DOI: 10.5061/dryad.tdz08kpxd
title: Data from: Isolated trees support lower bird taxonomic richness than trees within habitat patches but similar functional diversity

description: Large isolated trees are keystone structures that can help maintain
 biodiversity in fragmented landscapes, with evidence that open areas with
 isolated trees may support similar levels of taxonomic diversity to nearby
 patches of habitat. However, it is not clear if isolated trees can support
 the same diversity of ecological functions as trees in habitat patches. We
 compared species richness, community composition and functional diversity
 of birds in trees at forest edges and isolated trees. Twenty isolated
 trees and ten edge trees of American muskwood (Guarea guidonia) were
 selected, and sampled on 11 occasions, each of 20 minutes, over four
 months. All individual birds that landed at trees were recorded using a
 standardized protocol. Species richness was, on average, almost twice as
 high at edge trees than at isolated trees. Taxonomic composition differed
 between edge and isolated trees, with many forest-dependent birds
 restricted to edge trees, and some open-area birds restricted to isolated
 trees. Overall functional diversity was similar at edge and isolated
 trees, but some ecological functions (e.g. frugivory) were less frequent,
 while others (e.g. granivory) were more frequent at isolated compared to
 edge trees. Isolated trees are important for supporting many ecological
 functions in modified areas. However, the maintenance of forest patches is
 essential to complement the provision of such functions in modified
 landscapes.
description: We conducted this
 study in forests and pastures located in a countryside of Rio de Janeiro
 state, Brazil (within and adjacent to the Reserva Ecológica de Guapiaçu;
 22°24’S, 42°44’W). We carefully selected trees for sampling,
 controlling possible confounding factors. To control for potential
 differences in the attractiveness of different tree species to birds, we
 focused on a single tree species, American muskwood (<i>G.
 guidonia</i>), which is the dominant isolated tree in the study area
 (A. D. Azevedo, unpublished data) and common throughout the Atlantic
 Forest (Cartes, 2003; Lima et al., 2009). We measured and georeferenced
 102 <i>G. guidonia</i> trees within the study landscape and
 selected 20 isolated trees and 10 edge trees based on a careful systematic
 procedure. First, we selected trees that were at least 200 m apart, to
 prevent double counting of birds and to maximize the independence of
 sampling units (trees). Second, we selected trees spanning a broad range
 of sizes (i.e. circumference at breast height). Third, isolated trees
 varied in the number of surrounding
 isolated trees (from all species) and in the amount of
 surrounding forest cover, thus covering the range of conditions present
 within our study landscape. Edge trees were located at the edge of a large
 continuous forest area of ~ 100,000-ha. Thus, the edge trees served as a
 reference to determine the potential pool of bird species present at the
 edges of continuous forest that might use the sampled isolated trees.
 Fruit density of all isolated and edge, i.e., the volume of the canopy
 with fruits estimated by counting and attributing a score from 0 to
 5.   We sampled birds from September to
 December 2016, which corresponded to the period of greatest reproductive
 activity (Sick, 1997). Based on a pilot study conducted in September 2015
 and information in the literature (Fischer and Lindenmayer, 2002a, b;
 DeMars, Rosenberg & Fontaine, 2010), we determined 20 minutes to
 be the appropriate period for sampling. During each 20-min sampling event,
 an observer stood at 5 m from a
 sampled tree (ideal
 distance for bird identification) and recorded all birds that
 landed at the tree. Surveys were conducted between 5:00 and 11:00 a.m. and
 only during fine weather, with the same amount of effort employed for all
 trees. All trees were sampled in each of the four months of the study at
 all survey hours, summing to 11 sampling events of 20 min each (220 min in
 total for each tree).  
 To quantify
 functional diversity, we selected bird traits related to habitat
 requirements (open area, generalist, or forest; Stotz, 1996; del Hoyo et
 al., 2020), diet (carnivore, frugivore, nectarivore, granivore,
 insectivore, saprophage, or omnivore; Wilman et al., 2014), foraging
 strata (terrestrial, understory, midstory, superior, or generalized; Stotz
 1996, Wilman et al., 2014) and body mass (small – individuals smaller than
 the median, i.e. 24.75 g, and large – individuals larger than the median;
 Dunning, 2007), which are related to both the response of species to
 environmental change and their effects on ecosystem function (Luck et al.,
 2012). Therefore, we compiled data for a total of four traits containing
 16 categories. The traits classification was based on available
 information in the literature (e.g. Stotz, 1996; Dunning, 2007; Wilman et
 al., 2014; del Hoyo et al., 2020).
description: Three documents are available: one containing the information of
 each sampled tree (trees.csv); another containing the recorded species in
 the trees, and the number of times each species was recorded (bird
 composition.xlsx); and the last one containing the traits of each species
 (traits.xlsx).