A juvenile coho salmon preying on a recently hatched sockeye salmon in Bear Creek, Alaska.
Credit: Jonathan B. Armstrong
LONDON: Predatory fish display binge eating behaviour in order to see them through periods of limited food supply, say scientists.
Wild animals have to forage, stalk and capture their prey, which uses a lot of energy with no guarantee that it will result in an adequate meal. This unpredictability has led scientists to suggest that animals can store the energy from the extra food they eat to use during periods of starvation.
But there has been little work done to actually assess the digestive abilities of wild animals. A new study published in the current issue of Nature is the first comprehensive analysis of such abilities in 38 species of wild fish.
"When engineering the digestive systems of predators, natural selection has accounted for the [transient] nature of predator-prey interactions, which do not occur continuously, but instead as bursts of activity," said Jonathan Armstrong from the School of Aquatic and Fishery Sciences at the University of Washington. "To thrive in such a world, predators are built to binge."
Finding your prey
Fish in the wild have to forage for their food, expending precious energy in finding, capturing and digesting their prey. In order for this to a successful way to live the fish needs to have a 'positive pay load' meaning they need to get more energy from their food then what they use to track it down.
Observations of fish bred in the research laboratories have shown that when fish have an unlimited food supply they can grow much larger then their wild counterparts. This may seem obvious but it shows that these animals have the ability to digest much larger quantities of food then they find in the wild.
This could suggest that wild fish are able to digest large amounts of food when it is present, and then store away the energy for a rainy day when food is limited.
Identifying coping mechanism
Armstrong and co-author Daniel Schindler, also from the University of Washington, constructed a mathematical equation considering the pay off of fish having a large digestive ability with the energy costs of maintaining such a system. The equation enabled them to make 639 estimated recordings of digestive capability food consumption in 38 species of predatory fish.
They discovered that most of the fish were feeding at less then half what their digestive systems could support. This demonstrated a coping mechanism for starvation periods and also indicated that these fish must live in a world much more scarce of prey then scientists previously thought.
The research is the first to demonstrate the profitability of excessive digestive ability in wild animals, showing that through biological design predator and prey interactions may not be as frequent as thought.
"There are clear benefits in taking maximum advantage of those moments of spontaneous good fortune. Of course, these findings are based on average values and in many cases, the availability of prey can vary with time of day, or the time of year," said zebra fish researcher David Whitmore from the University College London Research Department of Cell and Developmental Biology, who was not involved in the research.
"It will be extremely interesting to see how the results of Armstrong and Schindler vary across the day, or perhaps more importantly across the year as animals move from seasons of abundance to months of relative starvation, digestive capacity vary[ing] in a dynamic world."
