For most species, an adult population of just 21 sparsely scattered individuals could be a pretty good indication of impending extinction.
For one critically endangered tree, however, the future doesn’t look quite as bad as you might expect.
The tree is known as faveiro de Wilson (Dimorphandra wilsonii), a legume-bearing species that grows in and around Brazil’s sixth-largest city, Belo Horizonte, about 440 kilometers north of Rio de Janeiro. Founded in 1701 and now home to more than 2.25 million people, Belo Horizonte (or “beautiful horizon”) has grown dramatically over the past century, causing a great deal of habitat fragmentation in the hills and mountains that surround it. Faveiro de Wilson is just one of the many species that have been pushed aside in the process.
Faveiro de Wilson has particularly suffered from its habitat’s fragmentation. The results of tests published April 29 in Tree Genetics and Genomics reveal that the trees have an extremely low level of genetic diversity, a sign that they have reached a genetic bottleneck. Other species with similarly low genetic diversity often face risks ranging from mutations to susceptibility to disease to the inability to successfully breed the next generation.
How low are we talking about for faveiro de Wilson? Try close to zero. But that’s not all: Not only are the trees almost genetically identical, they’re also inbreeding. Many of the trees are at least half-siblings of each other.
Yet despite the lack of diversity and fragmented habitat, the trees are still reproducing just fine. Although the trees are often geographically isolated from each other by agriculture and cattle pastures, some as-yet-unknown insect is flying between the locations to locate the trees and pollinate them. Even with the inbreeding, the trees’ fruit all bear viable seeds and young trees are sprouting. In addition to the 21 adults, the most recent surveys revealed 269 immature trees, although many of them were planted by conservationists from the Belo Horizonte Zoo-Botanic Foundation.
Because of the trees’ successful natural reproduction, the researchers concluded that “human intervention to aid the reproduction of D. wilsonii seems unnecessary at present.”
That doesn’t mean the trees are out of the woods. We still don’t know how they pollinate, and the large mammals and birds that used to eat their fruits and carry their seeds to new locations are either gone or in decline. Invasive African signalgrass—several species from the genus Urochloa imported to the area to feed cattle—continue to choke out the trees in many regions. This fragmentation and the distance between each tree could make it much harder for insects to accomplish necessary pollination. The authors recommend planting seeds in new locations in between existing trees to further improve pollination success rates and possibly minimize further inbreeding.
So far, faveiro de Wilson appears to be doing better than expected for a species with such a small population. That makes the critically endangered species something truly rare indeed.
Photo (uncredited) via PLoS One. Used under Creative Commons license