page 1 of 5

Submodule 8: Ecological Impacts

The Importance of Biodiversity

Interest in biodiversity (biological diversity) has increased in recent years. The concept of biodiversity, said to have been discussed by the great philosophers in ancient Greece, is not new. It can be defined as the number of different organisms or species that inhabit a given ecosystem or the earth overall. It can also refer to the variability within species and among species living on the earth or in a particular community. Many ecologists also include the interaction of species the environment when describing biodiversity. All biodiversity has its origins in the different combinations of genetic material (DNA) and how this is expressed in different organisms.

Humans in general are supported by an almost endless diversity of life – some 15 to 100 million different species are estimated to inhabit the earth at this time (the high figure is because of the enormous number of microbes thought to exist but not yet described). Living organisms provide America’s renewable resources that are used for building, food, fuel, and medicine, or for non-consumptive activities like recreation. These living resources constitute our natural capital and largely support the country’s economy. Agriculture and our ability to produce ever-larger amounts of food ever-smaller parcels of land is based in part on the tremendous amount on genetic diversity available in crop plants, and on plant breeders ability to tap into this variation and select desired traits.

Degree of species diversity is considered a measure of the stability of an ecosystem: high diversity is correlated with stability and low diversity is correlated with instability. Unfavorable environmental conditions usually tend to limit or decrease species diversity and lead increasingly to dominant populations of fewer, more common species. This can have serious consequences, as it is the interaction of many diverse species that is thought to contribute to environmental stability. The health of an ecosystem is dependent on a complex interlinking web of the contributions made by each individual species to that ecosystem. These contributions include total environmental services such as oxygen production (plants and alga), nutrient decomposition and recycling (fungi and bacteria), removal of carbon dioxide from the air (animals), and production of organic material (all living organisms). Less diverse habitats are at greater risk when exposed to new pests and pathogens.

Scientists are just beginning to understand the importance of biodiversity. Many would say that since high diversity is considered more stable, it is essential and resources should be managed to retain or increase it. Others would argue that there have been instances where biodiversity has decreased (e.g., the eradication of American chestnuts throughout the Appalachians and of the passenger pigeon throughout eastern North America) and ecosystems survived in spite of these changes. In fact, the web of inter-species interactions that sustain healthy ecosystems are so complex that, at present, ecologists and other scientists simply cannot accurately predict the short- or long-term effects of an overall decline in biodiversity or the eradication of species. What most ecologists do agree on is that proper management of our natural resources maintains biodiversity. By increasing our understanding of the diverse components of ecosystems and their interactions, we will be better equipped to constructively manage these natural resources. This requires research to enhance our understanding of dynamic ecological systems.

Biodiversity has been steadily decreasing in the U.S. since the beginning of European exploration in the late 1400s. Natural habitats have been and continue to be cleared for development and agriculture, and several hundred species have become extinct. So-called “keystone species” seem to have particular importance on their environment; a decline in their numbers has a more pronounced effect on the health of an ecosystem. Keystone species, for example, may have the effect of regulating the population size of other species, which in turn leads to a cascade effect on the ecosystem as a whole. For example, if a particular insect that is considered a keystone species decreases in numbers, this in turn may lead to a decrease in the number of fruits produced by local shrubs since this insect serves as its primary pollinator. In addition, the local population of certain birds may decrease because these insects are their primary source of food.

There are several factors that contribute to a decrease in biodiversity such as:

How land is used: Entire ecosystems are altered by the use of land for cities and agriculture. It is estimated that over 40% of the photosynthetic capacity of the earth’s surface is now occupied by man-made systems, primarily agriculture. Forests once located in the northern hemisphere were extensively cleared during the 1800s and 1900s for industrialization. More recently, extensive logging and other extractive activities are causing serious losses of rain forests in South America and SE Asia.
Exploitation of resources: Examples in the U.S. of species being brought to extinction (passenger pigeon) or the brink of extinction (bison and numerous fish species) are plentiful. Water and soil resources have also been over-used, producing damaging effects on nutrient cycles.
Effects of pollution: In general, the amount of toxic substances in air, water, and soil has increased throughout the U.S. Acid rain and side effects from the use of DDT have brought chemical pollution to the forefront for environmentalists, but the actual effects of pollution on biodiversity are not well understood. It is known that many chemicals used for pesticides or released as industrial wastes remain in the ecosystem for long periods of time.
Climate change: Currently there is growing evidence that the general trend is toward increased temperatures on earth. Many think this is due to the increased emissions of so-called “greenhouse gases” such as methane and carbon dioxide. Ecological models show that if the current trend continues, major changes in ecosystems may occur.
Invasive species: Most ecologists agree that overall, the biodiversity of terrestrial and aquatic environments in the U.S. has been diminished by the introduction of non-indigenous species. While some ecosystems seem to be more susceptible than others, invaders have negatively affected most.

We have limited ability to predict how ecosystems will respond to these and other stressors. Habitat destruction is the primary threat to biodiversity in the U.S. The next most serious threat, greater than pollution and disease, is infestation by invasive species.

page 1 of 5

Next >