Helmets and Invisible Armor: Structures Reducing Predation from Tactile and Visual Planktivores

• Published in: Ecology
• Main Authors: O'Brien, W. John, Kettle, Dean, Riessen, Howard
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1979
• Subjects: Zooplankton
• Online Access: http://dx.doi.org/10.2307/1937657; http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.2307%2F1937657; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.2307%2F1937657; https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.2307/1937657

Several arctic Alaskan lakes were found to have populations of both visual—feeding planktivorous fish and the tactile—feeding predaceous copepod Heterocope septentrionalis. Feeding experiments and reactive distance measurements were carried out to determine the relationship between zooplankton size and susceptibility to both types of predation. Heterocope was found to feed selectively on small prey forms and fish on large forms, thereby confirming that the zooplankton in these lakes are subject to conflicting selective pressures. Two of the species of zooplankton appear to have adapted to this situation by developing structures that increase their actual size, thus helping to protect them from invertebrate predation while not altering the visual body size they present to fish.