Factors affecting survival: Abiotic
Habitat and environment
An organism's habitat is the place where it lives. For example, swamps,
deserts, the bark of a tree, cities and rivers are all habitats.
The environment is the set of conditions that exist within the habitat
which affect the organism's survival.
Organisms thrive in habitats where they are best suited to the environmental
conditions. They have features (adaptations) which have evolved over
a long period of time which help them to survive under those conditions.
Changes in environmental factors (either natural or man-made) will affect
the ability of some species to survive and therefore alter relationships
within the food chains.
Abiotic (non-living) environmental factors
- Water availability
Water is essential for life. This can be a major problem for land
organisms! Water availability varies with climate, including total
annual rainfall, frequency of rainfall, and relative humidity, as
well as dehydration by winds and high temperatures. Water dictates
which plants will grow and hence the number and type of consumers
which can be supported. Desert plants have adaptations such as reduced
leaf size, large root systems, waxy covers to reflect excess sunlight,
internal water storage areas (e.g. cacti), and fewer stomata to reduce
dehydration. Desert animals are often diurnal (active at dawn and
dusk), burrow underground, produce concentrated urine, and have a
reduced surface area to minimise water loss (see Adaptations). Ice
and snow, though states of water, often reduce the amount of useable
water available to organisms.
- Sunlight
The total amount of production of food by plants (photosynthesis)
depends on the intensity of sunlight and the relative length of day
and night.. These factors change both with the season and geographical
location. sunlight varies within layers of a natural community (e.g.
very dim on the forest floor), and colour of light can vary at depths
in the sea due to differential absorption of some wavelengths. Pollution,
cloud cover and smoke from forest burning (as has occurred recently
in Indonesia) can drastically reduce light intensity.
- Temperature range
This varies with latitude (distance from the Equator), altitude (height
above sea-level) and the continental effect (distance from the stabilising
influence of the sea). Water habitats are much less variable in temperature
than land. Endothermic (warm-blooded) animals can survive better with
temperature variation than ectothermic (cold-blooded) animals can.(see
Needs of living things)
- Sub-stratum or soil
Soil texture (sandy, clay, rock), drainage, mineral content, level
of acidity (pH) and organic content all influence plant growth and
microfauna (worms, helpful bacteria and so on) as well as burrowing
or ground-nesting animals. In water habitats, the salt content can
vary (salt, brackish, estuarine or fresh) as can the stability (currents,
waves, tides).
- Geographical terrain
Whether the area is flat, undulating, hilly or mountainous,
will influence theorganisms present. The aspect (position relative
to north) will affect exposure to winds, Sun and rain. Caves
and rock overhangs provide shelter from weather and predators.
Altitude will affect temperature, and oxygen availability.
- Oxygen availability
This is not generally a problem on land although oxygen levels
are reduced at high altitudes. In water, however, limited oxygen
availability may reduce survival. Oxygen is produced by water
plants, but its solubility in water is greatly reduced by increased
temperature, and reduced flow of the water (often caused by
factories using streams
for water cooling of machines). A dimly lit, still pond does
not support much life at all.
- Exposure
Tides, waves and winds all pose problems for organisms that
depend on attachment to rocks. Deserts are very exposed environments
affected greatly by winds because the lack of trees means little
shelte
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