The Web of Life
No organism lives completely alone. Every living thing, from a tiny bacterium to a giant blue whale, interacts with other living things and with its non-living environment. Ecology is the scientific study of these interactions.
Levels of Organization
To study the complex web of life, ecologists look at different levels of organization.
An organism is a single living individual.
A population is a group of individuals of the same species living in the same area. For example, all the squirrels in a particular park make up a population.
A community includes all the different populations of different species that live and interact in an area. The community in the park would include the squirrels, the oak trees, the pigeons, the grass, the earthworms, etc.
An ecosystem includes the entire community of living organisms (all the biotic factors) plus their non-living physical environment (the abiotic factors).
Biotic vs. Abiotic Factors
Every ecosystem is made up of two types of components:
Biotic Factors: These are all the living or once-living parts of the ecosystem.
Examples: Plants, animals, fungi, bacteria, a fallen log.
Abiotic Factors: These are all the non-living parts of the ecosystem. These factors have a major influence on which organisms can live in a place.
Examples: Sunlight, water, temperature, soil type, oxygen levels, wind.
A Place to Live and a Role to Play
Two other important concepts in ecology are habitat and niche.
A habitat is the specific environment where an organism lives. It's the organism's 'address'. A habitat provides the food, water, and shelter that an organism needs to survive. The habitat of a polar bear is the Arctic sea ice. The habitat of a cactus is the desert.
A niche is the role or 'job' that an organism has within its ecosystem. A niche includes everything about how an organism lives: what it eats, what eats it, when it is active, and how it interacts with the biotic and abiotic factors of its environment. For example, the niche of a sunflower is to be a producer, using sunlight to grow, providing food for insects and birds, and providing shelter for small spiders.
Two different species can share the same habitat, but they cannot occupy the exact same niche for very long. They will compete with each other until one is forced to adapt or is outcompeted.