Invasive Species Hypotheses Losing Steam And Support
August 23, 2012

Support For Major Hypotheses Invasion Biology On The Decline

April Flowers for - Your Universe Online

Invasive species cost the world a whopping $1.4 trillion dollars a year.

Humans are the main culprit behind the introduction of invasive species such as plants, animals or even microbes. Specific examples of these include zebra mussels in the Hudson River, Burmese pythons in the Florida everglades, giant hogweed in the Czech Republic, and gray squirrels in the UK.

Invasive species are responsible for the loss of natural resources and biodiversity, damages to infrastructure, and an uptick in infectious diseases. However, not all invasive species cause damage or pose a threat.

Scientists around the world have spent the last several decades teasing apart the conditions that set the stage for debilitating invaders. A number of hypotheses have emerged to help predict the impact a species will have on a natural area. An analysis of 371 invasion studies using six dominant invasion hypotheses has revealed that their predictive power is weakening.

The paper, published in the open access journal NeoBiota, found empirical support for all six hypotheses declining, with recent studies showing the lowest levels of support. Theories that were too broad or omitted ecosystem interactions fared the worst, plants proved easier to predict than animals, and contrary to popular belief, diverse ecosystems are not inherently resistant against invaders.

"The observed decline effect means our confidence in making sound policy and management decisions based on the six analyzed hypotheses is lower today than it was in the past. Scientists were overly optimistic about the predictive power of these hypotheses. Given that invasive species are an expensive and ever growing problem, this is a situation that needs to be addressed," according to the paper's authors.

Declines in the efficacy of hypotheses has been noticed in other disciplines, among them pharmacological research, psychology, and animal behavior. Most attribute this to publication bias, inadequate sample sizes, and a tendency of early tests of the hypotheses to pick study organisms or systems where positive results are expected.

"The decline effect is both worrying and fascinating. It's a phenomenon that should be investigated across disciplines, as medical and psychological researchers have shown its effects can be strong, and it can distort the predictive power of hypotheses," states Jonathan Jeschke from Technische Universitat Munchen.

The paper's authors offer four solutions to improve current hypotheses in invasion biology:

(1) Existing gaps in empirical tests of hypotheses should be filled. The study revealed crucial gaps in empirical studies, showing that most studies have focused on terrestrial plants but have ignored other organisms and aquatic habitats.

(2) Existing hypotheses should be specified for groups of organisms and habitats.

(3) Interactions of invasive species with their new ecosystems should be regularly considered. The study shows that hypotheses considering such interactions are better supported by empirical evidence than other hypotheses.

(4) Revised hypotheses should be rejected if they do not work. Those hypotheses that still lack empirical support after specification for groups of organisms and habitats (solution 2), consideration of invader-ecosystem interactions (solution 3), or another form of revision should be discarded. Scientists should not waste time and resources to continue working with these hypotheses. Instead, fresh ideas and novel hypotheses are needed to further our understanding of biological invasions — something that is essential to effective management in today's rapidly changing world.