Organic matter processing and retention

I've already mentioned one of the papers from the big 25th anniversary issue of JNABS.  I've now read a handful of these papers, and they continue to be very interesting and a little bit annoying.  Why are they annoying?  Well, I like the review aspect of the papers, I don't like the "JNABS played X role in the development of X concept", because, really?  Who the hell cares?  This is a perfect example of the sometimes egocentric nature of scientists:  It isn't enough for something to be discovered or understood.  It must be clear that this person discovered or understood something.  And by extension, this society contributed this to science.  I know that the incentive structure of the entire scientific community is geared towards rewarding this kind of attitude, but that doesn't make it right.  If anything, it makes it more wrong.

But I digress.  Let's focus on "A review of allochthonous organic matter dynamics and metabolism in streams" by Tank and others (2010; full cite below).  Actually, because I know all these authors, I'm going to list out the others:  Emma Rosi-Marshall, Natalie Griffiths, Sally Entrekin, and Mia Stephen.  Frankly all these people are awesome, and so I fully expected this paper to be awesome.

I was not disappointed.

There is a hell of a lot of interesting stuff in here.  Lets bring out some of the highlights:

• There have been a hell of a lot of leaf-decomposition studies.  Essentially, inverts and microbes are the big players, with other factors influence the effectiveness of those two main players.  Some of those other factors:  Pollution (by reducing invert populations/diversity and sometimes increasing microbial activity, temperature, and leaf species (even different hybrids have different decomp rates).
• Biomonitoring using leaf decomposition (at least combined with invert measurements) might be a good way to measure ecosystem health or "stream integrity".  There are a lot of papers cited here that I'll have to read at some point (assuming I can get access).  
• Although production to respiration ratios (P/R ratios) have often been used to determine allochthnous versus autochthonous production (whether or not a stream is heterotrophic or autotrophic), this is a more complicated assessment than was first believed (although the authors here don't fully explain why).
• People have tried a lot of different things to measure organic matter retention:  using leaves, sticks, logs, particle analogs (waterproof paper cut into squares), plastic strips, wooden dowels, etc.  Why?  Because most small streams have energy budgets dominated by terrestrial inputs (at least, most small streams that have been studied).  Getting estimates of in-stream retention of little stuff (dissolved or just fine particles) has been a lot more difficult. 

As I said, there's a hell of a lot here, and I'm in no way going to reproduce all the interesting stuff here.  Those are just a few highlights.  However, it is worth pointing out that this kind of research is a natural extension of some of the oldest 'modern' ecological studies that have ever been done.  What do I mean by modern?  I mean studies integrating abiotic and biotic components to understand large-scale phenomena.  Maybe 'modern' isn't the right word...how about awesome?

Summary:

This paper offers a pretty comprehensive overview of organic matter dynamics in streams, including decomposition, metabolism, and budgets.  Prior to doing any research on this topic, I would recommend reading through this to get a good historical perspective.

Tank, J.L., Rosi-Marshall, E.J., Griffiths, N.A., Entrekin, S.A., & Stephen, M.L. (2010). A review of allochthonous organic matter dynamics and metabolism in streams Journal of the North American Benthological Society, 29 (1), 118-146 : 10.1899/08-170.1

Notes for March 18th

• Useful link if you have questions about...well...how the world works.  For instance, Why is the sky blue?
• Some interesting info on Jupiter's Great Red Spot.  
• I like to say that if an organism isn't aquatic, then it isn't interesting, and that birds are boring.  However, this is kind of interesting:  Are bird brains bigger or smaller when the birds must migrate?
• On the origin of animals.

Notes for March 17th

• This demonstration of being able to construct really, really tiny objects is actually sort of intimidating.  
• All about the history of measles...really interesting stuff.  (via the Loom)
• Interesting discussion about how 'restoring' a natural habitat actually caused an endangered lizard to further decline.  
• Pepsi is pulling sugary beverages from schools all over the world.  I can't believe this is something we have to have the company commit to.  Why can't the individual schools recognize the needlessness of soft drinks.
• You may think that because the environment tends to treat humans poorly, that the Arctic tundra is fairly tough.  In reality, the tundra is extraordinarily sensitive to disturbances.  Case in point.

A new test of the Light:Nutrient hypothesis

To review: I love ecological stoichiometry (ES). I find it a fascinating subject and a useful framework for understanding ecological phenomena. However, ES is still relatively new, with a lot of the empirical work restricted to plankton (esp. Daphnia and algae). So it is always interesting to see theories developed predominantly in the pelagic system examined in other habitats.

One of the more interesting ideas out there is the light:nutrient hypothesis of Urabe and Sterner (1996; the ideas have been expanded in several later papers). Essentially, Urabe and Sterner noted that as you increase the amount of light, you decrease the nutrient content of algae. That's because as the light increases, but the availability of nutrients doesn't, then the algae is able to produce a larger and larger amount of carbon. As the algae become more and more nutrient-poor, the herbivores that graze on these algae get less and less nutrients from their food.

So what happens is a unimodal curve relating growth to the amount of algae present. That's depicted in Figure 1 from Urabe and Sterner (on the left). Part A of this figure shows the growth of algae and the nutrient content of the algae along a gradient of increasing light. As the light goes up, there's more and more algae with less and less phosphorus (and important nutrient). Then in Part B, focus on the line labeled "G, herbivore growth rate". See what it does along that same light gradient? First it increases with light, then it slowly decreases with light.

This kind of response was documented by Urabe and Sterner (1996) and several papers since then, but almost entirely in zooplankton (specifically, Daphnia spp.). However, there are lots of questions about this, primarily revolving around: How often does this occur in natural ecosystems?

This effect depends on a lot of things: The nutrient demands of the algae, the nutrient demands of the consumer, having an appropriate level of nutrients and light, etc. There really isn't much investigation of this effect outside of lakes (most of those studies focused on zooplankton).

A paper just published in Ecology by Hill et al. (2010; full cite below) seeks to investigate whether this occurs for snails growing on periphyton in streams. The authors looked at snail growth in two streams for several years, and primarily looked for evidence of that hypothesized unimodal relationship between light and growth. They did this by measuring the nutrient content of algae, the amount of light, estimating algal productivity, and the amount of growth in snails from month to month.

What's pretty interesting is that they didn't find this effect at all (see figure to the right).

Still, there's good theoretical reason for this effect to be possible, so why wasn't it observed? Well, the authors speculate that the extremely high density of herbivores present cause algal density to be held very low (i.e., competition between snails is so great that food is always in short supply). Recall from the Sterner and Urabe figure above that the mechanism driving this effect is the amount of algal biomass: There's just a lot of food. However, if the food is kept so low that algae can never achieve high biomass production, then food will probably remain limiting despite becoming less nutritious.

The authors did confirm that the algal part of the light nutrient hypothesis was occurring: As light increased (due to changing canopy density), the nutrient content of the algae decreased (less nitrogen and phosphorus). That just didn't translate into less growth in the herbivores.

There were some other things happening in this study that I'd like to know more about. For example, the amount of light was varying with the season, so it was also varying with a lot of other factors, like temperature. Without having thought about it too much, I'm not sure how those other changing conditions might affect different aspects of this system. I'm also not sure I completely buy the explanation that exploitive competition was driving this relationship, but I'll have to think about that some more.

The authors also point to some evidence suggesting that this effect might be widespread for benthic herbivores, although I find that evidence to be weak at this point.

Summary:

The authors of this paper tested the light:nutrient hypothesis in a snail-periphyton system and do not see the predicted relationship between light and herbivore growth rates. The expected unimodal response may be suppressed by heavy competition between grazers.

Hill, W., Smith, J., & Stewart, A. (2010). Light, nutrients, and herbivore growth in oligotrophic streams Ecology, 91 (2), 518-527 DOI: 10.1890/09-0703.1

Urabe, J., & Sterner, RW (1996). Regulation of herbivore growth by the balance of light and nutrients Proceedings of the National Academy of Sciences, 93 (16), 8465-8469 DOI: 10.1073/pnas.93.16.8465

Notes for March 16th

• I love reading about the domestication of various animals.  Domestication is such a unique evolutionary strategy, and so specific.  So of course I read with interest about the domestication of chickens.
• Gee...climate change might affect migratory birds?  Really?  This is new?
• Apparently higher life forms are living under the ice.  I'm not sure what is more surprising, that they found something, or that they found 2 somethings.
• A life-sized picture of a whale.  No, really.  Actually, it seems a little small to me.  
• Seeding the ocean with iron to promote CO2 sequestration has always been one of the dumbest ideas.  Here's another reason.
• Bringing back the American Bison is probably not possible.  Not because the species can't recover, but because cattle have encroached throughout their territory.  Still, there's apparently ongoing discussion of this by many (and a full plan here).  This all brings us to the Buffalo Commons, a virtual blasphemy in Kansas.  I, on the other hand, am all for it.  For all the hyperbole about it, I've yet to meet anyone who has actually read the actual Buffalo Commons essay that started the whole conversation.

The bizarre history of rangeland management research

As with the paper from last Friday, today's paper comes from "Ecological Restoration", one of the few journals that is delivered, in print, to our office. So yeah, I've been reading through it.

This paper is by Sayre (2010; full cite below) and is basically about how the cultural and scientific beliefs of those living in the desert southwest have shaped the way that restoration has occurred there. Southwest refers to southwestern US (Arizona, New Mexico, etc.).

The paper is really a historical essay more than anything else, and so I'm not sure if it really qualifies as 'science'. However, it was really interesting. Basically, Sayre points out that three really big-picture things have dominated the way people have managed this part of the country:

1. The "Natural" aesthetic laid out by early-20th century writers, specifically John Van Dyke.
2. The belief that rangeland could be managed for and by livestock grazing (which depended on believing Clements' "climax community" theory).
3. The unwillingness of (virtually) anyone to look at fire as a management technique.

That's a pretty amazing list. The desert aesthetic laid out by Van Dyke was popularized by his book (Desert), and turned out to be primarily a documentation of a massive drought. So the ideal that so many people believed in was really a landscape already heavily degraded by overgrazing and drought. The climax community theory that Clements promoted, and that was so popular in ecology for the early part of the 20th century, has been shown time and time again to be a poor representation of what is actually happening. And finally, fire has now been shown to be one of the most important factors in maintaining grassland communities.

So people pretty much got that all wrong, which isn't surprising. What is surprising is how long people have clung to those false theories.

The basic idea was that the grasslands would restore themselves if you just 'leave them alone'. What everyone wanted was for the grasslands to be as rich and abundant as they were in 1874. Unfortunately, the southwest grasslands were probably maintained by a more dynamic equilibrium (periodic fire, flood, and drought keeping the native grasses abundant and undesirable species [like mesquite] rare). Even worse, it took these scientists the better part of a century to figure out that all three of those factors above were wrong.

The net effect of all this poor management and questionable science is apparently quite astounding (I haven't visited myself).

"The Nature Conservancy estimates 84% of perennial grasslands in the Apachean Highlands bioregion has been invaded by shrubs; three-fifths of this area is deemed by The Nature Conservancy to be beyond restoration, either because there is insufficient grass to provide the fine fuels needed to carry a fire (which would be necessary to set back shrubs), or because non-native grasses dominate to such an extent that fire, although possible, would not appreciably help the native grasses." (Sayre p 26)

Holy cow.

There's also some discussion in this paper about whether the goal of restoration should be the historical conditions of an area or something else, but that discussion is less fleshed out. I'm under the impression that the author sees no a priori reason to believe historical conditions should necessarily be the ideal.

Summary:

About a century of poor management in the desert southwest (USA) is directly attributable to the widespread adherence to a series of unfounded beliefs. As a result, large portions of this area are unlikely to ever be restored to 'pristine' or desirable conditions.

Sayre, N. (2010). Climax and "Original Capacity": The Science and Aesthetics of Ecological Restoration in the Southwestern USA Ecological Restoration, 28 (1), 23-31 DOI: 10.3368/er.28.1.23

Notes for March 15

• Birds and mammals are not alike. For instance...some birds are bilateral gyandromorphs. Yeah, I'd never heard the term either. Apparently it refers to animals that are half-male, half-female, only split right down the middle. If you want to know more (and see pictures) than I would not hesitate to read all about them here.
• Something I've wondered about for awhile is how much changing land use is directly affecting local weather conditions (humidity/temperature/etc.). For instance, if you cut down a forest, won't the surrounding areas get warmer too? I haven't had time to dig into the literature on this, but apparently other people are thinking along the same lines, and have created some quick and dirty approaches to estimating these kind of effects. (via Conservation Maven)
• I really don't know what to think about this ambiguous little worm. No head, no gut, no up, no down. Does the worm even know which way it is facing?
• Apparently drug users in Scotland have had their heroin contaminated by...anthrax? I guess just say no kids.
• Workout for less time with high intensity and achieve the same results. Ok. I'll start today (not kidding). I've got a recumbent exercise bike, and in order to get the same sweat and 'I've worked out sufficiently' feeling that I used to get out of 25 minutes of riding, I now have to stay on the damned thing for an hour pedalling pretty much as fast as I can. Not only is that an annoyingly long time, but I'm sick of spending an hour and a half (after stretching and showering) in my basement every other night. I'm going to start hitting the gym every day for thirty minutes over lunch instead. We'll see how it works out.
• Finally it is beginning to look like the legal case for the vaccine nutjobs is coming to an end. I won't lie, I hate reading stories like this, because I hate believing the worst about people. And Jenny McCarthy is pretty much the worst of people.