EVOLUTIONARY ECOLOGYBiology 303 – Tim Vines

OVERHEADS:Distribution of the twinflower (Linnaea borealis) in the UK. This rare plant requires high pHsoils in upland areas; these conditions are very uncommon in Britain.

The distribution of two Schistosomiasis species. S. mansoni requires snails of the genusBiomphalaria as an intermediate host, whereas S. intercalatum uses Bulinus snails. BothSchistosomasis species are limited by the distribution of their snails (and humans!).

NATURAL SELECTION AND EVOLUTION

Fact 1. Any species can increase its population geometrically.Fact 2. Population size remains constant over time.Fact 3. All organisms can be seen to be variable.

Postulate 1. (from facts 1 & 2): There is competition amongst progeny for survival.

Postulate 2. (from Postulate 1 & Fact 3): Since there is competition, some variants will bebetter adapted, compete more successfully and reproduce better. These variantswill comprise the next generation. This is the process of natural selection.

Postulate 3. (from Postulate 2): If the successful variants can pass their advantageouscharacteristics onto their offspring, they too will survive better than average. Theadvantageous characteristics will therefore spread through the population over anumber of generations. This is evolution.

The contrast between Lamarck’s and Darwin’s view of the origin of species (from Chapter 2 ofFutuyma (1998) Evolutionary Biology):

Natural selection in Darwin’s finches on Daphne Major in the Galapagos. Data from Boag andGrant (1981) Science volume 214 pages 82-85.