Marine subsidies alter the diet and abundance of insular and coastal lizard populations

We evaluated the impact of marine materials on the diet and abundance of arthropodivorous lizards inhabiting islands and the coast of the Gulf of California. Here, marine materials are brought onto land by seabirds and by tidal action, and both subsidy pathways cause arthropod abundance to increase. We evaluated Uta stansburiana (side-blotched lizard) diets in three habitats defined by having: (1) no marine subsidies available, (2) only seabird-derived subsidies, and (3) only tidal-derived subsidies. Stable isotope data indicated that lizard diets are subsidized indirectly by seabird and tidal activity. For example, in coastal areas we determined that 40% of a lizard's diet contains arthropods that have consumed algae. Such subsidies may explain why we found that lizards in coastal areas occupy a significantly higher trophic position than lizards in unsubsidized areas. We analyzed eight years of survey data on all arthropodivorous lizards to determine if diet subsidies result in increased lizard abundance. We found that lizards were more abundant in coastal areas than they were in inland habitats, and that they were more abundant on islands with seabirds than on islands without seabird populations. This study provides insight into the importance and effect of marine-derived nutrients from multiple sources on vertebrate consumers inhabiting islands and coastal areas.