Data from: Facilitated exploitation of pollination mutualisms: fitness consequences for plants

Mutualisms are only rarely one-to-one interactions: each species generally
interacts with multiple mutualists. Exploitation is ubiquitous in
mutualisms, and we would therefore expect that each mutualist interacts
with multiple exploiters as well. Exploiter species may also interact with
one another. For example, the action of one exploiter species might open
the opportunity for exploitation by a second species. Exploitation is
common in many plant–pollinator mutualisms: ‘primary’ nectar robbers feed
through holes they make in flowers, which can be subsequently used by
‘secondary’ nectar robbers unable to create holes themselves. The overall
effect of nectar robbing on plant fitness is often (although not always)
negative. No study has separated the effects of interacting with primary
vs. secondary robbers. Here, we examine the effects of primary vs.
secondary nectar robbing on pollinator visitation rate and female fitness
in Ipomopsis aggregata. Manipulating the type of nectar robbing that
flowers experienced, we found that secondary nectar robbing inflicted
fitness costs to plants beyond that inflicted by primary robbing alone.
Secondary nectar robbing significantly reduced pollen receipt to flowers,
as well as fruit and seed production. Although the causes are elusive, the
effect may be attributed to changes in pollinator behaviour at these
plants. Synthesis. Our findings provide evidence that interacting with
multiple exploiters can lead to increased negative effects for mutualists,
and highlight the importance of incorporating multiple exploiters into the
conceptual framework of mutualism.