Ecosystems Chapter 42

What you need to know How energy flows through the ecosystem The difference between gross primary productivity and net primary productivity The carbon and nitrogen biogeochemical cycles

Ecosystem The sum of all the organisms living within boundaries (biotic community) and all the abiotic factors with which they interact Two key parts: Energy flow (Conservation of Energy) Chemical cycling (Conservation of Matter)

1. Energy Flow Traced through feeding relationships (trophic levels) of food chains and webs Energy cannot be recycled (Entropy) It must be resupplied Sunlight provides 1022 J/day of solar radiation

Energy Pyramid Bottom Level: primary producers (aka autotrophs) support all other organisms 1.5 x 1014 kg/year Upper levels: consumers (aka heterotrophs) Herbivores (primary consumers) eat primary producers Carnivores that eat primary consumers are secondary consumers, carnivores that eat secondary consumers are tertiary consumers

Detritivores Decomposers that get their energy from detritus Detritus is nonliving organic material such as the remains of dead organisms, feces, dead leaves, and wood Essential organisms that recycle organic material from all trophic levels and deposit the nutrients back into the soil for use by producers

Primary Production The amount of light* energy converted to chemical energy by autotrophs Spending limit for energy budget Total primary production in an ecosystem is gross primary production (GPP) GPP is not all available to consumers (some is used by the autotrophs)

Primary Production Net primary production (NPP) = GPP minus the energy used for respiration by the autotrophs NPP = GPP - Ra Aquatic ecosystems depend on nutrients (nitrogen and phosphorus) and light availability (photic zone) Terrestrial ecosystems depend on temperature and moisture

Energy Transfer 10% of energy is transferred from primary producers to primary consumers Only 1% makes it to the secondary consumers Keeps food chains short

Secondary Production Food that is converted to new biomass relative to the total food consumed Production efficiency is the % of energy stored in assimilated food that is used for growth and reproduction (not for respiration). Production Eff =secondary production (new biomass) Assimilation of primary production Calculate secondary production and production efficiency for the caterpillar

Secondary Efficiency Birds and mammals are low: 1% - 3% High body temperature Fish are about 10% Insects and microorganisms are the most efficient: 40%+

2. Chemical Cycling Biogeochemical cycles are nutrient cycles that contain both biotic and abiotic components: Water cycle recycles fresh water Phosphorus cycle moves nitrogen throughout terrestrial and aquatic ecosystems Carbon cycle is a balance between photosynthesis and cellular respiration Nitrogen cycle moves nitrogen from the atmosphere through the living world Common limiting factor for plant growth (makes this cycle especially important)

Nitrogen Cycle Most nitrogen is N2 (unusable by plants) Nitrogen fixation: Bacteria convert N2 into usable forms of nitrogen Nitrification is the process by which ammonium is oxidized to nitrite and then nitrate Plants can absorb ammonium and nitrates Denitrification by bacteria releases nitrogen to the atmosphere (N2)

Human Activities Acid precipitation – rain, snow, or fog with a pH lower than 5.6 Created by the burning of wood and fossil fuels which mix into sulfuric and nitric acid Biological magnification – toxins become more concentrated in higher trophic levels Greenhouse effect – blanket of CO2 traps heat (global warming) Ozone layer reduces UV light