Last week we looked at the paper: Links between global taxonomic diversity, ecological diversity and the expansion of vertebrates on land, by Sandra Sahney et al. In the paper Sahneys team look at different molecular and fossil records and determine that the increase in tetrapod biodiversity was not due to competition but more because of the expansion into unoccupied ecospace. They decided to group these tetrapods based on their ranges and ecomorphs like size and diet. They compared this to what niches they actually occupy and saw that the actual rate was lower than the expected. With this information they thought it was enough evidence to prove that competition must not have been the determining factor in their expansion.
The conclusion reached from this paper is a huge overreach. The methods used by the researches are very subjective because a lot of tetrapods live in overlapping areas and diets. Therefore one scientist might look at the data and group these tetrapods in to far more or less than the methods used by Dr. Sahney and her team. The researchers also used fossil records to see if tetrapods lived in various areas. This seems to be a very unreliable method because the fossil record is famously incomplete. There may have been many tetrapods in an area but because the conditions were not right millions of years ago no fossils were formed. Furthermore the fossil record rarely tells us anything about the diet of the tetrapods which was one of the criteria that was sorted. I believe that this paper can be heavily criticized based on its subjectivness on the materials and methods section. This in no way refutes competition the means for diversification. Competition may have still been happening on a smaller scale and some of the radiations that took place may have been influenced by the new use of territory, but nevertheless competition was always taking place and was the major factor in almost all species radiations. The paper is only about tetrapods and cannot be extrapolated to the other 90% of all animals on earth. This paper seems to make a conclusion which is a far reach from the truth and in no way is a contradiction to Darwins theory of competition.