1. Honors Biology Chapter 34
Nature of Ecosystems
John Regan
Wendy Vermillion
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. 34.1 The biotic components of ecosystems
Populations of an ecosystem
Autotrophs- primary producers
Require an energy source and inorganic nutrients to produce organic food molecules
Manufacture organic nutrients for all organisms
Green plants and algae-photosynthesis
Bacteria-chemoautotrophs
Heterotrophs- consumers
Consume organic nutrients
Herbivores, carnivores, omnivores
Decomposers- fungi, bacteria
Break down decaying matter releasing nutrients
Detritus- partially decomposed matter
Detritivore-eats detritus

3. Biotic components
Fig. 34.1

4. The biotic components of ecosystems cont’d.
Energy flow and chemical cycling
Energy enters ecosystem in the form of sunlight absorbed by producers
Chemicals enter when producers absorb inorganic nutrients
Producers then make organic nutrients for themselves and all other organisms in the ecosystem
Consumers (herbivores and omnivores) gain nutrients and energy from eating producers
Higher level consumers (carnivores) then gain nutrients and energy from eating herbivores and omnivores
Some energy is released at each level to the environment in the form of heat and waste products

5. Energy flow and chemical cycling
Fig. 34.2

6. Energy balances
Fig. 34.3

7. The biotic components of ecosystems cont’d.
The following two slides illustrate food webs
Food webs illustrate the interrelationships between organisms in the food chain
Identify the producers, primary consumers, and secondary consumers
Laws of thermodynamics
First law- energy is neither created nor destroyed
Ecosystems depend on continual outside source of energy
Second law- with every transformation, some energy is given off as heat
The amount of available energy at each successive trophic level is less than the one below it

8. Grazing food webs
Fig. 34.4

9. Detritis food web
Fig. 34.5

10. 34.2 Energy flow Trophic levels
Trophic level is composed of all organisms that feed at a particular link in the food chain
Primary producers- first trophic level
Primary consumers- second trophic level
Secondary consumers- third trophic level
Ecological pyramids- diagrams of the community
Represent amount of available energy in each trophic level
Producers are at the base- the most available energy
Energy is given off in less usable forms as producers are eaten by primary consumers, etc.
Numbers, biomass, or energy
Biomass- the number of organisms at each level multiplied by their weight

11. Ecological pyramid
Fig. 34.6

12. 34.3 Global biogeochemical cycles
Pathways involve both biotic and abiotic components
Reservoir-source unavailable to producers
Exchange pool-source from which organisms take chemicals
Biotic community-chemicals move through community along food chains
2 main types of cycles
Gaseous cycle-drawn from and returns to the atmosphere
Sedimentary cycle-element is drawn from soil by plant roots, eaten by consumers, returned to soil by decomposers

13. Model for chemical cycling
Fig. 34.7

14. Global biogeochemical cycles cont’d.
The water cycle
Freshwater evaporates from bodies of water
Precipitation over land enters ground, surface waters, aquifers
Eventually returns to oceans over time
Hydrologic cycle is illustrated on the following slide
Note that size of arrow is proportional to rate of transfer
Human impact
In arid southwest and southern Florida, water mining is occurring
Aquifers are being drained faster than they can be naturally replenished

15. The hydrologic cycle
Fig. 34.8

16. Global biogeochemical cycles cont’d.
The phosphorus cycle
Phosphate enters soil as rocks undergo weathering process
Picked up by producers and cycles through consumers and finally decomposers
Human impact
Accelerated transfer rate due to phosphate mining, supplementation on farm fields, detergents
Cultural eutrophication- over-enrichment
Can lead to increased algal bloom
As algae die off, decomposers consume high levels of oxygen in the water
Results in massive fish kills
Phosphorus cycle is illustrated on the following slide

17. The phosphorus cycle
Fig. 34.9

18. Global biogeochemical cycles cont’d.
The nitrogen cycle
Nitrogen fixation-conversion of nitrogen gas N2 to ammonium NH4+ by bacteria
78% of atmosphere is nitrogen gas, but unusable by plants
Root nodules of legumes house nitrogen-fixing bacteria
Nitrification-production of nitrates which plants can also use
Nitrogen gas converted to nitrate in atmosphere by lightning
Ammonium in soil converted to nitrate by nitrifying bacteria
Nitrite bacteria ammonia →nitrite (NO2-)
Nitrate bacteria nitrite → nitrate (NO3-)
Denitrification-conversion of nitrate back to nitrogen gas by denitrifying bacteria
Human activities- N2 from fertilizers increases transfer rates

19. The nitrogen cycle
Fig

20. Global biogeochemical cycles cont’d.
The carbon cycle
Photosynthesis takes up carbon dioxide from the atmosphere
Cell respiration returns it to the atmosphere
Reservoirs of carbon
Dead organisms- fossil fuels
Forests
Human activities
More carbon dioxide is being deposited in atmosphere than is being removed
Due to deforestation and burning of fossil fuels
Increased carbon dioxide in atmosphere contributes to global warming

21. The carbon cycle
Fig

22. Ozone O2 → O3 Oxygen is converted into ozone in atmosphere by UV rays
Also by lightning and industry
Ozone in lower atmosphere –air pollutant
In stratosphere- blocks UV rays
UV rays cause sunburn, skin cancer, cataracts, slows growth of plants
Ozone has been depleted
10% ↓ ozone, 26% ↑ cataracts, skin cancer
Cause of ozone depletion- Chlorofluorocarbons (CFCs)
CFCs banned 2000