Competition and invasions: evolving perspectives

Guest post by Brechann McGoey.

The field of invasion biology was sparked with the publication of Charles Elton’s book “The Ecology of Invasions by Animals and Plants” (1958). Beginning in the 1980s (Simberloff et al., 2013), there was a rapid growth in research effort, most of which focused on the ecology of invasive species, including their traits and impacts (Lee, 2002). However, the evolutionary causes and consequences of colonization are also critical to our understanding of species invasions (Bacigalupe, 2009; Crawford & Whitney, 2010).

Figure 1- Research on invasive species has increased rapidly (Google ngram viewer). 

The influential book "The Genetics of Colonizing Species" (1965) is an early and important example of efforts to integrate concepts from the fields of genetics, ecology and applied sciences to better understand invasions. The volume covers a vast breadth of topics and its authors include some of the best minds in evolution and ecology of the last century. Many of the ideas raised at the conference were on the cutting edge, and although there are a staggering number of valuable insights in the book, the authors were often contending with a lack of data. In the fifty years since its publication, there has been an explosion of studies on invasion biology, and though there we may sometimes be frustrated by a lack of progress both in theory and management, we are in a much better position to evaluate how the hypotheses and assertions of 1965 stand up in the face of empirical data. 

In his chapter on competition and migration, Dr. Kan-Ichi Sakai sought to outline how evolution and competitive ability would influence plant invasion dynamics. He points out that, in order to become established in a new environment, a colonizer must be able to compete with the native flora. Since the initial population size is small, there is likely selection for genotypes that can exploit the low-density conditions, by growing and reproducing rapidly. We now have data demonstrating responses to this kind of selection, for example, in the cane toad invasion of Australia where individuals near the invasion front have accelerated development and so can reproduce more quickly (Phillips, 2009).  Sakai also raises the concept of trade-offs between migratory and competitive abilities during colonization, an idea that has found support in much more recent models (Burton, Phillips, & Travis, 2010).

Figure 2-Cane toads have increased the rate of their spread. Those on the edge of the rangeare better dispersers and reproduce more quickly.

Sakai argues that the lack of a covariance between fitness and competitiveness will lead to the maintenance of variation in competitive ability, essentially concluding that being a good competitor is not correlated with fitness. Modern invasion biology has veered away from this assumption. The prominent hypothesis of the Evolution of Increased Competitive Ability (EICA) is based on the idea that invasive plants will experience relaxed selection for defensive traits, have more available resources, and evolve to become superior competitors (Blossey & Notzold, 1995). This presupposes a positive covariance between competitive ability and fitness in their new context.

Sakai also asserts that competitive ability is not a heritable trait. This conclusion was perhaps due to a lack of data on the heritability of traits important to competitive interactions, and a somewhat murky definition of "competitive ability", and has since been abandoned (Hühn, 1975). Empirical work since 1965 shows that competitive traits can be heritable, for example in size and allelopathy, and artificial selection of crops can successfully increase competitive ability (Worthington & Reberg-Horton, 2013), demonstrating its heritability. In light of this, invasive populations will often be able to respond to selection and increase their competitiveness in their new habitats, with sometimes devastating consequences for their native competitors.

We now have a plethora of data on competition, migration and invasions, and are able to reject and find support for ideas laid out by Sakai five decades ago. Competition is a crucial interaction in plant invasions, both in determining how resistant a community is to invasion (Keane & Crawley, 2002), and how successful a novel species will be. If we hope to understand invasion processes, we must incorporate evolutionary and ecological perspectives, and recognize how ecological and genetic factors act in concert during the spread of a novel species. Competitive dynamics offer an excellent opportunity to examine how ecology and evolution intersect during colonization.

References

Bacigalupe, L. D. (2009). Biological invasions and phenotypic evolution: a quantitative genetic perspective. Biological Invasions, 11(10), 2243–2250. doi:10.1007/s10530-008-9411-2

Baker, H. G., & Stebbins, G. L. (Eds.). (1965). The Genetics of Colonizing Species. New York: Academic Press.

Blossey, B., & Notzold, R. (1995). Evolution of increased competitive ability in invasive nonindigenous plants: a hypothesis. Journal of Ecology, 83(5), 887–889.

Burton, O. J., Phillips, B. L., & Travis, J. M. J. (2010). Trade-offs and the evolution of life-histories during range expansion. Ecology Letters, 13(10), 1210–1220. doi:10.1111/j.1461-0248.2010.01505.x

Crawford, K. M., & Whitney, K. D. (2010). Population genetic diversity influences colonization success. Molecular Ecology, 19(6), 1253–1263. doi:10.1111/j.1365-294X.2010.04550.x

Elton, C. (1958). The Ecology of Invasions by Animals and Plants. London: Methuen.

Hühn, M. (1975). Estimation of broad sense heritability in plant populations: an improved method - Springer. Theoretical and Applied Genetics.

Keane, R. M., & Crawley, M. J. (2002). Exotic plant invasions and the enemy release hypothesis. Trends in Ecology & Evolution.

Lee, C. (2002). Evolutionary genetics of invasive species. Trends in Ecology & Evolution.

Phillips, B. L. (2009). The evolution of growth rates on an expanding range edge. Biology Letters, 5(6), 802–804. doi:10.1086/527494

Simberloff, D., Martin, J.-L., Genovesi, P., Maris, V., Wardle, D. A., Aronson, J., et al. (2013). Impacts of biological invasions: What's what and the way forward. Trends in Ecology & Evolution, 28(1), 58–66. doi:10.1016/j.tree.2012.07.013

Worthington, M., & Reberg-Horton, C. (2013). Breeding cereal crops for enhanced weed suppression: Optimizing allelopathy and competitive ability. Journal of Chemical Ecology, 39(2), 213–231. doi:10.1007/s10886-013-0247-6

Darwin in images (Darwin Day 2015).

Feb. 12 is the anniversary of Charles Darwin's birthday, a celebration of a man who nearly single-handedly (not to ignore Alfred Russel Wallace and others) laid the foundations for modern ecology and evolution. He championed the idea that evolution was descent with modification, where natural selection was the main means of modification. Darwin's work furthered achievements in science, medicine, and philosophy, perhaps in part because he helped disentangle science, society and religion. One outcome of being such a prominent figure is the frequency with which Darwin ends up in images, cartoons and illustrations, beginning in his own lifetime. So here is a short tour of Darwin and his big idea via cartoons and illustrations. 

A famous Vanity Fair caricature from 1971.

The oft-repeated mantra that evolution means that man evolved directly from a monkey or beast was an early (and still popular) theme. Darwin often took the role of the monkey.

John Tenniel for Fun magazine (1872)

From 1882, Punch’s Almanack, Linley Sambourne

 (Link)

Even in his day, some cartoons supported rather than poked fun. See the speech on the wall, a plea avoid ignorance of Science. (Link)

"Puck Presents Archdeacon Farrar’s New Year’s Hint — A Needed Course of Instruction for Our Religious Instructors"(1890).

The "evolution of man" meme has a long history - what was originally satire is primarily now a visual joke. (Link)

Harper's Bazaar 1871

Modern concerns.

(Link)

Darwin and evolution has been a repeated image in US politics, covering evolution and education, religious tension, science, and social darwinis, among other themes. (Link)

1925 SF Examiner

More recent, by Karl Wimer

Religion and Darwin have been unavoidable companions.

From pro-religion angles: 

1922 Moody's bible institute

And anti-religious:

Darwin pops up on motivational images and posters:

And evolution jokes remain eternally popular:

The Farside providing one of the better ones :)

source unknown

And finally, Darwin's own images have been incredibly influential. He was a talented naturalist and scientist and left many lovely illustrations. His sketches in his books, particularly the "tree of life" image has become an emblem for many scientists - of evolution and the origin of species, of immense intellectual accomplishment, of the birth of modern ecology and evolution.

1983

The famous "I think" image - the tree of life.

To learn more about Darwin in images, this is a great resource.

Charting Our Progress: Evolving Thoughts on Population Dynamics

By: Sarah Solomon

I have always been fascinated by the natural world – by the species that I encounter on a daily basis, and by those that exist on faraway lands. In thinking of how complicated and diverse human population dynamics can be, I’ve always sought to understand how other species’ populations are regulated. Why do some species go extinct, and what prevents others from meeting this same fate?

With ever-increasing human activity around the globe, some species are actually beginning to flourish beyond their natural ranges. From Asian carp to Dog-strangling Vine, the increased abundance and distribution of native and introduced species can be detrimental to the survival of others.

Louis Charles Birch, 1918-2009
University of Sydney

In the early 1940s, Australian insect ecologist Louis Charles Birch began to study how certain species of Dacinae fruit flies were becoming pests as a result of the expansion of cultivated fruit crops. Birch and his supervisor (and would-be lifelong colleague) Herbert Andrewartha were fascinated by the relationship of evolution to ecology, with a particular interest in how evolution can be charted in dynamic species of insects.

At the time of Birch and Andrewartha’s original research on the five most abundant species of fruit flies in eastern Australia, there was a prevailing hypothesis suggesting that all animal populations were self-regulating. This meant that populations of animals would increase under favourable conditions, and that eventually the population would grow so crowded that the birth rate would drop and the death rate would increase – hence the notion of self-regulation. It was believed that once a population reached a low enough density, the pressures on it would decrease and the population would be spared from extinction. Now in a laboratory setting, there was compelling evidence to support this hypothesis, but Birch had a different idea.

What actually happens to populations in nature? Why don’t they become extinct? How might we regulate populations of species that have extended beyond their natural ranges? Birch was part of a generation that started to wonder about these notions as they related to changes in natural environments due to human activities. He decided to look both within and outside of different fruit fly species in order to explore how external factors affect species density and changes in distribution.

In particular, D. tryoni had become a pest to fruit crops spanning the eastern coastal portion of Australia, with a significant increase in its range, adapting to cooler southern temperatures. He was also interested in charting this change – are species actively adapting to environmental changes, and are these changes observable? As it turns out, D. tryoni was even hybridizing with D. neohumeralis – another endemic fruit fly species of eastern Australia – to produce a population of flies with a 15 percent higher survival rate of immature eggs than D. tryoni. And all of this as a result of cultivating more fruit crops across the country!

Thus it seems that Birch was on to something – as it turns out, something very important indeed. It is unclear whether Birch could have anticipated just how much of an impact human activity would have on the environment, and in turn, just how much this change would affect species population dynamics. Today, conservation is at the forefront of science and policy, and the notion of studying the effects of abiotic factors on species population dynamics is imperative.

With scientists like Birch paving the way for thinking beyond the “self-regulating” hypothesis, research groups like that of Australian ecologist Euan Ritchie are committed to producing population models that can help inform conservation policies, and protect at-risk species from extinction.

In a 2009 study, Ritchie and colleagues uncovered how competition between the antilopine wallaroo and its wide-spreading counterpart, the Eastern grey kangaroo, is a threat to the survival of the former species. They also found that habitat – especially changes to landscape and the introduction of cattle ranching – contributed greatly to the viability of these species, and that of the common wallaroo (http://www.ncbi.nlm.nih.gov/pubmed/19175695). This type of modeling research is commonplace in the field of ecology today, as the notion of abiotic factors playing a significant role in species' survival is a widely accepted school of thought. With the growing impacts of climate change becoming more and more evident each day, it seems we have come a long way from the era when Birch’s ideas were considered a minority view.

More than fifty years later, the need to produce sound science with which to inform conservation policy is critical. Since Birch’s kick-start to understanding population dynamics, significant advancements have been made in genetics, and in the technologies for analyzing genetic diversity. Such techniques are helping to further highlight the types of genetic adaptations that Birch started to chart in the 1950s, producing fascinating insights into how populations are disappearing, appearing and adapting to external changes.

Overall, have we made all that much progress since Birch?

I would like to think that in many ways we have, but we still have yet to bridge the gap that exists between sound science and policy enforcement. It seems that despite strides being made on the scientific forefront, useful data are often not used or are discounted by policy decision-makers to suit the goals of various stakeholders. Research, like that of Birch and Andrewartha, and more currently Ritchie and colleagues, has major implications for conservation issues, and particularly for the growing concerns of harmful invasive species (see The Genetics of Colonizing Species).

Share your views, and leave a comment below!

References:

Baker, H. G., and Stebbins, G. L. (1965). The genetics of colonizing species: proceedings. Academic Press Inc.

Ritchie, E. G., Martin, J. K., Johnson, C. N., and Fox, B. J. (2009). Separating the    influences of environment and species interactions on patterns of distribution and abundance: competition between large herbivores. Journal of Animal Ecology, 78,    724-731. doi: 10.1111/j.1365-2656.2008.01520.x

Can an algorithm tell you where to submit your next paper?

Optimizing the Submission Decision Process. Santiago Salinas, Stephan B. Munch. 2015. Where Should I Send It? PlosONE. DOI: 10.1371/journal.pone.0115451

Choosing where to submit a manuscript is a difficult proposition. For a strong manuscript, you might hope for a high profile, high impact journal, but also to be considered is the hope (or need) for rapid publication, preferably without too many cycles of rejection, revision, and resubmission.

Maybe you saw this around twitter, but a little over a week ago, one paper offered a solution to the “where to publish?” puzzle. Published in PLoSONE (the journal chosen using their algorithm), authors Salinas and Munch provided one answer to "Optimizing the Submission Decision Process".

Surveys usually show that journal impact factor is the highest priority for authors, and a typical measure of paper success. Recognizing the importance of citations--and journal impact factors as an indirect predictor of them--the authors use Markov decision processes to determine the optimal submission process to maximize citation total. This model is a race against time, where delays reduce the total citations and worse, increase the probability that a paper will be scooped (and therefore have minimal citation value). They also considered a more complex model which maximizes citations, while minimizing delays due to rejection, resubmission and revisions.

The top choice of journals for the first model (maximize citations), were Ecology Letters, Science, and Molecular Ecology Resources. For the second model, the top journals to balance citations and time loss, were Molecular Ecology Resources, PLoSONE, and Ecology Letters.

Finally, if you know your willingness to tradeoff the number of times you submit your paper until acceptance and the number of citations it will receive, you can choose between several strategies. One option is a path that involves submission to a high impact journal (Ecology Letters in particular, possibly Ecological Monographs), accepting that you may actually need to resubmit your paper several times but will gain high citations. Alternately, you could choose a journal such as PLoSONE where resubmission is low and citation rate is moderate. Finally, many specialized journals may be faster, but provide relatively low citations. (Fig 3 below).

From Salinas and Munch 2015.

So what the authors get right is that choosing where to submit is a difficult task. Choosing journals is a skill that a scientist hones over a career. Graduate students have the hardest time, I think, not having experience with the underlying complexities (e.g. this journal is slow, this journal prefers experimental work rather than simulation approaches, Science will probably reject you, but at least it will be very fast...). Students usually have to rely on supervisors and more experienced collaborators precisely because they lack informed priors. That being said, the approach from this paper strikes me as a silly (and just bad) way of choosing journals.

The biggest reason is that even though everyone chooses "impact factor" as their primary criteria for choosing a journal in a survey, in practice impact factor is innately balanced against manuscript quality. Sure, there's the odd soul who always starts at Science and works their way down, but most researchers have a reasonably unbiased view of their manuscript's quality, and journal choice is conditioned by that estimate of manuscript quality. (More commentary on this from Marcel Holyoak and others, here). So it's really about maximizing citations, given the quality of a particular work. This implies authors must have knowledge of the journals in their field, not a simplistic algorithm.

Scooping doesn't strike me as the biggest concern for most ecologists either. There is a cost of declining novelty, perhaps, but it would be a rare ecological paper that lost all citation value because something similar had been published slightly earlier. (Or so I think. Is scooping a big issue in ecology?) 

Additionally, citations simply aren't the only thing concern for researchers, especially early-career people. The quality of journals that you publish in has important implications. Sending all of your papers to PLoSONE to reduce the time to publication while maximizing citations, while apparently a viable strategy, won't do a lot for a career application (not to pick on PLoSONE, which I think has an important role, but isn't usually the first choice journal for ecological research). Publishing in prestigious journals is usually considered an indicator of research quality. 

Journal choice will probably always be a subjective, imperfect behaviour. Even if a more complicated algorithm could be constructed, there are too much subjective inputs--paper quality, subject importance and novelty, journal quality--for the choice to be so simplistic.

Predatory open access journals: still keep'n it classy

As most academics are aware, there are hundreds of predatory open access journals that try to trick authors into submitting to their journals, charge exorbitant fees, and do not ensure that articles are peer reviewed or live up to basic scientific standards. The most celebrated cases are journals that embarrassingly publish non-sensical fake papers. I don't know why, but I sometimes go to the journal websites to see what they publish or who is on their editorial boards. I received such an e-mail this morning from SOJ Genetic Science published by Symbiosis, a recognized predatory publisher. This journal, unlike others, actually has a single published issue with an editorial! I thought: "wow, are they trying to be legitimate?"; then I read the editorial. The editorial is probably best described as a nonsensical diatribe about genetics, which lacks any real connection to modern genetic theory. Here is my favourite paragraph:

Predatory open access journals: still keep'n it classy.