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.ecosystem Different organisms depend on different parts of an ecosystem to survive. What are ecosystems?

Abiotic factors are the nonliving parts of an ecosystem. Abiotic factors 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. Biotic factors A population is made up of all the members of one species that live in an area.population 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.community Biotic Factors

A biome is a large region on Earth with a specific climate, physical features, plants, and other organisms.biome 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 factorsLimiting factors are factors that can limit the growth of a population.

Communities All 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.habitat A niche is the unique ways an organism survives, obtains food and shelter, and avoids danger in its habitat.niche Symbiotic Relationships

A symbiotic relationship is one in which two different species live together and interact closely over a long period of time.symbiotic relationship 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.)

ProducersProducers 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 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.food chain 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.food web Modeling Energy Flow (cont.)