Page 111 - Environment: The Science Behind the Stories

WEIGhING thE ISSUES Earth’s landscape altered by human impact, many communities
and ecosystems are severely degraded. Because ecological sys-
arE INvaSIvE SPECIES aLL Bad? Some ethicists question tems support our civilization and all of life, when degraded sys-
the notion that all invasive species should automatically be tems cease to function, our health and well-being are threatened.
considered bad. If we introduce a non-native species to a com- This realization has given rise to the science of restoration
munity and it greatly modifies the community, do you think that ecology. Restoration ecologists research the historical conditions
is a bad thing? What if it drives another species extinct? What of ecological communities as they existed before our industrial-
if the invasive species arrived on its own, rather than through ized civilization altered them. They then try to devise ways to
human intervention? What if it provides economic services to restore altered areas to an earlier condition. In some cases, the
our society, as the European honeybee does? What ethical intent is primarily to restore the functionality of the system—to
standard(s) (p. 154) would you apply to determine whether we reestablish a wetland’s ability to filter pollutants and recharge
should reject or welcome an invasive species?
groundwater, for example, or a forest’s ability to cleanse the air,
build soil, and provide habitat for wildlife. In other cases, the
aim is to return a community to its natural “presettlement” con-
We can respond to invasive species through dition. Either way, the science of restoration ecology informs
control, eradication, or prevention the practice of ecological restoration, the actual on-the-ground
efforts to carry out these visions and restore communities.
Scientific research and media attention to zebra and quagga Many ecological restoration efforts are underway today.
mussels helped put invasive species on the map as a major For instance, nearly all the tallgrass prairie in the United States
environmental and economic issue. In 1990 the U.S. Congress was converted to agriculture in the 19th century. Now, people
passed legislation that led to the National Invasive Species Act are restoring patches of prairie by planting native prairie vege-
of 1996. Among other things, this law directed the Coast Guard tation, weeding out invaders and competitors, and introducing
to ensure that ships dump their freshwater ballast at sea and controlled fire to mimic the fires that historically maintained
exchange it with salt water before entering the Great Lakes. this community (Figure 4.16). The region outside Chicago, Illi-
Since then, funding has become available for the control nois, boasts several of the largest prairie restoration projects
and eradication of invasive species. Eradication (total elimi- so far, including a 184-ha (455-acre) area inside the massive
nation of the invasive population) is difficult, so managers ring of the Fermilab nuclear accelerator in Batavia.
instead usually aim to control these populations; that is, The world’s largest restoration project is the ongoing
to limit their growth, spread, and impact. Managers have effort to restore parts of the Florida Everglades, a 7500-km
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tried to control zebra mussels by removing them manually; (4700-mi ) ecosystem of marshes and seasonally flooded
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applying toxic chemicals; drying them out; depriving them grasslands. This formerly vast wetland system has been
of oxygen; introducing predators and diseases; and stressing drying out for decades because the water that feeds it has
them with heat, sound, electricity, carbon dioxide, and ultra- been managed for flood control and overdrawn for irriga-
violet light. However, most of these are localized and short- tion and development. Economically important fisheries
term fixes unable to make a dent in the immense populations have suffered greatly as a result, and the region’s famed
at large in the environment. With one invasive species after populations of wading birds have dropped by 90–95%.
another, managers are finding that control and eradication The 30-year, $7.8-billion restoration project intends to
measures are so difficult and expensive that trying to prevent restore natural water flow by undoing the damming and
invasions in the first place (through strategies such as ballast diversions of 1600 km (1000 mi) of canals, 1150 km (720
water regulations) represents a better investment.
To prevent invasions, it helps to be able to predict where
a given species might spread. By analyzing the biology of the
organism, scientists can try to model the environmental con- Figure 4.16 Ecological restoration is being used to restore
ditions in which it will thrive. In 2007, researchers applied prairies. Here ecologists from the Midewin National Tallgrass
knowledge of how zebra and quagga mussels use calcium Prairie inspect native grasses in a prairie restoration area on the site
in water to create their shells to predict where the mussels of the former Joliet Arsenal in Illinois.
might do best. The researchers mapped low-risk and high-risk
regions across North America, and these mostly conformed
to the areas of actual spread. A remaining question is how
quagga mussels may differ from zebra mussels. As Figure
4.15b shows, quagga mussels have leapfrogged zebra mussels
by spreading into some western states, and no one knows why
they have so far been more successful in the West.

Altered communities can be restored
Invasive species are adding to the tremendous transformations
that humans have already forced on ecological systems through
habitat alteration, deforestation, pollution, climate change, the
110 hunting of keystone species, and other activities. With so much of

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