Invasive species change the composition of native ecosystems. Native plants and wildlife may not have evolved defense mechanisms against the invader; alternatively, native species may not be able to compete for needed resources with a species that has no predators. This leads an invader to spread quickly and perhaps take over an area.
Invasive species change not only the way natural systems look but also the way they function. Infestations can disrupt forest succession, species composition, water absorption and circulation, nutrient cycling, or even create toxic growing conditions for other plants and animals.
The direct threats of invasive species:
- out-competing native species for food or other resources
- preying on native species
- causing or carrying disease
- preventing native species from reproducing or killing their young
Invasive species can be harmful to human health as well. Research suggests that loss of trees to emerald ash borer is associated with an increase in mortality related to cardiovascular and lower respiratory tract illness. Invasive shrubs can increase populations of Lyme disease-carrying ticks. Heavy infestations of barberry – a thorny, multi-branching shrub – make particularly good hiding places for mice and cause populations to increase. Mice are an alternate host for Lyme disease. Larger mouse populations mean more Lyme disease-carrying ticks.
Many of our commercial, agricultural, and recreational activities also depend on healthy native ecosystems.