AFNS Academic test Ecology chapter
Good morning, class. Please settle down and open your notebooks to the section on Ecology. For those of you preparing for the AFNS Initial Test, this chapter is exceptionally high-yield. We are going to explore the intricate relationships between living organisms and their environment, a study known as Ecology—derived from the Greek oikos (house) and logos (study), a term famously coined by Ernst Haeckel in 1866.
I. Levels of Ecological Organisation
In ecology, we view life through a nested hierarchy. You must understand these levels clearly for your assessments:
- Individual: A single living organism, like one lion.
- Population: All individuals of the same species in a specific area at the same time.
- Community: All populations of different species interacting in an area.
- Ecosystem: The community plus its abiotic (non-living) environment.
- Biome: A large geographic area defined by climate, such as a desert or tundra.
- Biosphere: The entire zone of life on Earth.
Environmentally, we distinguish between Biotic factors (living components like predators and decomposers) and Abiotic factors (non-living components like temperature, pH, and light). A crucial concept here is the Limiting Factor, which restricts growth when in short supply. Remember Liebig’s Law of the Minimum: growth is controlled by the most scarce essential resource.
II. Habitat, Niche, and Population Dynamics
Every organism has a Habitat (its physical “address”) and an Ecological Niche (its functional “occupation”). A vital rule is the Competitive Exclusion Principle: no two species can occupy the exact same niche in the same habitat simultaneously.
When studying populations, we look at growth curves:
- Exponential (J-curve): Unlimited growth occurring under ideal conditions with no predators.
- Logistic (S-curve): Growth that slows and levels off at the Carrying Capacity (K)—the maximum population size the environment can sustainably support.
Population size is limited by Density-dependent factors (competition, disease) and Density-independent factors (natural disasters). We also see various species interactions:
- Predation/Parasitism: One benefits, one is harmed (+/-).
- Mutualism: Both benefit (+/+).
- Commensalism: One benefits, one is unaffected (+/0).
- Amensalism: One is harmed, one is unaffected (0/-), such as Penicillium killing bacteria.
III. Energy Flow and Trophic Levels
Energy moves linearly through a Food Chain, while a Food Web represents the more complex, realistic interconnected relationships.
- Level 1: Producers (Autotrophs like plants and algae).
- Level 2: Primary Consumers (Herbivores).
- Level 3 & 4: Secondary and Tertiary Consumers (Carnivores).
- Decomposers: Saprotrophs like bacteria and fungi that recycle nutrients.
⭐ The 10% Energy Rule: This is a cornerstone of ecological theory. Only approximately 10% of the energy at one trophic level is transferred to the next. The other 90% is lost as heat, undigested material, or through metabolic costs. This explains why food chains rarely exceed 4–5 levels and why an energy pyramid is always upright.
In terms of productivity, Gross Primary Productivity (GPP) is the total energy fixed by photosynthesis, while Net Primary Productivity (NPP) is what remains after the plant’s own respiration—essentially, the energy available to consumers.
IV. Biogeochemical Cycles
Unlike energy, which flows one way, matter is recycled. The Carbon Cycle: Carbon is fixed from the atmosphere via Photosynthesis and returned through Respiration, Decomposition, and Combustion. The Greenhouse Effect is a natural process where gases like CO₂ and CH₄ trap heat, but human activity has enhanced this, leading to global warming.
The Nitrogen Cycle (⭐ Extremely high-yield for AFNS): Most organisms cannot use N₂ gas directly; it must be converted through specific processes:
- Nitrogen Fixation: N₂ is converted to ammonium/nitrate. Primarily by Rhizobium in legume root nodules ⭐.
- Nitrification: Ammonium is oxidized to nitrates by Nitrosomonas and Nitrobacter ⭐.
- Assimilation: Plants absorb these nitrates to build proteins.
- Ammonification: Decomposers turn organic matter back into ammonium.
- Denitrification: Pseudomonas denitrificans ⭐ converts nitrates back into N₂ gas, usually in waterlogged soils.
V. Ecological Succession and Environmental Issues
Succession is the predictable change in a community over time.
- Primary Succession: Starts on bare, lifeless substrate (like volcanic rock). It involves Pioneer Species like lichens and is very slow.
- Secondary Succession: Occurs in disturbed areas where soil already exists (like an abandoned farm). It is much faster. The final stable stage is called the Climax Community.
Current Environmental Threats:
- Global Warming: Caused by excess CO₂ and CH₄ enhancing the greenhouse effect.
- Ozone Depletion: Caused by CFCs, leading to increased UV radiation.
- Eutrophication (⭐ repeated in AFNS): Fertilizer runoff leads to algal blooms, which block sunlight. When algae die, bacteria decompose them, depleting oxygen and killing fish (hypoxia).
- Acid Rain: Caused by SO₂ and NO₂ dissolving in rain.
VI. Conservation and Human Impact
Conservation can be In-situ (on-site, like national parks—considered the best method ⭐) or Ex-situ (off-site, like seed banks). International treaties like CITES regulate trade in endangered species, while the IUCN Red List tracks extinction risks.
Human impacts are visible in Intensive Agriculture (leading to pesticide bioaccumulation like DDT), Urbanisation, and the introduction of Invasive Species which outcompete native wildlife.
⭐ FINAL SUMMARY FOR AFNS TEST:
- Producers are the 1st trophic level; Decomposers recycle nutrients.
- The 10% Rule limits food chain length.
- Rhizobium fixes nitrogen; Nitrosomonas/Nitrobacter are nitrifying; Pseudomonas is denitrifying.
- Eutrophication involves fertilizer runoff and oxygen depletion.
- In-situ conservation is the most effective strategy.
Study these cycles and the roles of specific bacteria closely, as they are the most frequent targets of examination questions. Class dismissed.
1. Decomposers in an ecosystem are mainly:
- A) Plants
- B) Herbivores
- C) Bacteria and fungi
- D) Carnivores
✔ Answer: C) Bacteria and fungi
- Which of the following is a NON-living (abiotic) component of an ecosystem?
- A) Trees
- B) Bacteria
- C) Rocks
- D) Insects
✔ Answer: C) Rocks
- A food chain always starts with a:
- A) Herbivore
- B) Carnivore
- C) Producer (green plant)
- D) Decomposer
✔ Answer: C) Producer (green plant)
- Energy flow in an ecosystem is:
- A) Cyclic
- B) Unidirectional (one way)
- C) Bidirectional
- D) Random
✔ Answer: B) Unidirectional (one way)
- The study of the relationships between organisms and their environment is called:
- A) Genetics
- B) Taxonomy
- C) Ecology
- D) Physiology
✔ Answer: C) Ecology
- An organism’s habitat is:
- A) Its role in the ecosystem
- B) The physical place where it lives
- C) Its food source
- D) Its predator
✔ Answer: B) The physical place where it lives
- A niche is defined as:
- A) The physical location of an organism
- B) The functional role of an organism in its ecosystem
- C) The food an organism eats
- D) The species of an organism
✔ Answer: B) The functional role of an organism in its ecosystem
- Primary consumers are:
- A) Plants
- B) Herbivores
- C) Carnivores
- D) Decomposers
✔ Answer: B) Herbivores
- Secondary consumers are:
- A) Plants
- B) Herbivores
- C) Carnivores that eat herbivores
- D) Decomposers
✔ Answer: C) Carnivores that eat herbivores
- The greenhouse effect is mainly caused by excess:
- A) Oxygen
- B) Nitrogen
- C) CO₂ and methane
- D) Ozone
✔ Answer: C) CO₂ and methane
- Which gas is responsible for ozone layer depletion?
- A) CO₂
- B) Methane
- C) Chlorofluorocarbons (CFCs)
- D) Nitrogen
✔ Answer: C) Chlorofluorocarbons (CFCs)
- Acid rain is mainly caused by:
- A) CO₂ and O₂
- B) SO₂ and NOₓ from burning fossil fuels
- C) CFCs
- D) Methane
✔ Answer: B) SO₂ and NOₓ from burning fossil fuels
- The nitrogen cycle is important because nitrogen is needed for:
- A) Photosynthesis
- B) Building proteins and DNA
- C) Respiration
- D) Water balance
✔ Answer: B) Building proteins and DNA
- Nitrogen fixation is performed by:
- A) Plants directly
- B) Animals
- C) Nitrogen-fixing bacteria (e.g., Rhizobium)
- D) Fungi
✔ Answer: C) Nitrogen-fixing bacteria (e.g., Rhizobium)
- Biotic factors in an ecosystem include:
- A) Temperature and rainfall
- B) Rocks and soil
- C) All living organisms
- D) Water and light
✔ Answer: C) All living organisms
- The pyramid of energy shows that energy:
- A) Increases at each trophic level
- B) Decreases at each trophic level (about 10% passed on)
- C) Remains constant
- D) Doubles at each level
✔ Answer: B) Decreases at each trophic level (about 10% passed on)
- A community consists of:
- A) All organisms of one species in an area
- B) All populations of different species in an area
- C) Only plants in an area
- D) Only animals in an area
✔ Answer: B) All populations of different species in an area
- A population is defined as:
- A) All species in an area
- B) All organisms of the same species in an area at one time
- C) The entire ecosystem
- D) A group of different communities
✔ Answer: B) All organisms of the same species in an area at one time
- Mutualism is a relationship where:
- A) One organism benefits and one is harmed
- B) Both organisms benefit
- C) One benefits and one is unaffected
- D) Both are harmed
✔ Answer: B) Both organisms benefit
- Parasitism is a relationship where:
- A) Both organisms benefit
- B) One benefits and the other is harmed
- C) Both are harmed
- D) One benefits and one is unaffected
✔ Answer: B) One benefits and the other is harmed
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