Predation (AQA A-Level Biology): Revision Notes
Predation
What is predation?
Predation occurs when one organism consumes another organism for nutrition. In this relationship, a predator is an organism that feeds on another organism, known as its prey.
This feeding relationship represents one of the most important interspecific interactions in ecosystems, where two different species directly affect each other's survival and reproduction.
Predation is fundamental to energy transfer in ecosystems, as it represents a direct pathway for energy and nutrients to move from one trophic level to another. This relationship shapes community structure and influences biodiversity patterns across different habitats.
Evolutionary adaptations
Predators and prey have evolved together in what can be described as an evolutionary arms race. As predators develop better hunting abilities, prey species simultaneously evolve improved survival strategies.
Predator adaptations include:
- Enhanced speed and agility for pursuit
- More effective camouflage for ambush hunting
- Better sensory systems for detecting prey
- Improved capture mechanisms (claws, teeth, venom)
Prey adaptations include:
- Better camouflage to avoid detection
- Protective features such as spines or shells
- Alarm behaviours and group living
- Enhanced escape responses and speed
Co-evolution is Critical for Species Survival
If either predators or prey had failed to match the adaptations of the other, extinction would likely have occurred. This co-evolution ensures both species continue to survive in their shared environment, creating a delicate balance that has shaped ecosystems over millions of years.
Laboratory versus natural conditions
Understanding predator-prey dynamics requires careful consideration of environmental context.
In laboratory conditions, prey populations are often completely eliminated by predators. This occurs because:
- The confined space offers limited refuges for prey
- Environmental variety is restricted
- Prey cannot disperse to escape predation pressure
In natural ecosystems, the situation differs significantly:
- Larger areas provide numerous potential refuges
- Environmental diversity creates hiding places and alternative habitats
- Some prey individuals can escape predation due to the vastness of the habitat
- Complete extinction of prey populations rarely occurs
Interpreting Laboratory Studies
This difference explains why laboratory studies of predation must be interpreted carefully when applied to wild populations. The confined nature of laboratory environments creates unrealistic predation pressures that don't reflect the complexity of natural ecosystems.
Population dynamics and cycles
The predator-prey relationship creates characteristic fluctuations in both population sizes over time.
The population cycle
Predator-Prey Population Cycle
- High prey numbers → Abundant food allows predator population to increase
- Increasing predators → More predation pressure reduces prey population
- Declining prey → Food becomes scarce, predator population begins to fall
- Fewer predators → Reduced predation allows prey population to recover
- Cycle repeats
This cyclical pattern demonstrates the interconnected nature of species relationships in ecosystems.
Selection pressure effects
Predation creates selection pressure on both species. Individuals better adapted to either hunting or avoiding predation are more likely to survive and reproduce successfully. Over time, this leads to:
- Improved hunting efficiency in predator populations
- Enhanced survival strategies in prey populations
- Continued evolutionary development in both species
Case study: Canadian lynx and snowshoe hare
This classic example demonstrates predator-prey population cycles in nature.
Historical fur trading records from the Hudson Bay Company in Canada spanning over 200 years provide evidence of population fluctuations between Canadian lynx and snowshoe hares.
Canadian Lynx and Snowshoe Hare Population Study
Key observations:
- Both populations show regular cyclical patterns
- Predator population changes typically lag behind prey population changes
- The cycles repeat approximately every 9-10 years
Research methodology: Scientists used fur trading records as an indicator of relative population sizes, making the assumption that the number of furs traded reflects the abundance of each species in the wild.
This case study illustrates how predator-prey relationships can drive population cycles in natural ecosystems, though other factors like climate and food availability also contribute to these fluctuations.
Factors affecting predator-prey relationships
Several factors influence the intensity and outcomes of predator-prey interactions:
- Disease can affect both predator and prey populations
- Climate conditions influence food availability and survival rates
- Habitat diversity affects refuge availability for prey
- Alternative food sources can buffer predators against prey population crashes
- Human intervention through habitat modification or species management
Key Points to Remember:
- Predation involves one organism (predator) consuming another (prey) and represents a key interspecific relationship
- Both predators and prey have evolved adaptations in response to each other, creating an evolutionary arms race
- Population cycles occur because predator numbers typically lag behind changes in prey abundance
- Laboratory studies may not accurately reflect natural predator-prey dynamics due to limited space and refuges
- The Canadian lynx and snowshoe hare provide a classic example of cyclical predator-prey population changes in nature