8.6 Biodiversity

Biodiversity refers to the variety of different species of plants, animals, and other living organisms that exist within a particular ecosystem. It includes diversity within species, as well as between species. Ecosystems with a higher level of biodiversity are better able to respond to changes in their environment.

Biodiversity within a species, also known as genetic diversity, is important because it increases the adaptability and resilience of the species. Genetic diversity within a species can provide the genetic variation necessary for the species to adapt to changing environmental conditions.

For example, if a highly genetically 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 of selective pathogenic pressure. In contrast, a species with low genetic diversity may be more vulnerable to extinction because individuals will respond to the pathogen similarly based on having fewer genetic variations that may include resistance.

Genetic diversity within a species is also important for maintaining the health and viability of the species over time. Consider a species with low genetic diversity. This species may be more prone to inbreeding, which can lead to a number of negative consequences, such as reduced fertility and increased susceptibility to disease. A more genetically diverse species with more variation has an increased number of different alleles to build the species' resistance to ecosystem challenges.

An increase in genetic diversity always leads to an increase in protection from environmental changes. This concept is tested frequently on the AP exam!

How does biodiversity between species, also known as species diversity, help to maintain the health and functioning of ecosystems? Different species play different roles within an ecosystem. Less diverse ecosystems are more vulnerable to collapse if exposed to extreme ecosystem events like natural disasters or drought because they lack a greater number of species that may be able to adapt to changing conditions.

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.

An example of a keystone species is the sea otter. Otters are a large part of the marine ecosystem. By preying on sea urchins, which consume kelp, otters help protect kelp forests. Because kelp forests are an ecological niche for a variety of other organisms living in the marine ecosystem, otters provide an ecosystem service. If the otter population decreases, the rest of the ecosystem is at risk of collapse because the loss of this species causes a habitat ripple effect. 🦦

Other examples of keystone species include pollinator keystone species, like bees and hummingbirds, that act as mutualists in relation to producers. Bees benefit from the food of flower nectar, while pollination spreads plant gametes to aid reproduction and genetic diversity. 🐝

Engineer keystone species, including elephants and beavers, create habitats for other species similar to sea otters. By knocking trees and branches over, elephants make a source of food and habitat for smaller organisms more accessible. 🐘

Keystone species also consist of predators. Predators help control the populations of prey species, which creates a trophic cascade with a top-down impact on ecosystems. Wolves in Yellowstone are a predatory keystone species that control the elk population, preventing elk overgrazing on vegetation. Predation preserves habitat and prevents a single primary consumer from monopolizing the consumption of producers. 🐺

Increased species diversity means that there may be more species present to provide ecosystem services as keystone species.

The susceptibility of ecosystems to damage is related to ecosystem resistance and resilience. Ecosystem resistance measures how much a disturbance affects the functioning of an ecosystem. The more resistant an ecosystem is, the less it will be affected by environmental changes. On the other hand, ecosystem resilience measures how quickly an ecosystem is able to recover after a disturbance. Biodiversity increases ecosystem resistance and resilience.