How do invasive species cause native species to decline?

Invasive species disrupt ecosystems and cause native populations to decline through several primary mechanisms:

• Predation: Invasive predators, such as the brown tree snake on Guam or feral cats on islands, often prey on native species that lack evolutionary defenses, leading to rapid population crashes or extinction.123
• Resource Competition: Invasive organisms may outcompete native species for essential resources like food, water, or living space. By effectively monopolizing these necessities, they can displace indigenous populations.1
• Disease Transmission: Invasive species often act as vectors for parasites and pathogens. For example, the accidental introduction of a fungus caused chestnut blight, which decimated the American chestnut tree.13
• Hybridization: When an introduced species interbreeds with a rare native relative, the native species can be genetically swamped, threatening its distinct identity and survival.3
• Habitat Alteration: Invasive herbivores, such as goats, or aggressive plants like purple loosestrife, can fundamentally transform landscapes, destroying the natural vegetation that native species rely on for survival.23