Amphibians 两栖动物(英文)

– No embryonic membranes, – Egg must stay moist
• usually in water, rarely in moist soil
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Amphibian Life Cycle
• Larvae (immature form, tadpoles) hatch in water,
• H3: UV radiation from thinning of ozone layer
– More UV from sun reaching surface of Earth – Amphibian embryos in shallow water killed by UV – Genetic mutations make survivors less viable, less fecund.
• pesticides, excess fertilizers
– Sewage
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AMPHIBIANS as Environmental Indicators
• H2: Global warming (with changes in rainfall) ?
• Adult usually terrestrial, some exceptions
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Amphibian Life Cycle
• Live in two habitats
– exploit two sets of resources
• Produce large numbers of eggs • No parental care, tadpoles “on their own”
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AMPHIBIANS as Environmental Indicators
• H4: Parasites ?
– bird parasites use tadpoles/frogs as hosts for parasite larvae – malformed frogs, extra or missing limbs, etc. – malformed frogs easy prey for herons, cranes, etc.
– Water pollution, – Global warming, – UV radiation from thinning of ozone layer, and – Parasites, etc.
• Common cause ?
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– Gills for gas exchange. – Tail
• Metamorphosis to adult form
– growth of limbs – development of lungs and loss of gills – loss of tail in frogs, toads
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AMPHIBIANS as Environmental Indicators
• Decline in frog, toad, and salamander populations reported, world wide. • Is a worldwide decline real ? • If so, what cause or causes of decline (hypotheses):
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AMPHIBIANS as Environmental Indicators
• H1: Water pollution
– Industrial waste, toxins
• Acids, alkalai, PCBs, etc.
– Agricultural runoff
– cloud forest zones on tropical mountains moved up above mountains; loss of habitat.
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AMPHIBIANS as Envi源自文库onmental Indicators
• Disadvantages
– Each egg/tadpole has small chance of survival
• wasteful
– dependent on water, few can live far from surface water
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Amphibian Life Cycle
• Advantages
– Produce abundant offspring (less investment of matter, energy in each) – At least a few likely to survive.
• Birds, frogs, & parasites concentrated in shrinking wetland habitats
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AMPHIBIANS as Environmental Indicators
• Combination of effects ?
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Class Amphibians
• Less well adapted to terrestrial environment – Smooth skin, no scales (no keratin ?) – External fertilization
• depend on water for mating; sperm and eggs released together into water
Class Amphibians
• Order Salamanders
– Primitive form with four equal legs – Retain tail
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Class Amphibians
• Order Frogs
– Tail lost in metamorphosis – Hind legs enlarged, hopping or leaping locomotion
Amphibians
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Class Amphibians
• Old group of tetrapod (4-footed) vertebrates, older than reptiles. • Origin in mid-Paleozoic
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Class Amphibians
• Order Caecilians
– legless, burrowing (resemble earthworms, but with skull & backbone) – tropical
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