What is the significance of biodiversity in ecosystems according to the IB DP Biology curriculum?

Biodiversity is crucial for the stability and resilience of ecosystems. It ensures the availability of a wide range of genetic resources and ecosystem services, such as pollination, nutrient cycling, and climate regulation. In the IB DP Biology curriculum, students learn that high biodiversity increases an ecosystem's ability to withstand environmental changes and disturbances.

How do human activities impact ecosystems in the context of Ecology and Conservation?

Human activities, such as deforestation, pollution, and urbanization, significantly impact ecosystems by altering habitats, reducing biodiversity, and disrupting natural processes. In the IB DP Biology course, students explore how these activities lead to habitat loss, climate change, and species extinction, emphasizing the need for sustainable practices and conservation efforts.

What are the primary goals of conservation biology as taught in IB DP Biology?

Conservation biology aims to protect and restore biodiversity by preserving species, their habitats, and ecosystem functions. The IB DP Biology curriculum highlights strategies such as establishing protected areas, restoring degraded ecosystems, and implementing sustainable resource management to achieve these goals.

How do ecological succession and conservation efforts relate to each other?

Ecological succession is the process by which ecosystems recover and develop over time after a disturbance. Understanding succession is vital for conservation efforts, as it helps in planning restoration projects and predicting how ecosystems will respond to changes. In the IB DP Biology course, students learn how succession can guide conservation strategies to enhance ecosystem recovery and resilience.

What role do keystone species play in ecosystems, and why are they important in conservation?

Keystone species have a disproportionately large impact on their ecosystems relative to their abundance. They help maintain the structure and balance of ecosystems by controlling populations of other species and facilitating biodiversity. In the context of conservation, protecting keystone species is crucial because their loss can lead to significant changes in ecosystem dynamics, as covered in the IB DP Biology curriculum.

Why is "Forgetting the '1 minus' in Simpson's index." a common mistake in Ecology and Conservation?

Why it happens: Confusion between dominance and diversity formulas. How to avoid it: D = 1 - (n/N)^2. Higher D = more diverse.

Why is "Claiming most natural populations grow exponentially." a common mistake in Ecology and Conservation?

Why it happens: Textbook simplification. How to avoid it: Exponential growth happens only briefly; resources soon limit it to logistic.

Why is "Treating in situ as no human involvement." a common mistake in Ecology and Conservation?

Why it happens: Misreading 'natural'. How to avoid it: In situ INCLUDES active management (anti-poaching, controlled burns, invasive removal).

IB DP Biology (BI)

Ecology and Conservation

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Short Notes - Ecology and Conservation

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Detailed Study Notes

Detailed notes on Option C - Ecology and Conservation for IB DP Biology, covering key concepts, explanations, examples, and exam-focused revision points.

Option C — Ecology and Conservation: population ecology, biodiversity, ecosystem services, conservation strategies

Legacy 2014 Option C. The new 2025+ syllabus integrates conservation themes across Theme C (C4 Ecosystems, ecological niches, populations). This note maps the Option C content onto the modern syllabus.

At a glance

POPULATION dynamics: birth + immigration vs death + emigration.
Population GROWTH MODELS: exponential vs logistic (carrying capacity K).
BIODIVERSITY measures: species richness, evenness, Simpson's index.
ECOSYSTEM SERVICES: provisioning, regulating, supporting, cultural.
THREATS: habitat loss, overexploitation, invasive species, pollution, climate change.
CONSERVATION strategies: protected areas, ex situ (zoos, seed banks), in situ.
IUCN Red List: classifies species by extinction risk (Least Concern to Extinct).

What you’ll learn

Mapped to the IB DP Biology SL subject guide (2025 onwards (first assessment May 2025)).

Distinguish exponential and logistic growth.
Calculate Simpson's diversity index.
Outline ecosystem services.
Discuss conservation strategies.

Populations and biodiversity

Growth models and diversity indices.

Population dynamics. Change in population size $\Delta N$ :

$\Delta N = (\text{births} + \text{immigration}) - (\text{deaths} + \text{emigration}).$

Exponential growth. With unlimited resources, populations grow at a constant per-capita rate $r$ :

$\frac{dN}{dt} = rN.$

Logistic growth. Most realistic — growth slows as carrying capacity $K$ is approached:

$\frac{dN}{dt} = rN \left(1 - \frac{N}{K}\right).$

The curve is S-shaped: rapid growth at first, then plateau at $K$ .

Carrying capacity (K) = maximum sustainable population size. Set by limiting factors: food, water, space, predation, disease.

Biodiversity measures.

Species richness = number of species in a community.

Species evenness = how evenly individuals are distributed among species. A community of 100 cows + 1 chicken has lower evenness than 50 cows + 51 chickens.

Simpson's diversity index:

$D = 1 - \sum \left( \frac{n}{N} \right)^2$

where $n$ = number of each species, $N$ = total individuals. Ranges 0 (no diversity) to 1 (very diverse).

Worked example. A meadow has 20 dandelions and 30 buttercups. $N = 50$ . $D = 1 - ((20/50)^2 + (30/50)^2) = 1 - (0.16 + 0.36) = 0.48$ .

Exponential growth: unlimited resources.
Logistic growth: slows as $N \to K$ .
Simpson's index: 1 − $\sum (n/N)^2$ .

Ecosystem services and conservation

Why we conserve and how.

Ecosystem services. Benefits humans gain from ecosystems:

Provisioning — food, water, fibre, medicines.
Regulating — climate, pollination, water purification, disease control.
Supporting — nutrient cycling, soil formation, primary production.
Cultural — recreation, spiritual, aesthetic, scientific.

Threats to biodiversity (mnemonic HIPPO):

Habitat destruction — biggest single cause (deforestation, urban sprawl).
Invasive species — outcompete or prey on natives (cane toads in Australia, zebra mussels in N America).
Pollution — pesticides, plastics, chemicals.
Population (human) growth — drives all other factors.
Overexploitation — overhunting (e.g. blue whale), overfishing.

Plus climate change as an increasingly major driver.

Conservation strategies.

In situ (in place):

Protected areas (national parks, marine reserves).
Habitat restoration (replanting forests, rewilding).
Anti-poaching patrols.
Sustainable use (community-based conservation).

Ex situ (off site):

Zoos maintain captive breeding populations.
Botanic gardens preserve plant species.
Seed banks (e.g. Svalbard Global Seed Vault) store seeds long-term.
Frozen tissue/genetic banks preserve DNA.

IUCN Red List categories (severity):

Least Concern.
Near Threatened.
Vulnerable.
Endangered.
Critically Endangered.
Extinct in the Wild.
Extinct.

Indicator species — species sensitive to environmental conditions; their presence/absence reveals ecosystem health (e.g. lichen pollution sensitivity; mayfly larvae in clean water).

Case studies.

Bald eagle — DDT thinned eggshells; banning DDT + captive breeding recovered population from <500 pairs (1960s) to over 70 000 today.
Coral reefs — bleaching from warming; reef restoration via coral nurseries and breeding heat-resistant strains.
Rewilding — reintroducing wolves to Yellowstone (1995) restored trophic cascades (deer decline, riverbank vegetation recovery).

Ecosystem services: provisioning, regulating, supporting, cultural.
Threats: HIPPO + climate change.
In situ (protected areas) vs ex situ (zoos, seed banks).
IUCN Red List ranks extinction risk.

Quick recap

Population growth: exponential vs logistic.
Simpson's index: $D = 1 - \sum (n/N)^2$ .
Ecosystem services support human well-being.
Threats: HIPPO + climate change.
Conservation: in situ + ex situ; IUCN Red List.

Memorise this

Verbatim phrases, formulae and definitions IB DP mark schemes credit (key for AO1 knowledge marks on Paper 1).

Exponential: $dN/dt = rN$
Logistic: $dN/dt = rN(1 − N/K)$
Simpson: $D = 1 - \sum (n/N)^2$
HIPPO threats
IUCN Red List: 7 categories

How it’s examined

Option papers (legacy) or integrated questions in new 2025+ syllabus. Paper 2: 'compare in situ and ex situ conservation'; calculate Simpson's index from data.

Sources: IB Diploma Programme Biology subject guide (IBO, 2023 — first assessment 2025). Last reviewed 2026-05-31.

Take this whole topic with you

Step-by-step worked examples — Ecology and Conservation

Step-by-step solutions to past-paper-style questions on ecology and conservation, written exactly the way a tutor would explain them at the board.

1Calculate Simpson's index
Stretch• diversity
Question
A community has 40 individuals of species A and 60 of species B. Calculate Simpson's diversity index. (3 marks)
Step-by-step solution
1. Step 1
  $N = 100$ .
2. Step 2
  $\sum (n/N)^2 = (40/100)^2 + (60/100)^2 = 0.16 + 0.36 = 0.52$ .
3. Step 3
  $D = 1 - 0.52 = 0.48$ .
Answer
$D = 0.48$ .
2Why logistic growth plateaus
Building confidence• population
Question
Explain why logistic growth slows as a population approaches carrying capacity. (3 marks)
Step-by-step solution
1. Step 1
  As N increases, the available resources per individual decreases.
2. Step 2
  Competition for food, water, space intensifies; predation and disease may also increase.
3. Step 3
  Per-capita birth rate falls and/or death rate rises → net growth approaches zero at $K$ .
Answer
Resource competition + density-dependent factors reduce growth rate as $N \to K$ .
3Compare in situ and ex situ
Building confidence• conservation
Question
Compare in situ and ex situ conservation strategies. (4 marks)
Step-by-step solution
1. Step 1
  In situ: conserves species IN their natural habitat (national parks, marine reserves).
2. Step 2
  Ex situ: removes species TO managed environments (zoos, seed banks).
3. Step 3
  In situ preserves ecosystem context but vulnerable to habitat threats.
4. Step 4
  Ex situ allows controlled breeding but loss of natural behaviour and genetic diversity over time.
Answer
In situ: natural habitat, ecosystem preserved, vulnerable. Ex situ: controlled, allows breeding, loses ecological context.

Key Definitions and Keywords — Ecology and Conservation

Definitions to memorise and the exact keywords mark schemes credit for ecology and conservation answers — sharpened from recent examiner reports for the 2026 IB DP Biology SL sitting.

Carrying capacity (K)
Examiner keyword
Maximum population size that an environment can sustain indefinitely.
Simpson's diversity index
Examiner keyword
$D = 1 - \sum (n/N)^2$ ; measures species diversity considering richness and evenness.
Ecosystem service
Examiner keyword
Benefit humans derive from ecosystems (provisioning, regulating, supporting, cultural).

Common Mistakes and Misconceptions — Ecology and Conservation

The traps other students keep falling into on ecology and conservation questions — taken from recent IB DP Biology SL examiner reports and mark schemes — and how to avoid them.

✕Forgetting the '1 minus' in Simpson's index.
Why it happens
Confusion between dominance and diversity formulas.
How to avoid it
$D = 1 - \sum (n/N)^2$ . Higher $D$ = more diverse.
✕Claiming most natural populations grow exponentially.
Why it happens
Textbook simplification.
How to avoid it
Exponential growth happens only briefly; resources soon limit it to logistic.
✕Treating in situ as no human involvement.
Why it happens
Misreading 'natural'.
How to avoid it
In situ INCLUDES active management (anti-poaching, controlled burns, invasive removal).