The Earth can only support so many people without causing permanent damage to the environment. The maximum population of a species that can be supported by an area without causing permanent damage to the environment is known as the carrying capacity. If a species' population number rises above the carrying capacity, damage to the environment may occur, and the species numbers will eventually start to decline due to a lack of resources such as food, or because of increased predation or disease.
The carrying capacity for humans is very hard to measure because of changing technologies, and the variety of lifestyles and consumption habits of the world's population. Some people think the current estimated world population of 6.7 billion people already exceeds the Earth's carrying capacity. This would definitely be true if the entire world were to live the lifestyle of an average Canadian!
Arrival of the first settlers to Easter Island is thought to have occurred around the year 700. Trees and many different plant species were once widely abundant on the island, and the soils were rich and fertile. The civilization then grew as the agricultural and fishing industries provided much needed resources. The population deforested large sections of the island to aid in the construction and the movement of large stone statues, called the moai, which were a main part of their cultural identity. Deforestation eventually resulted in widespread soil erosion leading to the extinction of over half of the native plant species. Birds disappeared along with the loss of their nesting habitat. A loss of agricultural crops due to the degraded soils resulted in famine, sickness, and eventually death for much of the population. Two lessons can be learned from Easter Island. The first is that the rapid growth of the civilization possibly far exceeded the carrying capacity. The second is that if the civilization had practiced sustainable methods in harvesting the trees and their agricultural lands, perhaps the ecosystem would not have collapsed so quickly.
An ecosystem is a community of plants and animals within a particular environment. It is linked by the flow of materials through abiotic (non-living) and biotic (living) factors. Therefore, ecosystems can range in size from a drop of water to the whole Earth. They do not have clear boundaries as factors move in and out of different ecosystems (e.g., migrating animals or nutrients washed downstream).
How would you describe a tropical rainforest? Often times the response to this question would include descriptions of large, tropical deciduous trees with a wide variety of plants spread along the forest floor. There may also be a number of different animals ranging from weird insects to monkeys, snakes, and large jungle cats. What about the abiotic components of this ecosystem? Although not as easily seen and often overlooked, the abiotic factors will be the factors that allow a given ecosystem to develop. Without the right mixture of nutrients, temperature, precipitation, sunlight, and soil type, many species would not be able to survive. In the example of the tropical rainforest, underlying the lush forest is a loose soil rich in nutrients and a large amount of decaying organic matter, important in returning nutrients to the soil. Temperatures are generally warm and precipitation is abundant.
All ecosystems begin with producers, which are organisms capable of utilizing the Sun's energy and nutrients from the soil to produce food. The ecosystem ends with decomposers, which break down the dead organic matter, returning nutrients back to the soil. The types of living organisms living in an ecosystem range from generalist species, which do not have specific requirements (e.g., they eat a variety of foods) to specialists, which require specific resources to survive (e.g., the monarch butterfly caterpillars require the milkweed plant for food). Generalist species tend to endure changes better since no one resource is essential for their survival. Some species in an ecosystem are critical in maintaining ecosystem functioning and without them the ecosystem may begin to crumble. These species are called keystone species.
Predation occurs when predators feed on other individuals, usually the young and weak, of another species. These interactions are extremely important to ecosystems because they limit the size of prey populations, for example deer.
Competition occurs when two or more individuals, from the same or different species, require the same resource. For example, a coyote and a vulture compete for the same food source or two plants compete for nutrients in the soil.
Parasitism occurs when one species benefits from an interaction and another is harmed. However, unlike predators, parasites typically do not kill their host.
Mutualism occurs as a cooperative relationship between two species in which both species may benefit. For example, the strain of E. coli bacteria in your intestines produces vitamin K, while your body provides a home for the bacteria.