Indirect Effects in an Experimentally Staged Invasion by a Major Predator

Area of Science:

• Ecology
• Invasive Species Biology
• Food Web Dynamics

Background:

• Invasive species can disrupt native ecosystems.
• Understanding the cascading effects of introduced predators is crucial for conservation.
• Island ecosystems are particularly vulnerable to biological invasions.

Purpose of the Study:

• To experimentally assess the ecological impacts of the introduced lizard Anolis sagrei.
• To differentiate between direct and indirect effects of an invasive predator on a food web.
• To evaluate the long-term consequences of species invasion over a seven-year period.

Main Methods:

• A seven-year field experiment was conducted on a system of small islands.
• Lizard propagules (Anolis sagrei) were introduced to four lizard-naïve islands.
• Control islands included those with naturally occurring lizards and those without lizards.

Main Results:

• Lizard introduction significantly reduced shrub leaf damage.
• Anolis sagrei increased the abundance of small aerial arthropods but not large ones.
• Direct predation by lizards strongly and rapidly increased spider density.

Conclusions:

• Introduced Anolis sagrei can alter food web structure from producers to higher trophic levels.
• Direct ecological effects of predators are generally stronger and more consistent than indirect effects.
• Invasive predators can have profound and measurable impacts on island ecosystems.