Thursday, September 3, 2015

Fire, transpiration, local hydrology and some very happy sunflowers

The Rocky fire swept through McLaughlin Reserve at the end of July. Nearly five weeks later, I resurveyed some sites that I went through the week after. The amount of life that had survived in the completely wrecked sites was astonishing, as was the quick resprouting of some plants (Rhamnus, Salix, Quercus, Vicia, Brassica, Asclepias, etc.). But the most surprising thing was the "winners" of the fire. I've walked columbine this seep many times a week during the past two summers. This time, I was struck by how large several serpentine sunflowers (Helianthus exilis) and tumbling orache (Atriplex rosea) had become.

Several stupendously super-sized serpentine sunflowers stoutly standing in foreground. A couple orache visible in the background.
Before the fire and all of last year, these were quite small plants, reaching maybe 1-2' tall with a couple dozen flowers. In many places, they end at 6-10" with just a few flowers. These plants were over 3' tall and each had a hundred or more flowers. What happened?

Last year there was a little bit of odd late-summer weather, with a few overcast cooler days (it is usually above 90 and not a cloud in the sky here). On those days, one very small seep that I had a columbine population in would fill up a couple tiny puddles that hadn't had water for months. After a couple times, I mentioned this to the reserve manager here and she pointed out that the plants around the seep don't transpire as much on cloudy days, so the water being put out by the seep was not being used up before it got to the ground. 

What transpires less than plants in overcast conditions? Dead plants. Right after the Rocky Fire, the seep with the sunflowers was flowing again big time (it is much larger and had much denser vegetation around it than the one that I could see the changes before). The amount of water in this seep now is greater than it's been since April or so. While the sunflowers and Atriplex are past the end of the visible water in the seep by a few dozen yards, it is still flowing belowground and these are pretty much the first plants that would be getting any of that water, as all plants upstream are fried.  

This section had been completely dry for months before the plants stopped sucking up all of the water flow. Also note all the greenery. That is resprouting of Aquilegia eximia, Stachys albens, Salix sp. and a few grasses and sedges (you can fire me as your naturalist if you'd like - I have no idea what species are here).  
This was an cool and unexpected - though completely logical - thing to find in the aftermath of the fire. I'm sure its been described before, but it was really eye-opening to me to see how much water those plants were transpiring and just how much influence this had on the hydrology and the success of other plants far below them (it seems like asymmetric resource competition - the manzanita and willows above were dictating the reproductive potential of the sunflowers below).

Something similar may have been happening to trigger this flowering of Mimulus guttatus, but I'm a bit puzzled, as this was in a strange location for that to occur and nothing else around it was doing particularly well. It was certainly a pleasant surprise to see some spring-like color at the end of the summer!
I'll write a longer post about the Jerusalem fire (more lost experiments... but not all!) and some other interesting observations that I've had during my last couple days of wanderings. But I've got more field work to do now. 

Dragonflies were hanging out in the seep like nothing had changed. I believe this is Aeshna walkeri (common last year here and with the same gestalt), though I didn't have my net with me to confirm and I wouldn't have wanted to disturb her egg-laying anyway (I'm a bleeding heart when it comes to dragonflies... and snakes... and beetles... and others). 

Tuesday, September 1, 2015

New paper: plant external chemical defenses!

When I came to grad school, I was convinced I'd be working on plant-caterpillar-parasitoid relationships, with a focus on plant chemistry or biocontrol. I wrote my NSF-GRFP on the artichoke plume moth and several of its parasitoids. I spent a few months looking for plume moth caterpillars on thistles (a scratchy job) with relatively little success, though not for lack of trying. My focus then shifted to a cute little butterfly, Brephidium exilis, with strange population dynamics and then parasitoid sex ratios. All of these failed (either through logistical problems or me half-assing them because they just weren't that interesting to me).

And then I happened onto Blitum (=Chenopodium) californicum at Bodega and my research took an unexpected turn. As I describe here, I was fascinated by the little fluid-filled pockets on leaf surfaces. I ran a number of small tests and found a defensive function of the bladders (probably one of many, many functions) and wrote it up and it was quickly published in Oecologia, a good journal. This being the very beginning of my second year of grad school (fall 2013), I was pretty jazzed. My committee, however, thought that I should be working on "the bigger picture". And so the ideas for this new paper on external plant defenses came about.

Writing this paper was WAY harder than I thought it was going to be. Instead of a formulaic paper, here's why I did the study (intro), here's how I did it (m&m's), here's what I found (results) and here's why its important (discussion), I was faced with a blank slate. I could write this however I wanted and that was a bit daunting. Primary and secondary school taught me how to write a coherent 3-5 paragraph essay, secondary school and college taught me how to write a term paper and college and grad school have taught me how to write a scientific paper, but no one taught me how to write a synthesis/idea/review paper. I'm glad I did it, though I think it will be a few years before I start on another paper like this.

This caterpillar (an unidentified pterophorid) lives on a plant (Hemizonia congesta) with lots of glandular trichomes, the factories of many external defensive chemicals. It blends in nicely with its "glandular trichomes". 
Taking Rick's lab motto, a Buckminster Fuller quote - "dare to be naive" - to heart, I started by thinking of what ecological differences would occur if a defensive plant chemical was situated on the plant surface instead of inside plant tissues. I came up with five basic differences between chemicals on the surface of plants (external chemical defenses: ECDs) and those inside plant tissues (internal chemical defenses: ICDs):

(1) they are in direct contact with the abiotic environment;
(2) they are not in direct contact with plant tissues apart from the cuticle;
(3) they are first contacted by the vast majority of interacting organisms;
(4) they may contact more than just the feeding and digestive parts of interacting organisms;
(5) they are secreted from specialized structures or cells (or derived from a secretion thereof).

As discussed in a prior post, glandular exudates are often sticky and can have cool tritrophic effects. Here is a mayfly (Ephemeroptera) stuck on serpentine columbine (Aquilegia eximia). 
I then took this list and delved into the literature, reading hundreds of papers on plant chemical defenses over a several month period (I cited 180 in the final paper, but probably skimmed or read abstracts of  twice that number). While external chemical defenses had not been formalized as a class, many wonderful studies had investigated plants with ECDs and I was able to find many examples both in terrestrial systems and in marine alga. I wrote up a massive tome - over 18,000 words - with carefully detailed natural history of many of the studied systems. Of course, this was not publishable, though I was proud of it (I like nothing more than to put cool natural history into an ecology/evolution framework). I worked and worked on cutting it down to its basics. In the process, I found more references and presented it at ESA last year, getting some more feedback. The process dragged on and I got more and more interested in doing experiments and less and less interested in this mammoth synthesis paper. I submitted it a couple times in various stages of cutting and was basically told it was too long. So after this past field season, I sat down for a couple weeks with no other distractions and made it into a far more focused paper, which I submitted to Biological Reviews, as it was still a bit long for most other journals. Fortunately, it was accepted with helpful reviews and after tossing a few minor points back and forth with the editor, it is now out for you to read!

Without getting into the specifics (you can read them in the paper, if you so choose), I found that many chemicals are on plant surfaces, many of these chemicals are defensive, and these may be systematically different from internal chemical defenses in the ways I hypothesized. This paper is important for three reasons: 1) hundreds of papers are published on plant chemistry and plant chemical ecology each year, but it is ecologically important where certain chemicals are located; 2) we have a rich body of theory on plant chemical defenses, but some parts of it are rather untested, and ECDs may allow some tests of certain theories (e.g. optimal defense theory) and; 3) many important crop plants have external defenses, which are easily manipulable in many cases, and it may be useful to think about them in this way to come up with better pest management schemes.

I'm really curious about how this paper and this new classification scheme is received. Am I just cluttering the literature with new terms, or are these ecological differences informative and useful? We will see!

Castilleja minor, a species of paintbrush and a hemiparasite, has really cool oily exudates. The pictured caterpillar, possibly an Autographa (?) species, seems undeterred, though it does mostly eat the insides of the flowers and fruit, which may avoid the exudates.