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 the organisms 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
shelter.
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