Produção Nacional
Revisado por pares
Does Foraging Activity Change with Ontogeny? An Assessment for Six Sympatric Species of Postmetamorphic Litter Anurans in Central Amazonia
2000; The Society for the Study of Amphibians and Reptiles; Volume: 34; Issue: 2 Linguagem: Inglês
10.2307/1565415
ISSN1937-2418
AutoresWilliam E. Magnusson, Albertina P. Lima,
Tópico(s)Plant and animal studies
Resumo-We studied the foraging activities of six frog species in their natural habitat, the leaf litter of tropical rain forest in central Amazonia. To describe intraspecific ontogenetic change in general activity during foraging, we used four indices of general activity (movement frequency, velocity when moving, time spent moving, and total distance moved). The association between each of the four indices and the size of frogs varied among species. The indices of foraging activity do not represent independent information. Therefore, we reduced the dimensionality using a single ordination obtained by multidimensional scaling, and investigated its relationship to frog size and type and size of prey. There was a significant relationship between the combined index of foraging activity and frog size in three of the six species. Foraging activity predicted the intraspecific change in the type and size of prey for Eleutherodactylus fenestratus, partially for Adenomera andreae, Epipedobates femoralis, and Dendrophryniscus minutus, and not for Bufo cf. typhonius and Colostethus marchesianus. al of Herpetology, Vol. 34, No. 2, pp. 192-200, 2000 i ht 20 0 Society for the Study of Amphibians and Reptiles oraging Activity Change with Ontogeny? An A essment for patric Species of Postmetamorphic Litter Anurans in There is evidence that the composition of the diet of many amphibians and reptiles depends on how widely the species forages (Huey and Pianka, 1981; Magnusson et al., 1985; Toft, 1985; Wiggins, 1992). For species of leaf-litter frogs, Toft (1981) suggested that the mechanisms that determine the differences in size and type of prey are related to foraging mode. In general, 192 This content downloaded from 207.46.13.113 on Thu, 06 Oct 2016 04:02:39 UTC All use subject to http://about.jstor.org/terms ONTOGENY OF FORAGING ACTIVITY IN SIX LITTER FROGS species that forage actively eat small prey that occur in aggregations, that are slow-moving, that are often chitinous, and often have chemical defenses (e.g., ants, termites, mites). Species that are sit-and-wait foragers eat prey of large size that are normally solitary, such as orthopterans, beetles and spiders (see Striissmann et al., 1984; Toft, 1985; Pough and Taigen, 1990). Toft used frog morphology to infer foraging mode. Changes in sizes and types of prey with growth in size of frogs are expected for morphological reasons and because of changes in the spectrum of prey types that can be swallowed. However, changes in types and sizes of prey of the species of the community of diurnal litter frogs of central Amazonia are not due to a simple passive effect of selection for larger prey with growth of frogs (Lima, 1998). There is a significant relationship between electivity for prey type and frog size in six of the seven species studied, independent of electivity for prey size (Lima and Moreira, 1993; Lima, 1998). Optimal foraging theory is based on the assumption that predators adjust their foraging behavior as the relative availability of prey types shift, such that they always maximize the energy attained during the time spent foraging (Schoener, 1971). However, Pough et al. (1989) questioned whether predators should respond to shifts in the abundance of different sorts of prey by changing their foraging habits in that manner. Pough et al. (1989) suggested that physiological specializations that underlie behavior may limit the ability of a species to adjust its foraging behavior as the abundance of prey changes. Lima and Moreira (1993) suggested that, for one species of central-Amazonian leaflitter frog, Colostethus stepheni, there exists a species-specific level of foraging activity that does not change with frog size, even though the prey available for juveniles are different from those available to adults. Here we report the results of our investigation into whether foraging activity changes with growth for postmetamorphic individuals of six species of diurnal leaf-litter anurans in a central Amazonian assemblage. We compare these results to data on Colostethus stepheni (Lima and Moreira, 1993). We also examine whether the shifts in the sizes and types of prey that occur with the growth of frogs are associated with changes in foraging activity. MATERIALS AND METHODS Study Area and Species.-The study was conducted in a 10,000 ha tropical rainforest reserve, Reserva Florestal Adolfo Ducke (Reserva Ducke), located 25 km northeast of Manaus, Amazonas, Brasil (03?08'S; 60?04'W). The study was done at two sites separated by 4 km. The first, described by Lima and Moreira (1993), lies along six trails (+7 km) in an undisturbed part of Reserva Ducke. The second, described by Lima (1998), in an area of about 2 km by 200 m wide along the margins of a stream and about 2 km by 10 m on a plateau. The community of diurnal leaf-litter frogs of Reserva Ducke is composed of seven species: Adenomera andreae and Eleutherodactylus fenestratus (Leptodactylidae); Colostethus marchesianus, Colostethus stepheni, and Epipedobates femoralis (Dendrobatidae); Bufo cf: typhonius and Dendrophryniscus minutus (Bufonidae). The juveniles of all species metamorphose at close to 6.5 mm snout-urostyle length (SUL), except for Ep. femoralis and El. fenestratus which metamorphose at more than 8.0 mm SUL. Measures of Foraging Activity.-Foraging activity has generally been indexed by five measures of activity: total time in movement, number of movements, total distance moved, velocity while moving, and frequency of prey capture a tempts. To describe the general activity while raging, we used the first four of these indices. We did not use the frequency of prey capture att mpts because recently-metamorphosed litter anur ns are very small and it was not possible to confidently register all prey-capture events. Observations of the foraging mode of the frogs were made in both study sites between February 1991 and April 1992, and from March to June 1995. Individuals were followed for periods of 30 min in different hours throughout the day so that the entire activity period was covered (Fig. 1). The frogs were watched from distances of 1-5 m using binoculars when necessary. For each minute of observation we noted the number of movements, the total distance moved, and the duration of each movement. A movement was recorded only if it resulted in displacement of the entire body approximately 5 mm. Those observations were used to create f ur indices of activity of foraging: I movement frequency/30 min, II velocity when moving in 30 min (cm/sec), II time spent moving/30 min, and IV total distance moved in 30 min. Th time in movement was recorded with digital chronometers accurate to 0.01 sec. Velocity was estimated as the total distance moved divided by the time spent moving during 30 min. At the end of the observation period, the animals were captured and killed for diet analyses. Statistical Analyses.-Statistical analyses were done with the SYSTAT (Wilkinson, 1990) and PATN (Belbin, 1992) computer programs. The original data for each individual had high variance, were not multivariate normal, and could not be transformed to conform to the assumptions of the analyses. Therefore, to test whether variation of type and size of prey are associated 193 This content downloaded from 207.46.13.113 on Thu, 06 Oct 2016 04:02:39 UTC All use subject to http://about.jstor.org/terms A. P. LIMA AND W. E. MAGNUSSON
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