Complex riparian habitats predict reptile and amphibian diversity

Abstract

Altering stream flows and groundwater have modified how streams are connected to riparian floodplain vegetation. This disconnection has led to the proliferation of non-native and invasive woody plant species and altered habitat complexity. Squamate vertebrates such as lizards and snakes, and amphibians such as frogs and toads, are important food web links in riparian ecosystems of the Sonoran Desert. We explored the relationship between habitat heterogeneity and species diversity in aridland riparian ecosystems in the United States (US). Specifically, we measured riparian vegetation composition, cover, and habitat structure from the Middle Rio Grande in New Mexico, the San Pedro and Gila Rivers in Arizona, and the Virgin River in Nevada. We used pitfall arrays deployed in these riparian forests to document reptile and amphibian communities. We developed a habitat index by weighing variables based on their contributions to variation explained in the dataset and characterized the structural attributes and heterogeneity of the riparian vegetation. We validated the habitat index by relating it to abundance and richness of reptile and amphibian species and found a positive relationship. Native riparian trees and stands mixed with native and non-native trees supported greater diversity and abundance of lizard fauna compared to monotypic stands of non-native trees. We integrated elements of vegetation structure and composition with ectothermic wildlife to show how riparian areas provide complex habitat for species. Our results suggest that riparian woodlands provide higher quality habitat for riparian reptile and amphibians compared to non-native stands.