8.6 Biodiversity
Keywords
| English Term | 中文翻译 | Definition & Explanation |
|---|---|---|
| Biodiversity | 生物多样性 | The variety of life in the world or in a particular habitat or ecosystem, including genetic, species, and ecosystem diversity. |
| Ecosystem Resilience | 生态系统韧性 | The capacity of an ecosystem to respond to a perturbation or disturbance by resisting damage and recovering quickly. |
| Keystone Species | 关键物种 | A species on which other species in an ecosystem largely depend, such that if it were removed the ecosystem would change drastically. |
| Abiotic Factors | 非生物因素 | Non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems (e.g., sunlight, temperature). |
| Biotic Factors | 生物因素 | Any living component that affects another organism or shapes the ecosystem (e.g., predators, competitors). |
1. Biodiversity and Ecosystem Resilience
Biodiversity refers to the complexity and variety of life within an ecosystem. The diversity of species within an ecosystem profoundly influences its overall organization and stability.
A central rule in ecology is that diversity equals resilience.
- Highly Diverse Ecosystems: A natural ecosystem with a high species diversity (like a tropical rainforest) has a highly complex food web. If one species experiences a population crash due to a disease, predators have plenty of alternative food sources. The ecosystem can absorb the shock and maintain its structure.
- Low Diversity Ecosystems: Natural and artificial ecosystems with fewer component parts are often less resilient to changes in the environment.
- Artificial Example: A commercial farm growing only one genetic strain of corn (a monoculture). Because there is practically zero diversity, if a specific fungal pathogen arrives, it can wipe out the entire ecosystem overnight.
Analogy: The Ecological Jenga Tower
Think of an ecosystem like a tower of Jenga blocks. In a highly diverse ecosystem, the tower has thousands of interlocking blocks. You can pull a few out, and the tower remains stable (high resilience). In an ecosystem with low diversity, the tower only has a few thick blocks. Pulling just one out will cause the entire structure to instantly crash.
2. The Power of Keystone Species
When evaluating the organization of an ecosystem, not all species are created equal. Some species exert a level of control that seems entirely out of proportion to their actual numbers.
A keystone species is a species whose effects on the ecosystem are disproportionate relative to their abundance. They might not be the most numerous organism (like a producer) or the physically largest, but they hold the entire ecological community together.
When a keystone species is removed from the ecosystem, the ecosystem often collapses.
Classic Example: Sea Stars in the Intertidal Zone
In rocky intertidal zones, mussels are excellent competitors for space and will rapidly crowd out all other species. However, a specific species of sea star preys on these mussels. While the sea stars are not the most abundant organism, their predation keeps the mussel population in check, allowing dozens of other species (like algae, barnacles, and snails) to inhabit the rocks. When ecologists experimentally removed the sea stars, the mussels quickly took over, and the species diversity of the ecosystem collapsed from 15 species down to just 8. The sea star is the keystone species.
3. Maintaining Diversity: The Foundational Factors
While keystone species play a critical regulatory role, the overall diversity and structure of an ecosystem are also strictly maintained by other foundational components:
- Producers: As we learned in previous sections, autotrophs form the foundational energy base of the entire ecosystem. The variety and abundance of producers directly limit how many trophic levels and diverse consumer species an ecosystem can support.
- Essential Abiotic Factors: Non-living elements like climate, water availability, soil minerals, and sunlight availability set the baseline carrying capacity for the ecosystem. A sudden shift in these (e.g., climate change or severe drought) can wipe out sensitive species, reducing diversity.
- Biotic Factors: The interactions between species (predation, competition, mutualism) keep populations balanced and prevent any single species from dominating and reducing diversity (just like the sea star example).
Quiz
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