This phenomenon can be spotted quickly in yeast, which produces about 10 new generations per day, but measuring these population fluctuations for species such as fish or deer would take much more time. In hopes of finding more useful signals, the researchers turned their attention to spatial information.
There goes the neighborhood
In their new study, the researchers theorized a new type of indicator that they call "recovery length" the spatial counterpart to recovery time. This idea is based on the observation that populations living near the boundary of a less hospitable habitat are affected, because the neighboring habitats are connected by migration. Populations further away from the bad region gradually recover to equilibrium, and the spatial scale of this recovery can reveal a population's susceptibility to collapse, according to the researchers.
To test this idea, the researchers first established several linked yeast populations in a state of equilibrium. At the end of each day, a certain percentage of each population was transferred to adjacent test tubes, representing migration to adjacent regions.
The researchers then introduced a "bad" habitat, where only one in every 2,500 yeast survives from one day to the next. This reduction in population mimics what might happen in a natural population plagued by overfishing, or by a drastic reduction in its food supply.
The MIT team found that populations closest to the bad habitat had the hardest time maintaining an equilibrium state. Populations farther away maintained their equilibrium more easily.
"There's some distance you have to go away from the bad region in order to get recovery of the population density," Gore says. "How far you have to go before you reach equilibrium is the recovery length, and that tells you how close these populations are to collapse."<
|Contact: Sarah McDonnell|
Massachusetts Institute of Technology