Distinctive aquatic assemblages in water‐filled tree holes: a novel component of freshwater biodiversity in New Zealand temperate rainforests

Abstract

Abstract. 1. Water‐filled tree holes provide important freshwater microhabitats for a wide array of aquatic species in rainforest canopies. There is extensive indirect evidence of the distinctiveness of water‐filled tree‐hole faunas, but few direct quantitative comparisons with ground‐based freshwater habitats, in either tropical or temperate regions. Here, we explore the importance of water‐filled tree holes for aquatic invertebrate species in the temperate rainforests of New Zealand. It is well documented that freshwaters in New Zealand are dominated by relatively few ubiquitous genera, many of which are habitat generalists. The key question, therefore, is whether water‐filled tree holes in New Zealand’s temperate rainforest are also dominated by habitat generalists that typically utilise ground‐level water bodies, or whether water‐filled tree holes support habitat‐specialist species.2. Water‐filled tree holes were dominated by dipteran larvae, whereas ground‐based water bodies were dominated by mayflies, dipterans, and other arthropods. Most importantly, tree‐hole assemblage composition was markedly distinct from that of the ground‐based water bodies, with only eight (out of a total of 83) aquatic species shared in common between tree holes and adjacent ground‐based freshwater habitats.3. Although water‐filled tree holes are typically rare and patchily distributed within New Zealand’s rainforest canopies, our results show very clearly that a distinct assemblage of freshwater species has evolved to occupy these unique microhabitats. We emphasise the importance of incorporating the unique biodiversity of water‐filled tree holes into future conservation prioritisation exercises and biodiversity management plans for temperate rainforest remnants.