Adaptations, Interdependence and Competition¶

Part of Ecology.

Ecology begins by asking why organisms are found where they are. The answer depends on both environmental conditions and the relationships between different organisms sharing the same habitat.

What You Need to Learn¶

Connect individual organisms to populations, communities and their physical surroundings. Explain how resources, other species and environmental conditions affect survival and population size. Use examples and ecological data to link adaptations to their functions and to predict the consequences of competition or the loss of a species.

Organisation within Ecosystems¶

It helps to understand the levels of organisation before exploring how organisms interact:

Ecosystems are extremely complex. Every species is connected to others through feeding relationships, competition, and symbiosis. Removing one species can have knock-on effects throughout the whole community — this is called interdependence.

Abiotic Factors¶

Abiotic factors are the non-living physical and chemical components of an environment. They determine which organisms can survive in a habitat.

If an abiotic factor changes (e.g. a river becomes more acidic due to acid rain), populations of sensitive species decline while tolerant species may increase.

Biotic Factors¶

Biotic factors are the living components of an environment — the effects other organisms have on a population.

Examples of biotic disruption:¶

• Grey squirrels introduced to Britain outcompeted the native red squirrel, driving it to near-extinction in England.
• Cane toads introduced to Australia to control pests instead outcompeted native species and became a major ecological problem.

Adaptations¶

An adaptation is an inherited feature that improves an organism's ability to survive and reproduce in its particular environment. Adaptations arise through natural selection over many generations.

There are three categories:

Structural (morphological) adaptations¶

Physical features of an organism's body:

• Camel: wide flat feet (spread weight on sand), fat stored in the hump (not spread over body, so heat can escape), long eyelashes (protect against sand).
• Arctic fox: thick white fur (insulation and camouflage), small ears (reduce heat loss), short legs (reduce surface area).
• Cactus: thick fleshy stem (stores water), spines instead of leaves (reduce surface area for water loss, deter predators), shallow wide root network (quickly absorbs rain).
• Polar bear: thick layer of blubber (insulation), white fur (camouflage in snow), large paws (distribute weight on ice, paddle when swimming).

Behavioural adaptations¶

Changes in behaviour that improve survival:

• Courtship displays attract mates of the same species (peacock tail, birdsong).
• Pack hunting (wolves) increases success at catching prey.
• Migration allows animals to avoid cold seasons and track food.
• Dormancy — some plants remain dormant during drought and germinate when rain falls.
• Venus flytrap — closes its leaves to trap insects (an unusual plant behaviour to supplement nutrient intake in poor soils).

Physiological (functional) adaptations¶

Internal biochemical or metabolic features:

• Some animals produce venom or toxins (e.g. poison dart frogs, spitting cobra) to deter predators or immobilise prey.
• Some plants produce toxic chemicals (e.g. water hemlock) making them unpalatable or lethal to herbivores.
• Some bacteria have inherited features giving antibiotic resistance.
• Camels produce concentrated urine, reducing water loss.
• Animals in cold environments may have antifreeze proteins in their blood.

Extremophiles¶

Some organisms are adapted to survive in extreme environments that would kill most life. These are called extremophiles:

• Bacteria living in deep-sea hydrothermal vents (extremely high temperatures and pressures).
• Halophytes — plants adapted to very salty soils (e.g. mangroves, samphire).
• Acidophiles — microorganisms thriving in very acidic conditions.

Interdependence¶

In a stable community, species depend on one another. This is called interdependence. Relationships include:

Mutualism — both organisms benefit:

• Bees and flowers: bees receive nectar (food); flowers receive pollination service.
• Oxpecker birds and buffalo: birds eat ticks from the buffalo's skin (food); buffalo gets parasite removal.
• Fruit-eating birds and plants: birds obtain food while dispersing the plant’s seeds.

Parasitism — one organism (the parasite) benefits at the expense of the other (the host):

• Fleas on a dog — flea feeds on blood; dog experiences discomfort and potential disease.
• Tapeworms in a human digestive system — absorb digested nutrients from the host.
• Mistletoe growing on a tree — mistletoe takes water and mineral salts from the host tree.

Predation — one organism (predator) kills and eats another (prey). Predator-prey populations are linked:

• When prey is abundant → predator population increases (more food).
• More predators → prey population falls.
• Less prey → predator population falls.
• Fewer predators → prey population recovers. This produces a cyclical oscillation in both populations (e.g. snowshoe hare and lynx in Canada).

A stable community has population sizes that stay fairly constant overall, although seasonal changes and predator–prey cycles can still occur. Species depend on others for shelter and seed dispersal as well as food and pollination. In a population graph, compare the timing of rises and falls: a predator increase often follows a prey increase because reproduction takes time. Use the pattern and the habitat context together; a correlation alone does not identify the cause.

Competition¶

Organisms compete when they need the same limited resource. Competition reduces the survival chances of less well-adapted individuals.

Intraspecific competition — between individuals of the same species:

• Most intense because they need exactly the same resources.
• Limits population growth when numbers rise too high.

Interspecific competition — between individuals of different species:

• If two species occupy the same niche, one tends to outcompete the other — competitive exclusion.
• Red and grey squirrels compete for the same food and nesting trees in British woodlands.

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

Common Confusions¶

• Abiotic vs biotic factors: Abiotic factors are non-living (temperature, light, pH); biotic factors are living (predators, competitors, disease). Students sometimes say "climate" is a biotic factor — it is not.
• Adaptation vs acclimatisation: Adaptations are inherited (genetic) changes that evolved over many generations. Acclimatisation is a physiological adjustment to changed conditions within an organism’s lifetime, such as adjusting to a different climate. Do not call short-term changes "adaptations."
• Population vs community: A population is one species; a community is multiple species. A deer population is one species; the community of a woodland includes deer, squirrels, owls, oak trees and everything else living there.
• Mutualism vs parasitism: In mutualism, both species benefit. In parasitism, one benefits and the other is harmed. A common error is saying "bees and flowers are parasites" — they are not; both benefit.
• Intraspecific vs interspecific competition: Intra = within a species (same animals competing with each other). Inter = between different species.

Key Terms¶

• Habitat: the place where an organism lives.
• Population: all the organisms of one species in a habitat at the same time.
• Community: all the interacting populations of different species in a habitat.
• Ecosystem: a community of organisms interacting with the non-living components of its environment.
• Abiotic factor: a non-living physical or chemical factor that affects organisms in an ecosystem.
• Biotic factor: a living factor — the effect of other organisms — that affects a population.
• Adaptation: an inherited feature that increases an organism's fitness (ability to survive and reproduce) in its environment.
• Structural adaptation: a physical feature of the body suited to the environment.
• Behavioural adaptation: a behaviour pattern that improves survival or reproduction.
• Physiological adaptation: an internal biochemical or metabolic feature suited to the environment.
• Extremophile: an organism adapted to survive in extreme environmental conditions.
• Interdependence: the way in which organisms in a community depend on one another for survival.
• Mutualism: a relationship between two species where both benefit.
• Parasitism: a relationship where one organism (parasite) benefits at the expense of another (host).
• Intraspecific competition: competition between individuals of the same species.
• Interspecific competition: competition between individuals of different species.

Connected Pages¶

• Organisation of an Ecosystem
• Biology Key Terms Glossary
• Required Practical Reference