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Ecological determinants of tropical-temperate trends in insect diversity

Periodic Reporting for period 3 - Diversity6continents (Ecological determinants of tropical-temperate trends in insect diversity)

Reporting period: 2018-10-01 to 2020-03-31

This research aims to explain why tropical rainforest ecosystems support such an extraordinary plant and animal diversity, while temperate zone forests are comparatively impoverished. This tropical – temperate difference is one of the most striking features of global distribution of biota and as such needs to be understood and explained – for the curiosity’s sake, since we want to understand the world we are living in, as well as for better biodiversity conservation and maintenance of biodiversity-related ecosystem services. Our project examines plant – insect food webs in forest ecosystems in a global network of six study sites, representing three tropical – temperate pairs located at different continents. The study of plant and insect communities, and their interactions, is designed to reveal whether the diversity of insects can be fully explained by plant diversity alone. This would have important consequences for our strategies of biodiversity conservation, suggesting a strong focus on the vegetation. Further, the study will help us understand how approximately six million insect species, most of them still unknown to science, can coexist in tropical forests. The project includes a significant research infrastructure – a crane allowing access to rainforest canopy built in Papua New Guinea.
We have completed two years of sustained sampling of plants and their herbivores at two locations, in a tropical rainforest at Fort Shearman (Panama), using canopy crane of the Smithsonian Tropical Research Institute, and the temperate zone forest at Front Royal (USA), using forest felling in collaboration with local farmers and the Smithsonian Institution. The data, detailing the composition of plants and their herbivorous insects in the entire 0.1 ha forest plots, allows a rigorous comparison of food webs between lowland humid broad-leaf forests from temperate and tropical regions in the Americas, to be expanded to other continents in the course of the project.

Our studies of food webs have expanded also to include other important ecological gradients: elevational and successional. We have found that predation pressure on herbivores increases from temperate to tropical forests, and from montane to lowland forests. Both these trends are caused by changes in the activity of arthropod predators, especially ants, but not vertebrate predators such as birds or bats.

We have analyzed the relative importance of phylogenetical history of plants and insects, and their ecology, on the structure and diversity of the plant-herbivore food webs in the contemporary forests, and found an important imprint of history apparent in the structure of our current forest ecosystems. We cannot understand the ecology of insect pests attacking trees without being aware of the several million years of their historical interactions.

We have built a 45 m high tower crane in a rainforest in Papua New Guinea that gives full access to 1 ha of forest canopy to scientists for a variety of studies, including sampling insect herbivores and conducting ecological experiments in the tree canopies. This was a logistically difficult project as the crane in a remote location had to be built with the help of a helicopter. Together with similar cranes in Australia, Malaysia, China and Japan, we have now a latitudinal transect populated by cranes, suitable for studies of changes in forest ecology temperate to tropical forests.
The project is training 11 PhD students from five countries, and has also engaged citizen scientists in USA, interns in USA and Panama and para-ecologists in Papua New Guinea. Our studies also contribute to rainforest conservation in Papua New Guinea, where the canopy crane is situated in an indigenous Kau Rainforest Conservation Area, bringing thus training, research expertise and also income directly linked to rainforest conservation.

The project also helps to raise interest in science locally in the countries where it operates (the Czech Republic, Panama, USA, Papua New Guinea) and internationally; in particular there was a broad media coverage of the Science paper on dummy caterpillar predation in at least 50 media outlets (https://tinyurl.com/dummycats) as the simple use of children’s toy plasticine for ecological science seems to have captured imagination of the general public.
Rainforest caterpillars reared by paraecologists in Papua New Guinea
Canopy crane in Baitabag, Papua New Guinea, built during the project.
Building a canopy crane in Papua New Guinea (image (C) Heli Niugini Ltd.)
B. Koane exposing dummy plasticine caterpillars on tropical vegetation to measure predation.
Sampling insects from a canopy crane in a tropical rainforest in Panama
Studying herbivory on tropical foliage in Papua New Guinea - a public exhibition in Prague.
Rearing insect herbivores sampled in a temperate forest in USA.