#esa2013 Day 5: Survival mode

The final day crowd is usually a little worse for wear. 

(Adapted from phdcomics.com)

#esa2013 Day4: Sisters getting along, and our variable world

The talks I saw today were uniformly good and a number were excellent. At least half of them focused on the many implications for ecology of nature's innate variability. It appears that community ecologists have decided that now is the time to start considering the fact that the environment is not stationary, which was long a default assumption in most theoretical and empirical work. Many of the talks I saw reflected this changing approach. The other half were part of a symposium organized by Sharon Strauss that looked at coexistence among sister species. This topic, combining as it did large-scale evolutionary and biogeographic processes with local competitive interactions made for a broad range of talks and some interesting attempts to reconcile different methodologies and scales.

Our variable world

Many of the past studies on environmental variability and coexistence involve desert winter annuals. Desert winter annuals are limited by available water, and the yearly rains vary greatly in the amount and timing of onset. The hypothesis is that variable germination (via prolonged dormancy in seedbanks) may allow desert winter annuals to reduce the variance in their fitness between years. Alejandra Martinez-Berdeja presented some tidy hypothesis testing using biogeographical gradients: if variable germination is an adaptive response to variable precipitation, she hypothesized that differences in germination variability might be expected where precipitation is more or less predictable. Looking at the three North American deserts, she predicted that variable germination would be greater where rainfall was more variable (bi-seasonal) compared to winter rainfall deserts. She measured the involucres (dispersal structures determining seed release) on collected seeds and found that indeed they were larger in more variable rainfall deserts, producing greater variability in seed release. Further, in winter rainfall deserts, variability in the size of involucres was correlated with variability in rainfall at a site, again suggesting a link between germination variability and rainfall variability. Her next step will hopefully be to expand the tests look at the effect of autocorrelation in rainfall likelihood on bet-hedging, since this should increase selection for bet-hedging type adaptations.

David Vasseur gave a great talk showing how extreme environmental conditions--which we are seeing as part of the changes in mean and variance of the climate--could have particularly detrimental effects on population growth rates. Species have temperature performance curves that reflect the relationship between their fitness and the temperatures they experience. Vasseur showed that in the tropics, species tend to have much narrower temperature ranges over which they can grow and survive than species in the temperature regions, and experts agree that these narrower curves give tropical species less ability to deal with increasing temperatures. But variability is rarely considered in this equation. When variability is present, long-term species fitnesses will be subject to Jensen's inequality (nonlinear averaging) mean that shape of these performance curves is additionally important: that in some situations (concave curves) variability is particularly detrimental, and in some situations (convex curves) it may have a beneficial effect. Vasseur then used models to show that as temperature variation increases, it is increasingly likely that its effect will be negative, and high variation will produce high extinction rates. In fact, on average Vasseur predicted that temperature variation would have negative effects, a concerning conclusion.

Sisters getting along

This organized symposium was advertised as: “Whether closest relatives coexist reflects the often opposing effects of limiting similarity, mode of speciation, reproductive isolation, niche conservatism, competition and facilitation, which may be strongest in sister taxa; using new phylogenies, niche models, and experimental approaches, we explore coexistence in closest relatives in both plants and animals.” It was an interesting and useful idea – sister species (species who are each other’s most recent relative) are an important tool to understand how evolution, biogeography, and ecological interactions determine coexistence. The content of the symposium provided a number of example systems, methods, and approaches that suggested this was an important but still far from cohesive area of work. Mark McPeek spoke about the damselfly work he has done over the last many years, which shows that sister species are sympatric and ecologically identical, co-occurring happily through neutral dynamics. In contrast, Richard Glor talked about his work with Hispaniola anoles, where biogeography is an explanation for radiations, close relatives use different microhabitats and rarely compete locally and traits are divergent among close relatives. Looking at California plant species, Brian Anacker’s talk suggested something in between these extremes. A broad survey showed that 80% of sister pairs were sympatric, range overlap was modest but not uncommon, but asymmetry in range size was high. Ecological differences between sister species were not particularly clear in the handful of traits he examined, not even for reproductive traits. Sister species can and do co-occur, although not in large portions of their ranges. Having established the current state of knowledge, hopefully the symposium will stimulate greater focus on the construct of sister species as a way of understanding coexistence at multiple scales.

Finally, not being willing to miss another talk with the word “derby” in the title, I attended Daniel Atwater’s talk, “Is competition among plants like a boxing match or a demolition derby? Why competitor suppression may not matter in plant communities”. Atwater argued that there were two ways to win at plant competition – be good at suppressing your competitors, or be good at tolerating them. When in competition with a single individual, being a strong suppressor should be favoured, but in competition with multiple species, tolerance may be a better strategy. That’s because resources spent on suppressing one competitor may also benefit any other species involved in the competition. In such cases, tolerance of your competitors may provide the greatest benefit. (Apparently this scenario is like a successful (but frowned upon) strategy (sandbagging) in a demolition derby). Atwater used experimental data from blue bunch grass grown in competition with spotted knapweed to parameterize a model in which he found the optimum strategy in single versus multi-species competitions. The model agreed with his hypothesis that tolerating competitors is favoured when multiple species are competing. Although I am not clear on whether competitive strategies are easily classified as tolerant vs suppressing it was an interesting talk, and left me thinking about new questions.

ESA 2013 Day 3: Bolkerisms

All the best quotes that I caught today were undeniably from Ben Bolker, who also gave an interesting talk.

"The hallmark of great theoretical ecology is that it is obvious in hindsight. When you explain it to someone, they say well, of course."

In relation to a philosophical issue: "That's a beer question, not a coffee question".

To explain the reason he and his coauthors chose to build a model to explore the question, Bolker showed a Dilbert cartoon illustrating the truism "When all you have is a hammer, everything looks like a nail".

Only one full day left to go, and it looks like it will be a good one!

ESA 2013, day 3: Like a kid in a candy store.

Sometimes there are moments in my career where feel truly fortunate. Today I was fortunate enough to be a speaker in a session on evolution, biodiversity and ecosystem function. The other talks in this session were outstanding, full of amazing insights into how historical evolutionary dynamics affect modern-day ecological patterns. The presentations were followed by a fantastic panel discussion stimulated by thoughtful questions from the audience. The talks covered a range of topics from including species interactions in models of evolutionary change to using traits to understand coexistence to trying to find patterns when close relatives do not coexist.

The first talk from Luke Harmon on finding phylogenetic signatures on species interactions was incredible. He is an entertaining speaker and included references to his kids finding leaf cutter ants.  He show us how one could fit phylogenetic models that include coevolution. The negative effects of coevolution should affect trait evolution and one should see this signature in variance-covariance matrices. Random evolutionary change generates covariance between species. Stabilizing selection will remove this covariance, while with competition there should be negative covariances apparent. From models we see an interesting signature where older species are able to diverge and fill niche space (thus diverging rapidly) while later species are constrained in their evolution (thus remaining similar). Older species can contribute more to ecosystem function because of historical competitive effects.

Next was Nathan Kraft talking about how traits can potential shed light on fitness and niche differences in coexisting species. In a plant experiment with focal species grown alone and at different densities with competitors, he showed that very few pairs met the conditions for coexistence. For those that do appear to be able to coexist, no traits were associated with fitness difference, but several traits appeared to be associated with fitness differences. Multivariate analyses  showed that an assortment of five traits collectively appeared to be associated with niche differences. Some of these traits appeared to also explain fitness differences, revealing the complexity in assigning traits to specific ecological effects.

In Jeannine Cavender-Bares’ talk, she examined how evolutionary transitions in seed dormancy helped explain modern day ecological patterns in the Fabaceae family (the pea and bean family). The Fabaceae includes species that have dormant and non-dormant  seeds. Dormancy should be favored in certain environments (e.g., less predictable and poor environments). Large seeds are much less likely to be dormant, as well as those occurring at lower latitudes. Historical transitions in dormancy seemed to be correlated with changes in temperature lineages experienced.

Finally, Sharon Strauss critically examine dhow to separate history form ecology. We need to be cognizant of scale effects, where larger scale observations will include more close relatives than we usually see at local scales. Communities contain ‘ghosts’ of past competition and assembly. If species originate allopatrically (in separate places), then we expect that close relatives should not coexist, which can skew our inference about how ecological differences have evolved. Within habitats we seldom see closely related species coexisting . She gave a number of great Californian examples of species appearing to co-occur at large scales but not locally. For example, Limnanthes plants occur in the same region but species never co-occur in the same vernal pool.

These talks represent the collective excitement about the fact that we are entering a new synthesis in ecology. Evolution is required to understand ecological patters and ecological interactions are need for understanding evolutionary change. These talks exhibited where the forefront of this synthesis is, and it was a great afternoon of talks.

ESA Day 2: The problem with statistics...

These are just my favourite quotes from talks on day two of ESA:

(All from great, but anonymous, speakers)

After showing the results of a spatial statistics test: "...But still I was worried because that would be using statistics to prove something and that feels wrong."

On being asked how the speaker quantified earthworm abundance: "I used a non-invasive electroshock technique".
(I'm sure this is normal procedure, it just sounds hilarious to the uninformed).

ESA day 2: The shampoo salesman and new questions.

Day two started off on a high note with Bernhard Schmid's talk on evolution in biodiversity-ecosystem function (BEF) experiments. He is one of the originators of the Jena biodiveristy experiment, for years they have been maintaining plant species in monocultures and in polycultures to assess how much more ecosystem function is produced by multi-species assemblages over single species monocultures. However, it occurred to Schmid that species in these two contexts face different pressures, which may have resulted in evolutionary changes. In monocultures, species face high intraspecific densities and thus competition is severe, as is negative indirect effects like pathogen sharing and herbivory rates. Within polycultures, intrraspecific interactions may involve niche differences, with opportunities for character divergence to further stabilize coexistence. He reported on an experiment that took seeds and cuttings from monoculture and polyculture populations and grew then in monoculture or polyculture. He showed that individuals originating from monoculture did better in monoculture and species originating from polyculture did better in polyculture. The implications are fascinating. If the rate of evolutionary change in performance are equivalent between monocultures and polycultures, the BEF relationships should remain constant. However, if the rates of change are greater for polyculture populations the BEF relationship should get stronger over time. Conversely, BEF relationships should became weaker if higher evolutionary change in monoculture. 

It was hard to top this talk, but there were several other impressive talks as well. Jacob Vander Laan used a country-wide dataset on aquatic insect diversity across the USA and showed that at larger scales, beta-diversity decreases with connectivity, but is seemingly unaffected by environmental heterogeneity.

Restoration is community assembly with management goals and Emily Grman gave an interesting talk on assessing the success of prairie restoration by accounting for management activities, landscape, historical and local abiotic factors. She showed that management activities were the most important, with species-rich sowings result in rich communities, even though many of the species are not those in the sown mixture. Sowing a high diversity of grasses did not increase diversity, but high diversity of forbes did. Other factors like landscape influences and local factors were not important.

Will Pearse examined plant diversity patterns and homogenization across six large urban centres. He showed that there has been little taxonomic homogenization, but substantial phylogenetic and moderate functional trait homogenization. Beyond the interesting questions about how urban centres may cause biotic homogenization is the new tools that Pearse created for these analyses, and that are available online. As a self described 'shampoo salesman', he created a general tool called Phylogenerator that creates a pipeline that makes estimating trees form sequence data more efficient -definitely a tool that ecologists should be using. He further created a way to quantify complex leaf shapes and has a tool available for that, called Stalkless.

All in all , this was a good day, one that has stimulated new questions and approaches. These talks got me thinking about some of my data and experiments and how I can extend them to new questions. 

ESA 2013 Day 1: Temporal variation, roller derby, and topics in between

With day 1 over, ESA 2013 was off to an excellent start. Minneapolis seems like a very friendly place, and I enjoyed perhaps the most chatty bus ride I've ever experienced. As always, I failed to determine the best point on the trade off plot between cherry-picking certain talks based on topic, speaker and friends, and staying put in a session with an interesting topic. Nonetheless I managed to see some really good talks.

Among them, I saw Lauren Shoemaker in the Theoretical Ecology section, who illustrated how to model the four metacommunity paradigms (I.e. species sorting, mass effects, neutral, and patch dynamics) with the Chessonian framework of equalizing and stabilizing forces. She illustrated how both deterministic and stochastic models could replicate dynamics from the four paradigms. This suggests that rather than the usual description of the neutral paradigm as stochastic and the mass effect and species sorting paradigms as niche-based and therefore deterministic, the terms niche and deterministic and neutral and stochastic should not be synonymous. Rather, in the Chessonian framework, fitness differences drive neutral-type dynamics and spatial niches structure the species sorting and mass effects paradigms. More importantly, the results show how the paradigms are just a few sets of points on the much broader set of parameter values that could describe metacommunity dynamics.

It must be funny for Peter Chesson to follow up a talk in which his name is used as an adjective. After the talk on the Chessonian framework, he spoke about the fact that environment is fluid and non-stationary, yet models of communities have almost always treated it as being at equilibrium. Since it is not, ideally models of community dynamics would begin to incorporate environmental variation, and ask questions more relevant to non-equilibrium systems. For example: when is long-term persistence expected, given this non-stationarity and can communities in a non-stationary system still be stable? He showed that including environmental fluidity into models doesn't mean that communities are necessarily unstable, for example, when spatial and temporal trends of environmental variation match, communities may be stationary.

In another of many good talks about temporal variation (seemingly a popular topic of late), Colin Kremer showed that altering the basic characteristics of abiotic temporal variation (amplitude, means, periodicity) changed the amount of diversity present as communities evolved over time. Temporal variation isn't a simple concept anymore than spatial variability is - it has different characteristics with different effects on ecological dynamics and needs to be considered in greater depth.

My biggest disappointment was that I had a time conflict and couldn't attend a talk titled "Significant changes in the skin microbiome mediated by the sport of roller derby".  No doubt I would have learned a lot.

EEB & Flow on summer vacation

We will be back in time to blog from the Ecological Society of America's annual meeting in Minneapolis (Aug 4-9)!

Carnival of Evolution is up!

The latest Carnival of Evolution (#61 if you are keeping track) is up and running at Teaching Biology. It is the Crustie Lovin' Edition.

MacArthur's words still resonate 40 years on

I recently received an old library copy of “Geographical Ecology: Patterns in the Distribution of Species” by Robert MacArthur (1972). It’s the last book that MacArthur wrote before his early death to cancer. It is an ambitious book that connects repeated ecological patterns to mechanisms as broad as the earth’s rotations (producing climate as we experience it) and as focused as organismal behaviour.

But honestly, the thing that has struck me most so far as I read is the timelessness and wisdom in MacArthur's introduction. Issues ranging from focusing on questions versus systems, the value of repeated patterns, complexity, and what generality really means, aren't at all new.

“To do science is to search for repeated patterns, not simply to accumulate facts, and to do the science of geographical ecology is to search for patterns of plant and animal life that can be put on a map. The person best equipped to do this is the naturalist who loves to note changes in bird life up a mountainside, or changes in plant life from mainland to island, or changes in butterflies from temperature to tropics. But not all naturalists want to do science; many take refuge in nature’s complexity as a justification to oppose any search for patterns. This book is addressed to those who do wish to do science. Doing science is not such a barrier to feeling or such a dehumanizing influence as is often made out. It does not take the beauty from nature. The only rules of scientific method are honest observations and accurate logic. To be great it must also be guided by a judgment, almost an instinct, for what is worth studying. No one should feel that honest and accuracy guided by imagination have any power to take away nature’s beauty.

Science should be general in its principles. A well-known ecologist remarked that any pattern visible in my birds but not in his Paramecium would not be interesting, because, I presume, he felt it would not be general. The theme running through this book is that the structure of the environment, the morphology of the species, the economics of species behaviour, and the dynamics of population changes are the four essential ingredients of all interesting biogeographic patterns. Any good generalization will be likely to build in all these ingredients, and a bird pattern would only be expected to look like that of a Paramecium if birds and Paramecium had the same morphology, economics, and dynamics, and found themselves in environments of the same structure.”
--Robert MacArthur

It's interesting that an introduction written in 1972 is so relevant that it could have been written today. The pessimistic view is that ecology is just iterating through the same problems and solutions, or progress is slow. Or maybe classic books remain as classics because their authors understood and explored the issues at the core of the science and had the benefit of being there in the formative years. It's fun to see that when MacArthur thanks particularly four friends who influenced his work most, he means G. Evelyn Hutchinson, E.O. Wilson, Richard Levins, and Jared Diamond. I suppose any book influenced by the combination of all these scientists and written by MacArthur will always have something interesting to say.