Consequences of cattle introduction in a shrubsteppe ecosystem: indirect effects on desert horned lizards (Phrynosoma platyrhinos)

Abstract

Abstract Livestock grazing is one of the most common forms of land use in the western United States, yet scientists struggle to accurately predict grazing impacts. This study examined the initial response of desert horned lizards (Phrynosoma platyrhinos) to cattle introduction at a site in northwestern Utah. We sampled 21 grazed and 7 ungrazed study plots before grazing (2001), after grazing (2002), and 1 year after the cessation of grazing (2003). We were specifically interested in whether grazing influenced lizards through biotic or abiotic pathways. Lizard response (based on scat counts) to the initial impact of grazing (<6 months after cattle introduction) suggests that lizards abandoned areas protected from grazing (i.e., ungrazed exclosures) presumably in favor of grazed areas. Avoidance of ungrazed plots by lizards coincided with a decline in shrub and grass cover on grazed plots and with no significant change in relative abundance or richness of prey (ants) on grazed plots. In 2003, one year after...