Habitat can be defined as the environment in which a particular species is most often found in nature. It includes all of the physical factors a species needs in order to live, including adequate food, water, shelter, sunlight, temperature, and resources required to evade predators. Ideally, it is also big enough to deter the spread of disease and support a diverse genetic base for healthy reproduction among a population.
Simply put, a species will decline and eventually become extinct without sufficient habitat. Because habitat is an intricate network of living and non-living factors, the destruction of a single habitat affects many species of animals, plants, insects, and other organisms as well as the biodiversity of adjacent habitats.
Naturalist John Muir described this phenomenon of interdependence by saying, "When we try to pick anything out by itself, we find it hitched to everything else in the universe."
Causes of Habitat Loss
Habitat loss can happen as the result of natural causes such as climate change, volcanoes, earthquakes, and other geological changes that either destroy large areas of land very quickly or gradually alter the environment to the extent that current inhabitants can no longer survive.
Human activities cause habitat loss on a continuous basis. Natural resource extraction (logging, mining, and fishing), urban development, large-scale commercial agriculture, pollution, and the introduction of invasive species aggressively deplete, fragment, and alter natural habitats.
Habitat Loss and Endangered Species
According to the World Wildlife Fund, habitat loss poses the greatest threat to species and biodiversity, affecting 85 percent of all species classified by the IUCN's Red List as threatened and endangered.
Intact habitat is particularly crucial to endemic species which often have a limited range where their populations can survive. When an endemic species' habitat is destroyed, it is less likely to recover than a species with more generalized habitat requirements, so extinction becomes an imminent threat.
How Much Habitat Does a Species Need?
The size of contiguous habitat required for survival varies widely among species, but size invariably limits the number of organisms able to live in any given habitat. No matter what the species, smaller populations are more vulnerable to extinction via genetic bottlenecking. Not only are fewer individuals less likely to survive in the event of environmental catastrophe, there is also less genetic diversity in a smaller population, decreasing the chances of disease resistance and increasing reproductive failure as a result of inbreeding.
Modeling tools used to determine the amount of habitat needed to sustain a population or species tend to equate viability with a habitat's contiguous size, favoring a few large areas of habitat over many small areas. Weighing the benefits of "single large or several small" habitats became known as the SLOSS debate among ecologists in the 1970s, and while there may still be some controversy concerning the needs of particular species, it is commonly accepted that large reserves of habitat are more beneficial to any species that requires an extensive range to buffer human disturbance and also for activities such as food acquisition and migration.
Currently, habitat conservation is largely based on threatened and endangered species' occupation. If a habitat is determined to support a species of concern, it becomes the focus of preservation and restoration efforts.
Worldwide, certain habitats and ecosystems that have been determined to warrant conservation focus are called biodiversity hotspots. These are areas that support endemic and at-risk species, and they harbor a significant reservoir of biodiversity that is threatened by human encroachment.
Conservation International has identified 34 international biodiversity hotspots whose combined area covers only 2.3 percent of the Earth's land surface. Each hotspot faces extreme threats and has already lost at least 70 percent of its original natural vegetation. Over 50 percent of the world's plant species and 42 percent of all terrestrial vertebrate species are endemic to these hotspots. Conservation International is leading planning processes and initiatives to protect biodiversity hotspots.