Sudden collapse could await insect networks

Insect pollinators play a crucial role in food security and biodiversity and are already subject to increasingly harsh conditions – if these get any worse, numerous species could go suddenly extinct. Plants and insect pollinators have a mutually beneficial relationship – in return for nectar, plants rely on bees and hoverflies for the production of seeds and fruit. However, these pollinators are under pressure from insecticides, loss of habitat, parasites and disease – making it increasingly difficult for them to survive. A new study from Wageningen University used mathematical models to show that a further deterioration in conditions for pollinators is strongly influenced by the way in which interaction networks are put together. These networks allow pollinator species to support each other under difficult conditions, but when these conditions reach a critical point the whole network collapses. “The interactions between plants and pollinators that co-occur within the same area are organised in a way that optimises their benefit for the community,” Jelle Lever told Laboratory News. “Understanding the exact structural property that leads to this optimal organisation is not easy, but this example will give you an idea of how it works: Two pollinator species may compete with each other, for instance for nesting sites. Indirect facilitation may however occur between pollinators when pollinating the same plant species. A pollinator species may thus also benefit from the existence of another pollinator species, because this pollinator species enhances the growth of the plant that provides it with nectar. Such a beneficial effect can be especially strong when these pollinator species are present at different periods of a plants flowering period.” Lever said this type of indirect facilitation between pollinators becomes stronger as conditions become more difficult, meaning pollinator species can, together, survive under harsh conditions. But it also means that pollinator species collapse simultaneously when conditions pass a critical point. “A network collapse would lead to the loss of all pollinator species that are part of it. This may reduce the fruit or seed production of the plants that depend on this pollination substantially,” Lever said. “Such a collapse can occur suddenly when increasingly harsh conditions pass a critical point and recovery from such a collapse might not be easy. The improvement in conditions needed for pollinators to recover, could be substantially larger than the improvement needed to return to conditions at which the pollinator community collapsed.” The sudden collapse of pollinator communities