Unit 2: Global Biodiversity and Conservation Status
Levels of Global Biodiversity
As covered in Unit 1, global biodiversity is understood at three levels:
- Genetic Diversity: The total range of genetic variation within and between species.
- Species Diversity: The total number and variety of species on Earth.
- Ecosystem Diversity: The variety of ecosystems (deserts, forests, oceans, etc.) across the globe.
Keystone Species
Definition: A keystone species is a species that has a disproportionately large effect on its natural environment relative to its abundance. Its removal can cause the entire ecosystem to collapse.
They are not necessarily the most abundant species, but they play a unique and critical role in maintaining the structure of an ecosystem.
- Example 1 (Predator): The Sea Otter. It preys on sea urchins. Without sea otters, sea urchin populations explode and destroy kelp forests, which are habitats for hundreds of other species.
- Example 2 (Pollinator): Fig Wasps. Many species of fig trees are entirely dependent on their specific fig wasp species for pollination. If the wasp disappears, the fig tree (a major food source) cannot reproduce.
Biodiversity in the Tropics
Biodiversity is not evenly distributed on Earth. The highest concentrations of species are found in the tropics (the regions around the equator).
Why are tropics so rich in biodiversity?
- Higher Solar Energy: More sunlight leads to higher productivity (more plant growth), which can support more species.
- Climatic Stability: Tropical regions have a more stable climate (less seasonality) compared to temperate regions. This allows species to specialize and evolve without being wiped out by harsh winters.
- Longer Evolutionary History: Tropical regions have been relatively undisturbed by ice ages, giving species a longer, uninterrupted time to evolve and diversify.
Conservation, Ecology, Economy, and Bioethics
- Conservation of Biodiversity: This is the protection, management, and restoration of biodiversity to ensure it persists for future generations.
- Ecology and Economy: This concept links the health of ecosystems to economic well-being. Healthy ecosystems provide "ecosystem services" that have immense economic value, such as:
- Pollination of crops by insects.
- Water purification by wetlands.
- Climate regulation by forests.
- Bioethics and Conservation: This explores the moral and ethical reasons for conservation. It asks questions like:
- Do other species have an inherent right to exist?
- Do we have a moral duty to protect nature for future human generations?
IUCN Red Data Book and Red List Categories
- IUCN: International Union for Conservation of Nature.
- Red Data Book: A public database of the conservation status of species. It is a comprehensive inventory of the global conservation status of biological species.
- Red List Categories: The IUCN uses a set of precise criteria to evaluate the extinction risk of thousands of species. These categories are the global standard.
[Image of IUCN Red List categories hierarchy]
Causes of Extinction
Extinction is the complete disappearance of a species. While some extinction is natural, the current high rate is caused by human activities.
The "Evil Quartet": A term for the four main causes of human-driven extinction.
- Habitat Loss and Fragmentation: This is the number one cause. Forests are cleared for agriculture, cities expand, and habitats are broken into small, isolated patches.
- Overexploitation: Harvesting a species faster than it can reproduce (e.g., overfishing, poaching for horns/ivory, overharvesting medicinal plants).
- Invasive Species: The introduction of a non-native species to an ecosystem, where it outcompetes or preys on native species.
- Co-extinctions: The extinction of one species leads to the extinction of another that was dependent on it (e.g., a specific pollinator and its plant).
Climate change is now often considered the "fifth" cause, accelerating all the others.
Endemism
Definition: An endemic species is one that is native to and found only within a specific, limited geographical area.
- Example: Lemurs are endemic to the island of Madagascar. Kangaroos are endemic to Australia.
- Importance: Areas with high endemism are conservation priorities. If an endemic species' only habitat is destroyed, it becomes globally extinct. This is the principle behind "Biodiversity Hotspots."