0.18 First order effects  (Page 5/5)

When the rate of exploitation or utilization of a species exceeds its capacity to maintain a viable population, over-harvesting results. Living resources such as forests and wildlife are usually considered renewable resources. However, they can become non-renewable if over-harvested. Over-harvesting and habitat loss often occur together, because the removal of an organism from its environment can have a detrimental impact on the environment itself.

Humans have historically exploited plant and animal species to maximize short-term benefits, usually at the expense of being able to sustain the species in the long-term. A classic example of over-harvesting involves the passenger pigeon. It was once thought to be the most populous bird on earth, with numbers into the billions. Early settlers in North America hunted the bird for food. The hunting was so intense, that the bird disappeared from the wild by 1900 and was extinct by 1914. The American buffalo nearly suffered the same fate. Originally numbering in the tens of millions, fewer than 1000 were left by 1890. The species has, however, made a comeback in reserves and private ranches and is no longer considered threatened.

The fishing industry has a long history of over-harvesting its resources. The California sardine industry peaked in the 1930's. By the late 1950s, the sardines were gone as were the canneries in Monterey. The Peruvian anchovy fishery boomed in the 1960s and collapsed in the 1970s. Over-harvesting of fish has only increased over the years, as ships have become bigger and more "efficient" methods of harvesting fish (e.g. the purse-seine net,) have been developed. By the mid-1990s, over 40 percent of the species in American fisheries were over harvested.

Over-harvesting of tropical forests is currently a worldwide problem. More efficient methods for harvesting and transporting have made it profitable to remove trees from previously inaccessible areas. Mahogany trees are over harvested by loggers in the tropical forests of Brazil, Bolivia, Peru, Nicaragua and Guatemala. Many other types of tropical trees once considered worthless are now valuable sources of pulp, chipboard, fiberboard and cellulose for plastics production. Developing nations are often willing to sign over timber rights to foreign companies for needed hard currency. Logging operations also act as a catalyst for tropical deforestation. Farmers use roads built by logging companies to reach remote areas, which are then cleared of forests and used for ranching and agriculture.

When a species is transplanted into an environment to which it is not native, it is known as an introduced exotic . Whenever man has settled far away from home, he has tried to introduce his familiar animals and plants. Long ago, European explorers released goats and pigs into their colonies to provide a supply of familiar animal protein. Many exotics are accidentally introduced. Often, the introduction of exotics has disastrous effects on the native flora and fauna. Their new habitat may have fewer predators or diseases that affect them, and as a result so their populations grow out of control. Organisms they prey upon may not have evolved defense mechanisms to them and native species may not be successful in competing with them for space or food.

Some of the most abundant wild animals and plants in the United States are introduced species. For example, starlings, eucalyptus trees and many types of grasses are introduced exotics. Most insect and plant pests are exotic species. The kudzu vine, a Japanese species introduced in 1876, to shade porches of southern mansions and widely planted in the 1940's to control erosion, grows so rapidly (up to one foot per day) that it kills forests by entirely covering trees and shrubs. The gypsy moth was brought from France in 1869 by an entomologist who hoped to interbreed them with silk moths. They escaped and established a colony that invaded all of the New England states, defoliating trees of many different kinds. Exotics are a factor contributing to the endangered or threatened status of many animals and plants in the U.S.

Dangers of bird migration

All creatures are threatened by habitat degradation and destruction. For migrating birds, the problem is vastly compounded. Birds travel thousands of miles between summer and winter homes, and environmental disruptions anywhere along the route or at either destination can be deadly. Indeed, massive declines in many bird populations have been documented over recent decades.

Many of the species common in the United States are Neotropical – they breed in North America in the summer, then over winter in Central or South America. These songbirds, waterfowl, raptors, and shorebirds, who follow the same migration routes their ancestors did, face many hazards along the way. Night-time lighting (light pollution) can disorient them. Collisions with airplanes, wires, and buildings can kill and injure them.

Once the birds arrive at their destination, or when they stop in-route, they need food, water, and a place to rest. But urban sprawl is encroaching on bird habitat, and food and water supplies are contaminated by pollution.

Recently, a new problem has arisen. For migrating birds, timing is everything – they must arrive at their summer breeding grounds when food supplies are at their peak, so that they can rebuild their body fat and reproduce successfully. Global warming is beginning to upset the delicate balance between the lifecycles of plants and insects and birds. In some areas, birds are showing up early, before flowers open or insects hatch, and finding very little to eat.

Fortunately, many people value birds and several conservation efforts are underway, including:

• Creation of protective shelter belts and hedgerows around fields and community open space
• Easements to provide native habitat for birds in human activity areas
• Timing of insecticide applications to avoid loss of the food base during bird movement in the spring and fall
• Preservation of the quality and quantity of community wetlands
• Minimization of practices that negatively impact birds

In addition, many seek to coordinate activities along the migratory flyways to increase the success of the migrating birds. Although humans are working to create natural reserves, the problem of human impact on migratory birds still needs to be addressed to a significant degree.