We are moving up through the scale of ecology, having covered organisms, populations,
and communities. Now let’s pull back even farther to look at ecosystems. An ecosystem consists of
all the organisms in an area, meaning the entire community, as well as the abiotic factors that
influence that community. So we are looking past organisms here, towards the physical phenomena
that have an impact on them. Ecosystem ecologists often focus on the flow of energy and recycling of
nutrients. Think of an ecosystem as a geographic area where plants, animals, and other organisms,
as well as weather and landscape, work together to form a “bubble” of life.
The three broad categories of ecosystems based on their general environment include freshwater,
ocean water, and terrestrial ecosystems. Within these broad categories are individual ecosystem
types based on the organisms present and the type of environmental habitat, such as wetlands,
lakes, and forests, all of which we will explore in detail later in the series.
With regards to the flow of energy, the biotic and abiotic components of an ecosystem are
linked together: energy enters the system through photosynthesis and is incorporated
into plant tissue. By feeding on plants and on one another, animals play an important
role in the movement of matter and energy through the system. They also influence the
quantity of plant and microbial life. When decomposers break down dead organic matter,
they release carbon back to the atmosphere and facilitate nutrient cycling by converting
nutrients stored in dead biomass back into a form that can be readily used by plants and microbes.
Energy and nutrients can also be released from an ecosystem in the form of disturbances,
such as wildfires, or transferred to other ecosystems, like from a forest to a stream to
a lake through the process of erosion, which is the physical and chemical breakdown of
materials in the environment. Thus, ecosystems are controlled by both external and internal factors.
External factors such as climate, the parent rock material that forms the soil, and topography
are what control the overall structure of an ecosystem, but are not themselves influenced
by the ecosystem. Internal factors are controlled, for example, by decomposition, root competition,
shading, disturbance, succession, and the types of species present. While the kinds of resources
made available to the ecosystem are generally controlled by external processes, the availability
of these resources within the ecosystem is controlled by internal factors. Therefore,
internal factors not only control ecosystem processes, but are also influenced by them.
Ecosystems are dynamic entities, and they are subject to periodic
disturbances. More than likely, they are always in the process of recovering from
some past disturbance. The tendency of an ecosystem to remain close to its ideal,
or equilibrium state, despite these disturbances, is termed its resistance.
Scientists can study ecosystems through a variety of approaches including but not limited
to theoretical studies, monitoring specific ecosystems over long periods of time, direct
experimentation, and comparing or contrasting ecosystems to figure out how they work.
And with ecosystems better understood, we can begin to approach the biosphere as a whole.
Ecologists tend to work together to inform our collective knowledge about the biosphere,
and in order to understand the work that’s been done so far, we will have to learn quite
a bit about some other topics, so let’s move forward and start learning about climate next.