Decline in small mammal species richness in coastal-central California, 1997-2013

The richness and composition of a small mammal community inhabiting semiarid California oak woodland may be changing in response to climate change, but we know little about the causes or consequence of these changes. We applied a capture-mark-recapture model to 17 years (1997-2013) of live trapping data to estimate species-specific abundances. The big-eared woodrat was the most frequently captured species in the area, contributing 58% of total captures. All small mammal populations exhibited seasonal fluctuations, whereas those of the California mouse, brush mouse, and pinyon mouse declined during the study period. We also applied a multispecies dynamic occupancy model to our small mammal detection history data to estimate species richness, occupancy (psi), detection (p), local extinction (epsilon), and colonization (gamma) probabilities, and to discern factors affecting these parameters. We found that psi decreased from 0.369 +/- 0.088 in 1997 to 0.248 +/- 0.054 in 2013; gamma was lower during the dry season (May-September) than the wet season (October-April) and was positively influenced by total seasonal rainfall (slope parameter, beta = 0.859 +/- 0.371; 95% CI = 0.132-1.587). Mean mammalian species richness decreased from 11.943 +/- 0.461 in 1997 to 7.185 +/- 0.425 in 2013. With highly variable climatic patterns expected in the future, especially increased frequency and intensity of droughts, it is important to monitor small mammal communities inhabiting threatened California oak woodlands. We used dynamic occupancy models to understand the temporal variation of community parameters such as species richness, extinction, and colonization dynamics.image