Vol. 5 Issue 4, Fall 2000
By Leslie McCasker
Habitat is what plants and animals call home – where it finds what it needs to survive. Suitable habitat for a particular plant or animal consists of various elements. These elements may be tied to temperature, water, soil, sunlight, sources of food, refuge from predators, places to reproduce, and other living and non-living factors. Good habitat offers a tolerable climate, varied terrain, space to roam, a dependable supply of food and water, and places to play, hide and rest, and raise young. In short, habitat is everything that an animal needs everyday.
An animal’s needs may change throughout it’s life, from season-to-season, or even within the course of a day. An animal may need more than one habitat to fulfill all of its needs, just as you may live in one place, work in another town, and shop in still another.
Animals are driven by their desire to eat, avoid being eaten, and pass on their genes. Through millions of years of evolution, animals have developed traits that help them survive and become efficient in their quests. Some of the physical and behavioral characteristics (adaptations) that connect animals with their habitat, allow them to make the most of their environment. Animals naturally gravitate toward places where their adaptations provide them with the greatest benefits. In these preferred habitats, they have a distinct advantage over the animals that are not “designed” to compete there.
You might be able to guess where an animal lives based on its physical characteristics – their fur/feather consistency, body size and colors, eyes, ears, mouth/beak design, and even the kind of feet and toes they have. For example, bullfrogs, ducks and beavers have toes connected by webbing designed for life in the water; squirrels, woodpeckers and raccoons have sharp, gripping claws for climbing trees; and the hooves of deer are blunt for pounding the ground.
Each species develops and perfects these special adaptations through the process of natural selection, commonly known as “survival-of-the-fittest.” Better-adapted individuals of a species tend to live longer and produce more young than poorly adapted ones. As their genes are passed from one generation to another, and the species as a whole begins to reflect its affinity for the habitat.
For some species, this affinity is so strong that a single habitat fulfills all of its needs – it never needs to wander to another habitat. In many cases, it may be so specialized that it can’t survive anywhere else. Many of our endangered species fall into this specialized group. Their very existence depends on the health of one particular kind of habitat. Yet for other species, habitat flexibility is their key to survival. The ability to adapt to new and different habitats allows many species to thrive and develop large populations.
How does an animal know whether a particular area would be a good place to live, raise a family or find food? For some, its as simple as returning to where they were raised. While others must rely on instinct to guide them. They must evaluate the features of the area when choosing a habitat. Are the plants the right size and shape for nesting, feeding, resting, and singing? How many vertical layers are there? Is the mid-story open enough to catch prey? Are the under-story and ground layers sparse or dense?
How the vegetation grows may be more important than the actual type of plant. Each type of vegetation represents a vertical forest layer: upper canopy, lower canopy, under-story, trunk, shrub, herb and below-ground. Each layer provides places for nesting, hiding and feeding that differs from the layer above or below it. Different layers of the forest canopy have different temperatures, humidity levels, insect populations, and food sources. There are also different horizontal layers that entice animals to live in a particular habitat. For example, a river contains riffles, deep pools, and slow stretches that all have different combinations of food, space and cover, and cater to different species. The more layers there are in a habitat, the more opportunities there are for a species. Putting it in simple terms – a more dense and tangled forest has a greater role in the ecosystem than does a simple, manicured lawn.
In addition to the habitat layers, there are different types of habitat zones/ecosystems. There are three major types of ecosystems: saltwater, freshwater, and terrestrial. Within each of these ecosystems are more specialized habitats including: sandy beach and dune; salt marsh; mangrove forest; lake and pond; river and stream; marshland; everglades; meadow; swamp; bog; floodplain; field; and forest. Each of these specialized habitats supports a variety of wildlife and plant life.
There are transition areas between different habitat zones, often referred to as edges. This edge between the two areas is one of the most heavily trafficked places and one of the best places for watching wildlife – you are likely to see residents of both forest and field, as well as those who live in the in-between area. On the edge, wildlife can conveniently commute from one habitat to another to satisfy their needs.
The edge is also a stopover place when moving from the dense cover of forest to the sparse cover of the field. Cautious wildlife pause here to get the lay-of-the-land before they expose themselves. In turn, field dwellers often resort to the thickets for cover when predators threaten them. If you combine the visitors from both the field and the forest to the residents of the edge, you can see why edges have a greater variety then other communities.
Once animals have settled into suitable habitat, what happens when it changes? Natural communities are in a constant state of flux, changing and transforming in a process called succession. In succession, communities succeed one another, each one better adapted to the conditions of the site.
Imagine the succession from bare ground to dark forest. Annual weeds grow from seeds and make the soil fertile enough for grasses and perennial plants to get started. These stabilize and enrich the soil so that shrubs can break through. The shrubs shade the grasses and make room for tree seedlings, which finally shade out the shrubs. Even these sun-loving trees are not fated to remain for long. As they mature, an under-story of shade-tolerant trees rises and eventually overtops the pioneers. Although this “ultimate” community is more stable than most, it is far from static. One lightening strike can start the process all over again. Each plant community has animal communities that thrive and decline along with it. Any ousted species survive by moving to another habitat that meets its needs – if there is one.
When humans alter habitats, it doesn’t signal the beginning of a natural change. By pouring concrete, dumping wastes, introducing exotic pests, draining wetlands, or spaying chemicals, we often trigger an irreversible change—a possible journey toward extinction. If the change affects a large area, there may be nowhere for sensitive species to move. Other habitats may already be occupied or may lack the elements critical for survival. Crowding animals into less-than-ideal habitats diminishes their populations, until, on a local level at a minimum, they may become extinct.
When we lose a species, we also lose the free service that it performs in the ecosystem. Perhaps the lost species was a soil burrower, creating tunnels that rodents, toads, or insects use for shelter. Or perhaps by burying its food, it inadvertently “planted” acorns that grew into large oaks. If it was a predator, its prey may suddenly explode in number, stripping large swathes of food plants from the area, and forcing other species to seek new habitats.
It should come as no surprise to anyone that virtually every corner of America has experienced some decline in wildlife. While the plights of such key species as the elephant, bald eagle, and whale receive the lion’s share of media attention (and correspondent conservation dollars), everyday insects, birds, reptiles, amphibians, and small mammals dwindle in number in relative obscurity. Native songbirds, bats, butterflies, turtles, frogs, raccoons, and snakes are only a few of the species that are making fewer appearances in our backyards.
When extinction occurs on a worldwide scale, the loss is profound. Species are the unique result of millions of years of evolution. Once this genetically improved species is lost, it can never be recreated. On a purely selfish level, we humans have much to lose when a species fades into extinction. Nearly half of our medicines come from plants and animals, yet only 2 percent of all species have been tested for their usefulness. If extinction rates continue as they have, more than one-fifth of the species on earth today will be gone by the end of the century.
The real threat is the tear in the intricate fabric of the worldwide ecosystem. A tear that starts out small tends to enlarge, and soon the fabric no longer covers or insulates as well as it once did. By weakening the ecosystem, we sabotage its power to heal, nurture, support, and replenish all life, including ours.
It is very important that we distinguish between natural extinction, which has been occurring for millions of years, and the relatively recent phenomena of human-caused extinctions. In the past, as one species succumbed to the slowly changing environment, a better-evolved species takes its place. This changing of the guard took place gradually, and for the most part, there were more new species coming in to replace those that were going extinct. The result was a slowly growing pool of organisms.
Today, as we exploit organisms and whittle away at their habitats, we are actually allowing species to go extinct more rapidly. At the same time, we are interfering with nature’s ability to produce new species. In the early 1990’s conservative estimates said that we were losing one species a day, and that the rate may increase to one an hour by the year 2000. If those estimates are correct, new species cannot possibly evolve fast enough to keep the ecosystem in balance.