LECTURE Feb 19 - Energy Flow & Ecosystems

autotrophs (define -

• Make their own food —> “self-eaters”

  • photoautotrophs

  • chemoautotrophs

• Primary producers

photoautotrophs

use sunlight to make their own food

chemoautotrophs

use chemicals to make their own food

heterotrophs

• consume other organisms for food and energy

  • carnivores

  • herbivores

carnivores

1*carnivore eats herbivores, 2*carnivore eats 1*carnivores, etc.

herbivores

Eat plants = primary consumers

trophic levels

Producers → Primary Consumers → Secondary Consumers → Tertiary Consumers → Predator

• (decomposer is on the side)

ecological pyramids

About 90% of energy is used up moving from one trophic level to the next

• Not all prey is ingested

• Digestion is energetically costly

• Digestion is not 100% efficient; energy is lost in feces

ecological efficiency

The percentage of energy from one trophic level that is incorporated into the next.

• Generally, ~10% of energy is transferred

inefficiency of energy transfer among trophic llevels

1. The greater the amount of biomass at the bottom of a food web (primary producers), the higher the number of trophic levels a food web can support. 

2. The lower on the food web a species is, the greater the total biomass of organisms that can be supported

3. Lack of top predators (e.g. sharks, lions) in an ecosystem is a sign of trouble – not only are the number of trophic levels a sign of productivity, but “top down” control by predators is key for preventing “tipping points”.

ecological tipping points

• A tipping point is the threshold level where environmental degradation is essentially irreversible, or at least where conditions shift to a different “state” or “phase” from which it can be very difficult to recover.

  • Are rapid, sudden changes that are often the result of positive feedback loops when small changes become amplified

Can result from imbalances in food webs, such as the removal of a keystone predator or herbivore.

example of ecological tipping point - “urchin barrens”

As long as there are enough otters eating sea urchins, they keep the urchin population in check, resulting in a healthy kelp population and no “urchin barrens”.

hydrothermal vents

• Ecosystems without sunlight

• Based on chemoautotrophs

• Changed understanding of life

  • Ecosystem is independent of energy from the sun

food chain vs food webs

• Food chain = linear (simple)

• Food web = interconnected (complex)

decomposers

Allow recycling (recovery) of materials in ecosystems

• Energy cannot be recycled, but matter can

Without decomposers, waste would build up, and no recycling would occur.

• maintain ecosystems