Decomposers – Break down dead organisms & recycle nutrients.
Energy Levels in Food Chains
Only 10% of energy is passed to the next trophic level because:
Energy is lost as heat through respiration.
Some parts of the organism are not eaten (bones, fur, shells).
Not all food is digested (waste in feces).
Energy used during growth, reproduction, and movement.
This energy is not enough to sustain many quaternary consumers.
Producers have the most energy, and quaternary consumers have the least energy.
Pyramid of Energy
Definition: Shows the flow of energy at each trophic level, measured in kJ/m^2/year.
Shape: Always a pyramid because energy decreases as it moves up the food chain.
Example (Grassland Ecosystem): Plants (10,000 kJ) → Herbivores (1,000 kJ) → Carnivores (100 kJ) → Top Predator (10 kJ)
Pyramid of Biomass
Definition: Shows the total dry mass of living organisms at each trophic level, measured in g/m^2.
Shape: Usually a pyramid but can be inverted in aquatic ecosystems.
Why Biomass Decreases?:
Energy loss at each level leads to less biomass available for the next level.
In aquatic systems, phytoplankton reproduce quickly but have a small individual mass, leading to an inverted pyramid (small producer biomass but large consumer biomass).
Definition: Shows the number of organisms at each trophic level.
Shape: Can be a true pyramid, inverted, or irregular depending on ecosystem type.
Why Shape Varies?
In a grassland, many small producers (grass) support fewer herbivores (insects), and even fewer predators (birds).
In a forest, one large tree (producer) supports many herbivores (caterpillars), leading to an inverted pyramid.
Grassland: Many grasses → Fewer herbivores → Even fewer carnivores
Forest: Few trees → Many insects → Fewer birds
Comparison Between the Three Pyramids
Pyramid of Energy
Advantages:
Shows actual energy transfer between trophic levels.
Always pyramid-shaped (follows the 10% Rule).
No inverted pyramids, making comparisons easy.
Disadvantages:
Difficult to measure energy accurately.
Requires complex calculations over time.
Does not show population size.
Pyramid of Biomass
Advantages:
More accurate than a pyramid of numbers (accounts for size differences in organisms).
Shows how much living material is available at each level.
Helps understand food availability in ecosystems.
Disadvantages:
Difficult to measure dry mass without killing organisms.
Can be inverted (e.g., in aquatic ecosystems, where phytoplankton have less mass but reproduce quickly).
Does not show energy flow over time.
Pyramid of Numbers
Advantages:
Simple and easy to count organisms.
Gives a clear view of population structure.
No need for complex calculations.
Disadvantages:
Does not account for organism size (e.g., one tree can support many insects).
Can be inverted or irregular, making interpretation difficult.
Does not show the amount of energy or biomass at each level.
Prey-Predator Relationship
Predator population follows prey population in cycles.
If prey numbers increase, predators have more food and their population grows.
As predator numbers increase, they eat more prey, causing the prey population to decrease.
This leads to a fluctuating cycle of predator-prey populations.
Example:
More rabbits → More foxes
Too many foxes eat too many rabbits → Rabbit numbers drop
Less rabbits → Foxes starve → Fox numbers drop
Fewer foxes → Rabbits increase again
S-Curve or Population Graph
The S-Curve (or Population curve) represents the population growth of an organism in a habitat with limited resources.
Lag Phase
Description:
The population starts with a small number of organisms, so growth is slow.
Individuals are adapting to the new environment.
Reasons for Slow Growth:
Time Needed for Maturity – Organisms need time to grow and reach reproductive age.
Low Reproductive Rate – Few individuals mean limited mating opportunities, reducing the number of offspring.
Adaptation to the Environment – Organisms need time to adjust to new food sources, shelter, and climatic conditions.
Log Phase
Description:
Population size doubles rapidly due to abundant resources (food, space, mates).
Birth rate exceeds death rate.
Reasons for Rapid Growth:
No Competition – Plenty of food and space allow organisms to grow and reproduce freely.
Few Predators or Diseases – Low predator populations and minimal disease spread enable high survival rates.
Favorable Environmental Conditions – Optimal temperature, oxygen, and nutrients allow faster metabolism and reproduction.
Stationary Phase
Description: Population growth slows down and fluctuates around the carrying capacity. Resources become limited, leading to competition.
Reasons for Growth Slowing Down:
Resource Depletion – Food, water, and space become scarce, limiting further growth.
Increased Competition – Organisms compete for food, mates, and shelter.
Predation & Disease – High population density leads to higher spread of diseases and attracts more predators, increasing the death rate.
Decline Phase
Definition: The decline phase occurs when a population size decreases because the death rate exceeds the birth rate. This happens due to environmental pressures, resource depletion, and other limiting factors.
Reasons for Population Decline:
Severe Resource Depletion – Overconsumption of food, water, and shelter leads to starvation and malnutrition, reducing reproduction rates and increasing mortality.
Increased Competition – As population density rises, intense competition for limited resources causes weaker individuals to die out, lowering overall population numbers.
Predation and Disease – Higher population densities attract more predators and make disease transmission easier, leading to mass mortality.
Toxic Waste Accumulation – In some environments (e.g., bacteria in a closed system), waste products accumulate, creating harmful conditions that kill organisms.