When my best
friend's family decided to up sticks and move to Australia, she was gutted to find
that as well as leaving all her friends behind, “Rodney” the guinea pig
couldn’t journey with them either. Whilst some pets are welcomed with
(relatively) open arms in Australia, poor Rodney along with many other animals was not. This is
because the introduction of pets is one of the main ways which humans can
facilitate the transport of invasives. Historically before tight
controls were implemented, it was not uncommon for adventurers to take their
pets with them; sealers for example would travel with cats and dogs to oceanic islands (Taylor, 1979).
Without prior knowledge of the potential negative impact of invasives, this behaviour from our ancestors is understandable. Some rationale
behind the deliberate introduction of species however, is just downright crazy.
For example at the end of the 19th century, The American Acclimatization
Society decided that it was completely reasonable to try and introduce all of
the birds ever mentioned in a play written by William Shakespeare to North
America (Mirsky, 2008). This movement as a whole was inevitably
unsuccessful however, the European
Starling is now well established across the USA.
Perhaps more sensibly, species may be introduced to a new location to act as a biological control.
On that note I feel that it is perfect time to introduce one of the most notorious species of this topic, behold the Zebra Mussel:
Elena,
ReplyDeleteWhat an interesting introduction to the potential environmental impacts of invasive species!
As a Canadian, I am very familiar with some of the devastating effects invasive species can have, in particular those caused by the introduction of the zebra mussel to our Great Lakes. Although using invasive species as biological controls seems a very reasonable approach, I hadn't come across this method for population control. In your post, you mention that these biological controls can get out of hand, as in your Cane Toad example. Have you encountered any examples of this biological control concept working as a sustainable solution for population control? I'd love to learn more about this topic.
Cheers!
Hi Katherine, thank you for your comment!
ReplyDeleteThere are several occasions when the introduction of a natural enemy has been successful in controlling pest populations. An example of particular interest is the introduction of Rodolia cardinalis (vedalia beetle) to the Galapogas Islands in 2002, in order to control the Icerya purchasi (cottony cushion scale) population. This was in fact the first introduction of a biological control to the Galapogas Islands. The high number of endemics that this ecosystem supports, combined with the bad press that biological controls have had, meant that a number of people understandably had their reservations at first. Alvarez et al. (2011) provide a persuasive summary of the negative effect of I. purchasi on the endemic flora and fauna, giving reason for the programme to go ahead. The introduction of R. cardinalis was a success and viable populations were established. Furthermore, statistical evidence confirmed that the introduction of this natural enemy was at least in part responsible for the decline of I. purchasi from the Galapogas islands.
Here's the title of the journal article for a more detailed review: “Monitoring the effects of Rodolia cardinalis on Icerya purchasi populations on the Galapagos Islands”
Another great example of a sustainable biological control can be found in a paper written by Peter McEvoy and Caroline Cox (1991) “Successful biological control of Ragwort, Senecio jacobaea, by introduced insects in Oregon”.
If you want to find out more on the topic of biological controls, I also thoroughly recommend the book “Biological control by natural enemies” by Paul DeBach and David Rosen.
Enjoy!
Elena
Thanks for the detailed information, Elena! I'll definitely have a look at those sources. Comically, it turns out that biological control has somehow made its way into my next post at Picnics Past and Present - thanks for the inspiration!
ReplyDeleteGood work Elena,
ReplyDeleteIt answers my question from your last post well. Do you think the introduction for biological control is more successful in isolated areas, such as the Galapagos islands?
Hi, sorry for the incredibly slow reply I somehow managed to accidentally miss your comment.
DeleteI think that MacArthur and Wilson’s theory of island biogeography needs to be considered in order to answer your question. According to this theory, isolated islands have fewer species present on them in comparison to less isolated islands. (This is because there is a slower rate of immigration, so if the extinction rate remains constant on all islands, the equilibrium reached is smaller). (MacArthur and Wilson, 1967).
For a successful introduction of a biological control there needs to a be an empty niche that the organism can fill, and if there is a smaller number of species the chances of this is more likely. Therefore in terms of sustaining a viable population, I think that the introduction of biological controls is more likely to be successful in isolated areas.
However, due to a slower rate of immigration, isolated islands tend to have a greater number of endemic species meaning that the introduction of a biological control is more risky. Biological controls may prefer to consume other endemic organisms on the island instead which could lead to a very unsuccessful introduction!