The island of Spitsbergen in the high Arctic is home to a seductively simple food web. The food web includes just four vertebrates--three herbivores (reindeer, rock ptarmigans and sibling voles) and one secondary consumer (Arctic foxes). The simplicity of the Spitsbergen food web is precisely what makes it so enticing to scientists who study population dynamics. The effects extreme weather events have on vertebrate populations, for example, can be measured with relative ease.
Brage Hansen from the Norwegian University of Science and Technology in Norway and colleagues designed a study to measure the effect extreme weather events has on the vertebrates of Spitsbergen. They observed that during the winter in Spitsbergen, warmer temperatures mean that rain storms (instead of snow storms) are more frequent than they had been in the past. And that rain causes problems for the resident vertebrates.
When it rains during the winter in Spitsbergen, the rainwater freezes and thaws repeatedly. Crusty layers of ice form on the ground and over any exposed vegetation. Rainwater also seeps down through any existing snowpack and into the ground where it freezes. The result is a thick layer of ice that entombs vegetation. Herbivores--the reindeer, rock ptarmigans and voles--cannot get to the vegetation and they begin to starve.
Hansen and his team noted that rainy, icy winters result in herbivore population crashes. About a year later, Arctic fox populations follow suit. Initially, reindeer carcasses become more common, making food more plentiful for the Arctic foxes. But in subsequent years, there are fewer reindeer (as well as fewer ptarmigans and voles) and less food for the foxes. As a result, the fox population, too, crashes.
The study is the first of its kind to show the effects of climate on the populations of an entire community. The results raise concern for the stability of such communities in the future, when extreme weather events are expected to be come even more common.
Photos © Brage Bremset Hansen / Norwegian University of Science and Technology.
Hansen, B. et. al. (2013). Climate Events Synchronize the Dynamics of a Resident Vertebrate Community in the High Arctic Science, 339 (6117), 313-315 DOI: 10.1126/science.1226766