Environmental Science
Unit 1: Chapter 15 Notes
Species richness and biological diversity
 Species richness is the number of different species in a community.
 High species richness is associated with communities that are ecologically complex,
not isolated, geologically old and stable, and not subject to environmental stress.
 Species richness is also higher when no one species dominates the community
Biological Diversity:
 Is the number and variety of Earth’s organisms
 It consists of three components:
o Genetic diversity: Is the genetic variety within all populations of a given
species
o Species richness
o Ecosystem diversity: is the variety of interactions among organisms in natural
communities
 Ecosystems with greater species richness are better able to provide ecosystem
services:
o Environmental benefits such as clean air to breath, clean water to drink, and
fertile soil to grow crops
Endangered and Extinct Species:
 Extinction is the elimination of a species on earth
 Background extinction: a continuous, low level extinction of species, has occurred
throughout Earth’s history
 Mass extinction: many species disappear during a relatively short period of geologic
time; this has occurred only a few times in Earth’s history
 Endangered species: a species that faces threats that may cause it to become extinct
within a short period.
o A species is defined as threatened when extinction is less imminent but its
population is quite low
Humans cause species endangerment through habitat destruction, fragmentation, and
degradation:
Pollution, the spread of invasive species, and the overexploitation of biological
resources


Endemic species: are organisms that are native to or confined to a specific place.
Biodiversity hotspots: are areas that contain particularly high concentrations of
endemic species.

Invasive species: are foreign species, usually introduced by humans, that spread rapidly
in a new area where they are free of predators, parasites, or resource limitations that
may have controlled their population in their native habitat.
Conservation Biology:
 Conservation Biology: is the scientific study of how humans affect organisms and of
the development of ways to protect biological diversity
o In situ conservation: includes the establishment of parks and reserves to
preserve biological diversity in nature.
o Ex situ conservation: involves conservation of biological diversity in human –
controlled settings such as zoos and seed banks
 Restoration Ecology:
o is the study of the historical condition of human-damaged ecosystem, with
the goal of returning it as closely as possible to its former state.
Conservation Policies and Laws
 The Endangered Species Act (ESA)
o Authorizes the US Fish and Wildlife Service to protect endangered and
threatened species in the United States and abroad.
o Requires the FWS to select critical habitats and design a detailed recovery plan
for each species listed.
o Species are designated as endangered or threatened entirely on biological
grounds, not economic factors.
o The act does not compensate private property owners who suffer financial losses
related to its enforcement
 World Conservation Strategy
o Formulated by the International Union for the Conservation of Nature, The
World Wildlife Fund and the UN Environmental Program
 Seeks to conserve biological diversity worldwide
 To preserve vital ecosystem services
 To develop sustainable uses of organisms and their ecosystems