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Energetics of Vertical Migration in Chaoborus Trivittatus Larvae
Author(s) -
Swift Michael C.
Publication year - 1976
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1941056
Subject(s) - energetics , diel vertical migration , predation , instar , larva , growth rate , biology , ecology , zooplankton , range (aeronautics) , zoology , geometry , mathematics , composite material , materials science
One of the recent theories for the adaptive value of vertical migration states that migrants gain an energetic advantage over nonmigrants because by alternating between areas of high and low temperatures they are able to partition energy into growth more efficiently than nonmigrants. The energetics of the vertical migration of fourth—instar Chaoborus trivittatus larva in Eunice Lake, British Columbia was studied to identify and quantify this hypothesized energetic advantage. Fourth—instar C. trivittatus larvae undergo a regular, synchronous, diel vertical migration which exposes them to a wide range of temperature and prey density. Feeding occurs primarily at night and near the surface. Although all zooplankton in Eunice Lake are potential prey, Diaptomus kenai constitutes the majority of the biomass in the diet of fourth—instar larvae; Carbon assimilation efficiency of both copepods and cladocerans by C. trivittaus is ° 68%. Respiration rate increases linearly with temperature over the range 5—25 degrees C, although there is a suggestion of a plateau in O_2 consumption over the temperature range to which the larvae are exposed during migration. Temperature and ration size interacted to determine larval growth rate; fluctuating temperatures limited growth regardless of prey density while at constant high temperature prey density limited the growth rate. Analysis of several possible migration strategies showed that on an energetics basis alone growth will be maximized by either staying near the surface where there is food, or by vertically migrating with a physiologically determined periodicity based on individual feeding history. Laboratory growth experiments and the results of computer simulations of vertical migration show that the energetic hypothesis for the adaptive value of vertical migration does not hold for C. trivittatus larvae in Eunice Lake. These larvae do not follow either of the migration strategies that is energetically most efficient. No alternative hypothesis to explain their migration pattern is attractive. Possibly it is maintained by immigration from populations exposed to strong selection for this behavior pattern.