Monitoring the Rare Island Night Lizard on San Nicolas Island
The Island Night Lizard (Xantusia riversiana) was removed from the Federal list of Threatened species in May 2014. This rare and unique species represents an ancient lineage whose members are now sparsely distributed across parts of the Southwest North America, south through Mexico to the New World Tropics.
The information on population size and habitat helps to inform and guide conservation and management efforts by the U.S. Navy on San Nicolas Island over the coming years.
Background & Importance
The Island Night Lizard has a very small world range, occurring only on three of the southern California Channel Islands—San Clemente, San Nicolas, and Santa Barbara. Suitable habitat for island night lizards is extensive on San Clemente Island, and the species is quite abundant there. However, habitat is much more limited and fragmented on San Nicolas Island and small Santa Barbara Island.
The U.S. Fish and Wildlife Service requires a post-delisting program for "monitoring the overall health of the island night lizard..." to assure the continued long-term viability of the species in its restricted distribution.
This project fulfills that requirement for the Night Lizard on San Nicolas Island.
Positive results of research studies on San Clemente, Santa Barbara, and San Nicolas Islands led the U.S. Fish and Wildlife Service to formally remove the island night lizard from the U.S. Endangered Species list in 2014.
The monitoring program for the Island Night Lizard described here will address remaining concerns about maintaining and improving the species’ status on San Nicolas Island, tracking trends in the population size and distribution of the lizards, and trends in their native habitat.
Additional, accompanying work will use innovative techniques to evaluate the effective population size of island night lizards on San Nicolas Island, assess the degree of genetic connectivity among isolated populations, and prepare a GIS-based distribution and habitat map for the species on the island.
The combination of methods will provide the best understanding of the species’ current status, will provide valuable information for managing the species and its habitat, and will demonstrate a proactive approach on the part of the Navy to understanding the status of the species and its requirements.
This approach is the best way to aid the post-delisting process, which in turn will assist the Navy in meeting environmental requirements for their operations on San Nicolas Island and the Pacific Missile Test Range.
Population Monitoring
Monitoring fieldwork is conducted in late spring (April-May), corresponding to the period of high activity of adult lizards (based on results of previous studies), and in early fall, when young lizards are present. Lizards are safely captured using artificial cover boards, which are deployed in areas throughout the range of the species on the island.
Lizards are weighed, measured, and examined for general health at the capture location. Artificial cover sampling sites are present in all major lizard habitats on the island. Comparison of new capture information allows assessment of changes in relative abundance, size and age structure and associated information on population condition, and growth rate and longevity of the species.
We are also conducting genetic analyses using mitochondrial DNA based procedures, augmented by nuclear DNA techniques. The genetic analyses address both the degree of genetic differentiation among and within subpopulations, as well as evaluating gene flow among sites and possible loss of genetic diversity.
Importantly, genetic patterns can provide information on whether populations have been declining, expanding, or remaining stable, and analysis of similarity among populations can be used to analyze gene flow and connectivity among populations, which are important to the long-term health of the species. In addition, genetic variability is compared to estimated subpopulation sizes, to evaluate the relationship of population size and genetic diversity.
The Island Night Lizard (Xantusia riversiana) was removed from the Federal list of Threatened species in May 2014. This rare and unique species represents an ancient lineage whose members are now sparsely distributed across parts of the Southwest North America, south through Mexico to the New World Tropics.
The information on population size and habitat helps to inform and guide conservation and management efforts by the U.S. Navy on San Nicolas Island over the coming years.
Background & Importance
The Island Night Lizard has a very small world range, occurring only on three of the southern California Channel Islands—San Clemente, San Nicolas, and Santa Barbara. Suitable habitat for island night lizards is extensive on San Clemente Island, and the species is quite abundant there. However, habitat is much more limited and fragmented on San Nicolas Island and small Santa Barbara Island.
The U.S. Fish and Wildlife Service requires a post-delisting program for "monitoring the overall health of the island night lizard..." to assure the continued long-term viability of the species in its restricted distribution.
This project fulfills that requirement for the Night Lizard on San Nicolas Island.
Positive results of research studies on San Clemente, Santa Barbara, and San Nicolas Islands led the U.S. Fish and Wildlife Service to formally remove the island night lizard from the U.S. Endangered Species list in 2014.
The monitoring program for the Island Night Lizard described here will address remaining concerns about maintaining and improving the species’ status on San Nicolas Island, tracking trends in the population size and distribution of the lizards, and trends in their native habitat.
Additional, accompanying work will use innovative techniques to evaluate the effective population size of island night lizards on San Nicolas Island, assess the degree of genetic connectivity among isolated populations, and prepare a GIS-based distribution and habitat map for the species on the island.
The combination of methods will provide the best understanding of the species’ current status, will provide valuable information for managing the species and its habitat, and will demonstrate a proactive approach on the part of the Navy to understanding the status of the species and its requirements.
This approach is the best way to aid the post-delisting process, which in turn will assist the Navy in meeting environmental requirements for their operations on San Nicolas Island and the Pacific Missile Test Range.
Population Monitoring
Monitoring fieldwork is conducted in late spring (April-May), corresponding to the period of high activity of adult lizards (based on results of previous studies), and in early fall, when young lizards are present. Lizards are safely captured using artificial cover boards, which are deployed in areas throughout the range of the species on the island.
Lizards are weighed, measured, and examined for general health at the capture location. Artificial cover sampling sites are present in all major lizard habitats on the island. Comparison of new capture information allows assessment of changes in relative abundance, size and age structure and associated information on population condition, and growth rate and longevity of the species.
We are also conducting genetic analyses using mitochondrial DNA based procedures, augmented by nuclear DNA techniques. The genetic analyses address both the degree of genetic differentiation among and within subpopulations, as well as evaluating gene flow among sites and possible loss of genetic diversity.
Importantly, genetic patterns can provide information on whether populations have been declining, expanding, or remaining stable, and analysis of similarity among populations can be used to analyze gene flow and connectivity among populations, which are important to the long-term health of the species. In addition, genetic variability is compared to estimated subpopulation sizes, to evaluate the relationship of population size and genetic diversity.