of 2 mixture proportions of the population (i.e., pA or pB) was most important for predicting accuracy and precision, whereas capture probabilities of both mixture proportions (pA and pB) were important to explain variation in coverage. Based on sampling conditions similar to parameter estimates from the empirical dataset (pA = 0.30, pB = 0.05, N = 250, π = 0.15, and k = 10), predicted accuracy and precision were low (60% and 53%, respectively), whereas coverage was high (94%). Increasing pB, the capture probability for the predominate but most difficult to capture proportion of the population, was most effective to improve accuracy under those conditions. However, manipulation of other parameters may be more effective under different conditions. In general, the probabilities of obtaining accurate and precise estimates were best when ≥ 0.2. Our regression models can be used by managers to evaluate specific sampling scenarios and guide development of sampling frameworks or to assess reliability of DNA-based capture-mark-recapture studies.
Publications
- Laufenberg, J.S., F.T.van Manen, and J.D. Clark. 2012 In Prep. Effects of sampling conditions on DNA-based estimates of black bear abundance. Journal of Wildlife Management.
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Progress 01/01/11 to 12/31/11
Outputs
OUTPUTS: The black bear (Ursus americanus) population in the mountains of east Tennessee has increased steadily since population trend data were first recorded in the mid-1970s. The number of hunter-killed bears in Tennessee has also increased. As the bear population and the need to reduce nuisance bear problems have grown, so have public requests for increased harvests. With the increased harvest, however, the potential for overexploitation also increases. As the responsible agency for statewide bear management, TWRA needs reliable methods to evaluate effects of harvest on bear population growth. Mark-recapture methods based on DNA extracted from hair samples have received widespread use in recent years for estimating population size. However, insufficient sampling and capture biases can lead to erroneous or imprecise estimates of population parameters. Because microsatellite analysis is expensive, it is important to perform a preliminary analysis to address sampling issues before a range-wide study is attempted. We are collaborating with the Tennessee Wildlife Resources Agency to determine if DNA sampling using hair collected from glue traps can be used in combination with recaptures from bears harvested during the hunting season to provide accurate and precise estimates of bear population size and thus to monitor population growth. A final report was produced for the Tennessee Wildlife Resources Agency in December 2010 (after the 2010 CRIS reporting date). PARTICIPANTS: Lisa I. Muller, Associate Professor, University of Tennessee Frank T. van Manen, Adjunct Professor, University of Tennessee Joseph D. Clark, Adjunct Professor, University of Tennessee Partner Organizations: Tennessee Wildlife Resources Agency and National Park Service TARGET AUDIENCES: State and federal wildlife biologists and managers. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
The American black bear (Ursus americanus) population and the number of hunter-killed bears in eastern Tennessee have steadily increased since the mid-1970s. In July 2007, we performed a pilot study in 2 southeastern Tennessee counties to evaluate the feasibility of estimating the range-wide population size. We collected and genotyped 68 bear hair samples from 276 bait sites (the marked ample) and 25 tissue samples from hunter-killed bears (the recaptured sample). The capture probability was low (p = 0.041, 95% CI = 0.006-0.241) and the Peterson estimate of population size was imprecise (N = 1,287, 95% CI = 305-6,491) and likely biased due to capture effects. Therefore, we evaluated alternative approaches including closed population estimators or robust design methods for DNA sampling, estimators of population growth (λ) based on DNA mark-recapture, estimators of apparent survival (φ) based on DNA or tetracycline marking and hunter harvest recapture (i.e., recovery models), bait-station surveys for monitoring λ, and population reconstruction for estimating N, λ, and φ. Robust design mark-recapture would produce the most reliable estimates but a range-wide implementation would be cost-prohibitive. We suggest that monitoring λ based on DNA sampling would be less prone to capture heterogeneity biases and more cost effective. Recovery models to estimate male and female survival do not require intensive sampling but are less precise and genetic analysis costs would be high. Finally, maximum likelihood methods have recently been developed which, with ancillary data (e.g., survival from radio telemetry data, hunter reporting rates, catch per unit effort), enable researchers to estimate previously inestimable parameters based on population reconstruction methods, at little additional cost. We provide a breakdown of the advantages and disadvantages of each technique to help regional bear managers decide how to best balance the need for scientific rigor and the reality of budgetary limits.
Publications
- Clark, J. D., and F. T. van Manen. 2010. Efficacy of DNA Mark-Recapture Methods for Estimating Black Bear Population Parameters in Tennessee. Final report to Tennessee Wildlife Resources Agency. 28 December 2010.
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Progress 01/01/10 to 12/31/10
Outputs
OUTPUTS: The black bear (Ursus americanus) population in the mountains of east Tennessee has increased steadily since population trend data were first recorded in the mid-1970s. The number of hunter-killed bears in Tennessee has also increased. As the bear population and the need to reduce nuisance bear problems have grown, so have public requests for increased harvests. With the increased harvest, however, the potential for overexploitation also increases. As the responsible agency for statewide bear management, TWRA needs reliable methods to evaluate effects of harvest on bear population growth. Mark-recapture methods based on DNA extracted from hair samples have received widespread use in recent years for estimating population size. However, insufficient sampling and capture biases can lead to erroneous or imprecise estimates of population parameters. Because microsatellite analysis is expensive, it is important to perform a preliminary analysis to address sampling issues before a range-wide study is attempted. We are collaborating with the Tennessee Wildlife Resources Agency to determine if DNA sampling using hair collected from glue traps can be used in combination with recaptures from bears harvested during the hunting season to provide accurate and precise estimates of bear population size and thus to monitor population growth. A draft report was produced for the Tennessee Wildlife Resources Agency in August 2010. PARTICIPANTS: Lisa I. Muller, Associate Professor, University of Tennessee, Frank T. van Manen, Adjunct Professor, University of Tennessee, Joseph D. Clark, Adjunct Professor, University of Tennessee, Partner Organizations: Tennessee Wildlife Resources Agency and National Park Service. TARGET AUDIENCES: State and federal wildlife biologists and managers. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Effective black bear management is largely a matter of determining the level of scientific uncertainty and costs that are acceptable for decision making. The preliminary outcome of our study provides the following recommendations: 1) Lincoln-Peterson estimates of population size.-Although the most cost effective of the mark-recapture approaches we evaluated, we do not feel this method would produce estimates of population size that are reliable. Precision could be achieved with increased hair sampling at a significant cost, but the resultant population estimate could be biased with no way to evaluate those biases. Bears are particularly prone to exhibit sampling biases and such biases have been well documented by other researchers. Thus, the risk of incorrect management decisions based on such estimates would be high. Tetracycline baits would reduce costs as a marking procedure, but the technique introduces an entire suite of additional problems that violate the most basic mark-recapture assumptions and sample sizes likely would be inadequate for a precise estimate given the importance of the assumption that bears do not consume >1 bait. 2) Robust design mark-recapture. This technique, based on DNA sampling, would provide the most robust estimates of population size and several other parameters, but at the highest cost. A range-wide study clearly would not be feasible. A more localized study might be feasible for estimating population parameters there and extrapolated to the range-wide population, but such assumptions are dangerous unless hunter participation, hunter success, and so on were rigorously monitored. Levels of ingress and egress likely would be different for a small study area compared with a range-wide population. Consequently, this method is probably not feasible. 3) Open mark-recapture models. Rather than estimate population size, we suggest that population growth might be a more estimable and meaningful population parameter to monitor. Pradel estimators can be used to estimate lambda over time at a reasonable cost and reliability; our simulations suggest that a difference of 5% in lambda could be detected over a 10 years for about $7,734 in annual laboratory costs. However, the field work required to mark and recapture animals via hair sampling would be significant. Recovery models to estimate male and female survival do not require intensive sampling but are less precise and genetic analysis costs would be high. 4) Population reconstruction. When combined with auxiliary data, this technique has potential to be of value. An important benefit of this technique is that harvest data will probably be collected regardless and the age structure of harvested bears can be estimated with little additional expense. If mark-recapture data were used as auxiliary data to estimate male and female survival or growth as described above, age-at-harvest data could be used to estimate additional parameters such as population size and exploitation rate at little additional cost.
Publications
- No publications reported this period
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