Forest canopy ecology: what do we know about canopy species and their interactions?

Abstract

Abstract Forest canopies support a large proportion of global biodiversity, undertake most terrestrial primary productivity, and are major sites for species interactions and vital ecosystem processes such as pollination, seed-dispersal, nutrient cycling and decomposition. However, due to the logistical difficulties of accessing the tree tops, this habitat is relatively poorly studied. After 35+ years of increased research effort, we now have a much greater understanding of the distribution and diversity of canopy organisms, but still lack quantitative data on the structure and function of canopy assemblages, and the ecologies of more than a small fraction of canopy species. Canopy science is moving from descriptive studies towards more functional studies using novel experimental approaches. The relative roles of bottom-up (i.e. resource availability) and top-down (i.e. predation and competition) influences have been invoked to explain various spatiotemporal patterns in species distribution and activity, including vertical stratification, diel activity, seasonality and host-specificity. The evolutionary implications of antagonistic (e.g. herbivory and predation) and mutualistic (e.g. pollination and seed-dispersal) interactions have revealed valuable insights into the structure and function of canopy communities. Descriptive studies will remain an important aspect of canopy ecological research for many years to come, particularly at small (within tree) and large (regional) spatial scales. However, future local-scale ecological studies will be increasingly dominated by examinations of species interactions and ecosystem functions (e.g. food webs and network analysis), especially with respect to threats such as climate change and deforestation.