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Keywords:

  • Arthropod abundance;
  • climatic variables;
  • competition;
  • environmental filtering;
  • India;
  • leaf warblers;
  • morphological trait metrics;
  • net relatedness index;
  • niche conservatism;
  • phylogenetic structure

Abstract

Aim

To understand the relative importance of ecological and biogeographical processes structuring assemblages of Himalayan leaf warblers (family Phylloscopidae), through an evaluation of (1) the patterns of species richness and phylogenetic community structure, (2) their environmental determinants, and (3) dispersion of morphological traits within communities.

Location

Elevational gradients across the east and the west Himalayas, India.

Methods

Species presences were assessed at 16 sites along eight elevational gradients. Phylogenetic conservatism was assessed in three functional morphological traits (body size, tarsus length, beak shape) and phylogenetic structure in terms of the net relatedness index (NRI) was quantified using a published phylogenetic tree. Site-specific species richness and NRI were related to climatic variables and arthropod abundance. Morphological trait metrics were also calculated and the observed trait dispersion related to patterns of species richness and phylogenetic structure of the assemblages.

Results

The 16 assemblages, composed of two to eight species, ran the entire spectrum of significance in terms of their phylogenetic structure, resulting in many clustered assemblages at low elevations and a few overdispersed assemblages at higher elevations. Phylogenetic structure was not significantly correlated with species richness, although variation in both was largely explained by maximum temperature and arthropod abundance. At the regional scale, both trait filtering (beak shape) and trait convergence (tarsus length) seem to influence the distribution of species along the elevational gradients. Dispersion of body size metrics suggested filtering and competition as predicted by phylogenetic structure, while beak shape metrics suggested competitive interactions even in phylogenetically clustered assemblages.

Main conclusions

The interaction of multiple assembly processes (competition, filtering and history) appears to structure the Himalayan leaf warbler assemblages. Phylogenetic community structure largely reflected the biogeographical history of species accumulation into the Himalayas, while processes structuring local assemblages were better explained by the dispersion of traits.