Monday, June 8, 2009

Cetacean response to climate change

A very recent review paper by Colin McLeod (see here for Univ Aberdeen press release) in Endangered Species Research, titled, "Global climate change, range changes and potential implications for the conservation of marine cetaceans: a review and synthesis", raises some critically important points about the distribution of whales and how that is likely to be affected by expected changes in global climate. Obviously, this is very, very important for all of us that care about modern Cetacea as well as the health of the world's oceans in general.

But I would also urge marine mammal paleontologists to consider something else about this paper. Note that McLeod goes through and meticulously reviews the preferred habitats of most modern cetaceans. One should not be surprised to find that very few of these have a fossil record that goes back to the middle Miocene, when the world was much warmer, and the typical polarized distribution of modern cetaceans is, in reality, an effect of the repeated expansions and contractions of many cetaceans that have evolved in favor of colder waters (and its associated productivity) several times within the last 2-3 million years. This antitropical distribution splits sister species from each other by a warm patch of water in tropcical (and sometimes even subtropical) zones.

The conundrum in making the fossil record of whales informative of the problems we are facing today is that the fossil record of cetaceans is best for the Miocene, from a time when they were experiencing a cooling trend, not a warming. The fossil record of cetaceans during the Pliocene and Pleistocene may be better suited for such a comparison to the modern situation, but it is simply not as well studied (or perhaps as abundant) as the Miocene fossil record is. In that way, if one were to try to predict how marine mammals would respond to a warming trend, it would probably be ideal to very carefully explore how they handled this during glacial-interglacial cycles.

BUT, one edge that the Miocene (and likewise late Eocene) has over these glacial times is some insight in the way that cetaceans interact in marine ecosystems that are warm, like those that will eventually come with the changes being wrought on our world. If one wants to best understand how cetaceans may interact when warmer waters dominate the ocean landscape, the Miocene is perhaps a better model system than even the present day. Granted, modern animals are still FAR more important to understanding their future than any fossil taxon (with its own phylogenetic baggage to deal with that could influence the data), the total community structure, distribution patters, and even physical interactions may be in part better understood when looking at an almost worldwide warm world full of cetaceans in the Miocene. For instance, there are clear differences in the distributions of platanistids and eurhinodelphids in the West Atlantic during the Miocene, and better understanding why such similar animals would have latitudinally partitioned a very warm coast is almost impossible to understand from today's taxa, even though it may happen to many of today's species in the not too distant future.

If there are any graduate students looking for projects out there, one I can easily see would be ones utilizing some of Colin McLeod's other work on correlations of prey size and osteological correlates to answering these sorts of questions. Likewise, other groups that have a different response to climate change, seacows, may be a worthwhile avenue to explore some of these questions as well. I wish I could do it all, and though I am trying to get a start with the Sirenia part of the equation, in the end there are too many questions for one person to ask in a lifetime, and I hope someone out there will give some of these studies with cetaceans a try.

1 comment:

  1. Brian,
    This is very interesting, thank for bringing it to our attention.
    About sirenians, I will poke around with those too.