Dr Malthus would be pleased
Life is hard. Then you die
For the past month or so I've been watching a webcam that looks at a peregrine falcon nest with 4 eggs in a turret at Chichester Cathedral.
Watching birds sitting on eggs is a bit like watching paint dry but it is interesting to see how the mating pair interact.
No movement for a long time, The sitter's head starts looking around. Bird cries are heard. Then another falcon appears. The two swap places.
Last week the eggs started hatching. Three chicks have emerged. Looks like one won't.
Now the mother bird (I think its the mother) sits on the chicks all day while the father hunts and brings home dead birds or mice. Father gives to mother and mother pecks bits of flesh and feeds it to the chicks.
After the meal is done mother flies away with the empty skin to get rid of it.
It's a bit gruesome but a loving scene nonetheless.
I started to wonder about the survival rate of the chicks. How many of that clutch would live long enough to have a clutch of eggs of their own.
I started with 4 eggs and assumed that that could produce 2 breeding pairs who each laid a clutch of 4 eggs.
I assumed that no birds died and made a spreadsheet about how the population would grow.
4 8 16
4 8 16 32
4 8 16 32 64
4 8 16 32 64 128
4 8 16 32 64 128 256
4 8 16 32 64 128 256 512
4 8 16 32 64 128 256 512 1024
4 8 16 32 64 128 256 512 1024 2048
40 72 128 224 384 640 1024 1536 2048 2048
It turns out that after 10 years the initial breeding pair would produce over 8000 falcons. That obviously doesn't happen.
In 10 years, if the population doesn't grow that single breeding pair would replaced by just one other pair. That means that almost all the peregrines don't make it.
Thomas Malthus noted that "that population growth is potentially exponential while the growth of the food supply or other resources is linear, which eventually reduces living standards to the point of triggering a population die off."
It seems that Malthus was mistaken in assuming that population growth among (say) peregrines could be exponential.
Watching this nest makes it obvious why. These birds spend all day in the cold wind scrounging for their food. It's a hard life.
When I lived outside while crossing Canada on my bike I had a tent and sleeping bag and stores to buy food from
But Malthus was right. When conditions are right populations can and do grow to the point of eating all the food and then crashing due to starvation and disease.
This is a big factor in the expansion of the human population.
We don't have predators keeping our population under control.
Our worst natural enemies now are tiny things like viruses.
And we have been (largely) able to make the food supply grow as fast as the population.
But how long can that go on?
I read of an example (I think by EO Wilson) of a pond where the lily pads grow at a rate that doubles their area every day. On the last day before the lily pads covered the whole lake half of the water was still open.
Next day it was all covered.
Point being that things can seem fine for a long time - but catastrophe can come very quickly at the end.
What do you think?