Environmental Engineering Reference
In-Depth Information
are able to sequester toxins and pollutants in high concentrations and then
excrete them in feces leading to local concentrations of toxic chemicals,
which further kills native life.This creates clear water zones in lakes that fos-
ter invasions by other species (Ricciardi and MacIsaac 2000). Zebra mussels
are effective because they are potent exploitative competitors (drawing
down phytoplankton) and interference competitors (production of toxics),
two abilities shared by many other invasive species (Mack et al. 2000).
Interconnected Species as Conduits of Climate Effects
Recent evidence has shown that cyclic weather phenomena also can have
long-term (decade- to multiple decade-long) impacts on species interac-
tions in and properties of ecosystems.Analysis of forty years of annual data
on a well-studied system of wolves, moose, and balsam fir (
Abies balsamea
)
on Isle Royale, Michigan (Post et al. 1999) reveals that a cyclic weather phe-
nomenon with a decadal trend in temperature, moisture, and winter snow-
fall—the North Atlantic Oscillation (NAO)—has a strong influence on
ecosystem function.
The NAO phenomenon is determined by atmospheric pressure differ-
ences off of continental North America between Iceland and the Azores in
the North Atlantic. But, the NAO has profound effects on the continent.
Whenever NAO conditions are such that they cause high snowfall levels
in northeastern North America, Isle Royale wolves become extremely ef-
ficient predators of moose that are encumbered by deep snow. Conse-
quently, wolves reduce moose populations to levels where they cause very
limited damage to balsam fir.Wolves thus play an important direct and in-
direct role in determining the compositional make-up of forest vegetation.
This role of wolves becomes diminished when NAO causes snowfall levels
to be low. In this case, moose easily evade their predators causing moose
populations to abound and inflict considerable damage to balsam fir (Post
et al. 1999).
The connection between climate and species interactions also has some
surprising implications in the face of another long-term environmental
change discussed in chapter 3: global warming. Certain environmental con-
ditions realized under NAO forcing, namely winters with anomalously
warm temperatures and little snowfall, are akin to the kind of conditions
expected from global warming due to rising levels of the greenhouse gas
CO
2
. Over the long term, climate warming can cause a cascade of effects
including declining wolf populations, rising moose populations, and declin-
