Biol 208: Lecture 27 - Energy flow Through Ecosystems

Trophic Dynamics define again

• Why are there usually only 3-4 trophic levels?

Trophic Dynamics = The transfer of E from one part of the ecosystem to the next

• Only 3-4 trophic levels because Energy is lost every time it is transferred (Law of THERMODYNAMICS)

What are the 1st and 2nd laws of thermodynamics?

1st: Total amount of E in the universe is constant and cannot be created or destroyed only transformed

2nd: Energy transfer increases the Entropy (disorder) of the universe

• Entropy - the loss of usable E from the system in this course

What is Lindeman’s law in regards to E lost

• what are the 3 ways E is lost + which is the most E lost?

Lindeman’s 10% law = 10% of energy consumed by a trophic level is transferred

• Loss as HEAT (most) , RESPIRATION+ DECOMP. after death

What are 2 other limits to E transfer other than E lost?

1. Can’t eat everything (not all biomass is edible)+ can’t find everything to eat (Not all biomass is accessible)

2. High trophic level individuals occur at lower abundances than lower trophic levels (= unlikely to evolve a super-predator b/c there won’t be enough food for it)

About how many percentages of the Total E input by solar radiation enters the ecosystem as NPP?

only about ONE%

• Majority is lost through reflection, heat + evapotranspiration + plant respiration before it is available for consumption or decomposition

A relatively high portion of energy is captured where?

SOIL

What are 4 things that we can learn from this diagram of Energy budgets?

1. the bottom trophic level of primary producers is relatively large

2. Organic belowground matter stores a lot of E

3. Consumers components = much smaller than Primary Prod component

4. Ecosystems are inefficient systems

Define Allochthonous inputs

• give an example

= materials such as organic matter, nutrients, or energy that enter an ecosystem from an external source rather than being produced within the system.

eg. Salmon (aquatic) + bear (terrestrial)

eg. Leaf litter falling into a stream from surrounding forest trees

Define Trophic cascade

= when changes in the population size of a species in one trophic level alters populations in other trophic levels

Info Dump on the Trophic cascade between SEA OTTERS + KELP

Many kelp species exist along shore

Many invertebrates (herbivores) graze on kelp

Otter = Highest trophic level in the Kelp ecosystem

• Sea otter + fur trade = Extirpation

Removing sea otter = reduced kelp population

What are the 2 other trophic cascades mentioned in class?

Steelhead

Wolf + Elk