Forest Bird Community Structure in Central Panama: Influence of Spatial Scale and Biogeography

Abstract

Historical and biogeographic contexts can play important, yet sometimes overlooked, roles in determining structure of local communities. In particular, few examinations of historical influences on patterns of species richness and relative abundances in tropical communities have been conducted. In part, that gap in our knowledge has been caused by a paucity of data on tropical communities, even for relatively well‐studied taxa such as birds. In the Neotropics, only two sites, a 97‐ha plot in lowland Peru and a 100‐ha plot in French Guiana, have been inventoried on a spatial scale sufficient to estimate population densities for a majority of resident bird species. Results from those studies revealed extremely similar species richness, community biomass, and patterns of relative abundance. A third site in lowland Panama was originally censused in 1968–1969 and has often been compared with many other tropical and temperate sites. Results from Panama suggested an exceptionally different community structure from that observed at the Amazonian sites. Informative comparisons among sites have been hampered, however, by differences in sampling protocols. The Panama site was sampled on a much smaller spatial scale (2 ha) than the two Amazonian sites. To improve comparisons, we censused a 104‐ha area (the Limbo plot) encompassing the original 2‐ha Panama study area and used several census methods, including those used at the Amazonian sites. As expected, spatial scale had a strong effect on estimates of species richness. We detected 252 species on the Limbo plot, compared with 161 detected on the original 2‐ha area. Estimates of total individual birds per 100 ha were similar, but estimates from the original study were based on densities measured for one‐third fewer species than we measured on our larger study area. Of the 53 species for which both Panama studies estimated population densities, a significant number of estimates were higher in the original study. Thus, the small spatial scale of the original study apparently led to inflated density estimates. The primary cause of disparities appeared to result from undersampling in the smaller plot of many species with patchy distributions and large territory sizes. Compared with Amazonian communities, the Panama community had far fewer rare species. Although 33% of species in Amazonian sites had densities of ≤1 pair/100 ha, only 17% were equally rare in Panama. Furthermore, eight species in Panama were, by tropical standards, “superabundant,” attaining densities as high as 212 breeding individuals/100 ha; the most abundant species in Amazonia barely reached one‐third of that number. In total, those eight species accounted for 36% of all individuals at Limbo. The median abundance at Limbo was 7 pairs/100 ha, vs. 2.5 pairs/100 ha in Amazonia. Consequently, the total number of birds on the Limbo study area was nearly twice that found in Amazonia, despite species richness being only three‐fourths as great. We conclude, first, that spatial scale has indeed had an important effect o...

Insectivorous birds consume an estimated 400–500 million tons of prey annually

“…Accordingly, the food consumption values for insectivorous birds of these biomes were multiplied by a factor of 0.75, 0.95, and 0.85, respectively, to obtain arthropod consumption measures (kg fresh weight ha −1  season −1 ). See Supplementary material for exceptions.Assumption 3: The arthropod consumption measures for tropical biomes relate to annual totals (breeding season plus non-breeding season; see Karr (1975); Leigh and Smythe (1978); Reagan and Waide (1996); Robinson et al (2000); Sakai (2002)). By contrast, the arthropod consumption values for temperate biomes available in the literature in most cases constitute exclusively breeding season values.…”

“…Not included in these calculations are the amounts of arthropod prey consumed at migration stopover sitesBiome classNumber of assessmentsPrey consumption(kg ha −1  year −1 ) * Area (ha)Prey consumption of entire area (kg year −1 )( X )( Y )( X ) × ( Y )Tropical forests a 7112.5 ± 9.21750 × 10 6 196,875 × 10 6 Temperate and boreal forests b 4444.1 ± 6.22410 × 10 6 106,281 × 10 6 Tropical grasslands and savannas/Mediterranean shrubland c 715.8 ± 2.83040 × 10 6 48,032 × 10 6 Temperate grasslands (incl. meadows, pastures, old fields) d 117.5 ± 0.91500 × 10 6 11,250 × 10 6 Cropland e 820.9 ± 9.01350 × 10 6 28,215 × 10 6 Deserts f 184.1 ± 0.82770 × 10 6 11,357 × 10 6 Arctic tundra g 84.6 ± 1.3560 × 10 6 2576 × 10 6 Global total (without ice-covered area)103–13,380 × 10 6 404,586 × 10 6 a Karr (1975); Leigh and Smythe (1978); Reagan and Waide (1996); Robinson et al (2000); Sakai (2002) b Tima (1957); Uramoto (1961); West and DeWolfe (1974); Holmes and Sturges (1975); Karr (1975); Alatalo (1978); Szaro and Balda (1979); Smith and MacMahon (1981); Wiens (1989) (modified data from Wiens and Nussbaum 1975); Wiens (1989) (modified data from Weiner and Głowaciński 1975; Głowaciński and Weiner 1980, 1983); Weathers (1983); Keast et al (1985); Solonen (1986); Kartanas (1989); Harris (1991) c Karr (1971); UNESCO (1979); Gillon et al (1983) d Diehl (1971); Wiens (1977); Rotenberry (1980b); Smith and MacMahon (1981); Głowaciński et al (1984); combined data Faanes (1982)/Kirk et al (1996) e Wiens and Dy...…”

“…Assumption 3: The arthropod consumption measures for tropical biomes relate to annual totals (breeding season plus non-breeding season; see Karr (1975); Leigh and Smythe (1978); Reagan and Waide (1996); Robinson et al (2000); Sakai (2002)). By contrast, the arthropod consumption values for temperate biomes available in the literature in most cases constitute exclusively breeding season values.…”

“… a Karr (1975); Leigh and Smythe (1978); Reagan and Waide (1996); Robinson et al (2000); Sakai (2002) b Tima (1957); Uramoto (1961); West and DeWolfe (1974); Holmes and Sturges (1975); Karr (1975); Alatalo (1978); Szaro and Balda (1979); Smith and MacMahon (1981); Wiens (1989) (modified data from Wiens and Nussbaum 1975); Wiens (1989) (modified data from Weiner and Głowaciński 1975; Głowaciński and Weiner 1980, 1983); Weathers (1983); Keast et al (1985); Solonen (1986); Kartanas (1989); Harris (1991) c Karr (1971); UNESCO (1979); Gillon et al (1983) d Diehl (1971); Wiens (1977); Rotenberry (1980b); Smith and MacMahon (1981); Głowaciński et al (1984); combined data Faanes (1982)/Kirk et al (1996) e Wiens and Dyer (1975); Woronecki and Dolbeer (1980); Kartanas (1989); Ferger et al (2013) f Combined data Lasiewski and Dawson (1967)/Austin (1970) g Wielgolaski (1975); combined data Lasiewski and Dawson (1967)/Watson (1963); James and Rathbun (1981); Montgomerie et al (1983); Sokolov et al (2012) * Values of prey kill (kg ha −1  year −1 ) presented as x̅ ± SE…”

The Effect of Scale-Dependent Habitat Gradients on the Structure of Bird Assemblages in the Czech Republic

“…When moving towards larger scales, distribution of individual species seems to be less affected by habitat (Tomiałojć 2000, Rodewald & Yahner 2001, MacFaden & Capen 2002, Johnson et al 2007). In that case, dispersal limitations underlie the effects of historical factors or physical barriers on distribution (Holt & Keitt 2000) and abundance of species irrespective to changes in small scale habitat composition (Robinson et al 2000). The failure of habitat composition in explaining large scale patterns in bird community structure has been attributed to the greater influence of factors which are more closely connected to geography and history than to habitat (Jokimäki & Huhta 1996, Storch et al 2003.…”