Download Evolution Svarlbad Reindeer Voice Over Until almost exterminated

Evolution
Svarlbad Reindeer
Voice Over
Until almost exterminated by humans a few centuries ago, wolves and cat-like predators such
as lynx, ranged all over the northern forest, preying upon the herbivores. In Europe and
Canada wolves followed reindeer herds killing by chasing the pray to exhaustion. The very
young, the old, the sick and any others that could not keep up with the herds often feel prey.
Norwegian reindeer have long heads with the eyes far back, enabling them to spot intruders
even when grazing in deep snow holes. Herding provides some protection from predation,
particularly for the young. But there are snags. The available grazing is soon exhausted by
so many hungry mouths, and disease and parasites are easily transmitted. These grubs are
the larvae of the warble fly. The fly lays eggs on the reindeer’s skin. They hatch into larvae
which burrow through the skin. When the reindeer live close together in herds, parasites are
easily transmitted form host to host. Rangifer is the only genus of deer in which females as
well as males have antlers. Those of big, old males grow larger and are more elaborate,
reaching maximum size in the mating season when they are important for display and
fighting. Like the peacock’s tail, antlers are a high cost feature in an evolutionary sense.
Females rarely fight but they challenge each other for access to grazing; the one with the
largest antlers usually wins. In all deer except reindeer, the fur of newborn calves is mottled
and camouflages them as they lie hidden in undergrowth. Reindeer camouflage is more
adapted to deceiving the predator’s eye in winter where there’s nowhere to hide. The calves
are born in late spring. They can stand within an hour of birth, and at one day old they can
run as fast as a person. One population of reindeer has adapted to even harsher conditions,
and is the only large terrestrial mammal to spend its entire lifecycle above seventy-five
degrees latitude. Some time during the last forty thousand years some reindeer, probably
from Northern Greenland or Canada, colonised Svalbard. The climate must have already
been warm enough for there to be enough food to sustain them. Due to the influence of warm
ocean currents the vegetation is quite different here than in the continental areas of similar
latitude. Despite a growing season of only six to ten weeks a year a wide variety of plants
flourish, for example, Dryas octipatina with its tiny leaves; the Arctic Bell Heather, Cassiope
tetragona; the Svalbard poppy, Papaver dahlianum; and a plant parasitic on the roots of
others, the Pedicularis species, a member of figwort family. These examples are just four of
the 164 vascular plant species found on Svalbard. This land sat image shows the extent of
permanent ice and snow cover on Svalbard, but on lowlands near the coast the snow melts
and plants can grow and flower from late June to early October. However, the soil is subject
to erosion from melting snow, so even in July vegetation is sparse, except in bogs. Many sea
birds like these little auks nest on cliffs around the islands, bringing nutrients in their excreta.
Nutrients from the sea deposited on the uplands are washed down to the valleys when the
snow melts, so soil around long established sea bird colonies is greatly enriched, supporting
lush, green vegetation. This shows that it is a poor soil, more than the intense cold or lack of
light that limits plant growth. In summer Svalbard reindeer spend most of the time foraging.
They take many small bites of the tough plants. Their digestion is even more efficient than
that of the mainland reindeer. Apart from each other the reindeer have few competitors, very
few other kinds of animals have reached these islands and adapted successfully to the Arctic
conditions. There are no large terrestrial predators on Svalbard. Without any natural
predators the reindeer live in singly or in small groups, not in large herds. Consequently they
have very few parasites, certainly no warble flies. The reindeer don’t exhaust the food
supplies here quickly and they don’t migrate. Individuals stay in the same area for months at
a time. On average Svalbard reindeer live longer than mainland reindeer. However, this
elderly male is getting pretty thin now and he may not survive until the summer. Starvation,
not predation, is the main cause of death here. What they eat depends upon the snow cover.
The reindeer can most easily reach the plants on ridges where the wind has blown most of
the snow away, so it’s shallow enough for them to dig through. And what do they find? Often
nothing, or if they’re lucky some tiny, desiccated Dryas leaves, but just look how small a
mouthful of green leaves would be. No wonder Svalbard reindeer have to spend most of the
time eating. The main difference between Norwegian reindeer and the Svalbard sub-species
is that the former feed on lichens in the wintertime, while here the reindeer are adapted to
digest vascular plants of very poor quality. Their guts are relatively large and contain different
populations of micro-organisms that can digest this diet. Norwegian reindeer would starve to
death if fed only on this poor quality forage because they couldn’t digest it. At the end of the
winter food is difficult to obtain on Svalbard. Periods of thaw and refreezing forms layers of
hard ice between the wind-blown snows. Digging down to the frozen plants becomes
increasingly hard work and eventually impossible. Ironically a warm winter means snow
melting and icing over the feeding grounds. It can cause severe hardship. The only hope is
to wait for the spring melt. Fortunately the Svalbard reindeer are adapted to cope with this
climate. Twenty-five percent or more of the body mass can be adipose tissue, a tissue that
stores energy-rich fat and releases it as required. Svalbard reindeer fatten during the
summer and early winter, then deplete their reserves when food becomes scarce or
inaccessible. Females usually fatten more than the males and become very fat when food is
plentiful. Most of the females are pregnant during the winter and they need to sustain their
growing foetus as well as themselves. Under such conditions the fat reserves may not be
enough, and some old animals and yearling calves may die towards the end of the winter.
The pregnant females may reabsorb their foetus rather than give birth to a calf that is unlike to
survive. Food is also scarce at the end of the winter for mainland reindeer. Becoming fat in
the autumn would probably be adaptive for them too, but the need to run far and fast to
escape from the wolves may be what keeps them slim. They also need longer legs to dig
through the deeper, more powdery snow on the mainland. Note how lean the mainland
reindeer is in comparison. For Svalbard reindeer the requirement to fatten up for the polar
winter explains their anatomy too. In comparison with the mainland forms they have squat
bodies and relatively short legs. Even when alarmed they run only about a hundred metres
and their gallop is slow and inefficient. Clearly, this would be ineffective against serious
predators. Occasionally some animals, particularly young, inexperienced males, exhibit a
curious behaviour when disturbed. This spotting behaviour may persuade predators to
pursue a smaller, weaker member of the herd. Since there are no predators it would not be
much use on Svalbard, but it probably doesn’t do much harm either, and has not yet been
eliminated from the behavioural repertoire.