Unit 4: Ecosystem Ecology

1. Types of Ecosystems

Terrestrial (Land) Ecosystems

• Forest: Dominated by trees. Can be tropical, temperate, or boreal (taiga).
• Grassland: Dominated by grasses. Includes savannas (tropical) and prairies (temperate).
• Wetlands: Areas where soil is saturated with water. Includes marshes (grassy), swamps (woody), and bogs (mossy, acidic).

Aquatic (Water) Ecosystems

Freshwater Ecosystems

• Lotic (Flowing Water): Rivers and streams.
• Lentic (Standing Water): Lakes and ponds. Often have zones (littoral, limnetic, profundal).

Marine (Saltwater) Ecosystems

• Estuarine: An estuary is a highly productive area where a freshwater river meets the saltwater ocean (brackish water).
• Marine: The open ocean. Includes coral reefs, deep sea, etc.

2. Ecosystem Structure

An ecosystem consists of biotic (living) and abiotic (non-living) components.

Abiotic Components

• Climatic: Temperature, light, water.
• Edaphic: Soil, pH, minerals.
• Inorganic/Organic Substances: Water, CO₂, Nitrogen, humus.

Biotic Components (Trophic Levels)

1. Producers (Autotrophs):
   • "Self-feeders." Create their own food, usually via photosynthesis (e.g., plants, algae).
2. Consumers (Heterotrophs):
   • "Other-feeders." Eat other organisms.
   • Primary Consumers (Herbivores): Eat producers.
   • Secondary Consumers (Carnivores): Eat primary consumers.
   • Tertiary Consumers: Eat secondary consumers.
3. Decomposers (Saprotrophs):
   • Break down dead organic matter (detritus) and recycle nutrients (e.g., bacteria, fungi).

3. Energy Flow: Food Chains & Food Webs

Energy flow in an ecosystem is unidirectional (one-way). It is captured by producers and transferred to consumers, with most being lost as heat at each step.

Food Chain

A simple, linear pathway of energy transfer.

Example:
Grass (Producer) → Rabbit (Primary Consumer) → Fox (Secondary Consumer)

Food Web

A more realistic, complex network of interconnected food chains. It recognizes that most organisms eat, and are eaten by, more than one species, making the ecosystem more stable.

4. Ecological Efficiencies

Ecological efficiency describes the efficiency with which energy is transferred from one trophic level to the next. It is generally very low.

Lindeman's 10% Law

This is a general rule of thumb stating that, on average, only about 10% of the energy from one trophic level is stored as biomass in the next trophic level. The other 90% is lost, primarily as metabolic heat through respiration.

Example:

• Producers: 1,000,000 J of energy
• Primary Consumers: 10% = 100,000 J of energy
• Secondary Consumers: 10% = 10,000 J of energy

5. Ecological Pyramids

Graphical representations of the trophic structure of an ecosystem.

Pyramid of Energy

• Shows the amount of energy at each trophic level.
• It is ALWAYS UPRIGHT due to the 10% Law (energy is always lost).

Pyramid of Biomass

• Shows the total biomass (dry weight) at each level.
• Usually Upright: (e.g., in a forest).
• Can be Inverted: In some aquatic ecosystems. The producers are phytoplankton, which have tiny biomass but reproduce extremely fast. They are consumed so quickly by zooplankton that the zooplankton's biomass is greater at any one time.

Pyramid of Numbers

• Shows the number of individual organisms at each level.
• Usually Upright: (e.g., grassland).
• Can be Inverted/Spindle-Shaped: A single large tree (1 producer) can support thousands of insects (primary consumers).