AP Syllabus focus:
‘Many organismal adaptations relate to obtaining and using energy and matter in specific environments.’
Adaptations that improve resource capture and processing determine whether individuals survive long enough to reproduce. In population ecology, these traits shape where organisms can live, how they compete, and how efficiently they convert resources into biomass.
What it means to obtain and use energy and matter
Organisms must acquire energy (to power cellular work) and matter (atoms for building tissues). Because environments differ in light, water, oxygen, temperature, and nutrient availability, populations evolve features that improve resource acquisition and resource use efficiency in those specific conditions.
Adaptation: A heritable trait that increases an individual’s fitness in a particular environment by improving survival and/or reproduction.
A key idea is that the “best” trait depends on the environment: the same feature can be beneficial in one habitat and costly in another.
Common ecological constraints on resources
Low resource abundance (e.g., scarce nitrogen or water)
Resource patchiness (food in clumps, brief blooms, seasonal pulses)
High competition (many individuals using the same limiting resource)
Physical barriers to uptake (thick cuticles, cold water, low oxygen)
Major adaptation types linked to resource acquisition
Structural (morphological) adaptations
These traits affect how organisms physically capture and ingest resources.
Increased surface area for uptake or exchange
Diagram of plant root anatomy showing how the epidermis and root hairs increase contact area with soil, enhancing water and mineral ion uptake. The labeled cross-section also highlights internal transport tissues (xylem/phloem region) that move absorbed matter through the plant. Source
Plant root hairs increase absorption of water and mineral ions
Broad, thin leaves improve light capture where light is limiting
Specialised feeding structures that match resource type
Different beak shapes or mouthparts allow use of distinct foods
Long digestive tracts can improve extraction from cellulose-rich diets
Transport and support structures that enable access
Deeper roots in dry environments access groundwater
Streamlined bodies reduce energy cost of swimming while foraging
Physiological adaptations
These traits alter internal processes that extract, conserve, or process resources.
Enzyme and metabolic tuning
Digestive enzymes and symbiotic microbes improve breakdown of hard-to-digest foods
Water and ion balance mechanisms
Kidneys producing concentrated urine reduce water loss in arid habitats
Salt glands in some birds and reptiles help maintain osmotic balance while drinking seawater
Storage strategies
Starch, fat, or water storage buffers periods of low availability
Tolerance ranges that allow feeding when conditions are harsh
Proteins and membranes adapted to cold can maintain function, supporting continued feeding and growth
Behavioral adaptations that increase net resource gain
Behavior can rapidly change how organisms locate and use resources.
Foraging strategies
Marginal Value Theorem graph illustrating diminishing returns in a food patch: cumulative resource intake rises quickly at first, then levels off. The tangent line shows the optimal time to leave a patch when travel time between patches is included, maximizing net energy gain per unit time. Source
Optimal foraging behaviours reduce time/energy spent per unit food
Switching prey types when preferred prey declines
Activity timing
Nocturnality in deserts reduces water loss and overheating while feeding
Territoriality and spacing
Defending feeding areas can secure resources, but costs energy and risks injury
Migration and dormancy
Migration tracks seasonal resource peaks
Torpor/hibernation reduces energy use when food is scarce (supporting survival until resources return)
Trade-off: A situation where improving one function (e.g., faster growth) reduces another (e.g., predator avoidance) because energy and materials are limited.
Trade-offs help explain why populations show multiple strategies rather than a single “perfect” design.
Environment-specific resource adaptations (high-yield patterns)
Nutrient-poor soils
Plants may allocate more biomass to roots than shoots to increase mineral uptake
Associations with microbes can improve nutrient acquisition (e.g., nitrogen-fixing bacteria or mycorrhizae), increasing growth where nutrients limit populations
Schematic of a mycorrhizal mutualism, emphasizing bidirectional exchange between partners. The plant supplies photosynthetically fixed carbon to the fungus, while fungal hyphae increase effective absorptive surface area and deliver key nutrients (notably phosphate and nitrogen) to the plant. Source
Dry environments
Waxy cuticles, reduced leaf area, and stomatal control conserve water, indirectly supporting continued photosynthesis and growth
Animals may rely on metabolic water, efficient kidneys, and heat-avoidance behaviours to keep feeding and digesting functional
Aquatic and low-oxygen habitats
Increased gill surface area or ventilation improves oxygen uptake, supporting aerobic metabolism during foraging
Some species use behaviours (surface breathing, reduced activity) that balance energy gain against oxygen limitation
Why these adaptations matter in population ecology
Within a population, individuals vary in resource-related traits. When the environment favours certain phenotypes (for example, beak sizes that best exploit available seeds), those individuals tend to leave more offspring. Over generations, populations become better matched to their typical resource conditions, and their distribution and abundance reflect how effectively they obtain and use energy and matter.
FAQ
Local resource types and competition can favour different phenotypes.
Limited gene flow and consistent selection can shift trait frequencies over time.
They can unlock limiting atoms (e.g., nitrogen, phosphorus) by converting them into absorbable forms.
They may also synthesise essential compounds hosts cannot make.
Net gain depends on energy obtained minus costs (movement, handling, risk, heat/water loss).
Predation risk can reduce the “best” energetic choice.
Constraints and trade-offs limit simultaneous optimisation.
Specialisation for one resource or condition often reduces performance in others.
Adaptations are heritable and increase fitness across generations.
Acclimatisation is a reversible within-lifetime change in response to conditions.
Practice Questions
Describe two adaptations that increase an organism’s ability to obtain energy or matter in a specific environment. (2 marks)
1 mark: One correct adaptation linked to obtaining/using energy or matter (e.g., root hairs increase mineral/water uptake).
1 mark: Second correct adaptation linked to environment/resource capture (e.g., concentrated urine reduces water loss in deserts).
Explain how structural, physiological, and behavioural adaptations can each improve resource acquisition, and discuss one trade-off associated with these adaptations. (5 marks)
1 mark: Structural adaptation improves capture/uptake (e.g., increased surface area such as gills/root hairs).
1 mark: Physiological adaptation improves processing/conservation (e.g., digestive enzymes/symbionts; water conservation).
1 mark: Behavioural adaptation improves net resource gain (e.g., optimal foraging, timing of activity, migration).
1 mark: Clear link to higher fitness via increased survival/reproduction from improved energy/matter balance.
1 mark: One valid trade-off explained (e.g., territory defence increases energy expenditure/injury risk; deep roots reduce investment in reproduction).
