Pakenham's river frog

Pakenham's river frog (Phrynobatrachus pakenhami) is an endangered species that is only found on Pemba Island off Tanzania  © Mahler, Luke and Zimkus, Breda licensed under CC BY-SA 3.0 via African Amphibians

East African biodiversity study reveals gaps in protected areas

Some of the highest areas of wildlife diversity in east African forest regions are not within protected areas, a study suggests.

An international team of scientists analysed where the region's amphibians live and their evolutionary relationship to each other. The scientists then identified 10 hotspots of biodiversity, and found that the land with the highest biodiversity accounts for less than 3% of protected areas.

'There is an urgent need to consolidate the protected areas in these highly threatened biodiversity hotspots,' says Dr Simon Loader, Museum scientist and senior author of the paper.

Coastal forests of East Africa

The coastal forests of eastern Africa stretch in a narrow strip along the coast from southern Somalia through Kenya, Tanzania and Mozambique. The area is important for biological diversity as it contains many plants and animals that are found nowhere else.

But the forests are fragmented and endangered as agricultural expansion is replacing them with farmland. It is estimated that only 10% of the original forests remain, and just 17% of those forests have some level of protection.

The researchers studied the parts of the forest within Kenya and Tanzania, investigating whether the protected areas are safeguarding the richest biodiversity sites.

Map of coastal forests of east Africa

The coastal forests of east Africa (coloured in orange) stretch in a belt from Somalia to Mozambique. The area investigated for this study lies in Kenya and Tanzania (bounded by the black box).
 

Identifying habitats to protect

To pinpoint areas that need protecting, conservation planners need to not only identify areas that contain a wide variety of species, but also whether they contain species that live nowhere else. If such an area is lost, localised species will become extinct.

The scientists chose to focus on one group - amphibians.

'Amphibians are a good representative species to track overall biodiversity,' says Dr Loader. 'They are very sensitive to environmental changes and their ability to extend their range into new locations is generally quite low.'

The researchers used data from 41 of the 51 amphibian species known to live in the region.

Estimating diversity

The researchers began by building a map that divided the enormous region into a grid of one-square-kilometre cells. They then needed to work out the range (the geographic spread) for each species and the diversity of species within each cell.

To calculate a range, the researchers started by noting the locations where each of the 41 species has been recorded. They then estimated the probability that surrounding cells would also contain that species. The more similar the habitat was, and the more closely connected to an inhabited cell, the higher likelihood that the species lives there. The scientists could then build up a probability map for each species' range.

To examine diversity, the researchers used DNA from the different amphibians to build a phylogenetic tree. This shows the evolutionary relationship between species and how closely or distantly they are related to one other. A cell containing animals that were more distantly related to each other would have a higher diversity score than a cell with closely related animals.

Phylogenetic endemism heatmap for Kenya and Tanzania

The phylogenetic endemism (PE) heatmap for the regions in Kenya and Tanzania shows clear hotspots of high biodiversity
 

The scientists then calculated the phylogenetic endemism (PE) for each cell - meaning the likelihood of each species being present in the cell, that species' overall range and the total diversity of all species in the cell.

A cell containing animals that were distantly related to each other and confined to small ranges would have a high PE score. A cell populated with closely related animals with larger ranges would have a low PE score.

Biodiversity hotspots

The resulting PE mapping of the studied forest region showed that there were some pockets of high biodiversity, such as the Kenyan coast and the Pugu Hills in Tanzania. Ten hotspots, which cover 10% of the region studied, account for 25% of the total PE score. But in these hotspots, very little of the land is protected and it often excludes the areas with the highest PE levels.

Biodiversity heatmap of the Pugu Hills in Tanzania

The Pugu Hills in Tanzania are a biodiversity hotspot. The protected areas (in grey), however, miss many of the sites of highest phylogenetic endemism (PE).
 

Questions for conservation resources

What does this mean for conservationists? The paper's authors say that, ideally, protected areas should cover some of these unprotected hotspots - but there are significant challenges to this. The region's human population is rapidly growing, and there are limited funding and resources available for conservation efforts.

Dr Loader concludes, 'Given the rapid loss of most forests outside governmental reserves, our research suggests that strengthening protected areas that fall within identified PE hotspots would perhaps be the best strategy to conserve the biodiversity and evolutionary history of this region.