Ecology and Breeding Phenology of Larval Hyla Andersonii: The Disadvantages of Breeding Late

Abstract

We exploited natural variation in the breeding phenology of Hyla andersonii, the Pine Barrens Treefrog, to test whether offspring hatching at different times during the breeding season differed in growth and survival. We studied the growth and survival of two successive cohorts of Hyla tadpoles in 12 artificial ponds, where we also manipulated abundances of two kinds of organisms that might interact seasonally with Hyla: aquatic insects and Bufo tadpoles. We also measured whether the abundance of periphyton changed seasonally in response to manipulations of aquatic insects and tadpoles, to described temporal patterns of resource availability that might affect tadpole growth and survival. Additions of hatchlings occurred 34 d apart, and the first cohort completed development before the addition of the second cohort. Additions of aquatic insects and Bufo woodhousii tadpoles, separately or together, did not significantly affect survival in either cohort. Although the initial larval density of the fish cohort was 1.5 times that of the second, the first cohort survived better, grew and developed more rapidly, and metamorphosed at larger size that the second cohort. Competition from Bufo tadpoles and insects, as inferred from reduced growth rates relative to controls without these interspecific competitors, was more pronounced in the first cohort than in the second, and coincided with reduced standing crops of periphyton, and important food for tadpoles. Although breeding late in the season reduced the growth and survival of offspring, potential reductions in the fitness of late—breeding adults are problematic because of uncertainties about the number of breeding efforts made by each female each year. Breeding late would be disadvantageous if different subpopulations breed only early or only late in the season, and if the patterns seen in our study hold for natural ponds. However, if late breeding efforts represent additional clutches deposited by adults that have already reproduced earlier that year, production of additional offspring later in the season could increase fitness.