Do Elephants Support Frogs?

A major research question at our museum is: “What influences the diversity of organisms?”. Some factors are straightforward, e.g. meteorite impacts or loss of habitats like rainforests.

Others are more elusive. Recently we started to investigate the question whether large herbivorous mammals impact the amphibian diversity in African savannas.

West African savannas comprise many different vegetation types. They are home to a huge number of plants and animals, including more than 40 species of snakes and 30 species of frogs and toads.

Some examples of the amphibian diversity: The crowned bullfrog, Hoplobatrachus occipitalis

Variable Reed Frog, Hyperolius concolor

Ptychadena pumilio (the species has no English name!)

Hyperolius igbettensis, a species of the African reed frogs

Mating couple of Afrixalus vittiger, a species of the spiny reed frogs.

One reason for this high diversity of amphibians is the large variety of different breeding ponds: From tiny temporary puddles to large permanent lakes, from almost vegetation-free sites ...

... to ponds with dense vegetation.

The existences and persistence of smaller ponds without vegetation is the result of the activity of larger mammals (like elephants, buffalos, or warthogs), which use these sites for their mud-bathing.

We were in the fortunate situation to possess a large dataset of amphibian occurrences collected prior to the mammal decline. Now we only had to find the same ponds again …

... and then collect new data for comparison.

Some species, like the running frogs (here the Senegal running frog, Kassina senegalensis) seemed to be not affected by the habitat change at all. The tadpoles of these species can feed on a wide variety of different food sources, including animal and plant matter.

Others, like the minute leaf-folding frogs (Afrixalus, here A. weidholzi) dramatically increased in numbers. The mating couples of these species fold grass leaves growing in water and put the fertilized eggs into this envelope. About a week later, the tadpoles then drop into the water during heavy rains. The increase of dense pond vegetation apparently is a big advantage for these frogs.

However, some species like the African ornate frog (Hildebrandtia ornata) require shallow puddles with muddy edges. They became very rare.

This was also the case for the previously almost omnipresent Red rubber frog (Phrynomantis microps). This species actually accepts overgrown ponds for breeding. However, the tadpoles prefer open water. Their predators are manifold and numerous (e.g. dragonfly larvae, diving beetles, fish, or turtles). As they do not swim very fast, they congregate in schools. This strategy seems to be only effective in open water.