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Pathogens and insect herbivores drive rainforest plant diversity and composition
Robert Bagchi1, Rachel E Gallery2, Sofia Gripenberg3
11] Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK [2] Ecosystem Management Group, Institute of Terrestrial Ecosystems, ETH Zürich, Universitätstrasse 16, 8092 Zürich, Switzerland.
Nature
|January 28, 2014
Summary
Specialized natural enemies like fungi and insects maintain tropical forest biodiversity by increasing mortality at high plant densities. This study confirms the Janzen-Connell hypothesis, showing these organisms are crucial for structuring plant communities and preserving diversity.
Area of Science:
- Tropical ecology
- Community ecology
- Biodiversity science
Background:
- Tropical forests harbor immense biodiversity, yet the mechanisms sustaining it are not fully understood.
- The Janzen-Connell hypothesis posits that specialized natural enemies (insects, pathogens) cause negative density dependence (NDD), promoting species coexistence.
- While NDD is observed, its community-wide role in maintaining tropical plant diversity remains experimentally unverified.
Purpose of the Study:
- To experimentally test the Janzen-Connell hypothesis in tropical plant communities.
- To determine the roles of fungal pathogens and insect herbivores in structuring plant communities and maintaining diversity.
- To investigate how NDD influences seedling recruitment and species composition.
Main Methods:
- Experimental manipulation of fungal pathogens (using fungicides) and insect herbivores (using insecticides) in a tropical forest setting.
- Monitoring changes in plant species diversity and composition across the seed-to-seedling transition.
- Assessing seedling recruitment rates and the impact of conspecific seed density on NDD.
Main Results:
- Fungicide treatments significantly reduced seedling diversity, supporting the Janzen-Connell hypothesis.
- Insecticide treatments did not alter diversity but increased seedling recruitment and shifted species composition.
- NDD was confirmed, with reduced recruitment at high conspecific seed densities, particularly for abundant species.
- Fungal suppression lessened density-dependent effects on recruitment, highlighting fungi's role in diversity maintenance via NDD.
Conclusions:
- This study provides strong experimental evidence supporting the Janzen-Connell hypothesis in tropical forests.
- Fungal pathogens play a critical role in maintaining tropical plant diversity through NDD.
- Insects and pathogens are key drivers structuring tropical plant communities and preserving their exceptional biodiversity.
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