No Substitute for Surrogates?

Northern Spotted Owl
The Northern Spotted Owl deserves to return to a quieter life. Photo: P. Medved via Flickr
Mar 2014

Surrogate species have gained an important role in monitoring the health of ecosystems, but how useful are they in a time when scientists can analyse nutrient flow or carbon stored in trees?

Surrogate species have gained an important place in the regulator's tool-kit, as climate change and habitat destruction increase the demand for accurate ecological monitoring. But they can also cause confusion and spark policy disputes if they channel public attention onto a single animal. A 2013 article in the Stanford Environmental Law Journal criticised the U.S. Forest Service’s policies as “not supported by current science" because of their vague definition of a surrogate.

A surrogate acts as a proxy for something scientists are trying to measure. The average conservationist rarely has the resources to do a comprehensive census of an ecosystem, so looking at just one species makes some problems easier to grasp. Regulatory agencies started using one kind of surrogate – "indicator" or "sentinel" species – in the 1940s, when the US Fish and Wildlife Service began measuring accumulated toxins in fish to track industrial run-off. A good indicator species tightly follows the variable it's supposed to measure: Springsnails are used to indicate the water quality in ponds; lichens signal differences in air quality; and lynx populations track the numbers of their snow hare prey.

Another kind of surrogate – an “umbrella species” – shares habitat requirements with as wide a variety of other species as possible: If the umbrella can survive there, so can most other native species. Regulators often use the ranges of these species to define the boundaries of new protected areas. Surrogate types also include "flagship species," which are meant to serve as the public face of an ecosystem or campaign, such as the World Wildlife Fund's panda.

The trouble is, the aims and definitions are little understood.  A 2011 survey of popular science articles by Oxford University research fellow Maan Barua, reported that only 67% of "umbrella species" definitions were correct. Even officials can seem muddled, as pointed out by the Stanford Environmental Law Journal article. The Forest Service codified its regulations at a time when these distinctions were still fuzzy, and lumped all surrogates into the unscientific category of "management indicator species." As a result, said Ryan Kelly, co-author and University of Washington assistant professor, "The Service never had to say precisely what (if anything) their indicator species were indicating."

A prominent example of such confusion is the northern spotted owl. Beginning in the 1980s, the Forest Service used this as an umbrella species for Pacific Northwest old-growth forest, but public perception of the owls ended up clouding the larger issues at stake. Some environmental groups thought the bird was merely a good indicator for forest health, and not an adequate umbrella for the entire ecosystem: Its needs had little to do with the needs of the salmon living in the streams below them, for example. Timber companies ignored the owl's surrogate role altogether, and suggested conservation strategies that wouldn't entail reductions in timber, such as captive breeding programmes for owls. Some loggers seemed to accept that the owl was being used as a surrogate, but viewed this as a trick – as if the Forest Service were using the owl as a flagship rather than an umbrella. "The only reason why the environmentalists are using the owl is just to work on the emotions of the people,” one logger said in a TV interview.

Such arguments raise the question of how useful surrogates are in an age when scientists can get information by analysing nutrient flow or carbon stored in trees. But surrogates' big advantage is their simplicity of use. The US Forest Service implemented a new approach in 2013, including the use of "focal species" – surrogates used to establish specific threats to an ecosystem. "Hopefully you have the Service wanting to balance competing demands of use, conservation, etc., in a responsible way," said Kelly.


This article was updated on 17 March to more clearly reflect the definition of "umbrella species" and the criticism levelled at the U.S. Forest Service. The headline was changed from "Time to retire surrogate species."