By Julie Kray
More than 350 students, faculty, and local scientists piled into CSU’s Cherokee Park Ballroom for Tuesday afternoon’s keynote speaker, Dr. Dan Simberloff of the University of Tennessee and Institute for Biological Invasions. The unprecedented turn-out was a testament to Dr. Simberloff’s foundational contributions to invasion ecology and conservation biology (read a short biography and learn of his numerous accolades here). To describe the scene as a “packed house” would have been an understatement. The whole show had to be moved to a larger room, as we were violating the building’s fire code. Dr. Simberloff quipped, “I didn’t realize I had the reputation of being such an incendiary speaker.”
After settling in, Dr. Simberloff took us on a journey from the 18th century inception of invasion ecology, which began with people simply wondering “which species are where?,” to its present incarnation, where molecular genetics and the call to measure ecosystem-wide impacts of invasions are pushing the field steadily forward. Surprisingly, although Charles Elton penned a book on the subject in 1958, invasion research did not truly come alive until the 1980’s with the SCOPE project. At this time, scientists studied devastating island invaders like the mongoose, or the brown tree snake on Guam, and aquatic invaders like the Nile perch, which is solely responsible for the extinctions of 100-200 native cichlid fishes in Lake Victoria.
New frontiers in invasion ecology
Ecologists today can use genetic markers to identify where particular invasive species have come from (in some cases, they arrive through multiple introductions from several locations) and the extent of hybridization between invasive species and native relatives in their new environments (this can lead to newer generations of SUPER invaders). These markers can even be used to show how invasive species sometimes spread right beneath our noses as we mistake them for native look-alikes (a.k.a. “cryptic invasions”). Invasion research has also shifted from an initial focus on individual invasive-native species interactions to exploring how invasive species can alter many interrelated bits and pieces of ecosystems. Some examples include the discovery of multiple invasive plant, bird, and mammal species facilitating the spread of one another on the island of Hawaii (what Simberloff refers to as an “invasional meltdown,” see Vitousek et al. 1989 Ecological Monographs); and the effect invasions have at multiple trophic levels, from soil microbes to seabirds (Fukami et al. 2006 Ecology Letters).
But even though we are now understanding ever more the complexities wrapped up in the causes and effects of invasions, we still don’t have any easy answers for the question, “What should we DO about it?”
Controversies in invasive species management
The heart of Dr. Simberloff’s talk presented and diffused five common arguments against managing to control invasive species, many of which were most recently raised by a commentary published in Nature (Davis et al. 2011).
1. Which introduced species are truly harmful? Most of them don’t seem to be having any impact…
Dr. Simberloff pointed out that we often don’t know whether introduced species are having harmful impacts until it is too late–many negative impacts have a lag time before they are noticeable, and many impacts are not immediately obvious (such as a change in nitrogen cycling). We do know that many introduced species don’t spread quickly right away, but their populations “explode” suddenly at a later time. For this reason, Simberloff argues strongly for proactive management as soon as an introduced species is detected, as opposed to the “wait-and-see-if-it-becomes-a-problem” approach.
2. Introduced species often increase local biodiversity…
Sure, introductions can increase the number of species in an environment, but this is usually temporary, and often comes at the loss of native species–permanently. One example: prior to human colonization, there were 114 native bird species on the island of Hawaii. Now, the island has gained 53 introduced bird species, while at least 55 of the original native birds have gone extinct. We are left to consider, was this a “good” trade?
3. Are actions against introduced species xenophobic?
Some have suggested that the terms for invasive species and the reactions they provoke are unnecessarily emotionally charged. In reality, however, there is no parallel between invasive species and xenophobia related to human immigration.
4. Efforts to contain invasions are futile.
While the work of containing or halting the advance of invasive species can be challenging and at times extremely expensive, it is far from impossible, and new technologies are making it easier all the time. Again, Simberloff argues that stronger preventative measures and early action to eradicate introduced species are the best approach, before the task becomes increasingly daunting.
5. Animal rights objections to eradication and management of some invasive vertebrates.
This argument, he admitted, is difficult to counter if one believes that every living thing has a “right to exist” (versus the idea that a species has a right to exist). Reconciling these viewpoints may be one of the great challenges to future efforts of invasive species management.
We were fortunate indeed to hear Dr. Simberloff’s perspectives, given his vast experience working on invasion ecology from both science and policy angles. His provocative talk nicely set the stage for a memorable 19th annual FRSES.
