Chapter 2 Interactions of Living Things
Section 1: Everything is Connected
Introduction: alligators eat fish but digs holes under the water to escape heat. Other organisms live in these
holes once the alligator leaves them.
I.
Studying the web of life
A. Ecology is the study of the interactions of organisms with one another and with their environment.
B. The Two parts of an environment
1. biotic – all of the organisms that live together and interact with one another
2. abiotic – all the nonliving elements such as water, soil, light, and temperature
C. Organization in the environment
1. Level one is made of an individual organism
2. Level two is larger and made of similar organisms forming the population
3. Level three is made of different populations, forming a community.
4. Level four is made of a community and its abiotic environment, forming an ecosystem.
5. Level five (final level) contains all ecosystems, forming the biosphere.
D. Populations
1. population is a group of individuals of the same species that live together
2. individuals in the population often compete with one another for food, nesting spaces
and mates.
E. Communities
1. a community consists of all the populations of species that live and interact in an area.
2. the populations in a community depend on each other for food, shelter, and many other
things
F. Ecosystems
1. ecosystems are made up of a community of organisms and the abiotic environment of the
community
2. Examples, the rivers that empty into a marsh bring nutrients which affect the growth of
the cord grass and algae.
G. Biosphere
1. biosphere is the part of Earth where life exists extending from the deepest parts of the
ocean to high in the air where plant spores drift
2. ecologists study the biosphere to learn how organisms interact with the abiotic factors
Section 2: Living Things Need Energy
I.
The Energy Connection
A. Producers
1. Producers are organisms that use sunlight directly to make food.
2. Photosynthesis is the process producers use to make food from the sun
3. Producers are mostly plants, and algae and some bacteria
a. grass is the producer in a prairie ecosystem
b. cord grass and algae are producers in marshes and oceans
c. trees are the producers in a forest
B. Consumers
1. Consumers are organisms that eat other organisms
2. Consumers get their energy from eating producers.
a. herbivores eat only plants
Examples: grasshoppers, bison, cows
b. carnivores eat other animals
Examples: coyotes, hawks, owls
c. omnivores eat both plants and animals
Examples: grasshopper mouse
3. Scavengers eat dead plants and animals
C. Decomposers
1. Decomposers are organisms that get energy by breaking down dead organisms
2. Bacteria and fungi are examples
3. These organisms remove the stored energy from dead organisms, producing simple
materials such as water and carbon dioxide which can be used by other living things.
4. Decomposers are nature’s recyclers
D. Food Chains and Food Webs
1. Food chains are diagrams that show how energy in food flows from one organism to
another organism to another.
Example: nuts  squirrel fox
2. A food web is a diagram that shows the feeding relationship between several organisms
In an ecosystem
.
3. The arrow goes from “provider of energy” to the next. Only energy stored in the muscle
of the next consumer can be used by the next consumer in line.
E. Energy Pyramids
1. An energy pyramid is a diagram that shows an ecosystem’s loss of energy.
2. Grass uses most of the energy it gets from the sunlight for its own life process but some
is stored in the grass’ tissue which will give energy to the next consumer
II. Wolves and the Energy Pyramid
A. Gray wolves are very important to the flow of energy in an environment.
1. They control the populations of many other animals.
2. Their diet can include anything from a lizard to an elk.
3. They prey on animals at the top of the food pyramid
4. The elimination of gray wolves will allow populations to overpopulate and reduce
the amount of food for the lower levels of the pyramid.
B. Gray wolves and the Food Web
1. Gray wolves were reintroduced to Yellowstone National park in 1995 in hopes they
will restore the balance of the populations and restore the park’s integrity.
2. Ranchers though are concerned about their livestock in these areas.
C. Balance in Ecosystems
1. Reintroducing the gray wolf into Yellowstone will remove the old, injured, and
diseased elk reducing the number of elk.
2. Which in turn will allow more plants to grow.
3. This allows the food web to balance again.
Section 3: Types of interactions
I. Interactions with the Environment
A. Most living things produce more offspring than will survive.
B. Organisms interact with biotic and abiotic factors in the environment that can control the size
of its population.
C. Limiting Factors
1. limiting factors are resources that are so scarce that it limits the size of the population.
Ex. Food becomes a limiting factor when the population becomes too large and the
needed amount of food is not available.
D. Carrying Capacity
1. Carrying capacity is the largest population an environment can support
2. If there exists more than the “carrying capacity” some individuals will die off or leave,
decreasing the population.
II. Interactions Between Organisms
A. There are four main ways species and individuals affect each other.
1. Competition
a. Competition is when two or more individuals or populations try to use the same
resource, such as food, water, shelter, space or sunlight.
b. Competition happens between same populations and between populations.
2. Predator and Prey
a. A prey is the organism being eaten.
b. The organism that eats the prey is the predator.
c. Predator adaptations
1. a cheetah’s speed is its adaptation
2. a goldenrod spider can blend in with its environment to ambush his prey.
d. Prey adaptations
1. Some examples of adaptations are: blending in, staying in groups, running away.
2. Some are poisonous
e Camouflage
1. Camouflage is blending in with its environment or surroundings.
2. Examples: rabbit blends in with its natural color; others mimic twigs, leaves,
stones, bark or other materials in environment
f. Defensive Chemicals
1. Some animals can defend themselves with chemicals.
2. Examples: skunks and bombardier beetle spray chemicals; bees, ants, and
wasps inject a powerful acid into their attackers. The skin of a poison arrow frog
and a bird (hooded pitohui) contains deadly toxins and kills their predators
g. Warning Coloration
1. The most common warning colors to predators are bright shades of red, yellow,
orange, black, and white
2. Colors warn predators of pain, illness, and unpleasant experiences
3. Symbiosis
a. symbiosis is a close, long-term association between two or more species.
b. Mutualism
1. a symbiotic relationship in which both organisms benefit.
2. Example: You and the bacteria in your stomach. The bacteria get food from you
and you get the vitamins the bacteria produce.
c. Commensalism
1. Commensalism is a symbiotic relationship in which one organism benefits and the
other is unaffected.
2. Example: a shark and a remora (fish) the remora hitches a ride and eats from
the leftovers by the shark.
d. Parasitism
1. A symbiotic association in which one organism benefits while the other is harmed.
2. Parasite is the organism that benefits.
3. Host is the organism that is harmed.
4. Example: Tick (parasite) on a dog (host) female wasp (parasite) laying eggs on
a
Tomato hornworm (host), the young wasps eat the caterpillar alive.
5. Most hosts do not kill their host because they depend on them to survive.
4. Changes in Organisms
a. relationships between organisms change over time.
b. Interactions can also change the organisms themselves
c. changes happen over a long period of time
d. Changes and flowers
1. A pollinator is an organism that carries pollen from one flower to another
Examples are: bees, bats, and hummingbirds
2. Pollination is part of the reproduction for many plants
3. Pollinators are attracted to a flower because of its color, odor, or nectar.
4. As the pollinator feeds on the nectar, its nose is covered with pollen. The next
flower is pollinated by the nectar gained by the previous flower.