Adaptations and extremophiles: survival in extreme conditions
Ecology • Adaptations, interdependence and competition
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Key concepts
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Definition of adaptation
An adaptation is a heritable feature that increases an organism's chance of survival and reproduction in a specific environment. Adaptations arise through natural selection because individuals with beneficial traits leave more offspring. Lack of suitable adaptations causes reduced survival and competitive disadvantage against other organisms.
Types of adaptation: structural, behavioural, physiological
Structural adaptations are physical features that affect function; for example, a polar bear's small ears and compact shape reduce heat loss and thick fat and fur provide insulation, causing reduced heat loss in cold climates. Behavioural adaptations are actions or patterns that increase survival; for example, emperor penguins huddle together to reduce heat loss during extreme Antarctic cold. Physiological adaptations are internal processes; for example, venom production aids prey capture or defence, and cacti store water and reduce transpiration to survive in deserts. Each type directly addresses an environmental limiting factor such as temperature or water availability.
Cause → effect: how adaptations match limiting factors
Low light causes selection for larger, thin leaves and high chlorophyll content so plants capture more light; increased light and low water cause selection for water-storage tissues and reduced leaf surface area to limit water loss. Cold causes selection for insulating fat, fur or counter-current heat exchange to conserve core temperature; heat causes selection for behaviours or body shapes that increase heat loss. Each adaptation reduces the effect of a limiting abiotic factor and therefore improves survival and reproduction in that habitat.
Extremophiles and extreme environments
An extremophile is an organism that lives in an environment that is extreme for most life forms. Examples of extreme environments include polar regions with very low temperatures, deserts with minimal water, highly acidic or alkaline soils, and deep-sea hydrothermal vents with very high temperature and pressure. Extremophiles possess specialised adaptations that allow metabolic processes to function under these conditions. Bacteria around hydrothermal vents use chemical energy from sulfur compounds, allowing food webs to exist without sunlight.
Adaptations of hydrothermal-vent organisms
High pressure, lack of light and toxic dissolved chemicals around vents cause selection for chemosynthetic bacteria that metabolise hydrogen sulfide and other minerals. These bacteria form the base of local food webs, supporting worms, crustaceans and fish. Structural specialisations in larger vent organisms reduce pressure damage and allow attachment to vent chimneys, while physiological enzymes remain stable at high temperatures. These adaptations directly counter the abiotic stresses of pressure, temperature and chemical toxicity.
Adaptation, competition and evolutionary advantage
Adaptations provide competitive advantages by improving resource acquisition, predator avoidance or reproductive success. Individuals lacking effective adaptations suffer higher mortality or lower reproductive output and therefore decline relative to better-adapted individuals. Ongoing competition drives evolutionary change by favouring traits that match habitat conditions. Introduced species with advantageous traits can outcompete native species and alter community structure.
Key notes
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