by Melina Filzinger, IIASA Science Communication Fellow
Ecosystems worldwide are changed by the influence of humans, often leading to the extinction of species, for example due to climate change or loss of natural habitat. But it doesn’t stop there: as the different species in an ecosystem feed on each other and are thereby interconnected, the loss of one species might lead to the extinction of others, which can even destabilize the whole system. “In nature, everything is connected in a complex way, so at first glance you cannot be sure what will happen if one species disappears from an ecosystem,” says IIASA postdoc Mateusz Iskrzyński.
This is why the IIASA Evolution and Ecology (EEP) and Advanced Systems Analysis (ASA) programs are employing food-web modeling to find out which properties make ecosystems particularly vulnerable to species extinction. Food webs are stylized networks that represent the feeding relationships in an ecosystem. Their nodes are given by species or groups of species, and their links indicate how biomass cycles through the system by means of eating and being eaten. “This type of network analysis has a surprising power to uncover general patterns in complex relationships,” explains Iskrzyński.
Every one of these food webs is the result of years of intense research that involves both data collection to assess the abundance of species in an area, and reconstructing the links of the network from existing knowledge about the diets of different species. The largest of the currently available webs contain about 100 nodes and 1,000 weighted links. Here, “weighted” means that each link is characterized by the biomass flow between the nodes it connects.
Usually, food webs are published and considered individually, but recently efforts have been stepped up to collect them and analyze them together. Now, the ASA and EEP programs have collected 220 food webs from all over the world in the largest database assembled so far. This involved unifying the parametrization of the data and reconstructing missing links.
The researchers use this database to find out how different ecosystems react to the ongoing human-made species loss, and which ones are most at risk. This is done by removing a single node from a food web, which corresponds to the extinction of one group of species, and modeling how the populations of the remaining species change as a result. The main question is how these changes in the food web depend on its structural properties, like its size and the degree of connectedness between the nodes.
From the preliminary results obtained so far, it seems that small and highly connected food webs are particularly vulnerable to the indirect effects of species extinction. This means that in these webs the extinction of one species is especially likely to lead to large disruptive change affecting many other organisms. “Understanding the factors that cause such high vulnerability is crucial for the sustainable management and conservation of ecosystems,” says Iskrzyński. He hopes that this research will encourage more, and more precise, empirical ecosystems studies, as reliable data is still missing from many places in the world.
As a next step, the scientists in the two programs are planning to understand which factors determine the impact that the disappearance of a particular group of organisms has. They are going to make the software they use for their simulations publicly available, together with the database they developed.
Note: This article gives the views of the author, and not the position of the Nexus blog, nor of the International Institute for Applied Systems Analysis.