Monitoring aquatic amphibians and invasive species in the Mediterranean Coast Network, 2014 project report: Santa Monica Mountains National Recreation Area

Delaney, Kathleen; Riley, Seth

Santa Monica Mountains National Recreation Area (SAMO) is adjacent to the second largest city in the United States. Ecosystem changes that result from urban development include the destruction and fragmentation of breeding habitat for aquatic amphibians, degradation of air and water quality, altered stream discharge regimes, and the introduction and spread of non-native invasive species. Urbanization of as little as 8% of a watershed can have significant impacts on the distribution and abundance of native amphibians (Paul & Meyer 2001; Riley et al. 2005). A reduction in the distribution of native amphibians in the Santa Monica Mountains in association with increasing levels of urbanization and invasive species has been documented in the Santa Monica Mountains (Gamradt & Kats 1996; Goodsell & Kats 1999; Riley et al. 2005). Native aquatic amphibian species in SAMO include California newts (Taricha torosa), Pacific treefrogs (Pseudacris regilla), California treefrogs (P. cadaverina), western toads (Anaxyrus boreas), and California red-legged frogs (Rana draytonii). Red-legged frogs, formerly common in a number of streams in the region (De Lisle et al. 1987), were extirpated in the mid-20th century from all local streams but one. This species is now part of a re-introduction effort at SAMO. Non-native aquatic species within SAMO include red swamp crayfish (Procambarus clarkii) native to the southeastern United States, bullfrogs (Lithobates catesbeiana), and a number of fish species including bass (Micropterus spp.), bluegill (Lepomis macrochirus), and mosquitofish (Gambusia affinis). The Inventory and Monitoring program for aquatic amphibians in the Mediterranean Coast Network (MEDN; Delaney et al. 2011) focuses on two metrics: occupancy (MacKenzie et al. 2003) and indices of abundance. Occupancy modeling provides a statistical framework for assessing changes in species occurrence while explicitly accounting for differences in detectability (MacKenzie et al. 2003, 2006). Information from repeated observations at sample units (streams) is used to estimate detectability and adjust occupancy rates for imperfect detection (failure to observe a species that is actually present). The objectives of our long-term monitoring program are to 1) determine the status and long-term trends in abundance indices and percent area occupied by juvenile and adult aquatic amphibians in streams during the reproductive season, 2) determine the status and long-term trends in occupancy and abundance indices of non-native species, and 3) characterize the relationship between urbanization, non-native species and the occupancy and abundance indices of the focal native aquatic amphibians. This report summarizes data collected during 2014, the 15th year of monitoring stream amphibians and invasive aquatic species in SAMO. In this report, we present single-season occupancy and detectability estimates, naïve occupancy data, and abundance data.

Monitoring aquatic amphibians and invasive species in the Mediterranean Coast Network, 2014 project report: Santa Monica Mountains National Recreation Area

Series

Collections