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BIOL 4120: Principles of Ecology Lecture 22: Biogeographical Ecology Dafeng Hui Room: Harned Hall 320 Phone: 963-5777 Email: [email protected] 23 Terrestrial Ecosystems 23.1 Biomes and climate 23.2 Tropical forests (Equatorial zone) 23.3 Tropical savannas (semiarid regions with seasonal rainfall) 23.4 Desert 23.5 Temperate zone (Mediterranean climate) 23.6 Forest ecosystems (Temperate wetter regions) 23.7 Grassland ecosystems (Temperate zone vary with climate and geography 23.8 Conifer forests (cool temperature and boreal zones) 23.9 Arctic tundra (cold temperatures and low precipitation) Biomes are classified according to the predominat plant types Concept of Biomes: F.E. Clements and V.E. Shelford, 1939 Combining broad-scale distribution of both plants and associated animals into a single classification Biomes: classified according to the predominant plant types Campbell 1996: the world's major communities, classified according to the predominant vegetation and characterized by adaptations of organisms to that particular environment. Major terrestrial biome types: Tropic forest, temperate forest, conifer forest (taiga and boreal forest), tropical savanna, temperate grasslands, chaparral (shrublands), tundra, and desert. three general plant forms: trees, shrubs, and grasses. Robert Whittaker, Cornell Uni. Biomes and climate Boundaries between biomes are broad and often indistinct Other factors: topography, soils, and exposure to disturbances such as fire 23.1 Terrestrial ecosystems reflect adaptations of dominant plant life forms Why are there consistent patterns in the distribution and abundance of three dominant plant life forms that relate to climate and physical environment? Terrestrial ecosystems reflect adaptations of dominant plant life forms These three forms represent different patterns of carbon allocation and morphology Grass: less C to production of supporting tissue (stem) than do wood plants (shrubs and trees), more to photosynthetic tissues (leaves) Woody plants: shrubs allocate lower percentage to stem than trees. Trees: more to stem, advantage of height and access to light, cost more for maintenance and respiration. As environmental conditions become adverse for photosynthesis (dry, low nutrient, cold T), trees will decline in both stature and density until they are no longer able to persist as a component of the plant community. Forests Within broad classes of forest and woodland ecosystem (trees are dominant or co-dominant), leaf form is another plant characteristic. Based on longevity Deciduous (live for only one year or growing season) • Winter-deciduous (temperate regions, low winter T) • Drought-deciduous (subtropical and tropical, leaf shed on dry periods) Evergreen (live beyond a year) • Broadleaf-evergreen (tropic rainforest, no distinct growing season, year-round photosynthesis) • Needle-leaf evergreen (growing season is short or nutrient availability constrains photosynthesis and plant growth) Economic model to explain adaptation of leaf form: cost to produce leaf and gain from photosynthesis. Ecosystems characteristic of warm, wet climates with no distinct seasonality are dominated by broadleaf evergreen trees (tropic or subtropical rain forest). As conditions become drier, with a distinct dry season, broadleaf evergreen habit gives way to droughtdeciduous trees (seasonal tropical forest) As PPT declines further, trees decline and giving rise to woodland and savannas (shrub and grasses). PPT further declines, no trees can be supported, giving rise to arid shrubland and desert. Similar for T control. Winter-deciduous Drought-deciduous Broadleaf evergreen in tropic rain forest in Australia Needle-leaf evergreen in Sierra Nevada, US 23.2 Tropic rain forest Location: Equatorial zone between latitudes 10oN and 10oS T: warm all year, annual mean T>18oC PPT: rainfall occurs daily, min. monthly>60mm Typical example: Amazon basin of South America Tropic rain forests in Amazon (a), Malaysia (b), and Northeast Australia (c) High net primary productivity (NPP) High diversity of plant and animal life 7% land surface, >50% plant and animal species 10-km2 contain 1500 species of flowing plants and 750 tree species. Richest area in Malaysia, 7900 species 90% of all primate species live in the tropical rain forest orangutan (an arboreal ape) Gibbons, langurs, macaques (Malaysian) Gorillas, and chimpanzees (Africa) Lemurs Beetles, butterflies Vertical stratification of a tropic rain forest Plank-like buttresses Tropical dry forest droughtdeciduous trees Africa, South America, Central America, Australia, India, Southeast Asia Undergo a dry season, influenced by the seasonal migration of Intertropical Convergence Zone (ITCZ) 23.3 Tropic Savannas Location: Equatorial zone between latitudes 30oN and 30oS, Dry tropic and subtropical. T: warm all year, annual mean T>18oC PPT: distinct seasonality in rainfall, large interannual variation Typical example: South America Tropic Savannas Savanna: means the treeless areas of South America An array of vegetation types representing a continuum of increasing cover of woody vegetation, from open grassland to widely spaced shrubs or trees to woodland Characteristics Occur on land surfaces of little relief, often on old plateaus, interrupted by escarpments and dissected by rivers Poor in nutrients, especially P Dominant species are fire-adapted, subjected to recurrent fires. Grass cover with or without wood vegetation is always present Woody component is short-lived (less than a few decades). Two-lay vertical structure (ground level grass + shrubs or trees) Support a large and varies assemblage of herbvores, invertebrate and vertebrate, grazing and browsing. Interaction between annual PPT and soil texture in defining biomes Access by plants to soil moisture is more limited on the heavy textured soils (clay) than sandy oil. 23.4 Desert Area: 25 to 35% Location: latitudes between 15 and 30o Cause: Global air mass circulation T: High in summer, could be cold in winter PPT: low, <150 mm Typical examples: majority in Northern Hemisphere, Sahara in Africa, Gobi in Asia, western North America Deserts are not the same everywhere Cold desert: Great Basin of North America, the Gobi, Takla Makan, and Turkestan deserts of Asia Species: sagebrush, shadscale, chenopods, etc Hot desert: Mojave, the Sonoran, and Chihuahuan Vegetation: none to some combination of chenopods, dwarf-shrubs, and succulents Hot desert: a. Chihuahuan Desert, b. Great Victorian Desert in Australia, c. Dunes in Saudi Arabian desert. Desert Survive of desert plants: Adapted to scarcity of water, low primary productivity Flowering only when moisture is present Fast grow, flower, produce seeds and die Deep-rooted (mesquite, taproots reach water table) CAM pathway, species leaf structure Survive of animals Support a diversity of animal life (bettles, ants, locusts, lizards, snakes, birds and mammals) Grazing herbivores: generalists, consume a wide range of species. Desert carnivores,such as fox and coyotes, have mixed diet include leaves and fruits. 23.5 Temperate shrublands Shrublands: shrub is dominant or codominant, but difficult to categorize Shrub: no good definition, a plant with multiple woody, persistent stems but no central trunk and a height from 4.5 to 8 m. (Tree can grow less than 8m under severe environmental conditions) Temperate shrublands Location: between latitudes 30o and 40o, five regions T: hot dry summers, cool, moist winters PPT: 65% annual PPT falls during winter months. Five regions: semiarid region of western North America, regions bordering Mediterranean Sea, central Chile, cape region of south Africa, south-western and southern Australia Chaparral is the dominant mediterranean shrub vegetation of southern California Mediterranean vegetation (fynbos) of the western cape region of South Africa 23.6 Forest Ecosystems Forest ecosystems dominate the wetter regions of the temperate zone Deciduous forest covered large area of Europe and China, but mostly converted to croplands, only exist in eastern China Southern Hemisphere, temperate evergreen forest become predominant North America, deciduous forests consist of a number of associations (show later) Asiatic broadleaf forest found in eastern China, Japan, Korea is similar to the North American deciduous forest Large scale distribution of temperature forest in eastern US (showed before?) Temperate forest in fall and spring 23.7 Grassland ecosystems Rainfall is very important: 250 to 800 mm Other factors: fire, and human activity (convert from forest to grassland) Area: dropped from 42% to <12% of original size Location: mid-latitudes in mid-continental regions Typical: prairies of North America, steppes of central Eurasia Grassland in North America Tallgrass prairie Big bluestem, >1m Mixed-grass prairie Needlegrassgrama grass Shortgrass prairie Blue grama and buffalo grass a. Tallgrass prairie in Iowa, b. mixed-grass prairie; c. shortgrass steppe Aboveground primary productivity is related to MAP (52 grassland) Grasslands are most productive when MAP>800 mm and MAT > 15oC 23.8 Conifer forests Conifer forests: needle-leaf evergreen Location: Northern Hemisphere and mountain ranges Various composition: wide range of climate they can grow Europe: Norway spruce North America: Rocky: Engelmann spruce, subalpine fir; Douglas-fir, ponderosa pine, lodgepool pine; giant sequoia (in California Sierra) Boreal forest (11% of Earth’s land surface) Alaska and Canada in N. America, Euroasia (from Scotland to northern Japan) Black spruce in North America taiga (boreal forest) Some coniferous forest. A. Norway spruce, b. Rocky Mountaine subalpine forest, c. montane coniferous forest in Rocky Mountains 23.9 Arctic Tundra Tundra is treeless plain Arctic tundra is a frozen plain, clothed in sedges, heaths, and willows, dotted with lakes, and crossed by streams Cold Temperature and low precipitation Two types: tundra: up to 100% plant coverage, wet to moist soil polar desert: dry soil, less than 5% plant cover Unique conditions: permafrost: isolate and protect soil OM vegetation: simple form, slow growth, allocate more to roots transfer of heat Principles of Ecology What we covered in this course: Ecology is study of interaction of Organisms and environmental conditions Organisms: adaptation and evolution, life history Environmental conditions: Climate, terrestrial and aquatic environments Subdisplinary of ecology Population ecology: growth, competition, predation, parasitism Community ecology: structure and dynamics, influence factors Ecosystem ecology: Ecosystem energetic, decomposition, biogeochemical cycle Global change ecology: climate change and ecosystem researches Others: biogeography, human ecology Thank you!