Why isolated habitats like mountain peaks and city parks follow the same ecological rules
In short: The theory of island biogeography suggests that whether you are looking at a remote oceanic island or a fragmented forest, the number of species living there is a predictable balance between immigration and extinction. This framework explains how isolation and area shape life, from ancient rainforests to modern national parks.
Developed in the 1960s by Robert H. MacArthur and E. O. Wilson, the theory of island biogeography posits that species richness on an island reaches an equilibrium determined by the rate at which new species arrive and existing ones go extinct. While originally designed for oceanic islands, the concept applies to any 'island-like system'—habitat patches surrounded by unsuitable terrain, such as mountain peaks, oases, or even urban parks. The distance from a source of colonists dictates immigration rates, while the size of the area influences extinction risk; larger islands generally support more species because they offer more resources and habitat heterogeneity, which buffers against chance events.
The theory has profound implications for conservation biology. As human development fragments landscapes, protected areas effectively become islands. Ecologists have debated the 'SLOSS'—single large or several small—reserve design strategy, a conflict described by David Quammen as a form of trench warfare. While Jared Diamond argued that one large reserve is superior for maintaining biodiversity, others like Dan Simberloff cautioned that habitat diversity is often as critical as total area. The fear is that these 'islands' will suffer from ecosystem decay, losing species as they relax toward a new, lower equilibrium.
Beyond static geography, the theory helps explain evolutionary bursts. For instance, the Carboniferous rainforest collapse 300 million years ago fragmented forests, forcing reptiles to adapt to new niches and driving rapid diversification. Today, researchers use these principles to design wildlife corridors, though these tools are double-edged; while they increase connectivity and support more species, they can also facilitate the spread of disease. By studying how species navigate these isolated patches, scientists gain a clearer picture of how life persists in an increasingly fragmented world.
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Sources
- Summary by Intellect · source: Insular biogeography
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