topic 12 - ecosystem energetics Flashcards
what are ecosystems
communities of organisms interacting with their physical environment under the influence of environmental factors
what is ecosystem energetics
study of how energy is fixed by autotrophs and made available to heterotrophs (eat autotrophs)
how is energy measured in ecosystems
biomass - dry weight of organic matter in an organism or ecosystem (mostly carbon )
what are primary producers
autotrophic organisms that fix inorganic nutrients (C, N, P, O, etc) into organic molecules
carry out primary production
what is primary productivity
rate at which energy is fixed
amount of C fixed per unit area per unit time
what is gross PP
total amount of energy fixed into organic molecules in an ecosystem
what is net PP
what the producer makes minus what the producer uses for itself (E RMR, E activity)
amount of energy for growth
measured as biomass
AMOUNT OF ENERGY AVAILABLE TO OTHER TROPHIC LEVELS
what are factors affecting PP
light
temp
precip
nitrogen
phosphorus
CO2
how does light affect PP
as light increases, PP increases
until there is more light than the enzymes can use (PP plateaus)
PP drops off at too much light
how does temp affect PP
positive relationship between temp and net primary productivity
higher temp = higher net primary productivity
due to enzymatic reactions going faster in higher temps
PP also drops off at too high of temp - causes denaturation of enzymes and damage to plants
how does precip affect PP
In drier environments
- strong positive relationship between precip and net PP
- precip is a limiting factor
- as precip increases, net PP increases
In wetter environments
- very high precip means not enough sun (decrease in net PP)
- shows increases with increase in precip and then peaks and decreases
how does nitrogen affect PP
addition of N = increase in net PP
largest increase in the temperate grasslands
low increase in wetland (too wet) and desert (too dry)
N is soluble and tends to wash away with rain
Terrestrial ecosystems tend to be N limited
how does phosphorus affect PP
insoluble - doesn’t wash away from soils - tends to be more limiting in aquatic environments
positive relationship between P level and net PP
how does CO2 affect PP
higher CO2 increases plant growth as long as all other nutrient (water, etc} are available
plant only grows as well as it can with the limiting nutrient
what are primary consumers
herbivores
second trophic level
first level that eats another organism
consume the biomass of primary producers
- use energy consumed to support energy budget
- excess energy turned into new biomass (growth)
what is biomass production called
secondary production
what are secondary / tertiary consumers
carnivores / omnivores
3rd/4th trophic levels
Organisms that consume the organic molecules (biomass) of consumers in a lower trophic level
Omnivores = both producers and consumers
- use energy consumed to support energy budget
- excess energy turned into new biomass (growth)
what are decomposers / detritivores
organisms that consume the dead organic matter of primary producers, primary consumers, etc
important to the cycling of nutrients
complete secondary production
help break down primary producers and release nutrients back into ecosystem
what are we interested in inside food webs
loss of energy through heat
nutrients CYCLE and energy FLOWS
how does energy flow through ecosystems
gross PP = energy entering at the first trophic level
energy consumed is the energy that moves up to the next level
eventually all energy input from the sun is lost as heat from the system
what is ecological efficiency
Efficiency at which biomass at one trophic level can be created form the biomass at the previous trophic level (looking at net productivity only)
hwo to determine ecological efficiency between 2 levels
net PP level 2/net PP level 1
tends to be around 10% between all levels
do detritivores have a designated trophic level
no - eat across many
what is bottom up control
Resource abundance regulates trophic structure
Energy in each trophic level is determined by the energy in the lower trophic level
same effect on ALL levels (all increase or all decrease)
no way of avoiding bottom up control - always happening
what is top down control
Predation regulates trophic structure
Organisms in each trophic level are limited by predators in the next higher trophic level
what is a trophic cascade
adding / removing a top predator from an ecosystem often results in an alternating (cascading) effect down the rest of the food web
alternating impacts of increases and decreases in biomass
what is the effect of a keystone species
Removing them causes big changes
Small in number but large in effect
Doesn’t cause a trophic cascade, everything just kind of falls apart
what type of system is earth for nutrients
closed system
what is the biogeochemical cycle
Pathways that describe how nutrients more between biotic and abiotic components of an ecosystem
what are the types of nutrient reservoirs
short term (<200 years) and long term (>200 years)
biotic or abiotic
three major - terrestrial, aquatic, atmospheric
nutrients in 3 possible phases
- gases (water, CO2), soluble (C, N, O), and insoluble (P, K, Fe, Ca)
what is the generalised compartment model
short term reservoirs hold available organic (animals, bacteria, fungi, plants) and inorganic material (soil, water, sediments, atmosphere)
long term reservoirs hold unavailable organic (coal, oil, peat) and inorganic (rocks and minerals)
what is the importance of carbon
most abundant element in organisms (50% of dry mass)
unit of energy currency in organisms and ecosystems (organic molecules (glucose) are essential to energy transfer)
C cycles through all 4 nutrient compartments (organic, inorganic, short term, and long term)
what type of C does photosynthesis prefer
12C
therefore fossil fuels are remains of living organisms and 12C
- dilutes the 13C:12C ratio in atmosphere
