Reduced functional differentiation in seasonal community assembly of birds in tropical small‐scale agriculture and community‐managed forests

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Abstract
Effective and predictive biodiversity conservation strategies in human‐modified ecosystems require a sound understanding of community assembly. Three key mechanisms—homogeneous selection, neutral assembly and variable selection—have been postulated to influence assembly. These mechanisms often change spatiotemporally over disturbance gradients driven by niche availability. We evaluate how land cover interacts with season to alter assembly mechanisms and species richness of a bird community in a tropical forest‐agriculture mosaic. We focus on three land covers—small‐scale agriculture, community‐managed forests and a protected area—representing a forest disturbance gradient from most to least disturbed, across three seasons—post‐monsoon, winter and pre‐monsoon. We use functional dispersion as a metric combined with a null modelling approach to quantify changes in assembly mechanisms. We use multi‐species occupancy modelling to obtain probabilities of site use by species, corrected for imperfect detection, from which we estimate functional dispersion and species richness. Within the protected area, assembly mechanisms varied seasonally, shifting between variable selection, neutral assembly and homogeneous selection and had communities that were more functionally differentiated. In contrast, small‐scale agriculture and community‐managed forests witnessed only neutral assembly and homogeneous selection, associated with reduced niche availability. Habitat structure played an additional mediating role, with high bamboo, understorey and forest cover increasing functional differentiation. Species richness showed limited variation across land covers but composition changed. However, richness was higher in the protected area during winter. Species richness varied across seasons, being highest during the post‐monsoon season. High canopy and understorey cover increased species richness. Synthesis and applications . Our study provides novel insights into how tropical small‐scale agriculture subtly impacts seasonal assembly dynamics of forest bird communities leading to increased neutrality and homogeneous selection. We recommend that even for small‐scale farms in forest‐agriculture mosaics, high levels of canopy, bamboo, understorey and surrounding forest cover should be maintained. This could be facilitated by shifting away from non‐canopied crops and monocultures, and promoting agro‐forestry alternatives with native trees. Furthermore, we recommend that community forests should be managed to resemble contiguous stands of high‐integrity forests that can conserve assembly dynamics as found in protected areas.
Funding Information
  • National Geographic Society (EC‐67957R‐20)

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