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Ecosystems: All organisms living in a biotic community/interactions with abiotic factors
●Ecosystem ecology emphasizes questions about energy flow (it enters as light and
is lost as heat) and nutrient cycling
● 4 components: (We will focus on ecosystems with photoautotrophs as primary
○ Primary producers (Harvest energy (from nonliving sources) and convert it
to chemical energy (Photoautotrophs)
○ Consumers (Harvest chemical energy from organic molecules (Heterotrophs)
○ Decomposers (Break down remains from all trophic levels for recycling)
○ Abiotic environment
Food chains: Track the flow of energyénutrients from one trophic level to the next.
Food web: Complex feeding relationships within an ecosystem.
●Note that an organism can function at more than one trophic level
Energy flows: Solar energy enters Earth’s atmosphere
●Much is absorbed or reflected as heat by nonphotosynthetic surfaces
●Only a small % reaches primary producers and even less is converted to chemical
●Energy cannot be created or destroyed but only transferred or transformed:
● Gross Primary Productivity (GPP): Amount of light energy converted to chemical
energy per unit area (as carbohydrates in kilocalories/ m2 ) annually
○ Used for plant growth and maintenance (includes respiration and heat loss).
○ GPP (100%) = growth (NPP) (45%)+ maintenance (55%)
● Gross Photosynthetic efficiency: Ratio of GPP to total incoming solar radiation
(kilocalories/ m2 ): efficiency of capturing sunlight at surface by photosynthesis
● Net Primary Productivity (NPP): Energy used for new growth (Joules/m2 /year)
or biomass production (grams/m2/year) of wood and other tissues, in forestry or
■NPP is greater in terrestrial habitats than in the oceans
■NPP is greater near the equator than the poles (ENERGY & water)
■NPP is low in deserts
■NPP is limited by nutrients (oceans)
○Hotspots: Equatorial Amazon basin, central Africa, SE Asia
Nutrition as Limiting Factor
●When light and moisture are available, production is limited by nutrients.
●Nutrients are essential for growth (amino acids, nucleotides, lipids, carbohydrates)
● Limiting nutrient: The nutrient that must be added for production to increase
○ Most Common:
■ Nitrogen (N): Terrestrial (greening)
■ Phosphorus (P): Freshwater