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Knowledge about the distributions of species and the variables influencing their occurrence is important for their management and conservation, but factors affecting occurrence can vary across the range of a species. Northwestern pond turtles (Actinemys marmorata) are widespread generalist turtles, but are nonetheless of conservation concern throughout their range. To better understand the distribution of northwestern pond turtles and introduced American bullfrogs (Lithobates catesbeianus), we surveyed streams on private timberlands of the interior foothills of northern California using visual encounter surveys and collecting samples of environmental DNA. We found that northwestern pond turtle occurrence was negatively related to elevation in our sampling frame. Detection probabilities with environmental DNA were approximately twice those of visual encounter surveys, but both methods were effective for detecting turtles in streams. American bullfrogs were detected in a single sample at each of 2 sites (one by environmental DNA, one by visual encounter surveys). Management for northwestern pond turtles in forest streams within our sample area will likely have the largest effect at lower elevation sites where turtles are most likely to occur. [ABSTRACT FROM AUTHOR]

Species distributions are governed by processes occurring at multiple spatial scales. For species with complex life cycles, the needs of all life stages must be met within the dispersal limitations of the species. Multi‐scale processes can be particularly important for these species, where small‐scale patterns in specific habitat components can affect the distribution of one life stage, whereas large‐scale patterns in land cover might better explain the distribution of other life stages. Using a conditional multi‐scale model, we evaluated which aspects of the landscape and local environment are most strongly related to occupancy patterns of western spadefoots (Spea hammondii). In northern and central California, the proportion of grassland land cover within 2 km of a site was positively related to the occurrence of the northern clade of the western spadefoot. At the pond scale, we found that western spadefoots were more likely to breed in pools with lower pH. Our results indicate that protecting remaining grasslands for adult spadefoots and ensuring multiple pools with diverse characteristics and hydroperiods so at least some pools result in successful breeding will likely be necessary to conserve western spadefoots, especially with a changing climate. Considering the processes that affect species distributions at multiple life stages and spatial scales is an essential component of effective conservation. [ABSTRACT FROM AUTHOR]

Occupancy methods propelled the quantitative study of species distributions forward by separating the observation process, or the imperfect detectability of species, from the ecological processes of interest governing species distributions. Occupancy studies come at a cost, however: the collection of additional data to account for nondetections at sites where the species is present. The most common occupancy designs (repeated‐measures designs) require repeat visits to sites or the use of multiple observers or detection methods. Time‐to‐detection methods have been identified as a potentially efficient alternative, requiring only one visit to each site by a single observer. A comparison of time‐to‐detection methods to repeated‐measures designs for visual encounter surveys would allow researchers to evaluate whether time‐to‐detection methods might be appropriate for their study system and can inform optimal survey design. We collected time‐to‐detection data during two different repeated‐measures design occupancy surveys for four amphibians and compared the performance of time‐to‐detection methods to the other designs using the location (potential bias) and precision of posterior distributions for occurrence parameters. We further used results of time‐to‐detection surveys to optimize survey design. Time‐to‐detection methods performed best for species that are widespread and have high detection probabilities and rates, but performed less well for cryptic species with lower probability of occurrence or whose detection was strongly affected by survey conditions. In all cases, single surveys were most efficient in terms of person‐hours expended, but under some conditions the survey duration required to achieve high detection probabilities would be prohibitively long for a single survey. Regardless of occupancy survey design, time‐to‐detection methods provide important information that can be used to optimize surveys, allowing researchers and resource managers to efficiently achieve monitoring and conservation goals. Collecting time‐to‐detection data while conducting repeated‐measures occupancy surveys requires only small modifications to field methods but could have large benefits in terms of time spent surveying in the long term. [ABSTRACT FROM AUTHOR]

Effective species management requires knowledge of species distributions, but surveys for cryptic species near the boundaries of their geographical ranges can be difficult. We used environmental DNA (eDNA) and occupancy modeling to examine the distribution of Northern Redlegged Frogs (R am aurora) and federally threatened California Red-legged Frogs (R am draytonii) in a sample of 60 forested stream sites near where their ranges meet in southern Mendocino County, California, USA. For both species, the probability of occurrence (ψ) in forest streams in our study area was very low: California Red-legged Frog ψ( was <0.01 (95% credible interval = <0.01-0.05), and Northern Red-legged Frog ψ was 0.07 (0.02-0.15). DNA from both species was found at 1 pond site, suggesting either co-occurrence or introgression. Our results suggest that abundance, stream use, or both are very low for red-legged frogs in forested streams in southern Mendocino County. [ABSTRACT FROM AUTHOR]