Foraging Mode and Reproductive Seasonality in Tropical Lizards

-The hypothesis that in tropical habitats sit-and-wait lizards should be more affected by seasonal fluctuations in food availability than active foraging lizards (resulting in seasonal reproduction in the former and continuous reproduction in the latter) was investigated using 13 lizard species from six localities at the Brazilian Cerrados and Amazonian Savannas. Using fat body mass as an indicator of food availability, we predicted that active foragers should exhibit larger values of fat body mass than sit-and-wait foragers during the dry season. Contrary to our expectations, sit-and-wait lizards displayed larger fat bodies than active foraging lizards, thus being apparently less affected by dry season reductions in arthropod abundance. We postulated that higher accumulation of fat in sit-and-wait lizards during the dry season results from a higher production efficiency than active foraging lizards, as a consequence of lower maintenance costs, and that reproductive seasonality is not constrained by food limitation. The reproductive activities of a large number this reproductive seasonality: (1) the deterioraof tropical lizard species are reduced or intertion of egg deposition sites during the dry searupted during the dry season (Fitch, 1970, 1982). son; and (2) the decline of food availability for Two main hypotheses have been advanced for adults and/or juveniles during the dry season. blage of the Pantan l at Pocone, w stern BraVITr. 1980. Repteis da Caatinga. Acad. Bras. de l: Faunal composition and ecology summary. Cienc. , Rio de Janeiro. d. Neotropical. Fauna and Environ. 28:157-168. VILLALOBOS-DOMINGUES C. , AND J. VILLALOBOS. 1946. 490 This content downloaded from 157.55. 39.55 on Tue, 23 Aug 2016 05:00:58 UTC All use subject to http://about.jstor. org/terms FORAGING MODE AND REPRODUCTIVE SEASONALITY There is evidence that eggs of Anolis laid in the dry season are subject to desiccation (Andrews and Sexton, 1981) and that artificial watering during the dry season can enhance egg survival (Andrews and Wright, 1994; see also Overall, 1994). However, data are lacking for the vast majority of tropical lizard species. Evidence for the second hypothesis comes from studies demonstrating that food availability influences lizard reproductive output (Dunham, 1981; Andrews, 1982; Worthington, 1982; Anderson, 1994) and that, in some tropical habitats, seasonal precipitation results in cycles of arthropod abundance (Janzen and Schoener, 1968; Stamps and Tanaka, 1981; Levings and Windsor, 1982; Smythe, 1982). Arthropod abundance can provide, however, only indirect evidence of food availability, because a cause-andeffect relationship between arthropod abundance and lizard reproduction has not been established. In other words, fluctuations in arthropod abundance may have no significant effects on food availability unless a critical level of abundance is reached, and that critical level has not been determined for any lizard species. Some authors have attempted to address this problem by using stomach content mass or volume as an indicator of food availability (e.g., Lee et al., 1989). This approach is not without problems, given that to obtain the same quantity of food two individuals might spend very different amounts of time and energy, in response to different levels of food availability. Others have used fat body mass as an indicator of food availability (see Derickson, 1976), because, among the body lipid reserves, lipids of the fat bodies are the most labile (Derickson, 1974; Smyth, 1974) and variations in food availability are readily reflected in fat body lipid levels (Licht, 1974). Nonetheless, many studies show that fat bodies increase in mass during the dry season, indicating no food shortage during that period (e.g., Sexton et al., 1971; Colli, 1991; Rocha, 1992). A single explanation for seasonal reproduction, comprehensive enough to resolve a large set of organisms such as "tropical lizards," may simply not exist, considering the many sources of variation that may act simultaneously, such as design constraints, proximate environmental factors, and ecotypic adaptations (Ballinger, 1983). In this respect, it is more productive to isolate a single variable in order to understand better the effects of that variable. Such an attempt is seen in Vitt's (1990) study on the effects of foraging mode upon reproductive cycles in tropical lizards. Based on the reproductive patterns of a lizard assemblage from the Caatinga, Vitt (1990) concluded that active foraging species should have prolonged reproductive seaFIG. 1. Vegetation map of Brazil indicating the study sites: (A) Boa Vista, (B) Macapa, (C) Santar6m, (D) Carajas, (E) Humaita, (F) Minacu. Modified after Mapa de Vegetagao do Brasil, Fundacao Instituto Brasil iro de Geografia e Estatistica-IBGE, 1993. sons whereas sit-and-wait species should exhibit seasonal reproduction because active foraging species are less affected by seasonal variations in food availability than sit-and-wait species. Herein, w test the mechanism by which the two foraging modes differ with respect to reproductive seasonality, i.e., the differential impacts of season l variations in food availability. We used fat body mass as an indicator of food availability and examined several lizard species from two strongl seasonal South American biomes: Amazonian Savanna and Cerrado. MATERIALS AND METHODS We collected lizards at six localities in the seasonal Cerrado and Amazonian Savanna biomes (Fig. 1). The Cerrado is subject to the seasonal Aw climate in Kbppen classification (Eidt, 1968). Precipitation is usually 1500-2000 mm per year and is highly predictable, occurring almost entirely from October to April (Nimer, 1977). Annual temperatures average 20-22 C and there is a pronounced drop in minimum and maximum daily temperatures during the dry season (Nimer, 1977). During the dry season, some trees may lose part of their leaves, but there is no marked drop in vegetation cover as observed in deciduous or semi-deciduous tropical dry forests. Lizards were collected by shooting or noosing at Minaqu, Goias State, from 12 to 30 November 1992, during the rainy season (Fig. 2). Amazonian Savanna occurs as scattered patches throughout Amazonia. Most of these ar491 This content downloaded from 157.55. 39.55 on Tue, 23 Aug 2016 05:00:58 UTC All use subject to http://about.jstor. org/terms 492 G. R. COLLI ET AL.