Hello all, I really appreciate all of your suggestions and concerns. I recognize that it would be very challenging to prove the evolution of natives in the strict sense of documenting a change in allele frequencies specifically attributable to the selection pressure from an invader. Let me then elaborate a bit further on exactly how I am planning to conduct this study. I welcome any criticisms or suggestions for this system.
The rapid evolution of invasive species in novel landscapes has been well studied. Because these invasive species are capable of changing the environment (altering soil pH, limiting resource availability, altering pollinator activity), it seems possible that native plants might adapt to these changes. The broader question I'm getting at here is one of community construction. Are plant communities assembled by adaptive responses of plant competitors to one another or simply according to what abiotic factors offer suitable habitat for any plants that happen to disperse there? Studying both the ecological and evolutionary responses of a plant community to a new species could help to answer this question. Here are a few examples from the literature that might be helpful to understand where I'm coming from here: Callaway (2005) Journal of Ecology. Natural selection for resistance to the allelopathic effects of invasive plants Lau (2006) Evolution. Evolutionary responses of native plants to novel community members Strauss (2006) Ecology Letters. Evolutionary responses of natives to introduced species: what do introductions tell us about natural communities? I intend to choose an invasive species whose invasion history in the US is well documented and set up study sites along a gradient of invasion. I will compare populations of a native species that have been growing in competition with the invader for varying periods of time such as 100+, 75, 50, 25 years and recent invasion. I will also choose populations of the native in each environment that have not experienced invasion. I will then compare the strength and direction of selection on numerous traits of the natives in all of the populations using Lande and Arnold techniques for measuring selection gradients. If, for example, an invasive tends to bolt earlier and shade out the native, I might find the strongest selection for earlier bolting time in natives in the more recently invaded populations and less or no selection for earlier bolting time in natives that have not experienced invasion. I will also conduct reciprocal transplants to see if native plants grown for decades in competition with the invasives have a higher fitness when grown with the invasives than natives that have not experienced invasion. Finally, I will also conduct de Wit type greenhouse experiments where I grow flats of the native and invasive from each of my populations alone and together to see if the biomass of the natives when grown with the invasive is greater when the seeds for the flats came from populations that have experienced invasion. Sorry for the lengthy response, but I wanted to address all of the questions I've received. Again, I really appreciate all of your responses. Carolyn On Fri, Apr 9, 2010 at 12:36 AM, Wayne Tyson <[email protected]> wrote: > Ecolog: > > > > Meiss' post really moves the ball forward in some interesting ways, and I > will be most interested in Beans' responses. If I have anything to add, it > might be along the lines of wondering how one considers or measures the > strength (and how strength is defined or determined) of interactions the > number of generations required for genetic change, the kinds of genetic > changes that would be expected and on what basis, and what kinds of > interactions might be involved. > > > > I wonder also just how one might tease out and identify, not only the > "other environmental changes as a result of the invasion . . .," but as well > those not so associated. > > > > Meiss correctly anticipated the main question that lurked in the back of my > mind, how one would sort out the pre- and post-contact genetic differences, > not to mention the effects of those differences. > > > > I suspect that Meiss also is on the money with his suggestion that > ecological studies might be more productive; however, I eagerly anticipate > Beans' responses. I do not intend to discourage Beans from following her own > star in this, and, of course, she must be "practical" until she gets through > the academic gauntlet. If she can do that, while simultaneously making a > name for herself without incurring the ire of those "above" her, she should > soon be able to shift her research emphasis--if that is what the evidence > and her sense of ecology indicates. Unless her initial literature review has > revealed a sufficient number of similar studies that have disproved the > usefulness of her design, "failure" might contribute as much as success. > Apparently it has not, or she wouldn't be pursuing this particular line. > > > > WT > > > > PS: While I tend to tip in favor of Meiss' suggestion about studying > distributions, which, it seems to me, requires habitat study (which > includes, in my mind, the UPS AND DOWNS (dynamics) of pollination, dispersal > mechanisms, and soil factors--including nutrient dynamics, etc. Context > effects need to be considered, such as seasonal and site variations and, > this, I venture to assert, could be most important and perhaps all that is > needed (at least for starters) the GROSS changes that can be observed upon a > SINGLE sampling (again, for starters, but pregnant with possibilities, even > though continued repeat samplings would be necessary [especially to observe > trends and associated variables], perhaps for generations of students). The > catch (22?) of course, would not only be getting funding, but getting > committee approval for such a "simple" study. I stand ready to be corrected, > but it seems to me that the elegance of simplicity in research designs has > been swamped by obfuscatory convolutions that "reach" (for) conclusions that > seem to turn out to be self-ordained. I hope that subscribers will point out > specific evidence to the contrary or otherwise assure me that this > phenomenon is at least not widespread, if not a figment of my imagination. > > > > CORRECTION: The statement in my earlier post: "I must admit that I had not > thought much about evolutionary responses of (particularly) native plant > species until Bean's post, and I'm still thinking about it, but maybe Bean > and others can expand my consciousness further on this particular topic." > should have read: "I must admit that I had not thought much about > evolutionary responses of (particular) native plant species until Bean's > post, and I'm still thinking about it, but maybe Bean and others can expand > my consciousness further on this particular topic." I regret the errer. I > also apologize for mispelling Beans' name. > > ----- Original Message ----- > From: Martin Meiss > To: Wayne Tyson > Cc: [email protected] > Sent: Thursday, April 08, 2010 6:18 AM > Subject: Re: [ECOLOG-L] Plants Invasive and Evolutionary response Aliens? > Re: [ECOLOG-L] invasive and native plant competitors > > > While this seems an interesting and important area of study, I see > difficulties in making it an evolutionary study (as opposed to an ecological > study). To me, an evolutionary study implies that you can compare gene > frequencies in a population BEFORE the invasion with frequencies AFTER the > invasion. There are several problems with this: 1) How are you going to > sample gene frequencies from the 16 hundreds, which I'm guessing would be > about the time of the earliest invasions? 2) Even if you find a model where > invasion happened this long ago, that doesn't seem like many generations for > measurable change unless the interaction is very strong. 3) Assuming you > find measurable change, how will you know if it is caused by competition > with the invader, when there have been so many other environmental changes > as a result of the invasion of European humans and the concomitant changes > in land use patterns? > Just sampling present-day gene frequencies of populations with > and without invaders won't prove your case, since the populations might have > had these differences before the invasion. > An ecological study, on the other hand, could look at shifts in > the geographical distribution of populations, where there may be > presence/absence data from old records. Also, you might be able to > elucidate the means/mode of competition (i.e., for pollinators, dispersers, > habitat, use of soil minerals, etc.). Changes in morphology, as might be > revealed from old herbarium specimens, might reflect adaptive phenotypic > changes (without provable genetic basis) associated with habitat shifts, > though you would worry about whether old collections were statistically > representative of the old population. > Of course, Ms. Bean may have ways of addressing these issues, and > perhaps other readers of this listserv can point out some solutions or > useful approaches (and, of course, possibly other problems). > Martin M. Meiss > > > 2010/4/7 Wayne Tyson <[email protected]> > > Howdy y'all: > > I presume that Bean is referring to alien invasive species, but in the > purest sense, might one interpret the phenomenon more broadly? Indigenous > colonizers seem to be the orphans of the phenomenon, but might the > "evolutionary responses" to them be, in terms of evolutionary pressure, more > "seasoned?" > > I must admit that I had not thought much about evolutionary responses of > (particularly) native plant species until Bean's post, and I'm still > thinking about it, but maybe Bean and others can expand my consciousness > further on this particular topic. > > In a recent casual (insofar as they can be casual) trip to a > southwestern desert to observe the rampage of Brassica tournefortii, I > noticed some sharp "ecotones" between a depauperate-appearing Erodium > species and an indigenous indicator species, Lasthenia sp. (glabrata?). The > indigenous species appeared to be succeeding better in the "poorer" soils, > whilst the weedy alien (of long standing) seemed to be thriving in > apparently "better" soils. While this is nothing new, it may be an > under-studied phenomenon ripe for investigation. (This was an accidental > observation, however, while looking at a large colony of B. t.) Either of > these species would bear closer observations in a more disciplined way, and > I suspect that funding might more readily be found for B. t. Apparently > Robin Marushia has been looking at B. t., and there are undoubtedly others. > In my opinion, this species is a preeminent invader (not merely a ruderal > species), and extreme environments like deserts may be more instructive > places to work--especially if Bean wants to relocate and can find a "slot" > someplace. > > Just a thought . . . > > WT > > ----- Original Message ----- From: "Carolyn Beans" <[email protected] > > > To: <[email protected]> > Sent: Wednesday, April 07, 2010 7:39 AM > Subject: [ECOLOG-L] invasive and native plant competitors > > > > Hello All, > > I'm a first year graduate student and I'm planning to study the > evolutionary response of native plant > populations to an invasive plant competitor. Right now I'm at the > stage of trying to figure out exactly > which invasive and native plants to work with. I'm wondering if anyone > has noticed any invasive > plants that seem to be especially strong competitors with a specific > native plant species? I would also > be interested in instances where an invasive plant appears to be > facilitating a native plant species. > > I'll most likely be doing my field work in Virginia at Mountain Lake > Biological Station, but I could > potentially go anywhere. > > thanks for your help! > Carolyn > > > > > > -------------------------------------------------------------------------------- > > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 8.5.437 / Virus Database: 271.1.1/2796 - Release Date: 04/07/10 > 06:32:00 > > > > > > > ------------------------------------------------------------------------------ > > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 8.5.437 / Virus Database: 271.1.1/2796 - Release Date: 04/07/10 > 06:32:00 >
