Topic 7 ECOLOGICAL PYRAMIDS

What are Ecological Pyramids?

A pyramid is a kind of graph that can be

used to quantitatively represent differences

in the trophic levels in a single ecosystem.

•Three types:

1. Pyramids of numbers

2. Pyramids of biomass

3. Pyramids of productivity

Ecological Pyramids

• Label the trophic levels in

the pyramid to the right

• Why does a pyramid

shape make a good

model for food

chains/webs?

• Because each trophic

level supports the next.

Pyramid of Numbers

• Ecological pyramids are: based on the number of organisms at each trophic level.

• Generally, there are more producers than primary consumers, more primary consumers than secondary consumers, etc.

• Pyramids of numbers can be:

inverted (upside down)

• Pyramids of numbers depend

on the size of organisms

• For example, large trees can

take the place of many grass

plants

• Ex. One tree can support many

primary consumers

Pyramids of numbers

Pyramids of numbers

• These pyramids shows that forests have a smaller number

of producers than grasslands. Label them.

Pyramids of Biomass

• What is biomass?

“life mass” measurement of the amount of organic matter in a organism. Its “Dry weight.”

• The pyramid of biomass is an ecological pyramid based on the mass/weight of dry tissue of organisms at each trophic level in an area

• When could a pyramid of biomass be inverted?

Inverted Biomass Pyramid

• Compare Terrestrial vs Aquatic Biomass pyramids

Pyramid of Productivity

• Show:

the amount of energy that is passed from one trophic level to the next.

Can these pyramids be inverted? Why?

NEVER – Because of the Law of 10%

Implications of Pyramids

• Why are food chain lengths limited?

• Top carnivores are very vulnerable if there is a disturbance anywhere in the food chain.• Why?

Bioaccumulation

• Organisms absorb, breathe and ingest non-biodegradable toxins from the environment and store them in body tissues.

Bioaccumulation:

• The gradual buildup of non-biodegradable toxins over time in a organism

• What happens to bioaccumulated toxins in the food chain?

Biomagnification

• Accumulated toxins are passed up from one trophic level to the next

Biomagnification is:•Concentration of toxins in organisms increases (magnifies) as it is passed up the food chain.

• Which trophic levels are most vulnerable to biomagnification?

LABEL: Bioaccumulation and Biomagnification

CASE STUDY: DDT & AMERICAN BALD EAGLE

• DDT is a highly successful

pesticide

• Used in the U.S. until 1972 &

is still used in parts of the

World today.

• DDT is a non-biodegradable

toxin

• DDT bioaccumulated and

then biomagnified through

the food chain

Biomagnification: DDT

The hazard of DDT was to “non-target animals”

1.Who were the “target animal”?

2.Who were the “non-target animals”?

3.Why were they so affected?

4.How were they affected?

Thinned egg shells of birds of prey &

drastically lowered populations

Mosquitos & Other Pests

Birds of prey including Eagles & Falcons

These birds were at top of the food chain

https://www.youtube.com/watch?v=L8149TO0EU0

Biomagnification: Mercury

• How could

biomagnification

affect humans?

The food we

eat that have

toxins will

accumulate

and effect us

too!