Living Factors Affecting Communities Revision Notes | GCSE OCR Foundation Biology

What this lesson covers

Explore how biotic (living) factors impact communities, including food availability, predators, pathogens, and competition between species.

• Explain how living factors affect the size of populations in communities
• Describe the impact of food availability on community structure
• Analyse how new predators and pathogens can disrupt ecosystems
• Evaluate the consequences of interspecific competition on breeding populations

Key ideas to keep in view

Use this lesson to stay inside B4.1 Ecosystems while connecting the detail back to the wider B4: Community level systems topic.

• B4: Community level systems
• B4.1 Ecosystems
• GCSE OCR Foundation Biology

Lesson notes preview

Read the core explanations from Living Factors Affecting Communities before testing yourself from memory.

• Picture a woodland where deer numbers suddenly crash, or a pond where fish populations explode. What's controlling these changes? It's not just weather or temperature - it's the living world itself.
• Biotic factors are the living components of an ecosystem that directly influence which organisms survive, reproduce, and thrive. Unlike abiotic factors (temperature, rainfall), these involve interactions between living things.
• Living factors in an ecosystem that affect the distribution and abundance of organisms. These include food availability, predation, disease, and competition between species.
• Trap: Many students think biotic factors only include obvious predators. Actually, they include any living influence - from bacteria causing disease to plants competing for sunlight.
• Food availability is often the primary limiting factor for population size. When food is abundant, populations grow. When it becomes scarce, populations crash.
• This works through a simple mechanism: more food means better survival rates and more successful reproduction. Fewer offspring die from starvation, and adults have more energy to invest in breeding.
• Real ecosystems show this pattern clearly. Lynx populations in Canada closely follow snowshoe hare numbers - when hares are abundant, lynx thrive and reproduce more successfully.
• When a new predator arrives in an ecosystem, it can devastate prey populations that have no evolved defences. This is because the prey species hasn't had time to develop behavioural or physical adaptations.
• The classic example is cats introduced to islands. Native bird populations, which evolved without mammalian predators, have no instinct to avoid ground-dwelling hunters. The result? Population crashes of 90% or more.
• New predators affect communities through two mechanisms: direct predation (killing prey) and indirect effects (prey changing behaviour, spending more time hiding, less time feeding).

Continue through the topic

Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.