Energy and Nutrient Cycling I

Auto vs heterotrophs

Autotroph

- An organism that produces it's own energy (typically by photosynthesis) rather than obtaining it from others (eg. via consumtion)

- Primary producer

- Plants & algae

Heterotroph

- Organism that derives it's energy from other organisms

- Primary, secondary/tertiary consumer

- Animals & fungi

- Includes decomposes, which eat dead organic matter (important in nutrient cycling)

- Amount of heterotrophs/consumers depends on amount of autotrophs

What are the first & second law of thermodynamics; and the law of conservation of mass?

First law

- The energy of the universe is constant

- Energy can only be changed from one form to another but can't be increased/decreased

- This means all energy in ecosystems just cycles round

- The energy flow of an biosphere/world wide ecosystem can't increase or decrease, just change states

Second law

- Every energy transfer or transformation increases the entropy of the universe

- Applies to chemical cycling and energy flow in

- Becuase heat is a major product of living organisms there is an increase in entropy

Conservation of mass

- Mass cannot be created or destroyed

- For example if a lion eats a deer; it is not destroying it's mass only breaking it down into smaller pieces

Ecosystems are open systems that absorb energy and mass and release heat and waste products

^ these laws apply to them

Trophic levels

Primary producers (plants/algae)

Primary consumers (herbivores)

Secondary consumers

Tertiary consumers

Quaternary consumers

- Energy leaks out at every trohpic level

- Only 10% of energy at each level is passed up (eg 10% of energy from primary producers is passed up to primary consumers)

- Decompisition links all trophic levels

- Detritivores/decomposers break down non-living organic matter (cycles nutrients/important to ecosystem)

^ prokaryotes and fungi

- A food web is the interconnected trophic levels

What is primary productors role in ecosystems

- They hold up the WHOLE ecosystem

- In terrisitral ecosystems largest amount of of biomass

- The extent of photosynthetic production sets the spending limit for an ecosystem's energy budget

Global net primary production (GPP) vs net primary production (NPP)

GPP

- Total primary production of an ecosystem

- Calculated from the conversion of energy from light (or chemicals) to the chemical energy of organic molecules per unit time

NPP

- Calculated from GPP-energy used by autotrophs for respiration

- Only NPP is available to consumers (GPP is not)

What are the limiting factors of net productivity?

Light

- Regions near the equator are exposed to a lot of light=more photosynthesis=more productive (bc bigger amount of primary producers)

- Many marine ecosystems are aphotic and therefore are not very productive

Nutrients

- Soil nutrients can limit primary prodution in terristrial ecosystems

- Aphotic marine ecosystem may have fewer nutrients=less productive

Water

- Water is a limiting factor of photosynthesis

- Therefore more water=more photosynthesis=more net production

- Tropical rainforests are super productive becuase they have high light lvls (near the equator) and lots of rainfall

What is the typically value for energy transfer between trophic levels?

10%

- 10% of energy from primary producers goes to primary consumers

- 10% of that energy goes to secondary consumers

etc.

- This means that there are is much fewer organisms (predators) at the top of food chain

- Most of the biomass of an ecosystem comes from primary producers (think about how much trees there are compeared to predators)