Invasive Mutualists Erode Native Pollination Webs

Main Category: Biology / Biochemistry
Article Date: 11 Feb 2008 - 17:00 PDT

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Plant-animal mutualisms are characterized by weak or asymmetric mutual dependences between interacting species, such that if a plant species depends strongly on an animal species, the animal typically depends weakly on the plant, and vice versa. This limited reciprocal dependency or "mutualism strength" might increase species persistence by buffering plant and animal species against the extinction of any of their partners. Many plant-pollinator networks include a fraction of alien species and it is not clear how these invaders might affect the structure of pollination webs.

This week in the online open-access journal PLoS Biology, Carolina Morales, Juane Morales, and Marcelo Aizen show how they analyzed 10 paired plant-pollinator webs, eight from forests of the southern Andes and two from oceanic islands, with different incidences of alien species. Highly invaded webs exhibited, on average, weaker mutualistic interactions, and hence a potential increase in network stability, than less-invaded webs.

This was due to a disproportionate increase in the participation of some alien species in the most asymmetric interactions and their role as central nodes in the structure of the most invaded pollination webs. The increase in alien dominance involves the usurpation of interaction links, decreasing connectivity among native mutualists. Thus, many native species that rely on native generalists for either reproduction or survivorship become highly dependent on these super-generalist alien mutualists.

Invasive mutualists erode native pollination webs
Aizen MA, Morales CL, Morales JM
PLoS Biol 6(2): e31. doi:10.1371/journal.pbio.0060031
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