Relationships Among Organisms

• Ecology is the study of how organisms interact with each other and with their environments.• Every organism on Earth lives in an ecosystem—the living and

nonliving things in one place.• Different organisms depend on different parts of an ecosystem to

survive.

What are ecosystems?

• Abiotic factors are the nonliving parts of an ecosystem.• Important abiotic factors include water, light, temperature,

atmosphere, and soil.• The types and amounts of abiotic factors in an ecosystem help to

determine which organisms can live there.

Abiotic Factors

• Biotic factors are all of the living or once-living things in an ecosystem.• A population is made up of all the members of one species that live

in an area.• Organisms in a population interact and compete for food, shelter,

and mates.• A community is all the populations that live together in the same

place.

Biotic Factors

• A biome is a large region on Earth with a specific climate, physical features, plants, and other organisms.

• Biomes contain ecosystems, populations, and communities, as well as specific biotic and abiotic factors.

• All biomes are part of the biosphere—the part of Earth that supports life—and can be described as either terrestrial or aquatic.

• The 6 main biomes are: dessert, forest, tundra, grassland, salt water, and fresh water.

Biotic Factors (cont.)

• The area in which a population lives can be very large, such as the population of all the fish in the ocean, or very small, like fish in a lake. • If either biotic or abiotic factors that affect an organism change,

that organism’s population can also change.• Sometimes the size of a population changes because the

ecosystem changes.• Population density describes the number of organisms in the

population relative to the amount of space available.• If a population is very dense, organisms might have a hard time

finding enough resources to survive.

Populations

Limiting factors are factors that can limit the growth of a population.

CommunitiesAll the populations in the same area interact as a community. Some populations might compete with each other for resources and space.

• Each population has different ways to stay alive and reproduce.• All of the populations in a community share a habitat, the physical

place where a population or organism lives.• A niche is the unique ways an organism survives, obtains food and

shelter, and avoids danger in its habitat.

Symbiotic Relationships

• A symbiotic relationship is one in which two different species live together and interact closely over a long period of time.• These relationships can be beneficial to both organisms, beneficial to

one and harmful to the other, or beneficial to one and neutral to the other.

Symbiotic Relationships (cont.)

• Mutualism—two species in a community benefit from the relationship.• Parasitism—one species (the parasite) benefits while another (the

host) is harmed.• Commensalism—one species benefits and the other is neither helped

nor harmed.

Types of Symbiotic Relationships

• Scientists classify organisms by the way they get the energy they need to survive.• Some organisms, such as plants, are able to capture the Sun’s energy

directly and convert it into energy-rich sugars that they use for food.

Organisms and Energy

• A few organisms are able to capture energy from chemicals in the environment and make food by a process called chemosynthesis. • Other organisms cannot capture energy from sunlight or chemicals

and must obtain their energy by eating food.• Organisms that cannot make their own food using the Sun must

depend on organisms that can.

Organisms and Energy (cont.)

Organisms and Energy (cont.)

Producers change the energy available in their environment into food energy that they use to live and reproduce.

• Consumers use the energy and nutrients stored in other organisms for living and reproducing.• Consumers are classified as herbivores, omnivores, carnivores, or

detritivores, based on their diet.• Herbivores are animals that eat only producers, such as plants.

Organisms and Energy (cont.)

• Omnivores, such as human beings, are animals that eat both producers and other consumers.• Carnivores, such as lions, eat only other consumers.• Detritivores, including some insects, fungi, worms, bacteria, and

protists, eat dead plant or animal material.

Organisms and Energy (cont.)

A food chain models how food energy moves from the environment to several organisms.

Modeling Energy Flow

• Each stage of a food chain has less available food energy than the last one, because some food energy is converted to thermal energy and moves to the environment.• A food web is a model that shows several connected food chains.

Modeling Energy Flow (cont.)