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EEBIOL 151 Creatures of the rivers


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South American Rivers
Amazon, Orinoco
African Rivers
Congo (Zaire), Niger, Nile
Southern Asia Rivers
Mekong, Ganges
Amazon region
- was once a huge inland sea/lake - was caught between 2 higher, ancient geologic structures (Guyana highlands and Brazilian highlands) - River outlet was to the west before the Andes formed.
Amazon drainage
- not longest, but volume flowing is huge - twice per month major tides by force of moon (pororoca) - has been 80 m deep in the past - first fully explored by Francisco de Orellana
accounts of Amazon explorers
- First discoverer was Amerigo Vespucci - Traveled 150 miles up river - convinced Vespucci that the new land was not an island, that it must be a continent, so it couldn't be the West Indies - originally called Pinzon Rio Maranon
- only 3 living species, all occur in tropical regions - Amazon lungfish is closely related to the Congo/African one (remember that these two continents were once joined) - Queensland lungfish was derived from a once marine family of lungfishes, and adapted to fresh water. Other marine versions died out.
Fishes - Amazon and Africa
- most endemic freshwater fish spp. of Amazon are ancient and share ancestry with African versions. - characins (tetras, other aquarium fish) - catfishes - cichlids - knifefishes of S. America evolved from Amazonian characins - remnants of Gondwanaland connection more than 110 MYA
Cichlids of east african lakes
These are the fish that have radiated in the east african lakes. The ones they use as an example of adaptive radiation.
Big Animals of the Amazon River
- Giant catfish - black caiman - anaconda - amazonian manatee - amazonian sideneck turtle river dolphins (2 spp, pink and grey) - 6+ m sawfish in lower river
Amazon Sideneck River turtle
- also called arrau (tartaruga) - is a huge herbivore that can grow to 70 kg (150 lbs) and live 30 years, and can get a carapace (shell) up to 1 m long - females lay eggs resembling ping pong balls in sandbars during dry season; they choose certain sandbars that aren't eroded by storms or washed away by rain. - eggs incubate 2 months in warm sand - hatchlings scramble to get to water, high predation rate. - named for the s-shaped swan neck they have
Arapaima (amazon) and Dragon fish/arowana (s. asia)
- amazonian species up to 3 m, 250 lbs. - mother cares for young for 4 months with milky fluid from pores in head - amazonian arowana are excellent jumpers, sometimes called macaco d'aqua (water monkey) - can jump out of water and get stuff from low hanging branches - Asian arowana hatch young in mouth of male (parental investment)
River dolphins
- freshwater species, eat cichlids and characins. - in the Amazon, there's a pink species and a gray species - superstition: lure women into water to have intercourse with them
freshwater manatees and Dugong
- eat aquatic plants - amazon manatee - indo-pacific dugong - west african manatee - eat hyacinth, water lilies, water lettuce, etc. - can submerge for 3 minutes and have few natural predators except humans. - manatees are freshwater, dugong is sea water species, occurs along coastal forests
Aquatic plants
- abundant in quiet, warm waters - 3 general life strategies: floating plants/leaves with no anchoring, submerged, feather aquatics, or plants that only let leaves stick out of water. - life is easy, with all the water and nutrients they need. - food for mammilian herbivores like manatees, capybaras, and hippos.
Giant Water lily/Victoria water lily
- a giant amazonian water lily greater than 1 meter across - have pictures of babies in these, while they are still floating. - live in shallow backwaters
- a python and constrictor, so it squeezes prey - semi aquatic; will usually only come onto land to slither between pools in the dry season - lays eggs - rumored to prey on human children - females can grow 10+ m long, while males are only 1/5 this size. - may exceed 250 kg - females are largest snakes in the world
7 deadly plagues of Rivers Amazon
- anaconda - piranhas - piraiba candirus electric knifefish (saporo) - stingrays - black caiman
- have an exaggerated reputation - razor sharp teeth, powerful jaws, give coin sized bites - especially dangerous when trapped in shallow water - attracted by commotion, blood, red coloration
flesh-eating catfishes
- parasites of larger fishes in Amazon. chew holes in them and suck blood. - greatly feared because a school can skeletonize a human in less time than piranhas - attracted to smell of urine
Electric knifefishes (electric eels) of S. America
- described by Alexander von Humboldt - difficult to capture, he exhausted them with animals - use electricity to hunt, by creating a field around themselves and sensing disturbances in it - can emit shock of up to 800 volts - electric organ in tail generates the signal, and electric receptor pores are found in the head. - can swim backwards
Fishes and seed dispersal
Certain fishes eat fruits and thereby disperse seeds of plants in S. America, especially in Varzea where it is flooded for a few months of the year.
Perils of African Waterways
- hippos - crocodiles
- huge herbivores, easily angered, very territorial - large body size eliminates all natural predators - can hold breath up to 6 minutes. - feet have nails, and not hooves - stay in shallow water and walk along the bottom of the riverbed. Can't swim. - close ears and nose when submerged, but communicate through clicks that sound like dolphins. this is because they are closely related to dolphins.
- 22 species - are sit and wait hunters - eyes supposedly can see color - advanced brain - valves over ears, nostrils, and membrane over eye to protect these senses. - crocodiles, alligators, gavials - sex of offspring is determined by temperature. Lower temperatures make females, higher temperatures make males. - females guard nests and then care for young until they can forage on their own - only one species can deal with saltwater, and it has special adaptions such as salt glands on the tongue that excrete drops of concentrated salt solution
Australia aquatic animals - monotreme
- duck billed platypus, lays eggs - has a venom gland in thigh and a spur on the back foot by which this can be delivered - bottom feeder with a sensitive "bill"
anurans (frogs)
- saltatory movement (jumping) - see mostly sharp edges/movement, so they can't see well unless something moves in front of them. If it is bigger than them, they leave it alone, smaller and it is potential prey. - projectile tongue - tongue is attached to the front of the mouth. Jaw drops open, tongue flops out, and stretches, and catches prey on a stick tip before being yanked back in. - fertilized eggs are in water, protected from dessication but vulnerable to aquatic predators - have complete metamorphosis - about half of all frogs in the world are native to Neotropics. - pools can have up to 10 breeding spp at a time, with separation by mating calls.
Anurans - where they place eggs
- can place in ponds, but have high predation rates and competition with other tadpoles. - can also use tank epiphytes, or tree hollows - foam nest construction (where adults beat the jelly stuff surrounding the eggs into a foam, which then solidifies and provides protection and food for young) - highly humid leaf nest - several tree frogs have internal fertilization

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