Types of Interactions

Look at the seaweed forest below. How many fish do you see? How

many seaweed plants do you count? Why do you think there are more

members of the seaweed population than members of the fish population?

Interactions with the Environment• Most living things produce

more living things than will survive

• A female frog may lay hundreds of eggs, but the population of frogs in a pond will stay about the same as it was the year before—Why?

• An organism interacts with biotic and abiotic factors that control the size of its population

Limiting Factors• Populations cannot

grow without stopping, because the environment contains a limited amount of food, water, living space, and other resources

• A resource that is so scarce that it limits the size of a population is called a limiting factor

• Any single resource can be a limiting factor to a population’s size

Carrying Capacity• Carrying capacity: largest population

that an environment can support• When a population is larger than its

carrying capacity, limiting factors cause individuals to die off or leave

• As individuals die or leave, the population decreases

• The population will return to a size that the environment can support

Interactions Between Organisms

• Four main ways that species and individuals affect each other:

CompetitionPredators and prey

Symbiotic relationshipscoevolution

Competition

• When 2 or more individuals or populations try to use the same resource, such as water, shelter, space, or light, it is called competition

• Can happen in populations or between populations

• Some trees grow tall to reach light, which reduces amt. available to short trees

Predators and Prey• Predator Adaptations

– To survive, predators have to be able to catch prey, using wide variety of methods and abilities

– Goldenrod spider ambushes its prey by blending in with flower and waiting for its insect meal to arrive

• Prey Adaptations– Prey have to keep from

being eaten– Are able to run away, stay

in groups, or camouflage themselves

– Some are poisonous– May advertise poison with

bright colors– Many small fishes swim in

groups called schools– Other animals stay in

herds, increasing the likelihood of spotting a potential predator

Camouflage

• One way to avoid being eaten is by being hard to see

• Blend in with the background

• May mimic twigs, leaves, stones, bark

Defensive Chemicals• Skunk and bombardier

beetle both spray predators with irritating chemicals

• Bees, ants, and wasps inject a powerful acid into their attackers

Bird called the hooded pitohui contains a deadly toxin—any predator that eats, or tries to eat, one of these animals will likely die

Warning Coloration• Predators will avoid any

animal that has the colors and patterns they associate with pain, illness, or unpleasant experiences

• Most common warning colors are

bright shades of red, yellow,

orange, black, and white

Symbiosis

• Symbiosis: a close, long term association between two or more species

• Individuals in a symbiotic relationship can benefit from, be unaffected by, or be harmed by the relationship

• Classified into 3 groups: mutualism, commensalism, and parasitism

Mutualism

• Mutualism both organisms benefit

• Example: corals and algae. Coral provide home for algae, algae produce food for the coral by photosynthesis

Commensalism• One organism benefits and the other is

unaffected• Example: relationship between sharks and

smaller fish called remoras. Remoras “hitch a ride” on sharks and feed on scraps of food left by sharks. The remoras benefit and sharks are unaffected.

Parasitism• One organism benefits while the other is harmed

• Organism that benefits is called the parasite, organism that is harmed is called the host

• Female wasp lays eggs on a tomato hornworm; eggs hatch, young burrow into caterpillar body, and actually eat the caterpillar alive! Then adult wasps fly away

Coevolution• When a long term

change takes place in two species because of their close interactions with one another, this change is called coevolution

• Ant and acacia tree ant protects tree and tree has special structures that make food for ants

Coevolution and Flowers• Flowers have changed over millions

of years to attract pollinators• Pollinators are attracted to color,

odor, or nectar• Flowers pollinated by

hummingbirds make nectar with the right amount of sugar for the bird

• Some bats changed over time to have long, thin tongues and noses to help them reach the nectar in flowers

• They help pollinate as they travel from flower to flower