Field guide training: Amphib­ians – Part 1

The word „amphibian” originates from the Greek words “amphi” (doubled, shared) and “bios” (life). Both words connect to the characteristic way of life between land and water. The difference between reptiles and amphibians is that amphibians rely on the presence of water because even if they spend their life on land (there are few species which are entirely terrestrial), they must get back into water for reproduction and egg deposition, otherwise their offspring would not be able to survive. This leads to a second characteristic of amphibians. While they are growing they go through metamorphosis. At first tadpoles develop from the eggs. During this phase the amphibians are swimming and breathing through gills and are totally dependent on their aquatic surroundings. Over time the tadpoles grow to small amphibians and at some stage move from water to land. This is when their breathing system changes from gill to lung breathing.

The largest group of amphibians are the batrachian, to which frogs and toads belong. Worldwide over 3400 species are known in total. In Southern Africa there are 157 species, from which 115 can be found in South Africa. Another group of amphibians are the salamanders, including the newt. This chapter will focus on toads and frogs as they are the largest group of amphibians in Southern Africa.

Below you can find the important differences in characteristics between frogs and toads.

Frogs:

• A rather slender body shape
• Long legs made for swimming
• Moist skin with mucilage glands
• Eggs are laid in lumps
• Even though the animals live on land, they always try to stay in close distance to water

Toads:

• Compact body form
• Short legs made for walking
• Dry skin covered with warts and glands (a poisoning secretion is excreted when danger occurs)
• Eggs are laid in form of a line
• Toads are living on land and do not necessary stay close to water. Therefore, they can be found far away from water bodies

Ein Charakteristikum, dass sowohl bei den Kröten als auch bei den Fröschen zu beobachten ist, ist ihr Gesang während der Paarungszeit. In der Regel singen die Männchen, um die Weibchen zu beeindrucken. Im Okavango-Delta im Nordwesten Botswanas kann zur Paarungszeit ein wahres Froschorchester erleben. Kommt es zur Paarung (im englischen „mating“), besteigt das oft kleinere Männchen den Rücken des Weibchens und lässt sich von ihm herumtragen. Erst zur Eiablage trennen sich die beiden wieder voneinander. Einige Arten tragen gar ihren Laich auf dem Rücken mit sich herum; dieses Verhalten kann als Brutpflege bezeichnet werden.

One characteristic which can be observed in frogs and toads is their call during mating season. Generally, males call to impress the females. In the Okavango Delta in the northwestern part of Botswana a true frog-orchestra takes place during the mating season. When mating takes place the smaller male climbs on the back of the female and let her carry him around. They only separate for the egg deposition. Some species even carry their spawn on their back; this behaviour can be counted as brood care.

By the way: The difference in size between male and female is also called “sexual dimorphism”.
Batrachians play a vital role in many ecosystems as they are secondary consumers. They function as the connection between primary consumers (e.g. insects and spiders) and tertiary consumers like birds or other predators (e.g. fish otter). The disappearance of batrachians as a result of e.g. contamination would lead to a sensitive disturbance of the ecological balance and in severe cases to species extinction. Therefore, nature and species conservation projects in many wetlands are focused on this certain category of animals.