Wednesday, July 8, 2015

Taking stock of exotic species in the new wild: Acknowledging the good and the bad.*

Are exotics good or bad? They are neither. They just are. But some exotics cause harm and impede certain priorities, and debates about exotics often ignore reality.

Book review: Fred Pearce. 2015. The New Wild: Why Invasive Species Will Be Nature’s Salvation. Beacon Press

There has been much soul-searching in invasion biology, with attacks, and subsequent rebuttals, on the very nature of why we study, manage and attempt prevent the spread of exotic species (Davis et al. 2011) (Alyokhin 2011, Lockwood et al. 2011, Simberloff 2011). What is needed at this juncture is a thoughtful and balanced perspective on the nature of the discipline of biological invasion. Unfortunately, the book “The New Wild” authored by Fred Pearce, is not that balanced treatment. What is presented in this book is a very one-sided view, where counter-evidence to the thesis that exotics will save nature is most often overlooked, straw men are erected to aid in this goal, and the positions of working ecologists and conservation biologists are represented as simplistic, anachronistic or just plain incorrect.

What Pearce has written is a book-long argument about why exotics shouldn’t be feared, but rather embraced as a partial solution to anthropogenic land use change. I do not wish to undermine the reality that exotics can play important roles in urban landscapes, or that some ecologists and conservation biologists do indeed harbour suspicions of exotics and subscribe to unrealistic notions of purely native landscapes. Exotic policy is at the confluence of culture, science, economics and politics, and this is why the science is so valuable (Sandiford et al. 2014). For Pearce, the truth of what most ecologists do and think seems like an inconvenient reality.  There are a number of pervasive, frustrating problems with Pearce’s book, where bad arguments, logical flaws and empirical slight-of-hand obfuscate issues that desperately need honest and reflective treatment.

A monoculture of the exotic plant Vincetoxicum rossicum that spans open and understory habitats near Toronto, Canada (photo by M. Cadotte). This is a species that interferes with other management goals and needs to be actively managed.

There are major problems with ‘The New Wild’ and these include:

1) A premise built on a non sequitur and wishful thinking. The general premise of the book, that exotics represent a way out of our environmental doldrums, is myopic. Pearce’s reasoning seems to be that he has conflated “the world is not pristine and restoration is difficult…” with the alternative being that exotics are positive and “we should bring them on”. Certainly we can question exotic control efficacy, costs and conservation goals, but that does not mean that exotics are necessarily the solution.

      2)   Underrepresenting the observed effects of some invasive non-indigenous species. Pearce’s book is not balanced. The perceived benefits of exotics in this ‘New Wild’ are extolled while dismissing some of the problems that invasive ones might cause. He says that exotics typically “die out or settle down and become model eco-citizens” (p. xii). But there is a third outcome that Pearce ignores –they move in and become unruly neighbours. When he must acknowledge extinctions, he minimizes their importance. For example when discussing Hawaiian bird extinctions: “The are only 71 known extinctions” (p. 12 –italics mine), or with California: “But only 30 native species are known to have become extinct as a result [of exotics]” (p. 64 –italics mine).

He also implies throughout the book that exotics increase diversity because “Aliens may find new jobs to do or share jobs with natives.” (p. 113). The available evidence strongly suggests that the numbers of species inhabiting communities has not increased over time (Vellend et al. 2013, Dornelas et al. 2014). Which on the surface seems like a good thing, except that many communities are now comprised of 20-35% exotics. This means that there have been losers. Vellend and colleagues (2013) show that the largest impact on native species diversity has been the presence of exotics. So, they do not necessarily find new jobs, but rather outcompete some natives.

      3)   Conservation biologists and ecologists in the crosshairs. Pearce continually lauds those like-minded, outspoken advocates of exotics while belittling ecologists and conservation biologists who don’t agree with him. His disrespect for the process of science comes in two forms. First, he seldom considers evidence or presents opinions counter to his thesis. He gives a partial reason about this bias; he says that ecologists (except for those few brave pioneering souls) ignore novel ecosystems and the functional contributions of exotics (for example on p. 13). This is demonstrably false (see next section). Pearce has little affection for conservation biologists and mainstream ecologists. Both groups are disparaged and dismissed throughout the book. Conservation biologists get a particularly rough ride, and he never acknowledges the difficulty of their task of balancing multiple priorities: extinction vs. ecosystem function, habitat preservation vs. socioeconomic wellbeing, etc. For example, Pearce states: “Conservation scientists are mostly blind to nature outside of what they think of as pristine habitats and routinely ignore its value” –again a demonstrably false assertion.

In a particularly galling example, Pearce resorts to ‘guilt by association’ as an ad hominem attack to undermine the validity of opposing views. He links conservation with eugenics: “Many conservationists of the first half of the twentieth century were prominent proponents of eugenics” (p. 141). It would be equally valid to state that most journalists were proponents of eugenics in the first half of the twentieth century. Pearce, being a journalist, should see this as a specious argument at best.

Ecologists share in this odd and unfair derision. “Ecologists are tying themselves in knots because they refuse to recognize that these novel, hybrid ecosystems are desirable habitats for anything.” (p. 156). Unfortunately for Pearce, there are more than 4000 papers on ‘novel ecosystems’.

      4)   Misrepresenting modern ecology and conservation. Pearce attacks ecological science throughout the book and as an example Pearce makes observations about the role of disturbance and refusal to acknowledge this by ecologists “intent on preserving their own vision of balanced nature” (p. 144). However, disturbance has been a central component of community ecology for the past five decades. Because of this balance-of-nature view, Pearce says ecologists are not studying degraded, disturbed or recovering systems. For example, with secondary forests, he says: “Yet the blinkered thinking persists. Degraded forests and forests in recovery are almost everywhere under-researched and undervalued.” (p. 157). Yet there are almost 9,500 papers on secondary forests –highlighting the ecological interest in these widespread systems. There are numerous such examples.

      5)   A black and white, either-or dichotomy.  What Pearce provides is a series of stark dichotomies with little room for subtle distinction. He ties resilience and ecosystem wellbeing to the arrival of exotics, without adequately assessing the drawbacks: “Nature’s resilience is increasingly expressed in the strength and colonizing abilities of alien species …we need to stand back and applaud” (p. xii).

Invariably in ecology, debates over ‘either/or’ dichotomies end up with the realization that these dichotomies are endpoints of a continuum. This is exactly the case with exotics. Are they bad or good? The answer is neither. They just are. Some exotics species provide economic opportunity, ecosystem services and help meet other management goals. Some exotics cause harm and impede certain priorities. Modern management needs to be, and in many cases is, cognizant of these realities.

Alyokhin, A. 2011. Non-natives: put biodiversity at risk. Nature 475:36-36.
Davis, M. A., M. K. Chew, R. J. Hobbs, A. E. Lugo, J. J. Ewel, G. J. Vermeij, J. H. Brown, M. L. Rosenzweig, M. R. Gardener, and S. P. Carroll. 2011. Don't judge species on their origins. Nature 474:153-154.
Dornelas, M., N. J. Gotelli, B. McGill, H. Shimadzu, F. Moyes, C. Sievers, and A. E. Magurran. 2014. Assemblage Time Series Reveal Biodiversity Change but Not Systematic Loss. Science 344:296-299.
Lockwood, J. L., M. F. Hoopes, and M. P. Marchetti. 2011. Non-natives: plusses of invasion ecology. Nature 475:36-36.
Sandiford, G., R. P. Keller, and M. Cadotte. 2014. Final Thoughts: Nature and Human Nature. Invasive Species in a Globalized World: Ecological, Social, and Legal Perspectives on Policy:381.
Simberloff, D. 2011. Non-natives: 141 scientists object. Nature 475:36-36.
Vellend, M., L. Baeten, I. H. Myers-Smith, S. C. Elmendorf, R. Beauséjour, C. D. Brown, P. De Frenne, K. Verheyen, and S. Wipf. 2013. Global meta-analysis reveals no net change in local-scale plant biodiversity over time. Proceedings of the National Academy of Sciences 110:19456-19459.

 *This post is a synopsis of my book review in press at Biological Invasions

Monday, July 6, 2015

Can there be a periodic table of niches?

Are there a limited number of categories or groupings into which all niches can be classified?  I’ll 
admit that my first reaction is skepticism. For those ecologists who think of the similarities and generalities across systems, this may be an easier sell, compared to those who get caught up in the complexities of ecological systems. Classifying niches in this way is apparently a vision that distinguished ecologists have voiced: MacArthur: “I predict there will be erected a two- or three-way classification of organisms and their geometrical and temporal environments, this classification consuming most of the creative energy of ecologists.” 

From Winemiller et al. 2015.
Kirk O. Winemiller, Daniel B. Fitzgerald, Luke M. Bower, and Eric R. Pianka, takes on this rather ambitious goal in a new paper: “Functional traits, convergent evolution, and periodic tables of niches”. The periodic table, of course, is the foundation of chemistry – the predictive, descriptive arrangement of chemical elements based on their atomic number. Ecology may never achieve a similarly simple foundation, but the authors suggest that such a general classification of possible niches (and the species that are within them) is possible. A niche within a table would extend across taxa, habitats, and biomes, and would be seen repeatedly (i.e. periodically) across these.

Perhaps because they (and their reviewers) recognized the ambitious nature of this task, the paper helpfully acknowledges the reasons that a periodic table of niches might be a terrible idea right away. Unlike chemistry, ecology is strongly dependent on context, and stochasticity limits generality. The multi-dimensionality of the modern niche concept limits how few axes such a table could be reduced to. Evolution means that classifying a species’ niche is like trying to hit a moving target.

Examples of convergent evolution are common.
Still, even the chemical periodic table has some fuzzy matching going on – isotopes still group together under a given element, despite variation. “In the same way, elements can have different isotopes,…a niche category could have phenotypic variants but still have ecological properties or functions that are essentially the same.” In particular, the authors argue that convergent evolution has recreated particular suites of traits (niches) in different habitats and distantly related taxa. This has some connection to the idea that, perhaps, much like complex systems, complex arrays of traits may reoccur because they provide stability (e.g. are selected for).

How then to approach this task? Here the periodic table is rooted in a functional trait approach, where observable phenotypes capture niche information. The dimensions of the table are determined based on what must have been the result of long discussions and much difficulty, but the authors restricted themselves to five essential components: abiotic habitat, life history strategy, trophic position, defense mechanisms, and metabolic allocation strategies.
From Winemiller et al 2015.

From here, the use of various ordination approaches allow researchers to begin to identify species sharing trait combinations, allowing them to be classified within the table (see paper text for more detail). The combinations of these dimensions observed or unobserved in nature should inform us about the stability of certain niches, and perhaps provide predictions about which species to use for restoration approaches, which species may be invasive in a given system, or to predict shifting distributions.

If you had many different ecologists each develop a ‘periodic table of niches’, each table would be unique, evidence for how difficult drawing general principles and identifying the fundamental ecological dimensions is. Another person might consider dispersal its own dimension, for example, or dismiss defenses. This is especially true because the periodic table presented in this paper is phenomenological, lacking a clear connection with theoretical work, for example. The proof will be in its application and utility – do others adopt it, is it predictive, does it extend our understanding of the niche or improve applications? And I think there is a direction for functional ecology implicit in this work.

Their hearkening to MacArthur makes me wonder what MacArthur would think if he saw ecology today. His prediction that “there will be erected a two- or three-way classification of organisms and their geometrical and temporal environments, this classification consuming most of the creative energy of ecologists” falls short, but not in the ways he might have expected. Here then, is a classification system (and there have been other ideas and versions since his time), but even the 2 or 3 dimensions he generously offers aren't deemed nearly enough to capture ecological diversity. Is the simplicity that MacArthur mentions still considered possible? And I don't think the creative energy of ecologists has been focused on classifying niches in the way he mentions: it is more dispersed amongst topics, and human effects (climate change, fragmentation, habitat loss) have had a dominant role.

Winemiller, Kirk O., Fitzgerald, Daniel B., Bower, Luke M., Pianka, Eric R. 2015.  Functional traits, convergent evolution, and periodic tables of niches. Ecology Letters. DOI: 10.1111/ele.12462

Wednesday, June 24, 2015

The devil isn't always in the details: how system properties can inform ecology

Selection on stability across ecological scales. Jonathan J. Borrelli, Stefano Allesina, Priyanga Amarasekare, Roger Arditi, Ivan Chase, John Damuth, Robert D. Holt, Dmitrii O. Logofet, Mark Novak, Rudolf P. Rohr, Axel G. Rossberg, Matthew Spencer, J. Khai Tran, Lev R. Ginzburg. 2015. Trends in Ecology & Evolution,

This paper in TREE  on selection at higher level systems has been on my must-read list since it came out a few weeks ago, and it was worth the wait. It does what the best TREE papers do - makes you think a bit more deeply about a common topic. In this case, it develops an approach to understanding complex ecological systems (communities, ecosystems) that is blind to the details that ecologists often focus on.

The search for generalities and commonalities drives modern ecology. In short (though this paper deserves an in-depth read), this paper argues that we can learn much by considering stability and feasibility in complex ecological systems. That is, we can also study community structure or trophic webs by considered whether specific configurations of the system are stable. This is in contrast to a context-centric study of a system, where the usual list of proximate causes (productivity, niche availability, connectivity, etc, etc) may be used to understand why the system looks as it does.

The authors' premise is that nonadaptive (e.g. unstable) ecological systems will be unfavourable and selected against, and the resulting selective process “can produce many of those recurrent ecological patterns that have been observed in nature over large scales of space and time.” This requires that you accept a few underlying concepts: first, that large scale systems also experience selection (whether one prefers selection be in parentheses is up to the reader), in that unstable systems will be lost at faster rates leading to greater frequency of stable systems; and second, that this process of selection is determined by the properties of the system alone, not the specific conditions ecologists often focus on.

As an illustration, consider four possible food webs depicting intraguild predation that vary in their interaction strengths. All configurations are possible, but A-C are likely to lead to exclusion of the intraguild predator. D is most likely to be stable since the strong interaction between the resource and prey results in negative feedbacks between the densities of all species (i.e. when the resource is low, the prey should also be low, reducing the predator density as well) and thus more likely to be observed in natural systems. 
From Borrelli et al 2015.

A more specific example looks at attack rates and handling times in predator-prey interactions. When stability is considered, it seems that although predator-prey cycles may occur, it should be uncommon to have such extreme oscillations that populations reach dangerously low levels where stochastic extinctions may occur. Data suggests that oscillatory dynamics are less common in predator-prey relationships, but do occur particularly for specialist predator/prey pairings. Theory (Rosenzweig-MacArthur predator-prey models) predict that such pairings should be most stable if prey are weakly self-limited and predators have high attach rates/long handling times. Empirical evidence for this prediction supports it surprisingly well.
From Borrelli et al 2015.
Other related approaches consider feasibility across food webs, communities, and ecosystems. A community perspective might consider interactions across all species, perhaps using a network approach. Networks should tend towards formations that are the most stable – e.g. short chains rather than long ones. The commonness of nested network structures may reflect these constraints. 

Such an approach to ecology is not entirely new (Robert May's weak interactions comes to mind). But it provides perhaps the best potential explanation I’ve seen for ‘generality’ focused approaches in ecology, including ecological allometric relationships, macroevolutionary patterns, and network approaches. Macroecological patterns have often captured, rather than tidy linear relationships, occupied versus unoccupied parameter space. Thinking about feasibility as a macroecological ‘mechanism’ for ecological patterns at the system scale might lead to new research directions. 

Monday, June 15, 2015

From the Archives: Conservation now and then

For the rest of the summer (until ESA!), we’re going to highlight some of the older topics and posts from the EEB & Flow. The blog has been around since December 2008, and so it has covered a lot of ground: 345+ posts with topics ranging from ecological history, to research advances, to work life balance, to the silly.

The interesting thing is that posts are like an archive of the various topics and directions ecological research has taken (or at least the research interests of the various post authors). And in many ways, papers from 2009 are frankly indistinguishable in topic and approach from today.

Take, for example, these posts from 2009 about conservation and climate change:

Salamanders and climate change – impending extinctions?

Fisheries and food webs: a whole system approach to cod recovery

The sushi of tomorrow… Jellyfish rolls?

Conserve now or wait for data?

The topics wouldn’t be out of place today. Risk assessments for specific species, fisheries and other applied questions, and consideration of the agony of conservation choices. 
(Not sure what this signifies - Maybe that 5 years isn't long in the grand scheme of research?)

Thursday, June 11, 2015

The problem with collaboration in the electronic era...

E-communication has revolutionized every aspect of our lives. From how we shop, find love, watch movies and do science, the ability to interact with others globally has virtually eliminated barriers to the flow of ideas. I have fruitful collaborations with researchers in many different countries, which are greatly enhanced by e-mail and Skype. However, a new problem has emerged -scheduling people for meetings in multiple timezones!
Green = optional working time for researchers in different timezones; yellow = suboptimal; red = perhaps we allow people to sleep.
I routinely have Skype meetings with my editorial team in the UK at 5 or 6 am, but as the above graphic shows -scheduling a meeting amongst people in the UK, North America and Australia is virtually impossible.