ON JUNE 30, 2009, THE BRI PROGRAM OFFICE WILL BE CLOSING DOWN TEMPORARILY. THE ACTING DIRECTOR OF BRI AND THE BRI EXECUTIVE COMMITTEE ARE WORKING TO REINSTATE STAFF AND WE HOPE TO BEGIN PROGRAM ACTIVITIES AS SOON AS POSSIBLE. WE DO NOT ANTICIPATE ANY CHANGES TO THE UPCOMING FALL 2009 BRI BIOLOGY AND CONSERVATION LECTURE SERIES OR TO THE 2010 NORTHEAST NATURAL HISTORY CONFERENCE, SO PLEASE PLAN ACCORDINGLY.
Major Processes Depleting Biodiversity:
- Habitat Fragmentation, Destruction and Alteration
- Exploitation and Overharvesting
- Invasion by Alien Species
As we pave more and more of the earth's surface, once-connected populations of plants and animals are split and isolated from one another. A dead animal on the road offers a clear image in evidence of human interference in non-humans lives. People dam rivers to make lakes, and in doing so, change the flora and fauna that inhabit these areas. Organisms adapted to stream life, not to lakes, then experience local extinction, or extirpation. Although beaver dams have similar effects, humans often build dams in illogical places and at much larger scales, where the biota (the organisms) is not capable of adapting to the resulting changes. Another example is the loss of tropical rainforests, where experts believe most of Earth's biodiversity occurs. It is estimated that the annual loss of acreage through clearcutting and burning leads to the extinction of 27,000 species per year. These communities that evolved over millions of years cannot recover.
Pollutants fall into the category of habitat alteration. Toxic waste discharge into rivers, runoff from farms, acid rain, suburban sprawl, global warming, and pesticides such as DDT all change habitat characteristics. Some create a toxic environment that directly impinges on the biota, others extend the growing season, or, in the case of DDT, physically travel up the food chain affecting the number and quality of eggs that birds and reptiles can produce. Many human activities affect the environment, and we are often not aware of these effects until it is too late. Writer-scientist Rachel Carson, who wrote a book called Silent Spring in 1962, was one of the first to alert the public to such a problem, saying that DDT caused cancer in humans and killed carnivorous birds of prey. DDT has since been banned in the United States and this is one of the reasons that populations of bald eagles have rebounded. Rachel Carson has since died of cancer.
People have hunted and fished the world's lands and oceans for millennia, and while this caused little extinction of other species in the beginning, it was because of the small numbers of our species inhabiting the earth at the time. In recent times, geologically speaking, the large mammals of the Ice Ages, most notably the mammoths and mastodonts are believed to have been driven to extinction by human hunting. Hunting pressures drove the passenger pigeon to extinction in North America early in the 20th Century and the American buffalo recently approached extinction as well. (To learn more about mastodonts, visit the New York State Museum and see the permanent exhibit of a mastodont skeleton.)
Overhunting, commercial exploitation of fishes, shellfish and whales has driven many groups to near-extinction or unsustainable population levels. Fishermen choose the largest, most healthy individuals for human consumption, but this leaves smaller, weaker and younger individuals to propagate the species in the future. The average age of the species becomes too low for the species to reproduce successfully. Swordfish are a case in point. Ten years ago, the average weight of a swordfish sold to market was 200 lbs. Today it averages around 90 lbs. and 85% of these fish have not yet reached sexual maturity (and therefore have not reproduced). Smaller, younger populations of almost any species have a greater chance of extirpation. They are more susceptible to changes in the weather and other random events, such as floods, rock slides, turbidity flows and tornadoes. Note: Overhunting and overfishing are not always the pertinent problems. Underhunting, for instance in publicly owned lands, can lead to population explosions in herbivores like deer, because their natural predators, have long-ago been eliminated. They may deplete the food supplies, destroy natural habitats and then starve.
Waste of bycatch is an additional exploitation associated with overfishing. Commercial fishing boats are very selective in what they catch. Their organism of interest is called the target organism. Twenty-seven million metric tons of non-target organisms are caught, killed and returned to the sea every year. These killings are unintentional, but result in a huge loss for biodiversity every year. For example, for every pound of shrimp you buy, seven pounds of other marine life is lost.
Despite the science fiction images that this category-title might evoke, very real species invasions by foreign animals and plants are a common occurrence, aided and often purposely perpetrated by people. International travel and shipping have resulted in the accidental importation of weedy seed plants throughout the world, but sometimes introductions are not accidental. Purple loosestrife is a wetland plant that arrived from Europe about two hundred years ago. The plant was brought to the US as an ornamental plant. However, purple loosestrife escaped cultivation, and has changed the way the water flows at the edges of natural ponds and wetlands over a major portion of the northern United States and Canada. It forms hummocks, eliminating native plants that are food for wildlife, and even directly competes for space and nutrients with aggressive native wetland plants such as cat-tails.
There is such a large problem with purple loosestrife in New York state that scientists at Cornell University are introducing beetle species to attempt to control it. Additional information on purple loosestrife and its biological control is available from Cornell University.
Gardeners spend much of their time weeding. Most of the weeds are introduced, meaning that they were transported somehow from their natural, native areas of distribution to new places (for example, from Europe to the U.S.). Some species grow and reproduce more rapidly in “new” environments, where they have fewer predators. Not all invasions are “bad,” meaning that they reduce the diversity of native species. In fact, most are not. Think of a dandelion, a species imported from Europe. It is a pest and hard to get rid of, but little more than an annoyance. Dandelions will not crowd out the rest of your lawn or an entire natural area; however, there are some invasive species that are doing just that, like the purple loosestrife and Eurasian milfoil, a mossy plant that takes over shallow waters, eliminating both native plants and fish. New York alone has over 1,100 non-native and over 100 seriously invasive plant species.
An animal species that causes serious problems in New York State is the zebra mussel. Microscopic zebra mussel larvae arrived in ship's ballast water via the St. Lawrence river in the mid 1980s. They were first recorded from New York's Hudson River in 1991. Since then, they have permanently changed the river ecosystem and caused a considerable number of economic problems in the region. Zebra mussel larvae float in the water and settle on an appropriate surface. They even settle on one another at high population densities and may clog pipes and cause other problems for businesses located along waterfronts. The animal is also causing problems for native biota. Native freshwater clams, already in low diversity in the Hudson, are declining in numbers because zebra mussels filter out most of the microscopic food that both species use. Scientists at the New York State Museum are conducting research on the potential impacts of zebra mussels and also practical control strategies.