Ecosystem Ecology for Wildlife Scientists

Don White, Jr., Ph.D.

Key Concepts:

An ecosystem is an association of organisms and their environment

Every ecosystem is an open system, in that it has inputs and outputs of both energy and nutrients

Energy flows in only one direction through an ecosystem

Key Concepts:

Each chain in a food web extends in a straight-line sequence from producers through all the consumersWater, carbon, nitrogen, and phosphorus move through geochemical cycles that are global in scaleEach substance moves through a hydrologic, atmospheric, or sedimentary cycleHumans are disrupting the natural cycles

The Nature of Ecosystems

Primary producers

Consumers

Decomposers

Detritivores

Structure of Ecosystems

Trophic Levels• 1st - Primary producers

Autotrophs

• 2nd - Primary consumers

Herbivores, Decomposers, Detritivores

• 3rd - Secondary consumers

Primary carnivores

• 4th - Tertiary consumers

Secondary carnivores and parasites

Food Webs

“ Network of crossing, interlinked food chains involving primary producers, consumers, and

decomposers”

How Does Energy Flow Through an Ecosystem?

Primary source• Grazing food webs

Photosynthetic organisms to herbivores

• Detrital Food Webs

Photosynthetic organisms to detritivores and decomposers

Ecological Pyramids

Primary Producers

Herbivores

Primary carnivores

Top carnivores

Decomposers

Energy Flow at Silver Springs, Florida

Energy loss with each trophic level

Geochemical Cycles

Hydrologic Cycle

Rain and snow returns water to land

• Ocean currents and winds

• Evaporation

Watershed

Deforested area had greater calcium loss than undisturbed area.

Sedimentary Cycle

Phosphorus Cycle• From land to sediments at bottom of the sea then back

to land

• Earth’s Crust

Largest reservoir of phosphorus

Eutrophication

Activities that increase the concentration of dissolved nutrients

Nutrient enrichment of any aquatic ecosystem

Most minerals enter sedimentary cycles

Fertilizers use phosphates• Dense algae blooms

Carbon Cycle

Aerobic respiration ------> Carbon dioxide

Fossil fuel burning

Volcanic eruptions

Atmosphere, soils, plant biomass• Largest holding stations for carbon

Carbon dioxide fixation• Photosynthetic autotrophs

From Greenhouse Gases to a Warmer Planet?

Greenhouse effect

Increase in CO2 Increase in CFC’s

From Greenhouse Gases to a Warmer Planet ?

Greenhouse effect

Increase in methane Increase in nitrous oxide

Nitrogen Cycle

N2 gases converted to usable forms• Bacteria

Nitrogen fixation

• Bacteria and fungi

Decomposition

Ammonification

Nitrification

• Denitrification

Ecosystem Modeling

Prediction of unforeseen effects of disturbance

Computer programs

Models

Biological magnification• Use of DDT

In Conclusion

An ecosystem is an array of producers, consumers, detritivores, and decomposers and their environmentSunlight is the initial energy source for nearly all ecosystemsFeeding relationships are structured as trophic levels in an ecosystem

In Conclusion

Isolated food chains of who eats whom in an ecosystem are rare in natureThe rate at which primary producers capture and store energy is the primary productivityEnergy fixed by photosynthesizers passes through grazing food webs and detrital food webs

In Conclusion

Primary productivity depends on water and nutrientsCarbon dioxide is the main atmospheric gas in the carbon cycleBurning fossil fuels and converting natural ecosystems to farming and grazing add to imbalances and may be factors in long-term global warming

In Conclusion

Nitrogen availability is a limiting factor for the total net primary productivity of land ecosystemsMost mineral elements enter sedimentary cycles and become available Disturbances of an ecosystem can have unexpected effectsComputer modeling helps identify ecosystem relationships and can incorporate them into models