The influence of land cover and within-pool characteristics on larval, froglet, and adult wood frogs along a rural to suburban gradient

Abstract

Urbanization is known to extirpate many species, but far less is known about how suburbanization may affect amphibian populations. We studied wood frogs (Lithobates sylvaticus) to test the effects of site characteristics (within-pool conditions and land cover indicative of suburbanization within 1000 m) and larval morphology on newly emerged froglets and post-breeding males across a suburbanization gradient in 15 pools in greater Bangor, Maine, USA. We raised field-captured larvae in microcosms and examined froglet morphology and locomotor performance at emergence and one month post-emergence. Larval mass was positively correlated with 50% of froglet responses (survival, size, and locomotor performance) but was negatively associated with adult size. Among site characteristics, egg density had the most salient influence with negative effects on larval survival and morphology as well as on 11 of 14 froglet responses. Vegetation, hydrology, and suburban-associated cover near pools also influenced froglet performance, and hydrology and suburban-associated cover was associated with larger and smaller adult morphology. However the influence of suburban-associated cover on froglet performance and adult morphology was small compared to that of within-pool characteristics. Specifically, our findings support the idea that within-pool conditions experienced by larvae can influence terrestrial stages with potentially life-long consequences. Nevertheless, in suburban landscapes where there is evidence of population declines, it is likely that suburbanization has the greatest impact on populations via direct effects on terrestrial stages. We encourage planners to maintain high-quality habitat for aquatic and terrestrial stage wood frogs in suburbanizing landscapes to avoid extirpation.