Transcript Ecosystems - The Friary School

Ecosystems
Hot arid and semi-arid
environments
What is an ecosystem?
 Any
unit which involves the
interactions in a given area, of
organisms with the physical
environment; so that a flow of
energy leads to an exchange of the
materials between living and
nonliving parts of the system, can be
any size from cow pat to TRF
Or in simple terms
 The
living parts (plants and animals)
in a given area interacting with their
environment (soil, climate,)
What are the climatic conditions to
which the living parts of Hot arid
ecosystems have to adapt?
 Low
and unpredictable rainfall
 Low humidity
 Dry winds
 High summer temperatures
How do the soils limit plant life?
 They
are deficient in humus
 Lack essential plant nutrients (N and
Ph)
 Have a low water holding capacity
 May have hard pans (solidified
deposits of calcium carbonate) due
to evaporation
 Have a high salt concentration
What is the productivity of the
ecosystem?
(amount of new plant tissue
produced)
 Net
primary productivity is very low
30 -200 g m2 per year (rainforests =
1800g m2 per year.
Desert food webs
 Very
complex as most animals are
generalists
 Few secondary and tertiary
carnivores
 Most higher level animals are
omnivores
Biomass
 Very
low
 Food chains relatively short with just
2 or 3 trophic levels
Soils = Aridsols
 Little
leaching (loss of nutrients by
down-washing)
 Minerals ions therefore accumulate
 Causing high salinity or alkalinity
 Low biomass means organic content
is low
Two types of
Aridisols
 Solonetz
= soil
with a sodium
carbonate
horizon
 Solonchaks
soils with
saline horizon
Plant and Animal Adaptations
 Necessary
in order to survive
 Few species have been able to adapt
 Endemicism = outcome (only found
in one area e.g. 200 plant species in
Mojave desert)
 Little biodiversity
Plants
Xerophytes
Plants which have adapted their
structure to survive drought
Include
 Succulents (cacti)
 Phreatophytes (long tap roots)
1.
Behavioural adaptations
 Dormancy
for long periods become
active only when water available
 Annuals – drought evading.
Germinate, after rain and complete
the flower, reproduction, seed cycle
very quickly
Prickly pear
Prickly pear
 Cactus
 Stores
water in its body
 Waxy skin to prevent transpiration
loss
 Spines = modified leaves as well as
protection against animals
 Found Africa, Australia, Asia europe
Joshua Tree
 Rare
type of Yucca
 Native to Mojave
 Leaves are xerophytic –
– Needle shape to avoid water loss
– Leaf cells store water
– Covered with thick waxy cuticle to
reduce transpiration loss
Creosote bush
Found Sw USA
 Adaptations =
– Long lateral tap roots (absorbs distant
soil water)
– Can extract soil moisture unavailable to
other species
– High surface to volume ratio optimises
rate of heat loss and moisture retention
– Stomata on leaves close during the day
Creosote bush
Tamarisk
 Phreatophyte
(Long roots extending
to water table)
 Salt tolerant
 Native to North Africa
Desert annuals
 E.g.
Desert verbena or desert
paintbrush found in SW USA
 Germinate quickly after heavy rains
complete their life cycles very quickly
 seeds remain dormant unitl next
rains
Desert paintbrush
Desert verbena
Halophytes
 These
plants are adapted to survive
where there are high salt
concentrations (toxic to other
species)
 E.g. salt bush survives on salt pans
of USa southwest
Desert animals
 Need
to adapt to:
– Extremes of temperature
– Lack of water
 Physiological
adaptations
and behavioural
Physiological adaptations
 Such
as changes to body shape to
dissipate heat, colouration or
conserving moisture
Fennec Fox has large ears (to lose
heat) and large eyes (for nocturnal
hunting) – native of north Africa
JACK RABBIT usa
 circulates
blood through ears
Coloration
 Pale
fur, scales or feathers to reduce
heat absorption i.e. desert species
will be paler than similar species
elsewhere
Obtaining water from food
 E.g.
Turkey vultures and tortoises
get all the water they need in this
way
Excreting wastes as uric acid
therefore losing little water this way
 Common
to birds and reptiles
Kangaroo rats
 Recycling
their own
urine and have
special nasal
cavities to reduce
water loss when
breathing
Behavioural adaptations
 Migration
during the hottest season
(humming birds)
 Estivation during hottest season ( a
kind of hibernation) round tailed
ground squirrel)
Being active when it is cool
 Crepuscular
– being active at dawn
and dusk – rattle snakes and gila
monsters (lizards)
 Nocturnal – bats, most rodents, and
larger animals – they often burrow
beneath the surface
animal adaptations
Task
 Complete
page 152 Q1,2 and 3