Invasive Alien Species: The Nature of the Problem

Harold Mooney
Department of Biological Sciences
Stanford University
Stanford California 94305
Telephone: (650) 723-1179
Fax: (650) 723-9253
hmooney@jasper.stanford.edu

As commonly described, an invasive alien species is a species that is new to a region, and has a negative impact on the new environment, either, ecologically, economically or socially. Invasives represent all taxonomic groups and originate from all continents. There has been a massive mixing of biota globally driven by intercontinental commerce, and this mixing has been both purposeful and accidental. It has led to biotic enrichment as well as impoverishment. While only a small fraction of alien species have become invasive, these few have done enormous damage.

Invasive alien species represent a major disruption for all biotic systems including terrestrial and aquatic, managed and wild. Invaders can have enormous economic and human health impacts as well as degrading many system properties that society values. Invasive alien species have altered evolutionary trajectories, disrupted community and ecosystem processes, and caused large economic losses. There is a long list of ways that invasives can threaten the goods and services provided by natural systems and upon which society depends. Invasives can disrupt fire cycles, deplete water supplies, cause disease, decimate crops, forests and fisheries, impede navigation, clog water works, destroy grazing lands, homes and gardens, eliminate species, and even cause noise pollution.

Invasives pose special challenges for their control and eradication. Invasive microorganisms and insects, in particular, can quickly evolve responses to control efforts. Invaders alter and respond to community interactions in complex ways. As the global movement of people and goods increases, so too does the movement of potential invasive material. At the same time, other global changes -- like climate change -- mostly favor invasives.

Our information base for predicting, preventing, and controlling invasives is far from adequate. And, public awareness of the problem is also inadequate. Our responses to invasives are complicated by the lag times that commonly occur before their adverse effects are seen, rendering efforts to control them "too little, too late."

We require better information on:

• the kinds and conditions of habitats where invasives are most successful,
• the traits of successful invaders,
• the vectors of invasives,
• the mechanisms of habitat degradation due to invaders, and
• the cascading effects of invasives through ecological and socio-economic systems.

Scientists, managers, and policy makers require

• reliable predictive models of invasive potential and of habitat invasibility,
• environmentally benign, and inexpensive methods for the eradication or control of invasives, and
• the means to regulate the flow of potentially invasive organisms.

Yvonne Baskin captures the importance and complexity of the invasive species issue, stating

The spread of invasive alien species is creating complex and far-reaching challenges that threaten both the natural biological riches of the earth and the well being of its citizens. While the problem is global, the nature and severity of the impacts on society, economic life, health, and natural heritage are distributed unevenly across nations and regions. Thus, some aspects of the problem require solutions tailored to the specific values, needs, and priorities of nations while others call for consolidated action by the larger world community.