Page - 15 - in options, Volume summer 2021

Roots of biodiversity A solid theoretical understanding could fill data gaps, and make policy-facing models more realistic. One aim is to understand why some ecosystems are so rich in species. “All ‘why’ questions in biology have an evolutionary answer,” explains Ulf Dieckmann, a senior researcher in the IIASA Advancing Systems Analysis Program, who has spent 25 years at IIASA developing adaptive dynamic theory, a form of systems analysis that links ecology and evolution. A striking success of this approach has been to show how rainforest plants can be so diverse. According to niche theory, each species adapts to fit a unique position in an ecosystem. Animals compete for different foods, which creates many niches; but all plants eat sunlight. Because of this, niche models had predicted that rainforests should have few types of trees, and only one shade-tolerant species. Real forests however have many shade-dwellers, which cast niche theory into doubt. Dieckmann collaborated on a more realistic model, combining plant physiology, ecology, and evolution. It allows species to have two variable traits (height at maturity and leaf thickness). When tree-fall or fire opens up a new patch of forest, fast-growing colonizers move in, followed by slow-growers. In the model, evolution leads to a large number of shade-tolerant tree species with slightly different traits. It also shows realistic plant diversity in temperate forest, shrubland, and wooded riverbank. This kind of insight could inform conservation work. “One could ask what ecological processes must be kept intact to preserve biodiversity?” says Dieckmann. Plants also compete for water, and IIASA research scholar Jaideep Joshi is examining how that affects biodiversity. “Even more ambitious eco-evolutionary models will take into account topography, soil microbiomes, and other factors,” Dieckmann adds. Integrated future As well as being a desirable outcome in itself, biodiversity affects other systems: for example, maintaining forest resilience and so keeping carbon locked up. IIASA is building a new integrated biosphere model, iBIOM, which could capture some of these effects, such as the role of insect pollination on crop yields. As part of an overall integrated modeling framework now being developed at IIASA, iBIOM will help to explore the complex interplay between climate and biodiversity. “This is a huge challenge,” says Leclère. For one thing, models will have to capture land use in great detail, for example the effect of planting different plant species to sequester carbon. But the reward could also be huge, revealing which climate mitigation options are best for biodiversity – helping us fulfil the CBD’s 2050 vision to live in harmony with nature. © Esmehelit | Dreamstime Further information: pure.iiasa.ac.at/16699 pure.iiasa.ac.at/16804 pure.iiasa.ac.at/16779 pure.iiasa.ac.at/17171 pure.iiasa.ac.at/14354 pure.iiasa.ac.at/15832 pure.iiasa.ac.at/16772 Ulf Dieckmann dieckmann@iiasa.ac.at Martin Jung jung@iiasa.ac.at David Leclère leclere@iiasa.ac.at Ian McCallum mccallum@iiasa.ac.at Piero Visconti visconti@iiasa.ac.ac.at Even more ambitious eco- evolutionary models will take into account topography, soil microbiomes, and other factors Ulf Dieckmann 15Optionswww.iiasa.ac.at Summer 2021