What is the difference between interspecific and intraspecific competition?

Interspecific competition occurs between individuals of different species, while intraspecific competition occurs between individuals of the same species. Intraspecific is often more intense because the individuals require the exact same resources.

How does mutualism differ from parasitism in terms of interdependence?

In mutualism, both species benefit from the interaction (e.g., bees and flowers). In parasitism, one species (the parasite) benefits by taking resources from the host, while the host is harmed.

Why is it incorrect to say a species will 'die out' immediately if one of its food sources is removed?

Most organisms are part of complex food webs and have multiple food sources. Unless the removed species was the *only* food source, the population will likely decrease rather than go extinct as they shift to alternative prey.

What is a common mistake when describing plant competition for 'nutrients'?

Students often use the vague term 'nutrients' when they should specifically refer to 'mineral ions' or 'minerals' from the soil. Plants do not 'eat' food; they absorb ions like nitrates and magnesium to build molecules.

Why might a prey population benefit from the presence of a predator?

Predators often cull the weakest, oldest, or sickest members of a prey population. This reduces competition for resources among the survivors and can strengthen the overall genetic health of the prey species.

Define a 'Stable Community'.

A stable community is one where all the species and environmental factors are in balance so that population sizes remain fairly constant over time. Examples include ancient woodlands or mature coral reefs.

What four main resources do plants compete for?

Plants compete for light (for photosynthesis), space (for leaf and root spread), water (from soil), and mineral ions (for growth and chlorophyll production).

What three main resources do animals compete for?

Animals compete for food (energy), mates (reproduction), and territory (space containing water, food, and shelter).

How does seed dispersal demonstrate interdependence?

Plants depend on animals to eat their fruit and transport seeds away from the parent plant in their droppings. This reduces competition between the parent and offspring for light and space.

What happens to a community if a 'keystone' species (a highly interdependent species) is removed?

The removal of a highly interdependent species can cause a 'trophic cascade,' where the populations of many other species increase or decrease dramatically, potentially leading to the collapse of the community's stability.

Interdependence & Competition | OCR GCSE Science

Combined Science A Gateway / Biology

Community Level Systems

Interdependence & Competition

Summary

Interdependence and competition are the fundamental biological interactions that govern the structure and stability of ecosystems. Organisms rely on one another for survival through complex networks of feeding, reproduction, and protection, while simultaneously competing for limited resources that determine population limits and community health.

1. Definition & Core Concepts

Interdependence refers to the complex web of relationships where species within a community rely on each other for essential resources such as food, shelter, pollination, and seed dispersal. If one species is significantly impacted, the effects ripple through the entire ecosystem.
A Community consists of all the populations of different species living and interacting in a specific habitat at the same time.
An Ecosystem is the interaction of a community of living organisms (biotic) with the non-living (abiotic) parts of their environment.

2. The Nature of Interdependence

Feeding Relationships: Predators depend on prey for energy, while herbivores depend on plants. These relationships are often visualized in food webs where the removal of one organism affects multiple others.
Pollination and Seed Dispersal: Many plants rely on specific animals (like insects or birds) to transfer pollen for reproduction or to carry seeds to new locations via consumption and excretion.
Shelter and Protection: Organisms may provide physical habitats for others, such as trees providing nesting sites for birds or coral reefs providing cover for fish.

A diagram showing the flow of energy and interdependence between producers, pollinators, and consumers.

3. Competition Principles

Resource Scarcity: Competition occurs when the demand for a resource exceeds the available supply. This limits the growth and distribution of populations within a habitat.
Animal Competition: Animals primarily compete for food (energy), water, territory (space for resources), and mates (reproductive success).
Plant Competition: Plants compete for light (for photosynthesis), space (to expand leaves and roots), water, and mineral ions (like nitrates for proteins and magnesium for chlorophyll).

4. Key Distinctions

5. Stable Communities

6. Exam Strategy & Tips