Ant sharing by plant species bearing extrafloral nectaries in Central
Amazon has a low impact on plant herbivory
Abstract
Plant species bearing extrafloral nectaries (EFNs) may indirectly
influence other plant species by sharing protective ants, potentially
altering plant herbivory levels. However, the propagation of indirect
effects in this type of mutualism has seldom been investigated. We
investigated indirect effects via ant sharing among twenty-one
EFN-bearing plant species of the tribe Bignonieae distributed on 28
plots in the central Brazilian Amazon. Using an ecological network index
that quantifies potential indirect effects among plant species via ant
sharing, we distinguished plant species that could most strongly affect
and most strongly be affected by other species via shared dominant and
subordinate ant species. These Bignonieae species differ markedly in
attractiveness to ants, and we investigated how these differences
influenced the indirect effects between plant species. We also tested
whether plant species with a higher potential to influence ant
visitation to other plants experienced less herbivory due to attraction
of more aggressive/dominant ants. We found that the most attractive
plant species (here termed the promoter species) had the highest
potential to indirectly affect ant visitation to less attractive plant
species (here termed the receptor species) in the community, mainly via
changes in attraction of dominant ant species. However, the potential
indirect effects among plants did not translate into herbivory patterns.
We also found that ant attendance and herbivory did not differ among
promoter species, their neighbours, and non-neighbouring plants. We
conclude that, unlike patterns found in studies investigating indirect
effects in other mutualisms involving plants (e.g., pollination), the
consequences of indirect effects among plant species are limited in this
ant-plant network. This pattern could be explained by generally low
herbivory levels and the small foraging areas of shared ant defenders.
Indirect interactions and their effects between plant species that share
protective ants appear in this system to confer limited costs and
benefits.