Comparative Structure and Organization of Canopy Bird Assemblages in Honduras and Brazil
Core Canopy Species
The core canopy species in Honduras were represented by 66 species, or 60% of all species observed in the canopy. Twenty of these were observed exclusively in the canopy stratum, as represented by a stratum mean of 30. An additional 25 species were observed disproportionately more often in the canopy, as indicated by a stratum average of 2.9 or higher. Together these 45 species can be classified as canopy specialists. In Brazil, 107 species (74% of all species detected in the canopy) were core canopy species. A total of 49 genera encompassing 155 species were reported from the canopy at a minimum of three of the four sites (Honduras, Costa Rica, Panama, and Brazil). Historically, 25 genera occurred at all sites (Ara and Amazona having been extirpated from some), and three species (Florisuga mellivora, Chlorophanes spiza, Cyanerpes cyaneus) were observed at all sites (Table 2).
Together, the grouping of core species in Honduras and Brazil in genera observed at a majority of the sites can be taken to represent the core allospecies that characterize bird assemblages of the canopy of these lowland neotropical rainforests. By family, richness of the Tyrannidae was greatest, with 13 genera and 35 species represented. The most species-rich genera were Euphonia, with eight species represented, and Trogon, Dendroica, and Tangara, each with seven species. Migrants were well represented, with high richness in the genera Dendroica and Vireo (four species).
The distribution of species´ abundances in Honduras was significantly different from that in Brazil when sampling was restricted to 56 canopy censuses for each site (Kolmogorov– Smirnov test, P < 0.001). Three lines of evidence indicate that abundance distributions were more even in Brazil than in Honduras. First, three important differences in rank-abundance curves are noteworthy:
- Honduras has more superabundant species,
- The middle portion of the Brazil curve lies completely above the Honduras curve, and
- The tail of rare species is longer for Brazil (Fig. 2).
Second, the 20 most abundant species make up a greater proportion of the canopy assemblage in Honduras than in Brazil (Table 3). In Honduras, the top 20 species accounted for 68.9% of all detections in the canopy, and seven species (Hylophilus decurtatus, Psarocolius wagleri, Pyrilia haematotis, Ramphastos sulfuratus, Vireo olivaceus, Pteroglossus torquatus, Cyanerpes cyaneus) each accounted for ≥4% of total detections. In Brazil the 20 most abundant species accounted for 48.5% of total detections, and only one species (Brotogeris chrysopterus) accounted for ≥4% of total detections. Third, results from bootstrapping analyses of the inverse of the Simpson evenness index revealed greater evenness in the canopy assemblage in Brazil (assemblage value 52.11; 95% confidence interval 46.93– 56.26) and greater dominance in Honduras (assemblage value 24.92, 95% confidence interval 17.73–30.85).
|TABLE 2. Constituents of the core canopy assemblage as represented by genera observed in the canopy of four lowland neotropical rainforests with published studies: Pico Bonito National Park, Honduras (this study), La Selva, Costa Rica (Loiselle 1988), Barro Colorado Island, Panama (Greenberg 1981), and Manaus, Brazil (Naka 2004). Only genera observed at ≥3 sites are included. Genera constituting part of the core canopy assemblage at the sites in Honduras (Ho) or Brazil (Br) are noted.|
|Genus||Core species||No. Species||No. Sites|
|Attila b||Ho, Br||1||2|
a Ara and Amazona historically occurred at all sites but have been extirpated from some.
b Attila spadiceus is included because it was considered a core species for both Honduras and Brazil and occurred in high densities at both sites.