Temporal dynamics in plant-pollinator networks

Background/Question/Methods The plant–pollinator relationship is one of the most well-studied mutualistic interactions. Several studies held at community level have affirmed that the pattern of specialization is highly asymmetrical with specialist plants usually being visited by generalist pollinators and specialist pollinators usually having generalist plant hosts. Although well-depicted, the plant–pollinator network has been described as static whereas the interannual variations that may occur have not been examined. For instance, since the 1980s researchers have shown that the number of pollinator species may vary from one year to the other, and this may affect not only the network structure, but also the observed specialization/generalization pattern of both the partners involved. Recently, the temporal dynamics of this interaction has received increasing attention, firstly focusing on its stability through time, and secondly attempting to produce suitable theory linking network structure to the ecological mechanisms responsible for its formation.

Results/Conclusions This talk will focus on the temporal dynamics of a plant–pollinator interaction network of a Mediterranean scrub community surveyed over four consecutive years. Species number and composition within the four annual sub-networks showed high temporal variation both for plants and insects. Temporal dynamics were also evident in the topology of the network, as interactions among plants and pollinators did not remain constant through time. Strikingly few species and interactions were consistently present in all four annual sub-networks (53% of the plant species, 21% of the pollinator species, and 4.9% of the observed interactions). To elucidate the mechanisms that might cause such a dynamic network structure, we built a stochastic model to simulate the plant–pollinator interaction network, taking into account the duration of activity of each species. We were able to obtain simulated plant–pollinator interaction networks with properties similar to the real ones by assuming that there is a positive relationship between abundance and duration of activity and that the interaction among coexisting species occurs on a per capita basis. We conclude that the observed plant–pollinator network properties can be produced stochastically, and the mechanism shaping the network is not necessarily related to size or coevolutionary constraints. These results imply (i) that tight and specialized coevolution might not be as important as previously suggested and (ii) that plant–pollinator interaction networks might be less prone to detrimental effects of disturbance than previously thought.