Competition for resources caused extinction of canid lineages

Study suggests arrival of felids in North America may have caused disappearance of up to 40 species of the family to which modern dogs, wolves and coyotes belong.

By Elton Alisson

Agência FAPESP – Competition for resources among different lineages of canids and other groups of carnivores that have inhabited North America over the past 40 million years caused the extinction of two subfamilies within the family Canidae, which includes domestic dogs as well as wolves, foxes, jackals and coyotes, among other dog-like mammals.

This is one of the findings of a study by researchers at the University of Gothenburg and Gothenburg Botanical Gardens in Sweden and the University of Lausanne and Swiss Institute of Bioinformatics in Switzerland in collaboration with Tiago Bosisio Quental, a professor at the Ecology Department of the University of São Paulo’s Bioscience Institute (IB-USP) in Brazil.

The study resulted from the project “The Role of Extinction and Speciation Rates, and the Effect of Different Levels of Biological Organization on the Origin and Maintenance of Biodiversity,” conducted by Quental with support from FAPESP’s Young Investigators Grants program. A paper describing the results was recently published in PNAS (Proceedings of the National Academy of Sciences of the United States of America).

“We analyzed the fossil record for several families of Carnivora. Our findings suggest that interaction among different lineages of canids and between canids and other groups of carnivorans appears to have played a very important role in the extinction of two canid subfamilies,” Quental told Agência FAPESP.

Canids first appear in the fossil record 40 million years ago in North America. The three main subfamilies – Hesperocyoninae, Borophaginae (“bone crushers”) and Caninae – coexisted for a long period.

The former two (Hesperocyoninae and Borophaginae) became extinct at different times during the evolutionary history of canids. The only surviving subfamily is Caninae.

To determine what led to the extinction of Hesperocyoninae and Borophaginae, the researchers analyzed some 1,500 fossil occurrences of 120 species spanning the entire existence of the canid family in North America from 40 million years ago to the present.

They also studied 744 fossil occurrences for 115 species belonging to five additional carnivoran families that coexisted with canids in the period: Felidae (which includes modern tigers, lions, jaguars and domestic cats), Amphicyonidae (“bear dogs”), Nimravidae (false saber-toothed cats), Barbourofelidae, and Ursidae (bears).

Based on their analysis of these fossil occurrences, the researchers estimated the times of origin and extinction of all species, which they used to assess the effect of body size evolution (an indicator of diet), climate change and competition between Hesperocyoninae and Borophaginae on speciation and extinction rates.

One of the conclusions of the study was that competition for resources played a more important role in the evolution of canids than climate change.

“We found that competition among different lineages of canids and with other groups of carnivorans contributed markedly to the disappearance and replacement of the subfamilies Hesperocyoninae and Borophaginae, increasing their extinction rates and suppressing speciation,” Quental said.

Competition among groups

The researchers’ analysis of the fossil record also showed that the body size of Borophaginae, which had been smaller than that of Hesperocyoninae, increased steadily during the subfamily’s evolutionary history.

Borophaginae therefore became ecologically similar to Hesperocyoninae, and the two subfamilies probably competed more strongly for resources as a result.

This supposition is confirmed by significantly higher extinction rates of Hesperocyoninae between 20 million and 10 million years ago, according to the authors of the paper.

“We concluded that stronger competition between these two canid lineages probably caused the increase in the extinction rate for Hesperocyoninae,” Quental said.

The arrival of Felidae in North America from Eurasia some 20 million years ago intensified competition among the different carnivoran lineages then inhabiting the region and contributed to the complete extinction of Hesperocyoninae.

However, the study also found that this immigration of Felidae also appears to have played a significant part in the demise of Borophaginae.

Comprising some 30-40 species, the diversity of Borophaginae began to decline after the arrival of Felidae in North America, and this canid subfamily became extinct approximately 4 million years ago.

“Our analysis of the data suggests that extinction rates for Borophaginae and Hesperocyoninae correlate with the growth in diversity of Felidae in North America,” Quental said.

One of the researchers’ hypotheses for the devastating impact of Felidae on canid diversity as they moved into North America is that felids may have become more efficient predators than most extinct canid species.

“Apparently Caninae, the only surviving canid lineage, was not affected by competition from felids,” Quental said.

The researchers assume Caninae survived thanks to ecological differences between this subfamily and felids as well as the other canid subfamilies that became extinct.

“That doesn’t mean there were no extinctions in the Caninae lineage,” Quental said. “Extinctions did occur systematically over time in this subfamily, but the species that disappeared were replaced by others.”

The article “The role of clade competition in the diversification of North American canids” (doi: 10.1073/pnas.1502803112) by Quental et al. can be read at www.pnas.org/content/112/28/8684.full.