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CHAPTER 5

Interactions in the Ecosystem

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SECTION 3.3 - THE ECOSYSTEM

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SECTION 3.3 - THE ECOSYSTEMLevels of Organization

• Individual – one organism from a species.

• Species – a group of organisms so similar to one another that they can breed and produce fertile offspring.

• Since they all have the same needs they compete with one another for food, shelter, space, mates, etc.

• Populations – All the members of a species that live in the same geographic area, a group of the same species.

• Communities – are made up of different populations of organisms that interact in the same area at the same time.

• Ecosystems – are large places where all the biotic factors and abiotic factors interact with one another.

• Abiotic factors generally cause environmental differences.

• Biome – made up of ecosystems: grasslands, savannah, desert.

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SECTION 5.1 – HABITATS AND NICHES

• Habitat – the specific environment in which a particular species lives.

• Within their habitat individual organisms find the appropriate food, shelter, temperature and other factors needed to survive.

• Niche – the role or actions of an organism in an ecosystem; what the organism does in its habitat.

• An organisms niche is defined by all the biotic and abiotic factors in the environment.

• Competition occurs between species when they try to share the same niche.

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SECTION 5.1 – HABITATS AND NICHES

• Competitive Exclusion – the extinction of a population due to direct competition with another species for a resource in the same area.

• Not the extinction of the whole species!

• The presence of one species might limit the niche of another.

• Fundamental niche – a theoretical niche of an organism.

• The realized niche of an organism is an organisms actual niche.

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SECTION 5.1 – HABITATS AND NICHES

Predator vs. Prey

• Predator – an organism that actively hunts other organisms.

• Prey – the organism that is hunted.

• Predator vs. prey relationships help keep environments stable.

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SECTION 5.1 – HABITATS AND NICHES

• Keystone predator – a predator that promotes a great niche diversity in its habitat.

• It increases the biodiversity in a habitat.

• If they are removed from an environment; it often decreases the overall diversity of organisms because a chain reaction of events will occur.

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SECTION 5.2 – EVOLUTION AND ADAPTATION

Ecosystems change over time

• Change in an environment will affect the niches of organisms.

• Changes in the environment affect the evolution of populations

• Evolution – a change in the characteristics of a population of organisms over time.

• Evolution happens when some individuals have genetic variations that allow them to produce more offspring with a certain trait or gene that is more advantageous for survival.

• “Survival of the Fittest”

TIME

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SECTION 5.2 – EVOLUTION AND ADAPTATION

Evolving in a niche

• Specialized species – an organism with a small niche.

• Koala and eucalyptus trees.

• Pandas and bamboo.

• Vulnerable to extinction.

• Are less able to tolerate habitat disturbance, so would thrive in an area with outside human activity.

• Living on an island without human involvement.

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SECTION 5.2 – EVOLUTION AND ADAPTATION

Convergent Evolution

• If niches in two ecosystems are similar, the organisms that evolve there may also look alike.

• It is the independent development of similar adaptations (traits) in two species with similar niches.

• Wings of birds and wings of bats (mammals) because both their niches require flight.

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SECTION 5.2 – EVOLUTION AND ADAPTATIONCoevolution

• Organisms that live closely together and interact may have evolutionary responses to one another.

• Coevolution – species that interact closely may become adapted to one another through this process.

• Clown fish and sea anemone.

• Acacia (uh-kay-sha) tree and stinging ants.

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SECTION 5.3 - POPULATIONSPopulation Growth

• Populations can quickly grow past the environment’s ability to support it.

• As a result of growing populations, organisms experience increased competition for resources.

• So populations can continually grow exponentially unless prevented by limited resources.

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SECTION 5.3 - POPULATIONSCarrying Capacity

• As a population grows it takes move from its habitat and resources become scarce.

• The death rate rises because those who cannot compete die and the birth rate starts decreasing.

• The growth of the population slows down.

• The population will stop growing altogether because the number of births equal the number of deaths.

• Carrying capacity – the number of individuals of a species that can be supported by an ecosystem for a species.

• The carrying capacity for a species is usually determined by the ecosystem’s resources.

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SECTION 5.3 - POPULATIONSCarrying Capacity

• The S-shaped curve represents the change in the size of a new population over time.

• The population starts out small and then increases rapidly.

• As the size of the population approaches carrying capacity, the growth rate slows down.

• The population stops growing when it reaches the carrying capacity and levels off.

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SECTION 5.3 - POPULATIONSLimiting Factors

• Limiting factors – the force that slow the growth of a population.

Population Size

Climate

Human Disturbanc

eNatural Disaster

s

Predation

Water Availability

Disease

Parasitism Food

Competition

Living Space

Density- dependent

Density Independent

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SECTION 5.3 - POPULATIONSLimiting Factors

• 2 Kinds

1. Density-dependent limiting factors – limiting factors that are dependent on population size.

- Examples include: food supply, predation, and disease.

- Are related to competition and other interactions between organisms.

- Usually when one population declines, another population also declines.

2. Density-independent limiting factors – a limiting factor that affects the same percentage of a population regardless of its size.

- Examples include: Natural disasters, climate and human disturbance.