Preview
IB DP ESS — Topic 3: Biodiversity and Conservation | SL & HL | Paper 1 & Paper 2
🎯 Learning Intentions By the end of this note, you will be able to:
- Define biodiversity, genetic diversity, species diversity, and ecosystem diversity using IB-aligned ESS terminology.
- Explain how natural selection drives evolutionary change and how this process generates biodiversity over geological time.
- Describe the mechanisms of speciation, including allopatric and sympatric speciation, and their role in producing species diversity.
- Distinguish between the three levels of biodiversity — genetic, species, and ecosystem — and explain why each level is ecologically significant.
- Analyse how biodiversity is measured using species richness, species evenness, and the Simpson's Diversity Index, applying these tools to real ecological data.
- Evaluate the relationship between genetic diversity and a population's resilience to environmental change, using named real-world examples.
- Discuss contrasting worldviews — ecocentric, technocentric, and anthropocentric — in relation to the intrinsic and instrumental value of biodiversity.
Real-World Context & Relevance
In the early 1970s, a fungal pathogen called Ophiostoma ulmi swept through the elm trees of Europe and North America, killing an estimated 25 million trees in the United Kingdom alone. The devastation was catastrophic not simply because elms died, but because virtually every elm in the affected populations was genetically near-identical — the result of centuries of vegetative propagation. With no genetic variation, there was no variation in resistance, and the pathogen moved through populations like fire through dry grass. This single ecological disaster illustrates one of the most fundamental principles in environmental science: genetic diversity is not an abstract concept — it is the raw material of survival.
Zoom out to the planetary scale, and the stakes become even clearer. The 2019 IPBES Global Assessment estimated that approximately one million animal and plant species are currently threatened with extinction — a rate 10 to 100 times higher than the natural background rate (IPBES, "Global Assessment Report on Biodiversity and Ecosystem Services," 2019). This accelerating loss is not simply a matter of species disappearing from lists. It represents the erosion of three interlocking levels of biological organisation — genetic, species, and ecosystem diversity — each of which underpins the stability and productivity of the living systems that human societies depend upon. Understanding how biodiversity is structured, how it arose through evolution, and how it can be measured is therefore not merely academic: it is foundational to every conservation decision made at local, national, and global scales.
🌍 Why This Matters Biodiversity is the product of billions of years of evolution. Its three levels — genetic, species, and ecosystem — are interdependent: genetic diversity enables adaptation, species diversity stabilises ecosystems, and ecosystem diversity provides the full range of services on which human well-being depends. Understanding how biodiversity is generated, structured, and measured is the conceptual foundation for all conservation science and policy.
Core Concepts & Definitions
Before we can measure or protect biodiversity, we need to understand precisely what it is. The word "biodiversity" is used loosely in public discourse — sometimes meaning "lots of species," sometimes meaning "healthy ecosystems." In ESS, however, biodiversity has a precise, three-level structure that reflects the biological organisation of life itself. Each level is distinct, measurable, and ecologically significant in its own right.
📖 Key Definition — Biodiversity Biodiversity is the variety of life on Earth at all its levels, from genes to ecosystems.