Mahé Boulder Cricket (Phalangacris alluaudi)

Mohamed bin Zayed Species project number 152510829

Conservation status of the Critically Endangered Mahé Boulder Cricket (Phalangacris alluaudi)

The Seychelles Islands belong to the global hotspots of biodiverisity. The cloud forests of Mahé are particularly species rich, maintaining a unique insect fauna with many endemic species. However, the forest is highly threatened by invasions of many non-native plants. In 2013, we started a first survey of the endemic Orthoptera on Mahé, funded by the Mohamed bin Zayed Species Conservation Fund (project 13056280) and the German Academic Exchange Service. In 2014, we continued our studies, funded by the Zoological Society for the Conservation of Species and Populations (ZGAP), the German Academic Exchange Service and a special grant of Trier University.This study led to the rediscovery of the Mahé Boulder Cricket (Phalangacris alluaudi), which had not been found since 1909. The species is currently known only from two localities on Mahé. We now will study the ecology and threats to this species, in order to develop a conservation plan. Furthermore, we study the habitat preferences of the Seychelles Forest Groundhopper (Amphinotus nymphula), which is listed as Endangered and probably threatened by the invasive plant Clidemia hirta. The Seychelles Forest Groundhopper is also restricted to the highest altitudes (> 500 m) of Mahé and Silhouette.

The Mahé Boulder Cricket is Critically Endangered and was flagged as "possibly extinct" (IUCN Red List 2012).The species has only been found in a cave and on the underside of large boulders. The status of the population is insufficiently known. However, many non-native plants invade the forests of Mahé, which alter the habitat structure strongly. While our research of the last two years suggests that the dominant invasive cinnamon trees do not affect Orthoptera strongly, the invasive soap bush (Clidemia hirta) is very likely to have quite dramatic effects, due to its dense growth.

The major aims of the projects are (1) to obtain a population size estimate for the Mahé Boulder Cricket, (2) to understand the habitat preferences of both species, (3) to assess the role of invasive species as a threat to the populations, (4) to create a management plan. Without any knowledge on the population size or trends and without knowledge on the habitat preferences, it is impossible to re-assess the conservation status of both species and to propose a suitable management strategy. For the Critically Endangered Mahé Boulder Cricket, it will be important to obtain more information on the population size. Currently, the species is only known from two localities in Morne Seychellois National Park and "La Reserve". The analyses of habitat preferences will allow us to assess the negative influence of invasive plants. Currently, we assume that the soap bush (Clidemia hirta) is the main threat to both species. With the knowledge obtained during the project, we will be able to elaborate a more detailed strategy to control this invasive species and identify priority areas for control measures.

After the completion of the project, we hope to have sufficient information to implement an adaptive management plan to control the population of the invasive plant Clidemia hirta. We also will try to develop a monitoring scheme for the Mahé Boulder Cricket.