Occupancy

About: Occupancy is a research topic. Over the lifetime, 2757 publications have been published within this topic receiving 68288 citations.

Accounting for false positives improves estimates of occupancy from key informant interviews

Abstract: Aim Much research in conservation biogeography is fundamentally dependent on obtaining reliable data on species distributions across space and time. Such data are now increasingly being generated using various types of public surveys. These data are often integrated with occupancy models to evaluate distributional patterns, range dynamics and conservation status of multiple species at broad spatio-temporal scales. Occupancy models have traditionally corrected for imperfect detection due to false negatives while implicitly assuming that false positives do not occur. However, public survey data are also prone to false-positive errors, which when unaccounted for can cause bias in occupancy estimates. We test whether false positives in a dataset collected from public surveys lead to overestimation of species site occupancy and whether estimators that simultaneously account for false-positive and false-negative errors improve occupancy estimates. Location Western Ghats, India. Methods We fit occupancy models that simultaneously account for false positives and negatives to data collected from a large-scale key informant interview survey for 30 species of large vertebrates. We tested their performance against standard occupancy models that account only for false negatives. Results Standard occupancy models that correct only for false negatives tended to overestimate species occupancy due to false-positive errors. Occupancy models that simultaneously accounted for false positives and negatives had greater support [lower Akaike's information criterion (AIC)] and, consistent with predictions, generated systematically lower occupancy estimates than standard models. Furthermore, accounting for false positives improved the accuracy of occupancy estimates despite the added complexity to the statistical estimator. Main conclusions Integrating large-scale public surveys with occupancy modelling approaches is a powerful tool for informing conservation and management. However, in many if not most cases, it will be important to explicitly account for false positives to ensure the reliability of occupancy estimates obtained from public survey datasets such as key informant interviews, volunteer surveys, citizen science programmes, historical archives and acoustic surveys.

Improving species occupancy estimation when sampling violates the closure assumption

Abstract: Site occupancy models that account for imperfect detection of species are increasingly utilized in ecological research and wildlife monitoring. Occupancy models require replicate surveys to estimate detection probability over a time period where the occupancy status at sampled sites is assumed closed. Unlike mark–recapture models, few studies have examined how violations of closure can bias occupancy estimates. Our study design allowed us to differentiate among two processes that violate the closure assumption during a sampling season: 1) repeated destructive sampling events that result in either short- or long-term site avoidance by the target species and 2) sampling occurring over a time period during which non-random movements of the target species result in variable occupancy status. We used dynamic occupancy models to quantify the potential bias in occupancy estimation associated with these processes for a terrestrial salamander system. Our results provide strong evidence of a systematic decrease in salamander occupancy within a field season. Chronic disturbance due to repeated searches of natural cover objects accelerated natural declines in species occurrence on the forest surface as summer progressed. We also observed a strong but temporary disturbance effect on salamander detection probability associated with repeated sampling within a 24-h. period. We generalized our findings by conducting a simulation to evaluate how violations of closure can bias occupancy estimates when local extinction occurs within a sampling season. Our simulation study revealed general sensitivity of estimates from single-season occupancy models to violations of closure, with the strength and direction of bias varying between scenarios. Bias was minimal when extinction proba bility or the number of sample occasions was relatively low. Our research highlights the importance of addressing closure in occupancy studies and we provide multiple solutions, using both design- and model-based frameworks, for minimizing bias associated with non-random changes in occupancy and repeated sampling disturbances.

Predicting spatial occurrence of beetles and pseudoscorpions in hollow oaks in southeastern Sweden

Abstract: We modelled presence/absence per tree of beetles and pseudoscorpions living in tree hollows in relation to trunk circumference, habitat openness, and connectivity (= density of hollow oaks in the surrounding area), using data from 281 oaks. The presence/absence models were then used to predict species’ occurrences in a county (11,600 km2) in southeastern Sweden. For eight of the nine species, the most parsimonious occupancy model included a positive relationship with connectivity and at least one tree characteristic. Occupancy underestimates from occurrence records—the ratio of the area of occupancy based on our predictive model to the area of occupancy based on occurrence records—varied between 3 and 83 among species when using occurrence records up to 1993, with significantly larger underestimates for smaller beetle species. Today (after extensive surveys), underestimation has decreased to 1.3–25, confirming that calculations solely based on species occurrence records greatly underestimate the area of occupancy. We suggest this should be taken into account to a greater extent and in a clearer way than today when constructing red lists. The radius of the connectivity measure that generated the best fit varied between 135 and 2,857 m among species, with longer distances for more threatened species. Consequently, preservation of the most threatened species (Elater ferrugineus and Tenebrio opacus) requires conservation efforts at larger spatial scales than required to protect Osmoderma eremita, which frequently has been used as an indicator and umbrella species.

Traveling environment recognition device and method

Abstract: A traveling environment recognition device capable of accurately recognizing a traveling environment of a vehicle. An occupancy grid map that stores an occupancy probability of each obstacle to traveling of the own vehicle for each cell of the occupancy grid map is generated, and the occupancy probability for each cell is updated according to Bayesian inference. More specifically, for each cell of the occupancy grid map, the occupancy probability calculated from information from a radar device, the occupancy probability calculated from information from a communication device, and the occupancy probability calculated from information from a storage device that stores map data are blended to provide an occupancy probability of the obstacles to traveling of the own vehicle, which leads to more accurate traveling environment recognition.