Data from: Inter- and intrapopulation resource use variation of marine subsidized western fence lizards

Marine resource subsidies can alter consumer dynamics of recipient
populations in coastal systems. The response to these subsidies by
generalist consumers is often not uniform, resulting in inter- and
intrapopulation diet variation and niche diversification that may be
intensified across heterogeneous landscapes. We sampled western fence
lizards, Sceloporus occidentalis, from Puget Sound beaches and from
coastal and inland forest habitats, as well as the lizards’ marine and
terrestrial prey items to quantify marine and terrestrial resource use
with stable isotope analysis (SIA) and mixing models. Isotopic results
reveal beach lizards had higher average δ13C and δ15N values compared to
coastal and inland forest lizards, exhibiting a strong mixing line between
marine and terrestrial prey items. Across five beach sites, lizard
populations received 20 to 51% of their diet from marine resources, on
average, with individual lizards ranging between 7% and 86% marine diet.
The hillslope of the transition zone between marine and terrestrial
environments at beach sites was positively associated with marine-based
diets, as beach sites with the steepest slopes had the highest percent
marine diets. Additionally, within-beach variation in transition zone
slope was positively correlated with the isotopic niche space of beach
lizard populations. Together, these results demonstrate that the
physiography of transitional landscapes can mediate resource flow between
environments, and variable habitat topography promotes niche
diversification within a lizard population. Marine resource subsidization
of Puget Sound beach S. occidentalis populations may facilitate occupation
of the northwesternmost edge of the species range.  
Human impacts to the physiography of Puget Sound beaches, such as
shoreline armoring, may influence the quantity of driftwood habitat
available to support the unique ecology of beach-dwelling S. occidentalis.
This highlights the importance of shoreline restoration, and conservation
of intact beach habitat.