MEPS 216:181-189 (2001)  -  doi:10.3354/meps216181

Ratio-dependent functional responses ‹ tests with the zooplanktivore Mysis mixta

Sture Hansson1,*, Bart T. De Stasio2, Elena Gorokhova1, M. Ali Mohammadian2,**

Department of Systems Ecology, Stockholm University, 106 91 Stockholm, Sweden Biology Department, Lawrence University, PO Box 599, Appleton, Wisconsin 54912-0599, USA
*E-mail: **Present address: 4820 Crockett Court, Raleigh, North Carolina 27606, USA

ABSTRACT: The response of a consumer to varying densities of its food resources is essential to consumer-resource interactions, yet the proper way to describe this interaction (the functional response) has been intensively debated. Traditionally, consumption has been assumed to be solely a function of resource abundance (prey dependent). However, it has lately been suggested that consumption depends on the ratio between resource and consumer abundances (ratio-dependent functional responses). In this paper, we experimentally tested if the consumer density influences food consumption rates. As the consumer, we used a dominant Baltic Sea zooplanktivore, the mysid shrimp Mysis mixta. The prey used were of 3 types; the large but slow Daphnia magna, the small and slow Artemia sp., and a natural assemblage of Baltic Sea copepods that exhibit strong escape responses. Our results show that intraspecific interactions occurred among the consumers, supporting the hypothesis that a functional response can be dependent on the consumer density.

KEY WORDS: Ratio-dependent functional responses · Predation · Mysis mixta · Zooplankton · Baltic Sea

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