Abstract
ABSTRACT Natural communities are dynamic systems in time and space. The spatial distribution of plants and animals tends to coincide with the availability of resources needed for the survival and reproduction of each species. Natural treefall gaps offer a number of resources that influence the distribution of birds within the forest. We compared the understory bird assemblages of natural treefall gaps (15 sampling points) with those found in the adjacent forest (15 points) in the Humaitá Forest Reserve in southwestern Brazilian Amazonia. We used mist-nets to sample birds and obtained 700 captures of 105 species. Species richness, number of individuals, and species composition were all similar between gaps and forest, although six species presented some degree of association with the gaps, and nine with the forest. Nectarivores preferred gaps significantly over forest, whereas insectivores and frugivores were distributed equally between gaps and forest. Vegetation height and density differed between gaps and forest, and influenced the distribution of bird species in the two environments. Fruit availability was positively correlated with frugivore abundance in gaps. Overall, 33.3% of the birds associated with the treefall gaps are from lower forest canopy, while the others are understory species. We showed that the use of natural gaps by birds in a fragmented landscape of the Amazon forest contributes to the environmental heterogeneity and succession dynamics following natural events of habitat disturbance.
Highlights
Biological communities in natural forests are formed by a mosaic of microhabitats and their associated organisms (Whittaker and Levin 1977)
Reserve (HFR), a 2,000-ha forest fragment administered by Universidade Federal do Acre (UFAC), in Porto Acre, Acre state, southwestern Brazilian Amazonia (9o45’19’’S, 67o40’18’’W; Figure 1)
The assemblage of understory birds found in natural gaps was similar in species composition and richness to that of the adjacent forest in southwestern Brazilian Amazonia
Summary
Biological communities in natural forests are formed by a mosaic of microhabitats and their associated organisms (Whittaker and Levin 1977). Species assemblages tend to be similar in environments that have similar abiotic conditions, such as climate, soil, and water (Thompson and Sorenson 2000). Species will be favored distinctly by environmental conditions, including those created in novel environments (Sousa 1984), leading to the unequal spatial distribution of natural communities (Scheiner et al 2000). Mosaics of environments and their associated biological communities are mediated by events such as landslides (Garwood et al 1979), wildfires (Silva et al 2015), and natural treefall in forests, coupled with the succession process (Thompson and Sorenson 2000). The gaps promote ecosystem dynamics, help shape the structure of natural communities and contribute to the heterogeneity in the composition of tropical forests (Brokaw 1985; Wunderle et al 1987; Levey 1988; Hubbell et al 1999; Busing and Brokaw 2002; Lima 2005; Schnitzer and Carson 2010; Maranho and Salimon 2015; Terborgh 2017)
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