19. Food Webs

Trophic levels def.

the feeding positions of organisms in ecosystems

Trophic efficiency def.

amount of energy transferred from one trophic level to the next

A change of abundance in organisms can at one trophic level can…

Can influence energy flow at multiple trophic levels

Why are food chains not realistic?

Linear transference of matter and energy from a trophic level to the next(s) with no other trophic interactions

Why are food webs more realistic?

Diagrams showing multiple trophic connections among organisms

Trophic levels in Ecosystems

1. Producers

2. Primary Consumers

3. Waste and Remains

4. Decay (organic molcues)

5. Environmental phases

Trophic levels for animals

Feeding position / trophic level is based on the number of feeding steps by which an animal is separated from autotrophs

Trophic levels in a simple desert food web

Simple with straight levels and one dead organic matter

Increasing complexity def.

trophic levels jump with arrows like the ground squirrel

More complex desert food web

more arrow jumping between trophic levels

More complexity

Absolutely insane arrow jumps

Fod web complexity in Amazonian forests

The less forest area, the lower the network complexity

Energy flow between trophic levels

amount of energy at one trophic level divided by amount of energy at the trophic level immediately below it. Typically 10% or 0.1 = 10% Rule

Available energy decreases with each trophic level. Units kilocal, cal, kiloj, or even biomass

In a simple food chain, grass is consumed by grasshoppers, and grasshoppers are consumed by toads. If you have 100kg of grass, predict what mass of toads would be supported?

The 10% rule soooo 100kg of grass is 10kg of grasshoppers and thennnn 1kg but also 1,000 g

Trophic pyrmaid

A stack of trophic levels as a pyramid having the 10% rule of biomass moving

Energy flow and trophic efficiency

Very few is actually taken and most gets dismissed

Trophic efficenty veries by the level

Consumption efficiency = consumed energy / net production energy of lower trophic level

Assimilation efficiency = assimilated energy / consumed energy

Net production efficiency = net production energy / assimilated energy

Trophic cascade def.

changes in the abundances of organisms or rate of consumption at one trophic level can infleunce energy flow, compostion, and abudnace at lower trophic levels

Top down vs bottom up control

top down: preadtors contorl the lower levels by how much they consumer

bottom up: the resoruces as the base by producers impact the levels above