Question

What is the difference between symmetric competition and asymmetric competition? How would you expect species to react, adapt and evolve in response to each type of competition?

Answer 1

Asymmetric competition refers to forms of business competition where firms are considered competitors in some markets or contexts but not in others.[1] In such cases a firm may choose to allocate competitive resources and marketing actions among its competitors out of proportion to their market share.[2][3][4][5] Asymmetric competition can be visualized using techniques such as multidimensional scaling and perceptual mapping.

Forms of asymmetric competition[edit]

• Firm A may compete with B in some markets but not others.
• Firm A competes with B over certain attributes (such as reliability and design) but not over others (price).
• Firm A considers B as a competitor but B does not consider A to be a competitor.
• Firm A does not consider B to be a competitor, however, consumers see A's products as competing with B's products.

  Symmetric and asymmetric competition

  Interspecific competition (like intra-specific competition) is frequently highly asymmetric - the consequences are often not the same for both species. For instance, with Connell's barnacles, Balanus excluded Chthamalus from their zone of potential overlap, but any effect of Chthamalus on Balanus was negligible: Balanus was limited by its own sensitivity to desiccation. An analogous situation is provided by two species of cattail (reedmace) in ponds in Michigan; Typha latifolia occurs mostly in shallower water whilst T. angustifolia occurs in deeper water. When grown together (in sympatry) in artificial ponds, the two species mirror their natural distributions, with T. latifolia mainly occupying depth zones from 0 to 60 cm below the water surface and T. angustifolia mainly from 60 to 90 cm (Grace & Wetzel, 1998). When grown on its own (allopatry), the depth distribution of T. angustifolia shifts markedly towards shallower depths. In contrast, T. latifolia shows only a minor shift towards greater depth in the absence of interspecific competition.

  On a broader front, it seems that highly asymmetric cases of interspecific competition (where one species is little affected)

  generally outnumber symmetric cases (e.g. Keddy & Shipley, 1989). The more fundamental point, however, is that there is a continuum linking the perfectly symmetric competitive cases to strongly asymmetric ones. Asymmetric competition results from the differential ability of species to occupy higher positions in a competitive hierarchy. In plants, for example, this may result from height differences, with one species able to completely over-top another and preempt access to light (Freckleton & Watknson, 2001). In a similar vein, Dezfuli et al. (2002) have argued that asymmetric competition might be expected between parasite species that occupy sequential positions in the gut of their host, with a stomach parasite reducing resources and adversely influencing an intestinal parasite further downstream, but not vice versa. Asymmetric competition is especially likely where there is a very large difference in the size of competing species. Reciprocal exclusion experiments have shown that grazing ungulates (domestic sheep and Spanish ibex Capra pyrenaica) reduce the abundance of the herbivorous beetle Timarcha lugens in Spanish scrubland by exploitation competition (and partly by incidental predation). However, there was no effect of beetle exclusion on ungulate performanceIndividual-based modelling is a promising tool for scaling from the individual to the population and community levels that allows a wide range of applied and theoretical approaches. Here, we explore how intra-specific competition affects population dynamics using FORSITE, an individual-based model describing tree–tree interactions in a spatial and stochastic context. We first describe FORSITE design and submodels following the ODD (Overview, Design concepts and Details) guideline for individual-based models. We then use simulation to study how competition symmetry (i.e., the way individual size affects resource partitioning) changes temporal and spatial population dynamics. We compare our results to those of an earlier deterministic (analytical) model of annual plants which found that (i) under asymmetric competition (i.e., advantaging tall individuals), population dynamics converge quickly to a stable equilibrium and (ii) under symmetric competition, some values of competition strength and population growth rate make population dynamics exhibit long-term oscillations. We find generally similar results, despite the existence of overlapping generations in trees. A thorough analysis of stage structures in the model allows us to explain this behaviour. We also show that decreasing tree dispersal distances, in the case of symmetric competition, results in a wave-like spatial pattern, caused by desynchronized sub-populations. Finally, we link the results obtained with FORSITE to different types of resource limitation observed in northern temperate and sub-boreal forests, emphasizing the implications of such difference on long-term biome dynamics. We note that FORSITE is a flexible platform that can be easily adapted for other ecological modelling studies.