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TEMPERATE
WOODLANDS AND
GRASSLANDS
Across the Northern Hemisphere the temperate woodlands and grasslands form a broad belt encircling the globe, interrupted only by high mountains and seas. South of the equator temperate habitats are found only in isolated pockets.
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Temperate woodlands and grasslands are characteristic of middle latitude
areas, where warm sub-tropical and cool sub-polar air masses meet. This
boundary is
not fixed but moves north and south with the seasons and varies a great
deal according to the geography and relief of the region. In the lower
temperate
latitudes, the western edges of the continents tend to have hot, dry
summers and mild, damp winters, while the eastern edges are warm and humid
all
the year round with frequent summer thunderstorms. In higher latitudes
the cool
sub-polar air masses are the more dominant influence and the general
eastward movement of the air brings rain to the western margins, giving
damp, humid
conditions in both summer and winter.
The typical vegetation in humid areas is deciduous forest, but, in places
where the rainfall is high and there is little difference between summer
and winter
temperatures, evergreen forests of both coniferous and broadleaved trees
are found. Most of the tree species present are influenced by soil type
and local
relief. Pines are found on gravelly soils and rock outcrops, and alders
and willows on waterlogged soil by rivers and streams - but the main types
of tree
are oak, ash, maple and beech. The characteristic feature of deciduous
woodland is the difference between its summer and winter aspects. In the
summer the
leaves form an almost continuous canopy and little direct sunlight reaches
the ground. After the annual shedding of leaves the trees stand stark and
naked against the wintry skies and the inhabitants are faced with new conditions
of lighting and cover as well as of temperature and precipitation.
They react to this in many ways, including hibernation and migration. The
discarded leaf matter forms a thick, rich soil and contains three sources
of plant nutrients
- rotting plant material, humus and clay minerals. The humus slowly releases
nutrients into the soil and also traps essential minerals such as nitrates
and phosphates. The clay minerals store potassium, sodium and calcium -
important raw materials necessary for photosynthesis.
In areas of seasonal rainfall where the total precipitation is between
25 and 75 centimetres, grass forms the dominant vegetation. Although all
grassland
areas have an annual period of drought lasting several weeks or months
when the surface soil dries out completely, their fundamental characteristic
is
the total absence of moisture at depth in the soil. The lack of water at
this level does not impede the growth of grass, which is shallow rooted,
but prevents
trees, which have deep roots, from establishing themselves.
The temperate woodlands and grasslands probably represent the habitats
that suffered most during the Age of Man some 50 million years ago. Man
cut down
the forests to supply fuel and to provide space for agriculture and settlement.
He ploughed large tracts of grassland to plant cereals and created wide
expanses of pasture land for grazing animals. These disturbed areas did
not revert to
their natural state until a long time after man's disappearance. This interference
caused the extinction of a great number of animal genera native to the
original habitats. However, some creatures did survive, and it was from
these that the
animals of today's temperate woodland areas are descended.
The evolution of the major group of herbivorous animals
Several species of hopping rabbuck, Macrolagus spp., still survive. This evolutionary older group consists largely of woodland animals that feed on the leaves and shoots of trees.
The hopping rabbuck moves in a bounding motion (a, b, c, d) reminiscent of its rabbit ancestors, whereas the running form, Ungulagus spp., moves in a manner similar to that of the ancient deer (e, f, g, h).
The hopping rabbuck |
The development of the foot from the large springboard structure of the rabbit to the light, two-toed hoof of the rabbuck was crucial to its evolution. The three principal stages are shown here, although not to scale.
The running rabbuck |
During the period immediately before and during the Age of Man the principal
large-scale grazers and browsers were the ungulates, the hoofed mammals.
They were generally lightly built running animals, able to escape
quickly from predators
and with teeth particularly suited to cropping leaves and grasses.
The ungulates were widely used by man for his own purposes. Cows and
goats
were domesticated
for milk and meat, sheep were bred for wool and the skins of many
were used for leather. Horses and oxen were harnessed to work for man and
became the
classic beasts of burden. By the time man became extinct these animals
had become so dependent on him that they could no longer survive.
The deer, the wild ungulates of the temperate latitudes, fared little
better. Vast tracts of temperate woodlands had been destroyed to
make room for
man's cities and to provide agricultural land. This interference
with their habitat
was so intolerable and put such pressure on the deer that their numbers
fell to a level from which they never recovered. What then could
take their place?
A whole ecological niche was vacant with nothing to exploit it. Which
creature was best placed to take the initiative?
During the Age of Man a small-scale grazer was present that was so
successful it was considered to be a pest. The rabbit was so seriously
destructive
of man's crops, that man made numerous attempts to control it and
even attempted
to exterminate it. Yet no matter what actions he took he never succeeded
in getting rid of it completely. After man's disappearance, the
rabbit's versatility
and short breeding cycle enabled it to develop successfully into
a number of separate forms. The most successful, the rabbuck, Ungulagus spp., now
occupies
the niche left by the ungulates.
To begin with the rabbuck changed little from its rabbit ancestors
excepting for size. In an environment totally devoid of large, hoofed
grazing animals
the rabbit was left with no major grazing competitors and quickly
evolved to occupy the position they once held. The early rabbucks,
Macrolagus spp., retained
the hopping gait of their forebears and developed strong hind legs
for leaping. However, although jumping was ideal for moving around
the open
grasslands,
their traditional habitat, it was not the best method for the confined
spaces of the forest, and a more fundamental change had to take place.
Several species
of this earlier line still exist, but their place has largely been
taken by the running forms of rabbuck that more closely resemble
the deer of
earlier
times.
The second major development took place some ten million years after
the Age of Man. As well as developing rapidly into the size of a
deer the rabbucks
also began to evolve the typical deer leg and gait. The jumping hind
limbs and the generalized forelimbs of the rabbit grew into long-shanked
running
legs and the feet changed radically. The outer digits atrophied and
the second
and third toes grew into hoofs, strong enough to bear the animal's
weight. This was a highly satisfactory arrangement and this line
has now largely
replaced the leaping form as the dominant group.
The rabbuck has been so successful that it is found in a wide variety
of forms throughout the world - from the tundra and coniferous forests
of
the far north
to the deserts and rain forests of the tropics.
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The rise of the predator rats - the earth's principal carnivore group
The rapide, Amphimorphodus longipes, a native of the northern plains, is built for speed. Its highly flexible spine gives it the added impetus to reach speeds of over 100 kilometers per hour.
The ravene, Vulpemys ferox, is about the size of the extinct fox or wild cat and preys on small mammals and birds. It has long claws and pointed stabbing fangs.
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The janiset, Viverinus brevipes, is a long-bodied, burrowing predator, strongly resmbling the extinct stoats and weasels, and like them will swim, climb trees and tunnel underground in pursuit of its prey.
The falanx is the commonest species of predator rats found in temperate latitudes.
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In the mammal world the predators were traditionally carnivores (members
of the order carnivora) - specialized meat-eating animals with
teeth modified for stabbing, killing and tearing flesh. Their legs
were designed for leaping
and producing a turn of speed that could quickly bring their
chosen prey within
killing distance. Wolves, lions, sabre-tooths, stoats - these
were the creatures that fed on the docile herbivores and kept their
numbers
in check
both during
and before the Age of Man. However, being very specialized,
these species tended not to have a great life span. They were so sensitive
to changes
in the nature
and the populations of their prey that the average life of
a
carnivore genus was only six and a half million years. They reached their
acme just before
the Age of Man, but have since decreased in importance and
are now almost extinct except for a number of aberrant and specialized forms
found in
the coniferous
forest of the far north and in the South American Island Continent.
The place of the carnivores, as the principal mammal predators,
is now occupied by a variety of mammal groups in different
parts of
the world.
In temperate
regions the descendants of the rodents occupy this niche.
When the carnivores were at their peak, the rodents, particularly
the rats, began to acquire a taste for meat and animal waste.
The spread
of man to
all parts of the world encouraged their proliferation and
after man's demise they
continued to flourish in the refuse created by the disruption
and decay of human civilization. It is this adaptability
that has ensured
their
survival.
Despite the specialized nature of their teeth, rats were
able to live on a wide range of foods. At the front of their
mouths
they
had two
sharp
gnawing
incisors, which continued to grow throughout life to compensate
for wear and which were separated by a gap from the back
teeth. These
were equipped
with
flat surfaces for grinding vegetable matter. This is very
different from the typical carnivore dentition, which had
cutting incisors
at the front
followed
by a pair of stabbing canines and a row of shearing teeth
at the back.
As the rats expanded to occupy the niches left by the dwindling
carnivores their teeth evolved to fulfil their new role.
The gnawing incisors
developed long, stabbing points and were equipped with blades
that could cut into
and grip their prey. The gap between the incisors and the
back teeth became smaller
and the grinding molars became shearing teeth that worked
with a scissor action. To make the dentition effective the
jaw articulation
changed
from a rotary
grinding motion into a more powerful up-and-down action.
This dentition was crucial in the development of the predator
rats
and allowed
them
to radiate
into the numerous forms and varieties seen throughout the
world today.
In temperate latitudes the larger herbivores, the grazers
and browsers of the plains and forests that were one time
prey
to the wolf,
have now become the
prey of the falanx, Amphimorphodus cynomorphus, a very large
dog-like rat which hunts in packs. The evolution of this
form involved the
modification of the
limbs from the fairly generalized scampering legs of the
rat to very sophisticated
running organs with small, thickly padded feet, and long
shanks powered by strong muscles and tendons.
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Life beneath the trees of the broad-leaved forests
The tusked mole's strong limbs and powerful tusks enable it to burrow through the hardest and stoniest soils.
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The tusked mole lies in wait just the soil surface listening for sounds of movement above. When it hears its prey approaching, it springs out, using its tail as a lever, grasping the creature with its teeth.
The oakleaf toad lures its prey with its long, worm-like tongue.
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The undergrowth of a temperate wood, thick with humus and
leaf-litter and added to annually by the autumnal shedding
of deciduous
leaves, provides
a rich source
of nourishment and shelter for all sorts of animals.
The primary consumers of this material are bacteria and invertebrates,
such as worms and
slugs, which in turn provide food for many mammals
and birds. The insectivores are therefore
well represented in this habitat, not only in their
primitive role of small-insect
eater but also in a number of varieties that have adopted
a
predatory, carnivorous mode of life.
Among those that have kept to their original life style
is the testadon, Armatechinos impenetrabilis, a descendant
of
the primitive
hedgehog.
The spines of its ancestor
have been replaced by a series of hinged, armoured
plates which can be drawn together into an impregnable
sphere
when the animal
is threatened.
When rolled
up tightly it is almost impossible to grip or penetrate
and even the most
determined predator rat finds a meal from this little
animal more trouble than it is worth.
The tusked mole, Scalprodens talpiforme, comes somewhere
between the old order of insectivorous animals and
the newer carnivorous
ones.
Looking
very much
like a mole of 50 million years ago, it leads a burrowing
existence and has adopted the streamlined shape, velvety
fur and spade-like
feet of its
distant
cousin. However, here any resemblance stops. It has
two huge tusks extending from its jaws, and a paddle-shaped
tail.
As it burrows,
the animal pushes
forward with its feet in a rolling motion so that its
tusks ream out the soil in front
of it. The loose soil is pushed back by the feet and
compacted to the tunnel walls by its tail. As well
as
eating worms
and burrowing invertebrates,
it also preys on small surface-living animals, especially
mice, voles
and
lizards.
The most interesting example of a previously insectivorous
creature turned meat eater is the oakleaf toad, Grima
frondiforme. It
gets its name from
a peculiar fleshy outgrowth on its back that looks
exactly like a fallen oak
leaf. The toad lies partly buried in the leaf litter,
totally camouflaged and quite motionless except for
its round,
pink tongue which protrudes
and wriggles
about just like an earthworm. Any small animal that
approaches to investigate falls victim to the toad's
powerful jaws.
The animal's only real enemy
is the predator rat.
These two creatures, the oakleaf toad and the predator
rat, have a curious relationship. Within their blood
streams lives
a fluke
that
spends the
juvenile stage in the toad and the adult stage in the
predator rat. When the fluke approaches
adulthood it produces a dye that turns the leaf-like
outgrowth on the toad's back bright emerald green.
As this happens
in winter the
toad
becomes highly
conspicuous and is quickly eaten. In this way the fluke
is transferred into the body of the predator rat, where
it becomes
sexually
mature and breeds.
The fluke's eggs return to the toad through the predator
rat's faeces, which are eaten by beetles that are preyed
on by the
toad. As the
fluke needs to
spend a period of at least three years growing in the
toad's body before it is ready to parasitize the predator
rat,
and as the toad
is sexually
mature
at eighteen months, all toads have the opportunity
of reproducing before being exposed to predation.
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Mammals and birds of the tree-tops
The tree drummer's feet are covered with sensitive bristles that can detect the slightest movement in the bark beneath.
The tree goose or hanging bird in roosting position.
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After making a hole in tree bark with its chisel teeth, the tree drummer removes the grub with its gristle-tipped proboscis.
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Plant-eating mammals abound in the trees of the deciduous
forests, eating shoots and leaf buds in the spring
and fruits and nuts
in the autumn. The
long-bodied
squirrel, known as the chirit, Tendesciurus
rufus,
is a typical plant-eating mammal. Its peculiar
shape is
a legacy
from
an immediate ancestor
- the tree-burrowing rodent of the northern coniferous
forests. As it
spread
south into the temperate
woodlands it found that it no longer needed to
make deep tunnels in the trees to escape the harsh winter,
and
as a result the
animal's specialized
chiselling
and gnawing teeth became smaller, its dentition
reverting to be more like that of its distant ancestor the
grey squirrel. Its bodily
shape,
however,
was still
perfectly adapted to life in the trees and remained
unchanged.
Now that the animal no longer led a burrowing
existence, its legs and feet had to evolve to
suit its new
environment. Its
hind feet,
although
small
and short, became very powerful and developed
strong, gripping claws. The underside
of its short tail grew hard and scaly and with
its hind feet formed a strong three-point anchor
that
could secure
the
animal to the
tree while it reached
out to collect food.
As its squirrel ancestor's jumping ability has
completely disappeared, the animal can only move
from one tree
to another by reaching
out and grasping an extended branch. For this
reason the chirit is
found most
often in dense
thickets, where the trees are close together.
Its only enemies are birds of
prey, and it is really only vulnerable to these
when feeding in the topmost branches. It retains
the predilection
of
the burrowing squirrel
for making
nests in holes in trees and often occupies holes
and hollows excavated
by wood-boring birds.
Wood boring is the speciality of a group of insectivores
known as tree drummers, Proboscisuncus spp. These
animals, basically
shrew-like
in
form, subsist on
a diet of grubs and insects, which they gouge
out from crevices in the bark. They have masses
of
sensory bristles
on their
feet and
very large
ears, which
help them to detect the movement of grubs burrowing
in the wood. When a tree drummer finds a grub
it drives its chisel-like
teeth
into the
bark
to make
a hole big enough to enable it to remove the
grub with its trunk-like proboscis. Sometimes
the grub
becomes
skewered on its chisel
teeth and needs to be
carefully plucked off before being eaten.
It is really the birds that are the masters of
the trees. After the great reptiles became extinct,
over
a hundred
million years
ago,
the birds expanded
into an
enormous number of species. Being primarily designed
for flying, birds had access to the tree-tops
in a way that
few other animals
had, and
finding that
they were safer there than on the ground they
soon became perfectly adapted to this new habitat.
As
a result many
woodland birds
have developed feet
with curved opposable toes that are ideal for
gripping branches. In one species,
the tree goose or hanging bird, Pendavis
bidactylus,
these toes have been reduced to two. They are
permanently curved
and enable
the bird
to hang
upside down
without effort. Because of the bird's size and
weight, this attitude is much easier to maintain
over long
periods than
an upright
stance, and it
has taken
to spending long periods roosting in this position.
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The night-life of the temperate forest
The purrip bat's sensitive ears are positioned far forward at the front of its face to provide it with the largest possible sound-collecting surface.
The lutie's large rabbit-like ears betray its ancestry.
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The shrock's outward similarity to the badger is an excellent example of convergent evolution.
The largest of the owl-eyed predatory birds stands more than a metre high. |
As night falls in the temperate woodland, the sleeping
animals of the day are replaced by a completely
new set of creatures.
Nocturnal birds,
bats
and insects
- a whole array of creatures is found that
are as diverse and numerous as those of the daytime. As
dusk falls
and the moths
and night-active
flies take to
the air the insectivorous bats appear to feed
on them. Bats have proved so successful in their shape
and life
style that
in most
parts
of the
world they
have remained remarkably stable in shape and
form ever since they first appeared over a hundred million
years
ago. Save
for the development
of a more sophisticated
echolocation system, positioned at the front
of the face, and the absence
of eyes, little else has changed,
The purrip bat, Caecopterus sp., so called
because of its curious voice, is found throughout
temperate
latitudes.
Unlike the
earlier bats which
generally
navigated using high-pitched sounds, the purrip
bat uses a much wider range of frequencies
extending well into
the
audible
level,
giving
it a much
more sophisticated picture of the terrain.
Great birds of prey, which combine the characteristics
of the former eagles and owls, wing their way
silently through
the
branches, ever watching for
an unwary movement on the ground that would
denote the presence of a small animal.
Their large forward-facing eyes, acting like
wide-aperture lenses to increase the amount
of light reaching
the retina, give a three-dimensional
image
over their entire field of vision and enable
them to accurately gauge distances and hunt
in almost
pitch
darkness. Their
prey includes
the
lutie, Microlagus
mussops, a descendant of the rabbit.
The luties live in direct competition with
the ancient groups of small rodents - the mice
and
voles. In
some areas the
luties have
replaced
the rodents completely,
whereas in other parts of the woodlands, where
the conditions particularly favour them, the
rodents have remained successful.
The luties resemble
the small rodents in many respects, particularly
in size, but their rabbit ancestry
is obviously displayed in the shape of the
head and
tail. They feed mostly at night, nesting during
the day in
crevices among
tree roots
or in holes
in the ground.
Another small animal that provides food for
birds of prey is the truteal, Terebradens
tubauris,
an insectivore
related
to
the chisel-toothed
shrews of the trees.
The incisors of both the upper and lower jaws
of this animal are extended
forward to form a structure like a bird's beak,
which acts as a probe to catch worms
and burrowing insects in soft earth and leaf
litter. The truteal is completely blind and
retains
no
vestiges of
eyes. It is,
however, equipped
with a
large number of sensory whiskers and extremely
acute hearing. Its ears, which are
enormous for the size of its body, can be rolled
into trumpets by a unique set of muscles located
at their
base and then
pressed to
the
ground to
listen for sounds of burrowing.
The shrock, Melesuncus sylvatius, is a much
larger animal. Descended from insectivore stock,
it
has a size and shape
comparable to
that of the extinct
badger. It
makes nightly forays through the undergrowth
and will take any prey that it chances upon.
It has
a long snout
and
broad forepaws
with
which it digs
after
burrowing animals and excavates its own family
nest in soft soil under tree roots.
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Life in the fens and marshes
The pfrit's mouth extends forward into a long tubular snout, which carries a set of fine teeth at the tip capable of piercing the outer skin of an insect larva. Once the angler heron has baited its "fish pond" it remains close by, watching motionless from the reeds.
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The long-necked dipper Flying wing of juvenile The wing of the breeding adult is degenerate and used only for balance and in swimming under water.
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In temperate latitudes wetland areas are comparatively
isolated pockets of land found scattered widely
across the Northern
Continent, As
well as strictly
water habitats such as ponds, lakes and rivers,
they also include stretches of saltmarsh and
fenland found
near the
sea, mires
and peat bogs found
in poorly drained inland regions and areas
of regular inundation.
The conditions found throughout this range of
habitats is so diverse in terms of salinity,
oxygenation,
light penetration
and water
currents that
very nearly
every individual location has its own little
ecosystem and associated fauna, and almost
every animal group
is represented.
One of the most unusual water-living mammals
is the pfrit, Aquambulus hirsutus, a tiny insectivore
descended
from
the primitive shrews.
Its length, excluding
its tail, is less than five centimetres, which
puts it among the smallest mammals in existence.
Although
its
body is thin,
its feet
and tail
are broad and are
covered with water-repellent hairs, which spread
its weight over such a large area that it can
skate
across
the water
without breaking the
surface
tension.
It lives mainly on the larvae of mosquitoes
and midges that are
found just under the water surface. It feeds
on them by piercing their
outer cuticles
with its long, hairless snout and draining
them of their vital juices while they are still
in
the water.
In this
way the pfrit
avoids disturbing
the
water surface, which would both upset the surface
tension and frighten away its prey.
A mammal frequently found near river banks
and lake sides is the reedstilt, Harundopes
virgatus.
Its
long, slender
legs
and neck
and vertical stripes
render it almost totally invisible among reeds,
where it is frequently found fishing.
Its head and neck are most unusual. Practically
all mammals have seven neck vertebrae, but
the reedstilt
has fifteen.
In evolutionary
terms
the extra vertebrae
have appeared quite recently and result from
the fact that, in fishing, longer-necked individuals
have an
advantage over the
others. The
tooth pattern is degenerate
- the incisors, canines and molars having all
reverted
to an almost reptilian condition in which they
are all of the
same
shape. The
reedstilt uses this
combination of neck and tooth features to catch
fish by
darting out its long neck and snapping shut
its needle-pointed teeth.
Fishing skills have also been developed to
a high degree by the angler heron, Butorides
piscatorius.
This bird,
an inhabitant
of the North
American subcontinent,
creates shallow ponds at the water's edge in
the
shade of overhanging trees by scraping at the
river bottom
and constructing
shallow
dams. On the shore
nearby it accumulates a heap of droppings and
fish re¬mains to
attract beetles and flies. These it then picks
up and drops into the shallow
water to entice
the fish into its pond, where they are easily
caught.
Although there are many examples of flightless
birds, the long-necked dipper, Apterocinclus
longinuchus, a river
bird of the European
sub-continent, is the only bird that spends
part of its life with the capacity for
flight
and the
rest flightless. During its early life the
bird develops
wings in the normal way, but once it has migrated
away from its natal
nesting
site
it becomes
totally earth-bound and pursues a purely terrestrial
- aquatic existence. Its wings
now no longer necessary, lose their power and
gradually atrophy.
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INTRODUCTION BY DESMOND MORRIS 9
Cell Genetics : Natural Selection : Animal Behaviour
: Form and Development :
Food Chains
The Origins of Life : Early Living Forms : The Age of
Reptiles :
The Age of Mammals : The Age of Man
The World after Man
TEMPERATE WOODLANDS AND GRASSLANDS 36
The Rabbucks : The Predators : Creatures of the Undergrowth
:
The Tree Dwellers : Nocturnal Animals : The Wetlands
The Browsing Mammals : The Hunters and the Hunted : Tree Life
TUNDRA AND THE POLAR REGIONS 58
The Migrants : The Meaching and its Enemies : The Polar
Ocean :
The Southern Ocean : The Mountains
The Sand Dwellers : Large Desert Animals : The North American Deserts
The Grass-eaters : Giants of the Plains : The Meat-eaters
The Tree-top Canopy ; Living in the Trees : The Forest
Floor :
Living with Water : Australian Forests : The Australian Forest Undergrowth
ISLANDS AND ISLAND CONTINENTS 100
South American Forests : South American Grasslands :
The Island of Lemuria :
The Islands of Batavia : The Islands of Pacaus
The Destiny of Life
Glossary : The Tree of Life : Index : Acknowledgements
