Abstract
Variation in partner species and frequency of interaction between species pairs are potential drivers of the net outcome of generalized mutualisms. In ant-plant mutualisms, the quality of defence provided by ants is related to ant aggressiveness. Hence, we hypothesize that the performance of plants bearing extrafloral nectaries will be higher when they interact more frequently with more aggressive ant species. We estimated ant aggressiveness in the field by observing their behaviour towards soil baits. Afterwards, we observed the frequency with which individuals from these ant species visited plants through an entire reproductive cycle. We measured the production and persistence of plants reproductive structures through this period and the total seed production. Increasing in the interaction frequency with highly aggressive ants reduced the number of floral buds and seeds produced. Increased visitation frequency by less aggressive ants increased the number of floral buds and seeds per branch. The inverse relationship between ant aggressiveness and seed production may be influenced by the costs imposed by different mutualistic partners. Thus, frequent interaction with highly aggressive ants may lead to a higher accumulation of costs through time, resulting in a negative net outcome for the plants. Our results bring new evidence highlighting the importance to incorporate temporal aspects in the study of mutualistic interactions. We suggests that the quality of mutualistic partners must be understood as a function of its per-interaction benefit and their cumulative costs to their partner over time, what puts in check our current classification regarding partner quality in mutualistic systems.
Highlights
Mutualisms are positive interspecific interactions in which the net outcome is determined by the interplay between the costs and benefits of the interaction for the individuals of both interacting species [1]
It is possible that, in local scale, the net outcome of generalized mutualism for each individual is determined by the net benefit of interacting with each partner species available in the habitat and by the frequency of interaction between each different species pairs over time [4]
As we have no reason to believe that plant and ant species distribution on our study site have changed in the recent years, we argue that the visitation frequency we measured is a good estimate of the previous pattern of ant visitation on the focal plants in our study area
Summary
Mutualisms are positive interspecific interactions in which the net outcome is determined by the interplay between the costs and benefits of the interaction for the individuals of both interacting species [1]. It is possible that, in local scale, the net outcome of generalized mutualism for each individual is determined by the net benefit of interacting with each partner species available in the habitat and by the frequency of interaction between each different species pairs over time [4]. These two components have been evaluated as potential factors affecting mutualism outcome in empirical studies, its effects have been seldom evaluated jointly (e.g.[4,5,6], but see [7,8,9]). This approach contributes to a simplified view about the forces driving the net outcome of generalized mutualisms, once it neglects the cumulative effect of interactions with different partner species over time on individual’s fitness
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