Biodiversity and Evolution Notes

What is Biodiversity?

  • Biodiversity is a complex concept referring to the variety of life on Earth.
    • Includes:
      • Species richness: Numbers of species of different animals, plants, fungi, and microorganisms in ecosystems.
      • Species evenness: The relative proportion of individuals of each species.
    • Three interrelated types of diversity: Habitat, species, and genetic.

Different Types of Diversity

  • Habitat diversity:
    • Variety of physical environments where species live (e.g., forests, wetlands, deserts, coral reefs, tundra).
    • A region with many different habitats supports greater biodiversity.
  • Species diversity:
    • Number of species and abundance of each species in a particular location (richness + evenness).
  • Genetic diversity:
    • Variation of genes within individuals and populations of a species.
    • Allows species to adapt to changing environmental conditions, increasing survival chances.
  • Interdependence:
    • These types of diversity are interdependent; losses in one can weaken the entire system.

Importance of Genetic Diversity

  • High genetic diversity means more options for beneficial traits that help individuals/populations survive environmental changes.
  • Examples:
    • Cheetahs: Low genetic diversity. Vulnerable to disease and threatened long-term survival.
    • Bananas: No genetic diversity (genetically identical). Propagated through cloning, highly susceptible to pests and diseases (e.g., Panama disease).
    • Coral Reefs: High genetic diversity. Can adapt to varying water temperatures and acidities, helping resilience in the face of climate change.

Maintenance of Genetic Diversity

  • Crucial for resilience.
  • Economic importance:
    • Diverse crops are better able to resist disease outbreaks, ensuring food security and reducing the need for chemical intervention.
  • Environmental importance:
    • Supports ecosystem resilience and adaptability.

Ecosystem Resilience

  • Resilience: ability of an ecosystem to resist change and return to equilibrium despite disturbances.
  • How resilient an ecosystem is relies heavily on its biodiversity and complexity.
  • Ecosystems with high biodiversity tend to have more species interactions and greater stability, allowing them to withstand disruptions more effectively.
  • Elements:
    • Species diversity.
    • Genetic diversity.
    • Ecosystem diversity.

Biodiversity and Complexity

  • How complex an ecosystem is depends on its biodiversity and the number of connections within the food web.
  • High biodiversity means more species, more niches, more interactions which leads to greater stability.
  • More connections means species can shift between food sources when there are disruptions (maintains flow of energy and resources).
  • Negative feedback loops: more feedback mechanisms helps restore balance after disturbance.

Succession and Resilience

  • Succession = process by which ecosystems develop over time.
  • Which stage of succession an ecosystem is in influences its resilience:
    • Pioneer communities in early stages of succession: simple ecosystems, short food chains, low biodiversity, less resilient to change.
    • Climax communities in mature ecosystems: complex, greater biodiversity, more resilient.
    • Exception: if found in harsh environments such as deserts or tundras they may still have low complexity/resilience.

Limiting Factors and Ecosystem Health

  • Limiting factors: things like nutrient availability, water, sunlight (dictate how productive an ecosystem can be).
  • If limiting factors in high supply, promotes biodiversity and makes a highly productive ecosystem (e.g. tropical rainforests).

Human Impacts on Resilience

  • Human activities (e.g., deforestation, agriculture, urbanization) reduce resilience of ecosystems by simplifying their complexity.
    • Reduces biodiversity, shortens food chains, and disrupts species interactions.
  • Leads to:
    • Weakening of feedback loops.
    • Reduction of stability.
  • Potential for positive interventions (e.g. rewilding projects that reintroduce keystone species).
    • E.g., reintroduction of wolves in Yellowstone National Park (from topic 1 and trophic cascades).

What is Evolution?

  • Genetic changes in populations over time.
  • Driven by several key mechanisms:
    • Mutation.
    • Gene flow.
    • Genetic drift.
    • Natural selection.
    • Sexual Reproduction (HL).

Mutation

  • Random changes in DNA of organisms that lead to new variants of genes.
  • While most are neutral or harmful, some may provide advantageous traits that enhances survival and reproduction.
  • Introduces new genetic material into populations.

Genotype vs Phenotype

  • DNA exists in every cell of every living organism.
    • Contains all the info needed for them to develop, survive, and reproduce.
    • Genetic code = genotype (the sequence).
    • Genotype determines phenotype (outward expression of the gene).
  • Genotype:
    • An organism's genetic information.
  • Phenotype:
    • The set of observable physical traits.
    • BB = homozygous dominant = purple.
    • Bb = heterozygous = purple.
    • bb = homozygous recessive = white.

Types of Mutation

  • Beneficial: Improve survival or reproduction (e.g., disease resistance). These genes may become more common over generations.
  • Neutral: Do not affect survival but add to the gene pool.
  • Harmful: Reduce fitness and are often eliminated through natural selection.
  • DNA Mutation
    • Changes in DNA sequence (Deleted, Inserted, Substituted).

Gene Flow

  • Movement of genes between populations, typically through migration.
  • Increases genetic diversity.
  • When individuals from different populations interbreed, they introduce new genetic combinations that may help populations adapt to environmental changes.

Genetic Drift

  • Refers to random changes in gene frequencies, especially in small populations.
  • Over time, certain traits may become more common purely by chance, even if they do not provide a survival advantage.
  • This process can lead to reduced genetic diversity.
  • Founder Effect.

Natural Selection

  • Operates continuously and can take place over billions of years.
  • Organisms that are adapted to the environment have an advantage over those that are less well adapted; they survive, flourish, and reproduce.
  • Sometimes referred to as "Survival of the fittest".
  • Favorable traits (e.g., strong defense mechanisms, diverse gene pool, broad diet) lead to higher chances of survival with those traits then passed on and increasing in frequency.

Mechanisms of Natural Selection

  • Variation: Different populations have different traits.
  • Overproduction: Most species produce more offspring than can survive to adulthood which leads to a struggle for resources.
  • Competition: Individuals with traits that give advantages compete and are more likely to survive.
  • Differential Survival and Reproduction: Those that survive are more likely to reproduce and pass traits on to offspring.
  • Heritability: Variation is heritable; survival advantage passed from parent to offspring, making it more common in the population and driving evolutionary change.

Peppered Moth Example

  • Evolution of the Peppered Moth in a Polluted Environment.

Artificial Selection

  • Deliberate process where humans choose specific traits in plants or animals for breeding.
  • Can increase productivity, but also reduces genetic diversity (making more vulnerable to diseases, environmental changes, and other threats).
  • Decreases resilience of a system.
  • Examples:
    • Monocultures in agriculture.
    • Livestock breeding.
    • Belgian Blue cattle have been bred for increased meat production.

Advantages of Artificial Selection

  • Increased productivity: Higher crop yields, faster growth, or better-quality livestock.
  • Enhanced traits: Improves specific characteristics like disease resistance or drought tolerance.
  • Economic benefits: Leads to higher profits and more efficient food production.
  • Faster results: Achieves desired traits in fewer generations.
  • New varieties: Allows creation of new breeds and hybrids to meet human needs.

Disadvantages of Artificial Selection

  • Reduced genetic diversity: Narrow gene pool limits adaptability to environmental changes or disease.
  • Vulnerability to disease: Genetically uniform populations are more susceptible to widespread outbreaks.
  • Ethical concerns: Inbreeding can cause health problems and lower fertility in organisms.
  • Loss of resilience: Less diversity reduces the ability to adapt to climate change or new pests.
  • Long-term risks: Can lead to ecological imbalances and loss of important genetic traits.

Sexual Reproduction

  • Further increases genetic diversity by creating new combos of genes through:
    • Meiosis: homologous chromosomes exchange genetic material (recombination), leading to new gene combinations.
    • Fertilization: fusion of genetically unique gametes from two parents results in offspring with a unique set of genes.