Biological invasions: time to increase the pressure against invaders or lay down the pitch forks?

Katie Murray and Zarah Pattison


We recently held our departmental lunchtime “Conservation Conversation”, discussing whether or not invasive non-native species (INNS) are really that bad after all. This is an interesting concept to think about, especially for Zarah Pattison and myself who both work on different groups of invasive species in Stirling University’s Natural Sciences department. This is particularly in light of the flurry of books, namely Fred Pearce’s “The New Wild” and Ken Thompson’s “Where do camels belong?” which are promoting INNS. There has been a storm of surrounding media attention and outrage of invasion biologists worldwide. But who is right? And if they are “Nature’s Salvation” (Pearce, 2015), then are we wasting money on biological control of these organisms?

This debate was at the heart of our discussion, opening the floor to discuss what kinds of INNS were most prevalent in people’s minds and how they receive their information on INNS. This was a slightly biased sample as everyone in the room has studied or worked in an environmental academic department. We found that not one of the 15-20 people mentioned a vertebrate (which in my opinion is pretty awesome due the ‘fluffy-crew’ normally being particular popular!). There was a consensus with regards to the negative role INNS play in invaded ecosystems, except for one outlier who suggested the malicious role of these invaders to be species specific.


Fairly indiscriminate diners, coquies will eat almost anything that enters their range (R. Cauldwell)

Zarah: I always campaigned against INNS from undergrad. Digging deeper into the role these species play in native ecosystems is fascinating. I have definitely crossed over into the “intermediate” playing field of thinking that the impacts of INNS are both species and context specific. In a biodiversity hotspot such as the Western Cape, South Africa, Acacias (for example Acacia mearnsii) have a direct impact on water resources. Hawai’i, so well-studied for island invasions, is teaming with INNS. From Fountain Grass (Pennisetum setaceum) which dominates the landscape outcompeting native plant species, to the Coqui frog (Eleutherodactylus coqui) which has no natural predators and feats on native insects. However, we still receive mixed messages regarding impacts on native diversity, particularly for some of our most expensive invaders in the UK (in terms of clearing and management), such as Himalayan balsam (Impatiens glandulifera). Clarification is definitely needed. Are these species having a direct impact on native biodiversity, particular in degraded urban habitats, or are they merely passengers of some other human-mediated disturbance?


The harlequin ladybird is notorious invasive species that was originally released for biological control (Mike Majerus)

Katie: Before starting work on my PhD, I had worked on harlequin ladybirds (Harmonia axyridis) for my Masters project. I therefore also think of biocontrol going hand-in-hand with invasive species, and knowing that the harlequin had been initially released as a biocontrol agent, I had negative opinions towards when starting my PhD. As much as I applaud a reduction in the use of pesticides in agriculture, I was strongly of the opinion ‘this is what happens if you release a species into a novel area – it will take over and cause species declines’. However I take this all back! The harlequin is a particularly good example of biocontrol ‘gone wrong’. There are many examples of successes, preventing the use of pesticides that at times won’t even work due to the resilience of pest species. An example of research in this area currently being conducted in Ireland is the Eucalyptus beetle (Paropsistern selmani) which was accidentally introduced from New Zealand. These beetles defoliate Eucalyptus trees used in the floristry industry, and therefore causes an economic problem for growers. The parasitic wasp (Enoggera nassaui) has been proposed as a suitable biological control agent to bring the invasive beetle population under control. The use of pesticides in this system previously resulted in a native pest species left uncontrolled by native parasitoids (the pest species being resistant to the pesticides) and creating a further problem in the industry. Thorough research is necessary to ensure that the target beetle is the only species affected otherwise there could be risks to native beetles species.

eucalyptus beetle

The eucalyptus beetle causes economic problems for the floristry industry.


One of the most interesting things to come out of this discussion was that with every INNS debate that day, you could have argue both for and against the invader. In some ways the positive press has just highlighted the fact that we need more data and studies on the effects of INNS in invaded ecosystems, if not only to disprove the notion that these species have no impact. We cannot make science based policy, management etc. decisions without all the information. They say that all publicity is good publicity, well us invasion biologists are ready and willing to go all the way, fighting.


Tunnel of Japanese Knotweed (Fallopia japonica) partly cut back on the Black Cart Water, Scotland. (Z. Pattison)


One Comment on “Biological invasions: time to increase the pressure against invaders or lay down the pitch forks?

  1. Hi – interesting summary. Just writing this before heading out to spend another day with SNH pulling up Himalayan Balsam! The number of volunteer man hours spent tackling invasives is huge, and it seems to me that as a country we need to make our minds up. We need to decide which invasives we need to tackle and then invest properly in getting rid of them, and then accept the rest and live with the altered ecosystems. At the moment it feels like we’re just slowly losing on all fronts!

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