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Community Ecology

All the populations of different species living in a particular area comprise that area's community--the living portion of the ecosystem. The number of different species found in an ecosystem comprise that system's species diversity. Diversity varies greatly among ecosystems, and hence, so do the interactions among populations in those ecosystems.

A community is any assemblage of populations in an area or habitat.

Symbiosis

Symbiosis (from the Greek sym, meaning "together" and bios, meaning "life") refers to the members of two different species (i.e., two populations) having some sort of ecological interaction that affects both populations. When two species evolve in response to each other's activities, the process is known as coevolution.

Let's consider some of the coevolutionary results of predation...

crypsis - camouflaging coloration

aposematism - warning coloration (poisonous or venomous species)

mimicry - a species has evolved the superficial appearance of something else

    Batesian mimicry - a harmless mimic looks like a poisonous model.

    Mullerian mimicry - several poisonous/distasteful species resemble one another.

 

Ecosystem Ecology

You are probably familiar with a typical food web, and know what trophic levels are.

The Food Web reflects the flow of energy and nutrients through ecosystems.

Energy Flow begins with primary productivity, the amount of light energy converted to chemical energy (organic molecules) by an ecosystem's autotrophs over a given period of time.

  • Gross Primary Productivity (GPP) - Total primary productivity
  • Net Primary Productivity (NPP) - Total primary productivity - energy used for respiration

    NPP = GPP - R

Primary productivity (always expressed as a rate) can be expressed as
  • energy per unit area per unit time (e.g., Joules/m2/year)

    or

  • biomass, the dry weight of vegetation added to an ecosystem per unit area per unit time (e.g., grams per square meter per year).

Standing crop biomass is the dry weight of vegetation in an ecosystem at any given "snapshot moment" in time. It is not the same as primary productivity: it's not a rate!

Energy flow is never 100% efficient, and this results in the classic Pyramid of Productivity.

The efficiency with which trophic levels convert energy from the previous trophic levels varies greatly with ecosystem, and usually range between 5% - 20% (What does this mean in terms of how much is lost at each trophic level?), as reflected by the standing crop biomass of each level.

In a few ecosystems, there are some surprises.

Biogeochemical Cycles

A generalized cycle...

...can be superimposed on Biogeochemical Cycles for many different nutrients

Your activities any day have profound effects on these cycles, and on energy cycling in the biosphere. To test how much impact you have on our biosphere, take the following test of your Ecological Footprint.

Go forth and spread the word.