How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic

Keeping Up With Climate Change
Alford, R.A., Brown, G.P., Schwarzkopf, L, Phillips, B.L. and Shine, R. 2009. Comparisons through time and space suggest rapid evolution of dispersal behaviour in an invasive species. Wildlife Research 36: 23-28.

Many are the climate alarmists who contend that sometime in the future, the earth will warm so much and so fast -- due, of course, to anthropogenic CO2 emissions -- that both plants and animals will not be able to migrate poleward in latitude or upward in altitude fast enough to keep themselves within their current thermal comfort zones, and that when that time arrives, extinctions of entire species will abound.

What was done
In a study germane to this subject, the authors quantified four movement characteristics of three groups of radio-tracked cane toads (Bufo marinus) at three different places in Australia: (1) a location where the toads had been established for some fifty years at the time of their sampling, (2) a location where the first toads arrived about six months before sampling began in 1992 and 1993, and (3) a location where sampling occurred for a period of thirteen months, starting at the time of the toads initial arrival in 2005.

What was learned
Alford et al. discovered that for all movement parameters studied, "toads from the current invasion front differed dramatically from animals in the long-established population, while toads from the earlier invasion front were intermediate between these extremes."

So just how dramatically did the movement parameters differ? The five researchers report that "cane toads are now spreading through tropical Australia about 5-fold faster [our italics] than in the early years of toad invasion." As for why this is so, they say that "the current invasion-front animals achieved these [high invasion speeds] by rarely reusing the same retreat site two days in succession, by travelling further each night when they did move, and by moving along straighter paths."

What it means
In the words of the Australian scientists who conducted the work, the toad invasion front "advances much more rapidly than would occur if the toads retained ancestral behaviors (less frequent relocation, with shorter movements, and fewer toads using straight paths)." And because of the fact that "invasion-front toads in 1992 were more dispersive than origin-population toads in the same year, but that invasion-front toads have continued to evolve heightened dispersal ability and dispersed even more effectively in 2005 than they did in 1992," they say these observations suggest that "as long as toads continue to invade suitable new habitat, dispersal ability will be selected upwards."

Alford et al. write that "the rapidity and magnitude of these shifts in cane toads are truly remarkable," having been accomplished in only 50 generations (about 70 years); and they state that "such a major shift over such a brief period testifies to the intense selective pressure exerted on frontal populations of range-shifting species." This development, in their words, "not only has implications for our understanding of the rates of invasion by non-native species, but also for the rate of range-shift in native taxa affected by climate change," the implication being, in our view, that most species will do what they have to do (by evolving how they need to evolve) to meet whatever challenge a rapidly changing climate might place before them.

Reviewed 15 July 2009