Dennis M. Hansen

Resurrecting extinct interactions with extant substitutes.

There is increasing evidence that restoration ecologists should be most concerned with restoring species interactions rather than species diversity per se [1]. Rewilding with taxon substitutes, the intentional introduction of exotic species to replace the ecosystem functions of recently extinct species, is one way to reverse ecosystem dysfunction following the loss of species interactions [2]. This is highly controversial [3], in part because of a lack of rigorous scientific studies [4]. Here we present the first empirical evidence of an in situ rewilding project undertaken as a hypothesis-driven ecosystem management option. On Ile aux Aigrettes, a 25-hectare island off Mauritius, the critically endangered large-fruited endemic ebony, Diospyros egrettarum (Ebenaceae), was seed-dispersal limited after the extinction of all native large-bodied frugivores, including giant tortoises. We introduced exotic Aldabra giant tortoises, Aldabrachelys gigantea, to disperse the ebony seeds. Not only did the tortoises ingest the large fruits and disperse substantial numbers of ebony seeds, but tortoise gut passage also improved seed germination, leading to the widespread, successful establishment of new ebony seedlings. Our results demonstrate that the introduction of these exotic frugivores is aiding the recovery of ebonies. We argue for more reversible rewilding experiments to investigate whether extinct species interactions can be restored.

Reproductive ecology of the endangered enigmatic Mauritian endemic Roussea simplex (Rousseaceae).

Roussea simplex is the sole member of the endemic family Rousseaceae from Mauritius. Once widespread and locally common on Mauritius, today R. simplex is critically endangered, with 85–90 known remaining individuals in a few scattered populations. We documented the unusual flowering and fruiting phenology and studied the pollination and seed dispersal ecology of R. simplex in the accessible flowering and fruiting populations. Endemic diurnal Phelsuma cepediana geckos were the only pollinators and the only animals eating the pulp and dispersing the tiny seeds. In experiments with captive geckos, we confirmed that geckos ingest the seeds and pass them apparently unharmed. This makes R. simplex one of the few known plants that use the same animal species for both pollination and seed dispersal. However, none of the seeds from fruits or gut‐passed seeds germinated, highlighting the large gap that remains in our understanding of the germination and regeneration of R. simplex. Conservation management must address this in the near future to avoid extinction of this unique lineage, and we highlight several options for applied conservation.