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IB DP ESS — Topic 3: Biodiversity and Conservation (HL Extension) | HL | Paper 1 & Paper 2
🎯 Learning Intentions By the end of this note, you will be able to:
- Define genetic diversity, allelic richness, and heterozygosity using IB-aligned ESS terminology.
- Explain how genetic diversity functions as a component of biodiversity and why it underpins the long-term resilience of populations and ecosystems.
- Describe the mechanisms of allopatric and sympatric speciation and the role of reproductive isolation in generating new species.
- Distinguish between allopatric and sympatric speciation, identifying the conditions under which each occurs.
- Explain the latitudinal biodiversity gradient and the major hypotheses proposed to account for it.
- Analyse how island biogeography theory explains patterns of species richness on islands and habitat fragments, using relevant ESS parameters including scale, uncertainty, and trade-offs.
- Evaluate the significance of genetic bottlenecks and founder effects for conservation biology, with reference to named species.
- Discuss contrasting worldviews (ecocentric, technocentric, anthropocentric) in relation to the conservation of genetic diversity and the management of biodiversity hotspots.
Real-World Context & Relevance
In 2016, a survey of the last remaining northern white rhinoceros population confirmed that only three individuals survived — all in captivity at Ol Pejeta Conservancy in Kenya. When the last male, Sudan, died in 2018, the subspecies lost its ability to reproduce naturally. Yet the crisis was not simply one of numbers. Genetic analysis revealed that decades of population decline had stripped the subspecies of almost all its genetic variation, leaving it biologically incapable of adapting to new diseases, climate shifts, or environmental stressors even if numbers could somehow be restored. This case illustrates a fundamental principle in conservation biology: species survival depends not only on population size but on the genetic diversity that enables evolutionary flexibility.
The northern white rhino story is an extreme example of a pattern playing out across thousands of species worldwide. The IPBES Global Assessment (2019) estimated that approximately one million species face extinction, many of them already experiencing the genetic erosion that precedes demographic collapse. Meanwhile, the distribution of biodiversity across Earth's surface is profoundly unequal — tropical rainforests covering less than 6% of the land surface harbour over half of all terrestrial species, while polar regions support comparatively few. Understanding why biodiversity is distributed the way it is, how new species arise, and what genetic processes underpin population resilience are not abstract academic questions. They are the foundations of effective conservation strategy.
🌍 Why This Matters Genetic diversity is the raw material of evolution. Without it, populations cannot adapt to environmental change, making genetic erosion a silent precursor to extinction. Understanding speciation and biodiversity distribution patterns allows conservationists to prioritise where and how to protect life on Earth — decisions with profound implications for ecosystem services, human food security, and the long-term stability of the biosphere.
Core Concepts & Definitions
Biodiversity is commonly discussed at the species level — how many species exist in a given area — but this framing captures only one dimension of a much richer concept. Before species diversity can be meaningfully understood, it is necessary to examine the genetic