Biodiversity (College Board AP® Biology): Study Guide

Biodiversity & resilience to change

Biodiversity

• Biodiversity can be defined as:

the variation of genes, species, and habitats in a region

• Examples of measures of biodiversity include:

  • the genetic variation within each species

  • the number of different species and the relative abundance of each species

  • the number and range of different ecosystems and habitats

Ecosystem diversity

• Ecosystems with more components and greater biodiversity are more resilient to environmental change

• An ecosystem with fewer component parts may be unable to adapt to change in the environment, resulting in:

  • loss of species

  • instability where disturbance may result in potential ecosystem collapse

  • disruption to feeding relationships within food chains and food webs

  • reduced nutrient cycling and productivity

• Factors that contribute to the maintenance of ecosystem diversity include:

  • essential biotic and abiotic factors

    • Some ecosystems may rely on the presence or absence of particular factors, e.g. rainforests depend on a functional water cycle

  • producers

    • These organisms form the base of all food chains, so are an essential ecosystem component

  • keystone species

    • These are species that have a disproportionate effect on the structure and function of their ecosystem (see below)

Ecosystem structure

• The diversity of species influences the structure, or organization, of an ecosystem

• Adding or removing any component of an ecosystem will therefore affect its structure, either in the immediate-term, or over longer time periods

Keystone species

• The removal of keystone species can cause significant changes to the structure of an ecosystem, including:

  • loss of other species

  • possible ecosystem collapse

• Protecting keystone species can therefore maintain the stability of an ecosystem, which can in turn benefit other species in the ecosystem

• Examples of keystone species include:

  • elephants consume shrubs and small trees, maintaining grassland and preventing the growth of larger plants

    • This maintains food for grazers such as zebras, in turn maintaining the food supply for large predators such as lions

  • beavers build their homes in running water, slowing the water flow and creating a wetland habitat which can support many other species

  • sea otters, in the kelp forest ecosystem in the Pacific Northwest of the United States, help to control the population of sea urchins

    • Without this control, the sea urchins can overgraze vegetation and leave no food or habitats for other species

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