Functions of an Ecosystem

Learning Outcomes:

1. Understand the primary functions of an ecosystem: energy flow, nutrient cycling, and ecological succession.
2. Explore the dynamics of energy flow through trophic levels.
3. Differentiate between food chains and food webs and their significance.
4. Comprehend ecological pyramids and their types.
5. Learn the impacts of pollutants through bioaccumulation and biomagnification.
6. Recognize biotic interactions and nutrient cycles.
7. Grasp the principles of ecological succession.

Overview of Ecosystem Functions

An ecosystem is a dynamic and vast system with interconnected functions. The key functions can be categorized into: energy flow, nutrient cycling, and ecological succession. This interconnectedness is crucial for ecosystem stability and development.

Energy Flow

Energy flow drives metabolic activities and is unidirectional, moving from producers to top consumers. Understanding trophic level interactions provides insight into this energy transfer.

Trophic Level Interactions

Trophic levels depict the nutritional relationships within an ecosystem. The interactions can be studied through the following:

1. Producers (Autotrophs): The base of the energy flow, primarily consisting of green plants that convert solar energy into chemical energy.
2. Primary Consumers (Herbivores): Feed directly on producers, transferring energy to the next level.
3. Secondary Consumers (Carnivores): Prey on primary consumers.
4. Tertiary Consumers: Feed on secondary consumers.
5. Top Carnivores (Quaternary Consumers): Occupy the highest trophic level.

Energy moves sequentially from lower to higher trophic levels, with some energy lost as unusable heat at each stage. This loss limits the ecosystem to typically four or five trophic levels. Trophic level interactions encompass three core concepts:

1. Food Chain
2. Food Web
3. Ecological Pyramids

Food Chain

A food chain represents the feeding sequence among organisms, starting with producers and ending with top carnivores. It illustrates the transfer of energy through consumption.

Types of Food Chains

1. Grazing Food Chain: Begins with plants (primary producers) and progresses through herbivores to carnivores. Example: Grass → Caterpillar → Lizard → Snake.
2. Detritus Food Chain: Initiates with decomposing organic matter and proceeds through decomposers to predators. Example: Litter → Earthworms → Chicken → Hawk.

The main distinction between these chains is the energy source for the first-level consumers: living plant biomass in grazing chains versus dead organic matter in detritus chains. Both chains are interconnected, with detritus chains depending on waste from grazing chains.

Important Note: Bears exhibit a unique hibernation pattern compared to other animals. They enter a deep sleep without drastic body temperature drops, awakening only when necessary, such as giving birth.

Food Web

A food web is a more complex representation, showing all possible energy and nutrient transfers among organisms within an ecosystem. It accounts for interconnected food chains and provides multiple survival alternatives for organisms.

1. A food resource might be part of several chains, especially at lower trophic levels.
2. Removal of any intermediate food chain can significantly affect succeeding links.
3. Food availability and preferences often shift seasonally.

Important Note: Cetaceans, such as dolphins and whales, are water-living mammals with no hind limbs and breathe through a blowhole.

Ecological Pyramids

Ecological pyramids depict trophic levels in a diagrammatic form. The base is formed by producers, and the tip is occupied by top carnivores. These pyramids can represent:

1. Pyramid of Numbers: Shows the total number of individuals at each trophic level. May be upright (e.g., grassland ecosystems) or inverted (e.g., forests).
2. Pyramid of Biomass: Represents the total dry weight of organisms at each level. Can be upward (land ecosystems) or inverted (aquatic ecosystems).
3. Pyramid of Energy: Illustrates energy flow, always upright due to the loss of energy at each trophic transfer.

Important Note: Pyramid of energy helps explain biological magnification, where toxic substances concentrate more at higher trophic levels.

Pollutants and Trophic Levels

Pollutants, especially non-degradable ones, move through trophic levels via two main processes:

1. Bioaccumulation: The increase in pollutant concentration from the environment to the first organism in a food chain.
2. Biomagnification: The increase in pollutant concentration as it moves up the food chain.

Biotic Interactions

The interactions among organisms in an ecosystem are vital for its function and stability. They can be categorized as:

1. Mutualism: Both species benefit. Example: Pollinators and plants.
2. Commensalism: One species benefits, the other is unaffected. Example: Dung beetles and cow dung.
3. Amensalism: One species is harmed, the other remains unaffected. Example: A tree shading a smaller plant.
4. Competition: Both species suffer. Example: Species competing for the same food source.
5. Predation and Parasitism: One species benefits, the other is harmed. Example: Ticks on mammals.
6. Neutralism: Neither species benefits nor suffers.

Nutrient Cycling (Biogeochemical Cycles)

Nutrient cycling involves the movement of nutrients from the environment to organisms and back. These cycles maintain ecological balance.

Types of Nutrient Cycles

1. Perfect Cycles: Nutrients are replaced as quickly as they are utilized (e.g., gaseous cycles).
2. Imperfect Cycles: Nutrients may be lost from the cycle, locking into sediments (e.g., sedimentary cycles).

Nutrient Cycle Classification

1. Gaseous Cycles: The atmosphere or hydrosphere serves as the reservoir (e.g., carbon and nitrogen cycles).
2. Sedimentary Cycles: The Earth’s crust acts as the reservoir (e.g., phosphorus and sulfur cycles).

Important Note: Spiders inject their prey with poison to turn their insides into a liquid that they can suck up.

Water Cycle (Hydrologic)

The water cycle is crucial for nutrient transport. Water circulates between reservoirs like oceans, lakes, and the atmosphere through processes like evaporation, precipitation, and runoff.

Carbon Cycle

Carbon moves continuously between the atmosphere and organisms. It is essential for forming organic compounds like DNA. Carbon cycles through processes like photosynthesis, respiration, and decomposition.

Nitrogen Cycle

Nitrogen is vital for protein synthesis. It undergoes a cycle involving nitrogen fixation, assimilation, nitrification, and denitrification. Human activities, such as industrial processes, have significantly impacted this cycle.

Sedimentary Cycle

Phosphorus and other minerals circulate in sedimentary cycles, involving weathering, erosion, and biological transport.

Ecological Succession

Succession is the progressive change in an ecosystem, leading to the establishment of a stable community.

Primary Succession

Occurs on newly formed sites, beginning with hardy pioneer species like lichens. These species alter habitat conditions, enabling other organisms to establish themselves.

Secondary Succession

Follows the disturbance of a climax community. It involves the sequential development of communities, such as an abandoned farmland evolving into a forest.

Types of Succession

1. Autogenic Succession: Brought about by living organisms within the community.
2. Allogenic Succession: Caused by external factors.
3. Autotrophic Succession: Dominated initially by green plants.
4. Heterotrophic Succession: Characterized initially by heterotrophs.

Important Note: Dart Frogs are endangered due to habitat destruction and the pet market.

Tundra Ecosystems

The tundra represents barren lands found in extreme environments. They can be arctic or alpine, featuring hardy vegetation and animals adapted to cold climates.

Summary Table: Ecological Pyramids

Pyramid Type	Description	Shape	Example Ecosystem
Pyramid of Numbers	Number of individuals at each level	Upright/Inverted	Grassland/Forest
Pyramid of Biomass	Total dry weight at each level	Upright/Inverted	Land/Aquatic
Pyramid of Energy	Energy flow at each trophic level	Always Upright	All Ecosystems

Concept Note: Bioaccumulation involves pollutant entry into the food chain, while biomagnification describes pollutant concentration increase through trophic levels.

Do you know?: Pythons constrict their prey by squeezing it until it stops breathing, then swallowing it whole.

MCQ: Which of the following best explains biomagnification?

1. The transfer of energy through the food chain.
2. The increase in nutrient concentration at lower trophic levels.
3. The accumulation of pollutants at each step of the food

chain.

4. The recycling of nutrients in the ecosystem.

Answer: 3