LECTURE 27 - Trophic Ecology

Question 1

autotrophs

Answer 1

• producers
• make it themselves
  (synthesise organic from inorganic compounds – CO2, H2O using energy from sunlight)
• green plants, phytoplankton, algae (+chemosynthetic bacteria – use chemical energy)

Question 2

heterotrophs

Answer 2

• consumers, degraders, decomposers
• get it from others
• animals

Question 3

trophic level def

Answer 3

trophic levels are hierarchical levels in an ecosystem’s food chain or food web, where each level represents a position in the energy and nutrient transfer process. These levels categorize organisms based on their feeding habits and the flow of energy through an ecosystem. The primary trophic levels include:

Primary Producers (Trophic Level 1): Organisms, typically plants and algae, that convert energy from sunlight or chemicals into organic compounds through processes like photosynthesis or chemosynthesis.

Primary Consumers (Trophic Level 2): Herbivores that consume primary producers as their primary food source.

Secondary Consumers (Trophic Level 3): Carnivores or omnivores that feed on primary consumers.

Tertiary Consumers (Trophic Level 4): Carnivores that consume secondary consumers.

These trophic levels help scientists understand the flow of energy, nutrients, and biomass in ecosystems and how different species interact within these systems.

Question 4

energy hypothesis about why food chains have to be short

Answer 4

At each trophic level, some of the energy from the organisms at that level is transferred to the organisms at the next level when they are consumed but the transfer of energy is not very efficient and a significant amount of energy is lost as heat during each transfer.

Energy Loss: The energy hypothesis, proposed by Charles Elton in 1927, suggests that this energy loss is a key reason why food chains tend to be short. As you move up the trophic levels, less and less energy is available to support the organisms at the higher levels. This limits the number of trophic levels that can be sustained in an ecosystem.

Solar Energy Input: The ultimate source of energy for all ecosystems is solar energy. Plants capture this energy through photosynthesis, converting it into chemical energy stored in their tissues. Herbivores then consume plants, and carnivores consume herbivores. However, with each step, energy is lost.

Efficiency and Trophic Levels: The efficiency of energy transfer between trophic levels is relatively low, often around 10%. This means that only about 10% of the energy from one trophic level is passed on to the next. The rest is lost as heat or used for the organisms’ life processes.

Question 5

Hypothesis 2: the dynamic stability hypothesis
why food chains are short

Answer 5

• longer food chains less stable because
• fluctuations at low trophic levels magnify at high levels
  –> top predators more likely to go extinct

Fluctuations : such as a change in the abundance of primary producers (plants). can include factors like temperature changes, disease outbreaks, or variations in nutrient availability. In a longer food chain, these fluctuations are more likely to occur because there are more species involved.

This effect is magnified as you move up the food chain because each trophic level depends on the one below it. So, small changes in primary producers can lead to more significant changes in herbivore populations.

Top Predators at Risk: Ultimately, these magnified effects can reach the top predators in the food chain. These predators are more likely to go extinct or experience population declines because they depend on the stability of all the trophic levels below them.

Result: Shorter Food Chain: Due to the increased risk of top predator extinction and overall instability, longer food chains tend to become shorter. In other words, the food chain simplifies, with fewer trophic levels. This is because shorter food chains are more stable, as there are fewer links for disturbances to propagate through.

Question 6

what are Ecological interactions

Answer 6

Are exchanges and flow of energy and matter
* Within and between trophic levels
–> intimately linked with trophic ecology

Include:
* Mutualism: 2 organisms in close association, both benefit [+, +]
* Competition: [-, -]
* Predation: e.g., herbivory, carnivory; parasitism [+, -]
* Commensalism: [+, 0]
* Amensalism [0, -] e.g. plant releasing a toxin [0] that inhibits the growth of nearby plants [-].
* No interaction [0, 0]

Question 7

types of mutualism

Answer 7

• Obligate mutualism; symbiosis: partners
  can only survive together
• Facultative mutualism: partners gain
  benefit from associating, but can survive
  on their own

Question 8

Herbivory

Answer 8

[+,-]
Plants, in general, are not the most nutritious food for animals. Much of the energy and essential nutrients required by animals are locked behind the tough cell walls of plants. This makes it harder for herbivores to extract the nutrients they need for their own growth and survival. [- for animals]

Impact on Individuals: Herbivores play a significant role in the lives of individual plants and animals. Herbivores need to feed on plants to sustain themselves, which can lead to both direct benefits and costs for the animals involved. [+ for animals]

Population and Community Effects: Herbivory can influence the abundance and distribution of plant and animal species in an ecosystem. For example, the presence of herbivores can impact the composition of plant communities, as certain plant species may be more or less attractive to herbivores. []

Ecosystem Processes: Herbivory can also have cascading effects on larger ecological processes. For instance, it can affect nutrient cycling, which is essential for the functioning of entire ecosystems. As herbivores consume plants, they can alter the distribution of nutrients in the environment.