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IB DP Biology — Unit C: Interaction and Interdependence | SL | C4 Ecology
📋 What You Will Learn
- Identify the major threats to biodiversity and explain why species loss matters beyond individual species
- Explain the biological principles underpinning conservation strategies, including in situ and ex situ approaches
- Analyse population data, species richness indices, and ecological data to evaluate conservation outcomes
- Apply the concept of ecosystem services to evaluate the economic and ecological arguments for conservation
- Evaluate the effectiveness of protected areas, rewilding, and international conservation frameworks
🔍 Guiding Question How can knowledge of biological principles be applied to conserve biodiversity and manage ecosystems sustainably, and what are the limitations of current conservation strategies?
🌍 Why This Matters The current rate of species extinction is estimated to be 100–1,000 times higher than the natural background rate — a pace not seen since the mass extinction that ended the Cretaceous period 66 million years ago. Unlike previous extinctions driven by asteroid impacts or volcanic eruptions, this one has a single identifiable cause: human activity. Conservation biology exists precisely because biology has given us both the tools to understand what we are losing and the knowledge to do something about it.
Why Biodiversity Matters: The Problem the Planet Had to Solve
Here is the problem: ecosystems are not just collections of species. They are networks of interdependence — webs of feeding relationships, nutrient cycles, pollination partnerships, and decomposition chains that have been refined over hundreds of millions of years. Remove one thread and the web holds. Remove enough threads and the whole structure collapses. The challenge for conservation biology is to understand which threads matter most, and why.
Biodiversity is not simply a count of species. It operates at three nested levels, each of which matters for different reasons. Understanding these levels is the foundation of everything that follows.
📖 Key Definition — Biodiversity Biodiversity is the variety of life on Earth at all levels of biological organisation, including genetic diversity within species, species diversity within communities, and ecosystem diversity across landscapes.
Genetic Diversity
Genetic diversity refers to the range of alleles present within a population or species. It is the raw material on which natural selection acts. A population with high genetic diversity has a wider range of phenotypic variation, making it more likely that some individuals will survive novel environmental pressures — a new pathogen, a shift in climate, a change in food availability. When populations shrink, genetic diversity is lost through genetic drift and inbreeding, reducing the population's evolutionary resilience.
📖 Key Definition — Genetic Diversity Genetic diversity is the total number of genetic characteristics — including alleles, genes, and genotypes — present within a population or species, which determines its capacity to adapt to environmental change.
Species Diversity
Species diversity combines two components: species richness (the number of different species in a community) and species evenness (how equally individuals are distributed among those species). A forest with 100 tree species but 99% of individuals belonging to one species has high richness but low evenness — and low functional diversity. Both components matter for ecosystem stability.
📖 Key Definition — Species Richness Species richness is the total number of different species present in a defined area or community, used as a basic measure of biodiversity.
Ecosystem Diversity
Ecosystem diversity refers to the variety of habitats, ecological communities, and ecological processes across a region. Different ecosystems — coral reefs, tropical rainforests, peatlands, mangroves — provide different combinations of ecosystem services and support different assemblages of species. Losing an ecosystem type is not merely losing species; it is losing the ecological processes those species perform.
Measuring Biodiversity: The Simpson's Diversity Index
Counting species is