Lecture 13 Ecosystems

Question 1

Ecosystem

Answer 1

All organisms in a given area and the physical/chemical environment in which they live (community+abiotic environment).

Measure energy flow and nutrient cycle
Loss of metabolic energy through heat at each level of food web
Nutrient cycle - decomposers crucial

Question 2

Biomass through trophic levels

Answer 2

Net primary production: fixed carbon in plant biomass minus resp loss

Net secondary production: biomass obtained from consumption of others

Consumption efficiency - proportion of available biomass ingested by consumers
Assimilation efficiency - prop. Of consumed biomass assimilated by digestion
Production efficiency - prop. Of assimilated biomass used to produce new consumer biomass

Consumption/assimilation/product efficiency affect NSP net secondary production

Biomass produced by primary producer
Some consumed of which some is converted to consumer biomass and the rest lost in respiration or excreted as faeces/urine
The rest combined with the excretions and becomes detritus and nutrients are cycled by decomposers.

Question 3

Energy flow and biomass through trophic levels

Answer 3

Energy available to higher trophic levels decreases as it is lost through metabolism so less biomass can be supported at each level

In forests majority of biomass tied up in wood so energy not available to most herbivores

In grassland most biomass is plants so more energy available to herbivores than in forests

In open ocean primary producers - phytoplankton, reproduce so rapidly that a small standing biomass supports a much larger biomass of herbivores

Question 4

Predators

Answer 4

Need large areas to sustain viable population - large carnivores can require >1 million hectares per 1000 infividuals

Question 5

Carbon cycle

Answer 5

Primary production fixed carbon from atmosphere
Soils, detritus, fossil fuels and sediments in oceans are important carbon sinks
Decomposition respiration, fires and volcanic activity are nat sources of CO2 and CH4

Question 6

Nitrogen cycle

Answer 6

Via nitrifying and denitrifying bacteria - bio driven
N fixing bacteria break triple bond of atmospheric nitrogen producing ammonia/ammonium (NH3/NH4+)

Nitrites and nitrates taken up by denitrifying bacteria and plants

Nitrifying bacteria convert ammonia and ammonium to nitrites/nitrates

Fertilisation (modern agriculture)
Combined with NOX gas from fossil fuel have increased mobile N in cycle due to leaching and eutrophication of aquatic systems