Foraging behaviour and invasiveness:: do invasive Gambusia exhibit higher feeding rates and broader diets than their noninvasive relatives?

Serious impacts by nonindigenous species often occur via predation. The magnitude of impact is expected to be closely tied to the invading species niche breadth. For predatory impacts, diet breadth should be particularly important. We examined the relationship between a species foraging behaviour and its invasiveness and impact by comparing the feeding behaviour of four Gambusia species, two invasive and of high impact and two noninvasive. Individual feeding rates, feeding preferences, and diet breadths were tested across three prey items in a sequence of four laboratory feeding trials. Invasive Gambusia consistently fed at higher rates, but no species differences were found in feeding preferences or diet breadth. All Gambusia preferred Daphnia, avoided Lirceus, and consumed Drosophila in proportion to their availability. Female size affected most feeding variables. Larger fish consumed more prey per unit time and were able to incorporate larger prey items into their diets, thus increasing diet breadth.