Abstract

The discovery of overcompensatory responses to damage in some plant species has inspired attempts to classify some plant-herbivore interactions as mutualism. Since the debates over plant-herbivore mutualism and overcompensation have been intense, me attempt to outline three conceptual models of plant-animal interactions and evaluate the status of interactions with help of three different fitness criteria: relative fitness, absolute fitness, and mean absolute fitness. Our three plant-animal interactions are assumed to represent "plant-pollinator mutualism", "plant-herbivore antagonism" and "the evolution of overcompensation", respectively. Each case describes how absolute fitness, and consequently also the other two fitness criteria, is assumed to change with animal encounters for plants with special adaptations to cope with those encounters and for plants with no such adaptations. As a result, all these types of interactions may be considered as mutualism when taken relative fitness only into account. Obviously, this criterion is too weak because any trait, evolving under natural selection, should improve fitness relative to other, alternative traits. Absolute fitness increases with animal encounters for the adapted phenotype in the first and in the last case and thus, in the context of absolute fitness, overcompensation in plants would indicate plant-herbivore mutualism. However, absolute fitness as such mag not be sufficient when discussing the evolutionary history of plant-animal mutualism. In the light of mean fitness, overcompensation as presented in earlier studies does not represent mutualism between plants and herbivores. Mean absolute fitness in plant populations decrease with the risk of herbivore attack in our model of overcompensation, while the reverse trend characterises our plant-pollinator model. We, therefore, suggest that mean absolute fitness may well provide an appropriate criterion for distinguishing mutualistic and antagonistic plant-animal interactions in coevolutionary contexts. In order to evaluate our model-system, we compare the predicted patterns with empirical data on the grassland biennial Gentianella campestris.

Published in

Oikos
1999, Volume: 84, number: 2, pages: 313-320

SLU Authors

• Lennartsson, Tommy

  • Department of Conservation Biology, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Evolutionary Biology


Publication identifier

DOI: https://doi.org/10.2307/3546728

Permanent link to this page (URI)

https://res.slu.se/id/publ/101834