Dk. Branstrator, ECOLOGICAL INTERACTIONS BETWEEN BYTHOTREPHES-CEDERSTROEMI AND LEPTODORA-KINDTII AND THE IMPLICATIONS FOR SPECIES REPLACEMENT IN LAKE-MICHIGAN, Journal of Great Lakes research, 21(4), 1995, pp. 670-679
The zooplankton predator, Leptodora kindtii, declined in abundance at
an offshore reference station in Lake Michigan in the mid-1980s follow
ing the invasion of another zooplankton predator, Bythotrephes cederst
roemi. Both predators feed largely on daphnid prey and it was observed
that densities of three Daphnia species declined in abundance at the
reference station following the Bythotrephes invasion. Circumstantial
evidence would suggest that the native predator, Leptodora, was compet
itively suppressed by Bythotrephes. However, results of laboratory exp
eriments presented here show that Bythotrephes will readily attack and
eat Leptodora when the predators are maintained under concentrated de
nsities, even if alternative prey are available for the Bythotrephes.
There was no evidence in these experiments that Leptodora attacked or
ate Bythotrephes. These results imply that predation by Bythotrephes o
n Leptodora may alternatively account for the collapse of Leptodora in
offshore Lake Michigan. In this note I discuss evidence in support of
competition and predation as alternative hypotheses to explain the pa
ttern of species replacement, Bythotrephes for Leptodora, observed in
Lake Michigan. The existing data are not definitive and tempt further
inquiry.