Evol Ecol Res 9: 651-662 (2007)     Full PDF if your library subscribes.

Could whales have maintained a high abundance of krill?

Jay Willis*

QMS Program, School of Zoology, University of Tasmania, Hobart, TAS 7001 and CSIRO CMAR, Pelagic Fisheries, Castray Explanade, Hobart, TAS 7001, Australia

e-mail: jay.willis@csiro.au


Question: Several million large whales were killed between 1900 and 1970. All these whales preyed on krill (Euphausia superba). Why has krill population abundance declined after the elimination of their primary predator?

Hypothesis: Krill have changed their behaviour due to the absence of whales and this change in behaviour has resulted in a decrease in krill abundance.

Methods: I reproduced a computer model of krill life history. I then extended the model as an individual-based model to show the effects of habitat choice on individual lifetime reproductive success and abundance.

Conclusions: In the context of our current understanding of krill physiology, predator-invoked behaviour may lead to increased population abundance and, without the predator, natural selection may favour behaviour that would lead to lower abundance. This reverses the predictions of mass balance ecosystem models.

Keywords: computer model, IBM, regime change.

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