Britannica
Sources used in this answer
- biogeographic region - Components of species diversity: species richness and relative abundance
- species richness
- community ecology - Biogeographic aspects of diversity
- community ecology - Community equilibrium and species diversity
- conservation - Predictions of extinctions based on habitat loss
- conservation - Range size
- biogeography
Why do larger areas usually contain more species than smaller areas?
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ecology
Mourning doves (Zenaida macroura) on their nest protected within the prickly branches of a cactus in the Sonoran Desert, Arizona, U.S.
In ecology, the observation that larger areas typically contain more species than smaller ones is known as the species-to-area relationship. This pattern is remarkably consistent across a wide range of plants and animals and is a fundamental concept in biogeography.12
Several factors explain why this relationship exists:
- Habitat Diversity: Larger areas are more likely to encompass a wider variety of habitats, which can support a greater diversity of species with different environmental requirements.34
- Colonization and Extinction: According to the theory of island biogeography, the number of species in an area is determined by a dynamic equilibrium between immigration and extinction rates. Larger areas generally provide more resources and space, which can support larger populations, thereby reducing the probability of local extinction.21
- Sampling Effects: As researchers survey larger areas, they naturally encounter more species and a broader range of habitats, which mathematically increases the observed species richness.4
This relationship is critical for conservation, as it helps scientists predict how habitat fragmentation and loss—which effectively shrink the available area for species—will lead to declines in biodiversity.1