Using Ecological Niche Models for Population and Range Estimates of a Threatened Snake Species (Crotalus oreganus) in Canada

Abstract

Modelling the distribution and abundance of species at risk is extremely important for their conservation and management. We used ecological niche models (ENMs) to predict the occurrence of western rattlesnakes (Crotalus oreganus) in British Columbia (BC), Canada. We applied this to existing population estimates to support a threshold of occurrence for management and conservation. We also identified predictors influencing rattlesnake distribution and abundance in this region. Using a Geographic Information Systems platform, we incorporated ENMs, capture–mark–recapture (CMR) and radio-telemetry results, province-wide observations, Landsat imagery and provincial databases for agricultural land use to produce quantitative, spatially explicit, population estimates across BC. Using available western rattlesnake habitat estimated at 183.9 km2 and averaging estimates calculated from densities in three study populations, we generated a mean adult population size of 9722 (±SD 3009; 0.8 relative index of occurrence [RIO] threshold). Only a small area (21.6 km2) of suitable land cover was located within protected areas, potentially protecting an estimated 1144 (±354) adults. Most suitable land cover was within 500 m of roads (170.6 km2), representing potential habitat being used by an estimated 9017 (±2791) adults. At the threshold RIO value chosen (0.8), only a very small area of farmland provided suitable land cover. Our results highlight the possibility of high mortality rates for western rattlesnakes near roads and the fact that protected areas do not provide sufficient coverage to conserve the population. Given that this species has relatively low mobility and high site fidelity to home ranges, our population estimate for BC provides a useful reference for the northern part of the species’ range. It also fulfills a need to estimate population size within political jurisdictions where conservation management decisions are made, as well as presenting a method that can be applied to other parts of the range, including the southern United States. Our study provides an important benchmark for future monitoring of western rattlesnakes in BC using a repeatable and transparent approach. Similar applications can be extrapolated and applied for other threatened species to identify and quantify population distributions and threats, further supporting conservation prioritization tools to be used to maximize the effectiveness of conservation strategies under financial constraints.

The tale of the rattle: Using rattle size to understand growth and sexual dimorphism in an insular population of rattlesnakes (Crotalus oreganus caliginis)

“…The actual population density could be much higher. This is consistent with other qualitative reports (Grismer, 2002;Klauber, 1956) and much higher than most mainland populations of other Crotalus, which are typically estimated at around 50-100 snakes/km 2 (Diller & Wallace, 2002;Kirk et al, 2021;Maida et al, 2017). However, a density of ~500 snakes/km 2 is similar to densities observed in other island populations of vipers (Almeida-Santos, 2005;Shine & Sun, 2002;Wen et al, 2021).…”

Predicting the Potential Distribution of the Szechwan Rat Snake (Euprepiophis perlacea) and Its Response to Climate Change in the Yingjing Area of the Giant Panda National Park

“…Applying the MaxEnt model has yielded notable outcomes, such as a comprehensive understanding of 39 species of New World coral snakes spanning North, Central, and South America [60]. Additionally, the model has facilitated predictions regarding the potential distribution for many snake species, accompanied by an evaluation of the conservation status of existing protected areas for the species based on potential distribution assessments [61][62][63][64][65]. Within the context of our study, it is evident that the MaxEnt models for E. perlacea consistently achieve AUC values exceeding 0.79, underscoring how our study has, for the first time, established reliable models for predicting the potential distribution of E. perlacea.…”

The past, present, and future of predator–prey interactions in a warming world: Using species distribution modeling to forecast ectotherm–endotherm niche overlap

“…We then merged tiles together using QGIS. We also included terrain ruggedness index as increased ruggedness has been shown to increase microhabitat variation and therefore areas available for snake refuge (Kirk et al., 2021). TRI was calculated from the previously downloaded elevation layer using the terrain ruggedness raster analysis function in QGIS.…”

“…Despite this, individual models of similar taxa may provide insight into the potential temporal biogeography of our study system. Studies that created ecological niche models (ENMs) of snake species suggest both increases and decreases in suitable habitat under climate change conditions and there does not seem to be a consensus among ectothermic reptiles (González-Fernández et al, 2018;Kalboussi & Achour, 2018;Kirk et al, 2021;Kurnaz, 2023;Lourenço-de-Moraes et al, 2019;Piquet et al, 2021;Saptoka et al, 2021).…”

“…Despite this, individual models of similar taxa may provide insight into the potential temporal biogeography of our study system. Studies that created ecological niche models (ENMs) of snake species suggest both increases and decreases in suitable habitat under climate change conditions and there does not seem to be a consensus among ectothermic reptiles (González‐Fernández et al., 2018; Kalboussi & Achour, 2018; Kirk et al., 2021; Kurnaz, 2023; Lourenço‐de‐Moraes et al., 2019; Piquet et al., 2021; Saptoka et al., 2021). Similarly, models of small mammal distributions suggest different responses to climate change depending on the species and modeling method (Baltensperger & Huettmann, 2015; Mathewson et al., 2017; Morueta‐Holme et al., 2010; Riddell et al., 2021).…”