Diversity and host-networks of saproxylic beetles along a forest recovery gradient in the tropics

The high tree diversity in tropical forests is known to promote diversity of phytophagous insects. This principle should also apply to wood-inhabiting organisms and their interactions with host tree species. As tree biomass, diversity and deadwood diversity increases during the post-agricultural recovery of forests, we hypothesized that beetle abundances, species richness and network complexity should increase, whereas host specialization should decrease along a forest recovery chronosequence from active agriculture to early regenerating, late regenerating, and old-growth forests. We experimentally placed logs from five tree species differing in wood density in 62 plots distributed over the four stages of a forest recovery chronosequence in a small-scale agriculture landscape of the Ecuadorian Chocó. Based on 10,650 specimens of 91 saproxylic beetle species, we found that abundances and species richness (after controlling for abundances) increased significantly along the chronosequence. Rarefaction-extrapolation curves for the four stages of the chronosequence showed increasing taxonomic and network link γ-diversity, especially between logs from agricultural plots to the three forest stages. Network specialization did not show a consistent trend along the chronosequence, but was significantly higher in agricultural and late regeneration forest plots. Among the five host speciess, logs of tree species with low wood density harboured lower numbers of individuals but a higher γ-diversity, particularly of rare species. Our results indicate reduced abundances, taxonomic and network complexity for saproxylic beetles in agricultural areas, but a rapid recovery with forest restoration, which may be attributed to the robust beetle-host specificity along the recovery chronosequence.