Study Notes: Adaptations, Interdependence, and Competition

Welcome to Ecology!

Hello future Biologists! This chapter is all about how living things survive and interact within their environment. It’s like studying a giant soap opera—who is competing with whom, who needs whom, and how everyone manages to stay alive!

Understanding these concepts is vital because they explain why certain animals and plants live where they do, and how ecosystems remain balanced (or become unbalanced). Don't worry if some terms look intimidating; we will break them down into simple steps!

Section 1: Adaptations – The Survival Toolkit

What is an Adaptation?

An adaptation is any special feature or characteristic (structural, behavioural, or internal) that helps an organism survive longer and reproduce successfully in its specific habitat.

Think of it this way: If you lived in the Arctic, wearing a thin T-shirt wouldn't be very helpful. A thick, warm coat would be your adaptation for survival!

The Three Types of Adaptations

Adaptations are usually grouped into three main categories. You need to know these three types and be able to provide examples for each.

1. Structural (or Anatomical) Adaptations

These are physical features on the organism’s body. You can usually see them!

  • Definition: Features related to the organism's body structure.
  • Animal Examples:
    • Thick layer of blubber (fat) or fur on polar bears for insulation.
    • Sharp claws and teeth on predators like lions for catching prey.
    • Camouflage coloration (e.g., spotted fur) to hide from predators or prey.
  • Plant Examples:
    • Small surface area of leaves (like cactus spines) to reduce water loss.
    • Long, deep roots to reach water far underground.
2. Behavioural Adaptations

These are the things the organism does—the actions and routines.

  • Definition: Actions carried out by an organism that increase its chance of survival and reproduction.
  • Examples:
    • Migration: Birds flying south in winter to find warmer food sources.
    • Hibernation: Animals sleeping through the cold winter months to save energy.
    • Huddling together in groups (like penguins) to share warmth.
    • Nocturnal activity (only coming out at night) to avoid heat or predators.
3. Physiological Adaptations

These are internal body processes or functions. They happen inside the cells or tissues.

  • Definition: Features relating to the internal functioning of the organism.
  • Examples:
    • Producing venom (snake) or poisons (some plants) for defence or attack.
    • The ability of desert animals to concentrate urine, meaning they lose less water.
    • Shivering to generate heat when cold (a physiological response to a change in temperature).
    • Producing anti-freeze proteins in the blood of Arctic fish.


QUICK REVIEW: If a feature is what it looks like, it's Structural. If it's what it does, it's Behavioural. If it's how it works internally, it's Physiological.

Section 2: Competition – The Struggle for Resources

Why Compete?

Organisms compete because resources (like food, water, or space) are limited. If resources were unlimited, no one would need to fight for them!

Competition leads to a process called natural selection, where only the best-adapted individuals survive and pass on their advantageous genes.

What is Being Competed For?

The resources organisms compete for depend on whether they are plants or animals.

  • Plants compete for:
    • Light: Essential for photosynthesis (why trees grow tall).
    • Water: Absorbed through the roots.
    • Mineral ions (nutrients): Absorbed through the roots (e.g., nitrates, phosphates).
    • Space: For root systems and to spread out leaves.
  • Animals compete for:
    • Food: The source of energy and matter.
    • Water: For essential bodily functions.
    • Territory/Space: For nesting, hunting, and raising young.
    • Mates: Competition for partners to reproduce (crucial for passing on genes).

The Two Types of Competition

It is very important not to confuse these two types!

1. Intraspecific Competition

"Intra" means "within."

  • Definition: Competition between individuals of the same species.
  • Example: Two male lions fighting over the right to mate with a female lion. Or, two oak saplings competing for sunlight in the same patch of forest.
  • Impact: This is usually the most fierce type of competition because the organisms have exactly the same needs and rely on the same food source.
2. Interspecific Competition

"Inter" means "between."

  • Definition: Competition between individuals of different species.
  • Example: Foxes and badgers competing for the same supply of mice and worms in a field. Or, grass competing with bluebells for water.
  • Impact: One species may outcompete the other, leading to a reduction in the population of the weaker species in that area.

MEMORY AID: Think of the INTERnet – it connects BETWEEN different computers. Therefore, INTERspecific competition is BETWEEN different species.


Common Mistake to Avoid: Don't assume interspecific competition is always about direct fighting. Often, it's simply one species being better at getting a resource first (like one plant species shading another, depriving it of light).

Section 3: Interdependence – Relying on Others

The Web of Life

Interdependence means that different organisms rely on each other to survive, grow, and reproduce. If one population changes dramatically, it affects others within the ecosystem.

Did you know? The extinction of a single insect species can lead to the collapse of many plant populations if that insect was the only pollinator! This shows how tightly linked species are.

Key Examples of Interdependence

1. Predator-Prey Relationships

This is the most common example of interdependence you need to understand.

  • Prey: The organism that is hunted and eaten (e.g., rabbits, mice).
  • Predator: The organism that hunts and eats the prey (e.g., foxes, eagles).

The populations of predators and prey are linked in a cycle:

  1. If the number of Prey increases (more food), the Predator population has enough food to survive and reproduce, so their numbers increase.
  2. As the Predator population gets very large, they eat more and more prey, causing the Prey population to crash (decrease sharply).
  3. With less food available, the Predator population then begins to starve and decrease shortly afterwards.
  4. The cycle repeats. This pattern typically results in stable populations over time.
2. Other Vital Interdependent Relationships
  • Pollination: Animals (like bees or birds) gain food (nectar) from the plant, and in return, they move pollen, allowing the plant to reproduce. This benefits both!
  • Seed Dispersal: Animals eat fruit, and the seeds pass unharmed through their digestive system, dropping them far away from the parent plant (reducing intraspecific competition!).
  • Herbivory: Grazing animals (like cows) rely on plants for food, which in turn helps manage plant growth and nutrient cycling in the soil.

KEY TAKEAWAY: Interdependence creates stability. When the system is balanced, the populations rise and fall predictably, ensuring no single population explodes or crashes completely.


Final Quick Review

  • Adaptations help organisms survive. They can be Structural (physical), Behavioural (actions), or Physiological (internal).
  • Competition is the struggle for limited resources.
  • Intraspecific = Competition within the same species.
  • Interspecific = Competition between different species.
  • Interdependence means organisms rely on each other, often shown through the cycling populations in Predator-Prey relationships.

You've covered the foundation of how organisms interact! Keep practicing your examples, and you'll master this topic. Great job!