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5.2.4Unit 5: Respiration, Internal Environment, Coordination and Gene Technology

Factors Affecting Populations — IAL Edexcel Linear Revision Notes & Topical Questions

5 min read 5 parts Lesson 19 of 36 Unit quiz

📚 IAL Edexcel Linear Hub / Topical Revision
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Part 1 of 5Biotic Factors

Living factors arise from interactions between organisms.

Interspecific competition
  • Interspecific competition Different species compete for the same resource, which can reduce the numbers of one or both.
Intraspecific competition
  • Intraspecific competition Members of one species compete for food, space or mates, and this limits population growth.
Predation
  • Predation Predators reduce prey numbers, and prey numbers affect the food supply for predators.
Disease and parasitism
  • Disease and parasitism Parasites and pathogens spread more easily at high density and reduce survival.
Cooperation
  • Cooperation Some organisms gain benefit from each other, such as animals living in groups that avoid predators.

Part 2 of 5Abiotic Factors

Abiotic Factors
Temperature
  • Temperature Affects metabolic rate, enzyme activity and survival of the species.
Light
  • Light Limits photosynthesis and therefore the food supply for the community.
pH and salinity
  • pH and salinity Affect water balance and enzyme function, so some species tolerate only narrow ranges.
Water and oxygen
  • Water and oxygen Availability affects where organisms can live, especially in soil and water.
Tolerance
  • Tolerance Each species has a range of conditions it can tolerate, which limits where it can live.

Part 3 of 5Population Growth

A population introduced to a new habitat often follows an S-shaped curve.

1
In the lag phase growth is slow because few individuals are reproducing.
2
In the exponential phase resources are plentiful and the population grows rapidly.
3
In the stationary phase birth and death rates are equal, and the population stays near the carrying capacity.
4
Limiting factors such as food, space and disease stop growth continuing.

Part 4 of 5Predator and Prey

Cycles
  • Cycles Predator numbers often rise and fall a little after prey numbers.
Reason
  • Reason More prey allows more predators to survive, then the predators reduce the prey again.
Caution
  • Caution Other factors such as disease and food supply for prey also affect the cycle.
Density
  • Density Factors such as competition depend on density, whereas frost affects all densities similarly.
TypeExampleEffect
BioticPredationReduces prey population
BioticCompetitionLimits growth
AbioticTemperatureAffects survival and growth

Part 5 of 5Exam Checklist & Tips

5.2.4 – Key Points for the Exam

  • Carrying capacity The maximum population size that an environment can support.
  • Competition The struggle between organisms for a limited resource.
  • Predation Feeding by one organism on another, the prey.
  • Limiting factor A factor that restricts population size.

Common Mistakes

  • Saying that predators alone control prey numbers; food, disease and abiotic factors matter too.
  • Confusing intraspecific competition, within a species, with interspecific.
  • Describing carrying capacity as a fixed value; it varies with conditions.
  • Stating that abiotic factors are living factors.

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