Topography is the study of land surface shapes and features, such as mountains and valleys. More broadly, topography can refer to all of the features of a landscape, both natural and artificial. But in biogeography, we focus on topographic variables like elevation (height above a reference point, often sea level), slope (the steepness of a feature), and aspect (the direction that a slope faces).
Common patterns of biodiversity can be observed with changes in elevation, including: a) decreasing species richness (i.e. the number of species) as elevation increases and b) a peak in richness at intermediate elevations, with lower richness at the base and top of the mountain. An increase in species richness with elevation is very rare.
Elevational patterns of biodiversity can help scientists understand the potential impact of climate change on species distributions. Temperature decreases with elevation: it drops 0.3-0.6 degrees Celsius per 100 meters gain in altitude. And while the relationship between elevation and precipitation is less straightforward, rainfall generally increases with altitude. Therefore, as the climate warms, some species ranges may shift toward higher, relatively cooler elevations. This could be problematic if the amount of suitable habitat available to a species shrinks or becomes more disconnected.
References:
- Bertuzzo et al. (2016) in Proceedings of the National Academy of Sciences, 113(7), 1737-1742 [link]
- Grytnes and McCain (2007) in Encyclopedia of Biodiversity.
- McCain and Grytnes (2010) in Encyclopedia of Life Sciences.
Data source: U.S. Geological Survey, The National Map, 2017, 3DEP products and services