Diversity and co-occurrence patterns of wood inhabiting insects along a tropical forest regeneration gradient

Nina Grella, Ana Falconí-López, David A. Donoso, Jörg Müller, Heike Feldhaar

More than 90% of global carbon released during dead wood decomposition comes from the tropics, where insects contribute significantly to this process, especially in lowland rainforests. Understanding community assembly of dead wood-inhabiting insects is therefore important. We investigated diversity patterns between habitats and host trees, and co-occurrence of wood-inhabiting ants, termites, and beetles in the Chocó of northeastern Ecuador along a forest regeneration gradient spanning from agricultural land through regenerating forests (1–37 years) to old-growth forests. Using experimentally exposed dead wood from five locally occurring tree species, we quantified assemblages after six months of decomposition by rearing.
We found 174 insect species across 62 plots. Diversity was lowest in agricultural land and higher in regenerating and old-growth forests, indicating substantial recovery following tree regeneration. Differences among succession stages were strongest for rare species, whereas communities of dominant species were more similar across stages. Host tree identity further structured assemblages: Trema micrantha, Theobroma cacao, and Inga spp. supported higher diversity than Triplaris cumingiana and Hieronyma alchorneoides. These patterns could not be explained by wood density alone, and a comparison with tree availability suggests tree species abundance as a major driver. Co-occurrence analysis revealed predominantly neutral associations among insect species. A small number of positive associations occurred mainly among ambrosia beetles, suggesting facilitation, whereas negative associations including those between ants and termites were rare.
Our results demonstrate that diversity of wood-inhabiting insect communities is primarily shaped by coarse habitat filtering along the regeneration gradient and secondarily by fine scale filtering via the host tree, while biotic interactions leave only a limited signature in co-occurrence patterns. Our finding underlines that with return of trees in abandoned agriculture areas even the saproxylic insects, a cryptic but important functional group in the global carbon cycle from wood, rapidly recolonize, determined by local habitat conditions and resource availability, underscoring their conservation value alongside old growth forests.