BISC 102 Lecture Notes - Lecture 18: Ecosystem Ecology, Herbivore, Plant Litter

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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
producers)
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.
These include:
Herbivory
Predation
Parasitism
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
Energy cannot be created or destroyed but only transferred or transformed:
thermodynamic law
Primary Production:
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
agriculture applications
Globally:
NPP is greater in terrestrial habitats than in the oceans
NPP is greater near the equator than the poles (ENERGY & water)
○ Locally:
NPP is low in deserts
NPP is limited by nutrients (oceans)
● Limits:
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
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