Habitats and environments: Macro
Certain habitats of the world have specific major environmental features
which are worthy of study so that we can analyse the adaptations of
the organisms living there.
Deserts
Deserts cover about a third of the Earth's land
area. Cold deserts are usually found at high altitudes, and hot deserts
in subtropical zones, but both exhibit extremes of temperature and an
absence of permanent water. Insects, reptiles, some birds and small
mammals are the most common animals. Adaptations to prevent water loss
include waterproof exteriors, reduced surface area to minimise evaporation,
diurnal activity (dawn and dusk), burrowing behaviour, efficient kidneys
to concentrate urine, ability to store water (e.g. desert frog), short
reproductive life cycle and the ability to become dormant during dry
periods (e.g. brine shrimp).
Desert plants have adaptations including extensive root systems,
shiny waxy leaf cover, fewer stomata to reduce transpiration (see Plant
systems A: Transport and support), thin spiky leaves to reduce surface
area for water loss and drought resistant seeds.
Polar regions
Polar regions are extremely cold with Antarctic winters recording minimum
temperatures of -80°C. Almost no vegetation grows due to the extreme
cold and the six months of darkness in winter, so most food chains are
sea-based. Mammal adaptations for keeping warm include fat layers, thick
fur and winter migration behaviour. Swimming ability is essential to
gather food and travel between ice masses.
Freshwater pond
A freshwater pond is a relatively stable habitat with light and
water abundant for plant growth which in turn provides both food and
oxygen for animal life. The water contains dissolved nutrients for plant
uptake, and oxygen in solution is available to all organisms for respiration.
The water temperature remains fairly constant relative to the widely-fluctuating
surrounding air temperature.
The majority of photosynthesis is due to microscopic producers
(phytoplankton) in the water. Other plants are usually present in distinct
zones. The emergent plants of the water's edge give way to free-floating
and deep-rooted plants as well as submerged plants which use the sunlight
filtering down to the bottom. Food chains include microscopic consumers
(zooplankton), small crustaceans, insects (nymphs, larvae as well as
adults), small molluscs (snails and mussels), fish and birds. In the
muddy bottom, worms, fungi and bacteria are found, which decompose the
remains of plants and animals.
Marine habitats
Marine habitats include the open sea (approximately 80% of the
world's surface), tidal estuaries and mangrove swamps, the coastal intertidal
rockpools and the sandy beaches.
The ocean food chains are based on microscopic plants and animals
(plankton) that drift in the surface waters. Light intensity and temperature
decrease with depth but bottom-dwelling consumers can still survive
on other animals or decomposing matter.
Water provides buoyancy (uplift) supporting the body weight of even
the world's largest organisms such as whales, which on land would collapse
under their own weight. Due to the great size of the ocean, water temperature
fluctuates very little except on the shore line and in rock pools.
Intertidal rockpools
Intertidal rockpools are exposed to the force of breaking waves
as well as daily variations in water availability, temperature and salt
concentrations caused by the movement of the tides. Many animals have
adaptations such as a hard shell and tight muscular foot allowing them
to cling tightly to the rocks preventing dislodgment and drying out.
Plants are also often firmly attached to rocks. Some have a structure
called a "holdfast".
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