In New Zealand, Argentine Ants Collapse

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Linepithema humile, the Argentine ant

Argentine Ants have spent the past century following commerce around the world, aggressively subsuming the territories of native ants. However, a study by Meghan Cooling et al out today in Biology Letters reports a dent in the Argentine ant empire:

Argentine ants had disappeared from 40 per cent of our sampling sites. In many other sites, Argentine ant populations had been reduced from occupying multiple nests encompassing large areas to one or two small nests in a few square metres. These results are consistent with our observations of the slow shrinkage and disappearance of large Argentine ant infestations in areas, such as Wellington. They do not appear to move and to our knowledge are not managed by humans in any way that might reduce their abundance.

This result echos anecdotes I’ve heard from several people in California. Places once thick with Argentine ants have returned, in part, to a native fauna.

Cooling et al pair their collapse data with climate models to predict whether the process will continue under global warming. I wish they hadn’t. Without knowing the cause of the collapse (pathogens?) the whole climate model exercise is silly. Can’t a straightforward ecological finding just be published on its own?


Source: Cooling, M. et al 2011. The widespread collapse of an invasive species: Argentine ants (Linepithema humile) in New Zealand. Biology Letters, Published online before print , doi:10.1098/rsbl.2011.1014

18 thoughts on “In New Zealand, Argentine Ants Collapse”

  1. Interesting, but with such a large resource available, I would think it was only a matter of time before some suite of natural enemies began making hay. Nice that only a century, rather than a millineum, was needed. Maybe some day Argentine ant will be just another interesting species of the NZ fauna.

    If a ‘native’ pathogen or parasite is responsible, that would be pretty interesting, but many fungi and other microbes tend to be wind dispersed and have large distributions. Probably no need to invoke pathogen pollution through commerce. Could also be something that has been with the ant a longtime, but there was selection for low virulence – and that has now been relaxed and an opportunistic genome has taken off.

  2. > “Can’t a straightforward ecological finding just be published on its own?”

    Nope ! They needed to get their theory added here:

    A complete list of things caused by global warming
    http://www.numberwatch.co.uk/warmlist.htm

    right alongside this gem which explains all: “Expect Smaller Brains with Global Warming”

    roflao

  3. I’ve been noticing a similar thing with a number of local invasive species around my house. Just over the past 15 years or so, we’ve had green immigrant leaf weevils, clover weevils, earwigs, european paper wasps, snailcase bagworms, and multicolored asian lady beetles invade the area, establish themselves in great numbers to the point where they seemed to be forcing out the previous species, and then collapse back down to a reasonable population density.

    So, is that the way it generally goes with invasive species? Initial big problems as they insinuate themselves into an ecosystem, followed by a sudden population crash which leads to them settling down into being just one more species out of many?

    1. I suppose one could argue that everything was once an invasive species. Certainly, according to current theory, every species should have started as a small population and then expanded its range – the latter being the essence of an invasive species. But many ‘natural’ systems are dominated by a few species that must have once been ‘invaders’, so I don’t think there is any general rule about populations having to fit in. Some plants and animals seem to have been able to dominate their habitats for a long time and if a new one of those lucky species invades your backyard, it may be there in numbers for the long haul.

  4. FWIW, pretty much the entire research goals of USGS-BRD are geared towards climate change, so any results they get (i.e. opportunities for future funding) have to be tied to it somehow. I wouldn’t be surprised if there’s something similar in NZ.

  5. Argentine ants are obviously amazing opportunists, and it seems that much of their success is due to the ability to use a huge variety of resources. Part of this involves exploiting relationships that native species have developed symbiotically without participating in their ‘fair share’ – such as consuming the elaiosomes of plants that rely on myrmecochory. Perhaps as Linepithema humile continue their use of such resources without contributing to their sustainability, and by altering the ecological conditions that supported their initial explosive growth, the population inevitably plateaus and diminishes. I also wonder about circannual patterns of reproduction, dispersion, and nest founding in supercolonial, polygynous species (there’s probably literature out there I’ve yet to read), which could certainly be affected by climate change. Not having read the article (thank you, paywalls) in full, I cannot criticize it specifically, but I agree that it is sometimes better to let data stand on its own merits without prematurely correlating it with a particular pressure – something that seems to be in vogue in addressing CCD in honeybees, global amphibian decline (until a recent study finally suggesting several synergetic factors), and now apparently the fluctuation of L. humile in NZ.

  6. According to historical records, a massive outbreak of stinging ants occurred in the Caribbean during early colonial times. This ant is presumed to be Solenopsis geminata, as it dominates the islands today. It was probably introduced into mainland North America at the same time, but today it’s now just another occasional species in the South. I’ve long suspected that native ants adapt to invasives and regain lost ground. After all, they’re under tremendous evolutionary pressure. Given that many native genera must have arrived as invasive species given their distributions, the question is really, how long does it take native species to recover? Since ecology is still a relatively young discipline, maybe we haven’t observed invasives long enough to know the answer.

  7. Fifteen years ago, I thought Tetramorium tsushimae was going to be a serious invasive wave emerging from St. Louis, but now I’m not so sure. I’ve watched it surge, then retreat from many locations around here, and a recent dissertation by St. Louis University grad student (now Dr.) Keefe Reuther – http://gradworks.umi.com/33/83/3383231.html – though it concludes that this is a significant invader, also contains some evidence that natives are accomodating to its presence in some of the longest held, and heavily infested areas near the Mississippi River waterfront. Indeed, at one of Keefe’s peripheral study sites, the ants died out during the course of his study.
    Related to climate change?, no way to know, but not the first thing I would think of. Now I wish the pernicious, Asian Lonicera maackii, cluttering up the forests around here, would show signs of retreat!

    1. > Related to climate change?

      I say “Go for it !!” As always, should any member of your team be caught or killed, the Secretary will disavow all knowledge of your actions.

      Here is the St Louis climate data page.

      http://www.crh.noaa.gov/lsx/?n=cli_archive

      Year Ave Anomaly
      1990 59.0 2.8
      1991 59.2 3.0
      1992 57.2 1.0
      1993 55.6 -0.6
      1994 57.7 1.5
      1995 57.0 0.8
      1996 54.9 -1.3
      1997 55.1 -1.1
      1998 58.7 2.5
      1999 58.0 1.8
      2000 56.2 0.0
      2001 57.7 1.5
      2002 57.9 1.7
      2003 56.5 0.3
      2004 57.6 1.3
      2005 58.0 1.8
      2006 58.5 2.3
      2007 58.3 2.1
      2008 55.5 -0.7
      2009 56.6 0.4
      2010 58.0 1.8

      oops

      After a quick scan through the data, I have to say it’s too bad you didn’t do this in the 50’s or 30’s rofl.

      RECORD HIGHEST HIGHS
      115 14-Jul 1954
      112 18-Jul 1954
      111 24-Jul 1934
      110 12-Jul 1954
      110 9-Aug 1934
      110 20-Jul 1934
      108 14-Jul 1936
      108 8-Aug 1934
      108 23-Jul 1934
      108 28-Jul 1930

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  9. I was gonna make a Chilean joke about “What do you expect from f%#cking Argentinians,” but this bio talk took the wind out (of my sails).

  10. I was gonna make a Chilean joke about “What do you expect from f%#king Argentinians,” but this bio talk took the wind out (of my sails).

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