Cane Toads is one of the classics of nature documentaries that focus on biological invasions. It is a remarkable story of a species being extremely successful in an environment that is free from diseases, parasites and predators. On top of that, cane toad is a predator itself. Feeding on naive prey that have evolved no defenses boosts the reproductive success. Cane toad become a paradigm for invasive species that achieved abnormally high population densities compared to that of it’s native range. In such cases, the carrying capacity of the ecosystem becomes severely stressed.
Introduced species have had a rather bad record with unintended consequences. Nile perch exterminated cichlid populations in lake Victoria and caused deforestation because unlike naive fishes that can be sun dried it had to be smoked to store. Johnsongrass is a notorious agricultural weed in Americas. Starlings released in New York Central Park now migrates in the millions between north and south America. Africanized honey bees escaped in Brazil is changing pollination patterns of tropical rainforests trees while expanding towards north America. Lionfish is feeding voraciously on reef fish and altering the biological community structure. The list is very long.
The Cane Toads was so successful that the director Mark Lewis shot an extended version of it in 2010. The documentary has the wonderful Australian humor that makes us giggle in the face of this rather miscalculated ecological tragedy. It exposes us briefly to amphibian life history including the familiar amplexus mating position which is essential for external fertilization. We also see the metamorphosis of tadpoles developing legs and lungs while loosing tail to emerge on land. Most frogs don’t invest on their offspring through parental care but there are exceptions.
Cane toads (Rhinella marina) were brought in to control a pest of sugar cane plantations in the tropical northeast Australia. Sugar is a very effective driver in animal behavior. Glucose is the sole fuel of the brain. The history of humans with sugar goes back to more than 10 thousand years ago to the island of New Guinea where sugarcane was first domesticated. Together with humans sugarcane also spread and reached Asian mainland. Indian Ocean is the first place where a truly global economy emerged in human history thanks to Arab sailor merchants. These sailors brought sugar everywhere in the old world and until the discovery of the new world Ottomans controlled its trade. Sugarcane completed it’s world journey a few centuries ago when it was brought to the Americas.
Amphibians are on the decline globally due to a skin infection by the chytrid fungi and introduction of exotic species affects their survival negatively.