Trophic cascades in rocky shore tide pools: distinguishing lethal and nonlethal effects

• Published in: Oecologia 2004-05, Vol.139 (3), p.427-432
• Main Authors: Trussell, Geoffrey C, Ewanchuk, Patrick J, Bertness, Mark D, Silliman, Brian R
• Format: Article
• Language: English
• Subjects: Algae; Analysis of Variance; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Aquatic plants; Biological and medical sciences; Brachyura - physiology; Carcinus maenas; Chlorophycota; Chlorophyta - growth & development; Community development; Community Ecology; Community structure; Crabs; Crustaceans; Ecology; Ecosystem; Emigration; Feeding Behavior - physiology; Food Chain; foraging; Fundamental and applied biological sciences. Psychology; Gastropoda; General aspects; Marine ecology; Massachusetts; Population Density; Population Dynamics; Predation; Predators; Prey; risk; risk reduction; Sea water ecosystems; Snails; Snails - physiology; surface area; Synecology; Tide pools; Trophic cascades; Trophic relationships
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s00442-004-1512-8

The effects of predators on the density of their prey can have positive indirect effects on the abundance of the prey’s resource via a trophic cascade. This concept has strongly influenced contemporary views of how communities are structured. However, predators also can transmit indirect effects by inducing changes in prey traits. We show that the mere presence of predator risk cues can initiate a trophic cascade in rocky shore tide pools. In large (mean surface area =9 m²), natural tide pools, we manipulated crab density and their foraging ability to examine the relative importance of lethal (density-mediated) and non-lethal (trait-mediated) predator effects to algal community development. We found that perceived predation risk reduced snail density as much as the direct predation treatment, showing that green crab predation was not an important factor regulating local snail density. Instead, snail emigration away from resident crabs appears to be the most important factor regulating local snail density. As a result, the abundance of ephemeral green algae was similar in the predation risk and direct predation treatments, suggesting that the consumption of snails by crabs plays a minimal role in mediating the trophic cascade. Increased attention to trait-mediated effects that are transmitted by predator-induced changes in prey behavior may change our view of how predators exert their strong influence on community structure.