376 CHAPTER 15 Biodiversity and Conservation
© Yan Gluzberg/AlamyYou might think that the loss of some species from an
ecosystem would not endanger the rest of the organisms,
but this is far from true. If enough species are removed,
the entire ecosystem will change. Species richness within
a community may provide the community with resistance,
the ability to withstand environmental disturbances, nat-
ural or human events that disrupt a community, and with
resilience, the ability to recover quickly to its former state
following an environmental disturbance.Importance of Genetic Diversity
The maintenance of a broad genetic base is critical for
the long-term health and survival of each species. Con-
sider economically important crop plants. During the
20th century, plant scientists developed genetically uni-
form, high-yielding varieties of important food crops such
as wheat. However, genetic uniformity resulted in increased}>ÌÀÃÊÊÌ iÊiÛÀiÌÊUÊ}ÕÀiÊ£x°ÎÊ
The American alligator plays an integral role in its natural
ecosystem. Alligators help maintain populations of smaller
fishes by eating gar, a fish that preys on those smaller fishes.
Alligators dig underwater holes that other aquatic organisms
use during droughts when the water level is low. Their nest
mounds eventually form small islands colonized by trees and
other plants. The trees on these islands support heron and
egret populations. The alligator habitat is maintained in part
by underwater “gator trails,” which help clear out aquatic
vegetation that might eventually form a marsh.
%COSYSTEM SERVICES s 4ABLE
Ecosystem Services provided
Forests Purify air and water
Produce and maintain soil
Absorb carbon dioxide (carbon storage)
Provide wildlife habitat
Provide humans with wood and recreation
Freshwater systems Moderate water flow and mitigate floods
(rivers and streams,^ Dilute and remove pollutants
lakes, and^ Provide wildlife habitat
groundwater) Provide humans with drinking and
irrigation water, food, transportation
corridors, electricity, and recreation
Grasslands Purify air and water
Produce and maintain soil
Absorb carbon dioxide (carbon storage)
Provide wildlife habitat
Provide humans with livestock and
recreation
Coasts Provide a buffer against storms
Dilute and remove pollutants
Provide wildlife habitat, including food
and shelter for young marine species
Provide humans with food, harbors,
transportation routes, and recreationEcosystem Services and Species Richness The
living world is a complex system. Each ecosystem is com-
posed of many parts that are organized and integrated
to maintain the ecosystem’s overall performance. The
activities of all organisms are interrelated; we depend on
one another and on the physical environment, often in
subtle ways (}ÕÀiÊ£x°Î). When one species declines,
other species linked to it may either decline or increase
in number.
Ecosystems supply human societies with many envi-
ronmental benefits, or ecosystem s ervices (/>LiÊ£x°£).
Forests are not just a source of
lumber; they provide watersheds
from which we obtain fresh water,
limit the number and severity of
local floods, and reduce soil ero-
sion. Many flowering plant species
depend on insects to transfer pol-
len for reproduction. Soil dwell-
ers, from earthworms to bacteria, develop and maintain
soil fertility for plants. Bacteria and fungi perform the
crucial task of decomposition, which allows nutrients to
cycle in the ecosystem. Conservationists maintain that eco-
systems with greater species richness supply ecosystem ser-
vices better than ecosystems with lower species richness.
ecosystem
services
Environmental
benefits, such as clean
air, clean water, and
fertile soil, provided
by an ecosystem.Interpreting Data
Are any of the ecosystem services provided by all of
the listed ecosystems? If yes, identify. How does each
ecosystem contribute to pollution control?Source:Adapted from p. 527 ofClimate Change Impacts on the United States, a report of the NationalAssessment Synthesis Team, U.S. Global Change Research Program, Cambridge University Press (2001).