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The causes and consequences of sex‐specific mortality in a freshwater copepod 1
Author(s) -
Hairston Nelson G.,
Walton William E.,
Li Kao T.
Publication year - 1983
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1983.28.5.0935
Subject(s) - predation , copepod , biology , ecology , population , sex ratio , mortality rate , fish <actinopterygii> , zoology , fishery , crustacean , demography , sociology
We studied skewed adult copepod sex ratios in two ponds in an attempt to understand the ecological causes and evolutionary consequences of this life‐history phenomenon. In ponds containing populations of zooplanktivorous sunfish, female copepods suffered higher mortality rates than males, while in ponds lacking these predators, male and female mortality rates were similar. Field and laboratory experiments showed that females, especially those carrying eggs, were more visible than males and that added visibility accounted for higher predation by fish on these individuals. We calculated the cost of carrying eggs in terms of the decreased population growth rate it produces, and then estimated the magnitude of egg mortality necessary to select for the egg‐carrying strategy. Eggs not carried would have to suffer at least 58% mortality for egg carrying to evolve in the presence of selective fish predation. The response of the copepods to these strong selective pressures lies in a third direction, the production of diapausing eggs.