Two papers on plants caught my eye this week. The first is from Nature on the scaling of plant metabolic rate. Peter Reich and his colleagues say that plant respiration increases linearly with plant size — that is, a plant has a metabolic rate twice that of one half its size.
This seems to contradict the West, Brown and Enquist (WBE) model of metabolic rate, which says that metabolic rate in all organisms is proportional to the 3/4 power of body mass — so a plant would have a metabolic rate only about 1.7 times that of one half its size.
Whether this is true, and whether the WBE model is the right way to explain metabolic rate, is controversial. I think that there is good evidence for what's known as quarter-power scaling over a wide range of plants and animals, and I also think that the WBE model makes a lot of sense (but then I've written a book about all this, so I would say that). But these things take decades to sort out, so there will be a lot of to-ing and fro-ing between both sides before any hard consensus emerges. Don't expect the quarter-power people to give up their ideas in the face of this new evidence.
The other paper deals with another big issue in ecology — what maintains the high diversity in tropical forests? Writing in Science, a massive team of ecologists led by Christopher Wills present evidence from forest plots in Panama and Malaysia showing that rare species are more likely to survive than common ones — an advantage that buffers against extinction.
The team don't seem to plump for a reason as to why this should be. One possibility is the Janzen-Connell hypothesis, which says that mature trees attract pathogens, herbivores and so on that make it harder for seeds of the same species to germinate in the vicinity. Another possibility stems from the fact that all species compete most strongly with other members of their own kind — because their needs are so similar — than with other species, and that this competition is weaker for rare species.
I am reading Jonathon Silvertown's new book on plant ecology, Demons in Eden at the mo. He has an excellent discussion of these issues that comes down in favour of the J-C view of things. I don't think things are as clear cut as all that, but there does seem to be good evidence that the process is important in forests.