An ecosystem is the place where the organisms of an environment have interactions between their biotic and abiotic components. These organisms respond to the environment and their functional attributes are:
a) Energy flow
b) Trophic levels
c) Biogeochemical cycling of key elements
d) Environmental gradients of organism diversity in space and time
e) Ecosystem level or succession
f) Cybernetic control or feedbacks
There are 3 things that define an ecosystem:
1. Boundary state
2. Integration of Abiotic and Biotic Processes
3. Redundancy of the species concept
Species Redundancy is very important to consider in an ecosystem. As far as the ecosystem’s processes go, can one species replace another? Do we need wide diversity of species? Finally, does every species in an ecosystem make a contribution or are some redundant?
Keystone species within an ecosystem are those who have an impact on the community which is disproportionate to its abundance. Keystone species can include predators, herbivores, competitors, mutualists, earth movers, system processors and abiotic systems.
What is an example of the disproportionate effect for a keystone species? Consider starfish and the ecosystem they live in. What would happen if you were to remove all the starfish from an ecosystem? Predators, such as fish and starfish, feed on mussels and a variety of other invertebrates. The diversity of the invertebrate species in the ecosystem is very high when the starfish are part of it. However, when you remove starfish from the ecosystem, the species diversity amongst the invertebrates will fall. This is because the mussels are not being eaten as much. Therefore, their numbers grow and they eventually out-compete other invertebrates in the ecosystem. The other invertebrates decline in number, thus you have a loss of diversity.
The theory of productivity in an ecosystem tells us that all species matter. They are all linked to one another in some way, so you can not remove some of them without affecting the others. Consider the “Rivet Hypothesis” to further illustrate this. In an airplane, you have a lot of rivets holding things together. You can remove some of those rivets and the airplane will still fly. However, you will eventually get to the point that if you remove too many rivets, the airplane will crash.
Many different approaches are taken to study ecosystems. These include:
1. Experimental Systems (simple systems)
2. Mathematical Models (simulations)
3. Population Studies of Groups of Organisms
4. Studies of the entire ecosystem (generally this is too expensive given current research dollars available to the science)
Population studies are particularly interesting and can be done on ecosystems such as rain forests, or species such as panda bears or rare orchids. The study of ecosystems is a complex science, but a very important one for humans. It helps us learn more about the world around us and understand why changes occur in ecosystems that can affect our food sources, or even the plants and trees in our backyard.