zoology biology benno meyer rochow science blog dodo extinction

The Dodo and its Tree

A nice example of plant/animal mutualism or bad science?

When I was a young Senior Lecturer in New Zealand an interesting article had appeared in the prestigious journal “Science” by a certain Dr Stanley A. Temple, who claimed he had discovered why the tree Sideroxylon grandiflorum (then known as the calvaria tree) was no longer reproducing and in 1973 only 13 such trees were left on the island Mauritius, the only place in the world this tree could be found. He championed the idea of co-evolution of the tree with the extinct dodo bird (Raphus cucullatus), a grotesque-looking, turkey-sized, flightless pigeon also found only on that island. The dodo was plump and tasty and did not fear people when Portuguese sailors began to visit the island in 1507. In fact, so rapid was its demise, it never had time to acquire any sense of fear and in 1681 the very last dodo was bagged. Its relative, the solitaire (Pezophaps solitaire) on Rodrigues Island fared no better.

Following the disappearance of the dodo, forests of the calvaria tree also began to decline and it was the American Dr Temple who felt that perhaps not the reckless deeds of wood choppers, settlers and ship builders were to blame, but that the dodo had something to do with the decline. Many plants, he mused, produce fruits that are eaten by birds who digest the fruit flesh of the seed’s outer cover, the endocarp, but leave the seed’s ability to germinate untouched. It is in fact by this method that many plants spread and disperse. Fortunately some of the remaining 13 tress were still producing fruit and Dr Temple collected some of the 5 cm large yield, covered by an extremely tough and woody outer layer, and force-fed them to domestic turkeys, hoping that the birds’ gizzard would do the trick and anxiously awaiting for the re-appearance of the seed at the other end of the bird. When seeds did appear again they were without the tough endocarp and 1/3 germinated. Dr Temple had the joy to see the first “baby calvarias” produced in 300 years – or so it seemed.

No doubt Dr Temple’s idea (if in fact it was his, because some critics stated that he was told by local folk that dodos might have eaten the seeds) was great; a very nice example of plant and animal dependency, known as mutualism. However, did he carry out controls and try to germinate calvaria seeds without feeding them to his turkeys? No, he apparently had not done that. Had he considered whether other animals could have been involved in feeding on the seeds and removing the endocarp around them? No, he had not, although giant Mauritius tortoises became extinct more or less the time the dodo disappeared and probably also would have been consumers of the seeds. And finally, did Dr Temple investigate whether dodo and calvaria forests actually occurred together or in close proximity to each other? No, apparently not and it has been suggested that the dodo and the tree did not usually occur together on the island, but occupied different regions.

So, bad science? I would not go that far, because Dr Temple had a great idea, put it into practice and showed that it worked. Yes, he did not have any controls and failed to take into account other possibilities, but his research was stimulating, made others think and carry out further studies. I think Dr Temple deserves credit for that. And, by the way, seeds of that famous tree are apparently even now still fed to turkeys in order to facilitate germination.

© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2018.
Unauthorized use and/or duplication of this material without express and written permission from this site’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to V.B Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com with appropriate and specific direction to the original content.

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