Invasive Species Disrupt Ecosystems by Outcompeting Endemic Species
- Invasive species often outcompete endemic species for limited resources, leading to significant ecological disruptions.
- This competition can result in population declines, habitat displacement, and long-term ecosystem instability.
- Cane toads in Australia, which outcompete native species is an example of an invasive species.
- More on this later...
Endemic vs. Invasive Species
Endemic Species
- Naturally occurring in a specific region.
- Highly adapted to local environmental conditions.
- Often have specialized niches and rely on balanced ecosystem interactions.
Invasive Species
- Non-native species are introduced, often by human activity.
- Spread rapidly and can disrupt native ecosystems.
- Often lack natural predators in their new environment.
The Competitive Exclusion Principle
Competitive exclusion principle
The competitive exclusion principle states that two species cannot occupy the same ecological niche indefinitely.
- If an invasive species has a competitive advantage, it can displace endemic species by:
- Outcompeting for Resources: Taking over food, water, or breeding sites.
- Occupying a Broader Niche: Exploiting more resources than native species.
- Reproducing More Rapidly: Growing in population faster than endemic competitors.
The Gray Squirrel in the UK displaced the native Red Squirrel by competing for food and spreading disease.
AnalogyThink of an invasive species as an uninvited guest at a party who eats all the food and takes over the dance floor, leaving little room for the original guests.
A Local Example: The Cane Toad in Australia
- The Cane Toad (Rhinella marina) was introduced to Australia in 1935 to control agricultural pests.
- Instead of helping, it became an invasive species, rapidly spreading across northern and eastern Australia.
- Why Cane Toads Outcompete Native Species:
- Broad Diet: Generalist feeders, eating insects, small mammals, and even amphibians.
- Rapid Reproduction: A single female can lay up to 30,000 eggs at a time.
- Toxicity: Produces a potent toxin, killing most predators that try to eat them.
- High Adaptability: Thrives in diverse habitats, from wetlands to urban areas.
Cane toads are native to Central and South America but were introduced to Australia to control sugarcane beetles.
Impact on Endemic Species
The competitive advantages of cane toads have caused severe ecological damage, particularly for Australia’s native amphibians, reptiles, and predators.
- Predation & Poisoning: Native predators (e.g., snakes, lizards, quolls) die after consuming toxic cane toads.
- Resource Depletion: Outcompete native amphibians for food and breeding sites, reducing local populations.
- Ecosystem Disruption: Declines in native predators and prey disrupt food webs, altering ecosystem balance.
Declines in Northern Quolls due to cane toad poisoning have led to shifts in rodent and insect populations.
TipCane toads are nocturnal, allowing them to avoid competition with diurnal species for food and space.
Why Do Invasive Species Succeed?
- Invasive species thrive in new environments because they often:
- Lack Natural Predators or Pathogens that would control their populations.
- Have High Reproductive Rates, allowing for rapid expansion.
- Possess Broad Ecological Niches, making them highly adaptable.
- Show Resistance to Environmental Stresses, such as drought or pollution.
- Don't confuse the terms "invasive" and "non-native."
- Not all non-native species are invasive; a species is only considered invasive if it causes harm to the local ecosystem.
Zebra Mussels invaded the Great Lakes in North America, overwhelming native species by filter-feeding and altering nutrient cycles.
The Role of Human Activity
Human activities, such as global trade and travel, have accelerated the spread of invasive species.
ExampleIn the case of the cane toad, its introduction to Australia was a deliberate attempt to control agricultural pests.
- Unintended Consequences:
- Many introduced species lack ecological assessments, leading to uncontrolled spread.
- Human-modified environments (e.g., deforestation, urbanization) create new opportunities for invasives.
How do human actions shape ecosystems, and what ethical responsibilities do we have to mitigate the impacts of invasive species?
Managing Invasive Species
- Controlling invasive species is difficult but necessary for biodiversity conservation.
- Strategies include:
- Biological Control: Introducing natural predators or pathogens to reduce invasive populations.
- Chemical Control: Using pesticides or toxins, though this can harm non-target species.
- Physical Removal: Manually capturing or eradicating invasive species.
- Prevention: Implementing policies to prevent the introduction of new invasive species.
In Australia, researchers are developing a biological control method using a virus to target cane toad tadpoles without affecting native species.
Reflection and Broader Implications
- The competition between endemic and invasive species underscores the delicate balance of ecosystems.
- Invasive species not only threaten biodiversity but also impact ecosystem services, such as water purification and soil fertility.
- How can invasive species management be improved?
- Are there ethical concerns in using biological control?
To what extent should humans intervene in ecosystems to control invasive species?


