Although humans have successfully evolved to alter their environment in most any way to provide for the comforts of living, these changes to our environment have come with a cost. Ecosystem services provide us with a plethora of resources that most humans take for granted: clean water, erosion control, fertile soil, abundant food, and so on. However, these services are being interrupted by land-use change and other human induced alterations to the natural processes that provide us with these services. The effect from invasive species is among the top contributions to the degradation of ecosystem services.
These effects from invasive species can be quantified by large losses to the United States economy. In Florida, hydrilla (Hydrilla verticillata), an aquatic weed, is contributing to the loss of fish and aquatic animals, clogging waterways, and reducing the recreational use of waters. Florida agencies are actively controlling for this invasive species, spending $14.5 million each year. Regardless, hydrilla has costed $10 million per year in lost revenue due to reduced recreation in just two lakes. This case is just a part of the $100 million that is spend annually in the United States on control of nonindigenous aquatic weed species. Non-indigenous crop weeds have cost U.S. agriculture about $27 billion per year in relation to a total estimated crop value of $267 billion. This includes a 12% in crop reduction that is not being produced to feed American families.
Cats aren't often considered invasive species, but it has been estimated that feral and outdoor cats kill 568 million birds per year in the United States. By considering the cost of each individual bird through comparing values spent by bird watchers, hunters, and ornithologists at $30, cats cost the United States $17 billion in the loss of native birds. This does not include the cost of killed amphibians, reptiles, and small mammals.
It is also important to consider the non-marketed ecosystem services that are provided to us by the natural environment. European cheat-grass (Bromus tectorum) has established as a monoculture in 5 million hectares of Idaho and Utah. This invasion alters the fire regime in the shrub-steppe habitats of the Great Basin, excluding or reducing the abundance of shrubs, grassland vegetation, and the animals dependent on this ecosystem. Goats (Capra hirus), introduced onto the San Clemente Island in California for for farming, have caused the extinction of eight endemic lant species and are threatening eight more. A loss of biodiversity or habitat alteration may not just disrupt the ecosystem services, but also the intrinsic value that is associated with wilderness as it has been for generations.
This table shows the estimated cost of damages and control of a number of different major taxonomic groups of invasive species.
Pimentel et al. 2000. Environmental and Economic Costs of Nonindigenous Species in the United States. BioScience. 50(1): 53-65.