Lecture 4: Ecosystems and Living Organisms

Interactions Between Organisms

Intraspecific Interactions are interactions that occur between members of the same species. For example: mating, taking care of offspring and competing for resources.

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Interspecific Interactions is the interaction between members of different species. There are three interactions among organisms:

1. Predation is the relationship where an organism kills and consumes another for food.

   1. Predator is the organism that kills and consumes another while the prey is the organism that is killed and consumed.
   2. Predator Strategies: pursuit, ambush, camouflage and traps.
   3. Prey Strategies: camouflage, fleeing, mechanical defenses and group living.

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2. Symbiosis is a close relationship between 2 or more unrelated species usually involving nutrition. There are three main types of symbiotic relationships:

   1. Mutualism is the symbiotic relationship where both organisms benefit from each other.
   2. Commensalism is the symbiotic relationship where one organism benefits while the other is unaffected.
   3. Parasitism is the symbiotic relationship where one organism (host) is adversely affected by another which benefits (parasite). Well-adapted parasites do not kill their hosts.

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3. Competition

Types of Competition

Intraspecific Competition is the competition that occurs between the same species.

Interspecific Competition is the competition that occurs between different species.

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Habitat

Habitat is the physical & biological resources required by an organism.

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Ecological Niche

Niche is the sum total of all the requirements and activities of a species. It also includes the organism’s unique role and what they require to survive. This reduces competition between species.

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Fundamental vs Realized Niche

Fundamental Niche is the potential requirements and activities a species could use if there were no competition from other species.

Realized Niche is the portion of the fundamental niche that a species actually occupies. A species with a narrow realized niche (specialist species) are more susceptible to extinction.

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Competitive Exclusion Principle / Gause’s Principle

This principle dictates that two species cannot live in the same identical niche and if they try one will be excluded. To avoid competitive exclusion organisms often engage in resource partitioning.

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Resource Partitioning is a process of natural selection that will force competitors to use resources differently.

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Evolution and Succession

Evolution is the a process of natural selection that will force competitors to use resources differently.

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Natural Selection is a theory by Charles Darwin that dictates certain individuals are better able to survive and leave more offspring because of their genetic traits, then frequency of the genes will change over subsequent generations

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Succession is the process of community development that involves a changing sequence of species. The pioneer community is the first community to colonize or re-colonize an area. The climax community is the final set of organism that inhabits an area.

Types of Succession

1. Primary Succession is the community development in an area that has not been previously inhabited. This process takes thousands of years to reach climax community.
2. Secondary Succession is the community development in an environment that has been previously inhabited but was destroyed by some process. This process takes hundreds of years to reach climax community.

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