Integrating niche and occupancy models to infer the distribution of an endemic fossorial snake (Atractus lasallei)

Abstract

Understanding species distribution and habitat preferences is crucial for effective conservation strategies. However, the lack of information about population responses to environmental change at different scales hinders effective conservation measures. In this study, we estimate the potential and realized distribution of Atractus lasallei, a semi-fossorial snake endemic to the northwestern region of Colombia. We modelled the potential distribution of A. lasallei based on ecological niche theory (using maxent), and habitat use was characterized while accounting for imperfect detection using a single-season occupancy model. Our results suggest that A. lasallei selects areas characterized by slopes below 10°, with high average annual precipitation (>2500mm/year) and herbaceous and shrubby vegetation. Its potential distribution encompasses the northern Central Cordillera and two smaller centers along the Western Cordillera, but its habitat is heavily fragmented within this potential distribution. When the two models are combined, the species' realized distribution sums up to 935 km2, highlighting its vulnerability. We recommend approaches that focus on variability at different spatio-temporal scales to better comprehend the variables that affect species' ranges and identify threats to vulnerable species. Prompt actions are needed to protect herbaceous and shrub vegetation in this region, highly demanded for agriculture and cattle grazing.

Fig 1. Geographical location of study area.

(A) Study Area encompassing northern Western and Central Cordilleras. (B) Presence records of A. lasallei, where light blue dots depict specimens collected during the field phase of occupancy models, red dots represent iNaturalist records, and dark blue dots indicate specimens in biological collections. (C) Transects represented as black triangles. Green-Brown color-scale represents altitude. Reprinted from [56] and OpenStreetMap under a CC BY license, with permission from [56] and ©OpenStreetMap contributors, original copyright 2020 and 2024, respectively.

Fig 2. Occupancy modeling results.

(A) Relationship between the number of cover objects and detectability. (B) Occupancy as a function of vegetation height measured in meters (m), where dashed red lines represent the 4 m vegetation height and its expected occupancy value. Both graphs constructed from the best model.

Fig 3. Potential and realized distribution models.

Comparison between (A) potential and (B) realized distribution area estimated from niche modelling and the integration of niche and occupancy models respectively. Green-Brown color-scale represents altitude. Reprinted from [56] under a CC BY license, with permission from [56], original copyright 2020.