A key question in ecology is: who eats whom? This can be fairly straightforward to answer, by observing predatory or grazing activities, by opening up stomachs or sifting through feces, or even by analyzing chemical signals.

A more challenging follow-up question is then: how many do they eat? Calculating a rate of consumption is considerably trickier!

I've run up against this problem as a result of an astute comment on my Polluted Whales post a couple of days ago. Sure, sperm whales accumulate toxins from the squid they eat, and the squid accumulate it from their own diet, but what are the numbers here? How many squid does the average sperm whale eat in a day? How many krill does the average squid eat, and how much phytoplankton is consumed by each of those krill?

If we had answers to those questions, we could use data on toxin absorption by phytoplankton (if those data, in turn, can be found) to calculate exactly how much toxin gets bioaccumulated up the food chain.

But I can't seem to track down any of those numbers . . . help, anyone?