The Effects of Predation on the Fecundity of Lava Lizards, Tropidurus Delanonis, of the Galapagos Islands, Ecuador
Bouchard, Sarah S.
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Life history traits of an organism, such as number of reproductive events per season, number and size of offspring, and time of reproductive maturity, shape that organism's reproductive strategy. Lava lizards, Tropidurus delanonis, of Gardner Bay, Espanola Island, Galapagos Archipelago, constitute four reproductively isolated populations which provide appropriate conditions for investigating variation in this phenomenon. Each population inhabits a different island of the bay. Two of these four islands are inhabited by the snake, Phylodryas biserialis, which preys upon the lizards. On islands with snakes, females have significantly shorter life spans which may select for compensatorily increased fecundity. To investigate the effects of the increased predation various characteristics associated with life history were measured. Females who had just finished laying eggs were captured and weighed immediately after laying their eggs. Eggs were then removed from the nests and the lengths, breadths, and masses were recorded. Even though female body mass did not differ between islands with snakes and islands without snakes, lizards on islands with snakes laid larger clutches (more eggs with greater total mass) than lizards on islands without snakes. Additionally, eggs laid by lizards on islands with snakes were smaller than those found on islands without snakes. Thus, these observations are consistent with the hypothesis that, through an increase in clutch size and total clutch mass, the presence of snakes is selecting for increased fecundity in lizards inhabiting those islands. Also, eggs on islands without snakes may be larger resulting in improved hatchling survival in the presence of increased intraspecific competition. These data provide insight into the complex nature of life history traits and suggest approaches which may facilitate better understanding of the evolution of reproductive strategies.