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The Biosphere and Animal Distribution Chapter 37
Earth Environment - Overview Water has physical properties critical to life on earth. The steady supply of sunlight maintains a suitable range of temperatures for life metabolism. Living matter requires a supply of major and minor elements available on earth. The earth’s gravity is strong enough to hold an extensive gaseous atmosphere.
Earth Environment The environment is modified by organisms. Organisms are adapted by evolution to the environment. The earth is an open system with a continuous supply of energy. Building materials for life come from producers and are cycled through consumers. Life is part of a cycle of life-death-decayrecycling.
Earth Environment The primitive earth of 4. 5 billion years ago had a reducing atmosphere of ammonia, methane, and water and was fit for pre-biotic synthesis of early living forms. This early atmosphere would be fatal to today’s organisms. The appearance of free oxygen in the atmosphere is an example of the reciprocity of life and the earth. Living organisms produce changes in their environment and must adapt and evolve.
Biosphere The biosphere is the thin outer layer of the earth capable of supporting life. Includes living organisms as well as the physical environments.
Biosphere - Subdivisions Lithosphere – rocky material of the earth’s outer shell. Source of mineral elements required for life. Hydrosphere – water on or near the earth’s surface. Atmosphere – the gaseous component of the biosphere. Atmospheric oxygen is produced by photosynthesis.
Greenhouse Effect Materials in the atmosphere, such as CO 2 and water vapor retain heat, raising atmospheric temperature. Greenhouse effect Burning fossil fuels increases CO 2 in the atmosphere.
Greenhouse Effect The greenhouse effect provides conditions essential for life on Earth. Humans are increasing this effect. Increased temperatures could lead to a rise in sea level as polar ice melts.
Biomes Varying combinations of both biotic and abiotic factors determine the nature of Earth’s many biomes. Biomes are the major types of ecological associations that occupy broad geographic regions of land or water.
Biomes Each biome grades into the next – without sharp boundaries. Boundary areas are called ecoclines.
Terrestrial Biomes Climate is particularly important in determining why particular terrestrial biomes are found in certain areas. Temperature Rainfall Solar radiation
Terrestrial Biomes The sun’s rays strike higher latitudes at a lower angle. Atmospheric heating is less.
Terrestrial Biomes Air warmed at the equator rises and moves toward the poles. Replaced by cold air moving away from the poles. Rotation of the earth complicates this pattern. Three latitudinal cells result.
Terrestrial Biomes Hot, moist air rises at equator, cools, condenses and provides rainfall (tropical forests). Warm air flows northward, and sinks at 20 -30° latitude – dry. Air heats, absorbs moisture (desert areas), then the air flows toward the equator again.
The Distribution of Major Terrestrial Biomes
General Features of Terrestrial Biomes Vertical stratification is an important feature of terrestrial biomes. Canopy Low-tree Shrub understory Ground layer Forest floor (litter layer)
Temperate Deciduous Forest Temperate deciduous forests receive rain year-round. Cold winters and hot, humid summers. Animals may migrate, hibernate, or survive on scarce available food or stored fat through the winter.
Coniferous Forest Coniferous forests, or taiga, are common in the northern hemisphere. Evergreens dominant Colder, less rain than temperate forests.
Coniferous Forest Mammals that inhabit coniferous forests include deer, moose, elk, snowshoe hares, wolves, foxes, lynxes, weasels, bears. Adapted for long, snowy winters.
Tropical Forest Tropical rain forests receive lots of rain and are generally warm year-round. Stratified Diverse
Tropical Forest Canopy – insectivorous birds and bats fly above the canopy. Fruit bats, canopy birds, and mammals live in the canopy eating leaves & fruit. Middle zones are home to arboreal mammals (monkeys, sloths), birds, bats, insects, amphibians. Climbing animals move along the tree trunks feeding at all levels. Ground level contains larger mammals (capybara, paca, agouti, pigs) as well as a variety of reptiles and amphibians.
Tropical Forest Nutrients in a tropical forest are tied up in living organisms. Soil is poor. Slash and burn agriculture involves removing vegetation to grow crops – but the soil is so poor that the fields must be moved often.
Grassland Temperate grasslands receive seasonal precipitation and have cold winters and hot summers. Prairie
Grassland Grasses and herds of large grazing mammals are dominant. Jackrabbits, prairie dogs, and ground squirrels are common. Predators include coyotes, cougars, bobcats, raptors, badgers, and ferrets.
Grassland Savannas are tropical grasslands with seasonal rainfall.
Grassland Chaparral receives highly seasonal rainfall. Shrubs and small trees are common. Adaptations to fire.
Tundra has a permanently frozen layer of soil called permafrost that prevents water infiltration. Very cold, short growing season. Little rain
Tundra is often covered with bogs, marshes, or ponds. Grasses, sedges, and lichens may be common. Lemmings, caribou, musk-oxen, arctic foxes, arctic hares, ptarmigans and other migratory birds.
Desert Deserts have very low precipitation – less than 30 cm/yr. Variable temperatures. Animals often nocturnal and live in burrows. Reptiles and small mammals are common.
Aquatic Biomes Aquatic biomes account for the largest part of the biosphere in terms of area. Can contain fresh or salt water. Oceans cover about 75% of Earth’s surface. Have an enormous impact on the biosphere.
Inland Waters Only about 2. 5% of the earth’s water is fresh. Much of that is found in polar ice caps or underground aquifers.
Inland Waters Lotic, or running water habitats include streams and rivers. More oxygen Lentic, or standing water habitats include lakes and ponds. Less oxygen
Inland Waters LAKES Oligotrophic lakes – nutrient poor & oxygen rich. Eutrophic lakes – nutrient rich & sometimes oxygen poor. Eutrophication An oligotrophic lake A eutrophic lake
Inland Waters STREAMS AND RIVERS Streams and rivers have a current.
Inland Waters Animals living in vegetation or debris of the bottom (benthos) are called benthic. Snails, mussels, crustaceans, insects. Animals up in the water column are pelagic. Swimming animals are called nekton. Floating or weak swimmers are called plankton.
Wetlands WETLANDS Wetlands include areas that are able to support aquatic plants. May be freshwater or marine.
Estuaries ESTUARIES Estuaries are transition areas between river and sea. Salinity varies from nearly fresh to the salinity of seawater.
Aquatic Biomes Many aquatic biomes are stratified into zones or layers defined by light penetration, temperature, and depth. The photic zone is the most productive.
Rocky Intertidal Zone The rocky intertidal zone is alternately submerged and exposed by the tides. Upper zones are exposed to air longer. Physical stress (desiccation, waves, temp, salinity), predation, and competition produce distinct bands.
Rocky Subtidal Zone Kelp forests dominated by brown seaweeds occupy shallow subtidal waters. Grazing urchins and molluscs are common. Predators include sea stars, fishes, and otters.
Rocky Subtidal Zone CORAL REEFS Coral reefs are limited to the photic zone in tropical marine environments with high water clarity. Highly diverse
Nearshore Soft Sediments Intertidal and subtidal environments with soft sediments include beaches, mudflats, salt marshes, sea-grass beds, and mangrove communities.
Nearshore Soft Sediments Salt marsh habitat includes grasses, mussels, crabs, shrimp, and polychaetes. Burrowing organisms. Deposit or filter feeders. Small fishes and birds that feed on them are common.
Nearshore Soft Sediments Calm, tropical, coastal areas support mangrove communities. Mangrove trees grow submerged in soft sediments. Rich community of detritus feeders (oysters, crabs, shrimp). Many fishes – often used as a nursery ground.
Deep-Sea Sediments The deep sea includes the continental slope, continental rise, and abyssal plain. Sand where there are currents, fine mud where currents are weak. Suspension feeding invertebrates are common. Deposit feeders found in muddy areas.
Hydrothermal Vents Hydrothermal vents occur on the abyssal plain in areas of submarine volcanic activity. Archaebacteria that derive energy by oxidizing sulfides form the basis of the food chain. Grazed by bivalves, limpets, and crabs. Other organisms, like tube worms, have symbiotic archaebacteria.
Pelagic Realm The pelagic realm includes the open ocean area. High oxygen, low nutrient levels. Areas of upwelling bring nutrients up from the sea floor. OCEANIC PELAGIC BIOME
Pelagic Realm Epipelagic – surface waters Mesopelagic – twilight zone, supports a varied community of animals. Deep sea forms depend on a rain of organic debris from above.
Zoogeography describes patterns of animal distribution and species diversity. Why species and species diversity are distributed as they are.
Zoogeography The history of an animal species must be documented before we can understand why it lives where it does. Camels originated in North America and spread to Eurasia, Africa, and South America. Camels went extinct in North America 10, 000 years ago. Today, we see true camels in Eurasia & Africa and camel descendents (llamas, alpacas etc) in South America.
Zoogeography Geologic change is responsible for much of the alteration in animal distribution.
Zoogeography Phylogenetic systematics allows us to reconstruct histories of animal distributions. Geographical distributions of closely related species are mapped onto a cladogram to generate hypotheses of the geographic history.
Zoogeography Disjunct distributions are closely related species that live in widely separated areas. Dispersal – a population moves to a new location. Vicariance – environmental changes break up a once continuous population into small pockets.
Distribution by Dispersal involves emigration from one region and immigration into another. One way outward movement. Different from a periodic movement back & forth. Active or passive Center of origin Explains movement of animal populations into favorable habitats adjacent to the place of origin.
Distribution by Vicariance Areas once joined may become separated by barriers. Population becomes fragmented into smaller, isolated populations. Lava flows Continental drift Emergence of mountain ranges
Distribution by Vicariance by continental drift helps to explain the disjunct distribution of ratite birds. Ancestral species widespread throughout Southern Hemisphere.
Distribution by Vicariance As the continents moved apart, the ancestral species was fragmented into disjunct populations that evolved independently producing the diversity seen today.
Continental Drift The concept of continental drift was proposed by Alfred Wegener in 1912. Not fully accepted until the mechanism was found.
Continental Drift Plate tectonics is the mechanism of continental drift. The earth’s surface is composed of 6 -10 rocky plates which shift position on a more malleable underlying layer.
Continental Drift Pangaea – the single great landmass – broke up 200 million years ago. Two supercontinents resulted: Laurasia – North America, Eurasia, Greenland Gondwana – South America, Africa, Madagascar, Arabia, India, Australia, New Guinea, Antarctica
Continental Drift Continental drift explains several puzzling distributions of animals. Similarity between some organisms in South America and Africa.
Continental Drift - The Case of Marsupial Evolution Marsupials appeared about 100 million years ago in South America. They spread through Antarctica and Australia that were at that time joined together.
Continental Drift - The Case of Marsupial Evolution Marsupials encountered placental mammals in North America, could not compete, and became extinct. The modern opossums are recent arrivals from South America. The placental mammals expanded into South America, but the marsupials were well established there. About 50 million years ago, Australia drifted apart from Antarctica and remained in isolation with only marsupials to diversify on the continent.
Wallace’s Line Wallace’s line represents a geographic separation between Asian and Australian faunas. A collision of tectonic plates brought formerly distant land masses closer together.
Temporary Land Bridges Temporary land bridges have been important pathways for dispersal. Land bridge connected Asia and North America across the Bering Strait. Today, a land bridge connects North and South America
Climatic Cycles and Vicariance l Glacial cycles have occurred with durations of 20, 000 to 100, 000 years within the past three million years. l Taxa sharing the same areas typically differ greatly in evolutionary age and in phylogenetic branching pattern.
Climatic Cycles and Vicariance Cycling temperatures interact with the habitat requirements of animals.