Reproductive Ecology of the Green Treefrog (Hyla Cinerea) in Northwestern Florida

Article excerpt

ABSTRACT.-

Information on life-history traits is critical to understanding population dynamics of anurans. The objective of this study was to examine aspects of the reproductive ecology of Hyla cinerea in northwestern Florida. Four breeding localities in Leon County, Florida, were sampled over three seasons (2001-2003), amplexed pairs were found as early as 12 April and as late as 12 August. Egg clutches were counted from 51 amplexed pairs and adult size was measured in 43 pairs. Average clutch size was 1214 ± 528 eggs (x ± SE, range = 359-2658). Female H. cinerea were slightly larger than males (x ± SE tibiofibula length = 24.9 ± 2.2 and 24 ± 1.7 mm, respectively). Female size was significantly positively correlated with clutch size and weakly correlated with size of the paired male. Comparison of the results of this study with previous research indicates that the reproductive ecology of H. cinerea varies across its geographic range.

INTRODUCTION

In order to understand population dynamics, information on growth, survival and reproduction of each life-history stage is critical (Duellman and Trueb, 1994; Scott, 1994). For many anurans, characteristics of the larval stage such as growth and survival have been studied extensively (Wilbur, 1997). Life-history characteristics of the adult stage, including reproductive traits, are less well-known. Many studies of reproduction of treefrogs in the southeastern United States focus on adult behaviors such as selection of breeding sites, mate selection and male advertisement calls (Gerhardt et al., 1987; Resetarits and Wilbur, 1991; Murphy and Gerhardt, 2002). However, a critical component for understanding the lifehistory of anurans is the reproductive output of females (Williamson and Bull, 1995). Clutch size in anurans tends to be positively correlated with female size in species with a similar reproductive mode (Ritke et al., 1990; Duellman and Trueb, 1994). Many pond breeding anurans produce large clutches of small eggs and have low survival rates of both eggs and larvae (Duellman and Trueb, 1994). Clutch size and breeding phenology may vary over the geographic range of a wide-ranging species which may lead to variation in population dynamics (Ritke et al, 1990; Morrison and Hero, 2003).

The green treefrog, Hyla cinerea, breeds in permanent ponds and lakes with emergent vegetation and is the only species in the genus Hyla in the southeastern United States that regularly breeds in habitats with large predatory fish (Mount, 1975; Wright and Wright, 1995). Hyla cinerea breeds throughout the spring and summer months, from April to August (Carton and Brandon, 1975; McAlpine, 1993). This species occurs across a broad geographic range over which its reproductive ecology may vary. Previous studies of reproductive ecology have been conducted on this species in Illinois, South Carolina and Georgia (Carton and Brandon, 1975; Perrill and Daniel, 1983; Gerhardt et al, 1987; McAlpine, 1993). The objectives of this study were to describe the reproductive ecology of H. cinerea in northwestern Florida by quantifying breeding season length, clutch size and male-female size relationships. The results of this study will be compared to other previously published studies from throughout the range of H. cinerea. This information will contribute to understanding the population ecology of this widespread and abundant species of treefrog.

METHODS

I sampled four localities in Léon County, Florida, over three HyIa cinerea breeding seasons (2001-2003). Three of these localities (Chapman Pond, 1 ha; Harriman Pond, 0.56 ha; and Innovation Pond, 1.4 ha) were suburban ponds surrounded by mowed grass, trees and shrubs, with relatively sparse emergent aquatic vegetation. The fourth locality, Megginnis Arm, is an 8 ha portion of Lake Jackson (1620 ha) characterized by abundant emergent and floating aquatic vegetation and thick growth of shrubs and trees around the edge. …