Why are more species often found in larger areas than in smaller areas?

In biology, the observation that larger areas typically support more species is a fundamental principle often explained by the theory of island biogeography.1

This relationship occurs primarily because larger areas provide a greater diversity of habitats, which allows for a wider range of species to find the specific resources they need to survive. As researchers survey larger geographic regions, they inherently include more distinct habitats and environmental conditions, which increases the total species richness (the count of unique species) recorded.23

Furthermore, the theory of island biogeography posits that the number of species in an area is proportional to its size because larger areas generally experience lower extinction rates and higher rates of colonization. In smaller, isolated areas, populations are more susceptible to extinction due to limited resources and the loss of genetic variation, whereas larger areas offer more stable environments that can sustain more complex and diverse biological communities.143