The selfish huddle

As it is December now and the frost is creeping in I thought I’d talk about one of the all time favourite winter animals: the penguin! These happy footed, tuxedoed up cartoon-esque waddlers are among the most charismatic and endearing of creatures. They are favourites in films, books, documentaries, toys and of course a must on Christmas cards. Tales of their romantic dances, lifelong partnerships and working together to get through the winter have long been a part of the ‘nicer side’ of wildlife television and research. But are these loveable, laughable poster birds of cooperation and cuteness really all that genuine? Recent research would suggest not…

It has long been observed that emperor penguins form mass huddles to help prevent heat loss while they incubate their eggs amid Arctic storms. Anybody who has watched March of the Penguins can’t help but feel for the poor mites as they shuffle about with ice crystals covering their faces! Morgan Freeman also gives a heart warming narrative of their struggles during this time and how they “take turns” to be at the centre of these huddles so nobody is left at the edges long enough to freeze entirely. Nice thought, but it seems not quite the reality. A paper published in Plos one last week looked at the mathematics of the famous penguin huddles. What they found was that the shape and movement of these huddles over time was most accurately (although not perfectly) described by individual penguins setting out to minimize their own heat loss, rather than generously taking turns.  Penguins at the edges seek to move toward the centre while those in the centre have neither the space nor inclination to move anywhere so remain stationary. The result is a dynamic huddle that actually achieves pretty uniform heat loss from the huddle. So in this case being selfish can benefit the group.

This is not the first account of penguins acting in a less than Disney-like fashion: they have been observed stealing pebbles from neighbours’ nests and waiting to see whether other, more hungry, souls fare okay in orca/seal infested waters before jumping in themselves. There are stories too of them pushing their fellows off ice floats in to swelling seas to check for leopard seals but these are largely dispelled by researchers as misconceptions of the unfortunate results of the hustle and bustle of clumsy penguins perched on cliff edges!

I’m sorry to shatter any illusions of a wholly philanthropist snuggly-for-the-sake-of-it penguin but it is another nice example of how we humans often choose to perceive interactions in the animal world based on our own ideas of moral obligation: we like to see penguins cuddling in the cold to say “see what we can face when we work together?” Don’t worry though, I am sure that none of these findings will do much to shake the penguins off of their happy-go-lucky, cuddly pedestals and they will still be a key player in the Christmas festivities and focus points of many a blockbuster documentary to come. After all, who can resist that waddle!?

Author

Deirdre McClean: mccleadm[at]tcd.ie

Photo credit

www.funnycutepics.com

Cod, correlation and causation

so help you Cod

 at the Guardian reports on a battle between science and politics which is worth highlighting. The Atlantic cod fisheries in the Atlantic collapsed during the 90s due to overfishing. They have yet to recover. The Atlantic cod is an apex predator and its decline effected a trophic cascade, which modified the original food web, perhaps irrevocably.

The Canadian government is holding the grey seal responsible for this. They argue that the seals, which are growing in number, are preventing the recovery of the stocks and are planning to kill 70,000 of them next year.

This has vexed a group of marine biologists at Dalhousie University so much that they wrote an open letter arguing that cod are rarely preyed upon by the seals. Instead, the cod’s main predators are other, larger fishes. And in actual fact, the seal preferentially feeds on these fishes. So any reduction in seal numbers will produce the opposite result to the one intended, seals will be killed, the predatory fish population will increase, and the cod population will decline even further.

Correlation does not imply causation. But perhaps, the view of the Canadian government is that of Winston Churchill who once remarked, scientists should be on tap, not on top.  It will be interesting to see how this one plays out.

Author

Adam Kane: kanead[at]tcd.ie

Photo credit

wikimedia commons

What did what to what? Finding causality in chaos.

A new paper has been published in Science by George Sugihara and colleagues, which is an immediate contender for the most insightful paper I’ve ever read. In the paper they outline a new method, which they dub ‘Convergent Cross Mapping’ (CCM), for detecting causality between variables using time series data. Not only does CCM allow for the detection of causality but also its directionality. The method takes us well beyond the previous confines of Granger causality (which requires the assumption that systems are linear, or are showing linear behaviour near an equilibrium), and allows us to tease out causality in systems that show non-linearity and chaos. As examples of possible applications of their method the authors address two classic causality problems:

Predator-prey dynamics of Didinium and Paramecium. The authors show that there is bidirectional causality in this classic predator-prey system, but that top-down control is stronger than bottom up control (i.e. Didinium has a larger effect on the Paramecium population than vice-versa).

Dynamics of Pacific sardines and anchovies. There has been a long-standing debate about the cause of alternating dominance between sardines and anchovies in the Pacific. Some arguing that competition between the species is the driver, while others claim the pattern is caused by differing responses to temperature. The authors weigh in on this debate by showing that, while sardine and anchovy abundance is negatively correlated, this is a mirage as there is no causation in either direction. The authors also unambiguously show that sea surface temperature does causally affect the abundance of both species, indicating that climate is the main driver.

I think this method will be absolutely invaluable to future studies, and for me has already proved its worth from the results the authors present. The videos below are from the supplementary information of the paper and explain the method simply using beautiful illustrations.

watch?v=7ucgQE3SO0o

watch?v=NrFdIz-D2yM

watch?v=rs3gYeZeJcw

Author

Luke McNally: mcnall[at]tcd.ie

Photocredit

Wikimedia commons