Convergent acoustic community structure in South Asian dry and wet grassland birds

ABSTRACT Although the study of bird acoustic communities has great potential in long-term monitoring and conservation, their assembly and dynamics remain poorly understood. Grassland habitats in South Asia comprise distinct biomes with unique avifauna, presenting an opportunity to address how community-level patterns in acoustic signal space arise. Similarity in signal space of different grassland bird assemblages may result from phylogenetic similarity, or because different bird groups partition the acoustic resource, resulting in convergent distributions in signal space. Here, we quantify the composition, signal space and phylogenetic diversity of bird acoustic communities from dry semiarid grasslands of northwest India and wet floodplain grasslands of northeast India, two major South Asian grassland biomes. We find that acoustic communities occupying these distinct biomes exhibit convergent, overdispersed distributions in signal space. However, dry grasslands exhibit higher phylogenetic diversity, and the two communities are not phylogenetically similar. The Sylvioidea encompasses half the species in the wet grassland acoustic community, with an expanded signal space compared to the dry grasslands. We therefore hypothesize that different clades colonizing grasslands partition the acoustic resource, resulting in convergent community structure across biomes. Many of these birds are threatened, and acoustic monitoring will support conservation measures in these imperiled, poorly-studied habitats. This article has an associated First Person interview with the first author of the paper.


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presenting an opportunity to address how community-level patterns in acoustic signal space 1 9 arise. Similarity in signal space of different grassland bird communities may be due to 2 0 phylogenetic similarity, or because different bird groups partition the acoustic resource, 2 1 resulting in convergent distributions in signal space. Here, we quantify the composition, 2 2 signal space and phylogenetic diversity of bird acoustic communities from the dry semiarid 2 3 grasslands of Northwest India and the wet floodplain grasslands of Northeast India. We find 2 4 that acoustic communities occupying these distinct biomes exhibit convergent signal space.

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However, dry grasslands exhibit higher phylogenetic diversity, and the two communities are 2 6 not phylogenetically more similar than expected by chance. The Sylvioidea encompasses 2 7 half the species in the wet grassland acoustic community, with an expanded signal space 2 8 compared to the dry grasslands. Thus, dry and wet grassland communities are convergent 2 9 in signal space despite differences in phylogenetic diversity. We therefore hypothesize that 3 0 different clades colonizing grasslands partition the acoustic resource, resulting in convergent 3 1 community structure across biomes. Many of the birds we recorded are highly threatened,

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and acoustic monitoring will support conservation measures in these imperiled, yet poorly-3 3 studied habitats.

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If the two communities exhibited similar patterns of community organization in signal space, 2 4 8 then the average NND should be lower than that of a randomly drawn community.

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Therefore, we constructed 10000 randomly drawn "null communities" (Chek et al. 2003) 2 5 0 spanning the same range of principal component scores, calculated the average NND to 2 5 1 each of these communities, and calculated the Z score of the observed NND versus this 2 5 2 distribution of null values. All three statistical tests were performed twice, once for the entire 2 5 3 acoustic community and once for only the grassland species.
2 5 4 2 5 5 Phylogenetic diversity 2 5 6 After testing for patterns in community structure using the signal space of both acoustic 2 5 7 communities, we tested whether both acoustic communities were phylogenetically similar. Mean Nearest Taxon Distance (MNTD)), and two beta-diversity (between-community) Wet and dry grasslands exhibit convergent acoustic community structure 3 3 7 Next, we compared the community signal space of wet and dry grassland acoustic 3 3 8 communities. The first three principal components (PCs) accounted for about 85% of total

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Finally, a comparison of the observed between-community NNDs to those obtained from 3 5 9 10000 randomized null communities showed that the NNDs between dry and wet grassland 3 6 0 acoustic communities were significantly lower than expected by chance (Z=-3.43, P<0.01).

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suggesting that both these grassland biomes, in spite of possessing very few species in 3 6 3 common, exhibit a convergent community structure in acoustic signal space.
3 6 4 3 6 5 Dry grassland acoustic communities are higher in phylogenetic diversity 3 6 6 Summarizing our results so far, dry grassland acoustic communities exhibit slightly higher 3 6 7 species diversity, but convergent community structure with wet grassland acoustic

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Many threatened birds in this landscape remain very poorly studied. We recorded multiple Although phylogenetic diversity is higher in dry grasslands, acoustic community structure is 4 4 9 convergent with wet grasslands, both communities exhibiting overdispersion in signal space.

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This overdispersion is somewhat less pronounced in dry grasslands, likely because a slightly

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However, our phylogenetic analyses suggest the converse. Firstly, dry grassland acoustic 4 5 8 communities have higher phylogenetic diversity, and second, the two grassland communities 4 5 9 are no more or less phylogenetically similar than expected by chance (PCDp close to 1).

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The results of PCD hold even when considering all recorded species (and not just those