Ecosystems & PopulationsChapters 4 & 5

Levels of Organization in Ecology

• Ecologists study individual organisms, but this only provides part of the story of its life cycle.

• An individual organism interacts with others of its species; it is also dependant on other organisms for food, shelter, reproduction and protection.

Levels of Organization in Ecology cont.

• Population – a group of organisms of one species that interbreed and live in the same place at the same time

• Members of the same population may compete with each other for food, water, and other resources.

• How organisms share the resources determines how far apart organisms live and the size of the population.

Levels of Organization in Ecology cont.

• Community – a collection of interacting populations

• A change in one population in a community will cause changes in the other populations.

Levels of Organization in Ecology cont.

• Ecosystem – made up of the interactions among the populations in a community and the community’s physical surroundings

• Terrestrial, freshwater and saltwater (marine) ecosystems are the three major kinds.

Levels of Organization in Ecology cont.

• Biome – a large region characterized by a specific climate and certain plants and animals

• Biosphere – the portion of Earth that supports life

• The biosphere extends from high in the atmosphere to the bottom of the ocean.

Organisms in Ecosystems

• Habitat – the place where an organism lives out its life

• Niche – the role and position a species has in its environment – how it meets its needs for food and shelter, how it survives and how it reproduces.

Niche

• Several species may share a habitat, but the food, shelter, and other resources of that habitat are used in different ways.

• These differences lead to reduced competition.

• It is an advantage for a species to occupy a niche different from those of other species.

Living Relationships

• Predator-Prey Relationship – beneficial for one species and harmful to another, involves a fight for survival.

• However, some species enhance their chances of survival by forming close, permanent relationships with other species - symbiosis.

Symbiotic Relationships

• Commensalism –relationship in which one species benefits and the other species is neither harmed nor benefited

• The clownfish lives among the stinging tentacles of an anemone and is protected from potential predators not immune to the sting of the anemone.

Symbiotic Relationships cont.

• Mutualism – relationship in which both species benefit

• Some fish and shrimp clean the bodies and mouths of large fish and turtles.

• The cleaner fish get a meal while the large fish have parasites removed.

Symbiotic Relationships cont.

• Parasitism – relationship in which one organism derives benefit at the expense of the other.

• Ticks are parasites of animals like dogs, obtaining nutrients from the blood of their host.

• Parasites harm, but usually do not kill, the host.