Ginkgo

Ginkgoes and dodos are my two favorite icons of “ghost” mutualistic interactions. So, I had the two last posts on megafauna and extinct interactions dedicated to them.

There are only five living groups of seed plants, and ginkgo is one of them; just a single species. Ginkgoes (Ginkgo biloba, Ginkgoaceae) have fleshy “fruits” and their “seeds” were dispersed by animals including, most probably, from dinosaurs to Pleistocene megafauna, and to extant frugivores nowadays. The reason is that the ginkgo has survived on Earth for a really extended period of time, with the earliest fossils of ginkgo-like plants dated more than 200 million years ago. Among the many ginkgo-like tree species, only Ginkgo biloba has survived (up to five Ginkgo species are known as fossils).

gbiloba

Living ginkgo very nearly went extinct, in fact, as of two million years ago, existing in only a small area in eastern China, the Tian Mu Shan mountains in Guizhou Province. Ginkgoes have then survived just by human intervention, with an assisted dissemination for cultivation starting at least 1200 yr ago by Buddhist monks, and introduced to Europe just by 1730-1750.

captura-de-pantalla-2016-12-30-a-las-5-51-41-pm
From Engelbert Kaempfer in his Amoenitates, 1712: the first illustration of ginkgo by a Western botanist.

Most likely a combination of extreme dispersal limitation due to lack of efficient seed dispersers combined with large-scale climate shifts and habitat modification contributed to their nearly extinction in the wild. Contrary to other tree species, retractions to small refugia populations failed to recover the original range, especially in North America and Europe. As with other megafauna-dependent species, it resprouts vigorously from buds buried in its underground parts, and human use certainly rescued the ginkgoes, probably because of their nutritous “nut”. In Peter Crane’s words: “It is irrepressible; its capacity for self-preservation has helped it survive through millions of generations.”

We know very little about how seed dispersal works in living ginkgo. The fleshy “fruit” is really the mature, fertilized ovule with a a three-layered integument: a fleshy outer sarcotesta, a stony inner sclerotesta, and a thin endotesta. Its smelly, large seeds (20-30 mm x 16-24 mm) are one of its most well-known and distinctive features: the seed’s soft outer layer starts to break down after a few days on the ground and produces butyric acid, CH3(CH2)2COOH giving it the “interesting” odor. Germination improves after the fleshy seed coat has been removed by passing through the gut of an animal or being teared-off. In one of the potentially wild ginkgo populations in China it is documented that the seeds are eaten by a wild cat, and in Japan they are eaten by badgers. Yet, there were very few seedlings in this population, located in 1989 by Del Tredici, despite good fruiting. People harvested the nuts, which are very nutritious, as well as Pallas’s squirrels (Callosciurus erythraeus), which also may act as good dispersers by scatter-hoarding the seeds.

Yet who were the seed dispersers that mediated the range expansion of ginkgoes over continents and islands (Japan) before human-mediated propagation? As in other megafauna-dependent plants, most likely a combination of dispersal agents, including large and medium-sized mammals and, well before that, dinosaurs. As with other extant large-‘seeded’ Coniferopsida like Cephalotaxus and Torreya with very large seeds, scatter-hoarding animals like the extinct multituberculates (i.e., the ‘rodents’ of the Mesozoic; g. Ptilodus) would have played a role in active seed dispersal of ginkgoes by scatter-hoarding the seeds.

We can see ginkgoes as survivors with a long history of mutualistic interactions involving a diverse array of animals, whose actual diversity we can only speculate about, then replaced by extensive human use.

  • van Beek, T.A. (2003) Ginkgo biloba. CRC Press, NY.
  • Crane, P. (2013). Ginkgo. The tree that time forgot. Yale University Press, New Haven.
  • del Tredici, P. (1989) Ginkgos and multituberculates: evolutionary interactions in the Tertiary. Bio Systems, 22, 327–339.

Text: Pedro Jordano with excerpts from Del Tredici (1989) and Crane (2013). Illustrations: WikiMedia.

Our review on seed dispersal effectiveness just published in New Phytologist

Our review on seed dispersal effectiveness just published in New Phytologist: “Just appeared in the last issue of New Phytologist: our paper ‘Seed dispersal effectiveness revisited: a conceptual review’ [DOI: 10.1111/j.1469-8137.2010.03402.x], co-authored by Eugene W. Schupp, myself, and José M. Gómez. This has been a nice project and a timely review (after 17 years of Geno’s classic paper) on dispersal effectiveness. We expand the concept and review what we know and what we don’t know, suggesting new ideas for future research.”

(Via Weblog de Pedro.)

5 Annual Harvard Plant Biology Symposium Plants and the evolution of cooperation & trading

 5th Annual Harvard Plant Biology Symposium Plants and the evolution of cooperation & trading: “Just arrived from the Harvard Univ. symposium,dedicated this year to mutualisms and the evolution of coorperation. Very interesting inter-disciplinary meeting with ecologists, economists, etc. and nicely setup by Naomi Pierce’s lab. My talk was about: ‘Complex networks of interactions and their consequences in diversified plant-animal mutualisms’.”

(Via Weblog de Pedro.)

New paper in PNAS

We have just published our paper “Olesen, J.M., Bascompte, J., Dupont, Y., and Jordano, P. 2007. The modularity of pollination networks. Proceedings of the National Academy of Sciences USA, 104: 19891-19896”. These are great news since it represents a very nice work lead by Jens. Here we relate the concept of moodularity to our previous work on nestedness in mutualistic plant-animal assemblages.

New paper on coextinction cascades in plant-animal mutualistic networks

New paper in Nature

Three days ago we had the good news of our manuscript on coextinction cascades in plant-animal mutualistic networks being finally accepted in Nature. These are very good news for the group, especially for our efforts in the last 4 years working on complex webs of interactions. Enrico did a superb job leading this ms. Here is the abstract:

Rezende, E., Lavabre, J., Guimarães Jr., P.R., Jordano, P. and Bascompte, J. 2007. Non-random coextinctions in phylogenetically structured mutualistic networks. Nature 00: 000-000.

The interactions between plants and their animal pollinators and seed dispersers have molded much of Earth’s biodiversity. Recently, it has been shown that these mutually beneficial interactions form complex networks with a well-defined architecture that may contribute to biodiversity persistence. Little is known, however, about which ecological, evolutionary, and coevolutionary mechanisms contribute to generate these network patterns. Employing phylogenetic comparative statistical tools, here we show that the evolutionary history of plants and animals significantly predicts the number of interactions per species, and the identity of the species with whom they interact. As a consequence of phylogenetic resemblance on interaction patterns, simulated extinction events tend to trigger coextinction cascades across related species. This results on a non-random pruning of the evolutionary tree and a more pronounced loss of taxonomic diversity than expected in the absence of phylogenetic signal. Our results emphasize how the simultaneous consideration of phylogenetic information and network architecture can contribute to the conservation of species rich communities.

Collaborative project CSIC-CNPq with Brazil

We just received approval for a collaborative project with Mauro Galetti (UNESP, Rio Claro, Brazil), as a part of the agreement between the spanish CSIC and brazilian CNPq for years 2004-2005. We’ll focus on palm seed dispersal ecology, megafauna fruits, and comparisons of fruit-frugivore communities and keystone species characteristics in neotropical and Mediterranean habitats. It’s going to be great fun.