The relationship between local and regional species richness

One way to assess the degree to which communities are saturated with species is to plot the relationship between local species richness (assessed on a spatial scale where all the species could encounter each other in a community) and regional species richness (the number of species in the regional pool that could theoretically colonize the community). Local species richness is sometimes referred to as a richness (or a diversity) and regional species richness as y richness. If communities are saturated with species

(i.e. the niche space is fully utilized), local richness will reach an asymptote in its relationship with regional richness (Figure 21.2a). This appears to be the case for the Brazilian ground-dwelling ant communities studied by Soares et al. (2001) (Figure 21.2b). Similar patterns have been described for aquatic and terrestrial plant groups, fish, mammals and parasites, but nonsaturating patterns have just as often been described for a variety of taxa, including fish (Figure 21.2 c), insects, birds, mammals, reptiles, molluscs and corals (reviewed by Srivastava, 1999). Local regional richness plots provide a useful tool for addressing the question of community saturation, but they must be used with caution. For example, Loreau (2000) points out that the nature of the relationship depends on the way that total richness (y) is partitioned between within-community (a) and between-community richness (P), and this is a matter of the scale at which different communities are distinguished from one another. In other words, researchers might erroneously include within a single community several habitats that should be considered as different communities, or, alternatively, local vs regional richness - saturated or unsaturated communities?

Figure 21.2 (a) In a saturated community, local richness is expected to increase with regional richness at very low levels of regional richness, but to quickly reach an upper limit. In an unsaturated community, on the other hand, local richness is expected to be a constant proportion of regional richness. (After Srivastava, 1999.) (b) Asymptotic relationship between local richness of litter-dwelling ant communities in 1m2 quadrats in 10 forest remnants in Brazil in relation to the size of the regional species pool (assumed to be the total number of species in the forest remnant concerned). (After Soares et al., 2001.) (c) Nonasymptotic relationship between local species richness (number recorded over equal-sized areas of a river bed) and regional species pools (the number of species present in the entire drainage basin from which the local sample was drawn). (After Rosenzweig & Ziv, 1999.)

Figure 21.2 (a) In a saturated community, local richness is expected to increase with regional richness at very low levels of regional richness, but to quickly reach an upper limit. In an unsaturated community, on the other hand, local richness is expected to be a constant proportion of regional richness. (After Srivastava, 1999.) (b) Asymptotic relationship between local richness of litter-dwelling ant communities in 1m2 quadrats in 10 forest remnants in Brazil in relation to the size of the regional species pool (assumed to be the total number of species in the forest remnant concerned). (After Soares et al., 2001.) (c) Nonasymptotic relationship between local species richness (number recorded over equal-sized areas of a river bed) and regional species pools (the number of species present in the entire drainage basin from which the local sample was drawn). (After Rosenzweig & Ziv, 1999.)

they may study local communities at an inappropriately small scale (e.g. 1 m2 quadrats may have been too small to be 'local' communities in the ground-dwelling ant study of Soares et al., 2001).

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Responses

  • Elvin
    What is the relationship between local and regional richness?
    4 years ago
  • Dawit Kinfe
    How to plot local vs regional richness in r?
    26 days ago

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