8.1Ecology
Responses to the Environment — AP BIOLOGY Revision Notes & Topical Questions
5 min read 8 parts Lesson 2 of 8 3 quizzes
Lesson summary
8.1 Responses to the Environment — Notes — AP Biology notes: Explain how the behavioural and physiological response of an organism relates to changes in its internal or external environment.Behaviour = the response of an organism to a stimulus.Purpose — organisms respond to envir…
- Imprinting
- Photoperiodism
- Kin selection
- Adaptation
- Behavioural mechanisms — the actions of an organism
- Physiological mechanisms — biological processes inside the organism that maintain homeostasis
Section 1 of 8Responses to cues
1
Behaviour = the response of an organism to a stimulus.
2
Purpose — organisms respond to environmental change to maintain homeostasis and improve survival,
- increasing fitness.
- (survival and reproductive success)
3
Behavioural mechanisms — the actions of an organism.
4
Physiological mechanisms — biological processes inside the organism that maintain homeostasis.
5
Internal stimuli — such as hormone fluctuations (adrenaline gives an internal cue that drives a fight-or-flight reaction to an immediate threat).
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External stimuli — such as temperature, light or predators.
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Selection — behaviour that increases fitness is favoured by natural selection,
- including innate and learned behaviours that improve survival and reproduction;
- behaviours spread only if they increase fitness.
8
Response versus adaptation — a response is immediate, whereas an adaptation is a heritable trait that helps survival in new conditions.
Section 2 of 8Innate and learned behaviour
Innate and learned behaviour
Innate behaviour — genetically determined and performed correctly the first time, e.g. fixed action patterns.
Learned behaviour — modified by experience: imprinting, classical and operant conditioning, habituation.
| Response | Innate or learned | Organism | Example |
|---|---|---|---|
| Taxis | Innate | Animals, bacteria | Moths to light |
| Kinesis | Innate | Woodlice | Move faster in dry areas |
| Fixed action pattern | Innate | Geese | Egg-rolling |
| Imprinting | Learned (critical period) | Ducklings | Follow the first moving object |
| Classical conditioning | Learned | Dogs | Pavlov salivation |
| Phototropism | Innate | Plants | Shoot bends to light |
Section 3 of 8Responses in animals and plants
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Taxis — directed movement towards (+) or away from (−) a stimulus, e.g. phototaxis.
2
Kinesis — non-directional (random) change in speed or turning rate (woodlice move more in dry conditions) to find favourable conditions.
3
Nocturnal and diurnal activity — owls exploit night-time safety or prey and eagles rely on daylight for hunting or warmth.
4
Phototropism — growth towards light controlled by auxin to optimise photosynthesis; gravitropism is directional growth to gravity.
5
Photoperiodism — seasonal flowering and leaf shedding triggered by day length, detected by phytochrome.
6
Circadian rhythms — about 24-hour cycles of physiological activity.
7
Plant defence — mechanical damage from a herbivore triggers release of toxic chemicals that deter feeding; plant responses are triggered by hormones and cues, not conscious behaviour.
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Prokaryotes — respond by quorum sensing and chemotaxis.
Section 4 of 8Communication
Communication
Scope — organisms share information with their own species (intraspecific) or other species (interspecific).
Uses — establishing dominance, locating food, defending territory and warning of predators.
Reproductive success — signalling conveys fitness, status or genetic quality to mates, rivals and social partners and triggers adaptive responses in others.
| Signal | Example |
|---|---|
| Visual | Bright colours of a courting bird; flower colouration attracting pollinators |
| Audible | Alarm call (meerkats); bird song attracting mates and establishing territory |
| Tactile | Grooming in primates |
| Chemical | Pheromones in ants; scent marking by mammals deters competitors |
| Dance | Bee waggle dance (direction and distance of food) |
Section 5 of 8Cooperative and social behaviour
1
Cooperation — benefits individuals and populations, e.g. wolves hunting in packs, shared parental care, bees swarming.
2
Parent–offspring interactions — facilitate learning of survival skills (grizzly cubs learning to fish).
3
Courtship — helps identify mates with advantageous traits.
4
Herding, flocking and schooling — safety in numbers reduces predation (sardines).
5
Colony and swarming — ensures survival (bee colonies finding new habitats).
6
Kin selection and altruism — helping relatives raises inclusive fitness because they share alleles (an older moose diverting predators).
7
Timed responses — migration and hibernation respond to seasonal change and increase survival.
Section 6 of 8More from the specification
Energy efficiency across trophic levels
- Energy efficiency across trophic levels ecological energy transfer between trophic levels depends on organism biomass and cellular metabolic rates.
Consumer
- An organism that gets energy by feeding on other organisms.
Ecosystem
- Community plus environment.
Heterotroph
- Organism using organic molecules made by others
Trophic level
- The feeding level of an organism in a chain.
Metabolic rate
- The rate at which an organism uses energy.
Section 7 of 8Key terms
| Term | Meaning |
|---|---|
| Behaviour | response of an organism to a stimulus |
| Taxis | directed movement towards or away from a stimulus |
| Kinesis | non-directional change in movement rate |
| Imprinting | learning from the first object seen in a critical period |
| Photoperiodism | response to day length |
| Kin selection | selection favouring behaviour that helps relatives |
| Pheromone | chemical signal between individuals |
| Adaptation | heritable trait helping survival in new conditions |
Section 8 of 8Exam technique
1
Calling imprinting innate — it is learned during a critical period.
2
Confusing taxis (directed) with kinesis (non-directional).
3
Thinking behaviours have no effect on fitness — they affect survival and reproduction.
4
Thinking responses are the same as adaptations — responses are immediate, adaptations are heritable traits.
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