Sunday, January 18, 2009

Charles Darwin: ecologist

Our bicentennial Darwin Day celebrations in Birmingham are fast approaching (I will blog more on our exciting activities soon). Within our multi-disciplinary programme of events, we have a talk on invasive species by local ecologist/biogeographer, Jon Sadler. We have a rule stating that all speakers at our Darwin Day events have to include a quotation from Darwin in their talks, so Jon just asked me to help him find some appropriate quotes for his talk.

In The Rough Guide to Evolution I include a box highlighting Charles Darwin's status as an early ecologist:
The term “ecology” was not coined until in 1866 by Darwin’s German admirer Haeckel. However, in the third and fourth chapters of The Origin, Darwin’s emphasis on the “complex relations of all animals and plants throughout nature” guarantees him the status of an early ecologist. In Chapter 3, he puzzles out how enclosure of land can lead to a proliferation of fir trees and hits on the answer: the exclusion of cattle that graze on seedlings. He speculates on the cascade of ecological changes that might result from an increase in insectivorous birds in Paraguay. And he produces a beautiful English example of “how plants and animals, most remote in the scale of nature, are bound together by a web of complex relations”, by pointing out that (1) humble bees are needed for fertilisation of some plants; (2) the number of bees in an area depends on the number of mice; (3) the number of mice depends on the number of cats, so that the number of cats can determine the frequency of flowers in a district!
In Chapter 4, Darwin writes “It has been experimentally proved that if a plot of ground be sown with one species of grass, and a similar plot be sown with several distinct genera of grasses, a greater number of plants and a greater weight of dry herbage can thus be raised.” Many subsequent studies have confirmed this principle, which lies at the heart of organic farming methods. In his haste, Darwin unfortunately did not say when or where the pioneering study had been carried out. Recently, two British ecologists, Andy Hector and Rowan Hooper, have tracked the source of the information to George Sinclair, head gardener to the Duke of Bedford, who, in an 1826 article, described what must count as the first ecological experiments, conducted at Woburn Abbey in England, a few years earlier.
BUT, as if the above wasn't enough to establish Darwin's ecologist credentials, in trying to help Jon, I have just discovered this fascinating article from 2001:
Here, two modern ecologists, Stuart Ludsin and Andrea Wolfe, compare current thinking on the ecology of biological species with Darwin's views as expressed in the Origin. They draw on a conceptual framework on biological invasions set out by Williamson in 1996, considering Darwin's contributions under ten conceptual framework points:

  1. Most arrivals at present are from human importations, but natural arrivals also are of interest. 
  2. Most invasions fail; only a limited number of taxa succeed (“tens” rule). 
  3. Invasion (or propagule) pressure is an important variable, so invasions are often to accessible habitats by transportable species. 
  4. All communities are invasible, perhaps some more than others. 
  5. The a priori obvious is often irrelevant to invasion success. Among factors to consider: the intrinsic rate of natural increase (r), abundance in native habitat, taxonomic isolation, climatic and habitat matching, vacant niches. 
  6. Spread can be at any speed in any direction. 
  7. Most invaders produce minor consequences (tens rule). 
  8. The consequences of invasions can be severe, ranging from depressed populations to individual extinctions to ecosystem restructuring, and the causal mechanisms driving these changes can be diverse
  9. Genetic factors may determine invasion success; genetic factors affect events at the initial invasion; evolution may occur after invasion. 
  10. Invasions are informative about the structure of communities and the strength of interactions, and vice versa.
In each case, they provide good evidence that Darwin got there first (except for the point on genetic factors)!

They conclude:
"...The Origin of Species is so much more than a seminal text on evolution. Historians and biologists alike have argued that this work provided the basis of modern-day ecology, and a cursory read of The Origin of Species will reveal the true roots of many ecological theories and phenomena (e.g., competitive exclusion, limiting similarity, character displacement, predation, sexual selection, kin selection, island biogeography)...

Given that Darwin’s conceptualization of biological invasion success really does not differ much from the present conventional wisdom (regardless of the correctness of ideas, whether old or new), we, like others feel that Darwin’s insights into biological invasions should be recognized. Quite possibly, had some of Darwin’s observations on biological invasions been better noted, we might not be experiencing the severity and variety of problems that we currently face."
So, as well as one of the greatest travel writers, geologists, specimen collectors and natural historians, we should give Darwin additional credit as one of the founders of ecology!

1 comment:

Mark Pallen said...

This link provided me with fulltext access to the paper:

Not sure whether that is because I am benefitting from an institutional subscription, or whether it is free for everyone.