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Nature Notes February 2020

One of the most puzzling biological things to me is the bizarre variation in the longevity of individual animals.  We humans regularly live to 70 years these days, and often much longer such as the dancer recently featured on the news who was 98 and still winning dancing competitions.  However, our dogs (genetically, tame wolves) only live to about 14 years, but seem to have healthy lives.  Tortoises regularly exceed 100 years before dying, but adult mayflies only live for one day, and do not even have mouths or any other means of eating or securing energy.  Herring gulls and other seabirds frequently live longer than 30 years, but blue tits are lucky to make it to one year.  Slow worms can also live to 30 years or more and breed for most of those years, but pacific salmon all die after their first attempt at breeding.

Why is there so much variation in the length of time an organism can live.  A yew tree such as the one in the cemetery of St Margaret’s Church in Buxted park can live to excess of 3,000 years old and produce hundreds of seeds every year if it is a female, but if you plant a grain of wheat, it will grow and produce about 22 seeds per head and 5 heads (110 seeds) per plant which will die in less than one year.

We all hope to live as long as possible and have a productive life, but why don’t all organisms try to live as long as possible, some clearly do, but others are programmed to die after a very short time.  The pyramid of numbers in the trophic levels within an ecosystem makes a fascinating study.  For example, I have been studying blue tits recently, and I found that the caterpillars of several moth species can almost completely defoliate (eat all the leaves) of a mighty 300-year-old oak between April and June.  However, one family of blue tits can consume up to 1000 caterpillars on a single day for 18-22 days before the young birds leave the nest, they will carry on eating them after that as well.  However, one family of sparrow hawks can consume the equivalent of 40 blue tits per day for 24-30 days in the nest before fledging. 

The perpetuation of life on planet earth depends on the rapid reproduction of many organisms and consumption of others to support a complex ecosystem and the beautiful diversity of life that we all see.  

Dr. Martyn Stenning