Trophic Relationships in Ecosystems
o Ecosystem = all organisms living in a given area along with the abiotic factors with which they interact
--- Boundaries usually not discrete
--- Most inclusive level of organization
o Energy flow and chemical cycling
--- Not found at lower levels
o Energy flows through ecosystems and matter cycles within them
o Trophic structure = feeding relationships which determine paths of energy flow & chemical cycling
o Tropic levels = based on nutrition source
o Five levels:
--- Primary producers
--- Primary consumers
--- Secondary consumers
--- Tertiary consumers
--- Detritivors (decomposers)
o Comprise food webs
o Distinguish between ecosystem structure (trophic levels) & ecosystem processes(production, consumption, decomposition)
o Consumption: metabolic use of assimilated organic molecules for growth & development
o Decomposition: breakdown of organic to inorganic
--- Plants, algae, many species of bacteria
--- Deep-sea vents: chemoautotrophic bacteria
o Energy from oxidation of hydrogen sulfide
--- Many are opportunistic feeders
--- Primary (terrestrial)
o Insects, snails, plant parasites, grazing mammals, seed-eating & fruit-eating birds & mammals
--- Aquatic:
o Zooplankton, some fish
--- Links all trophic levels
--- Recycles organic matter to abiotic environment in user-friendly forms
--- Bacteria & fungi
o Digest materials externally, absorb products
o Budget depends on primary production = photosynthesis
o Global energy budget:
--- 1022joules of solar radiation
--- Regional variation
--- Intensity varies with latitude - tropics most
--- Radiation reflected, absorbed or scattered by atmosphere
--- 1-2% visible light reaches photosynthetic organisms
Primary productivity
o =the amt. Of light energy converted to chemical energy by autotrophs
--- Total= Gross Primary Productivity (GPP)
o Find by measuring total O2 produced
--- NPP = GPP - Rs (energy used by producers for respiration)
o Accounts for organic mass of plants (growth) & represents storage of chem. Energy
o NPP:GPP smaller for large producers
--- Not standing crop biomass (total biomass of photosynthetic autotrophs present at a given time) - accumulates over seasons
--- Tropical Rain Forests very productive, large contributor, cover large area
--- Estuaries & coral reefs productive, but only a sm. contribution to planetary PP
--- Deserts & tundra = low productivity
--- Open ocean = low production but large contribution = vast area
--- Increases as approach equator
o Water, heat, light increases
--- Limited by inorganic nutrients (limiting nutrient - loss of trace element)
o N, P, CO2
--- Greatest in shallows near continents & along coral reefs
--- Highest near surface, decreases with depth
--- Limits of N, P critical
o Upwellings bring nutrients
o Reason Antarctic more productive than tropics
o Amt. of energy available at each level determined by NPP & efficiency of energy to biomass conversion
o Secondary Productivity - rate at which consumers convert chemical energy in food into their biomass
--- Eat only sm. amt. of available plant material
--- Not all digestable
--- 17-18% of calories used for growth
--- Rest: cellular respiration (energy lost to system) & waste (energy stays in system)
o Use more for cellular respiration so
o Less available at next level
o ENERGY FLOWS THRU ECOSYSTEMS, DOES NOT CYCLE
--- % of energy transferred from one to the next
--- Varies from 5-20%
o Energy loss shown by pyramids:
--- Pyramid of productivity - blocks proportional to productivity
o Usually bottom heavy
--- Biomass pyramid - blocks symbolize standing crop biomass
o Some aquatic inverted - plankton short-lived
--- Pyramid of Numbers (of individuals)
o Biogeochemical cycles - Nutrient circuits involving both biotic and abiotic components of ecosystem
--- Gases cycle globally, stored in atmosphere (C, O, S, N)
--- Others (K,P, Ca,trace ) short cycle locally, stored in soil
--- Available organic
o Living organisms & detritus
--- Unavailable organic
o Coal, oil, peat
--- Available inorganic
o All matter present in air, soil or in water
--- Unavailable inorganic
o Tied up in limestone, rocks
--- Weathering, erosion
--- Burning of fossil fuels
--- Fossilization to coal, peat, oil
--- Sedimentary Rock Formation
--- Photosynthesis
--- Respiration, decomposition, excretion, leaching
o Water Cycle
o Carbon Cycle
o Nitrogen Cycle
--- Atmospheric deposition
--- Nitrogen fixation
o Nitrification, Denitrification, Ammonification
o Phosphorous Cycle
--- Effected by water, O2, temperature
--- Tropical forests = few months to a few years
--- Temperate forests = 4-6 years
--- Tundra = 50 yrs.
--- Aquatic = >50 yrs.
--- Rapid decomposition
--- Large biomass
--- High demand for nutrients
o 10% in soil; 75% in trees
o Little in litter
o Soil chemistry / fires play a role
--- 50% of all organic material
--- Slow decomposition
--- nutrients present in detritus & soil remain for long periods
o Aquatic
--- Nutrient sink
--- Very slow decomposition
o Long-term ecological research (LTER)
--- Hubbard Brook Experiment Forest
--- N.H. (1963)
--- Logging in 1966
o Study showed import of plants in retaining nutrients & effects of man on ecosystem
Human Impacts
o Disrupting chemical cycles throughout biosphere
--- Agriculture
o Nitrogen cycle
--- Eutrophication of lakes
--- Toxins
o DDT (biomagnification
o Composition of atmosphere
--- CO2 & greenhouse
--- Depletion of ozone
o Exploding Population
--- Alters habitats
--- Reduces biodiversity
o Ecosystems
o Food chain: pathway along which food is transferred from trophic level to level, beginning with primary producers
o Production:rate of incorporation of energy & materials into organisms
o Primary Producers:
o Consumers
o Decomposition
Energy Flow
o PP expressed as biomass (dry weight since water contains no useable energy) added to an ecosystem/unit time (g/m2/yr) or J/ m2/yr)
o Precipitation, temperature, light = limit productivity in terrestrial systems
o Aquatic systems: light, H2O temp., inorganic nutrients limiting factors
o Transfer of energy up the pyramid not 100%
o Carnivors more efficient than herbivores in converting energy to biomass, but
o Ecological efficientcy - ratio of NP at 1 trophic level compared to NP at the level below or
o Although sunlight continually added, essential chemical elements must be recycled
o Reservoirs:
o Processes involved in transfer of nutrients:
The cycling of materials through an ecosystem depends on biological AND geological processes
o Decomposition rates determine rates of nutrient cycling
o Tropical Rain Forests
o Temperate Forest
Field Experiments
