The current world population is over 6 billion and increases at a rate of 76,570,430 people every year. U.S. population has increased 85% since 1950, growing from 151 million to 283 million in just fifty years. If present trends continue, our population will reach 400 million by the year 2050. Take a look at the picture to the right. Notice the world's population now versus what it will be in 2050. At constant growth we will be at 13 billion people by 2050. Experts show that population growth is slowing down, but as long as more people are born each year than die, population will continue to rise. This is how it works. Imagine you live on an island with 10,000 people. Let’s say the growth rate for this year is 10%. Do it in your head: that means there are 1000 more people, or 11,000 total, at the end of the year. The next year, the growth rate goes down to only 1%. That would be only 100 people added to the number, but that raises our number to 11,100. See how it works? Even though the rate went down from 10% to 1%, the overall number still goes up. That’s the idea, Earth's population will continue to increase. What does all of this mean? More people means more pollution, more sprawl, less green space, and even more demands on the earth’s already overburdened resources. As humanity enters a new millennium, there will be a greater and greater impact on our planet. And that news isn’t good.

Half the planet’s tropical rainforests have been destroyed or degraded.

Chemical runoff, sewage, and oil spills have damaged many fresh and salt water ecosystems.

Almost 40% of the Earth’s land surface has been converted to farmland and pasture.

The ozone layer has suffered substantial damage. Carbon emissions are causing smog and acid rain, and contribute to global warming.

On average, three unique plant and animal species go extinct every hour. There are two main causes: our rapidly expanding population, and the high-consumption lifestyles some of us choose.

What role does the U.S. play?

U.S. citizens use 25% of the world's oil

U.S. citizens make up less than 5% of the world's population but...

U.S. citizens use 27% of the world's aluminum

U.S. citizens use one-third of the world's cars

U.S. citizens create two-thirds of the world's toxic waste

U.S. citizens use one-third of the world's paper

As the world's population grows, what will happen to our planet? The ability of an organism to spread throughout a geographic area is a result of how it adapted to its environment. However, one factor alone determines the success of the organism, this factor is known as the limiting factor. Any factor (abiotic or biotic) can act as a limiting factor. The distribution of organisms with respect to each other is also important. Individuals have one of three types of local distribution: random, clumped, or (even) uniform. The term random distribution is used whenever there is no obvious, identifiable pattern to the position of individuals. Clumped distribution are those in which the spacing between plants is either small or large, but rarely average. Uniform distribution are the types that occur in orchards and lawns in which individuals are evenly spaced from their neighbors. In natural populations, uniform distributions are not common; those that do occur are thought to result from competition. The roots of one individual may establish a zone that prevents the germination or growth of others. Zones can be established by the release of chemicals that inhibit other plants. Such chemicals are called allelochemics and the inhibition is allelopathy. Think of it as plants guarding their personal space.

The manner in which a population responds to various factors in its habitat is affected parly by its age distribution, its demography (the relative proportions of young, middle-aged, and old individuals). Intrinsic rate is the number of offspring produced by an individual that actually reproduce. To understand intrinsic rate think of this, it's not the number of seed produced but the number of seeds that actually germinate. Remember that a lot of seeds are destroyed and never germinate. For example, an oak tree will produce 50,000 acorns a year. Do they all germinate? Once a population becomes large, the plants must compete for water, nutrients, sunlight and space. So the number of populations that can live in a community is limited; that number is the carrying capacity. If a population increases above carrying capacity, what happens? That's right, a large number of individuals die off because resources become limited. Also disturbances like fire, flood, and drought help keep the number of individuals at the carrying capacity.

Species composition refers to the number and diversity of species that coexists in an ecosystem. Species are arranged into trophic levels or feeding levels. The bottom of any feeding level (food chain) begins with a plant. Plants are called autotrophs because they make their own food or energy. Autotrophs are known as primary producers because they provide energy and a nutrient supply for heterotrophs. Heterotrophs are organisms that cannot make their own food and must consume autotrophs in order to derive energy for survival. Heterotrophs are known as primary consumers or secondary consumers. Decomposers such as fungi and bacteria break down the remains of all types of organisms, even those of other decomposers. Take a look at the diagram below and follow the trophic levels.