Bracken Fern (Pteridium Aquilinum) and Nectra‐Feeding Ants: A Nonmutualistic Interaction

The hypothesis that ants attracted to the nectar secreted by bracken fern (Pteridium aquilinum Kuhn) foliar nectaries protect the frond from herbivore damage was tested experimentally in three New Jersey populations. There was no difference in the amount of herbivore damage experienced by control ferns and those from which ants were excluded. Sugar secretion rates were highest in fiddleheads just prior to the start of frond enlargement, and ant activity was highest on fronds in this developmental stage. Both sugar secretion and ant activity decreased during frond enlargement to low levels at maturity. Despite considerable variability among fronds in sugar secretion, population sugar production and ant activity remained constant through most of the summer. The developmental and seasonal patterns of nectar secretion therefore fit those that would be predicted if bracken and ants were engaged in a mutualistic interaction, but there is no evidence that the ferns in fact derived any benefit from their ant visitors.