RepRoductive consequences of a changing pRey base in island WateRsnakes (Reptilia: colubRidae)

island populations of the lake erie watersnake (Nerodia sipedon insularum) have experienced a dramatic environmental change in the form of a new abundant prey species, the round goby (Neogobius melanostomus). effects of this biotic change on watersnake reproductive characteristics were tested by comparing offspring size and the relationship between female size and offspring number before and after the round goby invasion. offspring number, but not offspring size, increased as a consequence of watersnake diet change. in addition, female size explained a greater proportion of the variation in offspring number following the round goby invasion (60% vs. 25%). the combined effects of increased female size and offspring number are projected to result in an increase in watersnake fecundity exceeding 25% and may be stimulating watersnake population growth since the round goby invasion. the rapidity of watersnake diet change and consequent change in fecundity is consistent with the maximization hypothesis of life history theory and suggests that watersnake life history may have been more strongly limited by resource availability prior to the round goby invasion. KeywoRds. diet change, invasive species, lake erie watersnake, Nerodia sipedon, reproductive allometry, round goby. (N. s. sipedon). this difference in color pattern is the result of a dynamic balance between natural selection and gene flow (king and lawson, 1995, 1997; Ray and king, 2006). visual predators impose selection favoring unpatterned snakes along the exposed limestone and dolomite shorelines of islands. in contrast, regularly patterned morphs are favored in more densely vegetated mainland habitats. however, the islands are incompletely isolated and gene flow between the mainland and the islands is responsible for the persistence of regularly patterned morphs in island populations (king and lawson, 1995). lake erie watersnakes are listed as threatened in the u.s. and endangered in canada, ontario, and ohio (fazio and szymanski, 1999). the rational for protection includes restricted geographic distribution (the island region occupies an area < 40 km in diameter and includes just 105 km of shoreline habitat) and a history of population decline. Recovery actions include long-term monitoring and research, habitat protection and management, and public outreach aimed at reducing human-caused mortality (united states fish and Wildlife service, 2003; king et al., 2006b). the north american great lakes have been impacted by a large number of invasive aquatic species (stewart et al., 1998; Ricciardi and Macissac, 2000; Ricciardi, 2001). one recent invader is the round goby, Neogobius melanostomus (Marsden and Jude, 1995; Jude, 1997; corkum et al., 2004). this fish was intRoduction island biotas can be especially sensitive to environmental change. this sensitivity arises from the fact that island populations are typically smaller and island communities are often simpler in structure than are mainland populations and communities. as a consequence, island biotas are particularly vulnerable to such threats as overexploitation; introduced predators, competitors, and pathogens; habitat loss and degradation; and climate change. because islands exhibit high levels of endemism, they are often a priority for conservation. and because they are physically bounded, islands provide useful natural laboratories for studying the mechanisms by which environmental change affects populations (e.g., aubret et al., 2004). the lake erie watersnake, Nerodia sipedon in‐ sularum (serpentes, colubridae, natricinae), is an endemic subspecies restricted to the island region of lake erie (conant and clay, 1937), the most southern of the north american great lakes. the island region straddles the u.s. – canadian border and includes about 20 islands that range in size from < 1 to > 4,000 ha and are < 1 to 22 km from the mainland (king et al., 2006b: fig. 1). lake erie watersnakes are highly variable in color pattern and island populations include high frequencies of unpatterned and reducedpattern morphs absent from mainland populations of regularly patterned (banded) northern watersnakes South American Journal of Herpetology, 3(2), 2008, 155-161 © 2008 brazilian society of herpetology