Spatial Patterns in the Abundance of the Coastal Horned Lizard

Area of Science:

• Herpetology
• Conservation Biology
• Ecology

Background:

• Coastal horned lizards (Phrynosoma coronatum) face severe population declines in Southern California.
• The species is a candidate for listing under the Endangered Species Act, highlighting a critical need for conservation data.
• Quantitative data on habitat use, abundance, and distribution remain scarce.

Purpose of the Study:

• To investigate the key factors influencing the abundance of coastal horned lizards across Southern California.
• To analyze habitat use and distribution determinants at multiple spatial scales.
• To inform conservation strategies by identifying critical habitat elements and threats.

Main Methods:

• Established 256 pitfall trap arrays across 21 sites in four Southern California counties.
• Conducted bimonthly sampling over 2-3 years to estimate lizard distribution and abundance.
• Measured 26 local site descriptors and integrated regional data to characterize site conditions.

Main Results:

• Lizard abundance positively correlated with the presence of native ant species and chaparral vegetation, and sandy substrates.
• Abundance negatively correlated with the presence of invasive Argentine ants (Linepithema humile).
• Argentine ant abundance at a regional scale was linked to developed edges, and fine-scale habitat factors were significant.

Conclusions:

• Absence of invasive Argentine ants and presence of native ants are crucial for coastal horned lizard abundance.
• Chaparral vegetation and sandy substrates are important habitat components.
• Conservation efforts should consider fine-scale habitat features and invasive species management in fragmented landscapes.