Thesis Title

The Effect Of Spatial Subsidies On The Diet, Density, And Species Richness Of Insular Lizards In The Gulf Of California

Date of Graduation

Summer 2002


Master of Science in Biology



Committee Chair

Alexander Wait

Subject Categories



I used lizards on islands in the Gulf of California to evaluate the effects of materials moving from onto islands. Materials are transported onto the islands by both tidal action and seabirds. I used the stable isotopes of carbon (¹³C/¹²C) and nitrogen (¹⁵N/¹⁴N) to analyze the diets of Uta stansburiana on islands near Bahia de los Angeles to determine to what degree these lizards indirectly consume marine materials. I also evaluated arthropodivorous lizard density in areas with and without access to marine materials on these same islands. Finally, I used patterns of lizard species richness on islands throughout the Gulf to examine the subsidized island biogeography hypothesis (SIB), which attempts to explain species richness patterns on small, subsidized islands. I also evaluate the small island effect, which suggest species richness patterns vary independent of island area for small islands. Stable isotope data indicated U. stansburiana are indirectly consuming marine materials. Density estimates revealed a positive relationship between the availability of subsidized arthropod prey and lizard density. Species richness patterns were not obviously related to the availability of marine subsidies on small islands; however, it is possible that the small island effect acts in concert with the concepts contained in the SIB hypothesis, such that no pattern could be detected This study increases the current knowledge on the impact of cross-ecosystem energy glow on organisms.


© Russel Barrett