Module 3: Biological Diversity

What are biotic factors? (+ examples)

These are pressures from other living things.

Examples:

• Predation (being hunted by predators)

• Competition (for food, mates, territory)

• Disease and parasites

• Availability of mates

• Human activities (e.g. hunting, farming, introducing new species)

Effect of biotic factors on organisms

• Species may develop better camouflage or escape behaviours to avoid predators
  

• May evolve stronger immune systems to survive disease
  

• May change feeding habits or physical traits to reduce competition
  

• Can lead to extinction if they can’t adapt

What are abiotic factors? (+ examples)

These are physical or chemical conditions in the environment.

Examples:

• Temperature
  

• Water availability
  

• Light intensity
  

• Soil type and nutrients
  

• Natural disasters (fires, floods)
  

• Climate change

Effect of biotic factors on organisms

• May develop thicker fur or heat-tolerance
  

• Drought may favor plants with deep roots or water storage
  

• Species may migrate or change reproduction timing
  

• May lead to loss of biodiversity if changes are too rapid

What are selection pressures

Selection pressures are factors in the environment that affect an organism’s ability to survive and reproduce.

What can selection pressures cause

Over time, these pressures can cause changes in the frequency of traits in a population, leading to evolutionary changes.

Changes in an organism population due to selection pressures over time - cane toads - background (why were they introduced and what happened with them)

• Background:

  • Cane toads were introduced in the 1930s to control pests.
    

  • They rapidly spread across northern Australia.

Changes in an organism population due to selection pressures over time - cane toads - selection pressures

• Selection Pressures:
  

  • Predation, climate, and habitat differences.
    

  • Human intervention and environmental challenges.

Changes in an organism population due to selection pressures over time - cane toads - changes observed

• Changes Observed:
  

  • Cane toads near the invasion front have evolved longer legs for faster movement, allowing them to expand their range more quickly.
    

  • Changes in behavior and physiology to adapt to new environments.

Changes in an organism population due to selection pressures over time - prickly pear distribution - background

• Background:
  

  • Prickly pear cactus introduced in the 19th century and spread extensively.
    

  • Became a major invasive weed affecting grazing land.
    

Changes in an organism population due to selection pressures over time - prickly pear distribution - selection pressures

• Selection Pressures:
  

  • Control methods (e.g., introduction of the Cactoblastis moth as a biological control).
    

  • Environmental conditions like soil type and climate.
    

Changes in an organism population due to selection pressures over time - prickly pear distribution - changes observed

• Populations adapted to different climates and soils across Australia.
  

• Biological control led to a dramatic reduction in prickly pear numbers, showing how selection pressure can reduce or change populations.

What Are Adaptations?

Adaptations are features that help an organism survive and reproduce in its environment.

They improve the organism’s chances of finding food, avoiding predators, coping with climate, or reproducing.

structural adaptations

• Structural Adaptations:
  Physical features of the body that help survival.
  
  

 Example: Thick fur on polar bears helps keep them warm in cold environments.

physiological adaptations

• Physiological Adaptations:
  Internal body processes or functions that help survival.
  
  

 Example: Snakes produce venom to capture prey or defend themselves.

behavioural adaptations

• Behavioural Adaptations:
  Actions or ways an organism behaves that help survival.
  
  

 Example: Birds migrating to warmer places during winter to find food and stay warm.

What is the Theory of Evolution by Natural Selection?

• Proposed by Charles Darwin in 1859.
  
  

• Explains how species change over time to become better suited to their environments.
  
  

• Main idea:
  ➤ Organisms that have traits better suited to the environment are more likely to survive and reproduce.
  ➤ These helpful traits get passed on to the next generation.
  ➤ Over a long time, this leads to evolution (a change in species).

What is Lamarck’s Theory of Evolution (Before Darwin)?

• Proposed by Jean-Baptiste Lamarck in the early 1800s.
  
  

• Believed organisms could change during their lifetime and pass on those changes.
  ➤ E.g. a giraffe stretches its neck to reach tall leaves → passes a longer neck to babies.
  
  

• This theory is now rejected because:
  ➤ Organisms can’t pass on acquired traits (like muscles from working out).
  ➤ Darwin’s theory fits better with genetics and evidence.

the observations and collection of data that were obtained by Charles Darwin to support the Theory of Evolution by Natural Selection

• finches of the Galapagos Islands

• Darwin saw different types of finches on different islands.
  
  

• Their beak shapes matched the type of food available (e.g. nuts, insects, seeds).
  
  

• He realised that all finches came from a common ancestor, but adapted differently on each island depending on food sources.
  
  

• This supported the idea that environment affects survival, leading to natural selection.

the observations and collection of data that were obtained by Charles Darwin to support the Theory of Evolution by Natural Selection

• Australian flora and fauna

• Darwin saw that Australian animals and plants were very different from those in Europe, even in similar environments.
  
  

• For example, marsupials like kangaroos and wombats lived in Australia but not in Europe.
  
  

• This showed that species evolve differently in isolated environments, further supporting evolution by natural selection.
  

biological diversity (biodiversity)

Biodiversity = the variety of life on Earth (different species, genes, and ecosystems).

biological diversity through Theory of Evolution by Natural Selection

Evolution by Natural Selection explains how biodiversity developed:

1. Variation exists within populations (due to mutations, genetic recombination).
   
   

2. Competition for resources means not all individuals survive.
   
   

3. Survival of the fittest – individuals with advantageous traits are more likely to survive and reproduce.
   
   

4. Inheritance – advantageous traits are passed to offspring.
   
   

• Over time – these changes accumulate → new species form (speciation).
  

biological diversity in terms Theory of Evolution by Natural Selection (changes in and diversification of life since it first appeared on the Earth)

Since life first appeared (~3.5 billion years ago):

• Life evolved from simple single-celled organisms to complex multicellular life.
  
  

• Mass extinctions and environmental changes drove diversification of surviving species.
  
  

• Natural selection + adaptation to different environments created Earth’s vast biodiversity.
  

Relationship:
Evolution by natural selection creates and shapes biodiversity by causing species to change and diversify over time.

how an accumulation of microevolutionary changes can drive evolutionary changes and speciation over time

Microevolution = small changes in allele frequencies within a population over generations.
Over long periods, these small changes accumulate, leading to macroevolution (large-scale changes) and sometimes speciation (formation of new species).

how an accumulation of microevolutionary changes can drive evolutionary changes and speciation over time - evolution of the horse

↑ body size, ↓ toes (4→1), stronger high-crown teeth for grass. Driven by grassland expansion & predator escape.

how an accumulation of microevolutionary changes can drive evolutionary changes and speciation over time - evolution of the platypus

Egg-laying + mammal traits, electric-sensing bill, webbed feet. Driven by isolation & aquatic hunting adaptation.

convergent evolution

Definition: Unrelated species evolve similar traits because they live in similar environments or have similar needs.

convergent evolution (Explanation with Natural Selection)

• Different ancestors → similar selective pressures → similar adaptations.
  
  

• Example: Sharks (fish) and dolphins (mammals) both evolved streamlined bodies and fins for swimming efficiently in water.
  
  

• Traits appear similar due to the environment, not because of close relations.

divergent evolution

• Definition: Related species become more different over time due to adapting to different environments.

divergent evolution (Explanation with Natural Selection)

• Same ancestor → different environments → different selective pressures → new traits.
  
  

• Example: Darwin’s finches on the Galápagos Islands evolved different beak shapes for eating different foods (seeds, insects, cactus flowers).
  
  

• Leads to speciation.

Gradualism

• Evolution occurs slowly and steadily over long periods, with small changes accumulating in populations.

Punctuated equilibrium

Long periods of little or no change (stasis) are interrupted by short, rapid bursts of significant change, often due to sudden environmental shifts or isolation.

Punctuated equilibrium vs gradual process of natural selection:

• Difference: Gradualism is constant and slow; punctuated equilibrium is mostly stable with rare, rapid evolutionary change.

investigate, using secondary sources, evidence in support of Darwin and Wallace’s Theory of Evolution by Natural Selection:

• Biochemical Evidence

1. Biochemical Evidence

• DNA and protein sequencing shows similarities between species.
  
  

• Closer related species share more DNA/protein similarities (e.g., humans and chimpanzees).

investigate, using secondary sources, evidence in support of Darwin and Wallace’s Theory of Evolution by Natural Selection:

• Comparative Anatomy

2. Comparative Anatomy

• Homologous structures → same basic structure, different function (e.g., human arm & whale flipper) → suggests common ancestry.
  
  

• Vestigial structures → reduced/unused features (e.g., appendix in humans) → evidence of evolutionary change.

investigate, using secondary sources, evidence in support of Darwin and Wallace’s Theory of Evolution by Natural Selection:

• Comparative Embryology

3. Comparative Embryology

• Early embryos of different vertebrates show similar features (e.g., gill slits, tails) → indicates shared evolutionary origins.

investigate, using secondary sources, evidence in support of Darwin and Wallace’s Theory of Evolution by Natural Selection:

• Biogeography

4. Biogeography

• Distribution of species matches continental drift and isolation patterns.
  
  

• Unique species on islands (e.g., Galápagos finches) evolved from mainland ancestors.

techniques used to date fossils and the evidence produced

• Fossil Dating Techniques

5. Fossil Dating Techniques

• Relative dating → using rock layers (strata) to determine age sequence of fossils.
  
  

• Absolute dating → radiometric methods (e.g., carbon-14, potassium-argon) to find numerical ages.

techniques used to date fossils and the evidence produced

• Fossil Evidence Produced

6. Fossil Evidence Produced

• Fossils show transitional forms (e.g., Archaeopteryx between reptiles & birds).
  
  

• Progressive changes in fossil record match evolutionary pathways.

explain modern-day examples that demonstrate evolutionary change, for example:

• antibiotic-resistant strains of bacteria

  • Definition

• Antibiotic resistance occurs when bacteria evolve the ability to survive doses of antibiotics that would normally kill them or inhibit growth.
  
  

explain modern-day examples that demonstrate evolutionary change, for example:

• antibiotic-resistant strains of bacteria

  • Cause

• Random mutations create variation in bacterial populations.
  
  

• Antibiotic treatment kills susceptible bacteria, but resistant individuals survive.
  
  

• Survivors reproduce, passing resistance genes to offspring — an example of natural selection.

explain modern-day examples that demonstrate evolutionary change, for example:

• antibiotic-resistant strains of bacteria

  • Example – Staphylococcus aureus
    
    

• A common bacterium causing skin, respiratory, and bloodstream infections.
  
  

• Some strains have developed methicillin resistance (MRSA) through mutations that change cell wall proteins, preventing antibiotic binding.
  
  

• MRSA is harder to treat, requiring stronger or multiple antibiotics.

explain modern-day examples that demonstrate evolutionary change, for example:

• antibiotic-resistant strains of bacteria

  • Evidence for evolution
    
    

• Increase in MRSA cases over decades shows a change in population traits over time.
  
  

• Direct observation of genetic adaptations in bacterial samples.
  
  

• Demonstrates natural selection occurring in a short timescale.

explain modern-day examples that demonstrate evolutionary change, for example:

• antibiotic-resistant strains of bacteria

  • Significance

• Confirms that environmental pressures (antibiotics) can drive evolutionary change.
  
  

• Shows how beneficial mutations become more common in a population.
  
  

• Highlights real-world relevance of evolutionary theory to human health.