Latitude-Niche Width Hypothesis

· Ecology and evolution
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Definition

The latitude-niche width hypothesis claims that niches of species are narrower in high diversity tropical than in low diversity cold-temperate regions.

A priori reasons for the hypothesis

The hypothesis is implicit in equilibrium ecology, i.e., it is a consequence of the view that habitats are generally saturated with individuals and species and that a greater number of species can be accommodated in a habitat only if their niches are narrower (e.g., Rosenzweig and Ziv 1999 [1]). Since tropical habitats are generally much more species-rich than cold-temperate ones (“latitudinal gradients in species diversity”), niches in the former therefore must be generally narrower.

Assumptions on which the hypothesis are based

The hypothesis is based on two widely accepted assumptions (e.g., May 1973 [2]), i.e., that there is a latitudinal gradient in population variability, and that there is a relationship between population variability and niche breadth. In other words, the tropics have greater stability and less seasonality than temperate regions, which makes populations there more stable and thereby permits narrower niches.

History of the concept

The hypothesis can be traced back to MacArthur (MacArthur 1965 [3], 1969 [4], 1972 [5], MacArthur and Wilson 1967 [6]), but is possibly even older.

Empirical evidence for and against the hypothesis

MacArthur (1965 [3], 1969 [4]) and Moore (1972 [7]), among others, have provided some evidence for the hypothesis; others (e.g., Rohde 1980 [8], Novotny and Basset 2005 [9]) have given evidence against it. A niche has many dimensions which can vary with latitude. We discuss some aspects of the niche that have been examined in this regard.Latitudinal ranges (Rapoport’s rule)Stevens (1989 [10]) provided evidence that latitudinal ranges of some groups of plants and animals are narrower in the tropics. Rohde et al. (1993 [11]) have shown that for marine teleosts at least, niches are wider and not narrower in the tropics than at higher latitudes; however, freshwater teleosts show an increase in latitudinal ranges with latitude, but only above latitudes of about 40
oN . Numerous subsequent studies examining the rule have been made, some providing support for it, but an even greater number failing to find support or even finding support for an opposite trend. Rohde (1998 [12]) therefore suggested two opposing trends: newly evolved species with little vagility may have narrower ranges in the tropics, species with greater vagility and of sufficient age to have spread into adjacent areas may have larger ranges in the tropics. In those species that have larger latitudinal ranges in cold regions, the increase is often restricted to high latitudes above approximately 40-50° N and S (review in Rohde 1999 [13]); Rohde (1996 [14]) concluded that the rule describes a local phenomenon, the result of the extinction of species with narrow ranges at very high latitudes during the ice ages.Stauffer and Rohde (2006 [15]), using the Chowdhury Ecosystem Model, also failed to find support for the rule. For a review see Rohde (1999 [13]) (for further details on Rapoport’s rule see the knol Rapoport’s rule).

Habitat width

According to Moore (1972 [7]), the average tropical species occupies about half as much of the intertidal zone as the average temperate species. According to MacArthur (1965 [3], 1969 [4]), tropical species often have a spottier distribution than high- latitude ones. Several authors (e.g. Beaver 1979 [16], review in Novotny and Basset 2005 [9]) have studied possible differences in host specificity of herbivorous insects in tropical and high latitude habitats. No major differences were found. – Rohde (1978 [17]) has shown that host ranges (the number of host species infected) of monogenean flatworms infecting the gills of marine fish are more or less the same at all latitudes, whereas host ranges of another group of (endoparasitic) flatworms, the Digenea, are markedly greater at high latitudes. After correction for intensity and prevalence of infection, however, host specificity was the same and very high at all latitudes for both groups (Rohde 1980 [8]). Other niche dimensions of these parasites, such as geographical range and microhabitat width, were also examined and found not to be correlated with diversity, although the data sets were small and more studies are needed (Rohde 1989 [18]). Lappalainen and Soininen (2006 [19]) found that the regional occupancy of fish species in freshwater was more strongly governed by the habitat position than the habitat breadth. The cool water species (percids and cyprinids) showed significant decrease in habitat breadth towards higher latitudes (and not towards lower latitudes, expected by the latitude-niche breadth hypothesis). Stauffer at al. (2007 [20]), using the Chowdhury ecosystem model, have show that tropical species with sufficient vagility and time to spread into adjacent habitats, tend to have wider habitats than high latitude ones, contradicting the latitude-niche breadth hypothesis.

Metanalysis (evaluation of all previous studies considered to be relevant)

Vázquez and Stevens (2004 [21]) made a thorough meta-analytical study of the evidence for the latitude-niche breadth hypothesis, concluding that the null hypothesis (i.e, that there is no correlation between latitude and niche width) cannot be rejected. They also critically examined the two assumptions on which MacArthur’s hypothesis is based, i.e., that there is a latitudinal gradient in population variability, and that there is a relationship between population variability and niche breadth, and found no convincing evidence for either of these assumptions. Indeed, as shown by Rohde (1992 [22]), there may be extreme variations (occurring over very short time spans of a few hours) in temperature, salinity and currents in tropical shallow waters, such as high diversity coral reefs.

Flawed a prioriassumptions of the hypothesis

As pointed out above, the latitude-niche breadth hypothesis makes equilibrium assumptions, implicitly and explicitly assuming that niche space is more or less saturated with species. However, there is much evidence for an overabundance of vacant niches and that most ecological including tropical systems are far from saturation (for a discussion and examples see Rohde 2005 [23] and the knol vacant niches).

References

Rosenzweig ML, Ziv Y 1999. The echo pattern of species diversity: patterns and processes. Ecography 22: 614-629.May RM 1973. Stability and complexity in model ecosystems. Princeton University Press, Princeton N.J.MacArthur RH 1965. Patterns of species diversity. Biol Rev 40 : 510-533.MacArthur RH 1969. Patterns of communities in the tropics. Biol J Linn Soc 1: 19-30.MacArthur RH 1972. Geographical Ecology. Princeton University Press, Princeton.MacArthur RH, Wilson EO 1967. An equilibrium theory of insular zoogeography. Evolution 17: 373-387.Moore HB 1972. Aspects of stress in the tropical marine envi- ronment. Adv Mar Biol 10: 217-269.Rohde K 1980. Host specificity indices of parasites and their application. Experientia 36: 1370-1371.Novotny V, Basset Y 2005. Host specificity of insect herbivores in tropical forests. Proc R Soc Lond B 272: 1083-1090.Stevens GC 1989. The latitudinal gradients in geographical range: how so many species co-exist in the tropics. Am Nat 133: 240-256.Rohde K, Heap M, Heap D 1993. Rapoport’s rule does not apply to marine teleosts and cannot explain latitudinal gradi- ents in species richness. Am Nat 142: 1-16.Rohde K 1998. Latitudinal gradients in species diversity: area matters, but how much? Oikos 82: 184-190.Rohde K 1999. Latitudinal gradients in species diversity and Rapoport ’s rule revisited: a review of recent work, and what can parasites teach us about the causes of the gradients? Ecography 22: 593-613 (invited Minireview on the occasion of the 50t h anniversary of the Nordic Ecological Society Oikos). Also published in Fenchel T ed.: Ecology 1999-and tomorrow: 73-93. Oikos Editorial Office, University Lund, Sweden.Rohde K 1996. Rapoport’s Rule is a local phenomenon and can- not explain latitudinal gradients in species diversity. Biodiv Letters 3: 10-13.Stauffer D, Rohde K 2006. Simulation of Rapoport’s rule for latitudinal species spread. Theor Biosci 125: 55-65.Beaver RA 1979. Host specificity of temperate and tropical ani- mals. Nature 281: 1139-141.Rohde K 1978. Latitudinal differences in host-specificity of marine Monogenea and Digenea. Mar Biol 47: 125-134.Rohde K 1989. Simple ecological systems, simple solutions to complex problems? Evol Theory 8: 305-350.Lappalainen J, Soininen J 2006. Latitudinal gradients in niche breadth and position – regional patterns in freshwater fish. Naturwiss 93: 246-250.Stauffer D., Schulze C. and Rohde K. 2007 Habitat width along a latitudinal gradient. Vie et Milieu (Life and Environment) 57, 181-187.Vázquez DP, Stevens RD 2004. The latitudinal gradient in niche breadth: concepts and evidence. Am Nat 164: E1-E19.Rohde K 1992. Latitudinal gradients in species diversity: the search for the primary cause. Oikos 65: 514-527.Rohde K 2005. Nonequilibrium ecology. Cambridge University Press, Cambridge.

Related knols

Competitive exclusion, vacant niches, niche restriction and segregation, effective evolutionary time, latitudinal gradients in species diversity

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