Chaos in natural populations appears to be much more common than previously recognized, according to a new analysis. Populations of organisms in natural ecosystems fluctuate a lot, and a key question for ecologists is whether those fluctuations are regular (varying around some theoretically ‘stable’ equilibrium), random (completely unpredictable), or chaotic. Chaotic systems, like the weather, can be predictable in the short term but not in the long term, and they are highly sensitive to small differences in the initial conditions.Chaos in natural populations appears to be much more common than previously recognized, according to a new analysis. Populations of organisms in natural ecosystems fluctuate a lot, and a key question for ecologists is whether those fluctuations are regular (varying around some theoretically ‘stable’ equilibrium), random (completely unpredictable), or chaotic. Chaotic systems, like the weather, can be predictable in the short term but not in the long term, and they are highly sensitive to small differences in the initial conditions.