Conditions for a Species to Gain Advantage from the Presence of Competitors

Abstract

The interaction between two species is usually assigned as though they were in isolation from all other species. Here we use a (known) method that determines species interactions more realistically, within the framework of the community to which they belong. This "inverse" method evaluates all the effects that one species experiences from another, both direct and indirect. We use this method to study the classical (though highly controversial) "competition community," where each species is considered (in the "isolated pair" approach) to suffer from the presence of every other. The model we use takes account of the fluctuations in interaction coefficients that one must expect in the real world, both from one species pair to another, and as the effect of ambient environmental variations. Remarkably, the "inverse" method finds that generally a high proportion (20—40%) of the interactions must be beneficial, or "advantageous," when not lifted out of the community context in which they actually occur. The contrary case, called here "hypercompetitive," in which each species suffers from every other species, can occur only if the environment is nearly constant, and the species closely akin to each other, with both of these conditions holding and persisting to a degree that must be considered implausible. The results of the model remain valid, even after incorporating a number of major structural modifications, thus indicating robustness in the predictions. We survey the available field data and show that they are in good general agreement with the conclusions reached, on the high proportion of interactions which must be "Advantageous in a Community Context" (ACC).

A competitive network theory of species diversity

“…Ecologists have long appreciated that resource competitors can indirectly benefit one another via the suppression of shared competitors (22,23). And more recent studies have demonstrated that intransitivity in competitive networks can maintain diversity (9,10,11,15).…”

Quantifying nonadditive selection caused by indirect ecological effects

“…Indirect effects may be especially common in diverse communities, as the number of possible indirect effects increases exponentially with the number of species in a community (Abrams 1992), and can have important fitness consequences (Walsh 2013). In many cases, the magnitude of indirect ecological effects is greater than that of direct effects on species abundances, species coexistence, and community diversity (Vandermeer 1969, Stone and Roberts 1991, Lawler 1993, Miller 1994, Menge 1995. Although the ecological implications of indirect effects have been well studied, the evolutionary consequences have only recently gained attention (Walsh 2013).…”

Epiphyte host preferences and host traits: mechanisms for species-specific interactions

“…Other research suggests that species-specificity in plant-plant interactions may develop as plants interact simultaneously via competition for resources, facilitation, and allelopathy (Bertness 1991;Callaway et al 1991;Callaway 1994Callaway , 1995Holzapfel and Mahall 1999;Pugnaire 2002). Species-specific interactions may be produced by different combinations of positive and negative mechanisms, and by variation in the strength and direction of these interactions (Stone and Roberts 1991;Miller 1994;Callaway 1998;Berlow 1999;Levine 1999).…”