Biodiversity & Species Extinction: Comprehensive Study Notes

Species and Species Diversity

• Species (General Definition)

  • The largest group of organisms where individuals can reproduce fertile offspring through sexual reproduction.

  • Key for tests: Offspring must be fertile to count as true species reproduction.

  • Why it matters: This ensures the species' gene pool stays healthy, allowing long-term survival and adaptation.

• Species Diversity (Community-Level Measure)

  • Refers to both the number of different species AND how common each species is in a specific community.

  • Millions of species are named, with countless more in every habitat (even inside us!).

  • Test takeaway: Diverse communities are usually stronger, more productive, and provide essential services like pollination and nutrient recycling.

Biodiversity: What It Is and Its Levels

• Biodiversity ("Biological Diversity")

  • The huge variety of all life forms—plants, animals, fungi, and tiny microbes—PLUS the communities and habitats they form.

  • Why it's important to humans (know these benefits for tests!):

  • Provides food, medicine, clothing fibers, building materials, and energy.

  • Offers cultural, recreational, aesthetic, and spiritual benefits.

• Three Main Levels of Biodiversity (MEMORIZE THESE!)

  1. Genetic Diversity

     • Variation in genetic makeup within a single species.

     • Key role: Helps a population adapt to changes, resist diseases, and avoid problems from inbreeding.

  2. Species Diversity

     • The variety and abundance of different species within an ecosystem or region.

     • Directly linked: To how stable and functional an ecosystem is.

  3. Ecosystem Diversity

     • The range of different habitats, living communities, and natural processes on Earth.

     • Focuses on: How everything is interconnected (e.g., energy flow, nutrient cycles).

High vs. Low Biodiversity

• High Biodiversity (The Good Kind!)

  • Many species, with individuals fairly even in numbers, creating complex food webs.

  • Result: Usually greater stability, higher productivity, and stronger resistance to major problems.

• Low Biodiversity (The Risky Kind!)

  • Few species, often with one or a few dominating, leading to simpler interactions.

  • Result: More vulnerable to new invasive species, disease outbreaks, and environmental changes.

Species Concepts (How Biologists Define “Species” – Know the Differences!)

• Typological Species Concept (Older Way)

  • Species are identified by shared, distinct physical traits (how they look).

  • Limitation: Can be misleading if species look alike but are genetically different.

• Biological Species Concept (MOST COMMONLY TESTED!)

  • Defines a species as populations that can successfully breed together AND are reproductively isolated from other populations.

  • Classic Example (for tests!): Western meadowlarks and Eastern meadowlarks look similar but do NOT interbreed, proving they are separate species.

• Phylogenetic Species Concept (Modern Way)

  • Defines a species as the smallest group of organisms that shares a unique evolutionary history (meaning they share a common ancestor and distinct traits).

  • Method: Uses genetic data (like DNA) and evolutionary family trees to define species, especially those that look very similar.

• Important Distinctions (Looks Can Be Deceiving!)

  • Organisms might appear alike yet be different species (e.g., the meadowlarks).

  • Organisms might look different yet be the same species (e.g., different types of ants within one colony).

Key Terms & Metrics for Measuring Diversity (Be Ready to Define!)

• Reproductive Isolation

  • Natural ways that prevent different species from producing healthy and fertile offspring.

  • Example for tests: A horse and a donkey can make a mule, but mules are usually sterile, showing this principle.

• Species Richness (R)

  • The simplest measure: just a direct count of the number of species in an area.

  • Formula: $R = \text{number of species}$

• Species Evenness (E)

  • How equally individuals are spread out among the different species.

  • High evenness: Means similar population sizes for all species. Low evenness: One or a few species dominate.

• Species Dominance

  • Happens when one species has a much higher number of individuals compared to others.

  • Implications: Can reduce overall diversity and change how resources are used in an ecosystem.

• Species Density (D)

  • Measures how packed a species is within a given unit of habitat.

  • Formula: $D = \frac{\text{number of individuals per species}}{\text{total unit area}}$

Species Extinction: Drivers & Illustrations (Know Causes and Examples!)

• Why Species Disappear

  • Natural causes: Historically, climate shifts (like for woolly mammoths) or huge disasters (like for dinosaurs) caused extinctions.

  • MODERN EXTINCTIONS ARE MOSTLY DRIVEN BY HUMANS (TEST FOCUS):

  • Over-killing / Over-harvesting: Taking too many individuals, faster than they can reproduce.

  • Habitat Destruction: The leading cause; includes cutting down forests, building cities, and changing land for farming.

  • Commercial Hunting, Harvesting & Sports: Demand for animal products like meat, fur, or ivory.

  • Introduction of Exotic (Non-Native) Species: New species brought in that become invasive predators or competitors.

  • Pollution: Harmful chemicals, plastics, and dirty air/water directly affecting survival and reproduction.

• Case Examples (Be familiar with these!)

  • Woolly Mammoth (Pleistocene Era): Vanished due to warming climate AND human hunting pressure.

  • Dinosaurs (Mesozoic Era): Extinct primarily due to a massive asteroid impact and volcanic activity (a key natural extinction event).

  • Dodo (\textit{Raphus cucullatus}): Lost due to human hunting and invasive species (rats, pigs) on Mauritius.

Solutions & Management Strategies (Understand How We Can Help!)

• Government Regulations

  • Laws that restrict building and land changes to protect critical habitats, while still allowing for careful development.

• Project Planning & Environmental Impact Assessment (EIA)

  • Designing new projects (like roads) to cause the least possible harm to habitats. This can include creating wildlife corridors (paths for animals), setting up buffer zones, and timing activities to avoid sensitive periods.

• Broader Conservation Tools (Goes Beyond Just Laws)

  • Protected areas: Like national parks and wildlife refuges.

  • Ex-situ conservation: Keeping species safe outside their natural environment (e.g., in zoos, botanical gardens, seed banks).

  • Ecological restoration: Repairing damaged ecosystems.

  • Community-based resource management: Involving local people in protecting their natural resources.

  • Public education: Raising awareness about how important biodiversity is.

  • Ethical Dimension: We have a responsibility to protect biodiversity, not just for what it gives us, but because all life has a right to exist and evolve.

Mathematical & Statistical Summary (Formulas to Know!)

• Species richness: $R$

• Species evenness: Often shown using Shannon evenness; formula $E = \frac{H'}{\ln R}$ (measures how balanced the species numbers are).

• Species density: $D = \frac{N}{A}$ where $N$ = number of individuals per species, $A$ = unit area.

• Note: These calculations help scientists understand the health of ecosystems.

Real-World & Ethical Connections (Why Protecting Biodiversity is VITAL!)

• Biodiversity is essential because it guarantees (key impacts):

  • Food security: Wild plant relatives provide crucial disease-resistance genes for our crops.

  • Pharmaceutical discovery: Over 50% of medicines come from natural compounds.

  • Climate regulation: Forests absorb carbon dioxide, helping control our climate.

• Loss of biodiversity leads to (negative consequences):

  • Erosion of ecosystem services (e.g., clean water, pollination).

  • Threatens the ways of life for many indigenous and local communities.

  • Diminishes our shared cultural heritage.

• Ethical imperative: We must protect biodiversity not only for its benefits to us, but also