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Lesson 1  Rapid population growth can cause renewable resources to be overexploited. Human Race...

Lesson 1  Rapid population growth can cause renewable resources to be overexploited. Human Race  The effects of population growth on natural resources are particularly critical in developing countries.  is the most powerful agent of environmental change  Economic growth of developing countries: on our planet  exploitation of their natural resources Human Impacts on the Environment  resources for export to highly developed countries Human population in 2009:  Developing countries dilemma:  exploiting natural resources to provide for  passed 6.8 billion individuals their expanding populations in the short  grown in a very brief span of time term; or  1960 – 3 billion; 1975 – 4 billion; 1987 – 5 billion  conserving those resources for future generations. human population consume vast quantities of food and water; use a great deal of energy and raw materials; and  Poverty is tied to the effects of population pressures produce much waste. on natural resources and the environment. Poverty Population Size and Resource Consumption A country is overpopulated if the level of demand on its  is a condition in which people are unable to meet their resource base results in damage to the environment. basic needs for food, clothing, shelter, education, or health.  People overpopulation – is a situation in which there Rich and Poor Countries are too many people in a given geographic area.  Consumption overpopulation – is a situation in Rich countries which each individual in a population consumes too large a share of resources.  are known as highly developed countries, examples are Norway, Switzerland, Qatar, USA, Canada and Fact: Highly developed nations represent less than 20 percent Japan. of the world’s population, yet they consume significantly more  Highly developed countries than half of its resources.  there are countries with complex industrialized bases, These countries also generate 75 percent of the world’s low rates of population growth, and pollution and waste. high per person incomes.  Ecological footprint – is an amount of productive Poor countries land, fresh water, and ocean required on a continuous basis to supply each person with food, wood, energy,  in which about 82 percent of the world’s population water, housing, clothing, transportation, and waste live, fall into two subcategories: disposal. 1. Moderately developed countries – are countries 3 factors in determining environmental impact: with medium levels of industrialization and per person 1. The number of people (P). incomes lower than those of highly developed 2. The affluence per person, which is a measure of the countries. Example of countries are Turkey, South consumption, or amount of resources used per Africa, Thailand and Mexico. person (A). Fewer Opportunities for: 3. The environmental effects (resources needed and wastes produced) of the technologies used to obtain  income and consume the resources (T).  education This method of assessment is usually referred to as the IPAT  health care equation: 2. Less developed countries - are countries with low 𝐼=𝑃×𝐴×𝑇 levels of the following: Note: The three factors in the IPAT equation are always  industrialization changing in relation to each other.  very high rates of population growth  very high infant mortality rates; and Sustainability and the Environment  very low per person incomes Sustainability ensures that the ecosystem can work  Examples are the Philippines, Bangladesh, Haiti and indefinitely without slipping behind the burden that human Laos activities put on natural systems. Population, Resources and the Environment  Environmental sustainability is the ability to meet We may make two important generalizations about the humanity’s current needs without compromising the relationship between population growth, natural resource use ability of future generations to meet their needs. and environmental degradation. This is based on the following ideas: (1) the quantity of resources vital to an individual’s survival is (1) We must consider the effects of our actions on the small, but rapid population growth (often found in developing health and well-being of the natural environment, countries) tends to overwhelm and deplete a country’s soils, including all organisms. forests, and other natural (2) Earth’s resources are not present in unlimited supply. resources. We must live within limits that let renewable resources (2) in highly developed nations, individual demands on natural such as fresh water regenerate for future needs. resources are far greater than the requirements for mere (3) We must recognize all the costs to the environment survival. Rich countries deplete resources and degrade the and to society of products we consume. global environment through increased consumption of (4) We must each share responsibility for environmental nonessential items such as televisions, jet skis, and gadgets. sustainability. 2 types of resources: 1. Nonrenewable resources - are natural resources that are present in limited supplies and are depleted as they are used. These include minerals and fossil fuels. 2. Renewable resources – are resources that are replaced by natural processes and that can be used forever, provided they are not overexploited in the short term. Examples are trees, fishes and fresh water. Lesson 2 Energy Ecology  is a necessary input, which sun is the ultimate energy source for the ecosphere and directly  is derived from the Greek word oikos (“household”) supports most natural ecosystems in the and logos (“study”). biosphere.  the study of household. This is the study of “life at  also flows out of the system in the form of heat home” with emphasis on “the totality or pattern of and in other transformed or processed forms, relations between organisms and their environment.” such as organic matter (food and waste products)  More scientific definition is the study of environmental and pollutants. house that includes all organisms in it and all the  Energy flow is one-way, some of the incoming functional processes that make the house habitable. solar energy is transformed and upgraded in quality (that is, converted into organic matter, a BASIC PRINCIPLES AND CONCEPTS OF ECOLOGY higher-quality form of energy than sunlight) by Levels-of-Organization Hierarchy the community, but most energy is degraded and passes through and out of the system as a low-  Levels of organization is a hierarchical quality heat energy (heat sink). arrangement of order ranging from the ecosphere (or  Energy can be stored and “fed back,” or exported beyond) to cells (or beyond) illustrating how each but it cannot be reused. In contrast with energy, level manifests emergent properties that are best materials, including nutrients necessary for life explained at a particular level of organization. (such as C, N, P) and water, can be used over  Hierarchy is the arrangement into a graded series, and over again. The community of autotrophs (A) while a system consists of regularly interacting and and heterotrophs (H) are linked together with interdependent components forming a unified whole. appropriate energy flows, nutrient cycles, and  A biosystem is a system that constitutes living storages (S). (biotic) and nonliving (abiotic) components; in the Trophic structure of the ecosystem diagram, this is ranging from genetic systems to ecological systems. 2 layers of ecosystem: Ecology is largely concerned with the system levels beyond 1. autotrophic stratum (upper) or the “green belt” of that of the organisms. chlorophyll-containing plants in which the fixation of light energy, the utilization of simple organic  Population is a group of individuals of the same substances, and the buildup of complex organic species occupying a common geographical area (for substances predominate example flock of kalapati in People’s Park, students 2. heterotrophic stratum (lower) or the “brown belt” of in a classroom, colony of hantik ant, and rice in a soils and sediments, decaying matter , roots, etc. in conventional farm treated with herbicide and which the utilization, rearrangement, and insecticide. decomposition of complex materials predominate.  A community is composed of two or more populations of different species occupying the same Components constituting an ecosystem are: geographical area (examples, herd of baka in a grass meadow, and normal flora “para ‘yes’ is the answer 1. organic substances that involved in material cycles to the question: okay ka ba tiyan?”). (ex. C, N, CO2 and H2O); 2. organic compounds that link biotic and abiotic Take note that populations and communities include only biotic components (ex. Protein, carbohydrates, lipids and factors. humic substances); 3. air, water and substrate environment, including the  An ecosystem is community plus its abiotic factors climate regime and other physical factors; (e.g. soil, rain, temperature and nutrients). The 4. producers (autotrophic organisms) in which mostly community and the non-living environment function green plants that can manufacture food from simple together as an ecological system. inorganic substances;  A landscape is defined as a heterogenous area 5. phagotrophs, heterotrophic organisms (animals), composed of a cluster of interacting ecosystems that they ingest other organisms or particulate organic are repeated in a similar manner throughout. matter;  Biome is a term pertaining to a large regional or 6. saprotrophs, decomposers (mainly bacteria and subcontinental system characterized by a major fungi), these are heterotrophic organisms that obtain vegetation type or other identifying landscape aspect. their energy by breaking down dead tissues or by While a region is not included in the diagram of absorbing dissolved organic matter (DOM) from ecological levels-of-organization hierarchy but it can plants and animals. be used to describe a large geological or political area that may contain more than one biome. Examples of Ecosystems  Ecosphere is the largest and most nearly self- sufficient biological system which include all the living A pond and an old field organisms of Earth interacting with the physical Plants, animals, and microorganisms not only live in the pond environment as a whole to maintain a self-adjusting, and the old field (or grassland), but they also modify the loosely controlled pulsing state. chemical nature of the water, soil, and air that compose the ATTRIBUTES OF A NATURAL ECOSYSTEM physical environment. Thus, a bottle of pond water or a scoopful of bottom mud or meadow soil is a mixture of living Concept of ecosystem organisms—both plants and animals—and organic and inorganic compounds.  Biotic (living) organisms  abiotic (nonliving) environment Abiotic substance Ecological system or ecosystem  includes inorganic and organic compounds, such as water, carbon dioxide, O2, Ca, N, S, and P salts,  is any unit that includes biotic community (all amino and humic acids, and others. organisms) in a given area interacting with the  A small portion of the vital nutrients is in solution and physical environment so that a flow of energy leads to immediately available to organisms, but a much larger clearly defines biotic structures and cycling of portion is held in reserve (“storage” S) in particulate materials between living and nonliving components. matter as well as in the organism themselves.  The ecosystem is the first in the ecological hierarchy that is complete with all the components important for The rate of release of nutrients from the solids, the solar survival. input, and changes in temperature, day length, and other  are open systems—that is, things are constantly climatic conditions are the most important processes that entering and leaving. regulate the rate of function of the entire ecosystem on a  A graphic model of an ecosystem can consist of a box daily basis. that we can label the system, which represent the area we are interested in, and two large circles that we can label input environment and output environment. Producer Organism 2 basic types of Food chains: Producers in a pond are: 1. the grazing food chain, which starting from a green plant base, goes to grazing herbivores and on to 1. rooted or large floating plants (macrophytes) that carnivores generally growing in shallow water; and 2. the detritus food chain, which goes from nonliving 2. minute floating plants, usually algae or green bacteria organic matter to microorganisms and then to or protozoa (phytoplankton) that are distributed detritivores and their predators. Food chains are not throughout the pond as deep as light penetrates. In isolated sequences; they are interconnected. The large deep ponds and lakes, phytoplankton is much interlocking pattern is often spoken of as the food more important than rooted vegetation in the web. production of basic food for the ecosystem. Accordingly, primary consumers are limited by secondary Consumer organisms consumers, and primary producers are thus resource limited rather than grazer limited. Research has resulted in “bottom- 1. Herbivores (primary macroconsumers) feed directly up” versus “top-down” perspectives in the understanding of on living plants or plant parts, hereafter, they will also food chain dynamics. be termed as primary (firstorder) consumers. The two types of microconsumers in the pond are  The bottom-up hypothesis holds that production is zooplankton (animal plankton) and benthos (bottom regulated by upstream factors such as nutrient forms). Herbivores in grassland and fields are the availability small, plant-feeding insects and other invertebrates,  the top-down hypothesis predicts that predators or and the large, grazing rodents and hoofed mammals. grazers regulate productivity. 2. The secondary (second-order) consumers or carnivores, such as predaceous insects and game Biogeochemical Cycles fish (nekton; free-swimming aquatic organisms) in the pond, and predatory insects, spiders, birds, and  The chemical elements, including all the essential mammals that feed on the primary consumers or elements of life, tend to circulate in the atmosphere in other secondary consumers (thus making them characteristic pathways from environment to tertiary consumers). organisms and back to the environment. These more 3. Detritivores are another important consumer that live or less circular pathways are known as on the organic detritus from autotrophic layers above, biogeochemical cycles and provides food for carnivores. Cycling of Nitrogen Decomposer organisms  Nitrogen gas (N2) accounts for almost 80 per cent of  The non-green bacteria, flagellates, and fungi are the Earth's atmosphere, and nitrogen is also the distributed throughout the ecosystem, but they are resource that in many ecosystems limits primary especially abundant in the mud-water interface of the production. pond and in the litter-soil junction of the grassland or  Many nitrogen-fixing species are free-living and old-field ecosystem. When temperature and moisture others are symbiotic nitrogen-fixers, who need close are favourable, the first stage of composition occur interaction with a host for the cycle to be carried out. rapidly. Dead organisms do not retain their integrity Most symbiotic relationships are very specific and for very long but are soon broken up by the combined have complex mechanisms which help to keep the action of detritus -feeding microorganisms and symbiosis going. physical processes. Some of the nutrients are  Some of these bacteria are aerobic, some are released for use. anaerobic; some are phototrophic, some are chemotrophic. Fundamental concepts related to energy  While there is a great physiological and phylogenetic Energy is defined as the ability to do work. The behavior of diversity among the species that perform nitrogen energy is described by the following laws: fixation, they all have a common enzyme complex called nitrogenase, which catalyzes reduction of N2  The first law of thermodynamics, or the law of to ammonia (NH3). conservation of energy, states that the energy may be transformed from one form to another but is 1. Nitrification is the mechanism that transforms neither created nor destroyed. ammonia into nitrite and then nitrate, which is another  The second law of thermodynamics, or the law of important step in the global cycle of nitrogen. Most entropy, may be stated as: no process involving an nitrification occurs aerobically, and is done by energy transformation will spontaneously occur prokaryotes alone. There are two distinct nitrification unless there is a degradation of energy from a steps which are performed by different types of concentrated form into a dispersed form. microorganisms. Its first step is ammonia oxidation to nitrite that is performed by microbes known as Organisms, ecosystems, and the entire ecosphere possess the ammonia oxidizers. Aerobic ammonia oxidizers use following essential thermodynamic characteristic: They can intermediate hydroxylamine to convert ammonia to create and maintain a high state of internal order, or a nitrite, a method that involves two different enzymes, condition of low entropy. Low amount of entropy is achieved by ammonia monooxygenase and hydroxylamine continually and efficiently dissipating energy of high utility (light oxidoreductase. or food, for example) into energy of low utility (heat, for 2. The second step in nitrification is the oxidation of example). nitrite (NO2-) to nitrate (NO3-). A completely different community of prokaryotes, known as nitrite-oxidizing Food resulting from the photosynthesis of green plants bacteria, performs this step. Nitrospira, Nitrobacter, represents potential energy, which changes into other forms of Nitrococcus, and Nitrospina are among the genera energy when the food is used by organisms. Because one type involved in nitrite oxidation. New type of oxidation of of energy is always equivalent in quantity (but not in quality) to ammonia taking place under anoxic conditions. another type into which it is transformed, we can calculate one Anammox (anaerobic ammonia oxidation) is from the other. Energy that is “consumed” is not actually used performed by prokaryotes belonging to the up. Rather, it is converted from state of high-quality energy to a Planctomycetes phylum of Bacteria. Anammox state of low-quality energy. bacteria oxidize ammonia by using nitrite as the electron acceptor to produce gaseous nitrogen. 3 Energy partitioning in food chains and food webs 3. Denitrification is the mechanism that converts nitrate The transfer of food energy from its source in autotrophs to nitrogen gas, thus eliminating bioavailable nitrogen through a series of organisms that consume and are and returning it to the atmosphere. Dinitrogen gas consumed is termed the food chain. At each transfer, a (N2) is the primary denitrification end result but there proportion (often as high as 80 to 90 percent) of the potential are other intermediate gaseous sources of nitrogen. energy is lost as heat. Therefore, the shorter the food chain— 4. If an organism excretes waste or dies, the nitrogen in or the nearer the organism to the producer trophic level—the its tissues is in the form of organic nitrogen like amino greater the energy available to that population. acids and DNA. Various fungi and prokaryotes then decompose the tissue and release inorganic nitrogen back into the environment as ammonia in the process known as ammonification. Cycling of Phosphorus earth in a form of rain, snow, or hailstorm where it may be stored temporarily in soils, lakes and icefields. Main supplies of phosphorus are present in surface water, rivers, lakes and seas, and in rocks and ocean sediments. The Niche phosphorus cycle can be described as an 'open' cycle because of the general tendency of mineral phosphorus to be While there are few environments on earth without life, no transported inexorably from the land to the oceans, mainly in single species can tolerate the full range of earth’s rivers, but also to a lesser extent in groundwater, or through environments. For each species, some environments are too volcanic activity and atmospheric fallout, or through the warm, too cold, too saline, or unsuitable in other ways. We abrasion of coastal land. Alternatively, the cycle may be already learned that organisms take in energy at a limited rate. referred to as a 'sedimentary cycle' since, essentially, The environmental limits of a species are related to its niche. phosphorus is absorbed into ocean sediments. Typical the niche summarizes the environmental factors that influence phosphorus atoms, which are released from rock through the growth, survival, and reproduction of a species. In other chemical weathering, can join and circulate within the words, a species’ niche consists of all the factors necessary for terrestrial community for years, decades or centuries until they its existence—approximately when, where, and how a species are transported via groundwater to a stream where they are makes its living. part of a nutrient. The atom is transported to the ocean within a The number of species in the population may be influenced by short period of joining the stream (weeks, months or years). a range of abiotic factors. Sometimes one or more factors, This is taken up by species that live on the surface of the known as limiting factors, are more important than other factors water, until they finally sink down into the oceans. in regulating population growth. This ecological principle is Cycling of Sulfur called the limiting factor principle: Too much or too little of any abiotic factor can limit or prevent growth of a population, even Three natural biogeochemical processes release sulfur to the if all other factors are at or near the optimal range of tolerance. atmosphere: This principle describes one way in which population control— a scientific principle of sustainability is achieved. 1. the formation of the volatile compound dimethylsulfide (DMS) (by enzymatic breakdown of an abundant Success of an organisms, a group of organisms, or a whole compound in phytoplankton biotic community depends on a complex of conditions. Any dimethylsulfonioproprionate); condition that approaches or exceeds the limits of tolerance is 2. anaerobic respiration by sulfate-reducing bacteria; said to be a limiting condition or limiting factor. 3. volcanic activity. Limits of tolerance concept Cycling of Carbon Not only may too little of something be a limiting factor but also  There is a chance that this carbon atom will become too much of such factors as heat, light, and water. Thus, part of the skeleton of the plankton, or component of organisms have ecological minimum and maximum; the range the bones of the larger animal that consumes it, and in between represents the limit tolerance. The concept of the then part of the sedimentary rock when the organisms limiting effect of maximum as well as minimum constituents die and only the skeletons are left behind. Carbon, was incorporated into the Shelford law of tolerance. which is a part of rocks and fossil fuels such as oil, coal and natural gas, can be kept away from the rest Some principle to the law of tolerance may be stated as of the carbon cycle for a long time to come. Such follows: long-term storage areas are called "sinks." Once fossil 1. organisms may have a wide range of tolerance for fuels are burned, carbon that was buried is sent to the one factor and a narrow range for another; air as carbon dioxide, a greenhouse gas. 2. organisms with wide ranges of tolerance for limiting  Carbon is a part of the seawater, the atmosphere, factors are likely to be most widely distributed; minerals in limestone and coal, soils, as well as all 3. when conditions are not optimal for a species with living organisms. On our complex world, carbon will respect to one ecological factor, the limits of pass from one of these domains to another as part of tolerance may be reduced for another ecological the carbon cycle. factors;  Carbon transfers from the atmosphere to the plants. 4. frequently, organisms in nature are not actually living Carbon is attached to oxygen in the air in a gas called at the optimum range of a particular physical factor; carbon dioxide (CO2). Through the method of 5. reproduction is usually a critical period when photosynthesis, carbon dioxide is drawn from the air environmental factors are most likely to be limiting. to create food produced for plant production. The concept of limiting factors is valuable because it  Carbon transfers from plants to animals. In the food gives the ecologists an “entering wedge” into the chain, carbon that is in plants moves to the animals study of complex ecosystems. that consume them. Animals that eat other animals get the carbon from their food. On land, precipitation often is the limiting abiotic factor. Lack of  Carbon moves from plants and animals to soils. When water in a desert limits plant growth. Soil nutrients also can act plants and animals die, their bodies, wood and leaves as a limiting factor on land. Suppose a farmer plants corn in decompose bringing the carbon into the soil. Some phosphorus-poor soil. Even if water, nitrogen, potassium, and are buried and will become fossil fuels in millions and other nutrients are at optimal levels, the corn will stop growing millions of years. when it uses up the available phosphorus. Too much of an  Carbon moves from living things to the atmosphere. abiotic factor can also be limiting. Each time you exhale, CO2 is released into the atmosphere. Animals and plants need to get rid of Important limiting abiotic factors in aquatic life zones include CO2 through respiration. temperature, sunlight, nutrient availability, and the low solubility  Carbon moves from fossil fuels to the atmosphere of oxygen gas in water (dissolved oxygen content). Another when fuels are burned. When humans burn fossil such factor is salinity—the amounts of various inorganic fuels to power factories, power plants, cars and minerals or salts dissolved in a given volume of water trucks, most of the carbon quickly enters the Regulatory Factors atmosphere as carbon dioxide gas.  Carbon moves from fossil sources to the atmosphere Soil as the fuel is burned. As human burn fossil fuels to power factories, systems, cars and vehicles, most of  Biotic and abiotic components are specially intimate in the carbon soon released to the atmosphere as soils, which by definitions consists of a weathered carbon dioxide gas. layer of Earth’s crust with living organisms  Carbon transfers from the atmosphere to the oceans. intermingled with products of their decay. The oceans, and other bodies of water, absorb some carbon from the atmosphere. When the carbon Fire molecules in the air touches the water surface, it  is major factor in shaping the history of vegetation in dissolves into the water. most of the terrestrial environment of the world. As The Hydrologic Cycle climate pulses between wet and dry periods, so does fire in the environment. It is thus an extremely The hydrological cycle is simple to understand. The main important limiting factor, if for no other reason than source of water is the oceans; energy from the sun makes that the control of fire is far more feasible than the water evaporate into the atmosphere, winds distribute it over control of many other limiting factors. the surface of the Earth, and precipitation brings it down to Temperature Lesson 3  Life as we know it can exist only within a tiny range of BIOME about 300 degrees Celcius—from about -200° to 100°C.  A large, relatively distinct terrestrial region with similar  Variability of temperature is extremely important climate, soil, plants, and animals, regardless of where ecologically. A temperature fluctuating between 10°C it occurs in the world. and 20°C and averaging 15°C does not necessarily  Encompasses many interacting ecosystems have the same effect on organisms as a constant  Considered the next level of ecological organization temperature of 15°C. Organisms that are normally above community, ecosystem, and landscape subjected to variable temperatures in nature tend to  Temperature and precipitation, have a predominant be depressed, inhibited, or slowed down by constant effect on biome distribution. temperatures. 9 MAJOR TERRESTRIAL BIOMES Light 1. Tundra  Light places organisms on the horns of dilemma:  Arctic tundra —Treeless biome in the far north that direct exposure of protoplasm to light causes death, consists of boggy plains covered by lichens and yet sunlight is the ultimate source of energy, without mosses; it has harsh, cold winters and extremely which life could not exist. Light is not only a vital factor short summers. but a limiting one, at both the maximum and minimum  Alpine tundra- similar ecosystem located in the levels. higher elevations of  Ecologically, the quality, the intensity, and the  Mountains, above the tree line. duration of light are known to be important. Both  Growing season is short, the days are long animals and plants respond to different wavelengths  Little precipitation, and most of the yearly 10 to 25 cm of light. Color vision in animals sporadically occurs in (4 to 10 in) of rain or snow falls during summer different taxonomic groups, apparently being well months developed in certain species of arthropods, fish, birds  Tundra soil is nutrient poor and have little detritus and mammals, but not in other species of the same  Permafrost beneath surface soil and impedes group. The rate of photosynthesis varies somewhat drainage with different wavelengths. In terrestrial ecosystems,  Limited precipitation, combined with low the quality of sunlight does not vary enough to have temperatures, flat topography (or surface features), an important differential effect on the rate of and the layer of permafrost, produces a landscape of photosynthesis, but as light penetrates water, the red broad, shallow lakes and ponds, sluggish streams, and blues are filtered out by attenuation, and the and bog recovers slowly from even small resultant greenish light is poorly absorbed by disturbances chlorophyll.  Oil and natural gas exploration and military use have caused damage to tundra likely to persist for Water hundreds of years.  a physiological necessity for all life, is from the  Supports relatively few species compared to other ecological viewpoint chiefly a limiting factor in land biomes but the species exist in great numbers environments and in water environments where the Flora: amount can fluctuate greatly or where high salinity fosters water loss from organisms by osmosis.  Cotton Plants, Lichen, Caribou Moss, Labrador Tea, Rainfall, humidity, the evaporating power of the air, Artic Willow, Bearberry and the available supply of surface water are the principal factors measured. Note: Tundra plants seldom grow taller than 30 cm (12 in)  Rainfall is determined largely by geography and by the pattern of large air movements or weather Fauna: systems. The distribution of rainfall over the year is an extremely important limiting factor for organisms. Lemmings, voles, weasels, arctic foxes, snowshoe hares,  0-25 cm per year—desert ptarmigan, snowy owls, and musk oxen  25-75 cm per year—grassland, savanna 2. Boreal Forest  75-125 cm per year—dry forest  Also called taiga.  >125 cm per year—wet forest  Region of coniferous forest (such as pine, spruce,  Humidity represents the amount of water vapor in the air. and fir) in the Northern Hemisphere; located just Absolute humidity is the actual amount of water in the air south of the tundra. expressed as weight of water per unit of air.  Winters in the boreal forest are extremely cold and Types of interaction between two species severe, although not as harsh as those in the tundra.  Receives little precipitation (50 cm (20 in) per year In theory, populations of two species may interact in basic  Soil is typically acidic and mineral poor, with a thick ways that correspond to combinations of neutral, positive and surface layer of partly decomposed pine and spruce negative that can be symbolized as 0 for neutral, + for needles. positive, and – for negative.  Permafrost deep under the surface  Has numerous ponds and lakes dug by ice sheets 1. neutralism – neither population is affected by during the last ice age. association with the other  World’s top source of industrial wood and wood fiber 2. competition, direct interference type – both populations actively inhibit each other Flora: 3. competition, resource use type – each population adversely affects the other indirectly in the struggle for  Black and white spruces, balsam fir, eastern larch, resources in short supply and other conifers (cone-bearing evergreens) 4. amensalism – one population is inhibited and others are not affected Fauna: 5. commensalism – one population is benefited 6. parasitism; and  Consists of some larger species such as caribou, 7. predation – one population adversely affects the which migrate from the tundra for winter; wolves; other by direct attack but never the less depends on brown and black bears; and moose. the other;  Most boreal mammals are medium sized to small, 8. protocooperation (facultative cooperation) – both including rodents, rabbits, and smaller predators populations benefit by the association but their such as lynx, sable, and mink. relations are not obligatory; and  Birds are abundant in the summer but migrate to 9. mutualism – the growth and survival of both warmer climates for winter. populations is benefited, and neither can survive  Insects are plentiful, but few amphibians and reptiles under natural conditions without the other. occur except in the southern boreal forest.  3. Temperate Rain Forest 6. Chaparral  A coniferous biome with cool weather, dense fog,  A biome with mild, moist winters and hot, dry and high precipitation. summers; vegetation is typically small-leaved  Occurs on the northwest coast of North America, evergreen shrubs and small trees. southeastern Australia and in southern South  Soil is thin and often not very fertile. America  Wildfires occur naturally and are particularly  Annual precipitation is high—more than 127 cm (50 frequent in late summer and autumn in)—and is augmented by condensation of water from dense coastal fogs Flora:  Seasonal fluctuation is narrow; winters are mild, and  Dominant: dense thicket of evergreen shrubs— often summers are cool. short, drought-resistant pine or scrub oak trees that  Relatively nutrient-poor soil, though its organic grow 1 to 3 m (3 to 10 ft) tall content may be high.  Cool temperatures slow the activity of bacterial and Fauna: fungal decomposers.  Rich wood producer, supplying lumber and pulpwood  Black tailed Jackrabbit, Golden Jackal, Puma, Cactus Wren Flora:  Mule deer, wood rats, chipmunks, lizards, and many species of birds  Dominant: large evergreen trees such as western hemlock, Douglas fir, western red cedar, Sitka spruce, 7. Temperate Grassland and western arborvitae  A grassland with hot summers, cold winters, and less  Rich in epiphytes mainly mosses, club mosses, rainfall than is found in the temperate deciduous lichens, and ferns, all of which also carpet the ground forest biome. Fauna:  Average annual precipitation ranges from 25 -75 cm (10 to 30 in)  Squirrels, wood rats, mule deer, elk, numerous bird  Grassland soil has considerable organic material species, and several species of amphibians and  Occur in the United States in parts of Illinois, Iowa, reptiles. Minnesota, Nebraska, Kansas, and other Midwestern 4. Temperate Deciduous Forest states  A forest biome that occurs in temperate areas where  Are temperate grasslands that receive less annual precipitation ranges from about 75 cm to 126 precipitation than moist temperate grasslands but cm (30 to 50 in). more precipitation than deserts.  Hot summers and cold winters  Soil consists of a topsoil rich in organic material and Flora: a deep, clay-rich lower layer.  Trees grow sparsely except near rivers and streams,  Among the first biomes converted to agricultural use but grasses taller than a person grow in great Flora: profusion in the deep, rich soil.  Periodic wildfires help to maintain grasses as the  Dominating in northeastern and mideastern United dominant vegetation in grasslands. States: Broad-leaved hardwood trees (oak, hickory,  Grasses that grow knee high or lower dominate and beech)  Plants grow less abundantly than in the moister  Trees form a dense canopy that overlies saplings and grasslands, and bare shrubs  Soil is occasionally exposed. Fauna: Fauna:  Originally contained a variety of large mammals, such  Formerly supported large herds of grazing animals as puma, wolves, and bison, which are now absent. (bison and pronghorn elk)  Deer, bears, and many small mammals and birds  Principal predators: wolves, coyotes  Smaller animals included prairie dogs and their predators (foxes, black-footed ferrets, and various birds of prey), grouse, reptiles such as snakes and 5. Tropical Rain forest lizards, and great numbers of insects.  A lush, species-rich forest biome that occurs where  Occur in parts of Montana, Wyoming, South Dakota, the climate is warm and moist throughout the year. and other midwestern states.  Are found in Central and South America, Africa, and Southeast Asia 8. Savanna  Annual precipitation is typically between 200 and 450  A tropical grassland with widely scattered trees or cm (80 to 180 in). clumps of trees.  Commonly occurs in areas with ancient, highly  Found in areas of low rainfall or, more commonly, in weathered, mineral-poor soil. areas of intense seasonal rainfall with prolonged dry  Little organic matter accumulates in such soils; periods. because temperatures are high year-round, bacteria,  Temperatures vary little throughout the year. fungi, and detritus-feeding ants and termites  Precipitation is the overriding climate factor: Annual decompose organic litter quite rapidly. precipitation is 85 to 150 cm (34 to 60 in).  Roots quickly absorb nutrient minerals from the  Soil is somewhat low in essential nutrient minerals, in decomposing material. part because it is heavily leached during  A fully developed tropical rain forest has at least  Rainy periods—that is, nutrient minerals filter out of three distinct stories, or layers, of vegetation the topsoil. (emergent story, canopy, understory)  Occur in Africa, also in in South America, western Flora: India, and northern Australia.  Converted into rangeland for cattle and other  No single species dominates domesticated animals  Emergent layer: very tall trees, some 50 m (164 ft)  Middle story, or canopy: trees 30 to 40 m (100 to 130 Flora: ft)  Has wide expanses of grasses interrupted by  Smaller plants in the sparse understory occasional trees like the acacia, which bristles with  Communities of epiphytic plants such as ferns, thorns to provide protection against herbivores. mosses, orchids, and bromeliads. Fauna: Fauna:  Herbivores such as antelope, giraffe, elephants,  About 90% of tropical rainforest organisms are wildebeest, and zebra adapted to live in the canopy  Large predators, such as lions and hyenas, kill and  Abundant and varied insects, reptiles, and scavenge the herds. amphibians  Mammals: sloths and monkeys  9. Desert  3 zones of a large lake: the littoral, limnetic, and  A biome in which the lack of precipitation limits plant profundal zones growth; deserts are found in both temperate and tropical regions. Lake  Consists of dry areas found in both temperate (cold  A standing-water ecosystem surrounded by land. deserts) and subtropical or tropical regions (warm deserts).  Low water vapor content of the desert atmosphere → daily temperature extremes of heat and cold  Desert environments vary greatly depending on the amount of precipitation they receive, which is generally less than 25 cm (10 in) per year.  Desert soil is low in organic material but is often high in mineral content, particularly salts Flora:  Plants in North American deserts include cacti, yuccas, Joshua trees, and sagebrush  Desert plants are adapted to conserve water and as Flowing-water ecosystems a result tend to have few, small, or no leaves.  Cactus leaves are modified into spines  Are highly variable; surrounding environment changes  Other desert plants shed their leaves for most of the greatly between a river’s source and its mouth year, growing only during the brief moist season.  Certain parts of the stream’s course are shaded by forest, while other parts are exposed to direct Fauna: sunlight.  Groundwater may well up through sediments on the  Typically small bottom in one particular area, making the water  Desert-adapted insects and arachnids (such as temperature cooler in summer or warmer in winter tarantulas and Scorpions)few desert-adapted than in adjacent parts of the stream or river amphibians (frogs and toads) and many reptiles, such  Organisms vary greatly from one stream to another, as the desert tortoise, Gila monster, and Mojave depending primarily on the strength of the current. Rattlesnake.  fast currents: some inhabitants have  Desert mammals in North America include rodents adaptations such as suckers, with which they such as kangaroo rats, as well as mule deer and attach themselves to rocks to prevent being jackrabbits. swept away.  Birds of prey, especially owls, live on the rodents and  With flattened bodies to slip under or jackrabbits, and even the scorpions. between rocks  During the driest months of the year, many desert  fish that are streamlined and muscular animals tunnel underground, where they remain enough to swim in the current inactive. Freshwater wetlands AQUATIC ECOSYSTEMS  Lands that shallow fresh water covers for at least part of the year; wetlands have a characteristic soil and The most fundamental division in aquatic ecology is probably water- tolerant vegetation between freshwater and saltwater environments.  Include marshes, dominated by grasslike plants, and Factors affecting distribution of organisms: swamps, dominated by woody trees or shrubs  Wetland soils: waterlogged for variable periods and  Salinity- the concentration of dissolved salts (such as are therefore anaerobic; are rich in accumulated sodium chloride) in a body of water organic materials  Dissolved oxygen  Provide excellent wildlife habitat for migratory  Nutrient minerals waterfowl and other bird species, as well as for beaver, otters, muskrats, and game fish. 3 main ecological categories of organisms  Provides ecosystem services  Threatened by pollution, development, agriculture, 1. Plankton- usually small or microscopic organisms; and dam construction tend to drift or swim feebly, so, for the most part, they  Ecosystem services- Important environmental are carried about at the mercy of currents and waves. benefits, such as clean air to breathe, clean water to drink, and fertile soil in which to grow crops, that the natural environment provides 2. Nekton- larger, more strongly swimming organisms such as fishes, turtles, and whales. Freshwater swamps  Are inland areas covered by water and dominated by trees, such as baldcypress 3. Benthos- bottom-dwelling organisms that fix themselves to one spot (sponges and oysters), Brackish Ecosystems: Estuaries burrow into the sand (worms and clams), or simply walk about on the bottom (crawfish and aquatic insect  A coastal body of water, partly surrounded by land, larvae). with access to the open ocean and a large supply of fresh water from a river. Freshwater Ecosystems  Water levels rise and fall with the tides  Salinity fluctuates with tidal cycles, the time of year,  Include lakes and ponds (standing water and precipitation; also changes gradually within the ecosystems), rivers and streams (flowing-water estuary, from fresh water at the river entrance, to ecosystems), and marshes and swamps (freshwater brackish (somewhat salty) water, to salty ocean water wetlands). at the mouth of the estuary  About 2% of Earth’s surface  Organisms must have a high tolerance for changing  Play an important role in the hydrologic cycle: conditions  Large bodies of fresh water help moderate daily and  Usually feature salt marshes seasonal temperature fluctuations on nearby land  hallow wetlands in which salt-tolerant regions, and freshwater habitats provide homes for grasses grow many species.  perform many ecosystem services, including providing biological habitats, trapping Standing-water ecosystem sediment and pollution, supplying groundwater, and buffering storms by  A body of fresh water surrounded by land and whose absorbing their energy, which prevents flood water does not flow; a lake or a pond. damage elsewhere.  Zonation is characteristic of standing-water ecosystems.   Mangrove forests  Plankton (small or microscopic organisms carried by  The tropical equivalent of salt marshes currents and waves) and small animals that drift  Cover perhaps 70 % of tropical coastlines nearby.  Provide valuable ecosystem services  Their interlacing roots are breeding grounds and Coral reef ecosystems are the most diverse of all marine nurseries for several commercially important fi environments. They contain hundreds of species of fishes and shes and shellfi sh, such as mullet, spotted sea invertebrates, such as giant clams, snails, sea urchins, sea trout, crabs, and shrimp. stars, sponges, flatworms, brittle stars, sea fans, shrimp, and  Mangrove branches are nesting sites for many spiny lobsters. Provide habitat for many kinds of marine species of birds, such as pelicans, herons, organisms and protect coastlines from shoreline erosion. egrets, and roseate spoonbills. Provide humans with seafood, pharmaceuticals, and recreation  Mangrove roots stabilize the submerged soil, and tourism dollars. thereby preventing coastal erosion and providing Sea grasses a barrier against the ocean during storms.  Are flowering plants adapted to complete submersion in salty ocean water Major Ocean Life Zones  occur only in shallow water (to depths of 10 m, or 33 ft) where they receive enough light to photosynthesize  Intertidal zone  Extensive beds of sea grasses occur in quiet  Benthic (ocean floor) environment temperate, subtropical, and tropical waters.  Two provinces—neritic and oceanic—of the  Eelgrass is the most widely distributed sea grass pelagic (ocean water) environment along the coasts of North America  most common sea grasses in the Caribbean Sea are Neritic province manatee grass and turtle grass  high primary productivity and are ecologically  Part of the pelagic environment from the shore to important: Their roots and rhizomes help stabilize where the water reaches a depth of 200 m (650 ft) sediments, reducing erosion, and they provide food  overlies the continental shelf. and habitat for many marine organisms Oceanic province The Neritic Province: From the Shore to 200 Meters  Part of the pelagic environment where the water  The part of the pelagic environment that overlies the depth is greater than 200m, beyond the continental ocean floor from the shoreline to a depth of 200 m shelf. (650 ft). The Intertidal Zone: Transition Between Land and Ocean  Organisms are all floaters or swimmers  euphotic zone- upper level of the pelagic environment which extends from the surface to a maximum depth of 150 m (490 ft) in the clearest open ocean water.  Area of shoreline between low and high tides  Large numbers of phytoplankton (microscopic algae)  Rocky shores provide fine anchorage for seaweeds produce food by photosynthesis and are the base of and marine animals organisms are exposed to wave food webs. action when submerged during high tides and  Zooplankton, including tiny crustaceans, jellyfish, exposed to temperature changes and drying out when comb jellies, and the larvae of barnacles, seaurchins, in contact with the air during low tides worms, and crabs, feed on phytoplankton.  Organisms and their adaptations:  Zooplankton are in turn consumed by plankton-eating  Mussels have tough, threadlike anchors secreted nekton (any marine organism that swims freely), such by a gland in the foot as herring, sardines, squid, baleen whales, and manta  Barnacles secrete a tightly bonding glue that rays hardens underwater.  These in turn become prey for carnivorous nekton  Some organisms hide in burrows or under rocks such as sharks, tuna, porpoises, and toothed whales. or crevices at low tide.  Nekton are mostly confined to the shallower neritic  Some small crabs run about the splash line, waters (less than 60 m, or 195 ft, deep), near their following it up and down the beach. food. The Benthic Environment The Oceanic Province: Most of the Ocean  The ocean floor, which extends from the intertidal  The part of the pelagic environment that overlies the zone to the deep-ocean trenches. ocean floor at depths greater than 200 m (650 ft).  Consists of sediments (mainly sand and mud) where  loosely described as the “deep sea.” (The average many bottom-dwelling animals, such as worms and depth of the ocean is 4000 m, more than 2 mi.) clams, burrow  All but the shallowest waters of the oceanic province  Bacteria are common at (1625 ft) below the ocean have cold temperatures, high pressure, and an floor. absence of sunlight.  Three zones in the deeper benthic (from shallowest to  Fishes of the deep waters of the oceanic province are deepest): the bathyal, abyssal, and hadal zones. strikingly adapted to darkness and scarcity of food  The communities in the relatively shallow benthic  adapted to drifting or slow swimming, often have zone that are particularly productive include coral reduced bone and muscle mass. reefs, sea grass beds, and kelp forests.  Many of these animals have light producing organs to Corals locate one another for mating or food capture.  Most organisms of the deep waters of the oceanic  are small, soft-bodied animals similar to jellyfish and province depend on marine snow, organic debris that sea anemones. drifts down into their habitat from the upper, lighted  live in hard cups, or shells, of limestone (calcium regions of the oceanic province. carbonate) that they produce using the minerals  Organisms are filter feeders, scavengers, and dissolved in ocean water. predators  forms from the accumulated layers of limestone.  Many are invertebrates, some of which attain great sizes. Coral reefs  The giant squid measures up to 18 m (59 ft) in length, including its tentacles.  are found in warm (usually greater than 21°C [70°F]), shallow seawater  The living portions of coral reefs grow in shallow waters where light penetrates.  The tiny coral animals require light for zooxanthellae (symbiotic algae) that live and photosynthesize in their tissues  coral animals capture food at night with stinging tentacles that paralyze Module 2 Projecting Future Population Numbers Lesson 1  zero population growth- The state in which the population remains the same size because the birth How Do Populations Change in Size? rate equals the death rate.  estimates vary depending on fertility changes  individuals of a given species are part of a larger organization called a population.  Small differences in fertility, then, produce large differences in population forecasts  Population ecology- Branch of biology that deals with the number of individuals of a particular species Demographics of Countries found in an area and why those numbers increase or decrease over time.  Demographics- The applied branch of sociology that deals with population statistics. growth rate (r)  infant mortality rate- The number of deaths of  The rate of change (increase or decrease) of a infants under age 1 per 1000 live births. population’s size, expressed in percentage per year.  Per person GNI PPP- a country’s gross national  birth rate (b) minus the death rate (d) income (GNI) in purchasing power parity (PPP) divided by its population. It indicates the amount of  r=b–d goods and services an average citizen of that  also referred to as natural increase in human particular country could buy in the United States populations  replacement-level fertility- The number of children a Dispersal couple must produce to “replace” themselves.  total fertility rate (TFR)- The average number of  movement from one region or country to another children born to each woman. 2 types of dispersal: The Demographic Transition- process whereby a country moves from relatively high birth and death rates to relatively 1. immigration (i)- individuals enter a population and low birth and death rates. increase its size 2. emigration (e)- individuals leave a population and Age Structure of Countries decrease its size  growth rate (r) of a local population must take into  Age Structure- The number and proportion of people account birth rate (b), death rate (d), immigration (i), at each age in a population and emigration (e)  age structure diagram- presents the number of males  r = (b – d) + (i – e) and the number of females at each age, from birth to death Maximum Population Growth  The age structure diagram of a country with a high growth rate, based on a high fertility rate (Ethiopia or  biotic potential- The maximum rate at which a Guatemala)—is shaped like a pyramid population could increase under ideal conditions.  Factors that influence the biotic potential of a species: Declining fertility rates have profound social and economic  the age at which reproduction begins implications because as fertility rates drop, the percentage of  the fraction of the life span during which an the population that is elderly increases. individual can reproduce  the number of reproductive periods per lifetime Population and Urbanization the number of spring produced during each  Urbanization- A process whereby people move from period of reproduction. rural areas to densely populated cities.  life history characteristics determine whether a particular species has a large or a small biotic Environmental Problems of Urban Areas potential.  Generally, larger organisms, such as blue whales and  Suburban sprawl that encroaches into former forest, elephants, have the smallest biotic potentials, wetland, desert, or agricultural land destroys or whereas micro organisms have the greatest biotic fragments wildlife habitat. potentials  brownfields—areas of abandoned, vacant factories, warehouses, and residential sites that may be Exponential population growth contaminated from past uses  Air pollution: airborne emissions, including particulate  The accelerating population growth that occurs when matter (dust), sulfur oxides, carbon oxides, nitrogen optimal conditions allow a constant reproductive rate. oxides, and volatile organic compounds (from Environmental Resistance and Carrying Capacity automobiles)  water flow is affected because they cover the rainfall  organisms don’t reproduce indefinitely at their biotic absorbing soil with buildings and paved roads potential because the environment sets limits, which  Contaminated runoff are collectively called environmental resistance  The environment controls population size: As the Environmental Benefits of Urbanization population increases, so does environmental resistance, which limits population growth.  well-planned city actually benefits the environment by reducing pollution and preserving rural areas.  carrying capacity ( K )- The largest population a particular environment can support sustainably (long  Compact development- Design of cities in which tall, term), if there are no changes in that environment. multiple-unit residential buildings are close to shopping and jobs, and all are connected by public  Sometimes a population that overshoots K will transportation. experience a population crash, an abrupt decline from high to low population density when resources  Urbanization is a worldwide phenomenon. are exhausted.  more than 50% of the world population lives in urban areas with populations of 2000 or greater Human Population Patterns Challenges faced by developing countries Thomas Malthus (1766–1834)  substandard housing (slums and squatter  a British economist settlements); poverty; exceptionally high  One of the first people to recognize that the human unemployment; heavy pollution; and inadequate or population can’t increase indefinitely was non-existent water, sewage, and waste disposal (left  pointed out that human population growth is not figure). always  Rapid urban growth also strains school, medical, and  Noted that human population can increase faster than transportation systems. its food supply, he warned that the inevitable consequences of population growth would be famine, disease, and war. Lesson 2 are grown together, they produce higher yields than when they are grown as monocultures. World Food Problems  Monoculture- is the cultivation of only one type of plant over a large area  average adult human must consume enough food to  Polyculture - a type of intercropping in which several get approximately 2600 calories, per day kinds of plants that mature at different times are  Undernutrition- a type of malnutrition in which there is planted together. an underconsumption of calories or nutrients that leaves the body weakened and susceptible to disease Challenges of Agriculture  Overnutrition- a type of malnutrition in which there is an overconsumption of calories that leaves the body  prime farmland- land that has the soil type, growing susceptible to disease. conditions, and available water to produce food,  Millions of children suffer from kwashiorkor, caused forage, fiber, and oilseed crops. by severe protein deficiency. Note the characteristic  Challenges: decline in prime farmland, coping with swollen belly, which results from fluid declining numbers of domesticated varieties, retention.Photographed in Haiti. improving crop and livestock yields, and addressing  Marasmus is progressive emaciation caused by a environmental impacts. diet low in both total calories and protein. Symptoms include a pronounced slowing of growth and extreme Loss of Agricultural Land wasting of muscles. Photographed in Somalia.  prime agricultural land is falling victim to urbanization  Globally, millions of adult men and women are and suburban sprawl by being converted to parking hungry. This homeless man is suffering from severe lots, housing developments, and shopping malls malnutrition and starvation. Photographed in New Delhi, India. Global Decline in Domesticated Plant and Animal Varieties Population and World Hunger  A global trend is currently under way to replace the many local varieties of a particular crop or  food insecurity- The condition in which people live domesticated farm animal with just a few kinds with chronic hunger and malnutrition.  farmers abandon traditional varieties in favor of more  Factors that contribute to food shortage: civil wars modern ones, which are bred for uniformity and and military actions, HIV/AIDS (which has killed or maximum production; great loss in genetic diversity incapacitated much of the agricultural workforce in  germplasm any plant or animal material that may be some countries), fl oods, droughts, and soil erosion used in breeding. from hilly, marginal farmlands.  Economic development- An expansion in a Increasing Crop Yields government’s economy, viewed by many as the best way to raise the standard of living.  Advances by research scientists since then have  According to National Geographic, by 2030 farmers dramatically increased food production in highly will have to grow 30% more grain than they do now so developed countries that the 8.3 billion people living then can be fed.  Greater knowledge of plant nutrition has resulted in production of fertilizers that promote high yields. Poverty and Food  The use of pesticides to control insects, weeds, and disease-causing organisms has also improved crop  Poverty- main cause of undernutrition yields.  Infants, children, and the elderly are most susceptible to poverty and chronic hunger The Green Revolution  world’s poorest people—those living in developing countries in Asia, Africa, and Latin America—do not  By the middle of the 20th century, serious food own land on which to grow food and do not have shortages occurred in many developing countries sufficient money to purchase food. coping with growing populations.  The development and introduction during the 1960s of The Principal Types of Agriculture high-yield varieties of wheat and rice to Asian and Latin American countries gave these nations the 2 types of agriculture chance to provide their people with adequate supplies 1. Industrialized agriculture- Modern agricultural of food methods that require large capital inputs and less land  But the high-yield varieties required intensive and labor than traditional methods.. It relies on large industrial cultivation methods, including the use of inputs of capital and energy (in the form of fossil fuels) commercial inorganic fertilizers, pesticides, and to make and run machinery, purchase seed, irrigate mechanized machinery, to realize their potential. crops, and produce agrochemicals such as These agricultural technologies were passed from commercial inorganic fertilizers and pesticides highly developed nations to developing nations. 2. Subsistence agriculture- Traditional agricultural  (1965) Mexico’s annual wheat production rose to methods that are dependent on labor and a large more than 2400 kg (2.65 tons) per hectare. amount of land to produce enough food to feed  Indonesia, formerly imported more rice than any other oneself and one’s family. country in the world. Today Indonesia produces enough rice to feed its people and export some.  Most farmers in highly developed countries and some in developing countries practice high-input agriculture, Critics of Green Revolution or industrialized agriculture  green revolution has made developing countries  Most farmers in developing countries practice dependent on imported technologies, such as subsistence agriculture agrochemicals and tractors, at the expense of  Shifting cultivation - a form of subsistence traditional agriculture. agriculture in which short periods of cultivation are  associated with higher crop production are the high followed by longer periods of fallow (land being left energy costs built into this type of agriculture uncultivated), during which the land reverts to forest.  environmental problems caused by the intensive use Shifting cultivation supports relatively small of fertilizers and pesticides. populations.  Slash-and-burn agriculture - a type of shifting  (1999) International Food Policy Research Institute cultivation that involves clearing small patches of projected that the world demand for rice, wheat, and tropical forest to plant crops. Farmers must move corn will increase 40% between 2000 and 2020. from one area of forest to another every 3 years or so.  concerted scientific effort to improve crops: genetic  Nomadic herding, in which livestock is supported by engineering land too arid for successful crop growth, is a similarly  Modern agricultural methods, such as water-efficient land-intensive form of subsistence agriculture. irrigation Nomadic herders must continually move their livestock to find adequate food for the animals.  Intercropping- a form of intensive subsistence agriculture that involves growing a variety of plants on