Posted by: oikosasa | January 31, 2013

Waste to hurry

Do animals spend too much energy on just being? Read Bas Kooijman’s new Early View paper “Waste to hurry: dynamic energy budgets explain the need of wasting to fully exploit blooming resources” to find out! Here, Bas gives you the background to the study:

Many years ago, I did a very simple experiment, which results puzzled me for a long time. Take 6 beakers, fill them with water, add 5 daphnids each, and feed them with algae daily. The beakers got 6, 12, 30, 60, 120 and 240 million cells per day, respectively, for 24 days. Except for the highest feeding level, all daphnid populations settled to constant numbers per beaker in this period and the numbers are directly proportional to the feeding levels. To convince myself that it really is the feeding level that controls the numbers, I gave all beakers 30 million cells per day after 24 days and indeed all numbers converged to that level. From this we learn that a 2.8 mm daphnid needs 6 algal cells per second at 20°C and they cannot grow or reproduce with this intake and all need it for maintenance only. With plenty of food they can become over 4 mm and produce some 20 young per day. It turns out that they have a specific maintenance cost that is two orders of magnitude bigger than is typical for animals. My problem was to understand why.

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Some two years ago, I started the add_my_pet collection of data on animal energetics, and fitted the standard Dynamic Energy Budget model to each species. These data and the model cover all aspects of energy and mass balances during the full life cycle of individuals, including the embryo stage. The collection has representative of most larger animal phyla, ranging from 2.4e-8 g hairy-backs to  1.6e8 g blue whales. I developed this model to separate overhead costs of assimilation, growth and reproduction from maintenance. Because of the presence of reserve as quantifier for metabolic memory, this task is less easy than is generally recognized. In fact, it requires a whole new view on the relationships between respiration, metabolic rate and maintenance. With help of many enthousiastic people, the add_my_pet collection grew till 165 species at present.

By comparing extremes in specific maintenance costs I found the explanation for the very high maintenance costs of daphnids and for why it took me that long to see it. It is namely completely counter-intuitive: animals need to waste resources to boost their growth and reproduction. Within the context of the Dynamic Energy Budget theory, it is completely logical and easy to understand, the only problem is to recognise it. It has been sitting right before me for 30 years and I didn’t see it. Intuition is not always a good advisor.

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