topic 12 - ecosystem energetics

Question 1

what are ecosystems

Answer 1

communities of organisms interacting with their physical environment under the influence of environmental factors

Question 2

what is ecosystem energetics

Answer 2

study of how energy is fixed by autotrophs and made available to heterotrophs (eat autotrophs)

Question 3

how is energy measured in ecosystems

Answer 3

biomass - dry weight of organic matter in an organism or ecosystem (mostly carbon )

Question 4

what are primary producers

Answer 4

autotrophic organisms that fix inorganic nutrients (C, N, P, O, etc) into organic molecules

carry out primary production

Question 5

what is primary productivity

Answer 5

rate at which energy is fixed

amount of C fixed per unit area per unit time

Question 6

what is gross PP

Answer 6

total amount of energy fixed into organic molecules in an ecosystem

Question 7

what is net PP

Answer 7

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

Question 8

what are factors affecting PP

Answer 8

light
temp
precip
nitrogen
phosphorus
CO2

Question 9

how does light affect PP

Answer 9

as light increases, PP increases

until there is more light than the enzymes can use (PP plateaus)

PP drops off at too much light

Question 10

how does temp affect PP

Answer 10

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

Question 11

how does precip affect PP

Answer 11

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

Question 12

how does nitrogen affect PP

Answer 12

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

Question 13

how does phosphorus affect PP

Answer 13

insoluble - doesn’t wash away from soils - tends to be more limiting in aquatic environments

positive relationship between P level and net PP

Question 14

how does CO2 affect PP

Answer 14

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

Question 15

what are primary consumers

Answer 15

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)

Question 16

what is biomass production called

Answer 16

secondary production

Question 17

what are secondary / tertiary consumers

Answer 17

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)

Question 18

what are decomposers / detritivores

Answer 18

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

Question 19

what are we interested in inside food webs

Answer 19

loss of energy through heat

nutrients CYCLE and energy FLOWS

Question 20

how does energy flow through ecosystems

Answer 20

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

Question 21

what is ecological efficiency

Answer 21

Efficiency at which biomass at one trophic level can be created form the biomass at the previous trophic level (looking at net productivity only)

Question 22

hwo to determine ecological efficiency between 2 levels

Answer 22

net PP level 2/net PP level 1

tends to be around 10% between all levels

Question 23

do detritivores have a designated trophic level

Answer 23

no - eat across many

Question 24

what is bottom up control

Answer 24

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

Question 25

what is top down control

Answer 25

Predation regulates trophic structure
Organisms in each trophic level are limited by predators in the next higher trophic level

Question 26

what is a trophic cascade

Answer 26

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

Question 27

what is the effect of a keystone species

Answer 27

Removing them causes big changes
Small in number but large in effect
Doesn’t cause a trophic cascade, everything just kind of falls apart

Question 28

what type of system is earth for nutrients

Answer 28

closed system

Question 29

what is the biogeochemical cycle

Answer 29

Pathways that describe how nutrients more between biotic and abiotic components of an ecosystem

Question 30

what are the types of nutrient reservoirs

Answer 30

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)

Question 31

what is the generalised compartment model

Answer 31

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)

Question 32

what is the importance of carbon

Answer 32

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)

Question 33

what type of C does photosynthesis prefer

Answer 33

12C

therefore fossil fuels are remains of living organisms and 12C
- dilutes the 13C:12C ratio in atmosphere