Understanding the Environment       Return to Science Standards                        (01/19/06)

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Before we can fully understand the present, we must understand the past. The biological field of ecology involves not only an understanding of how organisms function, but also the functioning of populations, communities, and ecosystems. This involves a knowledge of geology, geography, chemistry, physics, and mathematics. The field of environmental science involves many fields outside of the sciences.

Worldwide distribution of Biomes, major habitat types, each of which supports specific types of animal life.

Effects of temperature and precipitation on the major global habitat types (Biomes).  See world map above for locations.

Elevation and latitude both affect the distribution of biomes.

Effects of man on water supplies and resulting desertification.

Habitats have changed considerably in the Domesticated Lands. In addition, extermination of many species has occurred more rapidly in the regions with more people. Human population growth (and resulting development) is one of the most crucial problems that we face. World-wide, each human requires 4.5 acres to produce food and other needs; in the U. S., the average 'needs' per person is over 25 acres (Sierra Magazine, Jan/Feb 2003).

Endemic species are those found only in one place. These species are particularly subject to extinction through habitat disruption, and require special efforts to protect them.

One reason that it is so important to protect all species from extinction is illustrated below. The rosy periwinkle (Catharanthus roseus) occurs only in Madagascar, and it produces vinblastine and vincristine, both used to treat childhood leukemia, increasing chances of survival from 20% to over 95%.  We never know what drug will be found in any species of living organism until we isolate and experiment with each substance. Extinction is forever!

One specific example of habitat loss and extinction. 90 percent of the rain forest has been destroyed as the human population has increased along the east coast of Madagascar, resulting in extinction of many and threatened extinction of 16 of the 31 species of primates. Similar situations occur elsewhere as human populations increase (see below).

One particularly destructive habit is clear-cut lumbering. This photo is in a National Forest in 
Washington State. This same practice has been used in numerous places, and causes extreme environmental disruption, soil erosion, and pollution of streams.

Biodiversity, the number of different species of organisms in the environment, increases toward the equator, but the density (the relative number of individuals of each species per unit of area) increases toward the poles. The more diverse an area is, the more stability it has.  Wherever civilization has developed, both diversity and stability of the environment have decreased. Relative productivity rates for different types of habitats (shown below), is related to biodiversity.

Environmental conditions on an ocean front and a bay or lagoon usually allow for only a few species of grasses to grow. However, behind the first row of sand dunes, other species may thrive. Each location has its own microhabitat, inhabited by species unique to local conditions. Barrier islands are subject to rapid change when hurricanes occur.

Succession in communities occurs slowly (sometimes over hundreds of years) from the Pioneer stage to the Climax stage of a mature, long lasting community characteristic of the Biome in which it is found. Secondary succession occurs when a community has been disturbed (usually by man), while Primary succession begins with bare rock. Each stage is characterized by specific kinds of organisms, depending upon their tolerance to environmental factors that exist at the specific time and place. Each group of organisms changes the environment in which they occur, allowing additional species to survive.

Every species of organism (and every individual) has specific limits of tolerance for each physical condition in the environment.  Aquatic species have limits of depth, oxygen level, pH, salinity, light penetration, temperature, and several other factors that determine where they live. Terrestrial animals are influenced by soil, temperature, precipitation, winds, sunlight, types of plants, available food, and other factors.

When two different species have one or more similar requirements, they compete for resources, such as food or nesting spaces. They may either diverge (adapt to different conditions) or one may replace the other. The Niche is analogous to an occupation.  For example, a small town would not be able to support two or three neurosurgeons, but if one also specialized in cardiology, both may be able to survive. Likewise, you would not expect to see two auto dealers who sold the same brand of cars, but if one changed, both may be able to make a living.  Plants and animals are the same way.  

As a result of years of competition, species of warblers in some areas have developed specific niches for feeding.

Darwin discovered 13 different species of finches on the Galapagos Islands when he made his trip aboard the Beagle. These finches somewhat resembled other species of finches on the west coast of South America, but with isolation and competition on the small islands, they had adapted to the specific habitats of various islands, and had evolved into 13 species, each with slightly different ecological niches. These 10 species were all found on Santa Cruz Island. Just as no two pieces of matter can occupy the same space at the same time, no two species can occupy the same niche at the same time for an extended period.

A food web in the ocean. Each species of large animal may feed upon many different types of food item. Krill, small floating organisms serve as food for several species because of their abundance.  If they began to disappear, most of the large whales would compete for food.

Organisms occupy different trophic (feeding) levels within a community.

Ecological Pyramids: Energy Pyramid from Silver Springs, FL.  Energy always decreases, but biomass and numbers can vary in certain circumstances.

Biomass Pyramid - Biomass refers to the weight of each trophic level.

Pyramid of Numbers

When organisms feed, toxic and radioactive substances are magnified in the food chain, causing those organisms at higher trophic levels to receive higher doses of the substances. Many birds of prey became threatened by consuming DDT, which decreased calcium in the egg shell. As a result, eggs broke and populations decreased rapidly in hawks, owls, eagles, pelicans, etc. 

The exchange and flow of energy within an ecosystem is dependent upon the communities and species occupying that ecosystem, and is connected to various nutrient cycles, as shown in the next few illustrations.

Material cycling in the environment. The Carbon cycle. Any disruption in any of the nutrients can have major effects on the environment. Oil, gas, peat, and coal are formed from dead organisms over periods of millions of years. Most of these substances were formed from organisms that lived in the Carboniferous Period (over 300 million years ago). Therefore, these are not renewable resources; once gone, they cannot be replaced. 


The Nitrogen cycle.

The Phosphorus cycle.

The Sulfur cycle.

Dimethyl sulfide (DMS) produced by oceanic phytoplankton, may provide feedback control for global climate, since it helps form more clouds, thus blocking sunlight and lowering surface temperatures.

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