Sections

Services

Information

UK United Kingdom

Why cane toads give us small hope for climate change

Cane toads are one of the Australia’s most serious invasive species, killing predators such as goannas, quolls and crocodiles in the tropical north. We already know the toads are advancing from Queensland…

Cane toads spread faster when they arrive in a new area. Flickr/blundershot

Cane toads are one of the Australia’s most serious invasive species, killing predators such as goannas, quolls and crocodiles in the tropical north. We already know the toads are advancing from Queensland to the Kimberley. New research shows the toads may evolve to spread faster in new environments. But this may be good news for animals who have to move because of climate change.

So, how do we get from toads to climate?

Hopping to it

Most ecological theory starts with the assumption that a population of animals is stable in space: individuals and their offspring live in the same general area year after year. But, the reality is much messier: many populations are not stable. For example, invasive species expand their range as they spread.

As part of a long-term study by my University of Sydney-based “Team Bufo”, Greg Brown radio-tracked invasive cane toads as they first arrived at an area near Darwin, and continued to track newly-arriving toads over the next several years. Tom Lindstrom’s mathematical analysis of those radio-tracking results revealed a dramatic shift, published today in the journal PNAS.

The first toads that arrived near Darwin were incredibly mobile, often moving more than one kilometre within a single night – but within a couple of years that rate had more than halved. The super-speediness seen at the invasion front is probably driven by evolutionary forces that come into play only at an expanding range edge, and are not seen in stable populations. Earlier studies on the toad front had revealed these mechanisms, and the current work shows just how spectacular the acceleration can be.

That rapid decrease in mobility after the invasion front passes through means that studies on “normal” cane toads – that is, on animals from long-established populations – would underestimate the potential rate of movement. If we want to predict how quickly a species can expand its range, we need to look right at the expanding range edge.

Unfortunately, that’s logistically difficult, so most of our data on animal dispersal rates come from long-established, stable populations. As a result, we may be underestimating potential rates of population spread.

Adapting to a changing world

The problem doesn’t just relate to invasive species. Many species shift their ranges for other reasons. Climate change is rendering many areas unsuitable for the animals and plants that currently live there (for example, by becoming too hot or too dry). But at the same time it is creating those conditions somewhere nearby (in an area that previously may have been too cold or too wet).

If a species caught in this situation is to survive, individuals either must rapidly adapt to the new conditions, or move to the area that offers suitable conditions. The fast pace of climate change makes both of these options very tough to achieve, but not impossible.

Even in a species where individuals generally do not move about very much or very far, the process of expanding their range into a newly-suitable area will create an evolutionary pressure for faster and faster dispersal. The end result may be that many species will manage to shift their distributions more quickly than we would have guessed from the movement rates we can measure in existing stable populations. And perhaps that provides a glimmer of hope.

Articles also by This Author

Sign in to Favourite

Join the conversation

23 Comments sorted by

  1. Mike Swinbourne

    logged in via Facebook

    Hi Rick

    I well remember reading a lot of your stuff on snakes during my undergraduate studies - thanks for that!

    But I am going to question your assertion about species spread. I suggest that what you have said sounds reasonable, unless you factor in habitat fragmentation. For species to expand their range - or to move to new habitats - they would need to be able to travel. But given that humans have fractured the habitat of many species, it would be difficult if not impossible for many of them to move.

    This would mean that, far from being good news, it is even worse news for those sub populations that live in remnant habitat. Far from being able to move as the climate changes, they will be stuck in a isolated fragment that is changing around them, and would probably go locally extinct as the habitat becomes untenable.

    report
  2. Matt Stevens

    Senior Research Fellow/Statistician/PhD

    "The fast pace of climate change makes both of these options very tough to achieve, but not impossible"

    I would say that many animals are already adapting to changing climate conditions and they do so within a couple of generations (and possibly seasonally). Within a generation or two the ones that survive the new conditions are the ones that reproduce. No drama! It is only the long lived species that will struggle, but then again most long lived species are closer to the top of the food chain and are also quite mobile.

    report
    1. Matt Stevens

      Senior Research Fellow/Statistician/PhD

      In reply to Mike Swinbourne

      Hi Mike. Well maybe not adapt within a couple, but selection pressure is being constantly applied and couple this with a species ability to move into regions more suitable or even microclimates more suitable would seem to be an obvious response.

      report
    2. Matt Stevens

      Senior Research Fellow/Statistician/PhD

      In reply to Mike Swinbourne

      And the 10000 times figure seems a bit rich and would certainly lead me to question the sensitivity and specificity of the model

      report
    3. Mike Swinbourne

      logged in via Facebook

      In reply to Matt Stevens

      Matt

      No-one is arguing that selection pressure is not being constantly applied - of course it is.

      But perhaps you missed my post about the inability of many species to be able to move into more suitable regions because of habitat fragmentation. If you can't move - and many species can't - then if your isolated habitat fragment changes at a rate greater than your ability to adapt, the species will go locally extinct. And the inability of many species to 'adapt' is further exacerbated because population numbers are so low that they lack the genetic diversity to evolve through selection.

      report
    4. Matt Stevens

      Senior Research Fellow/Statistician/PhD

      In reply to Mike Swinbourne

      Agreed that habitat fragmentation is a big issue, but one that with thewill and inclination can be managed to a degree. I think the biggest threat to species diversity and local richness comes from habitat clearance which leads to fragmentation, while the mojority of species will simply adapt be it through natural selection or changing range.

      report
    5. Matt Stevens

      Senior Research Fellow/Statistician/PhD

      In reply to Matt Stevens

      The last point was referring to change associated with climate change

      report
    6. Mike Swinbourne

      logged in via Facebook

      In reply to Matt Stevens

      Well Matt, I admire your optimism, but I fear it is misplaced.

      I suggest that the majority of species won't be able to adapt either through natural selection (because they don't have the genetic diversity to do so) or changing range (because they are unable to move because of habitat fragmentation).

      At the moment the science backs up my view - but I guess time will tell.

      report
    7. Doug Hutcheson

      Poet

      In reply to Matt Stevens

      Matt, one option for dealing with change is to adapt by dying. Given the slow natural process of evolution, it is likely that more species will adapt by death than will adapt by evolution. Just my $0.02.

      report
    8. Mike Swinbourne

      logged in via Facebook

      In reply to Gavin Moodie

      Gavin

      Not really - it depends on how fast they reproduce. The shorter the time between generations and the more offspring produced, the greater the ability to adapt /evolve (in general terms, its not a hard and fast rule).

      report
  3. Gavin Moodie
    Gavin Moodie is a Friend of The Conversation.

    Adjunct professor at RMIT University

    Might a species' ability to adapt to its environment be related to the changeability of its environment? So a species in a highly variable climate might be more adaptable than a species in a more stable environment and a species in an environment that is changing relatively fast might be able to adapt faster than those in environments that change slower.

    report
  4. Doug Hutcheson

    Poet

    We are running a global experiment to determine the degree of climate change beyond which the human species will be unable to evolve quickly enough to adapt. If we had our generations as quickly as the cane toad, there might be less doubt about our future. Humo Stupidus stupidus.

    report
    1. Matt Stevens

      Senior Research Fellow/Statistician/PhD

      In reply to Doug Hutcheson

      haha homosapien will adapt, maybe humo stupidus poet won't

      report
  5. Geoffrey Harold Sherrington

    Boss

    Rick,
    Can you please give a few examples of your claimed 'Fast pace of climate change...'
    Fast with resect to which datum? Global temperatures seem to have taken a pause for the last 15 years, during which I presume much of your work was done.

    report
  6. Rex Gibbs

    Engineer/Director

    Isn't this old news? I recall research from several years ago that showed that toads at the advancing edge were longer limbed and faster and covered more ground. I believe I heard it on the ABC science show.

    report
    1. Eric Ireland

      logged in via Facebook

      In reply to Rex Gibbs

      Yes, I remember they called it the "Olympic Village Effect"! :)

      report
  7. John Campbell

    farmer

    Yes the grass is green and the sky is blue and us omphaloskeptics can speculate to the cows come home to graze. The value of such speculation may however only be in the eye of the beholder.

    report