A saproxylic weevil acts as an ecosystem engineer: Impacts across multiple trophic levels

Although the degradation of dead trees plays an important role in biodiversity maintenance, only a few species of pioneer saproxylic beetles trigger their early degradation, thus acting as ecosystem engineers. Pioneer saproxylic beetles may be functionally more important when the properties of dead wood hinder its decay. In Patagonian rainforests, recently dead evergreen trees are massively colonized by a unique pit weevil species (Psepholax dentipes), while Nothofagus tree species host several pioneer beetle species. We evaluated if P. dentipes acts as an ecosystem engineer in evergreen trees only, positively affecting saproxylophagous beetles and Magellanic woodpeckers. We compared P. dentipes abundance between dead trees of evergreen and Nothofagus species. A causal model was used to test P. dentipes facilitation on woodpeckers and saproxylophagous beetles, while the foraging preferences of woodpeckers for trees colonized by P. dentipes were evaluated with zero-inflated models. Psepholax dentipes were more abundant in evergreen trees than in Nothofagus trees, in both cases affecting positively foraging woodpeckers. However, the positive P. dentipes effect on woodpeckers was stronger in evergreen trees than in Nothofagus trees, while a positive P. dentipes effect on saproxylophagous beetles was found only in evergreen trees. Woodpeckers selected trees with more holes of P. dentipes, but this effect weakened as trees became more decayed. Our results support the role of P. dentipes as ecosystem engineers in dead ever-green trees as they improve microhabitat conditions for saproxylophagous beetles and foraging woodpeckers, while serving as prey for woodpeckers.