A Diversity of Traits Helps Species Slip Through The Cracks (4 Comments)

HRYA-golden-gardens

Diversity of leaf area found within a population of hairy cats ear (Hypochaeris radicata)

Sometimes, scientists have the opportunity to get in on the “ground-level” of an emerging frontier.  Such unexplored ideas are incredibly exciting, with hundreds of unanswered questions, undefined rules and laws, and what seems like endless potential.

I have been lucky enough to be involved in just such an emerging frontier: Functional Ecology.  This frontier was really only (sort of) formally defined in 1987 by Peter Calow, and has been growing and expanding rapidly ever since.  This relatively new concept, which defines organisms by their physical or physiological traits, rather than their species identity has helped move plant ecology toward the “holy grail” of becoming a predictive science.

One set of papers in particular has really set the stage for predictive ecology using plant functional traits.  The first, Diaz et al.’s “Plant Functional Traits and Environmental Filters at a Regional Scale” took what was essentially a foundational theory in ecology (namely, that where plants occur in an environment is due to the unique traits they possess) and sought to find consistent, statistically significant patterns between plant traits, and climatic conditions (which they did very convincingly).  Their findings helped support the idea that plant traits can be “filtered” by the environment.  That is to say, environments filter out variation in plant traits, selecting only those species that can survive.  If these patterns were true on a larger scale, plant traits could be used to predict where a given species might occur.

Diaz et al. followed that compelling work with another important piece: “The Plant Traits That Drive Ecosystems: Evidence from Three Continents”.   Here, the researchers looked at an incredible number of plant species traits (12 traits for 640 plant taxa) to determine whether there is evidence for trait-based specialization (e.g. Are there certain types of traits that occur together, regardless of environment?) across a broad geographic range.  They did indeed find that there was specialization; plants seemed to either be capable of rapid resource acquisition and growth, or inclined towards slow, protected acquisition (using thick, protective tissues to store resources).  Most importantly, they found that environmental conditions seemed to lead to a convergence of trait types, further evidence of environmental filtering.

These two papers really set the stage for a move toward predictive ecology, but there is still work to be done.  Recent work building on the foundations of Diaz has shown that, while Diaz and others had assumed that traits within species were pretty much identical and that the only significant trait differences existed between species, this is not the case.  Albert et al. found that variation within species could be quite high for several functional traits.  This variation, typically ignored, is important if we want to predict species presence, as some individuals of a species may survive filtering, although the filter selects against the “average” trait of that species.  In essence, those individuals that differ from the mean slip through the cracks, and maintain biodiversity.  And indeed, experiments show that this turns out to be the case!  Jung et al. found that variation within species was important for structuring plant communities along a flooding gradient, and promoted diversity and coexistence.

Ecologists are now attempting to use plant traits and filters to understand how specific abiotic conditions and plant traits interact to influence plant community composition.  A model has been developed in the past year that related important plant traits like height and seed mass to critical environmental gradients, with the hopes that such a model could be used to predict species responses to climate change.  Another model has been developed which incorporates plant traits, including intraspecific variation, to predict species presence/absence in response to climate.  My own research investigates the drivers and consequences of within-species trait variation, with the hopes of determining whether some species are more or less limited in their variation, an important consideration for conservation.

It is becoming clear, in this time of rapid environmental change, that considering the functional traits of a species may be the key to predicting how the world will look as species shift in response to changing climate.

March 7, 2013

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  • Hi Tor,

    Would you mind clarifying that question a bit more? There has been a good deal of work looking at how specific traits (especially specific leaf area, plant height, and seed mass) correlate with plant and, ecosystem function, but I don’t think that is what you are asking. There is some ongoing work looking at how genetics might constrain expression of functional traits…a question that has actually been receiving a lot of attention lately, in regards to intraspecific trait variation.

  • Sorry, should have been more clear!

    I was referring to either developmental or genetic constraints. If two traits are highly correlated in their expression, and so cannot increase or decrease out of synch, seeing a trait at high frequencies in a certain environment type may be due to its “riding along with” another trait, and not because the trait is in itself most useful for the environment.

    Hopefully that makes a bit more sense.

  • Hi Tor,
    Thanks, that DOES make much more sense. I think what you are referring to is a very active area of trait research… and one that I am actually currently investigating. How genetically constrained a trait may be is not really know, although there are people digging deep into that question…such genetic constraints may even differ across populations within the same species, making generalizations potentially difficult. This is sort of the basis of intraspecific trait research….initially, people assumed trait values were fixed for a species, and did not vary across populations or environments. Subsequent research has definitely debunked that belief, but the magnitude and importance of this type of variation is not clear, nor are the mechanisms driving it.

    There are also traits that are highly correlated or that represent direct trade-offs (the basis for the L-H-S hypothesis of Westoby (1998)), but it is my impression that people are currently working on quantifying those correlations. Certainly, if traits are necessarily directly correlated, changes in one trait could “piggyback” off of another trait, regardless of abiotic or biotic drivers.

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