Molecular food webs of bat-plant interactions during an extreme El Nino event

Interaction network structure reflects the ecological mechanisms acting
within biological communities, which are affected by environmental
conditions. In tropical forests, higher precipitation usually increases
fruit production, which may lead frugivores to increase specialization,
resulting in more modular and less nested animal-plant networks. In these
ecosystems, El Niño is a major driver of precipitation, however, we still
lack knowledge of how species interactions change under this influence. To
understand bat-plant network structure during an extreme ENSO event, we
determined the links between frugivorous bat species and the plants they
consume by DNA barcoding seeds and pulp in bat faeces. These interactions
were recorded in the dry forest and rainforest of Costa Rica, during the
dry and the wet seasons of an extreme El Niño year. From these we
constructed seasonal and whole-year bat-plant networks and analyzed their
structures and dissimilarities. In general, networks had low nestedness,
high modularity, and were dominated by one large compartment which
included most species and interactions. Contrary to our expectations,
networks were less nested and more modular in drier conditions, both in
the comparison between forest types and between seasons. We suggest that
increased competition, when resources are scarce during drier seasons and
habitats, lead to higher resource partitioning among bats and thus higher
modularity. Moreover, we have found similar network structures between dry
and rainforests during El Niño and non El Niño years. Finally, most
interaction dissimilarity among networks occurred due to interaction
rewiring among species, potentially driven by seasonal changes in resource
availability.