Does a giant tortoise taxon substitute enhance seed germination of exotic fleshy-fruited plants?

Aims The use of exotic species as taxon substitutes to restore lost ecological interactions is currently hotly debated.Aldabrachelys gigantea giant tortoises have recently been introduced to three islands in the Mascarene archipelago(Ile aux Aigrettes,Round Island and Rodrigues)to resurrect herbivory and seed dispersal functions once performed by extinct giant tortoises.However,potential unintended impacts by frugivore substitutes on native ecosystems,e.g.whether they will facilitate the germination of exotic plant species,are largely unknown.We investigated whether A.gigantea introduced to Rodrigues in 2006 could enhance the germination percentage of four widespread fleshy-fruited exotic species on the island.Using germination trials to forecast unintended impacts that could arise from the introduction of a frugivorous taxon substitute enables conservation managers to limit potential adverse negative interactions before they occur.Methods In germination trials that ran over 4 months,we investigated the effects of ingestion(gut passage and deposition in faeces)by subadult and adult A.gigantea on the germination percentage of four exotic fleshy-fruited plant species introduced to Rodrigues.We fed fruits of these plant species to sub-adult and adult A.gigantea to test how variation in age and size of the frugivore would affect seed germination.Feeding of distinctly coloured plastic pellets together with the fruits allowed us to test for individual tortoise effects on seed germination.Important Findings Ingestion by A.gigantea increased the percentage of seeds germinating of Mimusops coriacea and Lantana camara,but not percentage of germination of Veitchia merrillii or Wikstroemia indica.Seeds were more likely to germinate following ingestion by sub-adult rather than adult tortoises,which may be a consequence of the shorter gut passage time observed for sub-adults.Our results demonstrate that introduced frugivorous taxon substitutes could facilitate germination of exotic and invasive plants and highlight the need for conservation managers to weigh the risk of taxon substitutes potentially facilitating the germination and recruitment of exotic fleshy-fruited plants against the benefit of restoring lost seed dispersal functions of threatened indigenous plants.Our findings also highlight the importance of considering age and size variation in frugivores,in particular in long-lived taxa such as giant tortoises,when studying ingestion effects on the germination performance of plants.

Soil biotic and abiotic conditions negate invasive species performance in native habitat

Background:Most studies on plant invasion consider the enemy release hypothesis when analyzing native habitats.However,the lower performance of invasive species in the native habitats can be the result of unfavorable soil conditions in the native habitats.While soil biotic and abiotic factors have a potential to restrict the growth of invasive species in their native habitats,our understanding of belowground environment of invasive species in their native habitats is very limited.In this study,we analyzed soil characteristics associated with an exotic invasive plant,Old World Climbing Fern(Lygodium microphyllum),in its native habitat in Australia and the recipient habitat in South Florida.Rhizosphere soil samples from both habitats were analyzed for soil physical,chemical and biological characteristics.Results:Soil characteristics in the recipient habitats were significantly different compared to those in the native habitats.Soil samples from the native habitat had low soil pH,and high concentrations of elements such as aluminum and zinc which are phytotoxic in acidic soil environments.Additionally,mycorrhizal fungi spores were more diverse in the recipient habitat in Florida compared to the native habitat in Australia.Conclusion:Overall,our results indicate that growth of an invasive plant in its native habitats could be restricted by the toxic effects associated with strong soil acidity.Results from this study indicate that invasive plants not only escape from their natural herbivores but also from toxic soil environment in their native habitats.