8.L.3.1 Summarize the relationships among producers, consumers, and decomposers including the positive and negative consequences of such interactions including:
· coexistence and cooperation
· competition (predator/prey)
· parasitism
· mutualism
Students know:
· that organisms in an ecosystem constantly interact. These interactions among the organisms:
o generate stability within ecosystems.
o can facilitate or restrain growth.
o can enhance or limit the size of populations, maintaining the balance between available resources and those who consume them.
o can change both biotic and abiotic characteristics of the environment.
· that an ecosystem is defined as a community (all the organisms in a given area) and the abiotic factors (such as water, soil, or climate) that affect them. A stable ecosystem is one where
the population numbers of each organism fluctuate at a predictable rate. o the supply of resources in the physical environment fluctuates at a predictable rate.
o energy flows through the ecosystem at a fairly constant rate over time.
These fluctuations in populations and resources ultimately result in a stable ecosystem.
Predation is an interaction between species in which one species (the predator) eats the other (the prey). This interaction helps regulate the population within an ecosystem thereby causing it to become stable. Fluctuations in predator–prey populations are predictable. At some point the prey population grows so numerous that they are easy to find.
A graph of predator–prey density over time shows how the cycle of fluctuations results in a stable ecosystem.
○ As the prey population increases, the predator population increases.
○ As the predator population increases, the prey population decreases.
· that in any ecosystem, organisms and populations with similar requirements for food, water, oxygen, or other resources may compete with each other for limited resources.
○ Competition is a relationship that occurs when two or more organisms need the same resource at the same time. Competition can be among the members of the same or different species and usually occurs with organisms that share the same niche.
§ An ecological niche refers to the role of an organism in its environment including type of food it eats, how it obtains its food and how it interacts with other organisms.
§ Two species with identical ecological niches cannot coexist in the same habitat.
○ Competition usually results in a decrease in the population of a species less adapted to compete for a particular resource.
A symbiotic relationship exists between organisms of two different species that live together in direct contact. The balance of the ecosystem is adapted to the symbiotic relationship. If the population of one or other of the symbiotic organisms becomes unbalanced, the populations of both organisms will fluctuate in an uncharacteristic manner. Symbiotic relationships include parasitism, mutualism, and commensalism.
§ Parasitism is a symbiotic relationship in which one organism (the parasite) benefits at the expense of the other organism (the host). In general, the parasite does not kill the host.
- Some parasites live within the host, such as tape worms, heartworms, or bacteria.
- Some parasites feed on the external surface of a host, such as aphids, fleas, or mistletoe.
- The parasite-host populations that have survived have been those where neither has a devastating effect on the other.
- Parasitism that results in the rapid death of the host is devastating to both the parasite and the host populations. It is important that the host survive and thrive long enough for the parasite to reproduce and spread.
§ Mutualism is a symbiotic relationship in which both organisms benefit. Because the two organisms work closely together, they help each other survive. For example,
- bacteria, which have the ability to digest wood, live within the digestive tracts of termites;
- plant roots provide food for fungi that break down nutrients the plant needs.