Abstract
Food preferences and exploitation are crucial to many aspects of avian ecology and are of increasing importance as we progress in our understanding of community ecology. We studied birds and their feeding specialization in the Central Range of Papua New Guinea, at eight study sites along a complete (200 to 3700 m a.s.l.) rainforest elevational gradient. The relative species richness and abundance increased with increasing elevation for insect and nectar eating birds, and decreased with elevation for fruit feeding birds. Using emetic tartar, we coerced 999 individuals from 99 bird species to regurgitate their stomach contents and studied these food samples. The proportion of arthropods in food samples increased with increasing elevation at the expense of plant material. Body size of arthropods eaten by birds decreased with increasing elevation. This reflected the parallel elevational trend in the body size of arthropods available in the forest understory. Body size of insectivorous birds was significantly positively correlated with the body size of arthropods they ate. Coleoptera were the most exploited arthropods, followed by Araneae, Hymenoptera, and Lepidoptera. Selectivity indexes showed that most of the arthropod taxa were taken opportunistically, reflecting the spatial patterns in arthropod abundances to which the birds were exposed.
Highlights
Our knowledge of species richness patterns along elevational gradients has increased considerably over recent decades, but our understanding of the underlying mechanisms shaping these patterns has not[1]
78 bird species were represented by >3 food samples (35 species were represented by 4–5 samples, and 43 bird species by >5 samples; Table S1) and used in the subsequent analyses
We were able to further investigate and describe the intake of 12% of these frugivores, 22% of frugivore-insectivores, 47% of insectivores and 62.5% of insectivore-nectarivores. These numbers show that sampling was not balanced across the feeding guilds, and that we were more likely to mist-net insect-eating than fruit-eating birds
Summary
Our knowledge of species richness patterns along elevational gradients has increased considerably over recent decades, but our understanding of the underlying mechanisms shaping these patterns has not[1]. The relative importance (in terms of species richness and/or abundance) of individual feeding guilds, and trends in feeding preferences in avian communities along elevational gradients have rarely been studied[2]. Feeding preferences and trophic niche partitioning might be important mechanisms shaping patterns of species richness along environmental gradients[3,4]. Insectivores remained the dominant guild along entire elevational gradients in Costa Rica[12], the Himalayas[3] and Papua New Guinea[13]. The size-related feeding preferences were never studied directly on large scales, and the predator-prey relationship between birds and insect have rarely been investigated along elevational gradients
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