Elevational Gradients in Species Richness


The abiotic and biotic gradients on mountains have enormous potential to improve our understanding of species distributions, species richness patterns and conservation. Here we describe how abiotic factors change with elevation, how flora and fauna respond to these changes and how elevational species richness patterns have been studied to uncover drivers of biodiversity. There are four main trends in elevational species richness: decreasing richness with increasing elevation, plateaus in richness across low elevations then decreasing with or without a mid‐elevation peak and a unimodal pattern with a mid‐elevational peak. We discuss the history of elevational richness studies and overview the various hypotheses thought to be important in richness trends, including climatic, spatial, biotic and evolutionary factors.

Key Concepts:

  • Elevational gradients exhibit complex variation in abiotic conditions over short distances.

  • Patterns of elevational species richness follow four common patterns: mid‐elevation peaks, decreasing, low‐elevation plateaus and low plateaus with mid‐elevation peaks.

  • Patterns of elevational species richness vary between taxonomic groups.

  • A combination of water availability and temperature is often found to be related to elevational species richness patterns.

  • No consistent support is found for the importance of area or mid‐domain effects for elevational species richness patterns.

  • Support for the various mechanisms underlying elevational richness patterns tends to be related to the ecology and evolutionary history of the taxonomic group of interest.

  • Elevational gradients are valuable in our task to disentangle the causes behind broad‐scale patterns in biodiversity, and in our quest to understand threats to biodiversity with climatic change.

Keywords: climate; biotic interactions; diversity; elevation; environmental gradient; mountains; precipitation; productivity; species–area relationship; temperature

Figure 1.

Two examples of elevational gradients: a tropical mountain (left column; e.g., Venezuela) and a temperate mountain (right column; e.g., SW USA). (a) Temperature generally decreases linearly with elevation. Both mountains have similar wet adiabatic lapse rates of 5.68 and 5.24°Celsius per 100 m, respectively, but with much cooler average annual temperatures at the higher latitudes. (b) Precipitation varies greatly along elevational gradients. The tropical mountain has overall wetter conditions with peaks in precipitation at the lowest and mid‐elevations, whereas the arid‐based, temperate mountain shows the typical pattern of increasing precipitation with elevation. The combination of temperature and precipitation values result in habitat zonation with elevation. The tropical gradient changes from lowland tropical rainforest to premontane rainforest to montane rainforest to cloud forest, and finally elfin forest and alpine grasslands. The arid, high latitude gradient changes from desert scrub or grassland to chaparral to pinyon‐pine forests to mixed hardwood‐pine forests to ponderosa pine forests, and finally fir forests and alpine grasslands.

Figure 2.

The percentage of the four main elevational richness patterns demonstrated on mountain gradients across the globe, including decreasing, low‐elevation plateau, (LPMP) and midpeak for nonflying small mammals (McCain, ), bats (McCain, ), birds (McCain, ), reptiles (McCain, ) and plants (Rahbek, Figure 3f3). Preliminary results for salamanders and frogs are very similar to small mammals and birds respectively. A few studies of plants and frogs have found increasing richness with increasing elevation, but these appear to be quite rare.

Figure 3.

Studies of elevational species richness can be strongly influenced by methodological issues of scale, sampling and disturbance; here we show several examples. The scale of sampling falls into two broad categories: local transect studies which are sampled ideally at equal intervals from the base to the peak of the mountain usually within a 1–2 years (a1); and regional compilations of sampling from many researchers, slopes and years (a2). The regional compilations can be heavily influenced by the greater area at the base of mountains, thus potentially leading to more greater estimated richness at lower elevations. The distribution of sampling effort can influence the estimates of species richness by not spreading the effort evenly over the gradient (b1), which can lead to higher richness in areas of high sampling and low richness in areas of low sampling (e.g., compare a1 and b1). If sampling is only distributed over a portion of the gradient (b2), this truncation can lead to the identification of a very different pattern of species richness (e.g., compare a1 and b2). Reduced sampling at the highest elevations tends to have less influence on species richness estimates, since diversity is generally reduced at these elevations (b3). Habitat disturbance, particularly widespread and concentrated within a zone of elevation (e.g., lowlands, c2) can lead to reduced estimates of species richness in disturbed areas (e.g., compare c1 and c2).



Barry RG (2008) Mountain Weather and Climate. Cambridge, UK: Cambridge University Press.

Brehm G, Suessenbach D and Fiedler K (2003) Unique elevational diversity patterns of geometrid moths in an Andean montane rainforest. Ecography 26: 456–466.

Brown JH (1971) Mammals on mountaintops: nonequilibrium insular biogeography. American Naturalist 105: 467–478.

Brown JH (2001) Mammals on mountainsides: elevational patterns of diversity. Global Ecology and Biogeography 10: 101–109.

Brown JH, Gillooly JF, Allen AP et al. (2004) Toward a metabolic theory of ecology. Ecology 85: 1771–1789.

Brown JH and Lomolino MV (1998) Biogeography, 2nd edn. Sunderland, MA: Sinauer Associates, Inc.

Bryant JA, Lamanna C, Morlon H et al. (2008) Microbes on mountainsides: contrasting elevational patterns of bacterial and plant diversity. Proceedings of the National Academy of Sciences of the USA 105: 11505–11511.

Colwell RK, Rahbek C and Gotelli NJ (2004) The mid‐domain effect and species richness patterns: what we have learned so far? American Naturalist 163: E1–E23.

Evans KL, Warren PH and Gaston KJ (2005) Species–energy relationships at the macroecological scale: a review of the mechanisms. Biological Reviews 80: 1–25.

Gaston KJ (2000) Global patterns in biodiversity. Nature 405: 220–227.

Gotelli NJ and Colwell RK (2001) Quantifying biodiversity: procedures and pitfalls in the measurement and comparison of species richness. Ecology Letters 4: 379–391.

Grinnell J (1917) The niche‐relationships of the California thrasher. Auk 34: 427–433.

Grinnell J, Dixon J and Linsdale JM (1930) Vertebrate Natural History of a Section of Northern California through the Lassen Peak Region. Berkeley, CA: University of California Press.

Grinnell J and Storer TI (1924) Animal Life in the Yosemite. Berkeley, CA: University of California Press.

Grytnes JA (2003) Species‐richness patterns of vascular plants along seven altitudinal transects in Norway. Ecography 26: 291–300.

Grytnes JA, Heegaard E and Ihlen PG (2006) Species richness of vascular plants, bryophytes, and lichens along an altitudinal gradient in western Norway. Acta Oecologica 29: 241–246.

Grytnes JA and Romdal TS (2008) Using museum collections to estimate diversity patterns along geographical gradients. Folia Geobotanica 43: 357–359.

Grytnes JA and Vetaas OR (2002) Species richness and altitude: a comparison between null models and interpolated plant species richness along the Himalayan altitudinal gradient, Nepal. American Naturalist 159: 294–304.

Hawkins BA, Field R, Cornell HV et al. (2003) Energy, water, and broad‐scale geographic patterns of species richness. Ecology 84: 3105–3117.

Heaney LR (2001) Small mammal diversity along elevational gradients in the Philippines: an assessment of patterns and hypotheses. Global Ecology and Biogeography 10: 15–39.

Herzog SK, Kessler M and Bach K (2005) The elevational gradient in Andean bird species richness at the local scale: a foothill peak and a high‐elevation plateau. Ecography 28: 209–222.

Kessler M, Herzog SK, Fjeldsa J et al. (2001) Species richness and endemism of plant and bird communities along two gradients of elevation, humidity and land use in the Bolivian Andes. Diversity and Distributions 7: 61–77.

Lomolino MV (2001) Elevation gradients of species–density: historical and prospective views. Global Ecology and Biogeography 10: 3–13.

Martin PS (1958) A biogeography of reptiles and amphibians in the Gomez Farias region. Tamaulipas, Mexico. Miscellaneous Publications of the Museum of Zoology, University of Michigan 101: 1–102.

McCain CM (2004) The mid‐domain effect applied to elevational gradients: species richness of small mammals in Costa Rica. Journal of Biogeography 31: 19–31.

McCain CM (2005) Elevational gradients in diversity of small mammals. Ecology 86: 366–372.

McCain CM (2007a) Area and mammalian elevational diversity. Ecology 88: 76–86.

McCain CM (2007b) Could temperature and water availability drive elevational species richness? A global case study for bats. Global Ecology and Biogeography 16: 1–13.

McCain CM (2009) Global analysis of bird elevational diversity. Global Ecology and Biogeography 18: 346–360.

McCain CM (2010) Global analysis of reptile elevational diversity. Global Ecology and Biogeography 19: 541–553.

McCain CM and Sanders NJ (2010) Metabolic theory and elevational diversity of vertebrate ectotherms. Ecology 91: 601–609.

Merriam CH and Stejneger L (1890) Results of a biological survey of the San Francisco Mountain region and desert of the Little Colorado, Arizona. North American Fauna 3: 1–136.

Mittelbach GG, Steiner CF, Scheiner SM et al. (2001) What is the observed relationship between species richness and productivity? Ecology 82: 2381–2396.

Nogués‐Bravo D, Araújo MB, Romdal TS et al. (2008) Scale effects and human impact on the elevational species richness gradients. Nature 453: 216–220.

O'Brien EM (1993) Climatic gradients in woody plant species richness: towards an explanation based on an analysis of southern Africa's woody flora. Journal of Biogeography 20: 181–198.

Parmesan C (2006) Ecological and evolutionary responses to recent climate change. Annual Review of Ecology Evolution and Systematics 37: 637–669.

Pianka ER (1966) Latitudinal gradients in species diversity: a review of concepts. American Naturalist 100: 33–46.

Rahbek C (1995) The elevational gradient of species richness: a uniform pattern? Ecography 18: 200–205.

Rahbek C (1997) The relationship among area, elevation, and regional species richness in Neotropical birds. American Naturalist 149: 875–902.

Rahbek C (2005) The role of spatial scale and the perception of large‐scale species‐richness patterns. Ecology Letters 8: 224–239.

Romdal TS and Grytnes JA (2007) An indirect area effect on elevational species richness patterns. Ecography 30: 440–448.

Rosenzweig ML (1995) Species Diversity in Space and Time. Cambridge, UK: Cambridge University Press.

Sanders NJ (2002) Elevational gradients in ant species richness: area, geometry, and Rapoport's rule. Ecography 25: 25–32.

Srivastava DS and Lawton JH (1998) Why more productive sites have more species: an experimental test of theory using tree‐hole communities. American Naturalist 152: 510–529.

Terborgh J (1977) Bird species diversity on an Andean elevational gradient. Ecology 58: 1007–1019.

Terborgh J (1985) The role of ecotones in the distribution of Andean birds. Ecology 66: 1237–1246.

Terborgh J and Weske JS (1975) The role of competition in the distribution of Andean birds. Ecology 56: 562–576.

Wake DB, Papenfuss TJ and Lynch JF (1992) Distribution of salamanders along elevational transects in Mexico and Guatamala. Tulane Studies in Zoology & Botany 1(suppl): 303–319.

Whittaker RH (1952) A study of summer foliage insect communities in the Great Smoky Mountains. Ecological Monographs 22: 1–44.

Whittaker RH (1960) Vegetation of the Siskiyou Mountains, Oregon and California. Ecological Monographs 30: 279–338.

Wiens JJ and Donoghue MJ (2004) Historical biogeography, ecology and species richness. Trends in Ecology & Evolution 19: 639–644.

Wiens JJ, Parra‐Olea G and Wake DB (2007) Phylogenetic history underlies elevational biodiversity patterns in tropical salamanders. Proceedings of the Royal Society of London. Series B 274: 919–928.

Further Reading

Chen IC, Shiu HJ, Benedick S et al. (2009) Elevation increases in moth assemblages over 42 years on a tropical mountain. Proceedings of the National Academy of Sciences of the USA 106: 1479–1483.

Janzen DH (1967) Why mountain passes are higher in the tropics. American Naturalist 101: 233–249.

Moritz C, Patton JL, Conroy CJ et al. (2008) Impact of a century of climate change on small‐mammal communities in Yosemite National Park, USA. Science 322: 261–264.

Watkins JE Jr, Cardelus C, Colwell RK et al. (2006) Species richness and distribution of ferns along an elevational gradient in Costa Rica. American Journal of Botany 93: 73–83.

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McCain, Christy M, and Grytnes, John‐Arvid(Sep 2010) Elevational Gradients in Species Richness. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0022548]