Professor Tim Coulson

Research Interests

I am interested in what happens to ecosystems and the species within them when apex predator numbers are altered. I develop theory, and test the theory with field data collected from animals living in the wild.

When many large carnivores were deliberately eradicated from Yellowstone National Park in the 1920s, all sorts of things in the park changed: elk numbers increased, bison struggled, and young trees of many species failed to establish. When wolves were reintroduced in the 1990s, and as bears and mountain lions naturally re-established in the park, things started to return to the way they were, but whether the park will ever look like it did in when Europeans first discovered it is yet to be seen. It may never recover to its previous state.

On longer time scales, changing predator numbers can lead to evolution of prey. When guppies live in the same stream as predatory fish within Northern Trinidad, they are rare, living at low density. They are also well-adapted to live with predators, having high metabolic rates and exhibiting behaviours that help them escape a grizzly end in the jaws of a larger fish. When these guppies are released from predation and moved to predator-free streams, they rapidly evolve, using existing genetic variation within their population, to live slower lives, lower their metabolic rates, and display behaviours associated with living in an environment where food is scarce and has to be strongly competed for.

Over even longer time periods when genetic mutations can accumulate, animals can evolve into new species when they escape from predation. The textbook example is the dodo of Mauritius. However, many bird species show similar, if not quite so pronounced, responses to the dodo when they establish on predator-free Oceanic islands and survive their for very many generations. Silvereyes, a study species my wife Sonya Clegg is the real expert on, which live on mainland Australia and on Islands of its Eastern coast, are a fabulous example of a bird that is starting to evolve some of attributes of the dodo on some of the islands it has colonised.

My research is all about understanding why these ecological and evolutionary changes happen when predator numbers change, and what these changes might mean for ecosystems. I do this by developing theory that I can test with data collected from Yellowstone, Trinidad, and Oceania. However, I also work on several other systems, including some where changing apex predator numbers has little apparent impact on ecosystems.

I am also a keen populariser of science, and that motivated to write a popular science book, The universal history of us: A 13.8 billion year tale from the Big Bang to you, which will be published by Penguin in June 2024. 

Book cover for The Universal History of Us
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