Do Elephants Support Frogs?

Museum für Naturkunde Berlin

How do large herbivores impact African savanna amphibians – An example of research performed at the Museum für Naturkunde Berlin (Mark-Oliver Rödel)

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.

However, during several years of political instability in Ivory Coast, poachers dramatically reduced the numbers of these large herbivores. As a consequence almost all ponds in Comoé National Park in Ivory Coast are now heavily overgrown with vegetation. This pond was deep and vegetation-free in the mid-1990th. Now it is shallow and heavily overgrown. We wanted to know if the decline of the mammals and the resulting changes of pond features had an impact on the amphibian community. 

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.

Hence, the answer to our question „Do elephants (and other large mammals) support frogs“ is both yes and no. Some species suffer, some profit. However, clearly large mammals support more diverse habitats and higher species richness. Unfortunately we still have a long way to go until we can accurately predict the effects of change and human intervention on biodiversity and ecosystem functions. However, climate research does give us hope that hard-to-tackle modeling challenges can be solved, provided enough investment into funding an urgent scientific question can be mobilized. Image: The Chaucer astrolabe from 1326 is an early tool to predict astronomical events; British Museum

(For more information on amphibians we also recommend the presentations by
Frogs and Friends especially Frog Fields on African frog hunting!)

Credits: Story

Photos: Mark-Oliver Rödel (Museum für Naturkunde Berlin); Chaucer Astrolabium: British Museum, used by permission.
Text: Mark-Oliver Rödel, Gregor Hagedorn (Museum für Naturkunde Berlin)


Credits: All media
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