structural, physiological and behavioural adaptations of plants and animals that enhance survival and allow life to exist in a wide range of environments, including extreme environments

What this dot point is asking

VCAA wants the three categories of adaptation (structural, physiological, behavioural), with examples showing how plants and animals survive in their environments, including extreme environments.

The answer

What is an adaptation?

An adaptation is an inherited feature of an organism that increases its chance of surviving and reproducing in its environment. Adaptations arise by natural selection over many generations: random variation in a population is filtered by environmental pressures, and the variants that fit better leave more offspring.

Three categories:

Structural (anatomical) adaptations

Physical features of the body. Examples: a camel's long eyelashes, a polar bear's thick fur, a cactus's spines.

Physiological (functional) adaptations

Internal biochemical or physiological processes. Examples: countercurrent heat exchange, antifreeze proteins in Antarctic fish, sweat production, CAM photosynthesis.

Behavioural adaptations

Inherited actions or responses. Examples: migration, hibernation, nocturnality, schooling, courtship displays.

These categories overlap: a desert lizard's behaviour of basking on a rock to warm up depends on its skin's structural ability to absorb sunlight and its physiological tolerance of high temperatures.

Plant adaptations to extreme environments

Desert (xerophytes). Cacti, Australian spinifex, saltbush.

• Structural. Reduced leaves (spines); thick waxy cuticle to reduce transpiration; deep tap roots to reach groundwater or shallow extensive roots to capture rare rain; fleshy stems and leaves to store water; pale colour and reflective surfaces.
• Physiological. CAM photosynthesis (stomata open at night, fixing CO2 into malate via PEP carboxylase; Calvin cycle runs during the day with stomata closed). C4 photosynthesis (spatial separation of CO2 fixation, common in tropical grasses).
• Behavioural. Many seeds germinate only after substantial rain.

Polar and alpine (cryophytes). Mosses, lichens, low-growing tundra plants.

• Structural. Low growth form (cushion plants) to avoid wind chill; dense hairs that trap a warm air layer; dark pigments to absorb heat.
• Physiological. Antifreeze compounds (sugars, glycerol) lower the freezing point of cell sap.
• Behavioural (in the broad sense). Annual life cycles timed to short summers; rapid flowering when warmth returns.

Salt (halophytes). Mangroves, saltbush.

• Structural. Salt glands on leaves excrete excess salt; pneumatophores in mangroves bring air to roots in waterlogged soil.
• Physiological. Roots that exclude salt at uptake; tissues that tolerate high internal salt concentrations.

Aquatic plants (hydrophytes). Water lilies.

• Structural. Stomata on the upper surface of floating leaves only; air-filled tissues (aerenchyma) for buoyancy; reduced support tissues because water supports the plant.

Animal adaptations to extreme environments

Desert. Camels, kangaroo rats, fennec foxes, dingoes.

• Structural. Camels have long eyelashes and closable nostrils to keep out sand; large feet to spread weight on sand; fatty humps as a metabolic water source. Fennec foxes have huge ears full of capillaries to radiate heat. Kangaroo rats have long hind legs for hopping (efficient locomotion).
• Physiological. Concentrated urine via long Loop of Henle (kangaroo rats produce urine so concentrated they can survive without drinking, getting all their water from metabolism). Tolerance of high body temperatures (camels allow body temperature to vary 6 degrees Celsius). Metabolic water generation from fat oxidation.
• Behavioural. Nocturnal activity, burrow use during the day, drinking large volumes when water is available (camels can drink 100 litres in 10 minutes), seeking shade.

Polar. Polar bears, penguins, Antarctic fish.

• Structural. Thick subcutaneous fat (blubber) for insulation; dense fur with hollow hairs (polar bear hairs trap air for insulation); small ears and limbs (Allen's rule) to reduce surface area for heat loss; large body size (Bergmann's rule) to reduce SA:V.
• Physiological. Countercurrent heat exchange in limbs (warm arterial blood pre-warms cool venous blood returning from extremities). Antifreeze glycoproteins in Antarctic icefish that prevent ice-crystal growth in blood at temperatures below freezing. Brown adipose tissue (BAT) for non-shivering thermogenesis.
• Behavioural. Huddling for warmth (emperor penguins rotate the outer layer); migration to feeding grounds; seasonal coat changes.

Deep sea (high pressure, no light, cold).

• Structural. Bioluminescent organs to find mates and prey; large eyes or no eyes; gelatinous bodies that resist crushing.
• Physiological. Membrane lipids with more unsaturated bonds, keeping membranes fluid at low temperatures; pressure-tolerant enzymes.

Worked example: a comparison

A red kangaroo in the Australian desert and an Adelie penguin in Antarctica face opposite challenges (overheating vs freezing). The kangaroo has structural adaptations to lose heat (thin coat, blood vessels close to the skin in the forearms which it licks to evaporative-cool), physiological adaptations (long Loop of Henle to concentrate urine, sweating in mild heat), and behavioural adaptations (resting in shade during the day, foraging at dawn and dusk). The penguin has structural adaptations to retain heat (thick blubber, dense overlapping feathers, small flippers), physiological adaptations (countercurrent heat exchange in legs), and behavioural adaptations (huddling, rotating the outer ring of the huddle).

Adaptation and natural selection

Adaptations are the result of long-term natural selection: individuals with heritable traits that improve survival and reproduction leave more offspring. Over generations, the frequency of those traits rises in the population. Adaptation explains the extraordinary fit between organisms and their environments (covered in detail in the Unit 4 evolution dot points).

Examples in context

Example 1. Mallee fowl behavioural and physiological adaptations. The mallee fowl (Leipoa ocellata) in Wyperfeld National Park survives 40 degree summers and freezing winter nights by building incubation mounds. Behaviourally, the male spends 9 months a year tending a mound of leaf litter and sand. Physiologically, the mound's microbial fermentation generates heat that incubates the eggs at a near-constant 33 degrees C, even when external temperatures swing 30 degrees. Structurally, the bird has insulating feathers and large feet for digging. The mound itself is a behavioural adaptation that frees the birds from the energy cost of incubation, but it requires the structural adaptation of strong claws and the physiological adaptation of high thermoregulatory tolerance.

Example 2. Spinifex grass in the Australian arid zone. Triodia (spinifex) covers 25 percent of Australia and survives the central desert via structural, physiological and behavioural adaptations. Structurally, leaves are rolled into needles that minimise transpiration surface, with sunken stomata hidden in the groove. Physiologically, the plant uses C4 photosynthesis, which keeps photorespiration low at high leaf temperatures, and produces resinous compounds that deter herbivores. "Behaviourally" (in the developmental sense), spinifex seedlings establish quickly after a single rain event, then enter near-dormancy for years. Research at the Alice Springs Desert Park has shown that spinifex clumps can live 100 years, expanding outward as the centre dies and forming the iconic "fairy circles" visible from satellite.

Try this

Q1. Distinguish between structural, physiological and behavioural adaptations using one example for each. [3 marks]

• Cue. Structural: physical feature (e.g. thick fur). Physiological: internal process (e.g. concentrated urine). Behavioural: action (e.g. burrowing during day).

Q2. A desert kangaroo rat survives without drinking water by producing very concentrated urine, sheltering in burrows during the day, and metabolising fat to release water. Classify each adaptation and explain how the three combine to achieve water balance. [3 marks]

• Cue. Concentrated urine (physiological), burrow shelter (behavioural), metabolic water (physiological). All three reduce loss and increase gain.

Q3. Refer to the mallee fowl. (a) Classify the mound-building behaviour. (b) Explain how the mound regulates egg temperature. (c) Predict the impact of severe drought on mallee fowl breeding success. [2+2+2 marks]

• Cue. (a) Behavioural. (b) Microbial fermentation in leaf litter generates heat; sand insulates; male turns mound to adjust temperature. (c) Less leaf litter means less heat; fewer eggs hatch; population declines, which is why drought years are a conservation concern.