Darwinian Agriculture blog

Evolution, agriculture, and economics

2013-05-17T22:41:50Z

Alfons Balmann has reviewed my book in the Journal of Bioeconomics.

"As opposed to the somewhat ideological arguments frequently raised by the proponents of these approaches in public debates on topics like GMOs and organic farming, Denison's concerns are not motivated by a wholesale rejection of these approaches, but by a substantiated assessment of their limitations, and by developing alternatives."

I wasn't familiar with the journal, but keep running into interesting parallels and differences between economics and evolutionary biology. See, for example, this interview with economist Robert Frank, author of The Darwin Economy. I've enjoyed his previous books, but haven't read that one yet. And I've agreed to participate in a symposium on ""The Significance of Evolution for Understanding the Economy : Perspectives from Anthropology, Biology, and Economics" in September, hoping to learn more.

First, though, I'll be speaking at Evolution 2013, in Snowbird, Utah. I was also planning to speak at the Intecol (Ecology) meetings in London -- until I saw their outrageous registration fee, with no single-day option. I'll be at the the much-cheaper Ecology meetings in the US, though, right across the river in Minneapolis.

Local food?

2013-05-13T21:52:14Z

"We like to buy local food... despite the fact that the increased transportation costs of locally grown food make for a greater carbon footprint..." -- Comment from John Gorentz on blog Front Porch Republic

It's hard to argue with someone who says my book is "quite a page turner" but I think he may be over-stating his case a bit, to emphasize the point that buying local food doesn't necessarily save energy. I do the same thing on the last page of the book.

Ideotype breeding and tradeoffs? What tradeoffs?

2013-04-24T16:17:25Z

Near the beginning of the question period for this recent lecture at the University of Minnesota, I suggested that:

1) nobody has done a good comparison of ideotype breeding with breeding for yield, and
2) many plant breeders who use the word "ideotype" ignore tradeoffs.

The main point of Donald's 1968 paper, which coined the term, "ideotype" was that there are often tradeoffs between individual-plant competitiveness and the collective performance of plant communities, so we can improve the latter by sacrificing the former. That's a major theme of my book, as well.

But both my numbered points above turn out to be wrong, at least partly.

Yuan et al. (2011) compared ideotype breeding with breeding for yield. I criticized some of their choices for "ideotype traits" in my third lecture at the International Rice Research Institute, but it's still an impressive study.

And, rereading Rasmusson's 1984 paper on ideotype breeding, I find extensive discussion of tradeoffs, though he doesn't explicitly mention the tradeoff between competitiveness and yield potential hypothesized by Donald (1968).

I am correcting these errors in an perspective I'm writing for the journal, Evolution.

YouTube video goes fungal...

2013-04-15T18:25:51Z

...or whatever we call over 100 but fewer than 1000 views.

This page has links to an interview Michael Joyce did with me at the end of my week-long visit to the International Rice Research Institute, as well as the five lectures I gave there (plus audience questions and discussion).

Also still available are:
* a 60-second AAAS story on my most-cited paper.
* a video of my keynote talk at the Applied Evolution Summit
* a lower-quality video of a talk on Evolutionary Tradeoffs as Agricultural Opportunities
* an audio interview with science writer Carl Zimmer

Or, you can find an updated list of my publications, with links to many of them, here.

Darwinian Agriculture at IRRI 3: A solution to the phosphorus problem?

2013-04-12T21:54:49Z

"Crops that take up nutrients faster may reduce some wasteful nutrient losses (for example, leaching [see glossary] of nutrients in water percolating down through the soil), but every atom of nitrogen or phosphorus that is sold off-farm in grain, milk, or other farm products still needs to be replaced, for long-term sustainability... " -- Darwinian Agriculture, p. 67

This conservation-of-matter argument was the basis of my argument, in my fifth lecture at the International Rice Research Institute (IRRI), that rice with improved phosphorus uptake might offer mostly short-term benefits. (A slide with the only field data I've seen on this rice mysteriously disappeared, about 14 minutes into the talk.)

But the abiotic-stress group at IRRI called my attention to another approach to "the phosphorus problem" that seems really promising. Actually, there are several phosphorus problems:
* Phosphorus fertilizer is expensive, and it will get more expensive as high-phosphorus ore reserves are depleted.
* Some soils bind phosphorus, limiting its availability to plants.
* Phosphorus, mostly from livestock manure, is a major contributor to water pollution.

In the book, I mention crops with "proteoid" roots or increased symbiosis with mycorrhizal fungi as possible ways to increase crop uptake of less-available forms of phosphorus. But that doesn't solve the conservation-of-matter problem, i.e., the need to replace phosphorus in grain sent to distant cities or feedlots. The eventual depletion of phosphorus reserves seems such a severe (though perhaps distant) problem, that I briefly mention the "back to the land" option, to facilitate recycling of phosphorus in our waste.

But what if 1000 kg of grain contained only 1 kg of phosphorus, instead of 4 kg? We could then reduce phosphorus fertilization by 75%, making phosphorus reserves last four times as long. (OK, this isn't a permanent solution, but it could give us many more decades to find a permanent solution.) I didn't consider this option in the book, because I assumed that low-phosphorus grain would be less nutritious.

The abiotic-stress group at IRRI corrected my misinformation. It turns out that much of the phosphorus in grain is in the form of phytate, which neither we nor our animals can digest. So it ends up in manure. I'd heard about attempts to reduce phytate levels in seeds as a partial solution to the phosphorus-pollution problem. But low-phytate seeds would also reduce amount of phosphorus exported from a farm in each ton of grain, which would reduce the need for phosphorus inputs to replace it.

This seems like a win-win solution. Why didn't natural selection think of this? The phytate isn't there for our benefit; it's there to supply the phosphorus needs of the germinating seed and seedling, until it can grow enough roots to get phosphorus from the soil. We might therefore expect low-phosphorus seeds to grow poorly, although this isn't necessarily true for high-phosphorus seeds that have less of their phosphorus as phytate.

Low-phytate seeds with high total phosphorus would be more digestible, increasing the fraction of their phosphorus that ends up in meat or milk rather than manure. So they could reduce pollution. They wouldn't reduce the need for phosphorus inputs, however.

But what if we could supply the phosphorus needs of growing seedlings externally? If 99% of seeds get eaten, and only 1% get planted, could we give the 1% some extra phosphorus, perhaps as a seed coating? I don't see any fundamental (e.g., conservation-of-matter) reason why this wouldn't work, though it would probably require a clever combination of plant breeding and agronomy.

Darwinian Agriculture at IRRI 2 -- C4 rice?

2013-03-27T09:47:50Z

All five of my Darwinian Agriculture lectures at the International Rice Research Institute are now available on YouTube. My talks were prepared in advance, so I was only able to incorporate a small fraction of the interesting things I learned during my visit.

My last talk discussed the tendency (not necessarily by scientists themselves) to exaggerate research progress. For example:

"The researchers have already... successfully introduced 10 out of the 13 genes needed for C4 rice." -- Rice Today, January-March 2013, p. 5

Wheat, rice, soybean and tomato use C3 photosynthesis, named for the number of carbon atoms in the first product of photosynthesis. Maize ("corn" in the US) and sugar-cane use C4 photosynthesis. In hot climates, C4 photosynthesis can support higher rates of crop growth, using less water.

My book (p. 62) uses C4 photosynthesis as an example of "something that may have been easy for natural selection (given millions of years) [but] extremely difficult for humans." So I was surprised to learn, before arriving at IRRI, that C4 photosynthesis only needs 13 genes and that they have already transferred 10 of them. Maybe "skeptical" would be a better word.

I should have asked about this when I met with Paul Quick, who is leading the C4 rice project at IRRI. I'm guessing that he told the magazine that they've identified 13 key genes so far, and transferred 10 of them. My impression, from our discussions, is that they don't yet know the total number of genes they will need to transfer.

They have a lot of smart people, at IRRI and around the world, collaborating on C4 research. C4 rice will need :

* Some way to pump CO2 into bundle sheath cells around the leaf veins, from adjacent mesophyll cells.

* A diffusion barrier around the bundle sheath cells to keep the CO2 from leaking out again.

* More photosynthetic chloroplasts in the bundle sheath cells than rice has now.

* Ideally, closer vein spacing. The assumption is that CO2 can't be pumped very far, so if veins are widely spaced, only a fraction of the leaf will have C4 photosynthesis. But Paul Quick told me that corn husks have C4 photosynthesis throughout the leaf, despite widely-spaced veins. Interesting.

They seem to have made considerable progress on most of the above. I don't think he mentioned any progress on the diffusion barrier, though, which seems more critical than vein spacing, at least to me.

One of the clever approaches they are using is to knock out genes in a C4 plant, at random, to see which of them are essential to C4 photosynthesis. How do they tell if they've knocked out C4? Because of their CO2-concentrating mechanism, C4 plants can survive at much lower CO2 concentrations than C3 plants can. So they grow the random-knockout plant population at 15 ppm CO2 -- the atmosphere is 390 ppm and rising -- and look for plants that don't grow. Sounds like cruelty to plants, but they rescue them before they die, by transferring them to a high-CO2 tent. They're also drawing on IRRI's huge (100,000 genotype) collection of rice varieties and rice's wild relatives.

I don't know if they'll succeed, but this seems like a reasonable test of our current ability to improve complex traits in crops. At a minimum, they should get a lot of useful information about photosynthesis, leaf structure, the evolution of complex traits, etc. This information could have applications beyond improving photosynthesis. For example, the ability to develop crops with wider or narrower vein spacing would have applications in developing more-digestible crop leaves (for cows or for biofuel production). Vein spacing may also affect drought tolerance. Whether spending the same amount of money on other kinds of agricultural research would make more sense is a more-complex question. But the Gates Foundation is funding this "high-risk, high-potential-reward" research, so it doesn't come at the expense of their other work.

For more information, see IRRI's C4 rice page. For an interesting history of the project, see this video interview with John Sheehy, former head of the C4 rice project, who back visiting IRRI the same week I was there talking about Darwinian Agriculture.

Darwinian Agriculture Talks at IRRI 1

2013-03-23T12:12:54Z

My talks at the International Rice Research Institute are have been posted on Youtube and have already "gone reptile" or whatever you call it when a few people watch them.

I've been enjoying my meetings with staff here. Some highlights so far:

Paul Hilario, curator of the IRRI museum, told me about the "community rat-barrier" strategy for reducing rat damage to rice. A small plot of rice is surrounded with a fence with a few holes. Rats are attracted to the plot and crawl in through the holes, each ending in a trap, so most of them are killed before they can reproduce. Sort of a black hole for rats. But it only works if the "trap plot" is more attractive to rats than other rice nearby. So coordination among farmers (planting nearby rice later than the trap plot) is key.

Next I met with Ruaraidh Sackville Hamilton, who's responsible for IRRI's 100,000-genotype rice collection. Here's a great story about that. He mentioned another example of cooperation among farmers being key to disease control. If every farmer in a region plants the same barley variety, that increases the risk of disease epidemics. So farmers in the UK coordinated choices to ensure high levels of diversity, at a regional scale. I don't know if this works better than if each farm had high levels of diversity, but it's probably better than if one farmer had high diversity and her neighbors didn't.

John Sheehy's seminar was another highlight of my first day at IRRI. He initiated a program to develop rice with the efficient C4 photosynthetic pathway, with funding from the Gates Foundation. That work is being continued by Paul Quick. They're using some very clever approaches, which I'll discuss in a later post, but success isn't certain and it will certainly take a while. So, Sheehy asked, what else can we do to increase the yield potential of rice?

Sheehy presented a bunch of simple equations: photosynthesis equals solar radiation times the fraction of that radiation intercepted by green leaves, times a radiation-use efficiency term, and so on. This overall approach is similar to what I used to teach in my Crop Ecology class at UC Davis, which I inherited from Robert Loomis. (Sheehy and I each taught the class as sabbatical replacements for Loomis, years ago, and we've both published on the physiology of legume root nodules.)

Sheehy pointed out that maximum yield occurs at the point when net growth is zero, that is, when biomass gets large enough that maintenance respiration balances photosynthesis. Maintenance respiration increases with temperature, so maximum yield will be less in warmer climates. This explains some yield differences that had previously been attributed to better cultivars or better management. I suspect that maximum production per day occurs much earlier than maximum yield, so it may make sense to harvest and plant another crop rather than waiting. Hoping to discuss this with Sheehy.

He also pointed out that leaves aren't important only for photosynthesis, but also as a place to store nitrogen which eventually gets used for grain nitrogen. You don't want the leaves so close together that they shade each other, so there are limits to how short rice plants should be, even though investing resources in stems rather than grain seems wasteful.

Coming soon to a city near you?

2013-03-08T20:00:34Z

It's not a book tour, exactly, but an increase in speaking invitations from my usual 1-3 per year.

22-27 March 2013. Darwinian Agriculture. A five-part series of lectures and discussions at the International Rice Research Institute, Los Banos, The Philippines.

4 June 2013. Evolutionary tradeoffs as constraints and opportunities. LANGEBIO, Irapuato, Mexico.

23 June 2013. Darwinian Agriculture. Evolution 2013. Snowbird, USA.

4-9 August 2013. Darwinian Agriculture. Annual Meeting, Ecological Society of America, Minneapolis, USA.

18-23 August 2013. Evolving More Beneficial Crop Symbionts. INTECOL 2013. Joint meeting of the International Association for Ecology and British Association of Ecology. London, England.
Part of a symposium on "Applying Ecological and Evolutionary Knowledge to Increase Agricultural Yield and Sustainability", organized by Jacob Weiner.

I will also be attending the North American Congress on Symbiotic Nitrogen Fixation, here in Minneapolis, and a workshop on Evolutionary Origins of Multicellularity, in Durham, North Carolina.

Roundup-Ready Ragweed

2013-02-25T23:07:44Z

Glyphosate-resistant Giant Ragweed Over-topping Roundup-Ready Corn. Photo by Dr. Bill Johnson.
Source: International Survey of Herbicide-Resistant Weeds.

The same website has a list of herbicides, ranked by the number of weeds that have evolved resistance to them.

From p. 4 of Darwinian Agriculture:

"Widespread use of transgenic crops resistant to the weed-killing herbicide (see glossary) glyphosate presumably increases the use of that herbicide, while reducing the use of other, more-dangerous herbicides, at least until weeds evolve resistance to glyphosate."

Organic vs. sustainable?

2013-02-25T20:27:20Z

Do organic farming rules sometimes undermine sustainability? See this blog post by Andy McGuire, who earned an MS with me (for his research on legume cover crops) in 1996. Some of the comments are worth reading as well. The one by "RachelL" raises some of the same issues as the last chapter of my book.

More on ecosystem succession

2013-02-25T18:12:04Z

In the comments to a recent post, Timothy Crews writes:

"The reason Denison cited the Vitousek and Reniers model in the first place was to point out that late successional ecosystems might lose nutrients more than earlier successional ecosystems. But given that agriculture involves removal of moderate to large amounts of biomass in the harvest, there is good reason to believe that perennial agroecosystems would never reach the mature (and leaky) equilibrium stage of succession, but instead would be arrested in the aggrading biomass or nutrient sink stage indefinitely (where biomass production exceeds total respiration)."

This seems plausible. But if we have to intervene, by harvesting the right amounts at the right time, to keep further succession from increasing nutrient losses, that supports my main point:

"succession does not improve ecosystem function consistently enough that we can safely copy the overall organization of even late-successional ecosystems without extensive testing."

On the other hand, it's great if the intervention needed is something we want to do anyway.

Succession, predator-prey interactions, nutrient transformations by soil microbes... each of these ecological processes can be beneficial, from an agricultural perspective, but not always. So let's study them in nature and in agriculture, then apply what we learn, rather than blindly copying what we see in nature.

I'm using "nature" here as shorthand for "ecosystems with relatively little active management by humans." OK, Clem?

Also keep in mind that nutrient retention is only one of agriculture's goals. Its main goal is nutrient export as grain, milk, etc. Many natural ecosystems have demonstrated sustainability, in the absence of significant nutrient export. How would they do if we start harvesting as much food as we do from agricultural ecosystems? Could they export the same amount of food over decades, with fewer inputs? Any data?

More reviews!

2013-02-18T17:02:56Z

Janet Sprent, whose research I've admired for decades, reviewed my book in the Bulletin of the British Ecological Society. I couldn't find a web link to the review. She writes that "not all readers will agree with the arguments against these holy cows [perennial grain crops] but they deserve serious attention." Given our shared interest in nitrogen fixation, she was surprised by the lack of discussion of nitrogen-fixing cereals. But the book was already long enough to keep her "fully occupied on a 13 hour flight."

I probably could have lumped nitrogen-fixing cereals with C4 rice: both are big enough changes that we can't assume they have already been "tested and rejected by natural selection", but both may be "beyond anything humans today could design and implement from scratch." I may have to modify the latter statement for C4 rice after seeing what progress they've made at the International Rice Research Institute, next month, although copying other C4 plants isn't the same as designing a new photosynthetic system "from scratch." Making nitrogen-fixing cereals might be even more difficult, however, as I have discussed on my other blog.

Chris Smaje, a regular commenter here, reviewed my book for Permaculture Magazine (link to docx file here) and separately on this blog, Small Farm Future. Both reviews are examples of the kind of thoughtful discussion I hoped to generate with the book. He wrote:

"I suspect that it's ultimately impossible to create any kind of agriculture that can usefully be regarded as 'natural', but the further we depart from it the more we're flying blind..."

Similarly, I wrote (p. 74):

"the more we depart from nature, the more we enter unexplored territory, with possible unknown risks."

Still, the quantitative comparisons in Chapter 6 are consistent with my theoretical argument that it may be possible to improve on the overall organization of natural ecosystems. For example, crop rotation may be a good idea, even though natural ecosystems rarely have such dramatic changes in plant species from one year to the next. In contrast, Chapter 5 argues that making simple, tradeoff-free improvements in individual-plant traits like drought resistance will be much harder, even with biotechnology. This is because natural selection has tested individual traits competitively against alternatives, over millennia. Meanwhile, no natural process has consistently improved overall ecosystem organization on that time scale -- see previous post.

Does succession consistently improve ecosystem function?

2013-02-15T00:27:07Z

In a guest post, Timothy Crews quotes two representative statements from my book in which I argue that (in contrast to natural selection's improvement of individual adaptations) neither natural selection nor other natural processes have improved the overall organization of natural ecosystems over millennia. My doubts about "other natural processes" were based on actual data comparing the productivity and stability of natural and managed ecosystems. Dr. Crews argues that shorter-term ecological processes, specifically succession, may improve "ecosystem function with respect to agricultural goals." He doesn't seem to be claiming longer-term improvements, such as succession improving ecosystems more today than it did millions of years ago, which would be analogous to the longer-term improvement of individual adaptations by natural selection.

I don't doubt that some successional changes in some ecosystems qualify as improvements by criteria relevant to agriculture. So I agree that agriculture might "benefit from studies of niche complementarity" etc. As I wrote on page 1:

"Once we drop the assumption of perfection, however, we can learn much from studying natural communities."

"The assumption of perfection" may be an exaggeration of the viewpoint I intended to criticize. I could rephrase as "Once we drop the assumption that there are ecological processes that consistently improve the overall organization of natural ecosystems in ways that would make it safe for agriculture to copy their organization without first testing all the effects of that organization", but that seemed a bit lengthy for page 1.

But how consistently do successional processes improve productivity, stability, nutrient retention, etc.? If there's a good recent review of this question, I'd appreciate hearing about it. The papers I've found do not support the hypothesis that these measures of ecosystem performance consistently improve with succession.

Gower et al.(Gower et al. 1996) analyzed 13 datasets for forests around the world and reported that "Aboveground net primary production (ANPP) commonly reaches a maximum in young forest stands and decreases by O-76% as stands mature." In agriculture, productivity is arguably our most-important criterion, even for environmentalists, as it reduces the amount of land needed to grow a given amount of food. But other measures of performance are also important.

Crews' guest post emphasizes nutrient retention. Vitousek and Reiners (Vitousek and Reiners 1975) presented data compared nitrate loss in streams from younger versus older forests. The older forests lost more nitrate. They also discussed similar data from other forests. Similarly, Lamb (Lamb 1980) found higher nitrate levels in soils of older rather than younger tropical rainforests.

Comparisons among ecosystems are complicated by the possibility of differences unrelated to succession. The closest thing I know to a controlled comparison is that of Wardle et al.(Wardle et al. 1997) They compared islands whose differences in successional stage depended on how recently they had been struck by lightning and burned. This depended mostly on their size. Species diversity was greatest on islands in later successional stages, but "ecosystem process rates were lowest on those islands," perhaps because microbial biomass was greatest at early successional stages. The effects of succession on overall productivity and stability were apparently not measured, unfortunately.

Until I see some data to the contrary -- more than an isolated example or two -- I conclude that succession does not improve ecosystem function consistently enough that we can safely copy the overall organization of even late-successional ecosystems without extensive testing.

References

Gower, S. T., R. E. McMurtrie, and D. Murty. 1996. Aboveground net primary production decline with stand age: potential causes. Trends in Ecology & Evolution 11:378-382.

Lamb, D. 1980. Soil nitrogen mineralisation in a secondary rainforest succession. Oecologia 47:257-263.

Vitousek, P. M., and W. A. Reiners. 1975. Ecosystem succession and nutrient retention: a hypothesis. Bioscience 25:376-381.

Wardle, D. A., O. Zackrisson, G. Hornberg, and C. Gallet. 1997. The influence of island area on ecosystem properties. Science 277:1296-1299.

Guest post -- "Patterns and processes other than natural selection could improve agriculture"

2013-02-12T21:43:10Z

I don't promise to post everything people send me, but Timothy Crews (of the Land Institute) has obviously put a lot of thought into critiquing one of the main points in my book. I disagree with many of his conclusions and will respond via comments or another post, but here's what he wrote:

The following two quotes illustrate one of the most central, important and repeated points that R. Ford Dennison makes in his book Darwinian Agriculture.

p. 8 Natural selection "has bequeathed many sophisticated adaptations to individual plants and animals, but it has not consistently improved the overall organization of the natural communities where they live." The available evidence suggests that no other natural process has optimized natural communities either.(italics mine)
p. 43 "Some landscape-scale patterns in natural ecosystems have demonstrated their sustainability by persisting for millennia. However, only individual adaptations have been tested by competition among plants or animals with alternative adaptations. ...So ideas inspired by landscape-level patterns of even ancient ecosystems will require more testing, relative to ideas inspired by the competitively tested individual adaptations of wild species."

Contrary to Denison's evaluation of the available evidence, I argue that there are natural processes other than natural selection that "improve" upon native ecosystem function with respect to agricultural goals. In recent decades, ecologists have worked to understand "assembly rules" to clarify what we know and don't know about the forces that shape ecological communities (Diamond 1975, Weiher and Keddy 1999). This topic has received a lot of attention in recent years, and is complex and contentious (HilleRisLambers et al. 2012), and no one suggests that there are hard and fast "rules". But many would agree on some processes that are not natural selection, which occur predictably and consistently at the aggregate community level, and, I will argue, result in attributes that are worthy of consideration to improve agriculture.

The gradual development of niche partitioning in plant community development is a good example. Early in primary or secondary succession, when species are colonizing a new parent material or a recently disturbed site, it is common for a few (usually annual) plant species to establish and dominate the community. Whatever the composition of the initial community, propagules of new species will arrive and become established to the extent that unused soil and light resources remain, or the new species can appropriate resources better than already established ones. This process generally results in species turnover, or succession, and perennial growth forms almost always overtake annual forms. With time,later successional plant communities are commonly made up of species with differentiated niches that utilize slightly to largely different pools of resources in time and/or space.

The remarkably different plant co-existing growth forms that can be found in the desert grass and shrub lands of southern Arizona illustrate resource partitioning in a late successional community. Extremely deep rooted mesquite trees with C3 photosynthesis are found growing in close proximity to shallow rooted perennial grasses, like Bouteloua gracilis, that employ C4 photosynthesis, which can be found near cacti such as cholla, that maintain CAM photosynthetic pathways. Burgess (1995) described three functional categories that encompass the three species I mention here, 1) extensive exploiters (mesquite)--deeply rooted woody plants that exploit deep water resources, typically recharged by winter precipitation, 2) intensive exploiters(Bouteloua gracilis)--shallow rooted grasses and shrubs that rely on erratic summer rainfall and can persist for long durations in a drought-induced dormancy, 3) water storers (cholla)--cacti and succulents that maintain relatively low leaf surface area, tend to lose out to intensive exploiters in competition for water, but re-hydrate effectively during moderate to high rainfall events, and transpire water slowly. Ecologists believe the plants with these different water uptake strategies experience less head to head competition, and therefore have a greater likelihood of co-existing than groups of species from a common functional group. A similar diversity of resource use strategies have been found to exist for other resource axes, such as soil nitrogen (Weigelt et al. 2005, Kahmen et al. 2006). An ecosystem-level outcome of greater niche partitioning through succession is that plant resources (nutrients, water, light) are more completely utilized. More complete resource utilization should, ceteris paribus, result in greater productivity, and, importantly, less leakage or loss of water and nutrients from the ecosystem.

It is also important to point out that community composition is never static-- the environment is constantly changing, and new species are constantly being introduced from the outside. New arrivals of potential community members effectively "test" the resource uptake efficiency of the extant community. In some cases, the new arrival may be able to go deeper for water, or persist at a lower soil matric potential during drought. Such advantages can lead to species replacement, and a more productive and resource efficient community as a whole.

How might agriculture benefit from studies of niche complementarity or resource partitioning in native plant communities? The somewhat obvious but nevertheless important idea is one that has interested agroecologists for some time--the deployment of diversity in space through polycultures. While Denison seems to prefer the deployment of diversity in time through rotations, the potential to substantially improve uptake of soil resources, increase productivity and reduce vulnerability to weed invasions through crop mixtures in space is worthy of further attention. Even more interesting is the potential to improve on these ecological functions when the perennial growth form that is dominant in native systems is included in the polycultures.

In Darwinian Agriculture, Dennison identifies numerous significant shortcomings of modern agriculture. Many, if not most of them involve ecological functions above the species level, such as leakiness of nitrogen or soil erosion, and thus are not easily addressed by improvements in the performance of individual annual crops. Does it make sense to look at native community and ecosystem attributes to inform how we might make improvements? Absolutely. Especially when the functioning of native ecosystems appears to be superior with respect to attributes of interest (e.g., nutrient retention), and there are no alternative human constructed systems that provide models superior to the native systems from which to learn. If native ecosystem patterns and processes can be improved on with respect to desirable agricultural goals, then all the better--those projects are worthy of funding.

References
Burgess, T. 1995.Desert grassland, mixed shrub savanna, shrub steppe, or semidesert scrub?pp. 31-67 In: The Desert Grassland. M.P. McClaran& T.R. Van Devender (eds). University of Arizona Press, Tucson, Arizona
Diamond, J. 1975.Assembly of species communities. Pp. 342-444 In: Ecology and Evolution of Communities. M.L. Cody & J.M. Diamond (eds). Harvard University Press, Cambridge, Mass.
HilleRisLambers, J. P.B. Adler, W.S. Harpole, J.M. Levine & M.M. Mayfield. 2012. Rethinking community assembly through the lens of coexistence theory. Annual Review of Ecology, Evolution, and Systematics 43:227-248
Kahmen, A., C. Renker, S. B. Unsicker& N. Buchmann. 2006. Niche complementarity for nitrogen: An explanation for the biodiversity and ecosystem functioning relationship? Ecology 87:1244-1255
Weigelt, A. R. Bol& R. Bardgett. 2005. Preferential uptake of soil nitrogen forms by grassland plant species. Oecologia 142:627-635
Weiher, E. & P. Keddy. 2001. Ecological Assembly Rules: Perspectives, Advances, Retreats. Cambridge University Press, Cambridge, UK.

One person changing his mind isn't evidence

2013-02-11T19:29:06Z

Evolution deniers often claim "I used to believe in evolution... until I looked into the science." Many of them are lying, especially about the science part, but what if some of them really did change their minds?

So what? If one of your friends jumped off a bridge...
The evidence for evolution isn't diminished by one person changing his mind.

Similarly, one environmentalist (Mark Lynas) changing his mind about transgenic crops isn't evidence, one way or the other, that they are safe or useful. I don't have much to add to what Chris Smaje and John Vandermeer have written about this high-profile "defection."

My own guess is that the risks of current transgenic crops are less than many environmentalists fear, but the benefits (and potential benefits, at least within the next decade or two) are less than GMO supporters promise.

But, you may ask, as long as investing in biotechnology research will provide some net benefit, shouldn't we do it? As usual, an analogy based on rhizobia may be useful.

How should we view a rhizobial strain that provides some nitrogen to its legume host, but occupies a root nodule that would otherwise have been occupied by a more-beneficial strain? Wouldn't we be better off if the less-beneficial strain were less abundant in soil? Similarly, if some of the money invested in biotechnology would otherwise have been invested in more-beneficial ways, such as developing agricultural methods informed by ecology and evolutionary biology, wouldn't we be better off investing less (but not zero) in biotechnology?