Mating for most amphibians still takes place in water, with the males grasping the females and fertilization taking place externally, with the sperm cells swimming to the egg cells. Large numbers of eggs are produced to offset high mortalities of eggs and tadpoles. Other frog species have a different strategy whereby comparatively few eggs are laid, but considerable parental investment protects them from predators. Some tropical pond-dwelling frogs (e.g. Dendrobates pumilioand Osteopilus brunneus) find safety for their tadpoles by depositing eggs in centres of plants such as bromeliads which create small reservoirs of water in forests where the rainfall is high. These sites are safe from aquatic predators. In Dendrobates pumilio males and females divide parenting duties; males guard the eggs until they hatch (10 to 12 days) thereafter the females assumes care for the young. The females begin by transporting each newborn tadpole to from desiccation and predation, the tadpole has no food supply and is entirely dependant on its mother for nutrition until it metamorphoses into a froglet which takes six to eight weeks. In Brazil, another small frog builds its own ponds at the margins of forest pools, constructing a crater ringed with low mud (100 mm in height). The eggs are laid and the tadpoles stay in their exclusive water residence until the rain raises the level of the main pool and floods the crater created by the parent frogs.