Transcript Deserts - flora and fauna

Desert environments in Namibia
The flora and fauna of Namibia
Key Question 1.1 What are the characteristics of a desert environment that make it
extreme?
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The climatic, biotic and soil characteristics of a desert environment.
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The links between climate, biotic and soil characteristics.
Key Question 1.2 How is human activity causing pressures on the desert
environment?
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The threats that are posed by
(i)
population growth;
(ii)
mineral exploitation;
(iii)
farming;
(iv)
tourism.
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The positive and negative outcomes of human activity.
Key Question 1.3 What are the strategies that can be used to manage human
activity in deserts?
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Strategies that attempt to
(i)
conserve the desert environment;
(ii)
alleviate the impacts of human activity;
(iii)
control the use of the desert environment
(iv)
monitor the impacts of human activity.
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The role of local, national and international groups in the
management of the desert environment.
The biotic
environment
Vegetation zones
The major vegetation zones in Namibia are arid or
semi-arid. Along the coast vegetation is very sparse.
Deeper into the interior hardy succulents appear
followed by stunted acacias. Desert scrub is a
feature of the south with the quivertree growing
around Keetmanshoop. Over the Kalahari the scrub
make way for a combination of scattered trees with
bunch grasses (savanna). In the north deciduous
trees are more important.
Therophytes are annual plants which
regenerate from seed. These are very
common
Cryptophytes are adapted to extremes
of heat or cold and persist because they
regenerate from buds, bulbs or
rhizomes that are completely buried in
the soil.
Hemicryptophytes are typical of moist
temperate regions. They die back at the
end of the growing season and buds are
protected by the withered leaves and
soil.
Chamaephytes include small shrubs and
herbs that grow close to the ground.
Snow offers some protection during
cold winter months.
Phanerophytes are trees and small
shrubs. They carry buds on the tips of
branches. They are characteristic of hot
or mild moist environments where
plants are not subject to drought or
frost.
Types of plants found
in the desert
Factors influencing desert ecosystems
Small
leaved
Types of plants
Xerophytes plants which can cope with conditions of drought
Phreatophytes plants which have long tap roots to exploit water
resources deep underground
Halophytes plants which can cope with saline soils
Therophytes plants which are annual and grow from seed in the
ground, therefore are able to exploit rain straightaway
Characteristic plant life forms in
deserts
Succulent perennials – very specialised plants but which typify many
desert landscapes
Non-succulent perennials – these represent most of the plants in the
Namib Desert
Annuals – plants which exploit the little rain the desert gets by
growing from seed very quickly and having a quick life cycle
Succulent
perennials
Clockwise from top
Welwitschia mirabilis
Aloe dichomata (Kokerboom tree)
Euphorbia virosa
Euphorbia damarana
Pachypodium namaquanum
(Halfmens)
Pachypodium lealii (Cobas tree)
Aloe namibensis
Aloe pillansii Bastard Quiver
Tree
Moringa ovalifolia
Tylecodon paniculatus
Botterboom
Specialised succulents
Lithops ruschiorum looks like a rock camouflage
Conophytum stephanii has hairy
leaves to collect droplets of fog.
Conophytum
wettsteinii
Conophytum pupicalyx
also collects droplets of
fog
Non-succulent perennials
Grasses, e.g. Stipagrostis
Bushes, e.g. Nara melon
(Acanthosicyos horridus)
Trees, e.g.
Camelthorn
(Acacia erioloba)
Suaedia articulata
occurs as a low
lying shrub on the
salt pan at Etosha
Sporobolus spicatus
Commiphora saxicola
Commiphora
dinteri
Annuals
Gazania
Nineawn pappusgrass
Enneapogon desvauxii
Lovegrass - Eragrostis annulata
Sarcocaulon
patersonii
Cleome
hirta
Adaptations of plants to arid
environments
Drought escaping – therophytes (annual plants) which
grow from seed whenever rain falls. Although seed do
not rot easily in the desert environment many may be
lost to predators. Some plants display amphicarpy by
bearing seeds both above and below ground.
Adaptations of plants to arid
environments
Stipagrostis
obtusa
Stipagrostis sabulicola – Dune grass
Drought evading – perennial plants which live above
surface continually but wither during times of
drought and grow again when rain falls. Roots are
shallow but are able to remain dormant when water
is not available. In Namibia many of these are dune
grasses of the Stipagrostis family.
Adaptations of plants to arid
environments
Drought enduring – plants which can endure
drought by deep roots(up to 50m deep),
which grow even during periods of extreme
drought, which have small shiny leaves,
where the leaves can change direction in
order to face or avoid the sun (heliotropy),
and where stomata within the leaves are
rolled up to reduce transpiration
Acacia erioloba – the camelthorn has roots
up to 50m deep
Adaptations of plants to arid
environments
Drought resisting – plants
which have learnt to use
very little water, i.e.
succulent plants where
leaves are reduced to
spines, surfaces are
heavily waxed to reduce
water loss, and where
water is stored within a
thick trunk to be used
slowly
Many plants show allelopathy, i.e.
they are poisonous either to
herbivores or to the soil.
Allelopathy
There is an intense struggle for
resources in the desert – not so
much for light as in the tropical rain
forest, but for nutrients, space and
water.
The sap of Euphorbia
virosa is used by
bushmen to tip poison
arrows.
Euphorbia damarana leaves toxins in the
soil around it which create circular patches
where no other plants can grow and
compete for water.
Geigeria africana (above)
and Cotyledon orbiculata
(left) cause the disease
vermeersickte in cattle and
sheep if they eat the plant.
The animals become
paralysed.
Many flowers open at
night to attract moths.
Others open at midday for
bees to pollinate the plant.
Pollination
Hoodia has vibratile
hairs which move even
when there is no wind,
attracting flies. Its scent
and colour is that of
rotting meat so that
flies do the pollination.
Several plants, such as Hoodia
(right) and Euphorbia
Fenestraria is a plant which hides in the sand leaving only
ephedroides (below) are brown
the top of its leaves showing, which are transparent.
in colour as a protection against
the high radiation
Colour
Animal strategies to obtain water
The meerkat and African
ground squirrel stay
beneath the sand in
burrows during the day.
Tenebrionid beetles such as the species
Onymacris unguicularis collect water
from the fog by standing on their hind
legs and facing the moist wind.
The shovelsnouted lizard
The sun spider is
Meroles anchietae
a solifuge. It
buries itself in the
avoids the hot
sand where the
ground by
temperature is a
jumping off the
few degrees cooler ground every few
seconds.
The gemsbok or oryx saves water
by having solid urine. It pants to
lose heat and has a short shiny
coat. These are all characteristics of
a hyperthermic animal, i.e. one
which can cope with high
temperatures.
Some animals display aestivation (the
opposite of hibernation) and sleep for
the hot summer months.
Fauna - herbivores
Most animals are
nocturnal to avoid
the heat of the
day.
Animals are prepared to
migrate many miles in search of
water, e.g. the desert adapted
elephant.
Fauna - carnivores
Desert adapted lion can travel many
miles in search of prey.
The bat eared fox and caracal
have large ears which lose
heat rapidly.
The sand viper Bitis
peringueyi gets the
water it needs from
its prey.