ESS Topic 3: Biodiversity and Conservation Study Notes

Hello future environmental expert! This chapter, Biodiversity and Conservation, is arguably one of the most important in the ESS syllabus. Why? Because the variety of life on Earth (biodiversity) is the foundation of all healthy environmental systems. If we lose biodiversity, systems become unstable and fail to provide the essential services we rely on.

Don't worry if some of the formulas look scary—we will break down the complex parts into simple, manageable steps! Let's dive in!

3.1 Defining and Measuring Biodiversity

Biodiversity simply means the variety of life in a particular habitat or ecosystem. It is essential for maintaining stability, resilience, and productivity in any system.

The Three Levels of Biodiversity

Biodiversity is measured at three interconnected levels:

  1. Genetic Diversity: The range of genetic material (alleles) present in a species or population.
    Why it matters: High genetic diversity allows populations to adapt to changing environmental conditions (like disease or climate change). If all individuals are genetically similar, a single threat could wipe them all out.
  2. Species Diversity: The variety of species within a habitat or region. This is often the most commonly discussed type of diversity.
  3. Habitat (or Ecosystem) Diversity: The range of different habitats or ecosystems within a region or across the globe.
    Example: A region containing rainforests, deserts, and coral reefs has higher habitat diversity than a region containing only pine forests.
Measuring Species Diversity: Richness and Evenness

To accurately compare two different ecosystems, scientists look at two key components of species diversity:

  • Species Richness: This is the simplest measure—it is just the number of different species present in a community.
  • Species Evenness: This describes the relative abundance of each species.

Analogy: Imagine two forests, A and B, both have 10 species (high richness).
Forest A has 96 trees of Species 1, and 1 tree for each of the other 9 species. (Low evenness, dominated by one species).
Forest B has 10 trees of each of the 10 species. (High evenness).
Forest B is considered more diverse and stable because the ecosystem doesn't rely too heavily on one dominant species.

The Simpson's Diversity Index (SDI)

The Simpson's Diversity Index (D) is a common way to quantify diversity, taking both richness and evenness into account.

Important Note: The higher the value of D, the greater the diversity.

The formula for the Simpson's Diversity Index is:

\[D = \frac{N(N-1)}{\sum n(n-1)}\]

  • \(N\) = Total number of organisms of all species found.
  • \(n\) = Total number of organisms of a particular species.
  • \(\sum\) = The sum of (meaning you calculate \(n(n-1)\) for every single species, and then add those values together).

Quick Review: Diversity indices help us measure and compare the health of different ecosystems, providing crucial data for conservation efforts.

3.2 Factors Influencing Biodiversity

The biodiversity found in a location is determined by a continuous balance between the creation of new species (speciation) and the loss of species (extinction).

Natural Factors
  • Succession: As ecosystems mature (e.g., barren ground becoming a forest), species diversity often increases during the intermediate stages before sometimes decreasing slightly in the climax community.
  • Limiting Factors: Environmental factors (like temperature, rainfall, or nutrient availability) constrain which species can survive in a given area. Areas with favorable, stable conditions usually have high diversity (e.g., tropical rainforests).
  • Catastrophic Events: Natural disasters (volcanoes, severe wildfires, massive floods) drastically reduce biodiversity by killing large numbers of organisms and resetting successional stages.
Theory of Island Biogeography

This critical theory explains the patterns of species richness on islands (which can be real islands or "habitat islands," like isolated nature reserves).

The species richness of an island is a dynamic balance between two factors:

  1. Immigration Rate: How often new species arrive.
  2. Extinction Rate: How often existing species die out.

Two Key Predictions:

1. Effect of Island Size: Large islands support more species than small islands because they usually have:

  • Greater habitat diversity.
  • Larger populations, which are less prone to random extinction.

2. Effect of Distance from Mainland: Islands closer to the mainland (source population) have higher immigration rates than distant islands.

Analogy: Think of restocking a shop. A large shop can hold more inventory (size = richness). A shop closer to the supply warehouse (mainland) is easier to restock (distance = immigration rate).

3.3 Threats to Biodiversity: Human Impacts

The current global extinction rate is estimated to be 100 to 1,000 times higher than the natural background rate. This accelerated loss is driven almost entirely by human activity.

The HIPPCO Mnemonic (A Must-Know!)

Use this acronym to remember the five main anthropogenic (human-caused) threats to biodiversity:

H - Habitat Loss and Fragmentation
I - Invasive Species
P - Pollution
P - Population (Human overpopulation and increased resource consumption)
C - Climate Change
O - Overexploitation (unsustainable harvesting, hunting, and fishing)

Detailed Breakdown of Key Threats
  • Habitat Loss and Fragmentation: This is the number one threat. When large habitats are broken into smaller, isolated patches (fragmentation), it reduces species movement and increases the ratio of edge habitat (which is often less stable) to core habitat. This effect is especially devastating for species requiring large territories.
  • Invasive Species: Non-native species introduced intentionally or accidentally to a new area. Since they often have no natural predators, they outcompete native species for resources, leading to population crashes (e.g., the introduction of rats to islands or the cane toad in Australia).
  • Pollution: Toxins, excess nutrients, or trash that harm organisms.
    Example: Bioaccumulation (toxins building up in an individual organism) and Biomagnification (toxin concentrations increasing at successive trophic levels). DDT is a classic example of a toxin that biomagnified, leading to the thinning of eagle eggshells.
  • Overexploitation: Harvesting resources faster than they can regenerate. This includes unsustainable logging, poaching (illegal hunting), and overfishing, which often targets species high up the food chain, disrupting the entire ecosystem structure.

Did you know? Many scientists agree that Earth is currently experiencing the Sixth Mass Extinction Event, the first caused by a single species (humans).

3.4 Conservation Strategies

Conservation efforts aim to protect, maintain, and restore biodiversity. Strategies vary widely, focusing on species, habitats, or entire systems.

In Situ vs. Ex Situ Conservation

Conservation methods can be grouped into two main categories:

In Situ (In Place) Ex Situ (Out of Place)
Conservation within the natural habitat. Conservation outside the natural habitat.
Examples: National parks, nature reserves, protected areas, marine protected areas (MPAs). Examples: Zoos, botanical gardens, seed banks (e.g., Svalbard Global Seed Vault), captive breeding programs.
Advantages: Protects entire ecosystems and allows species to continue natural evolution/interactions. Generally cheaper. Advantages: Provides absolute protection from threats (poachers, disease, habitat destruction). Good for critical, immediate threats.
Species Focused Conservation

Conservationists categorize species based on their importance to focus efforts efficiently:

  • Keystone Species: A species that has a disproportionately large effect on its environment relative to its abundance. If removed, the ecosystem dramatically changes (e.g., sea otters, wolves).
  • Indicator Species: A species whose presence, absence, or abundance reflects the health of its ecosystem. They are often sensitive to pollution (e.g., lichens, amphibians).
  • Flagship Species: Charismatic species used as a symbol to attract public attention and funding for conservation (e.g., pandas, tigers). Protecting them often indirectly protects other species in the same habitat.
Habitat Conservation Debate (SLOSS)

A key debate in reserve design is the SLOSS debate: Is it better to have a Single Large Or Several Small reserves?

  • Argument for Single Large: Supports larger populations and wide-ranging species (like top predators). Reduced "edge effects."
  • Argument for Several Small: Reduces the risk of a single catastrophic event (e.g., disease or fire) wiping out the entire population. Can capture more diverse habitats.

Modern consensus often favors large reserves connected by wildlife corridors to facilitate gene flow and migration.

Legal Frameworks and Organizations

Conservation requires collaboration across governments and non-profit sectors.

  • IGOs (Intergovernmental Organizations): Organizations involving multiple governments that produce international treaties and laws (e.g., UNEP - UN Environment Programme).
  • NGOs (Non-Governmental Organizations): Non-profit groups that typically use direct action, lobbying, and public pressure (e.g., WWF - World Wildlife Fund, Greenpeace). NGOs are generally quicker to act but have less direct legal authority than IGOs.

Crucial Treaty: CITES
The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) is an international agreement that aims to ensure that international trade in wild animals and plants does not threaten their survival. It bans or severely restricts trade in endangered species.

Key Takeaway: Effective conservation relies on a mix of local action (managing reserves), international cooperation (treaties like CITES), and addressing the root causes of habitat loss driven by human activity (HIPPCO).

Final Quick Review Box

Biodiversity and Conservation Essentials
  • 3 Components: Genetic, Species, Habitat.
  • SDI (Simpson's Index) measures Richness and Evenness.
  • Island Biogeography: Size and Distance determine species count.
  • Human Threats: Remember HIPPCO.
  • Conservation: Use a mix of In Situ (parks) and Ex Situ (zoos/seed banks).
  • Keystone species are disproportionately important for ecosystem structure.