AP Biology, Chapter 54
Ecosystems

SUMMARY
INTRODUCTION

TROPHIC RELATIONSHIPS IN ECOSYSTEMS
	Introduction
		1. Describe the relationship between autotrophs and heterotrophs in an 
		ecosystem.
			a. Producers (autotrophs) convert sunlight into organic chemical energy
			b. Heterotrophs utilize that stored energy
				i. Primary consumers eat producers
				ii. Secondary eat primary, etc.
				iii. Most feed at more than one level = a food web
			c. Decomposers get all in the end			
	Trophic relationships determine an ecosystem's routes of energy flow and 
	chemical cycling
		2. Explain how the first and second laws of thermodynamics apply to 
		ecosystems.
			a. 1st: amount of energy is constant
				i. Energy is passed in food chains
				ii. Either it is stored or released to the environment
			b. 2nd: energy is degraded when it is used
				i. Most is lost as heat
				ii. 90% of the energy is lost at each level
	Primary producers include plants, algae, and many species of bacteria
	Many primary and higher-order consumers are opportunistic feeders
	Decomposition interconnects all trophic levels
		3. Explain how decomposition connects all trophic levels in an ecosystem.
			a. Organisms are recycled
			b. Their matter, released by decomposers, is used by other organisms

ENERGY FLOW IN ECOSYSTEMS
	Introduction
	An ecosystem's energy budget depends on primary productivity 
		4. Explain why the amount of energy used in photosynthesis is so much less than 
		the amount of solar energy that reaches Earth.
			a. Most is absorbed, scattered, or reflected by the atmosphere
			b. Also required: water, temperature, and nutrients
			c. Most that reaches the surface hits bare ground or water
			d. Only certain wavelengths are used
		5. Define and compare gross primary production and net primary production.
			a. Gross is the total light energy converted to chemical energy per time
			b. Net is gross minus that used for respiration
		6. Compare primary productivity in marine, freshwater, and terrestrial 
		ecosystems.
			a. Highest per m2
				i. Algal beds and reefs
				ii. Tropical rain forest
				iii. Swamp and marsh
			b. Highest total
				i. Open ocean
				ii. Tropical rain forest
				iii. Continental shelf
			c. Freshwater ecosystems are low
	As energy flows through an ecosystem, much is lost at each trophic level
		7. Explain why energy is said to flow rather than cycle within ecosystems. Use 
		the example of insect caterpillars to illustrate energy flow.
			a. Energy is lost and degraded at each trophic
			b. Of the food energy eaten by caterpillars
				i. 50% is lost in feces
				ii. 33% is used in cellular respiration
				iii. Only 17% is used for growth
		8. Distinguish between energy pyramids and biomass pyramids. Explain why 
		both relationships are in the form of pyramids. Explain the special circumstances 
		of inverted biomass pyramids.
			a. Distinction
				i. Energy in terms of net primary productivity
				ii. Biomass in terms of the total dry weight of organisms 
			b. Shape
				i. Smaller at higher trophic levels
				ii. Both energy and biomass are lost
			c. Exceptions
				i. Aquatic ecosystems with rapidly reproducing phytoplankton
				ii. Low phytoplankton reproduces quickly to feed zooplankton
		9. Explain why food pyramids usually have only four or five trophic levels.
			a. Starting biomass at the bottom, limits biomass at the top
			b. Most energy/biomass is lost at each level
			c. Ten times the area is required for each successive level
		10. Define the pyramid of numbers.
			a. # of individuals at each trophic level
			b. Exception: large producers like trees, support many insects
		11. Explain why worldwide agriculture could feed more people if all humans 
		consumed only plant material.
			a. Most of the energy is wasted by feeding grain to farm animals
			b. Hogs and chickens are more efficient at making meat than cattle
			c. Fish are more efficient than either

CYCLING OF CHEMICAL ELEMENTS IN ECOSYSTEMS
	Introduction
	Biological and ecological processes move nutrients among organic and 
	inorganic compartments
		12. Describe the four nutrient reservoirs and the processes that transfer the 
		elements between reservoirs.
			a. Available organic
				i. To and from available inorganic by photosynthesis and 
				respiration
				ii. To unavailable organic by "fossilization" 
			b. Unavailable organic: to available inorganic by erosion and burning
			c. Available inorganic
				i. See above for exchange with available organic
				ii. To and from unavailable inorganic by weathering and 
				sedimentation
			d. Unavailable inorganic: See above for exchange with available 
				inorganic
		13. Explain why it is difficult to trace elements through biogeochemical cycles.
			a. Many process for each material
			b. Many are geographically widespread
				i. Wind, erosion, etc.
				ii. Organisms may come and go
			c. Long periods of time may be involved
		14. Describe the hydrologic water cycle.
			a. Solar evaporation
			b. Condensation and precipitation
			c. Percolation and runoff
		15. Describe the nitrogen cycle and explain the importance of nitrogen fixation to 
		all living organisms.
			a. Cycle
				i. N2  NH3 by nitrogen-fixation bacteria in soil and nodules
				ii. NH3  NO2, NO3 by nitrifying bacteria
				iii. Assimilation into plants then animals
				iv. Decomposers release NH3 back into the soil
				v. NO3  N2 by denitrifying bacteria
			b. Importance: amino acids, nucleic acids, some carbohydrates and lipids
		16. Describe the phosphorus cycle and explain how phosphorus is recycled 
		locally in most ecosystems.
			a. Geological cycling
				i. Erosion and sedimentation
				ii. Rock formation
				iii. Tectonic processes including uplift
			b. Local cycling
				i. Plants assimilate phosphate from the soil
				ii. Decomposers release it back into the soil
	Decomposition rates largely determine the rates of nutrient cycling
		17. Explain how decomposition affects the rate of nutrient cycling in ecosystems.
			a. Decomposition varies widely: tundra 50 years; tropical forest a few 
			years
			b. Tropical forest soils have low nutrients because of rapid breakdown 
			and reassimilation
	Field experiments reveal how vegetation regulates chemical cycling: science 	as a process

HUMAN IMPACTS ON ECOSYSTEMS
	Introduction
	The human population is disrupting chemical cycles throughout the biosphere
		18. Describe how agricultural practices can interfere with nitrogen cycling.
			a. Nitrogen assimilated into crops is removed at harvest
			b. Disturbed soil loses nitrogen faster by leaching
		19. Explain how "cultural eutrophication" can alter freshwater ecosystems.
			a. Eutrophication is the increase in productivity as lakes age
			b. Wastes, leached nutrients, silting from human activities accelerate the 
			process
	Toxins can become concentrated in successive trophic levels of food webs
		20. Explain why toxic compounds usually have the greatest effect on top-level 
		carnivores.
			a. Fat-soluble substances stick, water-soluble pass in urine
			b. Consumers absorb and store the fat-soluble toxins in their food
			c. Consuption at successive levels gives biomagnification 
	Human activities are causing fundamental changes in the composition of the 
	atmosphere
		21. Describe how increased atmospheric concentrations of carbon dioxide could 
		affect Earth.
			a. Carbon cycle
				i. Producers fix CO2, consumers release CO2
				ii. CO2 is stored as carbonates in the ocean and in sediments
			b. CO2 in the atmosphere may double from 1850-2075
			c. Greenhouse effect
				i. Visible light penetrates the atmosphere and heats the ground
				ii. Heat is radiated as infrared
				iii. CO2 and other greenhouse gases absorb the infrared
	The exploding human population is altering habitats and reducing biodiversity 
	worldwide
		22. Describe how human interference might alter the biosphere.
			a. Two problems
				i. Exponential growth
				ii. Demand for a higher standard of living
			b. Exponential pressure on resources we share with ecosystems