Ecosystems

Levels of Organization in Ecology What is the correct level of organization (think back to the card activity from our previous class)? atom molecule organelle cell tissue organ organ system organism population community ecosystem Students should recall the correct order. Ask them to identify it before showing the correct answer. Wikimedia Commons free use from NASA

Populations vs. Communities What is the difference between a biological population and a biological community? A biological population is a group of organisms, all of the same species, which interbreed and live in the same area at the same time, while a biological community is made of interacting populations in a certain time.

Limiting Factors Do populations often grow exponentially? What are limiting factors? Limiting factors are any factors (things) that affect an organism’s ability to survive in its environment. These factors affect population growth. Examples? availability of food and water, predators, temperature, space/shelter, and disease Discuss the first question with students, then move onto the concept of limiting factors. Students should note that usually populations are not able to continue growing exponentially. You may need to explain the concept of exponential growth, depending upon students background in this concept in math class. Ask students to name possible examples first, before showing them the answer.

Competition What is competition? Examples? Competition is one of the many symbiotic relationships occurring in nature. Members of species compete for resources, especially for limited natural resources. Examples? trees that grow very close together vie for sunlight and soil nutrients, lions and tigers that vie for similar prey, and a farm of rice paddies with weeds growing in the field Again, discuss with students first, before showing them the “right answer”.

Competition What happens to competition between individuals as population size increases? Competition will also increase. If the demand for resources exceeds the supply, then the population size will eventually decrease. Again, discuss with students first, before showing them the “right answer”.

Density-Dependent Factors What are density-dependent factors? Factors that depend upon the size of the population. These factors will have an increasing effect as the population size increases. Examples? availability of food and water, competition, predators, and disease Discuss this with students before showing them the answer, see if they can come up with a reasonable definition based on their knowledge of the word “dependent”. Again, ask students to think of examples before showing them the examples on this PowerPoint.

Density-Independent Factors What are density-independent factors? Factors that are not dependent upon the size of the population and can affect any population. Examples? temperature, weather (storms, floods, drought), and habitat disruption by humans Again, discuss with students before showing the answer; they may be able to determine a good definition based on their knowledge of the word “independent”.

Carrying Capacity Ask students to interpret this graph, then lead a discussion on carrying capacity. The formal definition is on the following slide. “t” is time, “N” is number of individuals, and “K” is carrying capacity. At first, the population grows well, as resources are abundant, then as the population reaches it’s carrying capacity (limit), the growth of the population slows and will stay at a steady rate unless there is a disruption such as disease, storm, etc. Cephas Wikimedia Commons free use

Carrying Capacity The maximum number of individuals that an environment can support. Why is knowing carrying capacity important to ecologists? Discuss the importance of carrying capacity with students. They will likely come up with a variety of responses possibly including the following: it helps establish hunting restrictions/freedoms, it helps those at wildlife sanctuaries determine the right number of individuals for an area.