Lesson Outcomes

After completing this lesson, learners will be able to:

• Define an invasive alien species (IAS).
• Describe the characteristics of invasive alien species.
• Explain how invasive alien species affect biodiversity.
• Identify the environmental impacts caused by invasive alien species.
• Describe the Environmental Impact Classification for Alien Taxa (EICAT).
• Explain why identifying invasive alien species is important in biodiversity conservation.

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Overview

One of the greatest threats to biodiversity is the spread of invasive alien species (IAS). These are plants, animals or other organisms that occur outside their natural range and establish themselves in new environments where they negatively affect indigenous species and ecosystems.

The learner guide explains that invasive alien species have specific characteristics that allow them to spread successfully and compete with indigenous species. Understanding these characteristics enables Eco-Rangers to identify invasive species early and support conservation programmes aimed at protecting biodiversity.

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1. What Are Invasive Alien Species?

An invasive alien species is a plant, animal or other organism that has been introduced into an area where it does not naturally occur and causes harm to biodiversity, ecosystems, property or the economy.

To become invasive, a species generally:

• Adapts easily to its new environment.
• Reproduces rapidly.
• Spreads successfully.
• Competes with indigenous species.
• Causes environmental or economic harm.

Not every alien species becomes invasive, but those that do can significantly affect ecosystem health.

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2. Characteristics of Invasive Alien Species

The learner guide identifies several characteristics that make invasive alien species successful.

These include the ability to:

• Adapt quickly to new environments.
• Reproduce rapidly.
• Spread over large areas.
• Compete successfully with indigenous species.
• Survive under different environmental conditions.

These characteristics often allow invasive species to dominate habitats and reduce biodiversity.

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Illustration: Characteristics of Invasive Alien Species

      Invasive Alien Species

               │
 ┌─────────────┼─────────────┐
 │             │             │
 ▼             ▼             ▼
Adapt Easily  Reproduce   Spread Rapidly
              Quickly
 │             │             │
 └─────────────┼─────────────┘
               ▼
 Compete With Indigenous Species
               │
               ▼
 Reduce Biodiversity

Figure 1: Characteristics that allow invasive alien species to establish and spread.

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3. Environmental Impacts of Invasive Alien Species

Invasive alien species may negatively affect ecosystems by:

• Competing with indigenous species.
• Reducing biodiversity.
• Altering habitats.
• Disrupting ecological processes.
• Affecting ecosystem stability.

These impacts may result in the decline of indigenous plants and animals and reduce the ability of ecosystems to function naturally.

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Example

An invasive plant may spread rapidly through a wetland, reducing the space and resources available for indigenous vegetation.

As indigenous plants decline, animals that depend on them for food or shelter may also be affected.

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4. Environmental Impact Classification for Alien Taxa (EICAT)

The learner guide introduces the Environmental Impact Classification for Alien Taxa (EICAT).

EICAT is a method used to classify invasive alien species according to the environmental impacts they have on indigenous species and ecosystems.

It considers different impact mechanisms, including:

• Competition.
• Predation.
• Hybridisation.
• Transmission of diseases.
• Parasitism.
• Poisoning or toxicity.
• Biofouling.
• Grazing, herbivory and browsing.
• Chemical, physical or structural impacts on ecosystems.
• Interaction with other species.

This classification assists conservation organisations in identifying and prioritising invasive alien species for management.

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5. Why Identifying Invasive Alien Species Is Important

Early identification allows conservation organisations to:

• Protect indigenous biodiversity.
• Reduce environmental damage.
• Monitor ecosystem health.
• Support biodiversity conservation programmes.
• Plan appropriate management actions.
• Improve environmental decision-making.

The earlier an invasive species is identified, the greater the opportunity to reduce its environmental impact.

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The Role of an Eco-Ranger

Eco-Rangers contribute by:

• Identifying invasive alien species during patrols.
• Recording sightings accurately.
• Monitoring the spread of invasive species.
• Reporting observations according to organisational procedures.
• Supporting biodiversity monitoring programmes.

Accurate identification contributes to effective conservation management.

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Field Application

During biodiversity monitoring, an Eco-Ranger may observe:

• New invasive plant species.
• Changes in indigenous vegetation.
• Declining native species.
• Areas where invasive species are spreading.
• Environmental changes associated with invasive species.

These observations support conservation planning and biodiversity protection.

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Key Terms

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Key Notes

• Invasive alien species occur outside their natural range and may harm biodiversity.
• Successful invasive species adapt easily, reproduce rapidly and spread quickly.
• Invasive alien species may compete with indigenous species and alter ecosystems.
• EICAT classifies invasive alien species according to their environmental impacts.
• Early identification supports effective biodiversity conservation.
• Eco-Rangers play an important role in monitoring and reporting invasive alien species.