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...
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| Format: | Article |
| Language: | English |
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Elsevier
2022-06-01
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| Series: | Global Ecology and Conservation |
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| Online Access: | http://www.sciencedirect.com/science/article/pii/S2351989422000774 |
| _version_ | 1818489551846375424 |
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| author | Angela K. Fuller Ben C. Augustine Dana J. Morin Karine Pigeon John Boulanger David C. Lee Francesco Bisi David L. Garshelis |
| author_facet | Angela K. Fuller Ben C. Augustine Dana J. Morin Karine Pigeon John Boulanger David C. Lee Francesco Bisi David L. Garshelis |
| author_sort | Angela K. Fuller |
| collection | DOAJ |
| description | 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. |
| first_indexed | 2024-12-10T17:05:27Z |
| format | Article |
| id | doaj.art-0b8e36683031472d8666265330121253 |
| institution | Directory Open Access Journal |
| issn | 2351-9894 |
| language | English |
| last_indexed | 2024-12-10T17:05:27Z |
| publishDate | 2022-06-01 |
| publisher | Elsevier |
| record_format | Article |
| series | Global Ecology and Conservation |
| spelling | doaj.art-0b8e36683031472d86662653301212532022-12-22T01:40:28ZengElsevierGlobal Ecology and Conservation2351-98942022-06-0135e02075The occupancy-abundance relationship and sampling designs using occupancy to monitor populations of Asian bearsAngela K. Fuller0Ben C. Augustine1Dana J. Morin2Karine Pigeon3John Boulanger4David C. Lee5Francesco Bisi6David L. Garshelis7U.S. Geological Survey, New York Cooperative Fish and Wildlife Research Unit, Department of Natural Resources and the Environment, Cornell University, Ithaca, NY 14853, USA; IUCN SSC Bear Specialist Group; Corresponding author at: U.S. Geological Survey, New York Cooperative Fish and Wildlife Research Unit, Department of Natural Resources and the Environment, Cornell University, Ithaca, NY 14853, USA.Department of Natural Resources and the Environment, Cornell University, Ithaca, NY 14853, USAIUCN SSC Bear Specialist Group; Department of Wildlife, Fisheries and Aquaculture, Forest and Wildlife Research Center, Mississippi State University, Box 9690, Mississippi State, MS 39756, USAIUCN SSC Bear Specialist Group; BC Ministry of Forests, Lands, Natural Resource Operations, and Rural Development, 3726 Alfred Ave., Smithers, BC V0J 2N0, CanadaIUCN SSC Bear Specialist Group; Integrated Ecological Research, 924 Innes, Nelson, BC V1L 5T2, CanadaIUCN SSC Bear Specialist Group; School of Applied Sciences, University of South Wales, Pontypridd CF37 4BB, UKIUCN SSC Bear Specialist Group; Environment Analysis and Management Unit - Guido Tosi Research Group – Department of Theoretical and Applied Sciences, University of Insubria, Via J. H. Dunant, 3, I-21100 Varese, ItalyIUCN SSC Bear Specialist Group; Cohasset, MN 55721, USADesigning 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.http://www.sciencedirect.com/science/article/pii/S2351989422000774AbundanceDetection-non-detectionDensitySpecies occurrencePopulation trendFalse positive detection |
| spellingShingle | Angela K. Fuller Ben C. Augustine Dana J. Morin Karine Pigeon John Boulanger David C. Lee Francesco Bisi David L. Garshelis The occupancy-abundance relationship and sampling designs using occupancy to monitor populations of Asian bears Global Ecology and Conservation Abundance Detection-non-detection Density Species occurrence Population trend False positive detection |
| title | The occupancy-abundance relationship and sampling designs using occupancy to monitor populations of Asian bears |
| title_full | The occupancy-abundance relationship and sampling designs using occupancy to monitor populations of Asian bears |
| title_fullStr | The occupancy-abundance relationship and sampling designs using occupancy to monitor populations of Asian bears |
| title_full_unstemmed | The occupancy-abundance relationship and sampling designs using occupancy to monitor populations of Asian bears |
| title_short | The occupancy-abundance relationship and sampling designs using occupancy to monitor populations of Asian bears |
| title_sort | occupancy abundance relationship and sampling designs using occupancy to monitor populations of asian bears |
| topic | Abundance Detection-non-detection Density Species occurrence Population trend False positive detection |
| url | http://www.sciencedirect.com/science/article/pii/S2351989422000774 |
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