noc19-bt09 Lecture 10-Food chains, Food webs and trophic levels

Name: noc19-bt09 Lecture 10-Food chains, Food webs and trophic levels
Uploaded: 2019-02-15T06:05:45.000Z
Duration: 1 h 58 min 28 s

Ecological Energetics: Food Chains, Food Webs, and Trophic Levels

Introduction to Ecological Energetics

The module on Ecological Energetics begins with an overview of three key topics: food chains, food webs, and trophic levels.

A basic food chain example is introduced, illustrating the flow of energy from grass (producer) to insects (primary consumer), frogs (secondary consumer), snakes (tertiary consumer), and hawks or eagles (quaternary consumer).

Defining Food Chains

A food chain is defined as the transfer of food energy from plants through herbivores to carnivores and decomposers.

Energy from the sun is converted into chemical energy by plants, which then moves through various organisms in a community.

Autotrophs vs. Heterotrophs

Autotrophs are primary producers that create their own nutrition; examples include trees, plants, algae, and certain bacteria known as chemoautotrophs.

Heterotrophs cannot produce their own food; they rely on consuming other organisms for nutrition. Examples include most animals.

Types of Autotrophs

Autotrophs are categorized into photoautotrophs (using light for energy; e.g., most plants) and chemoautotrophs (using chemical reactions for energy; e.g., hydrogenovibrio crunogenus found in deep-sea hydrothermal vents).

Producers and Consumers in Food Chains

Organisms are classified as producers (autotrophs that make their own food) or consumers (organisms that consume others for sustenance).

Consumers are further divided into primary consumers (herbivores), secondary consumers (carnivores/omnivores), tertiary consumers, and quaternary consumers.

Classification of Consumers

Primary consumers eat producers; examples include grasshoppers and cows. They play a crucial role as prey species in ecosystems.

Secondary consumers eat primary consumers; these can be carnivorous or omnivorous. An example includes frogs eating grasshoppers.

Hierarchical Structure of Trophic Levels

The hierarchy continues with tertiary consumers eating secondary ones—e.g., snakes eating frogs—and quaternary consumers like hawks preying on tertiary ones.

Types of Feeding Strategies

Consumers can be classified based on their diets:

Herbivores: Only eat plants; e.g., cows.

Carnivores: Eat other animals but not plants; e.g., tigers.

Understanding Food Chains and the Role of Decomposers

The Concept of Decomposers

Decomposers are organisms that convert dead material into soil, recycling nutrients essential for plant growth. They play a crucial role in food chains by ensuring nutrient availability.

Nutrients like nitrogen from proteins move through the food chain—from plants to herbivores (e.g., grasshoppers), then to carnivores (frogs, snakes, hawks). If nutrients are locked in organisms, plants cannot access them.

Decomposers break down dead organisms and plants, releasing nutrients back into the soil. This process is vital for maintaining ecosystem health.

Types of Organisms in Food Chains

Different types of consumers include:

Herbivores: Organisms that eat plants (herbi = herbs).

Carnivores: Organisms that eat flesh (carni = flesh).

Omnivores: Organisms that consume both plants and animals (omni = all).

Detritivores: Organisms consuming decomposing matter and feces, aiding microbial decomposition.

The Role of Detritivores

Detritivores like earthworms consume decomposing plant material, breaking it down into smaller pieces. This action exposes it to microorganisms such as bacteria and fungi for further decomposition.

As detritivores digest organic matter, they convert it into fecal matter while enriching the soil with nutrients.

Types of Food Chains

Grazing Food Chain

Begins with plants followed by herbivores and then carnivores. It can be subdivided into predator food chains and parasitic food chains.

Detritus Food Chain

Starts with detritus or decaying matter followed by detritivores leading to carnivorous consumers.

Examples of Food Chains

Predator Food Chain Example

An example includes grass eaten by chital (a deer), which is then consumed by a tiger. The size generally increases up the chain—from small grass to large tigers.

Parasitic Food Chain Example

Involves a rat being consumed by a flea followed by parasitic protozoa. Here, organism size decreases as we move up the chain.

Detritus Food Chain Example

Fallen leaves from mangroves serve as detritus consumed by small fish or insect larvae; these are subsequently eaten by larger fish or piscivorous animals.

Understanding Food Chains and Food Webs

Differences Between Grazing and Detritus Food Chains

Vore refers to the process of eating, illustrated by fish-eating birds consuming fish. This exemplifies a detritus food chain.

The primary energy source in a grazing food chain is sunlight, utilized by plants, while in a detritus food chain, it starts with dead organic matter (detritus).

Grazing food chains typically have longer lengths due to multiple trophic levels: plants → herbivores → secondary consumers → tertiary consumers, etc.

Energy transfer between trophic levels is inefficient; only about 10% of energy is passed on at each level (e.g., 100 calories in plants results in 10 calories for herbivores).

Detritus food chains are shorter because they start with less energy from decomposed materials, limiting the number of organisms that can be supported.

Complexity of Food Webs

In nature, multiple interlinked food chains form complex systems known as food webs.

An example illustrates how grass serves as a base for various organisms like grasshoppers and frogs, leading to intricate predator-prey relationships.

A food web consists of interconnected and interdependent food chains where different species interact at various levels.

Trophic Levels Explained

A trophic level represents hierarchical positions within an ecosystem based on shared functions and nutritional relationships to primary energy sources.

Producers (like grass and trees), which utilize solar energy, form one trophic level; primary consumers (herbivores like grasshoppers) form another.

Interrelationships Within Food Webs

Different organisms can occupy multiple trophic levels simultaneously; for instance, a bird may act as both a primary consumer when eating fruits and a secondary or tertiary consumer when preying on caterpillars or frogs.

Understanding Ecological Pyramids

What is an Ecological Pyramid?

An ecological pyramid is a graphical representation that illustrates the biomass, numbers, or energy at each trophic level in an ecosystem.

It can also be referred to as a trophic pyramid, eltonian pyramid, energy pyramid, or food pyramid.

Types of Ecological Pyramids

Pyramid of Numbers

The pyramid of numbers displays the number of organisms present at each trophic level. For example, counting all plants (producers) in a given area provides data for this level.

Each section of the pyramid corresponds to different trophic levels: producers, primary consumers, secondary consumers, tertiary consumers, and quaternary consumers.

Observations on Trophic Levels

Typically, the number of individuals decreases as one moves up the trophic levels; for instance, fewer tigers exist compared to their prey species like chital or sambar.

In ecosystems such as tiger reserves, there may be around 30-40 tigers supported by thousands of prey animals like deer and millions of grasses below them in the hierarchy.

Inverted Pyramid Example

An inverted pyramid occurs when higher-level consumers outnumber lower-level ones; for example, one tree might support many birds and their parasites leading to a larger top section than base producers.

A single tree could support 100 birds which then host numerous parasites—illustrating how complex interactions can lead to unexpected population distributions within ecosystems.

Alternative Shapes in Ecological Pyramids

Spindle-Shaped Pyramid

A spindle-shaped pyramid features a larger middle range followed by smaller sections above and below it; this can occur when certain consumer populations are more abundant than expected without additional layers like parasites included.

Phytoplankton and Zooplankton Dynamics

Ecosystem Dynamics and Trophic Levels

Phytoplankton and Zooplankton Interactions

Microscopic animals (zooplankton) feed on microscopic plants (phytoplankton), which can reproduce rapidly under certain conditions.

A high reproduction rate of phytoplankton leads to an abundance of zooplankton, but fluctuations in phytoplankton populations can occur due to their rapid growth.

Exponential Growth of Phytoplankton

An example illustrates that starting with 1000 phytoplanktons, they can double every hour, leading to exponential population growth over time.

Despite potential high numbers, the ecosystem's balance is maintained as zooplankton consume phytoplankton, resulting in fewer phytoplanktons and more zooplanktons.

Trophic Pyramid Structures

The ecosystem exhibits a pyramid structure where fewer fish are present compared to zooplankton, which are supported by the abundant phytoplankton.

An example of a "dumbbell" shaped pyramid is presented: grasses support rabbits, while each rabbit supports many fleas.

Types of Pyramids in Ecosystems

The pyramid of energy shows energy distribution across trophic levels; it tapers off as one moves up the food chain.

The biomass pyramid typically resembles a tapering shape but can also be inverted in specific ecosystems like oceans where planktons support larger fish.

Standing Crop and Ecological Efficiency

Standing crop refers to the total dried biomass at each trophic level after removing water content from living organisms.

Understanding Energy Transfer in Ecosystems

The Relationship Between Food Intake and Weight Gain

Eating 1 kg of food does not equate to a 1 kg weight increase due to energy usage for movement, internal bodily functions, and respiration.

Not all food is fully digested; for example, plant materials like cellulose are often excreted undigested, leading to energy loss during the transfer between trophic levels.

Ecological Efficiency Explained

Ecological efficiency measures how effectively energy transfers from one trophic level to another, highlighting various subcomponents such as exploitation efficiency.

Exploitation efficiency is calculated by dividing the amount of food ingested by the total prey production available at that trophic level.

Calculating Different Types of Efficiencies

Assimilation efficiency refers to the proportion of ingested food that gets assimilated into the body, defined as assimilation divided by ingestion.

Gross production efficiency compares consumer production against total ingestion, while net production efficiency assesses consumer production relative to assimilation.

Formulating Ecological Efficiency

The formula for ecological efficiency combines exploitation efficiency with assimilation and net production efficiencies.

This results in a ratio comparing current trophic level production against previous levels, illustrating energy transfer effectiveness across levels.

The 10 Percent Rule in Energy Transfer

The "10 percent rule" states that only about 10% of energy is stored as biomass when transferring between trophic levels; most energy is lost through respiration or incomplete digestion.

Understanding Trophic Levels and Ecological Dynamics

The 10 Percent Rule in Energy Transfer

The "percent rule" indicates that only 10% of energy is transferred from one trophic level to the next. For example, if there are 1000 joules at one level, only 100 joules will be available at the next.

This energy transfer limitation explains why food chains cannot be excessively long; as they extend, the energy available for apex predators diminishes significantly, potentially threatening their survival.

The equation representing this concept shows that energy at any trophic level (n) can be calculated as: Energy = Energy intercepted from the sun / (10^(n+1)).

At the producer level (plants), only 1% of solar energy is converted into usable energy for higher trophic levels due to this rule.

Trophic Cascades: An Ecological Phenomenon

A trophic cascade occurs when changes in top predator populations lead to significant shifts in ecosystem structure and nutrient cycling.

Removing apex predators disrupts predatory pressure on primary consumers (e.g., deer), leading to population explosions and subsequent overgrazing of vegetation.

For instance, removing tigers from a forest leads to increased chital populations, which then deplete grass and saplings, demonstrating cascading effects throughout the ecosystem.

Conversely, adding top predators can also create reciprocal changes in predator-prey dynamics, affecting various species across different levels of the food chain.

Case Study: Wolves in Yellowstone National Park

The reintroduction of wolves into Yellowstone National Park serves as a classic example of a trophic cascade impacting an entire ecosystem.

After being absent for 70 years, wolves were reintroduced in 1995. Their presence not only reduced deer populations but also altered deer behavior significantly.

As deer began avoiding certain areas where they could easily be hunted, these regions experienced rapid ecological recovery with increased vegetation growth within just six years.

The Impact of Wolves on Ecosystems

The Role of Wolves in Biodiversity

Wolves kill coyotes, leading to an increase in rabbit and mouse populations, which subsequently attracts more predators like hawks, weasels, foxes, badgers, ravens, and bald eagles.

The presence of wolves influences river behavior; they cause rivers to meander less and reduce erosion by stabilizing banks through regenerating forests.

The recovery of vegetation due to reduced deer populations leads to decreased soil erosion and enhances the physical geography of Yellowstone National Park.

Effects on Forest Regeneration

Without herbivores like deer being controlled by predators (wolves), forest regeneration halts as deer consume grasses and saplings.

The absence of wolves previously led to a significant reduction in biodiversity due to overgrazing by deer.

Trophic Cascades Explained

Introducing wolves back into the ecosystem creates a negative impact on deer populations, allowing saplings and grasses to thrive once again.

Increased plant life supports a wider range of organisms; for example, insects feed on grasses which attract birds that prey on them.

Interconnectedness within the Ecosystem

With the growth of shrubs comes berry production that supports bear populations. Bears also influence other species such as coyotes through predation.

A decrease in coyote numbers results in an increase in rabbit populations since they are no longer primary prey.

Understanding Trophic Cascades' Importance

This chain reaction illustrates how one top predator can significantly affect various levels within an ecosystem—a phenomenon known as trophic cascade.

Trophic cascades demonstrate interconnected impacts across food webs; changes at one level can ripple throughout the entire ecosystem.

Conclusion: Implications for Ecology