One species hiding another

An endemic sapotaceous tree Calvaria major found on the island of Mauritius is nearly extinct because its seeds apparently required passage through the digestive tract of the now-extinct dodo Raphus cucullatus…’’

Temple, 1977

If Temple’s fairy tale was true, we should at present have coffins ready for the remaining ca 1000 trees of Calvaria major (Now Sideroxylum grandiflorum). But except for some outdated textbooks it is now widely recognized that there was no obligate mutualism between the dodo (below) and S.grandiflorum which turns out to be more threatened by invasive species. Yet though there was no evidence for this theory, it acquired quite some fame. Why? Maybe because of the aura already associated with the dodo or simply because species interactions are mysterious enough to trigger our imaginations.

Leaving this particular fantasy interaction aside, we may get more conscious of the real ones occurring in the natural world. Though we have more information on the disappearance of species, do we know what crucial roles they had in their respective habitats? And which functions have been lost with their extinction? There must, obviously, be some eventual consequences of decreased or lost links, but can we identify those?

Why is this important? The loss of a species is tragic in itself but as one species is lost several ecological interactions are also lost. And as we cannot resuscitate lost species (All my respect however to scientists trying to turn Jurassic park into a non-fiction story), why not resurrect the lost ecological interactions to maintain functional integrity of an ecosystem, as some scientific authors have suggested?

For example in Mauritius, the loss of its two endemic Giant tortoises (Cylindraspis inepta & Cylindraspis triserrata-picture of statue on right),important grazers and seed dispersers, about two centuries ago may have had a major impact on native plant community particularly when it comes to seed dispersal of  large-fruited plants.  ʺOn Mauritius the dodo Raphus cucullatus may be the most famous ghost, but empirical evidence strongly suggests that substituting the extinct Cylindraspis tortoises with extant counterparts will bring more benefits to habitat restoration’’ (Hansen, 2010).

No genetic manipulations or cloning of giant tortoise suggested by Hansen but rather the use of analogue species that is living species of a similar niche in the ecosystem that can perform the lost ecological roles of other extinct species. The use of  the Aldabra giant tortoise (Aldabrachelys gigantea) as analogue species on two Mauritian islet nature reserves have shown restoration of seed dispersal for one endemic species  as well as indicating its importance in habitat restoration through grazing of invasive grasses (Griffiths et al., 2011; Griffiths et al.,2009)

(Courtesy of C.Griffiths)

The use of analogue species can be controversial as it may involve the introduction of exotic species which can have unexpected impacts in the new habitat. So far no negative impact on native flora has been observed but it’s mostly that holistic approach that i wish to share.  This reminds us that conservation is not just about saving one particular species but consideration should also be given to the habitat and the intrinsic functions of an ecosystem.

How about, when we have our magnifying lenses focused on 1 species, that we take the time to really look around to discover these threads connecting our beloved species with others which can be just as fascinating?

Fabiola Monty

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