Welcome to Classification, Biodiversity, and Conservation!

Welcome to Topic 18! This chapter is where you connect the molecular biology you've learned to the grand scale of life on Earth. We will explore how scientists organize the millions of species (Classification), why having so many different life forms is crucial (Biodiversity), and what we can do to protect them (Conservation).
This topic is highly relevant to modern global issues like climate change and species extinction, making it an essential and engaging part of your A-Level studies. Let's dive in!

18.1 Classification: Ordering the Living World

18.1.1 The Meaning of 'Species'

Defining what a species is can be surprisingly tricky! Scientists use different concepts depending on the context:

  • Biological Species Concept: A group of organisms that can interbreed to produce fertile offspring.
    (Think: Horses and donkeys can breed to make a mule, but since the mule is sterile, they are separate species.)
  • Morphological Species Concept: Classifies organisms based on observable, physical characteristics (shape, size, structure). This is often used for fossils or asexual organisms where breeding data isn't available.
  • Ecological Species Concept: Defines a species based on its role (niche) in the community and its adaptations to specific environmental conditions.

Quick Review: The Biological concept is the most common, focusing on successful reproduction.

18.1.2 The Three Domains

All life on Earth is categorized into three major domains, reflecting major evolutionary splits: Archaea, Bacteria, and Eukarya.

Archaea and Bacteria are both prokaryotes (lacking a nucleus and membrane-bound organelles), but they are fundamentally different:

Key Differences between Archaea and Bacteria:

  • Membrane Lipids: Archaea have unique membrane lipids (often branched hydrocarbons) that differ from those in Bacteria. This helps Archaea survive in extreme environments.
  • Ribosomal RNA (rRNA): The sequence of nucleotides in their rRNA is structurally different.
  • Cell Walls: Bacteria have cell walls containing peptidoglycan, while Archaea do not.

18.1.3 The Taxonomic Hierarchy (Eukarya)

Eukaryotic organisms are classified using a system developed by Carl Linnaeus. This system groups organisms into increasingly smaller, more specific categories:

The hierarchy, from largest (most general) to smallest (most specific), is:

Kingdom
Phylum
Class
Order
Family
Genus
Species

Memory Aid: King Philip Came Over For Good Soup.

18.1.4 Characteristics of the Five Eukaryotic Kingdoms

We focus on the key features used to distinguish organisms in the domain Eukarya:

  • Protoctista (Protists): Mostly unicellular, but some multicellular algae exist. They are typically microscopic and lack specialized tissues. (Examples: Amoeba, microscopic algae.)
  • Fungi: Have cell walls made of chitin. They are heterotrophic (feed on organic matter) and use extracellular digestion (secrete enzymes and absorb digested nutrients). They are usually composed of threads called hyphae.
  • Plantae (Plants): Multicellular, have cell walls made of cellulose. They are autotrophic (perform photosynthesis).
  • Animalia (Animals): Multicellular, lack cell walls. They are heterotrophic (ingest food) and have specialized organs, tissues, and systems (like a nervous system).

18.1.5 Classification of Viruses

Viruses are non-cellular entities, often considered outside the standard three domains. They are classified primarily based on their genetic material:

  • Type of Nucleic Acid: They can contain either DNA or RNA (never both).
  • Strandedness: The nucleic acid core can be single-stranded or double-stranded.

Did you know? The Human Immunodeficiency Virus (HIV) is an RNA virus (single-stranded).

Key Takeaway (Classification)

Classification organizes life into three domains (Archaea, Bacteria, Eukarya). Eukarya are further sorted into kingdoms using a strict hierarchy, relying on fundamental biological differences like cell wall composition and feeding mechanisms.

18.2 Biodiversity: Variety of Life

18.2.1 Ecosystems and Niches

Before we measure biodiversity, we need key definitions:

  • Ecosystem: A unit containing all the organisms (biotic factors) of a particular area, interacting with each other and with their non-living (abiotic) environment. (Example: A forest ecosystem includes trees, deer, soil, and rainfall.)
  • Niche: The specific role and position a species occupies within an ecosystem. This includes all biotic interactions (what it eats, what eats it) and abiotic requirements (temperature, water, light).

Analogy: If the ecosystem is a company, the species is the employee, and the niche is the employee's unique job title and responsibilities.

18.2.2 Levels of Biodiversity Assessment

Biodiversity describes the variety of life, assessed at three main levels:

  1. Ecosystem/Habitat Diversity: The number and range of different ecosystems or habitats in an area.
  2. Species Diversity: The number of different species (species richness) and their relative abundance (species evenness) in an area.
  3. Genetic Diversity: The variation of alleles (genes) within a single species or population. Higher genetic diversity helps a species adapt to changes (e.g., disease or climate change).

18.2.3 Assessing Distribution and Abundance

To measure biodiversity, we use random sampling. Random sampling is essential because it minimizes researcher bias and ensures the data collected is representative of the whole area.

Common sampling techniques:

  • Frame Quadrats: Square frames used for estimating percentage cover or counting slow-moving/sessile organisms (plants) in a small, defined area.
  • Line Transects: A tape measure laid across a habitat. Organisms touching the line are recorded. Used to see how species distribution changes along an environmental gradient (e.g., moving away from a lake).
  • Belt Transects: Two parallel line transects defining a strip. Quadrats are placed sequentially along this strip. Provides more detailed abundance data than a line transect.

18.2.4 Mark-Release-Recapture (Lincoln Index)

This method estimates the population size (\(N\)) of mobile animals (like insects or fish).

The Method (Step-by-Step):

  1. Capture 1 (\(C_1\)): Capture a sample of the population, count them, mark them harmlessly (e.g., paint dots), and release them back into the habitat.
  2. Time Delay: Allow time for the marked individuals to redistribute randomly within the population.
  3. Capture 2 (\(C_2\)): Capture a second sample. Count the total number caught (\(C_2\)).
  4. Recapture (\(R\)): Count how many of the individuals in the second sample are marked.

Formula (Lincoln Index): $$N = \frac{C_1 \times C_2}{R}$$

18.2.5 Statistical Analysis of Biodiversity

We use mathematical tools to analyze relationships and quantify diversity.

1. Simpson’s Index of Diversity (D)

This index measures species diversity, taking into account both species richness and species evenness.

Formula: $$D = 1 - \sum \left( \frac{n}{N} \right)^2$$ Where:
\(n\) = total number of organisms of a particular species
\(N\) = total number of organisms of all species

Significance of D:

  • The value of D ranges from 0 to 1.
  • A value closer to 1 indicates high biodiversity (many species, evenly distributed).
  • A value closer to 0 indicates low biodiversity (few species, or one or two dominant species).

2. Correlation (Spearman's Rank and Pearson's Linear)

These statistical tests analyze the relationship (correlation) between two variables, such as how an abiotic factor (like temperature or light) or a biotic factor (like predator density) affects the distribution or abundance of a species.

  • Both tests provide a correlation coefficient (r-value) between -1 and +1.
  • A strong positive correlation (near +1) means as one variable increases, the other increases.
  • A strong negative correlation (near -1) means as one variable increases, the other decreases.
Key Takeaway (Biodiversity)

Biodiversity is measured at genetic, species, and ecosystem levels. Sampling (like quadrats and the Lincoln Index) provides raw data, which is analyzed using indices like Simpson's D to assess the health and stability of an ecosystem.

18.3 Conservation: Protecting Our Planet

18.3.1 Causes of Extinction

Populations and species face multiple threats leading to extinction:

  • Climate Change: Changing temperature and rainfall patterns shift habitats faster than species can adapt or migrate.
  • Degradation and Loss of Habitats: Deforestation, pollution, and draining wetlands destroy ecosystems, removing the place a species lives.
  • Hunting by Humans: Unsustainable harvesting or poaching drives population numbers down drastically.
  • Competition: Often, competition from invasive alien species (non-native species introduced to an ecosystem) outcompetes native species for resources.

18.3.2 Reasons for Maintaining Biodiversity

Why is conservation so vital?

  • Ecological Stability: Diverse ecosystems are more resilient to change and provide essential services (e.g., water purification, nutrient cycling).
  • Economic Value: Potential sources of new foods, medicines, and raw materials (bioprospecting).
  • Aesthetic/Ethical Reasons: Many believe every species has a moral right to exist, and nature provides beauty and recreational value.

18.3.3 Conservation Strategies: In-situ and Ex-situ

Conservation efforts are often split into protecting species in their natural habitat (in-situ) or outside it (ex-situ).

Ex-Situ Conservation (Off-site):

  • Zoos and Botanic Gardens: Maintain captive breeding programs and ensure genetic purity and diversity for eventual reintroduction.
  • Seed Banks: Store seeds from many plant species at low temperatures and humidity to preserve plant genetic diversity (e.g., the Svalbard Global Seed Vault).
  • ‘Frozen Zoos’: Facilities that store genetic material (sperm, eggs, embryos) from endangered mammals and other animals, often using cryopreservation techniques.

In-Situ Conservation (On-site):

  • Conserved Areas: Including National Parks and Marine Parks, which protect large areas of habitat and prevent human interference (like logging or fishing).

18.3.4 Assisted Reproduction in Mammals

To boost the numbers of highly endangered mammals, special techniques are used:

  • IVF (In Vitro Fertilisation): Eggs are fertilized by sperm outside the mother's body in a laboratory.
  • Embryo Transfer: Embryos from a genetically valuable but endangered mother are implanted into a less valuable, related species (or a surrogate mother).
  • Surrogacy: Using a female of a related, common species to carry the pregnancy of an endangered species. This allows the endangered mother to produce more eggs sooner.

18.3.5 Controlling Invasive Alien Species

Invasive species pose a huge threat to native biodiversity because they often have no natural predators in the new environment and can multiply rapidly, outcompeting or preying on native organisms.

Reasons for Control: To protect native species from competition, predation, and disease transmission introduced by the alien species. Control methods include biological (introducing a natural predator), chemical, or physical removal.

18.3.6 International Conservation Roles

Global conservation requires international cooperation:

  • IUCN (International Union for Conservation of Nature): The global authority on the status of the natural world. They maintain the Red List of Threatened Species, which assesses the risk of extinction for species globally. This list guides conservation priorities.
  • CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora): An international agreement that regulates (or bans) the trade of endangered plants and animals and their products (e.g., ivory). This helps reduce hunting by humans motivated by commercial gain.
Key Takeaway (Conservation)

Extinction is driven by human activity and habitat loss. Conservation utilizes both ex-situ methods (seed banks, frozen zoos) and in-situ protection (national parks). International bodies like IUCN and CITES are essential for coordinating global efforts and regulating trade.