Page 132 - Environment: The Science Behind the Stories

Hypoxic (dead) zone
Human footprint (%)
0– 1
1–10
10–20
20–30
30–40
40–60

Figure 5.10 Over 500 marine dead zones have been recorded across the world. Dead zones as of
2010 (shown by dots on the map) occur mostly offshore from areas of land with the greatest human ecological
footprints (here, expressed on a scale of 0 to 100, with higher numbers indicating bigger human footprints). Data
from World Resources Institute, 2010, http://www.wri.org/project/eutrophication/map and Diaz, R., and R. Rosenberg, 2008. Spreading
dead zones and consequences for marine ecosystems. Science 321: 926–929. Reprinted with permission from AAAS.

and East rivers were nearly eliminated once sewage treat- WEIGhING ThE ISSUES
ment was improved. The Black Sea, which borders Ukraine,
Russia, Turkey, and eastern Europe, had long suffered one of ECOSySTEMS WhErE yOU LIVE Think about the area where you
the world’s worst hypoxic zones. Then in the 1990s, after the live, and briefly describe this region’s ecosystems. How do these
Soviet Union collapsed, industrial agriculture in the region systems interact? For instance, does any water pass from one to
declined drastically. With fewer fertilizers draining into it, the another? Describe the boundaries of watersheds in your region.
Black Sea began to recover, and today fisheries are reviving. If one ecosystem were greatly modified (say, if a shopping mall
However, agricultural collapse is not a strategy anyone would were built atop a wetland or amid a forest), what impacts on
choose to alleviate hypoxia. Rather, scientists are proposing nearby systems might result? (Note: If you live in a city, realize
a variety of innovative and economically acceptable ways to that urban areas can be thought of as ecosystems, too!)
reduce nutrient runoff (p. 146).

Ecosystems interact with one another Landscape ecologists study
geographic patterns
Whether we stand at a river’s mouth or peruse a satellite image,
we can conceptualize ecosystems at different scales. An eco- Because components of different ecosystems may intermix,
system can be as small as a puddle of water or as large as a ecologists often find it useful to view these systems on a larger
bay, lake, or forest. For some purposes, scientists even view geographic scale that encompasses multiple ecosystems. For
the entire biosphere as a single all-encompassing ecosystem. instance, if you are studying large mammals such as black
The term is most often used, however, to refer to systems of bears, which move seasonally from mountains to valleys or CHAPTER 5 • Envi R onm E n TA l S y STE m S A nd E C o S y STE m E C ology
moderate geographic extent that are somewhat self-contained. between mountain ranges, you had better consider the overall
For example, the tidal marshes in the Chesapeake where river landscape that includes all these areas. If you study fish such
water empties into the bay are an ecosystem, as are the sec- as salmon, which migrate between marine and freshwater eco-
tions of the bay dominated by oyster reefs. systems, you need to know how these systems interact.
Adjacent ecosystems may share components and interact In such a broad-scale approach, called landscape ecology,
extensively. For instance, a pond ecosystem is very different scientists study how landscape structure affects the abundance,
from a forest ecosystem that surrounds it, but salamanders distribution, and interaction of organisms. Landscape-level
that develop in the pond live their adult lives under logs on approaches are also helping scientists, citizens, planners, and
the forest floor until returning to the pond to breed. Rainwater policymakers to plan for sustainable regional development
that nourishes forest plants may eventually make its way to (pp. 360–368).
the pond, carrying with it nutrients from the forest’s leaf litter. For a landscape ecologist, a landscape is made up of
Likewise, rivers, tidal marshes, and open waters in estuaries a spatial array of patches. Depending on the researcher’s
all may interact, as do forests and prairie where they converge. perspective, patches may consist of ecosystems or may sim-
Areas where ecosystems meet may consist of transitional zones ply be areas of habitat for a particular organism. Patches are
called ecotones, in which elements of each ecosystem mix. spread spatially over a landscape in a mosaic. This metaphor 131

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