Communities, ecosystems and adaptations

Ecology studies how living organisms interact with each other and their environment. The starting point is the levels of organisation within an ecosystem.

Levels of organisation

• Individual — a single organism, e.g. one rabbit.
• Population — all the individuals of one species in an area, e.g. all the rabbits in a field.
• Community — all the populations of all the species in an area, e.g. rabbits + grass + foxes + earthworms + ...
• Ecosystem — the community plus all the abiotic (non-living) factors of the environment, e.g. soil, water, light.

Interdependence — every species depends on others

In a community, organisms depend on each other for food, shelter, mates, seed dispersal and pollination. Remove one species and others suffer; this is called interdependence.

A stable community is one where all the species and the environmental factors are in balance, so population sizes remain roughly constant over time. Examples: tropical rainforests, mature oak woodlands, coral reefs.

Abiotic factors (non-living conditions)

Abiotic factors influence which species live where:

• Light intensity — limits photosynthesis (and so plant growth → all dependent species).
• Temperature — affects enzyme activity and so growth.
• Moisture / water availability — vital for all life.
• Soil pH and mineral content — affects which plants can grow.
• Wind intensity and direction — affects transpiration and pollen / seed dispersal.
• Carbon dioxide level — limits photosynthesis (especially in plants).
• Oxygen level — for aquatic organisms (fish in stagnant water suffer low O₂).

Biotic factors (living conditions)

Biotic factors are caused by other organisms:

• Availability of food — limits population size.
• New predators arriving — can collapse a population.
• New diseases / pathogens.
• Competition — for food, mates, light, water, space.

Competition

• Plants compete for light, water, mineral ions and space.
• Animals compete for food, mates and territory.

When two species need very similar resources, the better-adapted species often outcompetes the other locally — this is competitive exclusion.

Adaptations — how organisms thrive in their environment

Adaptations are features that help an organism survive and reproduce. There are three types:

Structural adaptations (physical features):

• Polar bear: thick fur, blubber, white camouflage, large feet for snow.
• Cactus: spines instead of leaves to reduce water loss; deep/wide roots; thick waxy stem stores water.

Behavioural adaptations (actions):

• Migration of swallows or wildebeest.
• Nocturnal habits to avoid heat (desert animals).
• Hibernation through cold winters.

Functional adaptations (physiological / biochemical):

• Camels: concentrated urine to conserve water; tolerate large body-temperature swings.
• Antifreeze proteins in Arctic fish.
• Anaerobic respiration in muscles during burst activity.

Extremophiles (extension)

Some organisms — extremophiles — live where most life cannot:

• Bacteria in volcanic vents (high temperature, high pressure).
• Bacteria in salt lakes (high salt).
• Archaea in acidic hot springs.

Links

Sets up B7.2 (food chains and sampling), B7.5/6/7 (human impact on biodiversity) and B7.8 (energy / biomass transfer).