Parrots eat nutritious foods despite toxins.

BACKGROUND: Generalist herbivores are challenged not only by the low nitrogen and high indigestibility of their plant foods, but also by physical and chemical defenses of plants. This study investigated the foods of wild parrots in the Peruvian Amazon and asked whether these foods contain dietary components that are limiting for generalist herbivores (protein, lipids, minerals) and in what quantity; whether parrots chose foods based on nutrient content; and whether parrots avoid plants that are chemically defended. METHODOLOGY/PRINCIPAL FINDINGS: We made 224 field observations of free-ranging parrots of 17 species in 8 genera foraging on 102 species of trees in an undisturbed tropical rainforest, in two dry seasons (July-August 1992-1993) and one wet season (January-February1994). We performed laboratory analyses of parts of plants eaten and not eaten by parrots and brine shrimp assays of toxicity as a proxy for vertebrates. Parrots ate seeds, fruits, flowers, leaves, bark, and insect larvae, but up to 70% of their diet comprised seeds of many species of tropical trees, in various stages of ripeness. Plant parts eaten by parrots were rich in protein, lipid, and essential minerals, as well as potentially toxic chemicals. Seeds were higher than other plant materials in protein and lipid and lower in fiber. Large macaws of three species ate foods higher in protein and lipids and lower in fiber compared to plant parts available but not eaten. Macaws ate foods that were lower in phenolic compounds than foods they avoided. Nevertheless, foods eaten by macaws contained measurable levels of toxicity. Macaws did not appear to make dietary selections based on mineral content. CONCLUSIONS/SIGNIFICANCE: Parrots represent a remarkable example of a generalist herbivore that consumes seeds destructively despite plant chemical defenses. With the ability to eat toxic foods, rainforest-dwelling parrots exploited a diversity of nutritious foods, even in the dry season when food was scarce for other frugivores and granivores.

Community patterns of nectivorous adult parasitoids (Diptera, Bombyliidae) on their resources.

Highly diverse assemblages of nectivorous bee flies (Diptera: bombyliidae) occur at desert sites in California presenting an opportunity to investigate the ecology of this little-known group. This study compared communities of adult bee flies visiting flowers at two sites, one in the Mojave Desert (Darwin Plateau) and one in the Great Basin (Mono Basin), during periods of higher and lower resource abundance. The range of resources used by single species varied inversely with the number of species present, with the greatest number of species and smallest niche breadths occurring at the Darwin Plateau. Adult bee flies did not visit flower resources at random. Rather the two major divisions of the family exhibited contrasting patterns of specialization on plant species. Results of this study support the hypothesis that resources were limiting for adult bee flies in the period of lower food abundance at the Darwin Plateau and not limiting at the Mono Basin during this study. Bee flies at the Mono Basin exhibited lower densities per flower (despite higher densities per unit area), lower frequency of feeding, a lower degree of specialization, and less pronounced phenological changes than bee flies at the Darwin Plateau. The data suggest that episodes of population regulation in the non-parasitic (i.e. adult) stage, due to short supply of the adults' food, contribute to determining the structure of parasitoid communities.

Seasonal variation in populations of panamanian litter frogs and their prey: A comparison of wetter and drier sites.

Various species of frogs and toads, belonging to the genera Bufo, Atelopus, Dendrobates, Colostethus, and Eleutherodactylus, occur in the leaf litter in rainforest in Panamá. This study compares the litter communities at two sites in Panamá: Pipeline Road, the drier site, and Carti Road, the wetter site. At both sites, frog abundance is greater in the dry season, when abundance of their prey, the litter arthropods, is greater. Species diversity does not change seasonally at either site; however, species diversity differs strikingly between sites, with Carti Road having the greater species diversity. Similarity in diet does not vary consistently with seasonal changes in food abundance at a single site or with differences in species diversity between sites. These results suggest that neither moisture nor food abundance alone influences the abundance or the diversity of litter frogs at these two sites in Panamá.

Feeding ecology of thirteen syntopic species of anurans in a seasonal tropical environment.

Thirteen species of anurans belonging to three families forage diurnally for arthropods in the leaf litter of the lowland rainforest at the Río Llullapichis in Amazonian Perú. This paper investigates the diets and patterns of coexistence in this group of ecologically similar species. All thirteen species use the forest floor habitat without apparent differentiation. Most species take prey in proportions significantly different from those occurring in the leaf litter and comprise two specialist guilds: dendrobatids and bufonids that eat hard-bodied, slow-moving arthropods such as ants and mites; and leptodactylids that eat soft-bodied, mobile arthropods, primarily orthopterans and large spiders. Dendrobates femoralis (Boulenger) is a generalist, taking prey in proportions not significantly different from those in the leaf litter. Within specialist guilds, body sizes of species vary and are correlated with the size of prey taken. Foraging behavior and predator defense also correlate with the type and sizes of prey taken. Ant specialists tend to be poisonous and active searchers, taking many small prey per day. Non-ant specialists are cryptic, sit-and-wait foragers that take few large prey per day. Similarity in diet within guilds tends tobe lowest in the dry season when food is less abundant, suggesting that food is in short supply in the dry season.