Ecosystems

An individual organism never exist in isolation (if it did, reproduction couldn't take place and the organism would be extinct); instead there are other members of the same species and together these members form a population. Populations of different species interact and together form a community. Think of a forest and the different populations of trees, oaks mixed with pines. All of these populations together with environmental factors form an ecosystem. The interactions between populations can be quite complex and in this section we will try to show the complexities that exists within ecosystems around the planet.

A habitat is a set of conditions (factors) in which an organism completes its life cycle. All interacting biotic and abiotic factors together make up an ecosystem. These factors may be other living organisms (biotic factors) or nonliving variables (abiotic factors), such as climate, soil, latitude and altitude. Climate itself has many components--temperature, rainfall, soil, disturbances, etc. Temperature is an important factor to think of because plants and animals can survive and flourish only when the temperature is between the tolerance range. The tolerance range lies between the low and high temperature extremes that an organism can withstand. If the temperature is above or below the tolerance range the organisms suffers greatly. Moisture occurs as rain, snow, or hail and supplies much needed water for the organism. Think of a habitat if it receives too much or too little water.

Flooding and drought would be the result. What do you think would happen to population? It is very important that organisms recieve the proper amount of moisture. Soils are formed by the weathering of rock and lacks proper mineral content for plant photosynthesis to occur. The first plants that invade a new soil are called pioneers. If a plant is able to survive such poor conditions, after many years of weathering a thick soil may result that increases a plants ability to undergo photosynthesis. Look at the diagram below and think about what happens to our soil as the size of our urban areas increase.

Latitude is another abiotic factor that affects an ecosystem. At the equator temperature remains constant, but as you move further North or South the temperature decreases. As temperature goes down what happens to a plant's ability to undergo photosynthesis? The same can be said of altitude. As elevation goes up, temperature goes down. Other abiotic factors that affects ecosystems are disturbances like fire, flooding, drought, earthquakes, tornadoes, blizzards, etc.

Look at the picture to the right and imagine all the complex interactions that must take place betweeen organisms. What biotic (living) factors affect an organism? An individual itself, just by being in a habitat, modifies the habitat and is a part of it. Habitat modification may be beneficial, detrimental, or neutral to the continued success of that species in the habitat. Think about competition? Competition occurs when interactions happen between two organisms and the interaction is beneficial to one but not the other. Think of an oak tree and an oak seedling. The oak trees canopy is high enough to reach maximum photosynthetic potential. But what about the seedling underneath? In essence, it is being out competed for sunlight. Is there a situation in which both organisms can benefit? Yes. What about birds and insect pollenating plants. The animals find food and the plants are able to reproduce. If the interactions between organisms is benefical for both mutualism occurs. Sometimes one species benefits and the other is unaffected. We've all seen bird's nests in trees. The bird is benefiting and the tree is unharmed. This type of relationship is called commensalism. Finally, if one organism gains at the expense of another predation occurs. Anytime we eat, it is at the expense of another organism. Cows grazing (eating herbs like grass), or deer browsing (eating twigs and leaves) are examples of predation. Sometimes organism interact and diseases are transmitted. Any organism that transmits a disease is called a pathogen.