Estimating the abundance or density of populations is fundamental to the conservation and management of species, and as landscapes become more fragmented, maintaining landscape connectivity has become one of the most important challenges for biodiversity conservation. Yet these two issues have never been formally integrated together in a model that simultaneously models abundance while accounting for connectivity of a landscape. We demonstrate an application of using capture-recapture to develop a model of animal density using a least-cost path model for individual encounter probability that accounts for non-Euclidean connectivity in a highly structured network. We utilized scat detection dogs (Canis lupus familiaris) as a means of collecting non-invasive genetic samples of American mink (Neovison vison) individuals and used spatial capture-recapture models (SCR) to gain inferences about mink population density and connectivity. Density of mink was not constant across the landscape, but rather increased with increasing distance from city, town, or village centers, and mink activity was associated with water. The SCR model allowed us to estimate the density and spatial distribution of individuals across a 388 km² area. The model was used to investigate patterns of space usage and to evaluate covariate effects on encounter probabilities, including differences between sexes. This study provides an application of capture-recapture models based on ecological distance, allowing us to directly estimate landscape connectivity. This approach should be widely applicable to provide simultaneous direct estimates of density, space usage, and landscape connectivity for many species.

Spatial heterogeneity in the environment induces variation in population demographic rates and dispersal patterns, which result in spatio-temporal variation in density and gene flow. Unfortunately, applying theory to learn about the role of spatial structure on populations has been hindered by the lack of mechanistic spatial models and inability to make precise observations of population structure. Spatial capture-recapture (SCR) represents an individual-based analytic framework for overcoming this fundamental obstacle that has limited the utility of ecological theory. SCR methods make explicit use of spatial encounter information on individuals in order to model density and other spatial aspects of animal population structure, and have been widely adopted in the last decade. We review the historical context and emerging developments in SCR models that enable the integration of explicit ecological hypotheses about landscape connectivity, movement, resource selection, and spatial variation in density, directly with individual encounter history data obtained by new technologies (e.g., camera trapping, non-invasive DNA sampling). We describe ways in which SCR methods stand to revolutionize the study of animal population ecology.

Riksbank. The views expressed in this paper are solely those of the author and may differ from official Bank of Canada views. No responsibility for them should be attributed to the Bank of Canada.

Wildlife tunnels are often installed under busy roads to help a variety of animals, from small frogs to bears, safely cross roads that bisect their habitats. One of the first roadway wildlife tunnel systems designed specifically for amphibian use in the USA was installed along Henry Street in Amherst, Massachusetts, in 1987 to protect spotted salamanders (Ambystoma maculatum). These salamanders cross Henry Street during their annual migration to their breeding pools. In recent years, volunteers monitoring the site suggested that salamanders were no longer using the tunnels. To evaluate this concern, we conducted salamander counts in 2016, 2017 and 2018 to quantify tunnel use. In 2016, 11% of observed salamanders used the tunnels—a substantial decrease from 68% in 1988, 1 year after tunnel installation, when the tunnels were last evaluated. Following 2016, we implemented two tunnel modifications: adding a light to the far end of tunnels (2017) and placing a ramp at tunnel entrances to reduce balking (2018). However, salamander tunnel use was not increased significantly by either the light modification or the ramp modification. Previous studies have demonstrated that salamanders prefer minimum tunnel apertures of >0.4 m, so it is likely that the 0.2 m apertures at Henry Street are too small. While many studies have evaluated amphibian tunnel use in laboratory and field settings, ours was one of the first studies to examine tunnel usage data long after initial installation. These long-term data are critical for evaluating factors necessary for maintaining wildlife tunnel effectiveness over decades.

16Culverts are often installed under busy roads to help animals ranging from small 17 frogs to bears safely cross roads that bisect their habitat. One of the first roadway culvert 18 systems designed specifically for amphibian use in the United States was installed along 19Henry Street in Amherst, Massachusetts in 1987. The purpose of these under-roadway 20 tunnels was to protect spotted salamanders (Ambystoma maculatum) during their annual 21 migration from their hibernation area to their breeding pools, which are separated by a 22 road. Anecdotal evidence from volunteers monitoring the site suggested that salamanders 23 were no longer using the tunnels. To evaluate this concern, we conducted salamander 24 counts to quantify the amount of tunnel use. In 2016, only 11% of the observed 25 salamanders used the tunnels. Subsequently, we implemented two tunnel modifications in 26 an effort to increase salamander tunnel usage above the baseline established in 2016. 27Unfortunately, neither retrofit was successful in increasing use. Previous studies have 28 demonstrated that salamanders prefer minimum tunnel apertures of >0.4 meters, so it is 29 likely that the 0.2 meter tunnel apertures used here are too small. This may create a 30 differential in light and humidity between the environments inside and outside the tunnels 31 that is recognized by the salamanders. While many studies have evaluated amphibian 32 tunnel use in lab and field settings, ours is one of the first studies to have examined tunnel 33 usage data long after initial tunnel installation. These long-term data are critical for 34 evaluating what factors are necessary for maintaining tunnels over decade-long time 35 scales. 36 37