Evolution Update

Evolution Update

The Road to Man's Best Friend Was Paved by Competition

Brandon Kieft July 21, 2015

A study of the North American family Canidae, which contains modern day dogs, found their evolutionary history was shaped mainly by competition between other closely related (and now extinct) carnivorous groups.

A change in climate or physical environment, whether rapid or gradual, is often shown to be the principal driver of species diversification and extinction. A profound example is the dinosaur to mammal transition, where a natural disaster caused the mass extinction of one group and a mass proliferation and diversification of another.

However, a study published in the July 2015 issue of Proceedings of the National Academy of Sciences showed that a process generally considered rare, competition among entire clades (a very broad group of species), was responsible for the evolutionary patterns of diversification and extinction in several North American carnivores.

The research team analyzed climatic data and an extensive fossil record of the family Canidae dating from 40 million years ago to the present. Their goal was to tease apart the roles of (1) body size, (2) climate change, and (3) competition on the evolutionary history of three subfamilies within Canidae (two of which have gone extinct, the other of which contains extant canines such as dogs and wolves). Their basic question was: what caused 2 groups to go extinct while one survived?

(1) To understand the role of body size on evolutionary history, fossils were used to determine the body size of members from each of the three subfamilies. Body size has been shown to be an accurate approximation for carnivore diet.

As a species becomes larger its diet tends to become more selective (hypercarnivory), putting that species at higher risk of extinction because of their reliance on a narrow food source. Therefore, a trend of increased body size over time in a clade should negatively affect the survival of species in that clade (cause accelerated extinction and slowed speciation).

The study, however, found no correlation between increased body size and species survival among the three subfamilies. Many canids from the extinct and extant subfamilies showed similar body size trends; increased body size and hypercarnivory could not explain why two went extinct while the other thrived.

(2) Similarly, the researchers used the trend in global temperatures, which decreased steadily over the 40 million years spanned in the study, to attempt to explain Canidae evolutionary history. This information also did not selectively correlate with the extinction of two groups and the selection of the dog subfamily.

(3) To gauge the contribution of competition between subfamilies, the scientists developed a model for competition based on the speciation (increased species in the fossil record over time) and extinction (decreased species) rates for each subfamily.

They found a strong overall trend between the three groups: Over the course of 40 million years, the speciation rates of the two extinct subfamilies (which arose first) remained steady then began to fall, just as the dog subfamily began to rise (it’s really awesome, check out the figures from the publication linked below!).

Based on their observations from this modeled data, the authors concluded that competition between subfamilies within Canidae was indeed the major cause of the evolutionary trends of this clade. It seems the superior competitive ability of the dog subfamily led to its radiation (a term for speciation) and the eventual extinction of the other two subfamilies (and you thought your family holidays were awkward).

The study also included data from North American cats, bear-dogs, false saber-tooth cats, and bears, but found that more extensive study would be needed to understand the complex competitive contributions of these species to Canidae evolutionary history.

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