Lecture 24

Patterns and Processes of Evolution in the Tropics Biodiversity of Neotropical Fishes Courtesy of Ray Troll The Aquatic Environment Physical Environment ? W ater body size varies from mudpuddles to the largest rivers on earth Availability of water varies on a seasonal basis W ater types include white, clear, and black The Neotropics has some of the largest rivers in the world. Orinoco Negro Amazon Parana/ Paraguay Water Body Size A small stream in Panama The Amazon floodplain near the Brazil-Colombia border Water Periodicity During the year, heavy rains and periods of drought contribute to large differences in the depth of water. In the wet season, the forest is submerged and in the dry season, water may be restricted to small channels or lakes. Low water/high water Low water season leaves much of the forest above the water. High water season is a time when much of the floodplain forest is inundated. Low water/high water A small floodplain river at lowest water level. Note the piece of wood indicated by the red arrow. The same location about 10 days into the flood season. Notice how the water level has changed. As the water rises, it will inundate the entire area. After the Flood : Receding water left a mat of water plants in the top of this tree. The water level now is at its lowest. Note how high it would have to be to leave the debris. During the Flood : As water rises, it carries debris onto the floodplain floor, providing much new food for young fishes in their nursery grounds. Low water/High water The Scale of the Floods Here the Amazon river floodplain is over 100 miles wide. Water Types C lear water runs off of the hard rocks of the Guyana highlands W hite water runs off of the sedimentary rocks of the Andes mountains B lack water comes from the sandy soils of the flooded forests White water and black water mixing from the Rio Negro and the Rio Solimoes, forming the Amazon Areas where the waters mix The Amazon begins where the Rio Solimoes and Rio Negro meet. The white water is cooler and more dense than the black water, and the two resist mixing, sometime staying apart for many miles downstream. The Biotic Environment There is a ?day fauna? composed primarily of Characiformes (characins) There is a ?night fauna? composed primarily of Siluriformes (catfishes) and Gymnotiformes (electric knife fishes) These two ?faunas? allow many species to live together and share resources The Characiform ?day fauna? includes vegetarian browsers... This pacu, Colossoma , is a piranha relative that feeds entirely on plant material in the wet season. It is often found schooling with red- bellied piranhas, which it closely resembles. Feeders on insects that fall into the water... Copella , with their straight backs, remain just under the water?s surface and are able to grab ants and other insects. Gasteropelecus , a ?hatchetfish,? is able to ?fly,? escaping predators by flapping its large pectoral fins. Pickers of algae and small invertebrates living on plants... Some species swim at particular angles and appear to be specialized to take food from particular places, such as the bottoms or tops of leaves and stems. Abramites Nannostomus Leporinus Nannostomus An example of specialized morphology to take food from particular places... These Anostomus and Leporinus have specialized up-turned mouths and often swim upside down to feed. There are many species of small fishes that are generalists, feeding on insects, detritus, or whatever else is available... Bario Cheirodon Thayeria Some of these small fishes are among the ?butterflies? of the rainforest pools and streams. Hyphessobrycon Nematobrycon Paracheirodon Schooling Paracheirodon In the black waters where these fishes usually live, predators would see a mass of moving bright blue stripes. Characiform predators are also specialized: some feed near the surface Ctenolucius Rhaphiodon Agoniates Some predators feed in midwater Crenuchus are less than 2 inches long, feeding near-shore on small fishes and invertebrates. Hoplias are large predators which make up to 70% of the biomass in some ponds. Some groups of predators have a broad range of diets Many piranhas feed in open water or nearshore on fishes, invertebrates, or even vertebrates. Some piranhas feed almost exclusively on fins and scales, while others feed on fruits and other plant parts. Pygocentrus Serrasalmus Diet of a Piranha Fish Feathers Seeds Insect p arts The stomach contents of a randomly chosen Serrasalmus Other members of the ?day fauna? are members of diverse groups, from elasmobranchs to spiny-rayed teleosts. Potamotrygon , a freshwater stingray. Osteoglossum , a bony-tongue Pterophyllum , a cichlid Aerial respiration is common among many Amazonian fishes Members of the ?Night Fauna? are primarily catfishes and knifefishes Catfishes are usually mid-water to bottom dwellers Pterodoras Pseudoplatystoma Platystomatichthys Other catfishes are specilized for other roles... Cetopsis is a mid-water, fast swimming predator. Ancistrus lives in sunken driftwood and feeds on it. Hypopthalmus feeds on plankton with enlarged gill rakers. ?There are thousands of river creatures we enjoy, but seven that enjoy us! ? Trichomycterus (called candiru) live in bottom sediments waiting to detect current from the excurrent gill openings of large catfishes settled on the bottom. Some catfishes are even parasites on other fishes About to enter the gill chamber of a large catfish. After the meal. Affixed to the gills. Ventral view of the head of Vandellia, showing interopercular odontodes and upper jaw teeth Gill Parasites sometimes make mistakes and swim into the orifices of bathers Courtesy of Ray Troll Alleged attack: From Manaus tabloid Popular da Tarde (early 1990?s) Jobert, 1898, Quoting Dr. Castro of Pará: ? I have myself extracted from the urethra of a woman a little candirú which had penetrated during micturation while bathing in the river. The patient experienced cruel suffering for, since I had to drag the animal out, the mucous membrane was lacerated and the extraction was difficult.? Medical case Description: Trauma and pathology Scrotal edema caused by the perforation of the corpus spongiosum Gymnotiformes, the electric fi shes are close relatives of catfishes that are able to generate their own electrical fields. They detect other fishes, prey, and even mates with this field. Apteronotus Gymnorhamphichthys Sternopygus Gymnotiformes, electric fishes Electrophorus , the ?electric eel? uses electric organs to search for prey and must keep its body straight to keep its electric field from distorting. It propels itself with undulating waves of an elongate anal fin. All gymnotiformes have electrical organs and electroreceptors but only Electrophorus puts out a field detectable without instruments. It has three electric organs, two for electrolocation and one to shock prey. Migrations recycle Nutrients Spawning takes place in main, energy rich, channels and lakes. Adults migrate upstream and enter tributaries into the flooded forests to feed. As water drops, fish migrate from the forests to the main channels, then swim upstream to another major tributary. Human Interactions with the Floodplain and its Ichthyofauna P eople must adapt to the water conditions just like all the other inhabitants. F ishes provide ample protein to indigenous people. Threats to the fishery come from overfishing, destruction of nursery grounds, habitat destruction, introduction of exotics, and pollution. Coping with the Floods Some people live in houses on rafts, moving up and down with the water. Some people live in houses on stilts, staying until the flood rises, then moving to higher ground to wait until the flood wanes. Transportation during the flood Fishes have always provided ample protein for the diets of local people The floodplain has supported vigorous fisheries The fish market in Manaus, Brazil was built during the rubber boom during the 19th century. On a typical day 20 years ago there would be 50-75 species of fishes there. Today the fish selection is much smaller. The fish being prepared on the right is now commercially extinct in this area. A typical catch in Manaus Osteoglossum Cichla Astronotus Impact of Human Development Virgin rainforest Forest destruction at an early stage. Complete elimination of rainforest for cattle ranching. Biodiversity of Neotropical Fishes Patterns and Processes of Evolution in the Tropics William L. Fink Neotropical Fish Diversity