Notes
Biomes
- Temperature and precipitation determine terrestrial biomes: tropical rainforest, desert, temperate forest, grassland, taiga, and tundra.
- Aquatic biomes are sorted by salinity and depth: freshwater (lakes, rivers, wetlands), marine (oceans, coral reefs), and estuaries where they meet.
- Wetlands filter water and absorb floods. Estuaries and coral reefs are among the most productive and diverse habitats.
Biodiversity
- Three levels: genetic, species, and ecosystem diversity. Richness is the number of species; evenness is how equally individuals are spread.
- High biodiversity gives resilience. Diversity is highest near the equator.
Special species and threats
- Keystone species (sea otters, wolves, beavers) have a large effect for their numbers. Indicator species show ecosystem health. Invasive species harm native species.
- HIPPCO: Habitat loss, Invasive species, Pollution, Population growth, Climate change, Overexploitation.
- Habitat fragmentation isolates populations. The Endangered Species Act protects listed species in the US.
Topics in this unit
Each topic has its own short notes and practice.
Practice
Permafrost prevents tree roots from growing deep.
Removing a keystone species changes the whole community, even if it is not numerous.
Richness is just the count of species: 10 is greater than 3.
Non-native species that spread and harm natives are invasive.
Small isolated groups lose genetic diversity and are more vulnerable.
Estuaries mix fresh and salt water and are nutrient rich.
Free response
Write your answer first, then open the scoring guide.
Free-response question
A coastal kelp forest supports fish, seals, and many invertebrates. Sea otters eat sea urchins, which graze on kelp. A disease sharply reduces the sea otter population.
(a) Identify the role of the sea otter in this ecosystem and define that type of species.
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The sea otter is a keystone species. A keystone species has a much larger effect on its ecosystem than its numbers would suggest.
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(b) Predict what will happen to sea urchins and kelp, and explain.
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Urchin numbers will increase because fewer predators eat them. The urchins will overgraze the kelp, so the kelp forest will shrink.
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(c) Explain how this change could affect the biodiversity of the area.
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Kelp provides habitat and food for fish and invertebrates. Losing the kelp would reduce species richness and ecosystem resilience, lowering biodiversity.
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