Monday, September 21, 2009

Everything but extinct: invasion impacts on native diversity

ResearchBlogging.orgThere has been a persistent debate in the plant invasions literature about whether exotic plant invasions are a major threat to native plant persistence. While there are clear examples of animal invasions resulting in large scale extinction -e.g., the brown tree snake or Nile perch, evidence has been ambiguous for plants. Most ecologists are not so sanguine as to actually conclude that plant invasions are not a threat, and I think most believe that plant invader effects are an issue of temporal and spatial scale and that the worst is yet to come.

In a forthcoming paper from Heinke Jäger and colleagues in the Journal of Ecology, Cinchona pubescens invasions on the Galápagos Islands were monitored in long-term plots for more than seven years. What they found was that there was a four-fold increase in Cinchona density as the invasion progressed and that this increase had measurable effects on native species abundance. While they did not observe any native extirpations in their plots, native densities decreased by at least 50%. Of the greatest concern was that Island endemics appear to the most susceptible to this invasion.

What these results show is that, while there were not any observed extinctions, there were serious deleterious changes to native diversity. Further, the native species, and especially the endemics, are now more susceptible to other invasions or disturbances due to their lower abundances. The impact of exotic invaders may not be readily apparent but may be a major contributor to increased extinction risk.

Jäger, H., Kowarik, I., & Tye, A. (2009). Destruction without extinction: long-term impacts of an invasive tree species on Galápagos highland vegetation Journal of Ecology DOI: 10.1111/j.1365-2745.2009.01578.x

Wednesday, September 9, 2009

BES day two...

It was a day full of talks, and I really enjoyed being able to spend the whole day just absorbing the presentations. Here are some highlights from today's events:

  • Ian Wright gave an interesting talk about the history of functional plant ecology. Basically, covering where trait ecology has been and where we are now. It is really amazing to see the truly large scale analysis and collaborations currently driving modern trait analysis.
  • In another overview type talk, Gerlinde De Deyn, talked about carbon sequestration in soils. I'm sure to many ecosystem ecologists this maybe well known, but I found it fascinating. Did you know that tundra ecosystem have as much soil carbon as tropical rain forests? The reason is that tundra has very slow process rates (cold) while rain forests have fast production rates. In fertilization experiments, soil carbon is reduced, so in order to manipulate soil carbon stores one must understand the interaction between plant traits and soil organisms.
  • Finally, Kyle Dexter, in a great field survey of Inga tree species in a region of Peru, showed that different functional diversity metrics show differing patterns of over- and under-dispersion. For example, phylogenetic diversity tends to be under-dispersed for Inga assemblages, while chemical and anti-herbivory traits are over dispersed and leaf size measures are under-dispersed.

Also, there was the annual general meeting, which was rather somber as three obituaries were read aloud. The three deceased, John Harper, Bob Jefferies and Simon Thirgood, were all superb ecologists who absences were obviously felt. Harper (my Master's advisor's advisor) and Jefferies (my colleague at Toronto) were both eminent ecologists with long and distinguished careers, while Thirgood (a fellow Senior Editor at the Journal of Applied Ecology) was in the prime of his very successful career.

Exploring ecology through GMOs

This year's Tansley Lecture at the BES meeting was a superb presentation given by Ian Baldwin from the Max Planck Institute for Chemical Ecology. He was enjoyable to watch as his folksy, mid-western American style disarmed the listener and leaving them unprepared for his ascorbic wit and, at times, controversial message. Prof. Baldwin* is a chemical ecologist who studies plant biochemical and physiological processes and their interaction with herbivores. Through his use of molecular tools and superb natural history, he has gained new insights into how and why plants respond to herbivory. He has discovered the pathways allowing wild tobacco, Nicotiana attenuata, to detect chemicals in tobacco hornworm spit and the resulting chemical defense response. More than this though, part of his talk was about the use of transformed plants to study this plant defense response. Using genetic tools, his group was able to knockout certain segments of these biochemical pathways in order to determine how various chemicals affected hornworms. He showed chemical responses involved signaling hornworm predators whereas other responses directly targeted wornworm's ability to digest plant material.

I think that ecologists are often wary of GMOs and his talk was a convincing case for their use in basic research, and he advocated for a more reasoned approach to their use.

*Note: He has run into trouble with German authorities over using the title 'Dr.' -see here.

Monday, September 7, 2009

An ecological meeting, British style.

I'm in Hatfield, outside of London, for the British Ecological Society (BES) meeting, and I'll be blogging thoughts, happenings, etc. I posted several observations from the American equivalent (ESA) last month, and one thing is readily apparent, even though talks do not start until tomorrow. While the ESA meeting is a great chance to meet a lot of people and see a lot of talks, at a few thousand conference goers, it can be a bit overwhelming. At any given time the ESA meeting had up to 26 concurrent sessions, which makes for a lot of running around if there are talks you want to see in different sessions. At the BES there is a maximum of 7 concurrent session. The BES is definitely smaller than ESA and the meeting and venue feel compact and intimate. I'm looking forward to experiencing the BES meeting this week.

Check back for more.

Wednesday, September 2, 2009

Ecology and evolution jobs 2009

After a horrendous year of canceled job searches and a barren landscape lacking many opportunities for academic-track job seekers, the jobs posted this season seem to be a stark contrast. In a previous post, I blogged about the best ecology job wiki, and when you look through last year's job postings you notice that the 'updates' column contains a multitude that had their searches canceled. Most people assumed that there wouldn't be very many tier-one academic jobs this year, but looking at the list of jobs announced so far this year, things look pretty good! I've also caught wind of a few other positions at good institutions that have not yet advertised. Job seekers keep your eyes open, and definitely check the job wiki regularly. This could be your year!

I for one have been (overly) optimistic and really didn't buy the hype that the job market would crash this year and for the foreseeable future. I think that many institutions over-reacted to the recession. Of course some states, like California, are in absolute dire straights. But my feeling is that over the next couple of years many institutions will try to recover from their self-imposed professor deficits, meaning that many similar-sounding job searches will be active at the same time. The net result is that schools will be competing against one another for good researchers.

Tuesday, August 25, 2009

March of the polyploids!

ResearchBlogging.orgSpeciation by polyploidy (see here for a general description of polyploidy) is one of the mechanisms of speciation and evolutionary diversification. We all learn about it in Bio 101, right after allopatry and sympatry. It is thought to be an especially important driver of speciation in plants, and anecdotal evidence, such as the origination of the invasive polyploid, Spartina anglica in the UK in the 1800's, reinforced that view. But how important has been unanswered until now.

In a new publication in PNAS by Wood et al. -from the Loren Rieseberg lab (one of the best lab homepages BTW) this questions has been answered. The authors go through all available chromosome counts on the Missouri Botanical Garden's Index to Plant Chromosome Numbers, and assess the proportion of polyploid species. They find that about 15% of all angiosperm speciation events coincided with an increase in chromosome number (and about 30% of fern species). Further, about 35% of all genera contain polyploids. Looking across the phylogeny of major plant groups, they find that all major lineages, except Gymnosperms, have significant proportions of polyploids (again with ferns have the greatest proportion). Polyploidy is a ubiquitous feature of plant diversity and a major driver of plant speciation. And now we can quantify just how important.

Wood, T., Takebayashi, N., Barker, M., Mayrose, I., Greenspoon, P., & Rieseberg, L. (2009). The frequency of polyploid speciation in vascular plants Proceedings of the National Academy of Sciences, 106 (33), 13875-13879 DOI: 10.1073/pnas.0811575106

Tuesday, August 18, 2009

Unifying invader success and impact

ResearchBlogging.orgSomething that has continuously bothered me about our collective narrative concerning invasions has been the conflicting processes determining invader success and impact. Numerous studies (including some of my own) show that invaders are successful often because they are different from residents. That is, they are thought to occupy some unique niche. However, occupying a unique niche means that competition is minimized and these successful invaders should have relatively low impact on residents. Conversely, species that have large impacts are thought to be superior competitors, but why are they able to be so successful?

In a new paper in the Journal of Ecology, Andrew MacDougall, Benjamin Gilbert and Jonathan Levin use Peter Chesson's framework where ability for two species to coexistence (or conversely the strength of competitive exclusion) is a process relative to two factors -the magnitude of fitness differences and the degree of resource use overlap. Here competitive exclusion is rapid if species have a large fitness difference and high resource overlap, and slow if fitness differences are low. Species that are successful because of reduced resource overlap likely have little impact unless there are large fitness inequalities.

If we then view the invasions process on a continuum (see figure), then by determining basic fitness and resource use, we can predict success and impact. This is an exciting development and I hope it inspires a new generation of experiments.

MacDougall, A., Gilbert, B., & Levine, J. (2009). Plant invasions and the niche Journal of Ecology, 97 (4), 609-615 DOI: 10.1111/j.1365-2745.2009.01514.x

Thursday, August 6, 2009

Macroecology is dead, long live macroecology!

I went to a session on a macroecology yesterday, which featured some wonderful speakers, and came away with an unsure feeling about this field. The Session started off with a fantastic talk by Rob Dunn on how macroecologists differ on what the main mechanisms are for explaining diversity patterns. He argued that perhaps the complexity of natural and human-altered systems make simple generalizations not very fulfilling. Next Lauren Buckley showed how species turnover had complex relationships with broad environmental changes and that species turnover patterns are better correlated with other species turnover then with the environmental variables we think drive the patterns. Next Brian McGill tried to make the case for a truly unified theory. He walked through several general models of random species packing, showing that some models fit observed data very well. I was impressed by the data/model fits but am skeptical of a general theory which lacks biological mechanisms. My view of a scientific theory is that it ought to contain basic mechanisms and that a unified theory should explain patterns and processes at multiple scales. That said, I also think McGill has done more to forward the field than almost any other younger ecologist. In Allen Hurlbert's talk, he nicely showed how independently accounting for energy and area can provide a better basis to constructing and understanding species-area relationships. The basic reason is that area and energy availability differentially affect the number of individuals.

Back to my real life tomorrow!

Wednesday, August 5, 2009

Pleasant invasions surprise

Normally I run around ESA looking for talks that have the best potential to inform or entertain me. This time around I decided to go to a session on invasions and communities and settle in for the long haul. Am I glad I did. I was afraid the session would be dominated by similar sounding talks, but instead each talk was wildly interesting and different. Talks included looking at the genetic variability of the dominant native resident as a proxy for niche preemption. Another good one looked at the role of propagule pressure for an understory invasion into tropical dry forests -I seldomly hear about invasions into these ecosystems. Next was a look at how invaders behave over long term successional trajectories and they by and large appear to follow native trends. Next was a great modeling talk where individual-based models and riverine networks were used to assess the role of distrubance and trait differences in invasion dynamics. The final one I saw was on how to potentially restore Californian serpetine plant communities using little more that gravel and a few chemicals, with the goal of reintroducing extirpated butterflies, which have not been able to cope with the shift to exotic-dominated grasslands.

I am looking forward to more great talks!

Tuesday, August 4, 2009

Species interactions & evolution

Hi from ESA Albuquerque!

I've been in the organized session on species interactions and evolution all morning and there were some great talks (e.g., Silvertown, Ackerly, Cavender-Bares, etc.). But I think what really got me excited were some of the questions after each talk. Following Jonathan Silvertown's talk, Steve Hubbell asked some questions that get to the heart of addressing what phylogenies mean for community assembly. Silvertown showed that within plots, species of a large South African family of plants in the Fynbos seemed to spatially segragate according to hydrological niches and that within these plots there was a lack of phylogenetic signal in this niche. Hubbell then asked two critical questions: How many other species (in other families) co-occur in these niches and if related species have similar niches at a larger scale. To me this is at the core of uderstanding how phylogenies inform our understanding of community assembly. Basically, what haven't we measured? If we include all sister species into a phylogeny, do we change our understanding of the processes structuring communities?

More later!