Saline wetlands - environmental gradients and competition

Drew Tyre Author

07/19/2018 Added

103 Plays

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Nebraska's Saline wetlands are home to a community of salt-tolerant annual plants. Are they competing with each other?

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[00:00:04.710]So today, what I wanna talk about is the Saline Wetlands
[00:00:07.810]field trip that's coming up,
[00:00:09.280]and a little bit of the science that's behind
[00:00:11.800]that particular exercise.
[00:00:13.750]Why are we going out there to do it?
[00:00:15.190]What are we trying to test?
[00:00:20.890]So we're gonna be heading to the Saline Wetlands
[00:00:23.330]north of Lincoln.
[00:00:25.160]This is a great photo that was taken by Ethan Freese,
[00:00:28.910]who's a former Fisheries and Wildlife major,
[00:00:31.680]just graduated last year.
[00:00:35.076]Well, I better walk a little closer here, there we go.
[00:00:37.891]The plants that we're interested in,
[00:00:40.020]this one right over here in the back,
[00:00:42.340]is called an area colon, or the common name is saltwort.
[00:00:46.230]This species is a restricted distribution.
[00:00:49.840]The only place where we find it in Nebraska
[00:00:52.310]is in the Saline Wetlands in Lancaster County.
[00:00:55.730]This reddish looking one down here is called sea blite,
[00:01:00.122]and this pale green one here is a different species.
[00:01:03.230]In the back, that I forget right at the moment,
[00:01:05.860]but we'll be identifying it when we're out there.
[00:01:07.980]In the back here, you can see cattails typha.
[00:01:11.780]And so the question is, some of these species
[00:01:15.490]are found in the same locations in the Saline Wetlands.
[00:01:18.260]We find sea blite and saltwort close together,
[00:01:22.930]but we don't find saltwort and cattail
[00:01:25.490]in the same locations.
[00:01:27.180]So the question is why?
[00:01:28.250]And so it is badgers?
[00:01:31.640]We've got the grumpy looking badger over here
[00:01:34.610]walking through the wetland.
[00:01:36.130]Probably not because they're not all that herbivorous.
[00:01:39.960]What exactly explains why we might find
[00:01:44.180]saltwort in one place, cattails in another,
[00:01:46.640]sea blite maybe a little bit mixed in with both of them?
[00:01:50.040]How do we understand the interactions
[00:01:52.380]between these sorts of species?
[00:01:56.990]We have two sorts of broad possibilities.
[00:01:59.100]One is, there could be an environmental gradient
[00:02:02.480]that both species are responding to in different ways.
[00:02:07.220]It could also be competition.
[00:02:08.650]In other words, both of these plants are competing
[00:02:11.200]for the same resources.
[00:02:12.230]They're competing for light, water, nitrogen, phosphorus,
[00:02:16.950]micronutrients, all of these sorts of things.
[00:02:18.930]And so it could also be both of those things.
[00:02:21.870]In other words, the effects of competition
[00:02:24.000]may also depend on environmental gradient.
[00:02:27.240]The environmental gradient that we've got
[00:02:28.830]in the Saline Wetlands is an obvious one.
[00:02:31.300]It's the salinity of the soil.
[00:02:33.790]So we have extremely high salinity in some parts
[00:02:36.250]of the wetland, and less so in other parts of the wetlands.
[00:02:40.690]What do I mean in general though
[00:02:41.980]by an environmental gradient?
[00:02:43.500]So here's an example
[00:02:46.970]from California in the Sierra Nevadas.
[00:02:48.940]There's two species of monkeyflower.
[00:02:52.050]Lewis' monkeyflower is found in the alpine regions,
[00:02:56.130]way up in the high mountains,
[00:02:59.090]and scarlet monkeyflower is found down
[00:03:01.910]in the lowlands in the valleys.
[00:03:04.040]And there's only a narrow band of elevations,
[00:03:06.757]around 1400 meters, where you can find both species.
[00:03:11.050]And so the experiment was to take seeds
[00:03:13.890]of both kinds of monkeyflower
[00:03:15.800]and plant them in different places,
[00:03:19.515]different elevations, together, and see
[00:03:23.230]whether they could grow in the places
[00:03:25.520]where you weren't finding the other one.
[00:03:28.080]And so this top graph here
[00:03:31.730]shows the proportion of the individuals,
[00:03:34.160]the seedlings that survived with one up at the top here.
[00:03:37.440]These are logarithmic axes
[00:03:38.710]and this is 1% down at the bottom.
[00:03:40.540]And so at the lowest elevation
[00:03:42.300]where they did the experiment, the scarlet monkeyflower,
[00:03:46.660]almost all of those plants survived,
[00:03:48.370]whereas very few of the Lewis' monkeyflowers survived.
[00:03:52.120]And as you go up in elevation, more and more
[00:03:55.470]of the Lewis' monkeyflower survive.
[00:03:57.690]So well up into the alpine zone,
[00:04:00.528]the Lewis' monkeyflowers are now surviving
[00:04:03.230]as well as the scarlet monkeyflower at lower elevations.
[00:04:07.515]The scarlet monkeyflower still does pretty well
[00:04:09.870]at those higher elevations in terms of survival,
[00:04:12.690]but not so great in terms of growth.
[00:04:14.970]So this lower graph here show the average amount
[00:04:19.130]of stem growth in centimeters per year
[00:04:24.300]for scarlet monkeyflower and Lewis' monkeyflower.
[00:04:28.070]At lower elevations, Lewis' monkeyflower
[00:04:29.960]doesn't do anything, doesn't grow at all.
[00:04:33.110]At higher elevations, still not growing very fast.
[00:04:35.570]When you're up over 2,000 meters of elevation,
[00:04:40.680]it's actually a pretty challenging environment
[00:04:43.610]for any plant, so then none of them grow particularly well,
[00:04:46.550]but again, the Lewis' monkeyflower
[00:04:48.700]is the one that does better.
[00:04:51.810]So this is an example
[00:04:52.670]of environmental gradient of elevation.
[00:04:54.990]Lots of things are provably changing in terms of elevation
[00:04:57.810]as you go from lwo to high, there's just gonna be,
[00:05:00.970]it's gonna be colder at higher elevations,
[00:05:02.810]you're gonna have less precipitation probably,
[00:05:06.320]shorter growing seasons,
[00:05:07.480]there's all sorts of things that change.
[00:05:10.330]But the Lewis' monkeyflower is adapted to those conditions,
[00:05:13.510]and the scarlet monkeyflower is not,
[00:05:15.470]and in contrast, the Lewis' monkeyflower doesn't do well
[00:05:19.500]when things are hot and the growing season is long.
[00:05:23.750]So that's an example of an environmental gradient
[00:05:26.700]that is affecting whether two species
[00:05:29.620]are co-occurring or not.
[00:05:32.310]Here's another experiment.
[00:05:33.980]So this case, there's two things going on.
[00:05:36.390]We've got a competition experiment,
[00:05:37.920]so we do competition experiments by growing the plants
[00:05:41.540]with and without the potential competitor,
[00:05:45.610]and in this case, there's also an environmental gradient.
[00:05:48.880]In this case, it's soil acidity.
[00:05:51.700]So if we have alkaline soils, that is,
[00:05:53.540]soils that are very basic,
[00:05:57.010]so not neutral but basic.
[00:06:00.800]Heath bedstraw grown by itself
[00:06:03.377]does better in acidic soils than in the alkaline soils.
[00:06:07.900]White bedstraw does better in the alkaline soil
[00:06:11.480]than it does in the acidic soil.
[00:06:13.930]So that's an environmental gradient effect,
[00:06:15.590]just like you saw with the monkeyflowers.
[00:06:18.536]But what happens when you grow both species together,
[00:06:21.570]is whichever of the two species that does better
[00:06:24.750]in that environment is the one that wins the competition.
[00:06:28.730]Okay, so in this case, you can grow them both together,
[00:06:31.570]but you're not gonna get both of them surviving
[00:06:33.980]in an alkaline soil, you only get the white bedstraw.
[00:06:37.050]In the acidic soil, you only get the heath bedstraw
[00:06:40.800]surviving and growing.
[00:06:45.950]You don't necessarily see this kind of an effect
[00:06:49.180]with competition, so you can do what's called
[00:06:50.920]a replacement series experiment like this,
[00:06:52.770]where you have different densities of plants,
[00:06:57.500]and you're going to see one species win or lose.
[00:07:00.592]But the point of the environmental gradient
[00:07:02.740]is that sometimes that gradient can modify
[00:07:05.410]the effects of competition, and so it can flip
[00:07:07.660]which species wins depending on where you are
[00:07:10.670]along the environmental gradient.
[00:07:14.410]So back to saltwort, this is another of Ethan's pictures.
[00:07:18.630]So this is just the saltwort reflected
[00:07:20.956]in the water of the wetland.
[00:07:25.560]Saltwort is very tolerant of salinity.
[00:07:29.430]So we expect to find saltwort where it's saline.
[00:07:34.650]Cattails, not so tolerant of salinity,
[00:07:37.150]and so we would expect to find cattails
[00:07:39.180]in parts of the wetland where the soil is less saline.
[00:07:43.127]It's a bit harder to tell whether or not
[00:07:44.480]competition is involved in those sorts of things,
[00:07:46.760]because what we're going to be doing is going out
[00:07:48.690]and looking at the plants as they're found,
[00:07:53.030]and it's really hard to tease apart
[00:08:00.527]whether the difference between the two species
[00:08:03.170]is caused by competition or by the environmental gradient.
[00:08:09.190]So Shoemaker Marsh, I don't have a good map of it,
[00:08:13.630]but this is an accumulation of the salinity estimates
[00:08:18.030]done by all of your previous cohorts.
[00:08:23.210]Dr. Dave Houdine has been taking students to Shoemaker Marsh
[00:08:26.300]since 2005 and doing this experiment,
[00:08:28.340]so we're just carrying on adding more data
[00:08:30.870]to that particular dataset,
[00:08:32.580]and the particular marsh that we're in,
[00:08:35.801]you see, there's sort of a patch of high salinity.
[00:08:39.902]Here's the electric conductivity over here on the side.
[00:08:44.380]So this is the patch of high salinity,
[00:08:46.200]and then the rest of the marsh has
[00:08:49.550]lower values of salinity.
[00:08:53.490]And if we look where we find the saltwort,
[00:08:55.580]each of these lines represents a transect
[00:08:58.960]that was estimated by one of the previous groups,
[00:09:02.510]so each lab section will estimate,
[00:09:08.810]will count the species identity
[00:09:12.920]in one meter square transects,
[00:09:14.400]that's what each of these dots represents
[00:09:17.721]along 100 meters.
[00:09:20.050]So we'll line up 20 quadrats along the 100 meter gradient
[00:09:25.440]in different angles, and then count
[00:09:28.010]where the different species are.
[00:09:30.010]And where the black dots are, that's where we find saltwort.
[00:09:33.940]The open circles are where we have not found saltwort.
[00:09:39.720]So what does it look like when you're out there?
[00:09:42.740]This is a team that is I think doing soil salinity.
[00:09:48.270]That's the salt marsh down there,
[00:09:50.350]so it doesn't look terribly exciting,
[00:09:54.010]but there's six different species in there
[00:09:55.680]that we will be looking at.
[00:09:58.734]In addition to marking out the transect
[00:10:02.760]and then evaluating which species are present
[00:10:05.530]in each of those areas,
[00:10:07.070]what you'll be doing is taking a soil core
[00:10:09.490]and then mixing that with some distilled water
[00:10:12.310]and then measuring the electroconductivity in there
[00:10:14.480]in order to get an estimate of how saline
[00:10:17.020]that particular location is.
[00:10:19.060]And here's what that looks like,
[00:10:20.660]so taking the soil core's pretty easy.
[00:10:22.730]Getting the soil off of the soil core
[00:10:25.610]into the cup, that's a little more challenging.
[00:10:28.900]It's pretty muddy and dense anaerobic soil.
[00:10:35.580]So the learning objectives for this particular lab exercise
[00:10:39.100]are to predict the effects of salinity
[00:10:40.967]on the occurrence of different plant species,
[00:10:44.860]quantify an environmental gradient,
[00:10:46.540]that's the part of the measuring the electroconductivity.
[00:10:52.150]We're going to statistically test
[00:10:54.040]for the occurrence of competition,
[00:10:57.110]and this year, I'm going to see if we can get you
[00:11:00.770]to design what we call a stratified random sample,
[00:11:03.700]instead of using the old linear transects,
[00:11:07.950]we'll see if we can do a slightly better job
[00:11:10.901]of monitoring the occurrence across the entire wetland
[00:11:15.810]by drawing a random sample of point,
[00:11:18.510]rather than sending people out
[00:11:23.770]to just walk along the transect.
[00:11:26.010]So it'll be a little more challenging,
[00:11:28.260]but it'll give us some better data.

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Saline wetlands - environmental gradients and competition

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