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But giant otters also live in the Orinoco. In regards to Orinoco crocodile they get out competed by caimans when their densities fall below a certain point because the caiman has a higher fertility rate. However I don’t know how quickly/slowly the American Crocodile breeds, but in either case that shouldn’t be an issue in coastal areas since caimans are freshwater.
Giant River Otters are indeed wide spread through other parts of northern South America but they are not present in the Orinoco regions where the Orinoco crocodiles are. You can look at the two maps that show their respective territories. Elsewhere the otters are in small enough numbers to not have any great impact on other predators but elsewhere they are also nowhere near in the same numbers as those numbers that occupy the Guianas where the largest populations of the otters remain, but there are no crocodiles there. Coincidences perhaps?
Giant River Otters are indeed wide spread through other parts of northern South America but they are not present in the Orinoco regions where the Orinoco crocodiles are. You can look at the two maps that show their respective territories. Elsewhere the otters are in small enough numbers to not have any great impact on other predators but elsewhere they are also nowhere near in the same numbers as those numbers that occupy the Guianas where the largest populations of the otters remain, but there are no crocodiles there. Coincidences perhaps?
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It is a compelling theory, by again are not the giant otters a freshwater species? The American Crocodile thrives in salt and brackish waters with the mangroves being their prime habitat. So in that regard shouldn’t the American crocodile move down the South American Atlantic coast unimpeded until it reaches the subtropics in southern Brazil? Even if they end up being restricted to just the coastal habitat?
It is a compelling theory, by again are not the giant otters a freshwater species? The American Crocodile thrives in salt and brackish waters with the mangroves being their prime habitat. So in that regard shouldn’t the American crocodile move down the South American Atlantic coast unimpeded until it reaches the subtropics in southern Brazil? Even if they end up being restricted to just the coastal habitat?
Seasonal temperatures are too cold for crocodiles to survive in southern Brazil, especially so in the winter months. Crocs everywhere in the world have to self-regulate their own body temperatures on a daily basis to maintain it at around 33 C. at all times. In the warmer equatorial climes, during the summer they spend the day time in the water to protect themselves from too much radiant sun heat and the night time is spent on land when temps are cooler and more tolerable. During the winter they spend the daytime on land to absorb radiant heat and the night time is spent in the water because the water is warmer than the ambient air temps on land. They can't do that in southern Brazil because, even in the summer, it's still too cold for them on either land or in water and the coastal regions are always colder than inland regions because of oceanic climate.
I think what k7 meant was that if there are dolphins around, the piranhas will skedaddle rather than become lunch. So if you're in the water playing with the dolphins, you don't need to be worrying about piranhas coming around to nibble on you. ;-)
In Amazonia, the only natural predator of piranhas are the fresh water dolphins aka pink dolphins. I was in my kayak early, early one morning and several piranhas literally skittering across the top of the water. Behind them was a graceful pair of beautiful pink dolphins, feeding early in the morning light.
You must have never heard of the payara, aka vampire fish. Their diet consists primarily of piranhas in certain areas. Fascinating creature.
Crocs were not able to swim through the more open salt water Atlantic Ocean to reach the mouth of the Amazon, like they could travel through the shallow and warmer Caribbean to reach the Orinoco or rivers in Central America. Not being able to reach the mouth of the river meant not being able to spread up its tributaries, so no Crocs in the Amazon basin.
Why did Caimans make it? My guess is because most are smaller and thus were able to "puddle jump" and survive in vernal pools, small streams, etc. to spread across broader stretches of land to reach the Amazon basin. Once there, they diversified and the larger species evolved.
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