The Living World - Environmental Science - page 33

Chapter 2: The Living World
For an ecosystem to function properly and remain healthy, countless organisms and the environment have in-
teractions that affect one another. To understand how an ecosystem functions, it is necessary to understand the
living components, how they work together, and how they are affected by other biotic and abiotic factors. This
chapter reviews the structure of ecosystems, the relationships between organisms and their environment, en-
ergy flow and nutrient cycling, and ecosystem changes.
Ecosystem Structure
Ecosystems are made up of all their living and nonliving components interacting in a specific area at the same
time. The parameters of an ecosystem can vary, but all ecosystems are made up of the same components. Every
ecosystem contains communities and populations of organisms, which are made up of a variety of species and
individual organisms, all interacting with the abiotic factors including rocks, water, and climate. Lifting up a
rock in a forest can expose a mini-ecosystem. A forest functions as an ecosystem, while Earth's entire bio-
sphere can also be considered an ecosystem.
Biological Populations and Communities
A group of individuals (organisms) of the same species living in the same area at the same time is considered
to be a population. For example, all the black bears currently living in eastern Oregon would be a population.
A community is made up of multiple populations of different species in a given area. As an example, in east-
ern Oregon, the American badger, bullfrog, painted turtle, deer mouse, elk, mountain lion, black bear, and
Douglas squirrel populations are all part of the animal community within this region, along with many other
species. Population ecology examines how the individuals within a species interact, while community ecology
examines how a variety of species interact. (For additional information on population ecology, refer to Chapter
3.)
Ecosystems are made up of not only the living organisms in an area but the nonliving components as well.
When studying populations and communities, the habitats are also important for understanding interactions and
ultimately species' survival and reproduction. An organism's habitat is the location in which it lives, and it in-
cludes the soil, vegetation, water supply, and many other factors.
Within most ecosystem communities are keystone species, which are species that have an important and dra-
matic affect on the ecosystem in which they live. This is not to say that other organisms are not important—a
keystone species has an effect on a wide range of other organisms, impacting both the ecosystem's structure
and functioning. Examples of keystone species include sea otters, elephants, beavers, and wolves.
Ecological Niches
An organism's niche is both how the organism uses its resources and its role in the community. Niche compon-
ents include habitat use, food consumption, interactions with other species, and shelter, among many other as-
pects. Organisms that have the ability to survive in a variety of environments and can adjust to different situ-
ations and niches are considered to be generalists. They can handle changing conditions and temperatures and
do not especially thrive in any specific type of environment. Specialists, on the other hand, have adapted to a