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Geographic Range

In ecology, a geographic range is the total area where all members of a particular species are found during their lifetime. While it often refers to a…

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Map showing the former and current geographic range of the leopard (Panthera pardus) across Africa, the Middle East, and Asia, with regions color-coded to indicate areas where leopards are currently present, possibly present, possibly extinct, or extinct. Most extant populations are in sub-Saharan Africa, with fragmented populations in the Middle East and Asia.
In 1750 the geographic range of the leopard (Panthera pardus) spanned nearly the whole of Africa south of the Sahara, as well as parts of north and northeast Africa, and extended from Asia Minor through Central Asia and India to China and Manchuria. By 2019 the species had lost up to 75 percent of its former range. © Encyclopædia Britannica, Inc./Kenny Chmielewski

What is geographic range?

In ecology, a geographic range is the total area where all members of a particular species are found during their lifetime. While it often refers to a species’ natural distribution, it also encompasses areas where a species has been introduced by human activity or other forces.1

A species’ range is shaped by:

  • Abiotic factors: Physical barriers like mountains or oceans, and environmental conditions such as temperature and humidity.1
  • Biotic factors: Interactions with other species, including competition for food and predator avoidance.1

Ecologists use geographic range, alongside population size, to assess extinction risk. Species with small, shrinking ranges are often of greater conservation concern than those with large, stable ones. Currently, climate change is forcing many species to shift their ranges toward poles or higher elevations to find suitable habitats.1

Map of Africa showing where populations of common hippopotamuses and pygmy hippopotamus live.
Hippopotamuses were extinct in northern Africa by 1800 and south of Natal and the Transvaal by 1900. They are still fairly common in East Africa, but populations continue to decrease across the continent. This map shows the current range of common hippopotamuses and pygmy hippopotamus in Africa. Image: Encyclopædia Britannica, Inc. / Encyclopædia Britannica

How does climate change affect the movement of species?

Climate change significantly influences the movement of species by altering the environmental conditions that define their natural geographic range. As global temperatures rise, many species are forced to shift their distributions to remain within their physiological tolerance limits.21

Patterns of Movement

  • Poleward and Upward Shifts: To find cooler environments, many species of trees, shrubs, and other plants are migrating toward the poles and to higher elevations on mountain slopes.1
  • Marine Migration: Many animals, particularly those in marine environments, are actively migrating toward new habitats in response to changing climate patterns.1
  • Seasonal Shifts: Warming temperatures are altering the timing of biological processes, leading to shifts in the seasonal migration patterns of birds, fishes, and other migratory animals.2

Challenges to Migration

While some species can adapt by relocating, others face severe impediments. Human-made structures such as highways, walls, and artificial waterways can block the paths of animals attempting to reach more favorable climates. Furthermore, the rapid pace of current climate change may exceed the natural adaptive capacity of many species, potentially pushing those unable to migrate or adapt toward extinction.21

World map showing the geographic ranges of camelid species, with color-coded outlines for each: alpaca, llama, guanaco, and vicuna ranges are marked in South America; Arabian camel or dromedary in parts of Africa, the Middle East, and South Asia; domesticated Bactrian camel across Central Asia; and wild Bactrian camel in a small area of East Central Asia. Australia is shaded for introduced dromedaries.
Present-day ranges of living members of the family Camelidae. Image: Encyclopædia Britannica, Inc./Kenny Chmielewski / Encyclopædia Britannica

What are some examples of physical barriers that limit a species’ range?

Physical barriers play a critical role in defining a species’ geographic range by restricting movement and dispersal. These barriers can be categorized as follows:

  • Geographic Features: Large-scale physical obstacles such as mountain ranges, oceans, and vast stretches of desert are often impassable for many species. For example, while birds may be able to cross the English Channel, terrestrial animals like bears are effectively contained by such water barriers.14
  • Climatological Extremes: Areas with harsh environmental conditions, such as extreme temperatures or lack of moisture, act as significant boundaries that limit where a species can survive and travel.4
  • Habitat Discontinuity: For species specialized to specific environments, the absence of suitable habitat acts as a barrier. For instance, air-breathing animals are generally restricted from large marine or freshwater environments, just as most fishes are limited to aquatic zones and cannot traverse terrestrial landscapes.1
  • Human-Made Structures: Infrastructure such as highways, walls, and artificial waterways can fragment habitats and prevent animals from reaching favorable climates or breeding grounds.14

Why do scientists track geographic range to determine extinction risk?

Scientists track geographic range as a primary indicator of extinction risk because it provides essential data on a species’ vulnerability to environmental change. The size and stability of this range are key factors in assessing conservation status, as established by the International Union for Conservation of Nature (IUCN).17

Why Range Size Matters

  • Vulnerability: Species with small geographic ranges are inherently more vulnerable to extinction than those with large, widespread ranges. It is significantly easier for localized threats to destroy a small habitat than a vast one.89
  • Climate Sensitivity: By monitoring shifts in range, scientists can determine if a species is successfully adapting to climate change. If a species’ “climate envelope”—the range of conditions it requires to survive—shrinks or disappears entirely, the risk of extinction increases dramatically.19
  • Predictive Assessment: The IUCN uses range size as one of five quantitative criteria to classify species status. Species found only in tiny, restricted areas or those experiencing rapid, precipitous declines in their spatial distribution are viewed as high-priority concerns.17

Sources

  1. geographic range — Encyclopædia Britannica
  2. Global warming - Environmental consequences of global warming — Encyclopædia Britannica
  3. Taiga - Origin — Encyclopædia Britannica
  4. dispersion — Encyclopædia Britannica
  5. Biosphere - Water currents — Encyclopædia Britannica
  6. Locomotion - Principles — Encyclopædia Britannica
  7. conservation - Range size — Encyclopædia Britannica
  8. IUCN Red List of Threatened Species — Encyclopædia Britannica
  9. conservation - Global warming — Encyclopædia Britannica

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