Seed natural enemies and tropical forest diversity

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The role of natural enemies in structuring and maintaining plant diversity in species-rich tropical forests is being increasingly recognised. To date, research has focused almost exclusively on enemies attacking seeds after dispersal from the mother plant, seedlings, and larger plants (e.g. 1, 2, 3). Recent, high-profile (4) work has shown that this post-dispersal predation provides a mechanism for the hyperdiversity of tropical forests. The potential role of pre-dispersal seed enemies, i.e. enemies attacking seeds prior to seed dispersal, has been almost completely ignored (5). One potentially important group of pre-dispersal seed enemies are the internally-feeding insect seed predators (typically Coleoptera, Lepidoptera) that feed on seeds in the canopy, killing them in the process. Our work on Barro Colorado Island in Panama shows that the majority of tree species are attacked by pre-dispersal seed predators. We also know that these enemies are highly host-specific, with only 20% of insect seed predator species feeding on more than one host plant species. This makes these insects an interesting and relevant group for further study. For example, if they tend to kill a large proportion of seeds where their host is abundant, they have the potential to promote the coexistence of plant species at the community level (6, 7). The aim of this project is to assess the impacts of pre-dispersal insect seed predators on individual plant species and at the wider plant community level. More specifically, the student will be able to 1) investigate the fitness consequences of pre-dispersal insect seed predation for individual trees; 2) assess spatial, temporal, and community-level variation in rates of enemy-inflicted pre-dispersal seed mortality, and 3) the potential implications of observed patterns on species coexistence at the plant community level. The project will also 4) assess the link between observed high (>50%) levels of premature fruit abscission and pre-dispersal enemy attack. The student will have access to data sets collected as part of previous research conducted by one of the supervisors and her collaborators, including information on community-level patterns of attack by insect seed predators across ~500 plant species and >30 years of seed rain data for hundreds of plant species on Barro Colorado Island. The student will receive training in statistical analysis of these data sets and modelling to address the role of pre-dispersal seed mortality on population and community dynamics. There will also be possibilities for field-based research (observational studies, experiments) on individual plant species on Barro Colorado Island. The project has the potential to yield novel insights into a poorly studied group of plant enemies. The research theme is particularly topical given recent concerns about declining insect populations in tropical forests (8), and more widely.