Environmental Engineering Reference
In-Depth Information
In searching for an explanation, the researchers noticed that the shore-
line was not an impermeable boundary. Rather, there was a considerable
abundance of nutrient rich resources in the form of algae and drowned an-
imal carcasses that washed up onto the shore from oceanic drift.This re-
source input was sufficient to sustain insect species that consumed the algae
and scavenged the decomposing carcasses, species that might not be as
highly abundant if they had to rely solely on plant production on the islands
themselves. In effect, the island economies received a subsidy from the ocean
that eventually supported very high abundances of top predators. Moreover,
the smaller islands were more productive because of the physical proper-
ties of their boundaries. Smaller islands have a higher perimeter to area ratio.
That is the smaller islands have more shoreline relative to their overall area
than do larger islands.This property allows consumers from all over the small
island to access the subsidy. By contrast, individuals living in the middle of
the larger islands have a lower likelihood of encountering the subsidy.The
subsidies also influenced the dynamics of the island ecosystem.The abnor-
mally high abundance of spiders led
to an unusually high capacity to con-
trol the abundance on the island's her-
bivorous insects, thereby lessening the
insect damage to plants.Thus, the ef-
fects of the subsidy reverberate through
the whole island system. Shut the sub-
sidy off and the ecosystem could col-
lapse to a comparatively barren desert.
The lesson from this study is that the two very different kinds of eco-
systems can be inextricably linked through resource flows across their
boundaries.The amount of subsidy provided and its attendant effects de-
pend very closely on the dynamics of species interactions within each
ecosystem.That is, if marine production is altered by environmental impacts
or from species imbalances in the marine food chain, then the amount of
subsidy to the island can become altered causing a cascade of effects on the
island. It is the broader landscape and the ebb and flow of resources across
ecosystem boundaries on that landscape that drives dynamics.
The effects of the shoreline subsidy
reverberate through the whole
island system. Shut the subsidy off
and the ecosystem could collapse
to a comparatively barren desert.
Species Link Ecosystems on a Continental Scale
The effects of subsidies can have more far-reaching effects by linking ecosys-
tems in vastly different parts of a continent. Agricultural production in the
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