Aug 16, 2012
Enmity and co-operation together bring stable ecosystems
To date, biological theory has indicated that the more species a community contains, the less stable it is. But this contrasts with reality, where complex ecosystems do occur, creating a problem known as the "complexity–stability" issue. Now researchers in Japan have found that having a mixture of types of interactions between species – such as antagonistic, competitive or mutualistic relations – can help to stabilize such networks.
"Everyone knows that an ecological community is built up on the wide variety of fascinating interspecific relationships," Michio Kondoh of Ryukoku University, Japan, told environmentalresearchweb. "However, earlier studies overlooked its role in community maintenance. We wanted to know what, if any, is the contribution of interaction-type diversity for the 'balance of nature'."
In the past, models such as food webs have considered only one type of interaction – the predator–prey relationship. Mutualistic networks, meanwhile, have looked only at relationships that are beneficial to both parties. Kondoh and colleague Akihiko Mougi from Ryukoku University used a theoretical hybrid community model to show that a moderate mixture of antagonistic and mutualistic interactions could stabilize population dynamics. What is more, in a community with a range of interaction types, increasing complexity led to increased stability.
"We hypothesize that the diversity of species and interaction types may be the essential element of biodiversity that maintains ecological communities," wrote the researchers in Science. The pair believe this is the first study that shows that diversity of interaction can, in theory, play a critical role in ecological community maintenance.
"In 1972 Robert May theoretically found that an ecological community is less stable when the community is more complex (that is, having more species or more interactions)," said Kondoh. "This counterintuitive theory cast the important question of what allows the existence of complex ecological communities in real nature. We have shown that increasing complexity can stabilize – not destabilize – population dynamics in the presence of a variety in interaction type, providing a possible solution to the long-lasting question."
The results could have implications for ecosystem-management decisions. "The diversity of interspecific interaction is one of the most attractive parts of nature," said Kondoh. "Our theory implies that this diversity of interaction may be a necessary part of an ecosystem for the maintenance of biodiversity itself. Species loss is of vital conservation concern. Yet we may also need to identify the interaction types lost or maintained."
The concern is that a biased loss of one interaction type may destabilize the entire community and that self-sustaining communities may be more vulnerable to cascading biodiversity losses.
Kondoh said that he would now like to test the theory by using real ecological community data. "If interaction-type diversity really matters for the maintenance of ecosystems, we should be able to detect this by analysing how real ecological communities are structured – which species are interacting in what way to form the complex ecological networks," he said.
Kondoh and Mougi reported their results in Science.
About the author
Liz Kalaugher is editor of environmentalresearchweb.