Geoscience Reference
In-Depth Information
in height in the High Arctic. It provides vital grazing for
herbivores such as caribou, hares, musk ox and ptarmigan.
Photo: Ken Atkinson
(Silene acaulis) in the arctic. In laboratory trials, this species
has survived temperatures of -80°C!
Photo: Ken Atkinson
copepods and bivalves make up the herbivore compart-
ments of the food web. The keystone species in the
ecosystem is Arctic cod, with 125,000 t being consumed
by marine mammals and 23,000 t by sea birds annually.
This fish consumes micro-sized animals and concentrates
the energy into larger 'packets' which can be eaten
efficiently by its predators, i.e. seals, whales and birds. In
Figure 24.20
the links in the food web which relate to
Arctic cod are highlighted. The ecological integrity of this
ecosystem is dependent upon this one keystone species,
and the fragility of Arctic marine ecosystems is caused by
energy flow being channelled through a restricted number
of species, and overfishing of arctic cod, in this case,
would lead to the collapse of the entire marine ecosystem.
Many arctic species are locally rare, and live in small
populations, e.g. the polar bear. As a result, such eco-
systems have a much lower constancy than temperate
ecosystems; their low numbers are more susceptible to
species loss, with the smaller populations being prone to
positive feedback loops of inbreeding and genetic drift.
This is not true of all arctic mammal populations, and
caribou and walrus, in contrast, herd in large numbers.
This, in theory, makes them vulnerable to a mega-disaster
like an ice-storm or an oil-spill, but realistically the
large population allows rapid recovery after small and
moderate impacts.
Unpredictable short-term variations in climate and
topographical processes lead to innately unstable eco-
systems in polar and alpine regions. Cold summers in
the arctic may not allow birds to breed successfully, so one
entire year's increase can be lost (
Plate 24.18
).
An avalan-
che in alpine regions can entirely remove, or severely
reduce, biological populations, and the impact can
penetrate throughout the ecosystem by trophic-cascade
