January American Naturalist highlights

Davidia involucrata, the handkerchief tree or dove tree, is widely cultivated in parks and gardens because of its striking white bracts, which can reach 50 square cm in size. What might be the function of these bracts" This question had never been investigated, partly perhaps because in its native habitat in subtropical western China the tree flowers during the rainy season. To find out the bracts’ function, scientists at Wuhan University in China observed pollinators and seed set in natural and manipulated flower heads that had their bracts removed or replaced by white or green paper. Davidia flowers are tiny and have no petals; their sole reward is pollen, which is offered over several days and collected by many species of bees. Experimental immersion of pollen grains in water resulted in rapid loss of viability, and flower heads that had their bracts removed lost a lot of pollen to rain. Together with the pollinating bees’ preference for white-bracted flower heads, these findings suggest that the huge bracts serve as a rain umbrella as well as a pollinator signal. Rain is a surprisingly understudied selective factor on flowers, especially as regards its effects on pollen viability. The results of this study also highlight the difficulty of experimentally dissecting a structure’s multipurpose function.

"Extending nonlinear analysis to short ecological time series"
Chih-hao Hsieh, Christian Anderson, and George Sugihara (University of California, San Diego)

Animal populations and the stock market are hard to forecast. Both are generated by complicated, interdependent systems. Unlike financial stocks, where trades are meticulously recorded, scientists began estimating animal populations only a few decades ago. But a new technique makes it possible to use the same tools some banks use to forecast the stock market and apply them to ecology. The newly developed “Dewdrop Regression” can forecast fish populations with 3% the data previously required through other methods, according to Hsieh, Anderson, and Sugihara in an article appearing in The American Naturalist.

The migration of the forecast tools from finance to ecology parallels Dr. Sugihara’s own journey. After proposing simplex projection in 1990 with Lord Robert May, later Chief Science Advisor of the UK and President of the Royal Society, Sugihara became a managing director of a major bank for several years. Returning to academia and ecology, “I realized that even great ecologists were working with time series only a few tens of points long,” Sugihara said. To apply data-hungry techniques to short time series, Hsieh et al. take data from several species collected simultaneously over a few years and stitch them together. A few test manipulations need to be applied; but when done properly, the technique is able to forecast with 15-20 points instead of 1,000. “You’re doing significantly better than chance within four years,” said Anderson.

But does it work for real world ecological problems" Using 40-year time series from 23 California fish species, Hsieh et al. showed that though they were <10% predictable alone, they become >60% predictable with the new procedure, combined with others from the same habitat. “When you consider that we’re predicting the change, not just raw abundance, this accuracy becomes very exciting,” Anderson said.