An overview of the field of biogeography, covering its definition, history, and the importance of studying the distribution of organisms on Earth.
Introduction to Biogeography
The study of the distribution of life on Earth and the processes that shape those patterns.
| Aspect | Description |
|---|---|
| Definition | The scientific discipline that examines where organisms live, why they are found there, and how they got there. |
| Scope | • Spatial patterns (global, continental, regional, local) • Temporal patterns (past, present, future) • Taxonomic groups (plants, animals, microbes) |
| Key Questions | 1. Why are species concentrated in some areas and absent in others? 2. How have past events (e.g., plate tectonics, climate change) influenced present distributions? 3. What mechanisms drive the spread, isolation, and extinction of species? |
| Period | Milestones & Contributors |
|---|---|
| Early Observations (18th‑19th c.) | • Alexander von Humboldt – “law of the geographic distribution of plants.” • Charles Darwin – noted species similarity on neighboring islands (Galápagos). |
| Wallace’s Contributions (1850s) | • Alfred Russel Wallace formulated the “Wallace Line” separating Asian and Australian fauna. • Introduced the concept of vicariance (species split by emerging barriers). |
| Modern Synthesis (20th c.) | • Integration of ecology, evolution, and geology. • Development of island biogeography theory (MacArthur & Wilson, 1967). |
| Molecular Era (1990s‑present) | • DNA sequencing reveals phylogenetic relationships and historic dispersal routes. • Phylogeography merges genetics with geographic data. |
| Term | Meaning | Example |
|---|---|---|
| Endemism | Species restricted to a defined area. | Lemurs – Madagascar |
| Cosmopolitan Distribution | Species found worldwide (in suitable habitats). | Herring gull (Larus argentatus) |
| Dispersal | Movement of organisms from one area to another. | Wind‑borne seeds, bird migration |
| Vicariance | Geographic separation of a population by a barrier (mountain range, ocean). | Split of Gondwanan flora by continental drift |
| Ecological Niche | The set of environmental conditions a species can tolerate and use. | Temperature, moisture, substrate |
| Biogeographic Realm | Large-scale region with a distinct assemblage of flora and fauna. | Nearctic, Palearctic, Neotropical, Afrotropical, Indomalayan, Australasian, Oceanian, Antarctic |
| Ecoregion | Subdivision of a realm with relatively homogeneous ecosystems. | Amazon Rainforest, Sahara Desert |
| Island Biogeography | Theory describing species richness on islands as a balance of immigration and extinction rates. | Species‑area curve for Hawaiian islands |
| Mechanism | Process | Typical Scale | Illustrative Case |
|---|---|---|---|
| Plate Tectonics & Continental Drift | Landmasses move, creating/closing connections. | Millions of years | Distribution of Nothofagus (southern beech) across South America, Australia, New Zealand |
| Glaciation & Climate Oscillations | Ice sheets expand/retreat, altering |