Few biologists, including ecologists, realize that large top carnivorous vertebrates, such as crocodiles, play important roles in structuring aquatic ecosystems. According to Robert Paine, such top carnivores are called keystone species.
It took me a long, long time to appreciate crocodiles as performing this ecological role. From the 1950s to the late 1980s, a period of four decades of study of small amphibians and reptiles, I fully realized that crocodiles, which are generally feared — even hated — by many people, are indeed, in the final analysis, friends and ecological allies of human beings.
For in terms of biomass, a crocodile is several hundred times more massive than the vertebrates such as frogs, lizards and snakes. They, therefore, have a larger ecological impact on aquatic environments compared with the much smaller amphibians and reptiles. It is expected then that when crocodilians are present in moderate to large numbers, the river systems they inhabit are highly productive of fish.
Unfortunately, it is too late to demonstrate this fact because the Filipinos have almost exterminated these animals in their natural habitats, except on few islands where they are few individuals still remaining to this day.
It was the German scientist, E.J. Fittkau, who showed the positive relationship between crocodilians and fisheries in rivers systems of the Amazon.
Fittkau observed that when caimans (a type of crocodilian) were heavily exploited in river streams, there were fewer fish, but when there were many caimans in the wild, fish was abundant in the lower portions of rivers.
He explained this phenomenon as due to a large supply of nutrients from the feces of crocodilians. These nutrients caused the high plankton concentrations, which in turn caused the high fishery production in the aquatic habitats.
Crocodilians also fed on terrestrial animal species, thus, adding to the total nutrients available for fish production in the river systems. Crocodiles, in effect, link the aquatic environment with the terrestrial environment. Because crocodilians are large carnivores with large biomasses, and require large amounts of animal food, their ecological impact on the productivity of aquatic ecosystems is very high.
For example, Crocodile Lolong, the largest crocodile of the species, Crocodylus porosus, in the world (20.4 feet in mean total length and a weight of 1,075 kilograms) requires 10 kilograms of animal feed every 10 days, or 30 kilograms per month. One can imagine the large mounts of nutrients produced by this crocodile.
Of course, smaller individuals require smaller amounts of animal feed. If their numbers are large, the nutrients released into the water could be substantial to result in high productivity of aquatic ecosystems in which they occur.
There is, of course, a conflict between humans and crocodiles, but in our land where a multiplicity of habitats exists, there should be a policy and programs that would allow both humans and crocodiles to co-exist. And there should be room for humans and crocodiles to co-exist in certain localities, provided, care is exercised to prevent them from disturbing, or coming in direct contact with each other.
For this to happen, we, as creatures of a higher order, should take the lead in ensuring that humans and crocodiles continue to exist in our land. This is what is being done in many countries of the world; we can do no less.
