Integrating occupancy models and structural equation models to understand species occurrence.

Area of Science:

• Ecology
• Conservation Biology
• Environmental Science

Background:

• Species occurrence is fundamental to ecology, but imperfect detection in surveys complicates analysis.
• Traditional occupancy models assume covariate independence, limiting the study of indirect effects.
• Complex ecological interactions require advanced modeling to understand species distribution drivers.

Purpose of the Study:

• To integrate structural equation modeling with occupancy models for analyzing complex species occurrence drivers.
• To account for imperfect detection while evaluating direct and indirect effects on pond-breeding amphibians.
• To identify key factors influencing the occurrence of native amphibians, including threatened species.

Main Methods:

• Combined structural equation modeling (SEM) and occupancy modeling.
• Accounted for imperfect detection in field survey data.
• Evaluated direct and indirect effects of cattle grazing, water chemistry, vegetation, nonnative fishes, and pond permanence.

Main Results:

• Nonnative fishes had a strong negative effect on the occurrence of four of five native amphibians, including threatened species.
• Cattle grazing significantly impacted pond vegetation and water chemistry but had smaller overall effects on amphibian occurrence.
• The integrated SEM-occupancy approach revealed complex ecological relationships influencing species distributions.

Conclusions:

• Nonnative fish are a primary driver of amphibian declines in the studied system.
• Integrated modeling approaches provide mechanistic insights into species occurrence and distribution.
• Findings can inform targeted conservation strategies for amphibians and other wildlife.