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AP Bio



Unit 8

8.6 Biodiversity

2 min readmay 31, 2020


Caroline Koffke

Diversity in Species

Biodiversity refers to the amount of diversity in species and within species in an ecosystem. Ecosystems with a higher level of biodiversity are better able to respond to changes in their environment. This is due to the increase in potential defenses to various problems. For example, if a highly diverse population is infected with a specific pathogen, it is likely that at least a few individuals within the population possess some sort of immunity or enhanced ability to fight the pathogen. This allows the population to survive through the challenging environmental shift. Less diverse ecosystems may collapse if exposed to extreme changes in the environment or other detrimental events. Using the previous example, it is less likely that individuals within a population would possess immunity to the pathogen, and it is more likely that the entire population may be wiped out from the pathogen. An increase in genetic diversity always leads to an increase in protection from environmental changes. This concept is tested frequently on the AP exam.

Keystone Species

Keystone species are species that have a disproportionate effect on the ecosystem. The disruption of keystone species can lead to catastrophic effects within an ecosystem. The effects are disproportionate to the number of species affected. An example of a keystone species is the sea otter. Otters are a large part of the marine ecosystem, as shown by the food web below. When the otter population decreases, the rest of the ecosystem is at risk of collapse.

Image courtesy of WikiMedia Commons.

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