Pyramids of Numbers in Ecosystems

• A cycle constitutes a sequence of reactions that repeat, regenerating and reusing a product.

Pyramids of Numbers

• A pyramid of numbers represents producers (green plants/algae) with its widest base.
• Organisms are eaten by primary consumers (herbivores).
• There are more producers than primary consumers in an ecosystem.
• Secondary consumers are fewer than primary consumers, and tertiary consumers are fewest.
• The number of organisms decreases from lower to higher trophic levels.
• Not all pyramids have a true pyramid shape
• In a pyramid, grass serves as the producer, rabbits as primary consumers, foxes as secondary, and fleas as tertiary consumers.
• One fox can support many fleas, which is a parasitic relationship.
• A pyramid of numbers can be misleading because of energy presence.
• The fourth trophic level has less energy than the third trophic level in reality.
• The width of the bar = # of organisms at each trophic level, not energy stored.
• When a large producer (tree) supports herbivores, a pyramid of numbers has a small base.
• One tree has more energy than the caterpillars feeding on it.
• Pyramids of numbers don't reflect sizes/available energy of organisms.

Pyramids of Biomass

• A pyramid of biomass is a more accurate way of assessing energy at each trophic level.
• Biomass = dry mass of organisms.
• Dry mass indicates the mass of organic matter in an organism accurately.
• Fresh mass is variable, data obtained won't be reliable.
• Biomass involves heating organic material around 100°C to remove water until mass is constant.
• Temperature should stay around 100°C or organic material degrades.
• Using biomass ensures data per trophic level is representative.
• Redrawing pyramids of numbers as pyramids of biomass would resemble a true pyramid shape

Nutrient Cycles

• Water, carbon, oxygen, and nitrogen cycle through ecosystems.
• Without recycling, ecosystems would run out of raw materials and nutrients.
• Nutrient availability is key to an ecosystem's structure.
• Nutrients move from environment to organisms and back through biogeochemical cycles.
• A biogeochemical cycle occurs when a substance moves from the Earth's biotic part (biosphere) to the abiotic part of Earth (lithosphere, atmosphere, & hydrosphere).
• The water, carbon, and nitrogen cycle is critical.

The Water Cycle

• The water cycle involves water's movement on Earth as solid, liquid, and gas.
• Liquid water is present in oceans, seas, rivers, and lakes.
• Liquid water exists underground between rocks and soil.
• Another reservoir for water is in living organisms.
• Water in its gaseous state is present as vapor.
• Solid water is mainly stored in glaciers and polar ice sheets.
• Water evaporates into the atmosphere, which is driven by the sun's energy.
• Organisms release water vapor.
• Plants absorb water through roots, releasing most of it as vapor.

Explore pyramids of numbers showing the number of organisms at each trophic level in an ecosystem, starting with producers. The number of organisms decreases from lower to higher trophic levels. The width of the bar corresponds to the number of organisms, not the stored energy.