ANPN Science Brief

Francais Avec leur réputation de super-prédateur et carnivore obligatoire, les crocodiles sont généralement supposés être incapables de digérer les plantes et jusqu’à maintenant, n’ont pas été considérés comme agents disséminateurs de graines. Une nouvelle étude prouve que cela est une supposition fausse, avec un examen de la littérature existante et de nouvelles données sur le régime alimentaire de 18 espèces de crocodiliens. Les auteurs ont trouvé de nombreuses preuves de comportement frugivore dans 72% des espèces, avec un large éventail de fruits consommés. Au Gabon, le comportement frugivore a été observé dans 9% des crocodiles nains ( Osteolaemus tetraspis ) étudiés et ils sont réputés pour manger Sacoglottis gabonenis (Pauwels et al ., 2007). Alors que la plupart des fruits sont ingérés accidentellement, une consommation délibérée de grande quantité de fruits a été observée. Cependant, le devenir et la viabilité des graines n’ont pas été étudiés, même si la plupart des r...

Francais Une revue d’études antérieures dans la nouvelle édition de "Philosophical Transactions of the Royal Society B" présente un tableau sombre du futur des forêts pluvieuses d’Afrique centrale si le contrôle de la chasse n’est pas effectif. Rédigé par nos collègues de l’Université de Stirling, Oxford et WCS, l’article examine les données existantes sur l’impact de la chasse dans la région, discute les facteurs qui favorisent la chasse et explore les conséquences potentielles à long terme de la chasse face au changement d’utilisation des terres et le changement climatique. L’article montre qu’alors que nous avons enregistré le déclin catastrophique de la mégafaune dans les forêts pluvieuses d’Afrique centrale, nous commençons seulement à réaliser les sérieuses conséquences de la chasse abusive sur le fonctionnement des écosystèmes ; notamment la structure des forêts, la dispersion des graines, la pollinisation, le cycle des éléments nutritifs du sol et du bilan carb...

In a special issue of Biological Conservation this month ('Defaunation's impact in tropical terrestrial ecosystems'), ANPN afflilates John Poulsen and Connie Clark published a study looking at the relative effects of logging and hunting on forest structure. Comparing different sites in Northern Congo, they measured the effects of logging and hunting on seed disperal, seed predation and herbivory. All sites still contained a full complement of large mammals, but differed in relative densities. They found that even partial defaunation reduced herbivory rates and seed dispersal distances. In addition, they found that logged and hunted sites had lower above-ground biomass than logged-only forests, despite similar timber extraction practices having been employed. They suggest that the removal of herbivores could favour the survival of fast-growing, low wood density species, with consequences for long-term carbon storage potential. Poulsen JR, Clark CJ, Palmer TM, 2013. Ecolog...

A new study published in the Proceedings of the Royal Soc. B. this month adds more weight to the growing body of evidence that removing seed dispersers from rainforests affects plant community structure (see Harrison et al., 2013, reported in Blogpost “Over-hunting causes reduction in tree diversity over time” and Beaune et al., 2013, reported in Blogpost “Elephant-dispersed trees suffer population declines when elephants are hunted out”).

These are the results of a long-term study that also support the findings of Beaune et al (2013), reported here (Blog post: Elephant-dispersed trees suffer population declines when elephants are hunted out): when animals are removed from the ecosystem, drastic changes to forest composition soon follow (Harrison et al., 2013). In an impressive long-term experiment carried out in a 52 hectare plot in Borneo, Harrison’s team tracked the performance of over 470,000 trees of more than 1,100 species for a 15-year period, from the onset of intensive hunting. During that time the site lost nearly all its animals larger than 1 kg.   They found that while the density of saplings increased by over 25 per cent (because animals were no longer present to browse saplings), overall species diversity fell. Furthermore, there was a relative decline in animal-dispersed species compared to gravity or wind -dispersed species. Animal-dispersed species were also more clustered than they were prior to hu...

English A new study has found that elephant-dependent tree species suffer catastrophic population declines when elephants are removed from the forests (Beaune et al., 2013). The study was conducted in Salonga NP in DRC, where forest elephants ( Loxodonta cyclotis ) are almost extinct. Here, the researchers explored how elephant-dispersed trees reproduce without elephants and how this affects their demography and spatial distribution. 18 fruit-bearing trees that rely on forest elephants as their primary means of seed distribution were studied. Of those that were entirely elephant-dependent, they either did not recruit enough young for self replacement, or produced no young trees at all.   There is no alternative partner for seed dispersal for the majority of the megafaunal trees which are actually elephant dependent. The authors conclude that the decline in this last cohort of elephant-dependent trees is likely to have been produced during elephant massacres in the last 30 year...