- Position‹3 of 3
- Invasive species help ecosystems
- Argument1 of 2›
Invasive species are pest killers
Pests are a universal problem. No one likes them, and they often carry diseases. Invasive species have often been introduced into habitats where pests run rampant. Because of the invasive species, the pests’ populations have successfully diminished.
The argument
Not every species that arrives from elsewhere arrives by accident, and not every arrival is a loss. Some are introduced deliberately, as a control measure, because they prey on something already doing damage. Harlequin ladybirds were brought into North America and Europe for exactly this reason: to eat aphids, which feed on crops and garden plants in large numbers and are difficult to suppress by other means. The reasoning behind such introductions is straightforward. Pests are, by definition, organisms whose presence subtracts from an ecosystem or from the human use of it. If a pest population is reducing the health and productivity of the plants around it, then anything that reduces that population restores what was being lost. A predator does this continuously and without further input: once established, it finds the pest, feeds on it, and keeps feeding on it for as long as the pest is there, which a single intervention cannot do. The suppression is self-sustaining in a way that other methods are not. On this view the label "invasive" describes where a species came from rather than what it does. A species that arrives and suppresses a damaging pest is doing the ecosystem a service, and judging it by its origin rather than its effect is the wrong test. Proponents of this position argue that the case against introduced species rests on the examples where an introduction went badly, and that the cases where it went well — where a pest was brought under control and the plants it was destroying recovered — show that introduction as such is not the problem. Where an introduced species does the job it was brought in to do, it can be a way of saving an ecosystem rather than a threat to it.
Premises
Counter-arguments
Pests are beneficial, and bring balance to an ecosystem. For example, cockroaches are pests, but their consumption of waste provides Nitrogen to plants to help them grow and stay healthy. Without pests, the ecosystem would be thrown in disarray.
Rejecting the premises
[Rejecting P1] Some invasive species kill off beneficial organisms too. [Rejecting P2] Pests are beneficial to an ecosystem.