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Transcript
Chapter 25 Lecture Outline Ecology Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Outline Plants and the Environment Life Histories Natural Cycles Succession The Impacts of Humans on Plant Communities Global Warming Erosion Aquifer Depletion Loss of Biodiversity At the Regional Level Restoration of the Land Plants and the Environment Ecology - Involves the relationships of organisms to each other and to their environment • Determines whether or not a species or individual member of a species can survive and reproduce in a particular habitat Environment of each habitat determined by biotic (living) and abiotic (nonliving) factors. • Biotic - Other organisms in habitat • Abiotic - Wind, rain, sunlight, soil, temperatures Plants and the Environment Populations - Groups of individuals of the same species • May vary in numbers, in density, in genetic diversity and in total mass of individuals • Ways to investigate populations: – Count number of individuals – Estimate population density - Number of individuals per unit volume – Calculate biomass - Total mass of living individuals present Plants and the Environment Plant community - Unit composed of all species of plants in a given area • If include other organisms = biotic community • Within a region, similar environments have similar species composition. • However, each species distributed according to own responses to changes in physical and biotic environment. • Species composition of a community determined by local availability of species, by unique historical events, and by chance. Plants and the Environment Plant community • Practical reasons to analyze and classify plant communities (vegetation maps): – Land-use planning – Natural resource management – Biological conservation – Landscape restoration – Analyze changes in vegetation over time – Infer qualities of environment Plants and the Environment Ecosystems - Communities and their physical environments, which interact and are interconnected by physical, chemical and biological processes • Distribution of a plant species in an ecosystem controlled mostly by temperature, precipitation, soil type, and effects of other organisms. – Mineral content of soil – Competition for resources – Herbivory – Dispersal by animal community – Pattern of available water Plants and the Environment Ecosystems may be sustained entirely through photosynthetic activity, energy flow through food chains, and nutrient recycling. Producers - Photosynthesize and store produced energy • Primary consumers - Feed on producers • Cows, caribou, caterpillars Secondary consumers - Feed on primary consumers • Plants, algae Tigers, toads Decomposers - Break down organic material to forms that can be reassimilated by producers • Bacteria, fungi Plants and the Environment Ecosystems: • Producers and consumers interact, forming food chains or food webs. – Determine flow of energy through different levels Plants and the Environment Ecosystems: • Trophic efficiency - Percentage of available energy actually transferred from one trophic level to next – Available energy to secondary consumers quickly drops off. – Sharp reduction in numbers of individuals and in total mass at each level of food chain Plants and the Environment Interactions among plants, herbivores and other organisms: • Allelopathy - Production of chemicals that inhibit growth of other plants • Phytoalexins - Chemicals that kill or inhibit disease fungi or bacteria • Some bacteria and fungi limit plant growth by producing inhibitory compounds. • Some plants do not produce chlorophyll and depend on plant hosts for energy. • Plants have mutualistic relationship with mycorrhizal fungi. • Herbivores and plants involved in co-evolution. Plants and the Environment Association between Acacia and ants: • Ants live in hollow thorns. Special bodies at leaflet tips • Ants feed on sugar, fats and proteins from petiolar nectaries and from special bodies at tips of leaflets. • Ants attack other organisms that come into contact with plant. Hollow thorns Life Histories A species life history is composed of traits that control its survival and reproduction. • Big bang reproduction - Devote all resources to growth for most of life until favorable conditions and then energy goes into single reproductive burst – Desert agave plants • Repeated reproduction - Produce seeds throughout lifetime – Most trees • Annuals - Grow, reproduce and then die at end of season • Biennials - Grow for one year, reproduce second year and die after seeds produced • Perennials - Produce vegetative structures that survive for many years Life Histories Life histories also described in functional terms: • Habitats with low stress and little disturbance select for traits that confer competitive advantage: – Large, persistent, fast growing, slow to reproduce • Habitats with high stress, but little disturbance select for stress tolerance: – Small, slow growing, limited reproductive ability, do not respond to nutrients • Habitats with low stress, but substantial disturbance select for weedy traits: – Fast growing, small, annual, reproduce quickly Life Histories Phenology - Timing of crucial life events: germination, bud burst, flowering, seed production • Photoperiod or light quality trigger germination and flowering in some species. • Growth rates controlled by available moisture and temperature. – Effect of global warming Natural Cycles The water cycle: • Earth’s water is constantly being recycled; total amount remains stable. – 98% of water in oceans, rivers, lakes. – Remaining water in living organisms, glaciers, polar ice, water vapor and soil. – Rainfall percolates down through soil to water table, while water is evaporated from bodies of water and is transpired by plants. – Water vapor rises into atmosphere, condenses, and falls back to earth in the form of rain, snow and hail. – Water cycle disrupted by humans. o Aquifer depletion, creation of reservoirs, irrigation, global warming Natural Cycles The water cycle: Natural Cycles The carbon cycle: • Plant life uses CO2 for photosynthesis. – CO2 = 0.038% of atmosphere. • Respiration from all living things replace CO2. – As much as 90% produced by bacteria and fungi. • Burning of fossil fuels significantly increases amount of CO2 in air. – C3 plants increase growth with increased CO2 levels, but C4 plants do not. o – May give C3 plants competitive advantage and effect C4 crops Oceans become more acid, making shelled organisms vulnerable. Natural Cycles The carbon cycle: Natural Cycles The nitrogen cycle: • Most nitrogen in living organisms is in protoplasmic proteins of cells. • Nitrogen in air unavailable to plants and animals. • Most of nitrogen supply of plants derived from soil in form of inorganic compounds and ions taken up by roots. – Nitrogen-fixing bacteria convert nitrogen from air to ammonia or other nitrogenous compounds. o Some plant species, particularly legumes, produce root nodules in which these bacteria multiply. • Constant flow of nitrogen from dead organisms into soil and from soil back to plants Natural Cycles The nitrogen cycle: Natural Cycles The nitrogen cycle: • Large amounts of nitrogen leach out of soil by erosion of topsoil. • Nitrogen lost by crop harvests. • To offset loss, nitrogenous fertilizers added to artificially increase soil nitrogen content. – Large amounts of energy expended to produce inorganic fertilizer, with much lost by erosion. – If organic matter not added to soil at same time as inorganic fertilizers added, then hardpan soil created. Succession Occurs wherever there has been disturbance of natural areas • Initially no signs of life • Living organisms appear and alter environment as they carry on metabolism and reproduction. • Accumulation of wastes, dead organic material and inorganic debris and other changes favor different species. • These, in turn, alter environment until further changes in species composition occur. • Communities are constantly changing in response to array of disturbances. – May help to enhance species diversity Succession Primary succession - Involves formation of soil in beginning stages • On bare rocks and lava: – Tiny cracks permit plants to invade. Fern spores blow into cracks of bare lava Succession Primary succession: • On bare rocks and lava: – Lichens and mosses become established on surfaces. o Contribute to organic matter and small amount of soil builds up – Other species become established. – As soil buildup continues, larger plants take over. – Eventually vegetation reaches equilibrium of a stable plant community = climax community. o Communities can differ in response to available species and chance events. Succession Primary succession: • In wet habitats - Ponds and lakes left behind by retreating glaciers, like those in northern parts of Midwestern states – Grow a bit smaller each year as a result of succession – Algae carried in by wind or on feet of waterfowl. – Algae concentrated along water margins and dead parts of algae sink to bottom. – Duckweeds form band around body of water just offshore. Duckweeds floating on pond Succession Primary succession: • In wet habitats - Ponds and lakes left behind retreating glaciers: – Peat mosses encroach and become dominant floating plants. – Water lilies and other rooted plants with floating leaves become established. – Accumulating organic matter turns to muck. – Cattails and other plants take root in muck around edges. – Algae, duckweeds and peat mosses move farther out. – Surface area of exposed water diminishes. – Floating mat may form. – Sedges, herbaceous plants and shrubby plants move in. – Coniferous trees eventually grow across entire site and pond or lake disappears. Succession Primary succession: • In wet habitats - Stream-fed lakes and ponds: – Eventually become filled with silt and debris – Nutrient content (particularly nitrogen and phosphorus) of water rises = eutrophication. – Eutrophication facilitates growth of algae and other organisms. – Eutrophication accelerated by: o Sewage and other pollutants o Clearing trees from land - Land erodes, carrying soil into water. Succession Secondary succession: • May take place if soil is already present and there are surviving species in vicinity • On burned or logged land: – Grasses and other herbaceous plants become established. – Followed by trees with widely dispersed seeds – Ending in climax community • Fewer stages than primary succession Succession Fire ecology: • Natural fires, started primarily by lightning, have occurred for thousands of years. • In the Western US, forest burned on average of every 6-7 years. • Trying to eliminate fires disrupts natural habitats. • Fire plays role in composition of forests. – – Many species repeatedly replace themselves after fires. Seeds of some species must be exposed to fire in order to germinate. Succession Fire ecology: • Fires benefit grasslands, chaparral and forests by converting accumulated dead organic material to mineral ash, whose nutrients are recycled within ecosystem. • In prairies of Midwest, grasses better adapted to fire than woody plants. – Some of North American grasslands originated and maintained by fire. – Since fire has been controlled, many areas invaded by shrubs. The Impacts of Humans on Plant Communities At the global level: • Many problems are global in scope and have long-lasting impacts. – Climatic changes – Stratospheric ozone depletion – Loss of biodiversity • These problems traced to human activities. Global Warming Human activities are accelerating the rate at which global warming is occurring. • Glaciers shrinking. • Permafrost disappearing. • Sea levels rising. • Greenhouse effect - Accumulation in atmosphere of gases that permit radiation from sun to reach earth’s surface, but prevent heat from escaping back into space • Gases involved - Carbon dioxide, methane and others, such as chlorofluorocarbons Global Warming – Carbon Dioxide Carbon dioxide emissions from transportation and burning fossil fuels are increasing dramatically. • From 1990 to 2008 - CO2 emissions increased globally by over 25%. • Since1850, CO2 increased by 37%. • Resulting unwelcome events: – Sea level rising, resulting in flooding – More extreme storms – Huge swings between wet and drought years – Rapidly expanding deserts – Dramatic drops in crop yields – Massive extinctions due to habitat changes – Expansion of vector-borne diseases Global Warming – Methane Methane is a greenhouse gas 23 times as potent as CO2. Produced by: • Anaerobic bacteria in swamps and wetlands • Animal digestive processes • Wood-digesting organisms in guts of termites – Termites increasing as tropical rainforests are cleared. • Melting of permafrost that releases trapped methane Global Warming – Ozone Depletion Methane gas and chlorofluorocarbons (CFCs) (refrigeration and industry) - Broken down into active compounds by sunlight at high altitudes • Breakdown products destroy ozone in the stratosphere. – Ozone provides natural shield against UV radiation. – Increased UV radiation increases skin cancers. Halons (bromine-based), found in electronic equipment, reported to be 3-10 times more destructive than chlorofluorocarbons. • Increased 20% per year between 1980 and 1986 Erosion Wind and water remove productive soil and degrade land. Soil erosion is most significant limitation to sustainable agriculture productivity. Erosion removes topsoil faster than ever before. • Takes away organic matter that makes soil fertile • Ability to soak up water lost, so water runs off land, increasing erosion. • Runoff carries fertilizers and pesticides into streams and lakes. Direct result of overgrazing, clearing land for urbanization and roads, and plowing Aquifer Depletion Overpumping of aquifers is probably the most underestimated ecological problem in the world. • Water pumped from underground for: – Irrigation - 70% – Industry - 20% – Homes - 10% Demands for water is growing, while sustainable yield of aquifers is fixed. Loss of Biodiversity When natural habitats are destroyed, a few species may be able to adapt, but most are not capable and ultimately perish. Extinction rates have accelerated enormously over past 50 years as many types of habitats have been damaged or destroyed. Keeping crops from succumbing to diseases often depends on our ability to breed new diseaseresistant strains by tapping into gene pools of wild relatives. Loss of biodiversity in an ecosystem reduces efficiency of production and nutrient use, and makes the ecosystem less resistant to disturbances. At the Regional Level Acid deposition • Burning fossil fuels releases sulfur and nitrogen compounds into the atmosphere. – Chemical reactions with sunlight and rain convert the compounds into nitric acid (HNO3) and sulfuric acid (H2SO4). – Acid rain adversely effects living organisms. o Mycorrhizal fungi susceptible. o Trees die. – Alters soil fertility – Large amounts of nitrogen accumulate - Eutrophication o Increases soil fertility - Loss of plant species due to competition At the Regional Level Water contamination • Pollution in lakes and streams – Dumping toxic wastes – Runoff over polluted land – Pesticide spraying – Exhaust from aircraft and ships – Combustion of fossil fuels • Ground-water supplies – Pesticides – Wastes from septic tanks – Fertilizers At the Regional Level Wetlands - Swamps, marshes, bogs, lagoons, river margins, estuaries, floodplains • Wetlands historically regarded as wastelands and routinely drained and converted to agricultural land. • One hectare of tidal wetland can perform same recycling functions that wastewater treatment equipment capable of. • Wetlands also: – Provide habitat for a wide variety of wildlife – Purify streams and lakes – Reduce erosion – Reduce flooding At the Regional Level Hazardous Waste • Earlier generations routinely disposed of toxic industrial wastes in a casual fashion. • Even under increased regulations, serious accidents and spills occur. • At most solid waste dumps, it is now illegal to dispose of almost any form of hazardous material. • Promise for future - Genetically engineered bacteria that can dismantle and render harmless many types of wastes At the Regional Level Invasion of foreign species • Often aggressive weeds – Reproduce quickly and crowd out native plants – Have no natural pests or herbivores, thus selection for reproduction and less for defense, allowing outcompetition of native plants – More phenotypic plasticity – More genetic differentiation (rapid evolution) Restoration of the Land Restoration ecology assumes that much of environmental damage can be mitigated. • Applies successional concepts to assist and accelerate recovery process Restoration ecology “is the means to end the great extinction spasm. The next century will, I believe, be the era of restoration in ecology.” E. O Wilson Review Plants and the Environment Life Histories Natural Cycles Succession The Impacts of Humans on Plant Communities Global Warming Erosion Aquifer Depletion Loss of Biodiversity At the Regional Level Restoration of the Land