Fluctuation

Why do the Populations of the Banff Springs Snail Fluctuate?

One of the reasons the Banff Springs Snail is Endangered is because snail populations fluctuate yearly by more than one order of magnitude (10 fold). Highest numbers of snails are observed in the dead of winter – typically from January through February. As winter comes to an end, snail populations crash and are at the lowest over the summer – typically from May through August. After the end of summer, their numbers then begin to increase.

Number of Banff Springs Snails in selected thermal springs and all seven springs combined, January 1996 through 19 December 2010.

Number of Banff Springs Snails in selected thermal springs and all seven springs combined, January 1996 through 19 December 2010.

Population lows of 30 and 43 snails have been observed in different springs since January 1996, when intensive monitoring began. When populations are this low, any chance event, or human disturbance, could result in the extirpation of that population. An act as simple as picking up a stick lying half in the thermal spring water and tossing it for a dog to chase could drastically reduce or eliminate a snail population at this time, if most of the spring’s snail population is found on that stick.

The causes of the annual population fluctuations are uncertain but are most likely related to food supply and / or the seasonal dynamics of the thermal spring ecosystems.

Next Page – Ecological Role of the Banff Springs Snail