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Conservation Genetic Assessment of the Island Night Lizard, Xantusia riversiana, Under Contemporary and Future Environmental Conditions

  • Author(s): Rice, Stephen Edward
  • Advisor(s): Clark, Rulon
  • Anderson, Kurt
  • et al.
Creative Commons Attribution 4.0 International Public License
Abstract

The island night lizard, Xantusia riversiana, is an endemic reptile to three California Channel Islands that was recently delisted from the Endangered Species Act. Several long-term ecological studies have characterized the species throughout its range, yet there are aspects of the ecology which remain unresolved including sensitivity to climatic change. I collected 917 lizards from the full range of the subspecies X. r. reticulata on Santa Barbara Island and San Clemente Island and genotyped all individuals at 23 microsatellite loci. I used these genetic data to determine contemporary patterns in genetic structure and landscape-level correlates with genetic divergence on each island. I found significant population structure on each island with collection sites displaying effects of fragmentation from crystalline ice plant, coastal cholla, unpaved roadways, and canyons. I used genetic and capture data to identify average parent-offspring differences of 14 m on Santa Barbara Island and 41 m on San Clemente Island. A permutation based logistic regression revealed that related individuals >0.8 years old were more likely to be captured together on both islands, suggesting the presence of cryptic sociality. Spatial autocorrelation analyses of inter-individual genetic distances revealed different scales of spatial independence on each island (102 - 169 m on SBI and 955 - 1,424 m on SCI). These results suggest scale-dependent effects of each island below which individuals are more genetically related than expected by chance and may indicate a patch size for familial territory or ranges. I leveraged capture data and historical climate data to construct species distribution models (SDMs) focused on Santa Barbara and San Clemente Islands and projected to the year 2100 under climate change. These models predicted >93% loss in suitable habitat by 2038. I used the SDM for Santa Barbara Island and the results of genetic and spatial analyses to parameterize stochastic demogenetic simulations to determine the sensitivity of island night lizards to climate change using a coupled niche-population model framework. These simulations demonstrate X. riversiana is highly vulnerable to climate change with expected minimum abundances of 0% - 1% of contemporary population size. Conservation implications and management suggestions are discussed throughout each chapter.

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