Refuge (ecology)

A refuge is a concept in ecology, in which an organism obtains protection from predation by hiding in an area where it is inaccessible or cannot easily be found. Due to population dynamics, when refuges are available, populations of both predators and prey are significantly higher, and significantly more species can be supported in an area. Coral reefs provide the most dramatic demonstration of the ecological effects of refuges. Refuge-rich coral reefs contain a full 25% of ocean species, even though such reefs make up just 0.1% of the ocean's surface area. On the other hand, in the sunlight-illuminated open ocean just offshore, there are no places to hide from predation, and both diversity and quantities of organisms per unit area is much lower. Additionally, coral reefs enhance non-local diversity by providing spawning grounds and a refuge habitat for juvenile fishes that will live in the open ocean as adults. Rainforest species diversity is also in large part the result of diverse and numerous physical refuges. Prey animals typically maintain larger populations when they have a place to physically hide from predation. For example, rats maintain a higher population density if the rats have refuges such as tall grass, allowing them to hide from predators such as owls and cats. Sea birds often have nesting colonies on islands but not on nearby, apparently suitable, mainland sites. The islands lack the mammalian predators found on the mainland, such as cats, dogs, and rats, all of which typically decimate seabird colonies. Semiaquatic animals, e.g. mouse-deer, may use bodies of water as refuges. Game reserves have been deliberately used to enhance the total population of large game, e.g. deer, for at least a century. Limiting hunting by humans in a relatively small area allows the overall population to rebound. The same principle applies to fisheries, which produce more fish when there is a nearby refuge from human predation in the form of a nature reserve, resulting in higher catches than if the whole area was open to fishing.