Biodiversity and Conservation of Amphibians in the Delta

Region: Okavango Delta, Botswana

The uniqueness of the Okavango ecosystem is well known and well documented. However, despite the fact that Northern Botswana has the distinction of being known as an amphibian hotspot, the amphibians of this area are in fact relatively poorly known.

In addition, a primary conservation issue of recent times is the global decline in amphibian populations – both because the causes of the decline are unclear and because amphibians frequently have complex life histories and occupy multiple niches, so that the loss of species can have wide-ranging consequences.

The project aims to conduct a species diversity study of two regions in Northern Botswana. This will entail a detailed population and habitat survey which will provide baseline data for amphibian species currently present in the region. Intense field sampling sessions of five days per month for the duration of the rainy season will be undertaken in both the Xigera and Linyanti concessions where the majority of frogs will be caught by hand following chorus cues and tadpoles will be collected with dipnets.

Terrestrial and leaf litter species will be collected with the aid of pitfall traps, while baited funnel traps will be used to collect aquatic species. Volunteers will be invited to participate in the collection. A photo database of each species per study area will be kept for future reference and a voucher collection of amphibians of Northern Botswana will be created.

Species lists will be supplemented with detailed ecological data information on habitat preference, life histories and breeding behaviour through the use of GPS coordinates and observational notes at the capture sites.

Recent research has uncovered a fungal pathogen of amphibians (Batrachochytrium dendrobatidis, or amphibian chytrid) that is apparently responsible for numerous amphibian declines and extinctions worldwide, indicating that global declines may have a common proximate cause. Compelling evidence to date suggests that the geographic source of amphibian chytrid is Southern Africa and that the spread of the disease has been greatly facilitated by the global trade in amphibians. The prevalence of the amphibian chytrid fungus among the various amphibian species in the region will therefore be assessed and its threat status determined. Frogs collected will be checked for symptoms associated with the disease and swabbed; the swabs will be sent to the National Zoological Gardens of South Africa (NZG) in Pretoria for detection of chytrid fungus through real time PCR. Tadpoles will also be screened for chytrid fungal infection.

Data from the Global Amphibian Assessment, Southern African Frog Atlas and Red Data Book and any other recent literature will be compiled to determine any perceived threats to amphibians of the region. The impacts of each threat will be evaluated and a priority list of threats in need of mitigation will be compiled.

The final objective is to create public awareness of amphibians in the region by increasing knowledge about amphibians as well as the importance of their conservation to local stakeholders via publications, talks and interactive tools.

This study is a timely one, undertaken to ensure that the unique amphibian diversity of the Okavango ecosystem be managed in such a way that future generations will still be able to enjoy and appreciate this system with its unique biodiversity.

Final Update 2010
Amphibians are of significant ecological importance and a loss of species will have widespread and dire consequences. Recent population declines and extinctions have resulted in amphibians being labelled the most threatened vertebrate class on earth. The unique Okavango ecosystem is well known and documented, yet its amphibians are poorly known. This project aimed at assessing diversity in the Okavango Delta by testing isolation as a possible driver for community composition; determining the effect of hydrology on breeding behaviour; and assessing the status and prevalence of the pathogen Batrachochytrium dendrobatidis (Bd) responsible for the widespread epidemic, chytridiomycosis, implicated in amphibian decline.

Using various monitoring techniques, observations of species occurrence were made at three locations representing different degrees of isolation over a 20-month period. Breeding indicators were observed and frogs were screened for amphibian chytrid fungus.

A total of 29 species were recorded, and results indicated that there were no significant differences in community composition between sampled localities. Species presence, however, was significantly correlated with habitat type. Thus, the availability of suitable habitat appears to be driving amphibian diversity patterns, rather than geographic isolation; and increased habitat diversity near the Delta periphery explains increased amphibian diversity in these areas.

249 swab samples were collected and screened for amphibian chytrid fungus. The geographical distribution of collection samples were evenly spread throughout the localities, and were obtained from at least 25 amphibian species. Analyses proved negative for Bd for the 79.92% swabs analysed thus far and it is concluded that Bd seems absent in the study region, a result which has massive conservation implications for the region.

Despite the fact that the Okavango Delta has benefitted from conservation and tourism efforts in the past, the system and its biodiversity remains threatened and effective conservation management strategies must be devised and implemented to ensure its preservation. This project was completed in 2010.

Update March 2010
Results for this portion of the study provided novel insights into amphibian breeding in the Delta. It was always assumed that moisture limitations and temperature requirements resulted in amphibians in southern Africa breeding in the summer rainfall months. It was therefore significant to observe breeding indicators for some amphibian species (namely Ptychadena, Amietophrynus and possibly Xenopus) during a field trip in the winter, non-rainy (but peak flood) season. This phenomenon was only realised as the project progressed; monitoring will continue in 2010.

All results from chytrid swabs analysed to date (34.8% of total samples) have proved negative for Bd. These preliminary results suggest that Bd may not be present in the system (dependent on future results), which is surprising, since Africa is believed to be the origin of amphibian chytrid fungus. The absence of amphibian chytrid fungus (as well as the alternative of its presence) will have major conservation implications for the Okavango Delta.