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Ecological determinants of tropical-temperate trends in insect diversity

Periodic Reporting for period 4 - Diversity6continents (Ecological determinants of tropical-temperate trends in insect diversity)

Reporting period: 2020-04-01 to 2021-09-30

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 been able to meet the goals of the project, obtaining and analysing six large data sets on plant-herbivore food webs from six continents. We have built a new canopy crane in Papua New Guinea which is now one of the premier facilities in the country that harbours 5% of global diversity but has seriously under-developed local academic community. Our field work also inspired and trained over 80 university students, interns, paraecologists and volunteers in six countries. Our findings have provided new insights into the ecological drivers of diversity and food web structure along latitudinal gradients.
We have completed sampling of plants and their herbivores at all six locations, in tropical rainforests of Panama, Cameroon and Papua New Guinea and temperate broadleaf forests in USA, the Czech Republic and Japan. We used canopy cranes and forest felling in collaboration with local farmers to access the forest canopy. We have complemented our observational studies with manipulate experiments of rainforest communities in Papua New Guinea. Last but not least, we have built a new canopy crane in Papua New Guinea as the major improvement of the local research infrastructure.

We demonstrated parallel strategies of plant defence escalation and diversification against herbivores in diverse tropical rainforests and were able to partly predict plant-insect interactions from the phylogeny, ecology and species traits of the interacting taxa. We combined our globally distributed highly detailed censuses of forest food webs with community-level manipulative experiments in the tropics to demonstrate the top-down effects of herbivores on successional vegetation. Our inter-disciplinary study of ethnobiological knowledge in 392 indigenous languages used a novel quantitative approach to ethnobiology and language surveys and sounded alarm at the rapid decline of the inter-generational transfer of ethnobiological knowledge. We have significantly invigorated local ecological research in under-developed tropical countries of Cameroon, Papua New Guinea, and Panama, where we have trained and worked with 65 local paraecologists, research technicians and students. Many of them were recruited from the rainforest-dwelling indigenous communities. In Papua New Guinea we have developed the local research infrastructure by building the canopy crane, ranking among the most significant research facility in the country. We have recruited four PhD students from Papua New Guinea for the project. The crane has excellent potential for future use as it is a part of an informal latitudinal gradient of canopy cranes, from Japan through China, Malaysia and now Papua New Guinea to Australia.

The project was featured by media, particularly in Papua New Guinea and the Czech Republic with the stories about the newly build canopy crane. The results were disseminated in 26 popular articles and 19 participations at scientific conferences. The project was also featured in a six-part TV series produced by the Czech TV and in a documentary film about the canopy crane construction, both produced in English and Czech languages.
We have developed detailed standardized census methods for forest food webs and proposed a modern research agenda for the use of canopy crane as a research tool for food web studies. We have advanced phylogenetical measures of host specialization and developed a new analytical approach to the study of phylogenetical signal in the structure of food webs, examining the importance of past plant diversification events for the current herbivore communities supported by plants. We have demonstrated the importance of bottom-up resource control of tropical herbivores by plants, but also the unexpected importance of herbivores shaping the regeneration of rainforest vegetation in the early successional stages. Finally, we combined our ecological team with linguistic experts and used our long-term experience from work with indigenous rainforest dwelling communities for a methodologically novel, quantitative survey of indigenous ethnobiological knowledge on unprecedented scale, comprising over 5% of the world’s languages. This inter-disciplinary collaboration found an alarmingly rapid decline of the traditional orally transmitted knowledge of the natural world that requires urgent action.
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.)
Postdoctoral researcher C. Redmond training local assistants in Cameroon
B. Koane exposing dummy plasticine caterpillars on tropical vegetation to measure predation.
Our multi-national research team during the field work in Cameroon.
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.
Sampling from the new canopy crane in Papua New Guinea
Rainforest community experiments manipulating herbivores in Papua New Guinea
Rearing insect herbivores sampled in a temperate forest in USA.