Ecological Pyramids

What is an ecological pyramid?

A diagram that shows the relative amounts of energy or matter contained within each trophic level in a food chain or food web.

What are the three types of ecological pyramids?

Energy pyramids, biomass pyramids, and pyramids of numbers.

What does an energy pyramid show?

The relative amount of energy available at each trophic level.

How much energy is transferred from one trophic level to the next?

Only about 10% of the energy is transferred.

What happens to the remaining energy that is not transferred to the next trophic level?

It is used for life processes or lost as heat.

Example of energy pyramid percentages?

Grass – 100%
Rabbit – 10%
Hawk – 1%
Coyote – 0.1%

What is biomass?

The total amount of living tissue within a trophic level.

What does a biomass pyramid show?

The amount of living organic matter at each trophic level; typically the greatest biomass is at the base.

Example of biomass pyramid amounts?

Grain – 5000 g
Chicken – 500 g
Human tissue – 50 g

What does a pyramid of numbers show?

The relative number of individual organisms at each trophic level.

When does the pyramid of numbers have the same shape as energy and biomass pyramids?

In ecosystems like meadows, where many producers support fewer consumers.

Why does the pyramid of numbers not resemble a typical pyramid in forests?

Because there are fewer producers (trees) than consumers (insects). A single tree has high energy and biomass but is only one organism.

In a forest pyramid of numbers, why are there many consumers above the producer level?

Many insects and organisms live on one tree, even though they contain less energy and biomass.

Why can each trophic level only support one-tenth the amount of living tissue as the level below?

Because only about 10% of the energy is passed up to the next trophic level.

What organisms are found at the lowest level of energy pyramids?

Producers, which transform sunlight into biomass through photosynthesis.

What is the first trophic level of consumers called and what do they eat?

Primary consumers; they eat plants.

What are secondary consumers and what do they eat?

Animals that eat animals; often omnivores that eat both plants and animals.

What are tertiary consumers?

Top predators that eat secondary consumers; they are at the top of the food chain.

Why do higher trophic levels have fewer organisms?

Because energy decreases as it moves up levels—only 10% is transferred, so fewer organisms can be supported.

What are examples of producers?

Green plants, grass, trees, flowers, bushes.

What is a primary consumer?

A herbivore that eats producers (plants).

What are examples of primary consumers?

Rabbits, deer, squirrels, insects, birds, elephants.

What is a secondary consumer?

An organism that eats primary consumers; can be a carnivore or an omnivore.

What are examples of secondary consumers?

Snakes, frogs, fish, baboons, some birds (hawks, eagles), chickens.

Why are primary consumers important in an ecosystem?

They transfer energy from producers to higher trophic levels.

Why do secondary consumers rely on primary consumers?

They obtain energy by eating herbivores.

What are examples of tertiary consumers?

Humans, bears, sharks, alligators, lions

Food chain

• Shows one singular flow of energy

Food web:

Shows many interconnected flows of energy, made up of many food chains.

(True or False) Primary consumers always make up the first trophic level in a food web.

False

• Producers (plants, algae) are always the first trophic level.

• Primary consumers are the second trophic level.

(True or False) Ecological pyramids show the relative amount of energy or matter contained within each trophic level in a given food web.

True

(True or False) On average, about 50 percent of the energy available within one trophic level is transferred to the next trophic level.

False — Only 10% is transferred, 90% is lost as heat

(True or False) The more levels that exist between a producer and a given consumer, the larger the percentage of the original energy from producers is available to that consumer.

False; the opposite is true, More levels = less energy available to higher level consumers

What is Succession?

Succession is the progressive, natural change in the structure, species, and community of an ecosystem over time.
It describes how an ecosystem grows, develops, and evolves.

What is primary succession?

The first stage of ecosystem development where plants and animals colonize a barren habitat with no soil.

What conditions start primary succession?

Bare rock, no soil, no previous ecosystem.

What is an example of primary succession?

Plants and animals establishing an ecosystem on land exposed after glaciers melt.

What is the typical order of growth in primary succession?

Small plants → larger plants → shrubs → trees.

What is secondary succession?

Ecosystem recovery that occurs after a major disturbance (wildfires, lava flow, tsunamis, or human activity) when soil remains intact.

How is secondary succession different from primary?

Secondary starts with existing soil, primary starts with no soil.

Is secondary succession faster or slower than primary succession?

Faster, because soil and nutrients are already present.

What is an example of secondary succession?

A forest regrowing after a wildfire.

What is aquatic succession?

The gradual process in which an aquatic ecosystem turns into terrestrial land.

How does aquatic succession occur?

Sediments fill up the water → water becomes shallow → becomes land over time.

What is the main idea of aquatic succession?

Water becomes land as soil builds up.

What is an example of aquatic succession?

A pond filling with sediment and becoming a meadow, then eventually a forest.

What does the nitrogen cycle describe?

How nitrogen moves between plants, animals, bacteria, the atmosphere, and soil.

What percentage of the atmosphere is nitrogen?

About 78%.

Why can’t plants and animals directly use atmospheric nitrogen (N₂)?

It has a triple bond, making it too difficult to convert into a usable form.

What is the main reservoir of nitrogen on Earth?

The atmosphere.

Why is nitrogen considered a limiting factor for plants?

Plants need nitrogen to grow, but they cannot absorb it in its atmospheric form (N₂).

What abiotic factor can fix atmospheric nitrogen?

Lightning, which converts N₂ into usable nitrogen compounds.

What are the major usable forms of nitrogen?

Nitrates (NO₃), nitrites (NO₂), and ammonium (NH₄).

What organisms are most important in the nitrogen cycle?

Bacteria, especially decomposers.

How do animals obtain nitrogen?

By eating plants (or animals that ate plants).

What happens during nitrogen fixation?

Bacteria convert atmospheric nitrogen (N₂) into ammonium (NH₄).

What is assimilation?

Plants absorb nitrates from the soil through their roots.

What happens during ammonification?

Decomposers convert dead organisms and waste back into ammonium (NH₄).

What is denitrification?

Bacteria convert excess soil nitrogen back into atmospheric nitrogen (N₂).

Why is nitrogen important to life?

It is essential for amino acids, proteins, DNA, and chlorophyll in plants.

What percentage of the human body is nitrogen?

About 3%.

How do humans alter the nitrogen cycle?

By producing and using excessive fertilizer, which disrupts the cycle.

What environmental problem can excess fertilizer cause?

Eutrophication—toxic algal blooms that harm aquatic life.

What greenhouse gas released by humans also alters the nitrogen cycle?

Nitrous oxide (N₂O) from agriculture, fossil fuel burning, and industry.

What harmful environmental effect can too much nitrous oxide cause?

Acid rain.

Name two human activities that add too much nitrogen to the environment.

Burning fossil fuels and mining.

what is the role of decomposers in nitrogen cycle?

they return nitrogen to soil or atmosphere.