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IB DP ESS — Topic 2: Ecology | SL & HL | Paper 1 & Paper 2A
🎯 Learning Intentions By the end of this note, you will be able to:
- Define the biological species concept and explain the role of reproductive isolation in species formation.
- Explain the principles of binomial nomenclature and why a universal classification system is essential for ecological science.
- Describe the hierarchical classification system (domain to species) and place organisms correctly within it.
- Distinguish between the fundamental niche and the realised niche of a species, using named ecological examples.
- Explain how competitive exclusion and resource partitioning shape the realised niches of coexisting species.
- Analyse how niche concepts relate to biodiversity, ecosystem stability, and conservation decision-making.
- Evaluate the limitations of the biological species concept when applied to asexually reproducing organisms, fossil species, and ring species.
Real-World Context & Relevance
In the Galápagos Islands, thirteen species of finch — collectively known as Darwin's finches — occupy the same archipelago yet rarely compete directly for food. Each species has evolved a beak shape precisely matched to a different food source: crushing hard seeds, probing cactus flowers, or picking insects from bark. When researchers from Princeton University tracked the medium ground finch ( Geospiza fortis ) and the large ground finch ( Geospiza magnirostris ) during the 2004–2005 drought, they documented a measurable shift in beak size within a single generation as food availability changed — one of the fastest recorded examples of natural selection in a wild population (Grant and Grant, "Evolution of Character Displacement in Darwin's Finches." Science , vol. 313, no. 5784, 2006, pp. 224–226). This story is not just about evolution; it is about how species carve out distinct ecological roles that allow them to coexist without driving each other to extinction.
Understanding what a species is , how we name and organise species, and what ecological role each species plays are foundational questions for all of ecology and conservation biology. When the IPBES Global Assessment (2019) reported that approximately one million species face extinction, the precision of that figure depends entirely on our ability to define, identify, and classify species consistently. Without a shared language of classification and a clear understanding of ecological niches, conservation planning, invasive species management, and biodiversity monitoring would be impossible.
🌍 Why This Matters The concepts of species, classification, and niches underpin every practical decision in conservation biology — from identifying which species to protect under the IUCN Red List, to predicting how an invasive species will disrupt an ecosystem by occupying the niche of a native species. They are the vocabulary of ecology itself.
Core Concepts & Definitions
Before ecologists can study populations, communities, or ecosystems, they need a precise answer to a deceptively simple question: what counts as a species? The answer shapes everything from how we measure biodiversity