Rapoport's rule
Encyclopedia
Rapoport’s rule is an ecological
hypothesis that states that latitudinal
ranges of plant
s and animal
s are generally smaller at lower than at high latitudes.
, who had earlier provided evidence for the phenomenon for subspecies of mammal
s (Rapoport 1975, 1982). Stevens used the rule to “explain” greater species diversity in the tropics in the sense that latitudinal gradients in species diversity
and the rule have identical exceptional data and so must have the same underlying cause. Narrower ranges in the tropics would facilitate more species to coexist. He later extended the rule to altitudinal gradients, claiming that altitudinal ranges are greatest at greater altitudes (Stevens 1992 ), and to depth gradients in the oceans (Stevens 1996 ). The rule has been the focus of intense discussion and given much impetus to exploring distributional patterns of plants and animals. Stevens’ original paper has been cited about 330 times in the scientific literature.
), which would counteract Rapoport’s rule. The tropics have far more uniform temperatures over a far wider latitudinal range (about 45 degrees) than high latitude species. As temperature is one of the most important (if not the most important) factor determining geographical distribution, wider latitudinal ranges in the tropics might therefore be expected.
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
hypothesis that states that latitudinal
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
ranges of plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s and animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s are generally smaller at lower than at high latitudes.
Background
Stevens (1989) named the rule after Eduardo H. RapoportEduardo H. Rapoport
Eduardo Hugo Rapoport is an Argentinian ecologist and emeritus professor at Universidad Nacional del Comahue. His is widely known for his fundamental work on soil biology, biological invasions, urban ecology and, in particular, for his contributions to the biogeography .Eduardo Rapoport studied at...
, who had earlier provided evidence for the phenomenon for subspecies of mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s (Rapoport 1975, 1982). Stevens used the rule to “explain” greater species diversity in the tropics in the sense that latitudinal gradients in species diversity
Latitudinal gradients in species diversity
The increase in species richness or biodiversity that occurs from the poles to the tropics, often referred to as the latitudinal diversity gradient , is one of the most widely recognized patterns in ecology. Put another way, in the present day localities at lower latitudes generally have more...
and the rule have identical exceptional data and so must have the same underlying cause. Narrower ranges in the tropics would facilitate more species to coexist. He later extended the rule to altitudinal gradients, claiming that altitudinal ranges are greatest at greater altitudes (Stevens 1992 ), and to depth gradients in the oceans (Stevens 1996 ). The rule has been the focus of intense discussion and given much impetus to exploring distributional patterns of plants and animals. Stevens’ original paper has been cited about 330 times in the scientific literature.
Generality of the rule
Support for the generality of the rule is at best equivocal. For example, marine teleost fishes have the greatest latitudinal ranges at low latitudes. In contrast, freshwater fishes do show the trend, although only above a latitude of about 40 degrees North. Some subsequent papers have found support for the rule, others, probably even more numerous, have found exceptions to it . For most groups that have been shown to follow the rule, it is restricted to or at least most distinct above latitudes of about 40-50 degrees. Rohde therefore concluded that the rule describes a local phenomenon. Computer simulations using the Chowdhury Ecosystem Model did not find support for the rule.Explanations of the rule
Rohde (1996) explained the fact that the rule is restricted to very high latitudes by effects of glaciations which have wiped out species with narrow ranges, a view also expressed by Brown (1995). Another explanation of Rapoport’s rule is the “climatic variability” or “seasonal variability hypothesis”. According to this hypothesis, seasonal variability selects for greater climatic tolerances and therefore wider latitudinal ranges (see also Fernandez and Vrba 2005).Methods used to demonstrate the rule
The methods used to demonstrate the rule have been subject to some controversy. Most commonly, authors plot means of latitudinal ranges in a particular 5o latitudinal band against latitude, although modal or median ranges have been used by some. In the original paper by Stevens, all species occurring in each band were counted, i.e., a species with a range of 50 degrees occurs in 10 or 11 bands. However, this may lead to an artificial inflation of latitudinal ranges of species occurring at high latitudes, because even a few tropical species with wide ranges will affect the means of ranges at high latitudes, whereas the opposite effect due to high latitude species extending into the tropics is negligible: species diversity is much smaller at high than low latitudes. – As an alternative method the “midpoint method” has been proposed, which avoids this problem. It counts only those species with the midpoint of their ranges in a particular latitudinal band. An additional complication in assessing Rapoport's rule for data based on field sampling is the possibility of a spurious pattern driven by a sample-size artifact. Equal sampling effort at species-rich and species-poor localities tends to underestimate range size at the richer localities relative to the poorer, when in fact range sizes might not differ among localities.Biotic and abiotic factors which act against the rule
Marine benthic invertebrates and some parasites have been shown to have smaller dispersal abilities in cold seas (Thorson's ruleThorson's rule
Thorson's rule states that benthic marine invertebrates at low latitudes tend to produce large numbers of eggs developing to pelagic and widely-dispersing larvae, whereas at high latitudes such organisms tend to produce fewer and larger lecithotrophic eggs and larger...
), which would counteract Rapoport’s rule. The tropics have far more uniform temperatures over a far wider latitudinal range (about 45 degrees) than high latitude species. As temperature is one of the most important (if not the most important) factor determining geographical distribution, wider latitudinal ranges in the tropics might therefore be expected.