Invasive Species & Biodiversity Loss

You’ll be able to

Explain why invasive species succeed and the harm they cause
Use HIPPCO to organize the major causes of biodiversity loss
Describe conservation strategies that protect endangered species

Why invasive species thrive

An invasive species is a non-native organism that spreads rapidly in a new environment and causes ecological or economic harm. They succeed because, in the new range, they typically have no natural predators, parasites, or competitors to keep them in check, often reproduce quickly (r-selected), and are generalists with broad tolerance. Freed from the controls of their home ecosystem, they outcompete or prey on native species. Examples include zebra mussels clogging Great Lakes pipes, kudzu smothering southern forests, Burmese pythons in the Everglades, and cane toads in Australia.

HIPPCO: the drivers of biodiversity loss

Biologists summarize the causes of biodiversity loss with the acronym HIPPCO: Habitat destruction (the single biggest cause — including fragmentation), Invasive species, Population growth (of humans, magnifying every other pressure), Pollution, Climate change, and Overexploitation (overhunting, overfishing, poaching). Most endangered species face several of these at once. Recognizing HIPPCO lets you diagnose why any given species is declining and target the right conservation response.

Protecting biodiversity

Conservation works on several fronts. Laws like the U.S. Endangered Species Act (1973) protect listed species and their critical habitat, and the international CITES treaty bans trade in endangered wildlife. Protected areas — national parks, wildlife refuges, marine reserves — preserve habitat, ideally large and connected by corridors (recall island biogeography). Captive breeding and seed banks preserve genetic diversity for species on the brink. Because habitat destruction is the leading threat, protecting and restoring habitat is the most powerful conservation tool of all.

HIPPCO — causes of biodiversity loss

Habitat destruction · Invasive species · Population growth · Pollution · Climate change · Overexploitation

Habitat destruction is the #1 cause of extinction; invasive species are #2. Most threatened species suffer from several HIPPCO factors simultaneously.

Worked example

The brown tree snake, accidentally introduced to the predator-free island of Guam, exploded in number and drove several native bird species to extinction. Explain, using invasive-species biology, why it caused such damage.

1.The snake is non-native to Guam, so it arrived without the predators, parasites, and competitors that limit it in its home range.
2.Guam’s native birds had never evolved alongside such a snake, so they lacked defenses against it.
3.Free of population controls and facing defenseless prey, the snake reproduced rapidly and preyed heavily on the birds.
4.With no checks on the snake and no bird defenses, native bird populations collapsed to extinction — the "I" in HIPPCO in action.

Answer: Released from its natural predators and facing prey with no evolved defenses, the brown tree snake multiplied unchecked and wiped out native birds — a textbook invasive-species catastrophe.

Checkpoint

Which factor best explains why an introduced invasive species often spreads explosively in its new environment?

Tip

Memorize HIPPCO for the causes of biodiversity loss, and remember the ranking: Habitat destruction is #1, invasive species #2. When a question asks for the greatest threat to biodiversity, habitat destruction/loss is almost always the correct answer.

Checkpoint

According to the HIPPCO framework, what is the single greatest cause of biodiversity loss and species extinction worldwide?

On the exam

Tie the units together on the exam: invasive species succeed for the same reasons r-strategists and generalists do (Unit 3, Unit 2), and corridors between protected areas apply island biogeography (Unit 2). HIPPCO with habitat loss at #1 is the framework graders look for on biodiversity free-response questions.

Answer the 2 checkpoints as you read.