| Oceanography
Lecture A Review of Ecosystem Ecology |
Food webs:
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How might an ecologist go about determining who eats who?
Given two food webs below, what would happen to species diversity in each if snails were removed?
Are all species keystone species? If not, is there some point (some number of species removals) in which removal of non-keystone species results in a dramatic change in the system?
This suggests that diversity reflects stability of a community.
What is "diversity" as measured by ecologists?
Typically "diversity" in ecology refers not only to species number, but also how evenly the number of individuals per species comprise the total ('eveness').For example, which is most "diverse" according to the above definition?
Several different indices have been developed so that both species richness and eveness are incorporated into a single community number so that diversity among communities can be compared (for example, the Shannon Diversity Index)
Trophic level / Energy pathways - Once it is established who eats who, organisms can be classified into trophic levels.A trophic level comprises all organisms in a ecosystem that are the same number of steps away from the energy input into the system (also defined as a functional classification according to feeding relationship).Producers are organisms responsible for producing organic carbon compounds from inorganic sources of energy and carbon (i.e. making new biomass, fixing carbon,...). What biochemical pathways do this? The rate at which producers generate biomass is referred to as primary productivity. Biomass generated by organisms consuming this biomass directly or indirectly is referred to as secondary production.
The proportion of an ecosystem that is represented by each trophic level can be represented the the following 'pyramid'-type diagrams:
'Pyramid'-type diagrams can represent the proportion of biomass, numbers, or energy in each trophic level. Energy pyramids are always pyramids that are broadest at the base and this can be explained from the second law of thermodynamics (energy is always lost when transferred).What does this imply about:
- the number of trophic levels in an ecosystem?
- the requirement of energy inputs into ecosystems?
Does energy in all ecosystems move along the same pathways as diagrammed above?
Nutrient Cycles
In the diagram above, blue lines trace energy flow
and the broken red lines trace matter cycles.
How does the movement of matter in ecosystems differ from the movement of energy in ecosystems?
What is the advantage to organisms in each of these transformations of matter?
Two examples of nutrient cycles:
Carbon Cycle
Over geologic and historical time, how has the rate (flux) of fossil fuel burning compared with the rate of fossil fuel formation? Which components of the ecosystem have been affected in terms of amount of carbon stored in that component? What environmental problem is related to these change in rates of carbon transformation?
