RESUMO
Patterns of habitat use directly influence a species' fitness, yet for many species an individual's age can influence patterns of habitat use. However, in tropical rainforests, which host the greatest terrestrial species diversity, little is known about how age classes of different species use different adjacent habitats of varying quality. We use long-term mist net data from the Amazon rainforest to assess patterns of habitat use among adult, adolescent (teenage) and young understory birds in forest fragments, primary and secondary forest at the Biological Dynamics of Forest Fragments Project in Brazil. Insectivore adults were most common in primary forest, adolescents were equally likely in primary and secondary forest, and all ages were the least common in forest fragments. In contrast to insectivores, frugivores and omnivores showed no differences among all three habitat types. Our results illustrate potential ideal despotic distributions among breeding populations of some guilds of understory birds where adult insectivores may competitively exclude adolescent individuals from primary forest. Secondary forest recovery appears to hold promise as a breeding habitat for frugivore and omnivore species but only as a pre-breeding habitat for insectivores, but as the forest ages, the demographic structure of bird populations should match that of primary forest.
Assuntos
Aves , Ecossistema , Floresta Úmida , Animais , Aves/fisiologia , Brasil , Fatores Etários , Comportamento AlimentarRESUMO
The effects of habitat alteration and climatic instability have resulted in the loss of bird populations throughout the globe. Tropical birds in particular may be sensitive to climate and habitat change because of their niche specialization, often sedentary nature, and unique life-cycle phenologies. Despite the potential influence of habitat and climatic interactions on tropical birds, we lack comparisons of avian demographics from variably aged forests subject to different climatic phenomena. Here, we measured relationships between forest type and climatic perturbations on White-collared Manakin (Manacus candei), a frugivorous tropical bird, by using 12 years of capture data in young and mature forests in northeastern Costa Rica. We used Cormack-Jolly-Seber models and an analysis of deviance to contrast the influence of the El Niño Southern Oscillation (ENSO) on manakin survival. We found that ENSO had little effect on manakin survival in mature forests. Conversely, in young forests, ENSO explained 79% of the variation where dry El Niño events negatively influenced manikin survival. We believe mature forest mitigated negative effects of dry El Niño periods and can serve as refugia for some species by buffering birds from climatic instability. Our results represent the first published documentation that ENSO influences the survival of a resident Neotropic landbird.
Assuntos
Ecossistema , El Niño Oscilação Sul , Florestas , Passeriformes/fisiologia , Animais , Costa Rica , Humanos , Modelos Teóricos , Análise de Componente Principal , Clima TropicalRESUMO
Nearctic-neotropic migrant birds need to replenish energy reserves during stopover periods to successfully complete their semiannual movements. In this study we used linear models to examine the habitat use of 11 migrant species in northeastern Costa Rica to better understand the influence of food and structural resources on the presence of birds during stopover periods. Our models indicated that frugivorous migrants primarily used food abundance, while insectivorous migrants chiefly used vegetation structure as cues for habitat use during stopover. In addition to habitat use models, we documented fruiting plant phenology and found a general relationship between migrant arrival and the timing of ripe fruit availability. Our results suggest that insectivorous migrants probably rely on structural features when using habitat because it may be inherently difficult to assess cryptic-arthropod availability during a short period of time in a novel habitat, such as stopover periods.
Assuntos
Aves/fisiologia , Ecossistema , Migração Animal/fisiologia , Animais , Costa Rica , Estações do AnoRESUMO
Our understanding of how anthropogenic habitat change shapes species interactions is in its infancy. This is in large part because analytical approaches such as network theory have only recently been applied to characterize complex community dynamics. Network models are a powerful tool for quantifying how ecological interactions are affected by habitat modification because they provide metrics that quantify community structure and function. Here, we examine how large-scale habitat alteration has affected ecological interactions among mixed-species flocking birds in Amazonian rainforest. These flocks provide a model system for investigating how habitat heterogeneity influences non-trophic interactions and the subsequent social structure of forest-dependent mixed-species bird flocks. We analyse 21 flock interaction networks throughout a mosaic of primary forest, fragments of varying sizes and secondary forest (SF) at the Biological Dynamics of Forest Fragments Project in central Amazonian Brazil. Habitat type had a strong effect on network structure at the levels of both species and flock. Frequency of associations among species, as summarized by weighted degree, declined with increasing levels of forest fragmentation and SF. At the flock level, clustering coefficients and overall attendance positively correlated with mean vegetation height, indicating a strong effect of habitat structure on flock cohesion and stability. Prior research has shown that trophic interactions are often resilient to large-scale changes in habitat structure because species are ecologically redundant. By contrast, our results suggest that behavioural interactions and the structure of non-trophic networks are highly sensitive to environmental change. Thus, a more nuanced, system-by-system approach may be needed when thinking about the resiliency of ecological networks.