Welcome to Topic 18: Classification, Biodiversity and Conservation!

This chapter is all about understanding the incredible variety of life on Earth (biodiversity) and the systems we use to organize it (classification). Crucially, we'll also look at why this variety is under threat and what biologists and policymakers are doing to protect it.
This is a key A-Level topic that ties together genetics, ecology, and human impact. Let's dive into the amazing world of biological order and variety!

18.1 Classification

The Concept of Species

The term species seems simple, but scientists use different definitions depending on the context. You need to know three main concepts:

  1. Biological Species Concept: A group of organisms that can potentially interbreed to produce fertile offspring.
    (Limitation: Does not apply to organisms that reproduce asexually, like bacteria.)
  2. Morphological Species Concept: Defines a species based on its shared anatomical features (its morphology or physical form).
    (Limitation: Different species can look very similar, and individuals within the same species can look very different due to environmental factors.)
  3. Ecological Species Concept: Defines a species based on its niche (its specific role and habitat in an ecosystem).
    (Limitation: Boundaries between ecological niches can be difficult to define.)

The Three Domains of Life

All living organisms are classified into three major Domains. These distinctions are based primarily on differences in cellular structure and genetics (specifically, ribosomal RNA).

  1. Archaea: Prokaryotes (lack a nucleus). Often found in extreme environments (extremophiles).
  2. Bacteria: Prokaryotes. Includes most common forms of bacteria.
  3. Eukarya: Eukaryotes (cells contain a nucleus and membrane-bound organelles).
Differences between Archaea and Bacteria

While both are prokaryotes, they are fundamentally different:

  • Membrane Lipids: Archaea have unique membrane lipids (often branched hydrocarbons) that differ significantly from those in Bacteria.
  • Ribosomal RNA (rRNA): Their ribosomal RNA sequences are different.
  • Cell Walls: Bacterial cell walls contain peptidoglycan, which is generally absent in Archaea.

Taxonomic Hierarchy (The Linnaean System)

Organisms within the Eukarya domain are organized into a strict hierarchy:

Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species

Memory Aid: Struggling to remember the order? Try this mnemonic:
King Philip Came Over For Good Soup.

Key Features of the Eukaryotic Kingdoms

The Eukarya domain is further divided into four major kingdoms:

  • Protoctista: Mostly unicellular eukaryotes. They don't fit into other kingdoms. (e.g., Algae, Amoeba)
  • Fungi: Eukaryotic, heterotrophic (feed by absorption), possess cell walls made of chitin, and reproduce using spores. (e.g., Yeast, Mushrooms)
  • Plantae: Eukaryotic, autotrophic (photosynthesis), possess cell walls made of cellulose, and store food as starch. (e.g., Flowering plants, Mosses)
  • Animalia: Eukaryotic, heterotrophic (feed by ingestion), lack cell walls, usually move, and possess nervous coordination. (e.g., Mammals, Insects)

Classification of Viruses (The Non-Cellular Structures)

Viruses are non-cellular, so they are classified differently than living organisms. Their classification is limited to:

  • The type of nucleic acid core: RNA or DNA.
  • Whether the nucleic acid is single-stranded (ss) or double-stranded (ds).

Quick Takeaway 18.1

Classification helps us organize life. Remember the three species concepts and the key differences between the three Domains (especially the presence/absence of peptidoglycan in prokaryotes). The hierarchy organizes life from broad groups down to the specific species.

18.2 Biodiversity

Definitions: Ecosystem and Niche

Before discussing diversity, we must establish the context:

  • Ecosystem: A unit containing all the organisms (biotic factors) and their non-living environment (abiotic factors) interacting together in a specific area. (e.g., A forest, a pond.)
  • Niche: The specific role and position an organism occupies within its ecosystem. This includes all the biotic (e.g., food sources, predators) and abiotic factors (e.g., temperature, light) required for its survival and reproduction.

Levels of Biodiversity

Biodiversity is the variety of life on Earth. It is assessed at three distinct levels:

  1. Ecosystem/Habitat Diversity: The number and range of different ecosystems or habitats in an area. (e.g., a region containing mountains, forests, rivers, and grasslands has high habitat diversity.)
  2. Species Diversity: This includes two components:
    • Species Richness: The total number of different species present in an area.
    • Species Relative Abundance (Evenness): The degree to which the species population sizes are similar. (A community with 10 species where all have 10 individuals is more diverse than a community where one species has 91 individuals and the other 9 species have 1 each).
  3. Genetic Diversity: The genetic variation within each species, reflected by the total number of different alleles in a population (the gene pool). (High genetic diversity makes a species more resilient to environmental change.)

Sampling Methods to Assess Distribution and Abundance

To determine biodiversity, biologists must sample the area. Since it's impossible to count everything, random sampling is vital to avoid bias and ensure the results are representative.

Quantitative Sampling Methods (Plants/Sessile Organisms)

  • Frame Quadrats: Square frames of a standard area (e.g., 0.25 m2) placed randomly to count the number of individuals or estimate percentage cover of species.
  • Line Transects: A line (tape measure) stretched across a habitat. Species touching the line are recorded at regular intervals. Good for showing changes across a boundary (e.g., from forest to field).
  • Belt Transects: Extends the line transect by placing quadrats continuously or at intervals along the line. Provides more detailed abundance data linked to the environmental gradient.

Estimating Population Size (Mobile Organisms)

The Mark-Release-Recapture method is used for estimating the population size of mobile animals (like insects or fish).

The population size \(N\) is estimated using the Lincoln Index:
\[N = \frac{(n_1 \times n_2)}{m_2}\]
Where:

  • \(n_1\): Number caught and marked in the first sample.
  • \(n_2\): Total number caught in the second sample.
  • \(m_2\): Number of marked individuals found in the second sample.
(Assumption: The marked individuals mix fully back into the population and marking doesn't affect their behavior.)

Analyzing Biodiversity Data

Simpson's Index of Diversity (D)

This index is a measure of species diversity that accounts for both richness (number of species) and evenness (relative abundance).

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

Where:

  • \(n\): The number of individuals of a specific species.
  • \(N\): The total number of all individuals of all species.

Significance of D:

  • A value of D close to 1 indicates high biodiversity (many species, high evenness).
  • A value of D close to 0 indicates low biodiversity (few species, or one dominant species).

Did you know? A habitat with high D is often more stable and less vulnerable to disruption than a habitat dominated by one or two species.

Correlation Coefficients

These statistical tools help analyze the relationship between two variables (e.g., how the abundance of a species relates to a specific abiotic factor like soil pH or temperature).

  • Spearman's Rank Correlation: Used for measuring the relationship between ranked (non-parametric) data.
  • Pearson's Linear Correlation: Used for measuring the strength of a linear relationship between two sets of normally distributed (parametric) data.
We use these to show if biotic and abiotic factors affect species distribution and abundance.

Quick Takeaway 18.2

Biodiversity exists at three levels: ecosystem, species (richness + evenness), and genetic. We measure this using random sampling techniques like quadrats and the Lincoln Index. Simpson's D is essential for quantifying species diversity.

18.3 Conservation

Causes of Extinction and Loss of Biodiversity

Populations and species face four main threats that can lead to extinction:

  • Degradation and Loss of Habitats: Deforestation, drainage of wetlands, and fragmentation of ecosystems reduce available living space. This is the single biggest threat.
  • Hunting by Humans: Unsustainable hunting or fishing that reduces population size faster than they can recover.
  • Competition (especially with Invasive Alien Species): Introducing non-native species can drastically reduce native populations as the natives cannot compete for resources or fight new predators/diseases.
  • Climate Change: Changing global temperatures and weather patterns shift the geographical range where species can survive, often faster than the species can adapt or migrate.

Reasons for Maintaining Biodiversity

Why should we care about conservation?

  • Ethical/Aesthetic: Species have an inherent right to exist, and humans enjoy the natural world.
  • Economic: Biodiversity provides resources (food, timber, medicine) and services (pollination, water purification). Many drugs originate from compounds found in wild plants and microbes.
  • Ecological Stability: High biodiversity means greater resilience. A diverse ecosystem can recover faster from environmental shocks (like disease or flood) because there are more species available to fulfill essential roles.
  • Genetic Pool: Preserving genetic variation may be essential for future breeding programs (e.g., breeding disease resistance into crops).

Conservation Strategies: In-situ vs Ex-situ

Conservation efforts are generally split into two types:

1. In-situ Conservation (On-site): Protecting species in their natural habitat.

  • Conserved Areas: Establishing National Parks and Marine Parks to protect large ecosystems and the species within them.

2. Ex-situ Conservation (Off-site): Protecting species away from their natural habitat.

  • Zoos: Maintain populations in captivity for breeding and research (e.g., captive breeding programs).
  • Botanic Gardens: Collect and maintain collections of plant species, vital for research and education.
  • Seed Banks: Store seeds at low temperatures, preserving the genetic diversity of plants, especially wild relatives of crops (e.g., the Svalbard Global Seed Vault).
  • 'Frozen Zoos': Cryogenically store genetic material (sperm, eggs, embryos) from endangered animals.

Assisted Reproduction in Conservation (A-Level Detail)

For critically endangered mammals, high-tech methods are sometimes necessary:

  • IVF (In Vitro Fertilisation): Eggs are fertilized by sperm outside the body (in a glass dish) before the embryo is transferred into a surrogate mother.
  • Embryo Transfer: Embryos from a genetically valuable endangered animal are implanted into a surrogacy mother (often a common, related species) to allow the endangered female to produce more offspring rapidly.

Controlling Invasive Alien Species

Invasive species are those introduced to an area where they don't naturally occur, often causing massive damage. Reasons for controlling them include:

  • Preventing competition with native species for limited resources.
  • Stopping them from acting as novel predators on native species that have no natural defense.
  • Protecting local biodiversity and ecosystem stability.

International Conservation Organizations

Conservation requires global cooperation:

  • IUCN (International Union for Conservation of Nature): Assesses the conservation status of species worldwide, publishing the Red List (which categorizes species by their risk of extinction). This role guides global conservation priorities.
  • CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora): An international agreement that ensures international trade in specimens of wild animals and plants does not threaten their survival. It regulates or bans trade based on the species' conservation status.

Quick Takeaway 18.3

Habitat loss, climate change, and human activities are the main threats. Conservation is essential for ethical, economic, and ecological reasons. Strategies involve both protecting habitats (in-situ) and maintaining populations/genetic material elsewhere (ex-situ, often using seed banks or assisted reproduction). Global organizations like IUCN and CITES enforce policy and monitor threats.