Understanding Populations

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Understanding Populations

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Understanding Populations

Ch8, Section 2: How Species Interact with Each Other

Standards: SEV3e, SEV5a, b


What is a species’ niche?

Niche- role a species has within an ecosystem.


Species physical homeFactors needed for survivalInteractions with other organismsEx: Bison are grazers & help control tree sapling populations as well as fertilize soil for grassEx: Fungi & bacteria are decomposers, recycling nutrients to soil.


What is a



Place where a species livesAn organism performs its niche in its habitat.


How do species interact with each other?





1. Competition

Relationship where individuals or populations share limited resources

Both species are harmed

-/- interaction (“lose/lose”)Intraspecific competition- within the same species.Ex: caterpillars of the same species eating the same leaf.Interspecific competition- between different species

When members of different species compete we say their niches have overlapped.Ex: hyenas compete for kill with lions


1. Competition

Indirect competition-

compete even though they do not come in contact with each other.

Ex: An insect that eats a leaf during the day competes indirectly with an insect that eats the same leaf at night.Ex: Plants compete for pollinators; humans compete with insects for food crop.


1. Competition

Adaptations to competition-

When 2 species compete for a resource, usually only one will win.

The other species must move to find new resources.This is called competitive exclusion.


1. Competition

Competitive exclusion can lead to

niche restriction.

These species share the same niche & habitat but use a smaller portion of it.Ex: Two barnacle species Chthamalus & Balanusshare the same intertidal zone of a rocky shore lineChthamalus

lives at higher tide line (realized niche)When Balanus is removed, Chthamalus will move further down into the original Balanus habitat. (fundamental niche)

Realized niche-

where the species actually lives

Fundamental niche-

where the species could live if given a chance.


1. Competition

Realized niche-

where the species actually lives

Fundamental niche-

where the species could live if given a chance.

Copy this down!


2. Predation

Predator feeds on prey

Predator benefits, prey is harmed

+/- interaction (win/lose)Some predators are very specific about what they eatCanadian lynx only eat snowshoe haresCreates predator/prey oscillationsMost predators generally eat any prey they can capture

Not all predators are carnivores


2. Predation

Animals adapted to avoid predation:


hard to see; blend inEx: some caterpillars; lizardsWarning coloration- alert potential predator that they are dangerousEx: poison dart frogsMimicry- look like something more dangerous even if it isn’t

Ex: some flies have same coloration as beesProtective coverings- too hard for predator to eat.Ex: porcupine, turtle, cactus


3. Parasitism

Parasite lives and feeds on host organism.

Parasite benefits, host is harmed

+/- interaction (win/lose)Parasites are different from predators because they do not usually kill their host (what else would they eat if they killed their host?)Parasite can weaken host & make them more susceptible to disease.Ex: ticks, leeches, mistletoe, fleas


4. Mutualism

Each species benefits from the relationship


interaction (win/win!)Some species couldn’t live without each otherEx: bacteria in your intestine; acacia tree & ants; insects & flowers


5. Commensalism

One species is benefited and the other is neither harmed nor helped.

+/0 interaction

Ex: orchids in trees; clownfish & anemones; remoras and sharks


What is Symbiosis

Relationship where two species live in close association

Often one species benefits.

Which of the five species interactions are considered symbiosis?


What is Coevolution


When species have such close relationships they often coevolve.

These two species would be less likely to survive if one were missing.Ex: bee orchidsThis bee orchid has a dark region with yellow spots that resemble the abdomen of a female bee. Male bees will try to copulate with the orchid and in the process will pollinate the orchids.

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