Habitat fragmentation

Habitat fragmentation is a process by which habitats, or the natural living spaces of animals and plants, become divided. Traditionally, habitats are continuous and include few borders or obstacles to the natural motion and development of living things. However, some natural processes, along with a wide range of human activities, have caused these huge habitats to be split into smaller parts, or patches. Patches may be surrounded by dangerous obstacles and left disconnected or completely isolated. This fragmentation of the original habitat into patches can have an array of mostly negative, sometimes disastrous, effects on the animals and plants that live there. Fortunately, humans have learned of these problems and some scientists have devised ways to alleviate some danger.

Background

Millions of kinds of animals and plants inhabit Earth. Each of these living things needs a place to live, or a habitat. A habitat is an area of an environment that forms an ecology, or a system of interrelated living things. Living things are usually born into a particular habitat that is well-suited to their needs. Plants or animals that move to new habitats often finds ways to adapt to the particular circumstances of the ecosystem there. These organisms rely on their habitats for most or all of their basic needs of life. A proper habitat provides a living thing with food, water, shelter, protection from predators and other dangers, and access to related organisms for mating.

Habitats range greatly in location, land and water features, and climate. They can be extremely cold or extremely warm, very wet or completely arid. Living things in a habitat usually find ways to survive in their unique conditions. Some of their adaptations are remarkable. For example, monkeys living in some rainforests have highly mobile tails that serve like extra hands to help them climb. Plants and animals in deserts have found ingenious ways to gather and store moisture. These sorts of adaptations are crucial for life and allow living things to inhabit almost all regions of Earth. However, adapting to new habitats can be a difficult and dangerous process that takes a long time, generations to millennia, to fully manifest.

Before large-scale human development, living things spread throughout much of the planet into giant habitats with few borders. Habitats flowed naturally into each other, creating an ongoing continuum of ecosystems. Ecosystems were finely tuned, with all parts contributing to their overall functioning. This situation created an enormous amount of biodiversity, or variety of life forms from the microscopic to the enormous. In general, most living things had access to ample food, water, shelter, mating opportunities, and protection from invasive species and disease.

Human development, beginning with the establishment of small villages and farms and continuing through the mass deforestation and construction projects of the modern era, led to a vast array of advantages for people. However, this development also forever altered the natural flow of ecosystems and animal and plant habitats. Almost every human creation, from a sidewalk to a skyscraper, interrupts natural land and environmental processes. In many cases, development has destroyed entire ecosystems, leading to the extinction or evacuation of their native organisms. In other instances, human activity has led to other alterations to habitats that may have equally disruptive results. One such alteration is known as habitat fragmentation.

Overview

Habitats are systems of living areas and resources necessary for the flourishing of animals and plants. In habitat fragmentation, a large, continuous habitat is broken into smaller distinct pieces, known as patches. These patches are separated from one another and often isolated. Patches no longer feature the same qualities as the original continuous habitat, and some become significantly different—usually in a negative way that disrupts the lives of their animals and plants. Habitat fragmentation is usually the result of human activities such as land conversion or the construction of roads, fences, cities, or other structures that break up the land.

For example, building a highway through a forest may destroy tens of thousands of trees, disrupt the flow of water, and bring in pollution. Just as importantly, it fragments the habitats of creatures that live in the forest. Animals that once roamed freely across many miles now have to cross busy roads and come in contact with humans, which can lead to great dangers for both, to access the rest of the original habitat. The highway leads to a so-called edge effect. The fragmented habitat, in this case divided by the highway, develops edges along both sides of the roadway. These edges are dangerous for animals and plants, and thus do not encourage healthy living or growth of species. They also inhibit the free motion and spread of living things, compressing them into a small patch, which creates a host of problems.

With the ease of modern transportation, and ready access to many needed materials, humans may have trouble understanding the critical effects of habitat fragmentation. An analogy from human history might be the Berlin Wall, a guarded wall built in Germany following World War II. The wall separated the German capital into two zones, West Berlin and East Berlin. Democratic forces occupied West Berlin while communist forces controlled East Berlin. Residents who once regularly crossed the city to go to work, visit family, travel and recreate, or buy or sell goods were suddenly stopped. Most people were required to stay in a single zone. The Berlin Wall separated neighbors, families, and friends, and kept people from easily visiting the places important to them. It made living in Berlin very different and, in many cases, much more difficult.

Habitats can become fragmented for a wide variety of reasons. Many of these reasons are not directly caused by humans. Rather, they are the result of natural processes such as fires, climatic changes, or volcanic eruptions. Natural forest fires might destroy large swathes of habitat, leaving zones of empty burned land between previously flowing, continuous habitats. Volcanoes might have a similar effect. These destroyed zones create similar dangers, obstacles, and edge effects for animals and plants. Climatic changes, such as the droughts or floods causing rivers to change course, can also dramatically shift the nature of habitats and create fragmentation.

Most often in modern times, however, fragmentation occurs due to human activities. One of the first to impact the environment was rural development, or the establishment of farms and livestock grazing areas. Farming is more a human invention than a regular feature of nature, and converting natural habitats into farms, whether for crops or animals, seriously disrupts traditional ecosystems. Similarly, urban development, or the creation of towns and cities, is also extremely disruptive. A large percentage of new housing and other buildings are constructed on previously undisturbed natural land. Entire ancient ecosystems have been completely eradicated for the building of cities and their many elements, such as highways, railroads, and airports. Edge effects are many and serious, with animals and plants in surrounding habitats both facing dangers, and causing dangers, when they attempt to enter the developed areas.

Other major causes of habitat fragmentation are logging and deforestation, in which potentially massive amounts of trees are cut either for valuable timber or to clear land for development. Animals and plants that once lived there are now pushed into smaller areas separated by obstacles and that may lack food and shelter. Water reservoirs as well as oil and gas exploration projects can also create barriers to animal and plant species and contribute to habitat fragmentation.

The effects of habitat fragmentation are diverse and extensive. Many effects relate to the restricted size of the patches. Living things that once roamed or spread freely through a wide area are confined to smaller areas. Any benefits gained from greater motion, such as access to more food or water, availability of mating opportunities, or improved living areas, are removed or made much more difficult to attain. Other effects are related to the edge areas between the habitat patches. These areas are seldom conducive to healthy living. They may contain dangers and obstacles ranging from a lack of food sources to speeding vehicles and high fences. They also tend to be less forested and more exposed to sun, wind, and rain, thus providing minimal shelter. Additionally, these edge areas may promote the spread of invasive species into an area that can further upset a delicate ecosystem. Finally, patches left in isolation will likely experience their own serious problems. Not only are their occupants unable to reach new lands or resources, but they also have limited mating opportunities. Small populations living in confined areas often results in inbreeding, which can bring a host of genetic problems to future generations.

In the twenty-first century, the problems caused by habitat fragmentation are well-known, and many scientists and other experts are searching for ways to reduce fragmentation or at least reduce its harmful effects on wildlife. Laws and legal procedures, such as zoning, land-acquisition deals, and easements, can help to preserve ecosystems from alteration or development, thus preserving more natural habitats. Some ingenious inventions have also provided some alleviation of fragmentation concerns. Among these is the wildlife corridor, a passageway that connects related habitat areas. One promising type of corridor is a wildlife crossing, a footbridge meant to allow animals to walk safely across highways or other normally dangerous obstacles.

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