Types of Interactions

In natural communities, populations of different species vary greatly. The

interactions of these populations affect the size of the populations.

The seaweed forest is home to a large number of interacting populations.

Limiting Factors

Amount of food

Amount of living space

Amount of water

When a population becomes too large for the amount of a given resource, it will become a limiting factor.

Carrying Capacity

The largest a population can get in a given environment over a long period of time.

When a population get larger than the carrying capacity, a limiting factor causes the population to decline.

Competition

When two or more individuals or populations try and use the same limited resource.

Food

Water

Shelter

sunlight

Competition

Can be with in a

population

Weird Science

Green herons make interesting use of biotic and abiotic part of their environment in Japan. They will drop sticks and even break crumbs

into the water to attract fish. Sometimes they catch a fish 2-3 seconds after they drop the bait!Pretty Cool!

Misconception Alert While it’s true that all members of an ecosystem have important

roles, some members are more important than others to the overall health of the ecosystem. Such species are called keystone species. Like removing the keystone that holds up the other stones in an arch, removing the keystone species can cause the whole system to collapse. This occurred when the sea otter was hunted to near extinction in the kelp forests of the Pacific Ocean. With the otters gone, nothing was left to eat the sea urchins, which multiplied and ate all the kelp. The kelp was home to dozens of animals, all of which disappeared, along with most of the sea urchins. When the sea otter

was reintroduced, all these organisms returned!

Discussion

The lynx relies primarily upon the snowshoe hare for food.

How would the abundance of plants affect the hare population?

What will happen to the lynx?

What happens when the food

runs out for the hare?

Predator

Predators must adapt to catch the prey

Speed

Ambush

camouflage

Prey

Prey need adaptations to escape the predator

Run/hide (burrow)

Live in groups

Camouflage

Poison/color warning

Symbiosis

Close long-term association between two or more species.

Individuals within a symbiotic relationship may: benefit be unaffected be harmed

Mutualism

Both organisms benefit

Bacteria in our intestine.

They get food

We get vitamins

Coral and algae

Coral provides home to algae

Algae provides food for the coral.

Commensalisms

One organism benefits

Other organism is unaffected.

Parasitism

One organism benefits = parasite

Other organism is harmed = host

Can cause death of the host!

Coevolution

A long-term change that takes place in two species because of their close relationship with one another.

MimicryWhen one organism “mimics” another to take advantage of their defense’s.

Viceroy Butterfly

 The viceroy and monarch were once thought to exhibit Batesian mimicry, where a harmless species mimics a toxic species.  Studies conducted in the early 1990's suggest that the viceroy and the monarch are actually examples of Mullerian mimicry where two equally toxic species mimic each other to the benefit of each. Just goes to show you there's always something new to discover in the natural world!

Monarch Butterfly

Both species benefit by this mimicry. A predator that avoids one will avoid the other.

The killdeer is a ground-nesting bird that will distract a predator from its nest or chick with a “broken-wing” display. It will limp and drag a wing on the ground making itself appear to be an easy catch. But because it is actually quite healthy, it always stays one step ahead of the predator.

Misconception Alert

The phrase balance of nature does not imply that the components of an environment are static. Populations are in balance when their sizes are stable. That stability is the result of constant interactions between individuals of a population, between populations in a community, and between populations and environmental factors.

Brain Food

Studies have shown that ducks can have one-half of their brain asleep while the other half is awake. The side that is awake can even have an eye opened and respond to stimuli. The sides can also switch so that the half that was awake can rest and the rested half can become alert. Why might this be helpful to ducks?

Honeyguides live in Africa and India and are so called because they lead honey badgers and humans to the nests of wild bees using a series of calls. After the nest has been raided for honey, the bird gets the chance to feed on bee grubs from the open nest.

The bird’s unique digestive system allows it to eat wax as well. Which animals in this story are in a mutualistic relationship?

Which animals are prey? Which are predators?

Weird Science

Pancake tortoises live on rocky hillsides in Africa. They are very flat and can wedge themselves into the cracks in the rocks for protection from predators. Their bottom shells are pliable and can “inflate” so that a predator can’t pry the tortoises out.