Hi folks,

A week or so ago, Bruce and I derailed a simple question of winter collecting, and it would be more appropriate to take up the discussion in its own thread.

Some of our current research is focused around what ecologists call "resources partitioning". Theoretically, species using similar habitats must have "partitions" or differences in use among the resources available to avoid competing directly. We might simply call these "microhabitats" and the response that allows a particular species to dominate in that microhabitat can be morphological, behavioral, or both. The classic example is beak polymorphism in Darwin's finches:

http://en.wikipedia....arwin's_finches

Much of the work in community ecology has been done with birds, although there's a handful of studies that have investigated other vertebrate groups like small mammals, herps and reef fishes. In each case, limiting the routes of migration is critical to control, and so many of these studies have used "island-like" habitats such as oceanic islands, prairie dog colonies, desert seeps, coral reefs... Really unique habitats among the continuum of "environment".

If you know a little about darters, it may already be apparent why they are an ideal to investigate these processes... Many species live in riffles, which are somewhat of an island among the river continuum, and the dominant geologic characteristics are easily quantified. There are potentially multiple species and evolutionary lineages in the same riffle, there are a gob of different species to "assemble", and each has slightly different morphology. Males, females and juveniles have different patterning, so it's easy to discern - a member of one's own species may be the greatest competitor because they all need the exact same things. And individuals can only migrate in two directions... upstream and downstream. Furthermore, there's a bunch of unrelated species using the same habitats.

And most of all, we all know that darters just plain out rule It's an ideal system.

To conceptualize this, below is a graphic of a river in Ohio that has a pretty simple community. The darker colors for environmental variables are deeper and faster, each species has it's own color and number of individuals captured in one seine haul.


Figure 1

What you may notice is that while there is a ton of overlap, although each species occupies it's own space. This might be expressed in a conceptual model like this, where each ring is the species' distribution within this environment.


Figure 2

And then you take a bunch of samples at a bunch of different riffles and you can make something that looks like this to help visualize where species fall out in relation to one another:


Figure 3

Each of the arrows are an environmental variable, the length of the arrow describes the strength of that variable in shaping the distribution of species and assemblages you are comparing. The distance of the species name from the center describes the average strength of association for that species to that variable. So, for example, zonale has a weak association to sand in silt compared to maculatum's strong association to depth and cobble. And samples taken in deep sandy places (the least riffle-like habitat) have no darters. You might also overlay the total distribution of any one species with "rings" like you see in Fig 2 to help see what's going on here.

Now... that's great. They live in different space at very local scales (such as a riffle or even a reach of river). There was a bunch of this work done in the 80's and 90's and people tried to come up with "rules of assembly", as though species distributions were some kind of fixed entity. Furthermore, a resulting assumption is that competitive have ended, it's all peace and love in darter communities, right?

But that's not what I observe, especially traveling the gradient from the Great Lakes into the species rich streams of Tennessee and over the hills to the darter deplete Atlantic Slope. I find that distributions are incredibly plastic (flexible) and are determined locally by both local geology and the potential pool of species.

To provide an anecdote to this effect, I had the fortunate chance of someone giving me an experiment. A year after I sampled the riffle in Fig 1, I returned to sample other riffles in the area. I felt the simplicity of this particular riffle was prime to take a high school teacher (with whom I was working) to better understand my work and have an enjoyable day in the field. A canoeist had placed a wing dam of cobble to cause a chute through the structure. This is the result:



I am going to leave this to your interpretation for now... I think that's enough to digest in one post. Hopefully you'll find this engaging and we can get more deep into the discussion (I'm particularly eager to ask the question "What, then, is an invasive species?").

There are some things I will definitely address in consequent posts with Bruce in regards to his work and some pitfalls we've found... so regardless, this will continue whether you want it or not But it's my hope that there's participation in these thoughts... There is a lot to consider with data such as these, and I'd be glad for any input or criticism of the ideas as I go forward.

Todd

OK, no more threadjack is necessary, good. One question off the top of my head -- is your discharge just above the substrate, or at the surface? When we put our data together we'll have some discharge at just under a meter/second in the Flint, with depths up to about 50 cm, making for a somewhat more violent environment. We also have zonale and blennioides, and interestingly they're much more specialized in habitat preference; zonale mostly found in moderately deep, flowing water, and blennioides (especially big ones) in deeper, faster water. We haven't run our data through CCA yet, so I can't really compare our data. But your CCA shows zonale as arguably the generalist in that system, whereas I know we'll find zonale as more of a specialist; we'll have the black snubnose, duryi, as our generalist. Also, were your data collected year-round or just warm weather? We have little threat of ice in flowing water, so our sites were sampled about every 6 weeks over a little more than a year.

Each of the arrows are an environmental variable, the length of the arrow describes the strength of that variable in shaping the distribution of species and assemblages you are comparing. The distance of the species name from the center describes the average strength of association for that species to that variable. So, for example, zonale has a weak association to sand in silt compared to maculatum's strong association to depth and cobble. And samples taken in deep sandy places (the least riffle-like habitat) have no darters. You might also overlay the total distribution of any one species with "rings" like you see in Fig 2 to help see what's going on here.

Now... that's great. They live in different space at very local scales (such as a riffle or even a reach of river). There was a bunch of this work done in the 80's and 90's and people tried to come up with "rules of assembly", as though species distributions were some kind of fixed entity. Furthermore, a resulting assumption is that competitive have ended, it's all peace and love in darter communities, right?

But that's not what I observe, especially traveling the gradient from the Great Lakes into the species rich streams of Tennessee and over the hills to the darter deplete Atlantic Slope. I find that distributions are incredibly plastic (flexible) and are determined locally by both local geology and the potential pool of species.

Todd what you said above doesn't bother me one bit, but I say that not just based on my own personal observations and data, but beacuse the "plasticity" of resource use at the microhabitat scale is supported in the literature. A number of papers on the (poor) transferability of habitat suitability curves and microhabitat use and partitioning among sites within a basin have illustrated resource use to differ due to differences in habitat availability. To me, these have shown quite well that distributions aren't fixed for a species with a wide range or even basin to basin. This might be a bit of a generalization, but the coarser scale factors among basins typically exist that allow a species to inhabit it and while the species have adapted to the local conditions present that favor it the most. A lack of multi-drainage, multi-scale studies have likely just not made this as evident in our minds as it should be. Mattingly and Galat (2002) or Leftwich et al. (1997) would be a good example for darters.

From what it sounds like Bruce is saying, which I would totally agree with, the same species may exhibit different degrees of specialization based on the species it has co-evolved with. Again, not something I know of that has ever been accounted for in such a study, because these types of study rarely take place across such large scales. Not exactly the flashiest type of study to fund at large scales becuase it would likely have to involve species with low conservation ranking to be that common and wide ranging in the first place. Perhaps if the methods used to collect this type of data were more common a synthesis could happen, but with what is currently available, I think you would have quite a bit of uncertainty to assume in habtiat measurements and rates of species detection.

You're right, Matt, about the difficulties in comparing different studies because of methodological differences. I suspect that my data, and that of Todd, were similarly collected in terms of sampling technique; at least I hope so, we still have to compare notes in more detail. The studies share at least a few common species: Etheostoma flabellare, E. caeruleum, E. blenniodes and E. zonale, most notably. And maybe another difference is that we were able to work all winter.

In my next big post will be the landscape level, which will address your points Matt, and pull in what Bruce is exploring. Hopefully I'll have some time to assemble that this weekend. I wanted to get this established at the riffle scale first for any reader.

I agree those papers show this (I assume you talking about Ensign etal. 1997 Tranactions 126:895-907). The trouble is, as you point out... No one followed up on it at the community level because there weren't endangered species involved, or just looked where invasive species "ran" everything else off. However, if you've got a good Sugar Momma and an advisor with start up, you might pull it off... And is the context for why I drove across the Ohio to investigate it

Bruce, we took measurements 2 cm from the bottom because we wanted to balance the difference between columnar flow with roughness. And for what it's worth, in PCA, depth and discharge are insignificant and fall to PC3. I'll get into that as we develop the story.

Todd

Edited by farmertodd, 16 December 2011 - 04:45 PM.

OK, we're close, we measured stream flow 6 cm above the substrate. As to doing this work on various scales, it has the advantage of being very cheap in terms of overhead. As long as you can get to the stream and have legal access (!), the most expensive equipment is a flowmeter; we were able to buy one from Forestry Suppliers for $275. Anyway, we'll talk and see where this goes.

I just love listening to ecologists debating species interactions and distribution theories, and sometimes I even toss in an observation or argument of my own, secure in the comfort that I don't have to BE one of them.

Once again I think we need a "Like" button here.....

Interesting article (though having to look up every scientific name to know what species you were talking about is a pain). I heard a few articles on petitioning before but never that in depth. One talked about panfish restricting themselves to certain cover types when competitors were added. The other talked about the survival of species in san francisco bay in light of introduced exotics. This is the first time I seen anything on partitioning not made in response to introduced species.

The main issue here appears to be plasticity verses specialism, or equilibrium verses stability. I think Todd is onto somewhat of a conservationist bias that extends well beyond species specific habitat specializations, and also includes the plasticity of the environment itself and many species dependence on this habitat variability as much as they do specific habitat characteristics. Tadpoles can be particularly dependent on fresh new micro habitat formations. You can almost think of habitats with particular characteristics as an organism in itself. As this habitat ages the species dominance of in progresses. So what happens when we try to conserve some habitats in perpetual youth and others in perpetual old age?

Furthermore, a resulting assumption is that competitive have ended, it's all peace and love in darter communities, right?

(Slightly out of context but getting to Todd's case soon.)

The consequences are not always good for species dependent on particular age progressions of habitats. Perfect equilibrium is absolutely not a property of ecology, else evolution would be moot, and the lack of equilibrium in both species and environments is a part of many species survival strategy. The Lotka–Volterra model, even with a simplistic single predator and prey with an unlimited food supply for the prey, does not allow perfect equilibrium.

Now to the case Todd brings up:

But that's not what I observe, especially traveling the gradient from the Great Lakes into the species rich streams of Tennessee and over the hills to the darter deplete Atlantic Slope. I find that distributions are incredibly plastic (flexible) and are determined locally by both local geology and the potential pool of species.

When you stop and think about it Darwin's finches could not have developed the variability of beak structure without a preexisting single species plasticity long before any speciation occurred. We generally refer to these variances as polymorphism, but polymorphism is not restricted phenotypic characteristics. Polymorphism is more or less synonymous with plasticity and is expressed on an entire spectrum, even among the habitat selections of a single individual. An ideal preferred habitat for an individual is generally not attainable and closeness of fit often depends on the character of the competition in that preferred environment. This spectrum entails that we cannot think of polymorphism strictly in terms of phenotypic characteristics, or even strictly limited to differences between two individuals. Single individuals can have varying levels of plasticity with respect to the habitat characteristic those choose. Zero plasticity is almost certainly a death sentence.

The interplay between plasticity and equilibrium itself has characteristics similar to the Lotka–Volterra model. You can think of plasticity like the predator of equilibrium prey. When an ecological community settles into a quasi-stable system, through specializing in their own way, the system becomes ripened for predators, or agents that do not play by the previously established rules of equilibrium. It makes no difference whether that predation comes from newly evolved polymorphism within an ecosystem microcosm or an invader from the outside. Many predators are dependent on moving from one microcosm to the other over areas while the newly disturbed microcosms recover. Many prey species are dependent on these disturbances to reestablish the favorable conditions in it that they need. Geological, seasonal, and other disturbances can play the same role.

So then why is it a big deal that the "exotic" has "shift" the "native"? If natives shift natives, then why are we so proud of ourselves when we show that exotics shift natives?

Good question. The justifiable answer is that the lack of genetic variability, when exotics have free range of all environments they can conform to, is indeed a bad thing for the long term viability of the ecosystem in general. Yet mere shifts in population distributions is something that will eventually happen in any stable system, even if only through the development of a new level of polymorphism. Such as what drives evolution.

I guess that's what I'm after. I'm interested in what it can tell us about all these ongoing invasions, and how we can best mitigate, and even better, stop them. Otherwise, we're going to continue doing this Han-Solo-Running-Out-of-the-Bunker-Hands-Flailing "The snakeheads are coming!" dance over and over and over. Which results in management policies where they dip out entire ditches so we can better apply rotenone from helicopters. And... removes ALL ecological resilience against the invasion.

This is where I would be more cautious. Mitigation is something we attempt in our aquariums, where the variability of the suitability of a specific natural micro-habitat from year to year cannot be tolerated. Yet species in natural habitats often depend on this variability to maintain some subset of the environment suitable for their needs. Case in point: http://www.chiltonra...rest_fishes.pdf. In the American Southwest the non-natives are outcompeting the native 4 to 1. Yet on high flow years when our dams and diversion are overrun the natives outcompete the non-natives 4 to 1. The natives depend as much on the ecosystems variability as they do on any specific set of environment conditions. They depend as much on the low flow most of the year as they do on the seasonal high flows.

In thinking of the stability/volatility in terms of a Lotka–Volterra model we have a condition under which our environmental impacts are driving volatility way out of proportion to stability. This drives up an extinction rate greater than a speciation rate. Hence a stabilization policy is well warranted. However, when we conserve a microcosm of an ecosystem expecting complete stability we are intensifying the systems sensitivity to volatility, which cannot be avoided. That's why we have to go through so much trouble attempting to keep our aquariums from crashing. Oversensitivity to volatility can drive the extinction/speciation ratio up just as fast as as the increased volatility we are presently imposing on the ecosystem as a whole. A healthy ecosystem requires some level of volatility in order to maintain a quasi-stable state. Life is an entropy producing machine that feeds on volatility (enthalpy) to produce stability. Yet once that volatility is gone there is nothing left to feed on and the system starves to death.

The solution is not to stop the invasions between natives, but to keep their frequency in line with the birth, growth, and death cycles of the multitude of microcosms in the environments they live in. That the population dynamics of a given set of interacting natives is constantly shifting is a necessary component of a healthy quasi-stable ecosystem. Too much stability gets you the ecosystem the moon has, just as too much volatility gets you Venus.

----
Anyway, that is how I tend to picture ecology and the plasticity Todd is talking about. The plasticity in population dynamics among natives is merely a natural part of the cycling of environmental microcosms as they age, and under normal circumstances reborn anew in some other location. The environmental polymorphism in individual specimens is simply a normal mechanism for dealing with such variability. Using the term polymorphism here may technically be improper in this context but there is no distinct dividing line where polymorphism suddenly begins. In creeks bends are formed and washed out over time, and formed again. Deep pockets are filled and new deep pockets form. Sand barges are washed out, exposing clay, rock, and gravel in various circumstances and reformed elsewhere. With each of these variations the population dynamics among natives progresses through stages in which no one location will be perpetually dominated by any one species indefinately. Yet the cycling and rebirth of environmental niches as older ones age and become unsuitable for its previously dominant inhabitants keeps the system and species alive. Conserving such systems in perpetual old age harms species dependent on particular parts of the aging cycles of that microcosm and homogenizes the ecology for an invasion by the few exotics well suited to it. Maintaining stability in an ecosystem requires a life support system like that used on an aquarium, and still falls prey to crashes and instability. The same instabilities natural ecosystems depends on for sustenance.

Todd, I have another methodology question for you: How did you score different substrate types for CCA? There seems to be a wide range of possibilities, and we're just setting that up now. Thanks, as always...

There's another way to view this... Banded aren't competitors, they're adapted to anywhere someone else isn't. They are the most sensitive species in my pool to everything else. Even still, they cause shifts for other species because they can occupy some space.
Todd

Does this mean that E. zonale are less aggressive than most other darter species, and, if so, is that knowledge derived from the fact that the other darters are still there after the introduction of E. zonale?

Sorry to bring this up from the other thread. Just trying to play catch up in my mind. Much of what is given on this thread explains what was being said on the other one. Fascinating stuff. Thanks for posting.

Steve.

Okay, since methodology and applications have a special place in my heart, I have to ask why 6 cm Bruce? 2 cm has been pretty standard for "near bottom" velocity. I said it once to Todd too, but categorizing substrate is a whole nother can of worms. In my opinion, going with more is better because you can always lump after the fact (small and large gravel into gravel), but you can't seperate. Plus, analyses can dictate what you end up using in the end depending on the frequencies you find available or occuppied...

I'm fairly dismayed that my origional darter community level data collection was abandoned as part of my thesis work because I think that would have been really interesting considering the darter communities were quite different though geographically not that far apart. What I did collect wouldn't be enough or likely stand up to review, and the rest is just personal observation or communication/conjecture. In hindsight,dad I really had adequate funding and really spent the necessary time, I would have prefered to do have done the study in the French Broad, Little, Hiwassee, and Sequatchie or Paint Rock. It would have been an interesting continuum of the Tennessee River at the least.

Todd, nope I meant Leftwhich et al. (1997), it's a hundred or so pages further up that issue of TAFS. Have you collected banded darter data from the Susquehanna?

I think the community level data could be available among various studies of the late 90's early 00's with similar fauna (e.g., Elk River, French Creek) and I'm really surprised a synthesis was not part of something like the recent community ecology of stream fishes book to incorporate those larger scales. One other interesting line of inquiry would be to bring in life history traits since those SHOULD be conserved among widely seperated populations even more so than something like microhabitat use, and if not, differences in community composition (i.e., "invasive"/aggresive species) that could ultiamtely cause behavioral responses could be a potential mechanism.

There is a methodological concern I would like to ask about. When we talk about "resource partitioning" one of the ways in which a resource can be shared and partitioned is by preferred time of use, such as a preferred feeding time. If two species A and B share a common riffle for feeding, but A prefers morning feeding while B prefers evening feeding, then resource partitioning can occur through time shares. Plasticity may also complicate matters. If the population of A increases beyond that which their food needs cannot be met within the preferred feeding time then the effective use time can be extended. Hence A can begin encroaching on the time share partitioning of B. Time share partitioning is most strongly polarized between day and night time, but even there many species show a high degree of plasticity between day and night time feeding. Often choosing different locations for both.

So in the raw data are the individual records time stamped to allow searching for such a bias? Temperature and the light intensity on the surface likely also effects timing of use preferences of a given partition.

Matt, I say 6 cm because the rotor measuring current on our flowmeter is centered at 6 cm from the end of its support rod, and the rotors have about an 8 cm diameter. So I suppose it's about the same thing since the bottom of the rotor goes to within 2 cm of the bottom. As to substrate, the site at the Flint is mostly boulder (slightly broken bedrock) with some sorting for cobble and gravel on the edge of the main flow; Estill Fork is more complex, with more expansive areas of sand, gravel and cobble mixed around. At Estill Fork we found more YOY of several species, and they were almost in different microhabitats than the adults; YOY stripetails were often in deep, slow water over sand along a bank, and YOY tennessee snubs and rainbows were often in shallow, moderately flowing water with emergent vegetation. So there is evidence of some life history differences, but... we'll wait and see what the final analysis shows.

There is a methodological concern I would like to ask about. When we talk about "resource partitioning" one of the ways in which a resource can be shared and partitioned is by preferred time of use, such as a preferred feeding time. If two species A and B share a common riffle for feeding, but A prefers morning feeding while B prefers evening feeding, then resource partitioning can occur through time shares. Plasticity may also complicate matters. If the population of A increases beyond that which their food needs cannot be met within the preferred feeding time then the effective use time can be extended. Hence A can begin encroaching on the time share partitioning of B. Time share partitioning is most strongly polarized between day and night time, but even there many species show a high degree of plasticity between day and night time feeding. Often choosing different locations for both.

So in the raw data are the individual records time stamped to allow searching for such a bias? Temperature and the light intensity on the surface likely also effects timing of use preferences of a given partition.

Another great point I've only seen address in one or two studies in streams that made visual observations during night time. Most studies explicitly state observations are made from XXXX to XXXX, usually 10-1800. Before or after those hours the angle of the sun is usually so sharp that light reflecting (or refracting?) off the waters surface makes for some pretty terrible glare underwater plus shadows. So your rate of detection is going to change, just as it would if you took it during more turbid conditions. It would be terribly boring to put qualifiers of space, time, and season with a manuscript title, which is probably why only space or season end up being noted and the rest end up in the methods. Time, say chunks of hours, probably also has some yet to be quantified effect in regulated rivers when studies are conducted within 20 or so KM of a water release structure too since discharge fluctuates throughout the day due to pulses from dams to maintain minimum flow.

Ah, okay Bruce, I gotcha. So it probably is 2 cm off bottom or 4 cm. Really rough substrates tend to complicate things as do vast macrophyte beds.

Oh and just so I clarify in my head, you're both using seine hauls or kicks to collect fish? Any thought to species specific detection rates, especially Percina spp.?

Edited by ashtonmj, 18 December 2011 - 08:06 AM.

We were using kick-seining. In the Flint the only Percina that we rarely encountered on our transects in pretty strong riffles was common logperch; duskies are along one bank, and we only caught one. In Estill Fork we routinely captured blotchside logperch which are almost common, along with common logperch. So I think we were efficient at capturing Percina when present in particular, and other darters in general. We used a 12-foot seine usually with a crew of 4-5 people. And speaking of flow rate measurement, the substrate at the Flint is very broken up and it was always a judgement call about where to place the meter precisely, with various fissures and outcroppings. Estill Fork is much less complex for that.

I'll try and pick the low hanging fruit this morning so you know I'm not ignoring this... Some of this will be answered in my next installment (this was just the intro) and has helped guide that outline (MyWan, Steve, Matt ). I'm really glad people are engaged in thinking about this

How did you score different substrate types for CCA?

Importance values based on visual % cover. So you might have a sample that is 60% cobble, 20% gravel, 20% sand. Or 30% cobble, 50% gravel, 20% sand. And so on. Yes, there's variance that can be reported as error, but that's why we've taken 1,000's of samples. We've test this across basins and samplers, the patterns are similar and support most of our hypotheses generated from data collected in my project.

And while I'm on patterns, a pattern is all you can reliably take from the wild, unless you have some really novel system that allows you to control some variables (which I will say is what we're hoping to get out of the Pigeon River in NC and TN). If you really want to "know", you need to do a manipulative controlled experiment. So we feel our quick, dirty method is the level of detail we need to explore the question we're examining (we'll see what the reviewers say).

That said, if you're trying to figure out what's different between the Flint and Paint Rock, you most likely need to take Matt's suggestion to do a more fine scale analysis than a visual inspection, IF the geologies are that similar. This is the Ecological skill - knowing what information is important and that you can reliably collect at the spatial scale you're measuring.

I'm fairly dismayed that my origional darter community level data collection was abandoned as part of my thesis work because I think that would have been really interesting considering the darter communities were quite different though geographically not that far apart.

It may not be lost Matt. One of the things I want to compare is snorkel data vs seine data. I'll talk about that with the gear biases a little further down to answer another question of yours...

Todd, nope I meant Leftwhich et al. (1997), it's a hundred or so pages further up that issue of TAFS.

Yes. We're looking at the regional scale, finding out what is important (say to spotted darter), which provides new hypotheses to test at the microhabitat scale in flume tanks and at the site riffle scale during reintroductions. We hope to apply this to more pertinent conservation concerns in the upper T. I don't know if I told you, but I put in a Smith Fellowship proposal with Paul Angermier and Anna George, and I'm working with CFI and the Pigeon Recovery Project to get a grasp on the important habitat variables. So hopefully I can get funding to work on this specifically, AND down there!

PCA of substrate values from the Little River are weird. I'll show some of what we've collected in a future long post.

Have you collected banded darter data from the Susquehanna?

I looked for them in the Lehigh River, but I'm not sure they're there yet. Found plenty of tesselated darters while snorkeling, and I will note that the big bofo males were all in what I'd call "johnny darter" habitat (however this is not quantified). It was all young fish out "in" the riffle along with P. peltata.

One other interesting line of inquiry would be to bring in life history traits since those SHOULD be conserved among widely seperated populations even more so than something like microhabitat use, and if not, differences in community composition (i.e., "invasive"/aggresive species) that could ultiamtely cause behavioral responses could be a potential mechanism.

I think I've addressed this in part by using Great Lakes darter communities (which zonale is strangely absent perhaps mainly due to the curious fact of their absence in the Wabash River drainage). The remaining Etheostoma species have all successfully colonized the Atlantic slope, either naturally (whatever that "flabellare" is), or anthropogenically. They all have extremely wide habitat use, and show competitive release when the remainder of the community is gone. This makes them excellent colonizers, and gives them an advantage in homogenized situations (whether that be abiotic or biotic). I'll had planned to show this data in a long post.

As for the time of sampling that both Matt and MyWan have brought up... Yes. It's probably different. First, I'll ask, if you get a result during daylight, do you need to bother with night? That said, yes, I'd like to see what happens at night, esp to investigate the distributions of madtoms day vs night. I think there's incredibly interesting ecological information to be gained from that specific question. And... a 1-man seining technique is a beautiful approach to answering it, because it controls the sample area and can be done without seeing.

As for gear biases, and now having tried it in mountain streams, yeah, the seine method is prime for turbid, high density communities - and the bigger the trophic cascade to darters, the more you can get at their interspecific and intraspecific interactions. It works okay for some Percina, I have yet to capture enough numbers to use them in statistics. But these are the limits. I want to do some depletion curve work with seines, back pack shocking and snorkeling eventually. This is where your data may come into play, if this is something you'd like to work on

Steve, I'll answer that banded darter question in a long post with some graphics included.

I think that's what I could grab now. I'll have more time to write once the holiday starts. Again, I'm really glad for the engagement. I find this all fascinating, I hope you all do as well.

Todd

Looking forward to more info. I'm never really happy with the detail in sampling data or the number of controls, but that's just the nature of sampling data. Such limits don't harm the validity of the statistics that can be gained. Often just side noting the raw data with uncorrelated extraneous variables of note can lead to good clues about what to look for next.

It would be nice to have a dictionary of ecological variables pertaining to river environments, both local and regional. A lot of data shouldn't really need resampled for every new study and would make meta studies a lot easier. I would also like to see some technological advances in remote monitoring equipment for aquatic habitats. Electronic vocal identification is starting to play a larger role for some species, but is still not very accurate. Facial recognition technologies could eventually do the same for fish identification.

One thing I noticed about E. stigmaeum in Swamp Creek was that the riffle areas that had mixed sunlight and shade was the best indicator of their presents. Either no shade or too much and I never seen any. The most prolific numbers I seen were strong riffles with partial direct sunlight just after exiting or just before entering well or moderately well shaded pool habitats with a decent flow rate. I'm also still highly suspicious that pond snails in creaks are having an as yet unrecognized effect on water chemistry and the invertebrate available in the food chain.

Edited by mywan, 22 December 2011 - 02:43 PM.

Random amateur thoughts:

(1) Todd, I like your stream-flow-species-distribution diagrams. And I don't like them. The circle/pie-charts give a visually misleading impression of where certain species are most dominant. I'd suggest replacing them with some kind of density-dot pattern, so that , visually, pie(7) > pie(1), and slice(4) > pie(1), so to speak. (I say this while having no idea how I would have made the ones you do have.)

(2) In one of your diagrams ... I can't see it while I'm posting ... it's intriguing that Eth. caeruleum lines up in a flow depth/flow regime on one side of the stream, but something else is in what looks to be the corresponding depth/flow on the other side. Any thoughts on why? Different substrate? My mis-read of the diagram? Randomness ?

(3) You are, we hope, recording sex/age/size of these fishies as you collect sample data. For some species, males, females and young locate differently some or most of the time. Eth. rufilineatum (redline darter) comes to mind as a conspicuous example of a niche-partitioning strategy that seemingly reduces intra-species competition.

(4) Are you capturing food preferences and availability? A competitively defensible micro-niche doesn't have to be unique in ALL dimensions ... just one.

(5) This kind of study is going to be complicated by the fact that the micro-niches available to a species, at any given time of the year, may vary from optimal to tolerable. If you assume that, compared to other critters, darters have relatively low migration skills, then
* population per species will fall somewhere between an upper bound of the "breeding/food potential of the primo micro-niches" and a lower bound of the "carrying capacity of the tolerable niches, during the least favorable time of the year" (if that makes any sense),
but
* species location, when you sample, will be a function of the best available micro-niches for that species, at the time when you sample.

(6) From a Darwinian point of view, the micro-niche concept says we will see specialists (species evolved genetically and/or behaviorally to exploit some specific micro-niche) over generalists. Whether a specialist "strategy" can be successful in the medium-to-long run in a particular locality will depend to a large degree on the stability/availability of that niche, and if the local environment is highly unstable, the ease of re-immigration from a nearby refuge. As we know, stream habitats are often subject to significant amounts of seasonal variation in flow regimes, flooding, etc. Specialists can do very well in the best of times, but periodically can be whacked by the worst of times. To take an extreme example, none of the predators who specialized in eating only penguins still live in the wild in Tennessee and Alabama. (Sorry, off the top of my head I couldn't come up with a fish example not involving human activities.) So seasonal stability/variability could be an important study variable.

The whole system is really very dynamic, and not easy to analyze. Fun stuff, look forward to hearing more.

(Having dropped a big load, the seagull flies off.)