What is the fundamental difference between a biotic factor and an abiotic factor?

A biotic factor is a living component of an ecosystem, such as a predator or a pathogen, while an abiotic factor is a non-living physical or chemical part of the environment, such as temperature or sunlight.

How does interspecific competition differ from intraspecific competition?

Interspecific competition occurs between members of different species competing for the same resources, whereas intraspecific competition occurs between individuals of the same species.

Why is 'food availability' considered a biotic factor rather than an abiotic one?

Food availability is biotic because food sources are other living organisms (plants or animals). The interaction involves the consumption of biological matter, which is a living component of the ecosystem.

What is a common mistake when identifying the cause of a population decline in an exam?

A common error is failing to specify whether the cause is biotic or abiotic. Students often forget that a lack of food is a biotic issue, while a lack of water or space is typically abiotic.

Why is it incorrect to say a population will 'die out' immediately after a new predator is introduced?

Ecosystems are complex; a population usually decreases gradually as mortality rates rise. Using the term 'decrease' is more scientifically accurate than 'die out' unless total extinction is confirmed.

What error occurs if a student lists 'temperature' as a biotic factor affecting a forest?

This is a classification error. Temperature is a physical, non-living condition of the environment, making it an abiotic factor, not a biotic one.

Define a 'Pathogen' in the context of biotic factors.

A pathogen is a living microorganism, such as a bacterium or virus, that causes disease in its host. It acts as a biotic factor by increasing mortality and reducing the fitness of a population.

What is meant by 'Interspecific Competition'?

It is the competition between different species for the same limited resources in an ecosystem, such as two different bird species competing for the same type of nesting site.

What defines a 'Biotic Factor'?

A biotic factor is any living part of the environment with which an organism might interact, including animals, plants, fungi, and bacteria.

How can a new predator cause an ecosystem to become 'unbalanced'?

A new predator may over-consume prey species that have no natural defenses, leading to a crash in prey numbers. This disrupts the food web, as other species relying on that prey will also suffer.

Biotic Factors | AQA GCSE Science

Combined Science Trilogy / Biology

Ecology

Biotic Factors

Summary

Biotic factors are the living components of an ecosystem that directly or indirectly affect the survival and distribution of organisms. These factors involve complex interactions between different species, such as predation, competition, and disease, which collectively determine the stability and population dynamics of a biological community.

1. Definition & Core Concepts

Biotic factors refer to any living component that affects another organism or shapes the ecosystem. This includes not only the organisms themselves but also their interactions and the biological byproducts they produce.

In a biological community, these factors are responsible for the interdependence of species, where the presence or absence of one organism can significantly impact the population levels of others.

Common examples of biotic factors include the availability of food sources, the presence of predators, the spread of pathogens, and the intensity of competition for limited resources.

A diagram showing the interaction between three biotic factors: a predator, its prey, and a pathogen affecting the prey.

2. Food Availability & Population Growth

The availability of food is a primary biotic factor that determines the carrying capacity of a habitat. When food resources are abundant, organisms have a higher probability of surviving to reproductive age and successfully raising offspring.

Conversely, a decrease in food supply leads to increased mortality and lower birth rates, causing the population size to decline. This creates a feedback loop where the population of a consumer species is directly tied to the population of its food source.

3. Predation and Pathogens

New predators can drastically alter the balance of an ecosystem, especially if the local prey species have not evolved defensive mechanisms against them. This often leads to a rapid decline in prey populations, which can then trigger a cascade of effects throughout the food web.

Pathogens (disease-causing organisms like bacteria, viruses, or fungi) act as biotic factors by regulating population sizes. If a new pathogen enters a community where the organisms have no natural immunity, it can lead to widespread illness and potential extinction of vulnerable species.

4. Interspecific Competition

5. Key Distinctions

6. Exam Strategy & Tips

Biotic Factors

Summary

1. Definition & Core Concepts

Common examples of biotic factors include the availability of food sources, the presence of predators, the spread of pathogens, and the intensity of competition for limited resources.

A diagram showing the interaction between three biotic factors: a predator, its prey, and a pathogen affecting the prey.

2. Food Availability & Population Growth

3. Predation and Pathogens

4. Interspecific Competition

Competition occurs when two or more species require the same limited resource, such as food, water, or nesting sites. When these species occupy the same niche, they must compete to survive.

The principle of competitive exclusion suggests that if one species is even slightly better adapted to utilize the resource, it will eventually outcompete and displace the less-adapted species, potentially leading to the latter's local extinction.

5. Key Distinctions

It is vital to distinguish between biotic and abiotic factors to understand ecosystem dynamics correctly. Biotic factors are always biological in origin, whereas abiotic factors are physical or chemical.

Feature	Biotic Factors	Abiotic Factors
Origin	Living organisms (plants, animals, microbes)	Non-living environment (climate, soil, sunlight)
Examples	Predation, Food, Disease, Competition	Temperature, pH, Light intensity, Water
Interaction	Involves biological relationships	Involves physical constraints

6. Exam Strategy & Tips

Graph Interpretation: When presented with a population graph showing one species rising while another falls, look for evidence of competition or predation. Always cite specific data points from the axes to support your conclusion.
Identify the Factor: If a question asks for a biotic factor, ensure your answer is a living thing. For example, 'water' is abiotic, but 'aquatic plants' (as a food source) is biotic.
Avoid 'Die Out': In long-answer questions, avoid saying a species will simply 'die out' without explanation. Instead, use terms like 'population decrease' and explain the mechanism, such as 'reduced breeding success' or 'increased mortality due to predation'.