Seasonal variation in the role of non-native plants in an old field plant-pollinator interaction network

Background/Question/Methods

In the last decade, the network approach to investigating mutualistic interactions has created a prolific and dynamic field which has identified important patterns in community structure.  Interaction networks which sum interactions across time or include information from only a portion of the flowering season may not provide a complete representation of which species pairs interact and may overlook important intra-annual patterns.  I explored seasonal changes in network structure of an old field community in New Jersey within and between years by comparing networks among seasons, defined by peaks in abundance of flowering plants.  Floral abundance and visitation were monitored weekly during the entire flowering period at this site for two consecutive years.  Comparisons of network properties among seasonal networks tested whether networks structure varied seasonally.  I also explored whether the role of non-native plants in network structure varied among seasons.

Results/Conclusions

Network properties of connectance, nestedness, and modularity remained fairly consistent within and between years, but the relative importance of native and non-native plants, as measured by species degree and species strength, varied among seasons.  During seasons when overall native floral abundance was low, non-native plants received the majority of pollinator visits.  When native floral abundance was high, native plants received the most visits, regardless of the relative abundance of non-native flowers.  On a community-scale, non-native plants do not seem to be disrupting insect visitation to native plants and may be supporting pollinator populations when availability of native floral resources is low.