Mutual interference is common and mostly intermediate in magnitude

Abstract

BackgroundInterference competition occurs when access to resources is negatively affected by the presence of other individuals. Within a species or population, this is known as mutual interference, and it is often modelled with a scaling exponent, m, on the number of predators. Originally, mutual interference was thought to vary along a continuum from prey dependence (no interference; m = 0) to ratio dependence (m = -1), but a debate in the 1990's and early 2000's focused on whether prey or ratio dependence was the better simplification. Some have argued more recently that mutual interference is likely to be mostly intermediate (that is, between prey and ratio dependence), but this possibility has not been evaluated empirically.ResultsWe gathered estimates of mutual interference from the literature, analyzed additional data, and created the largest compilation of unbiased estimates of mutual interference yet produced. In this data set, both the alternatives of prey dependence and ratio dependence were observed, but only one data set was consistent with prey dependence. There was a tendency toward ratio dependence reflected by a median m of -0.7 and a mean m of -0.8.ConclusionsOverall, the data support the hypothesis that interference is mostly intermediate in magnitude. The data also indicate that interference competition is common, at least in the systems studied to date. Significant questions remain regarding how different factors influence interference, and whether interference can be viewed as a characteristic of a particular population or whether it generally shifts from low to high levels as populations increase in density.

The body-size dependence of mutual interference

“…Instead, the value of m must be determined from a linear regression of ã against C [15]. Nonetheless, equation (2.1) clearly demarcates the typical range of mutual interference values found in the literature (0 to 22) [11,15]. It produces a dependence of ã on C that ranges from the power of 22 when the prey are stationary (when V r 2 ¼ 0, ã is a function of C…”

Predation by Macrolophus pygmaeus (Hemiptera: Miridae) on Acyrthosiphon pisum (Hemiptera: Aphididae): Influence of prey age/size and predator's intraspecific interactions

“…However, the number of prey consumed is also determined by competition between individuals of the same species (Andersen, 1960;Klomp, 1964). In this sense, intraspecifi c competition is a key factor, which also modulates the dynamics of prey-predator systems (Andersen, 1960;Klomp, 1964;Lucas & Alomar, 2002;DeLong & Vasseur, 2011).…”

“…Diverse types of potential interactions may occur between two or more individuals of the same species when competing for food, space and/or oviposition sites (Klomp, 1964;Alley, 1982;Symondson et al, 2002;DeLong & Vasseur, 2011). When predators compete for prey, one often observes non-interactive as well as interactive individuals, which by mutual interference or synergic interactions (density dependent predation), infl uence in different ways prey population dynamics (Klomp, 1964;Alley, 1982;Losey & Denno, 1998;DeLong & Vasseur, 2011).…”

“…When predators compete for prey, one often observes non-interactive as well as interactive individuals, which by mutual interference or synergic interactions (density dependent predation), infl uence in different ways prey population dynamics (Klomp, 1964;Alley, 1982;Losey & Denno, 1998;DeLong & Vasseur, 2011). Until now, the effect of intraspecifi c competition between individuals of M. pygmaeus has only been recorded in two studies in which whitefl y was the prey (Lucas & Alomar, 2002;MorenoRipoll et al, 2012).…”

Ratio‐dependent predation in a field experiment with wasps

“…However, it can be calculated from the direct observation of the number of prey eaten over a finite period of time. Following Holling (1959), hundreds of experiments have measured the dependence of the functional response on the prey density N. Several dozens have measured the dependence on the predator density P, a dependence known as 'interference' (see, e.g., the reviews of Hassell 1978and DeLong and Vasseur 2011. However, surprisingly few experimental studies have studied the bivariate dependence on (N, P), which is clearly what is needed in order to confirm or refute prey dependence, predator dependence or ratio dependence.…”