🐸 Invasive species
Invasive species
Invasive species often spread rapidly because they escape their natural predators, parasites, and diseases from their original habitat.
- Arrive through trade, travel, pets, farming, or ship ballast
- Outcompete native species for food and space
- Can become predators, pests, or disease carriers
Why this is an indirect human impact: Invasive species are an indirect human impact because humans introduce them, but the damage occurs through altered species interactions. By outcompeting or preying on native species, invasive species redirect energy through food webs and reduce ecosystem stability.
Invasive species often succeed because they have few or no natural predators and access to abundant resources.
Case studies (know 1–2 for exams)
- Cane toads (Australia): introduced for pest control → poisonous → predators die → toads spread widely
- Zebra mussels (USA): arrived in ship ballast water → clog pipes → filter plankton → disrupt food webs
- Rabbits (Australia): introduced for hunting → population explosion → overgrazing → habitat damage
What actually happened (in simple terms):
- Cane toads: Released in 1935 to eat crop pests. They are toxic, so native predators died after eating them. With no predators, toads multiplied rapidly and spread across Australia.
- Zebra mussels: Accidentally brought from Europe in ship ballast water. They reproduce very quickly, block pipes, and remove plankton from the water, starving native species.
- Rabbits: Introduced in 1859 for sport hunting. With plenty of food and no predators, their numbers exploded. They overgrazed vegetation, damaged soils, and outcompeted native animals for food.
Exam technique: Use the arrow summary to recall the case quickly, then explain why each step happened to gain full marks.