COS 12-6
Temporal consistency in mutualistic networks
Mutualisms are essential for the functioning of natural ecosystems, and serve as links joining large suites of species in mutualistic networks. An explosion of recent research has examined the structure of these networks, yet comparatively little is known about the extent to which this structure remains consistent over time. We therefore undertook research designed to answer the following question: what is the within- and between-year temporal consistency of pairwise interactions and community structure in mutualistic networks? To address this question, we investigated the temporal consistency of a frugivory/seed dispersal mutualistic network in a seasonally-dry tropical forest community in Madagascar that enabled detailed investigation of pairwise interactions among all partner species. Specifically, we measured the strength of pairwise interactions among vertebrate frugivores (fruit bats, lemurs, and birds) and fig trees (Ficus) to develop a detailed model of community structure. Analyses were repeated during the early and late dry season periods in two years to evaluate the seasonal and between-year consistency of pairwise interactions and overall community structure.
Results/Conclusions
Our results suggest that both pairwise interactions and community structure are highly variable within the dry season period. Interactions were generally stronger, and the community was more strongly connected during the late dry season period, relative to the early dry season period. During the early dry season some frugivore species were completely absent from the focal tree species. In contrast, both pairwise interactions and community structure remained relatively stable during the same season between years, especially during the late dry season period. These outcomes may result from a strong seasonal variation in availability of alternate resources; alternate food resources were widely available early in the dry season period but scarce in the late dry season during both years. The scarcity of alternate food resources during the late dry season may force frugivores to visit fruit-bearing Ficus trees to survive, but they have more choices during the early dry season. We conclude that temporal variation, and particularly within-season variation, may have a strong influence on community structure. This result calls into question the generality of the large number of mutualistic network studies that have been conducted during only one time period. Future studies should seek to sample representatively across varying ecological conditions.