Abstract:
It is widely believed that mutualisms, interspecific interactions that benefit both species, have been grossly neglected relative to their true importance in nature. I have reviewed the recent primary literature in order to assess quantitatively the frequency of studies of mutualism, the types of questions they address, and their general scientific approach. All articles appearing from 1986 to 1990 in nine major journals that publish ecological and evolutionary research were examined. It is clear that mutualism research is not in fact rare. Studies of interspecific interactions made up about 22 % of the over 4500 articles published during this period; of these, about one-quarter investigated some form of mutualism. Over 90 % of them investigated plant-animal interactions, primarily pollination (52 %) and seed dispersal (31 %), a bias probably related in part to the particular journals examined. The diversity of questions addressed in these articles was surprisingly low. The majority (63 %) focused simply on identifying the mutualists of some species of interest. Furthermore, almost all studies were unilateral, that is, they focused on only one of the interacting species, plants being studied much more frequently than their animal partners. Mutualism studies do not appear to have focused on mutualism as a form of interaction in the same way as studies of competition and predation. Rather, researchers have treated mutualism primarily as a life history attribute of one of the two partners. Consequently, although an impressive amount of information has accumulated about these interactions, we are still far from achieving an overall picture that transcends the boundaries of particular taxa or combinations of taxa. Three other obstacles have prevented data on mutualisms from being brought together: the historical isolation of studies of different kinds of mutualism, a nearly total disconnection between mutualism theories and empirical studies, and the unilateral approach almost always used to study these bilateral interactions. I identify eight research questions whose answers have the potential to reveal broad-based generalizations about the evolution and ecology of mutualism.
PMID: 22583047;Abstract:
Mutualisms are interspecific interactions that yield reciprocal benefits. Here, by adopting a consumer-resource perspective, we show how considering competition is necessary in order to understand the evolutionary and ecological dynamics of mutualism. We first review the ways in which competition shapes the ecology of mutualisms, using a graphical framework based on resource flows rather than net effects to highlight the opportunities for competition. We then describe the known mechanisms of competition and show how it is a critical driver of the evolutionary dynamics, persistence, and diversification of mutualism. We argue that empirical and theoretical research on the ecology and evolution of mutualisms will jointly progress by addressing four key points: (i) the existence and shape of physiological trade-offs among cooperation, competition, and other life-history and functional traits; (ii) the capacity for individuals to express conditional responses to variation in their mutualistic and competitive environment; (iii) the existence of heritable variation for mutualistic and competitive traits and their potentially conditional expression; and (iv) the structure of the network of consumer-resource interactions in which individuals are embedded. © 2012 New York Academy of Sciences.
Abstract:
The Costa Rican fig tree, Ficus pertusa, is pollinated by a species-specific wasp (Agaonidae) whose female offspring transfer pollen between trees. Pollination success (the proportion of inflorescences pollinated) ranged from 1-100% and averaged only 65%. Resource availability evidently was limiting to fruit set as well: every crop abscised many inflorescences at a predictable point during growth. This abscission period usually preceded the brief but variably timed period of pollinator arrivals; in most cases every pollinated, undamaged inflorescence set fruit. Fruit abortion would not be expected in plants that evolved under conditions of pollen limitation; although pollinators have been thought to be overabunadnt in highly coevolved pollination mutualisms, figs' unique flowering phenology may in fact make pollen limitation common. The fact that future pollen carriers as well as seeds mature within fruits may also help explain these unusual fruit maturation patterns. -from Author
Abstract:
A total of 26 species of birds in 10 families took F. pertusa fruit. Visitors' identity, abundance, and importance (estimated by an index of the number of fruits removed) all varied among trees and over time for individual trees. Compared with its obligate, species-specific pollination mutualism, F. pertusa's highly variable interactions with its present-day disperser assemblage are less likely to be products of coevolution. -from Authors
