Abstract
Altitudinal patterns in the population ecology of mountain bird species are useful for predicting species occurrence and behavior. Numerous hypotheses about the complex interactions among environmental factors have been proposed; however, these still remain controversial. This study aimed to identify the altitudinal patterns in breeding bird species richness or density and to test the hypotheses that climate, habitat heterogeneity (horizontal and vertical), and heterospecific attraction in a temperate forest, South Korea. We conducted a field survey of 142 plots at altitudes between 200 and 1,400 m a.s.l in the breeding season. A total of 2,771 individuals from 53 breeding bird species were recorded. Altitudinal patterns of species richness and density showed a hump-shaped pattern, indicating that the highest richness and density could be observed at moderate altitudes. Models constructed with 13 combinations of six variables demonstrated that species richness was positively correlated with vertical and horizontal habitat heterogeneity. Density was positively correlated with vertical, but not horizontal habitat heterogeneity, and negatively correlated with migratory bird ratio. No significant relationships were found between spring temperature and species richness or density. Therefore, the observed patterns in species richness support the hypothesis that habitat heterogeneity, rather than climate, is the main driver of species richness. Also, neither habitat heterogeneity nor climate hypotheses fully explains the observed patterns in density. However, vertical habitat heterogeneity does likely help explain observed patterns in density. The heterospecific attraction hypothesis did not apply to the distribution of birds along the altitudinal gradient. Appropriate management of vertical habitat heterogeneity, such as vegetation cover, should be maintained for the conservation of bird diversity in this area.
Highlights
Altitudinal changes in bird species diversity provide important information on the limitation of species distribution within mountain areas (Adolfo & Navarro, 1992; Kosicki, 2017) and often serve as time-space substitutes and provide valuable predictive information (Chamberlain et al, 2016)
This study aimed to identify the altitudinal patterns in breeding bird species richness or density in a temperate montane forest, and we tested the hypotheses that (1) climate, (2) horizontal habitat heterogeneity, (3) vertical habitat heterogeneity, and (4) heterospecific attraction to explain the cause of such patterns
We developed a set of 13 candidate models using this generalized linear model (GLM), using 13 combinations of variables to identify the causes of altitudinal patterns in bird species richness and density in relation to spring temperature, migratory bird ratio, vertical coverage of vegetation, and horizontal habitat diversity variables
Summary
Altitudinal changes in bird species diversity provide important information on the limitation of species distribution within mountain areas (Adolfo & Navarro, 1992; Kosicki, 2017) and often serve as time-space substitutes and provide valuable predictive information (Chamberlain et al, 2016). McCain (2009) suggested that, from the point of view of climate zones, four elevational richness patterns are represented. These are (1) decreasing, (2) low plateau, (3) low plateau with a mid-elevational peak, and (4) mid-elevational peak. To explain these altitudinal patterns, numerous hypotheses have been proposed (Rahbek, 2005; Rahbek et al, 2007; McCain, 2009; Pan et al, 2016)
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