Archive for February, 2018

Energy budget models

February 26, 2018

In a previous post I mentioned a talk I gave on dinosaurs and promised more information at a later date. Now a paper related to this has appeared and I will keep the promise. A basic issue is the way in which dinosaurs regulated their body temperature. The traditional idea was that they were cold-blooded (exotherm) like crocodiles. Later it was suggested that they might have been warm-blooded (endotherm) like birds or mammals. Then it was claimed that this was unrealistic and that they were mesotherm. This means something in between exotherm and endotherm, with a limited control of body temperature. There do exist organisms like this, a notable example being the tuna. I was involved in a project with Jan Werner, Eva Maria Griebeler and Nikos Sfakianakis on this subject. The first published result coming from this effort has now appeared (J. Theor. Biol. 444, 83).

The long-term goal of this project is to understand the evolution of warm-blooded animals in connection with the evolution of birds from dinosaurs. This involves understanding the way in which animals allocate energy to different tasks. How much do they use for generating body heat and how much do they use for other tasks such as maintenance or reproduction? A first step is to find a parametrization of the possible energy allocation strategies. In other words we want to identify suitable variables which could be used to describe the evolutionary process we want to understand. This is the content of the paper which has just appeared. At this point it might be asked how we can find out about the energy consumption of dinosaurs at all. It turns out that there are general relations known between the energy consumption of an animal and its growth rate over its lifetime. Thus the growth curve of a dinosaur gives indirect information about its energy consumption. But how can we get information about the growth curve? This is something I learned in the course of this project. The large bones of dinosaurs exhibit annual growth rings like those known for trees. The rings are of different thicknesses and thus give information on the growth rate in different years.

The paper does not contain a detailed dynamic model of the energy use of an animal over its lifetime. Instead it introduces a set of possible time evolutions depending on a finite number of parameters and then tests (by numerical methods) whether these suffice to reproduce the experimental growth curves of a number of animals with sufficient accuracy. It is also checked that the results obtained are consistent with known facts about the age of sexual maturation of the different species. It turns out that the mathematical model is successful in fitting the experimental constraints. It is found that, as expected, the model predicts that exotherms continue to grow as long as they live while endotherms stop growing at a time comparable to the age of sexual maturity.


Trip to Ushuaia, Part 2

February 26, 2018

The reason for visiting El Calafate was its proximity to the glacier Perito Moreno. In the garden of our hotel there was a Buff-Necked Ibis, an attractive species which we saw repeatedly during the rest of our trip. Perito Moreno has interesting dynamical properties. I wonder if it has ever been modelled mathematically? Let me describe the process. The glacier comes from a peninsula and its lower end enters a lake, the Lago Argentino. It then proceeds until it has crossed the lake, which is quite narrow at that point. When it has reached the other side it separates one arm of the lake from the main part. The lake has an outflow but none in the smaller separated part. Thus the water level in the separated part rises compared to that in the main part. At the moment the difference in the levels is about thirty meters. This results in flooding of the surrounding land. We visited one farm there where an important part of the grazing land has already been submerged. The process just described leads to the water exterting a strong force on the glacier. This pressure is first released to a limited extent when water starts to flow under the glacier. This flow increases in intensity and produces a kind of arch which is flows under. Pieces of ice break off the arch successively, making it higher and higher. Eventually, about three days after the water has first penetrated the ice the arch is so narrow and high it collapses and then the obstruction has been removed. We are back at the starting point of the process. All this could be seen in a video in the glacier museum. The next breakthrough of the water is expected within the next few months but nobody knows exactly when it will happen.

From El Calafate we travelled overland and crossed the border into Chile.We had hardly crossed the border when we saw our first Andean Condor. This part of Chile has no road connection within the country to the rest of Chile. All necessary goods are imported by ship and the prices are correspondingly high. We were first in Puerto Natales. There it was convenient to observe the local ducks and cormorants along the waterfront. There is a statue of a giant sloth, a creature whose remains were found in a cave in the region. We travelled to the Torres del Paine, a spectacular mountain range. What you can see there is heavily dependent on the weather and we were quite lucky. Only the very top of the largest of the three ‘Cuernos’ (horns) refused to emerge from the clouds as long as we were there. What sounded like thunder turned out to be an avalanche. From Puerto Natales we travelled to Punta Arenas on the Strait of Magellan. There we visited some reconstructions of famous naval vessels. There is the Beagle, with which Darwin travelled, one of the ships of the expedition of Magellan himself and the modified lifeboat with which Shackleton sailed from Elephant Island to South Georgia and thus saved the lives of the members of his expedition. The text of the famous advertisement with which Shackleton recruited men for this expedition is reproduced there. According to Wikipedia the story of this advertisement is apocryphal but the text is so delicious that I cannot resist repoducing it here: ‘Men wanted for hazardous journey. Low wages, bitter cold, long hours of complete darkness. Safe return doubtful. Honour and recognition in event of success’.

From Punta Arenas we flew to Puerto Montt and travelled from there to Puerto Vargas. Here the attraction was the volcano Osorno. This time our luck with the weather seemed to be at an end. Our guide explained in a quite amusing manner how if the weather had been different the wall of cloud which we saw in a certain direction would have been replaced by a view of the beautiful volcano. In fact it turned out that there was a small window before breakfast the next day where the volcano could be seen from the hotel. The last step of the journey was a flight to Santiago. The city did not make a very good impression at first sight. Compared with Buenos Aires all the signs seemed to be reversed. Later we learned that the city is divided very strictly along economic lines. The rich upper part of the city looks quite different to the rest. We learned about the story of Chile as a model system for testing neoliberal theories. Just now the Chileans, who used to be considered as very backward are proud to be doing better (economically) than their neighbours, the Argentinians. We also had the opportunity to learn from our guides about the politics of Allende and Pinochet, in particular that Pinochet still enjoys considerable popularity in Chile.

We flew back from Santiago to Frankfurt via Madrid, our heads full of many images of Argentina, Chile, their people and their natural environment.

Trip to Ushuaia

February 25, 2018

Eva and I have just come back from a trip to Argentina and Chile. I had been in Argentina twice before, for conferences. The country made a positive impression on me but I did not have time to see very much. At that time I thought I should come back to see more. Now I have finally got around to doing so. The trip could have ended almost before it started since we almost missed our flight. I usually leave plenty of time when travelling to the airport and this was no exception. The ICE which we intended to take to travel from Mainz to Frankfurt airport was cancelled, without a explanation being offered. We then got into the regional train which was the next possibility. It just sat there instead of leaving. Then there was an announcement to say that because of a problem with points it would take a different route and, in particular, would not stop at Frankfurt airport. Our only hope was to travel to the main station in Frankfurt and then back to the airport. The situation seemed chaotic due the problem with the points already mentioned and the fact that there were people on the tracks somewhere. Even the ticket collector on the train did not seem to be able to give us a reasonable suggestion. Eventually we got to the airport and after running throught the airport and jumping a few queues we did get to our flight. We would have preferred a less stressful start to our journey. We flew via Sao Paulo to Buenos Aires and joined the group there. (This was an organized group trip).

The first time I visited Argentina I also flew to Buenos Aires but I saw almost nothing of the city. I just took a taxi from the international airport to the domestic one and my memory was that it drove around the periphery. Looking at how the airports lie this impression was probably mistaken. During my first trip I had a few hours to wait for my continuing flight to Cordoba and I was able to watch the for me exotic gulls, since the airport is close to the water. This time we were warned on arrival about the dangers of the city and how to behave so as to avoid them. We actually had no problems although we did not pay that much attention to security issues. One member of the group was attacked in the middle of the day close to our hotel. A man jumped on his back and tried to steal his watch. I do not think the watch was of particular value but the thief could not know that. Two brave women came and intervened and the thief ran away without the watch. The victim was left with some nasty-looking bruises on his arm but there was no further damage.

Our impression of Buenos Aires was of a beautiful city with a very pleasant atmosphere. It must be said that the days we were there were holidays, so that we experienced the city in a much more relaxed mode than it would be in on a working day. We discovered that there is a very nice nature reserve within easy walking distance of the city. My experience travelling with groups which are not specialised on birds is that if you go anywhere which might be good for birds you see so little that it is frustrating. The present trip was an exception to this rule. In the reserve area near Buenos Aires one of the most prominent species was the Jacana, whch was numerous. Some other prominent sightings were Roseate Spoonbill, Black-Necked Swan (which we later also saw in many other places), Red-Crested Cardinal and a Hummingbird of an undetermined species. From our guides we learned a bit about the complicated subject of Argentinian politics. One story which stuck in my mind and which I reproduce here without further comment is the following. There was a time when many Argentinians were protesting about the meat prices being too high. The Kirchners banned the export of beef. The result was a situation of overproduction which did lead to a decrease in the prices. This led in turn to many producers going out of business or drastically cutting their stocks. The final results were then shortages (beef had to be imported to Argentina from Uruguay!) and that a key national industry had been damaged in a major and probably irreparable way.

After a couple of days in Buenos Aires we flew to Trelew and spent some time exploring the Valdes peninsula, staying in Puerto Madryn. We learned what dry pampa looks like, a brown very dry landscape which in that area forms huge monotone expanses. At that stage I did not find the landscape attractive although other variants we saw in other areas later looked better. We were able to see some of the standard wildlife: sea elephants, sea lions and a huge colony of Magellanic Penguins. The temperature was around 30 degrees (I mean Celcius, not Fahrenheit) and the penguins were suffering a lot from the heat. I was pleasantly suprised to get a close view of an armadillo. The towns in this area was established by settlers from Wales, which explains the curious names. I would be interested to read about the adventures of these pioneers.

After this we flew to the town mentioned in the title of this post, Ushuaia. Before the trip I felt that Ushuaia was more like a mythical place than a real one. But now I have been there. Because of a last-minute change of plane schedule we had less time in Ushuaia than planned. Despite this we were able to take a trip on the Beagle channel with a catamaran in the late afternoon. The weather was excellent. For me this was the highlight of the whole trip. In the town itself we saw Dolphin Gulls and the first Giant Petrels. We visited some seabird islands with breeding colonies of terns and cormorants. We even landed on one island where there were Great Skuas flying around. In one place I saw a couple of Sheathbills on the beach. What was special is that we came to one place where there was a big concentration of fish. There was a corresponding concentration of seabirds, including several Albatrosses. Afterwards one Black-Browed Albatross followed the ship for quite a long time. At 22.00 we caught a flight to El Calafate.