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ENVIRONMENTAL SCIENCE - UNIT 1

dumb himbo Biology Englisch

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CHAPTER 2 : Environmental Systems: Matter, Energy, and Life
- SYSTEMS DESCRIBE INTERACTIONS
  - SYSTEMS
    - a network of interdependent components and processes, with materials and energy flowing from component of the system to another
    - ECOSYSTEM
      - complex assemblage of animals, plants, and their environment, thru which materials and energy move
      - OPEN SYSTEMS
        those that receive input from their surroundings and produce outputs that leave the system *all ecosystems are open
        CLOSED SYSTEMS
        exchanges no energy or matter with its surroundings
        THROUGHPUT
        energy and/or matter that flow into, through, and out of a system
        ALL ECOSYSTEMS ARE OPEN
  - FEEDBACK LOOPS HELP STABALIZE SYSTEMS
    - POSITIVE FEEDBACK
      - tends to increase a process or component ex. more plants equals more rabbits
    - NEGATIVE FEEDBACK
      - diminishes a process or component ex. less plants equals less rabbits
  - ALL OF LIFE IS DEPENDENT ON THE SUN
- ELEMENTS OF LIFE
  - ATOM
    - smallest particle that exhibits the characteristic of an element
    - STRUCTURE OF AN ATOM
      - NUCLEUS
        consists of PROTONS (positively charged) and NEUTRONS (neutral, no charge)
      - ORBITALS
        consists of electrons (negatively charged)
      - IONS
        charged atoms caused by loss or gain of an electron(s)
        ANIONS
        CATIONS
        positively charged ion, LOSS of electrons
        IONIC BONDS
        electrical attraction between two oppositely charged ions; forms compound
        negatively charged ion, GAIN of electrons
        MOLECULE
        pair or group of atoms that can exist as a single unit ex. H2
        COMPOUND
        substance composed of 2 or more different kinds of atoms ex. H2O
        COVALENT BONDS
        atoms form bonds by sharing electrons
    - UNIQUE PROPERTIES OF WATER
      - water molecules are POLAR; is the UNIVERSAL SOLVENT
      - is the predominant inorganic liquid in nature; CRITICAL FOR LIFE
      - exhibits high degree of COHESION (sticks to itself) and ADHESION (sticks to other surfaces)
      - EXPANDS when it turns SOLID
      - HIGH HEAT vaporization; requires lots of heat to become water vapor (gas)
  - MOST COMMON ELEMENTS
    - MATTER
      - anything that takes up space and has mass; matter consists of elements
        ELEMENTS HAVE UNIQUE STRUCTURE
        ATOMIC NUMBER
        number of protons per atom
        ATOMIC MASS
        protons + neutrons = mass
        ISOTOPE
        forms of a single element that differ in their atomic mass
      - THE LAW OF CONSERVATION OF MATTER
        matter is neither created nor destroyed but is recycled over and over again
      - ACIDS AND BASES
        ACID
        substance readily gives up hydrogen ions in water (H+); RED; BELOW 7
        BASE (ALKALINE)
        substance that releases hydroxide ions in water (OH-); BLUE; ABOVE 7
        NEUTRAL
        7
        ORGANIC COMPOUNDS HAVE A CARBON BACKBONE
        ORGANIC COMPOUNDS
        formed by chains of carbon atoms; make up biomolecules
        FOUR CATEGORIES:
        LIPIDS
        CARBOHYDRATES
        PROTEINS
        NUCLEIC ACIDS
        NUCLEOTIDES
        complex molecule made of a 5-carbon sugar, one or more phosphate groups, nitrogenic base
        form long chains called NUCLEIC ACIDS that store and express genetic info ex. RNA, DNA
        composed of chains of amino acids; provides structures and enzymes; many functions
        sugars and starches; store energy (short term); cellulose, cell structure, long chains of simple sugar
        fat and oils; store energy (long term); provide structure for cell membranes
        HYDROCARBON
        hydrogen and carbon
        CELLS ARE FUNDAMENTAL UNITS OF LIFE
        cell is basic unit of life
        protists are unicellular, ur mom is multicellular
        NITROGEN AND PHOSPHORUS ARE KEY NUTRIENTS IN ALL ECOSYSTEMS
        carbon is captured from air by plants
        oxygen and hydrogen derive from air and/or water
        nitrogen and phosphorus are essential parts of proteins, lipids, sugars, and nucleic acids in cells
        LOW levels of NITROGEN and PHOSPHORUS LIMIT growth in ecosystems
        ex. yellow corn leaves hint at low nitrogen levels in soil
        ABUNDANCE of NITROGEN and PHOSPHORUS cause RUNAWAY growth
        ex. excessive algae growth in ponds
        EUTROPHICATION
        blooms and/or explosion of plant growths (i.e. mostly algae), plant consumes all nutrients, plants then die, they decay, bacteria that consume the decay use up all of the available oxygen, water becomes oxygen deprived, resulting in mass dies offs of the surrounding organisms (i.e. usually aquatic species)
    - NCHOP; nitrogen, carbon, hydrogen, oxygen, phosphorus
- ENERGY AND LIVING SYSTEMS
  - ENERGY
    - ability to do work
    - FORMS OF ENERGY
      - kinetic, heat electricity, chemical, potential, nuclear, thermal
      - POTENTIAL ENERGY
        KINETIC ENERGY
        energy in moving objects
        HEAT
        energy that can be TRANSFERRED between objects of different temperatures
        stored energy; chemical energy ex. foods, gasoline
  - 1ST LAW OF THERMODYNAMICS
    - ENERGY is always CONSERVED
    - 2ND LAW OF THERMODYNAMICS
      - with each successive energy transfer in a system, less energy is available to do work
        entropy tends to increase in all natural systems
      - ENERGY FOR LIFE
        SUN IS ULTIMATE ENERGY SOURCE
        energy is CAPTURED by green PLANTS called PRIMARY PRODUCERS
        green PLANTS CREATE carbohydrates and other COMPOUNDS using SUNLIGHT, AIR, WATER
        CHEMOSYNTHESIS
        organisms gain their energy from a process which allows them to extract energy from inorganic chemical compounds such as hydrogen sulfide (H2S)
        GREEN PLANTS GET ENERGY FROM SUN
        thermonuclear reactions from the sun emit powerful forms of radiation, including potentially deadly ultraviolet (UV) and nuclear radiation
        solar radiation is captured by green plants, algae, and some bacteria
        PHOTOSYNTHESIS
        converts light energy into useful chemical energy in the bonds that hold together organic molecules
        HOW DOES PHOTOSYNTHESIS CAPTURE ENERGY?
        photosynthesis occurs in CHLOROPLASTS, chlorophyll absorbs visible light waves
        photosynthesis relies on TWO interconnected cyclic REACTIONS: LIGHT DEPENDENT REACTIONS and LIGHT INDEPENDENT REACTIONS
        photosynthesis requires WATER and CARBON DIOXIDE; results in OXYGEN and CARBOHYDRATES
        GLUCOSE
        energy-rich molecule that fuels all metabolic processes of cells
        energy in its chemical bonds can be released in a process called CELLULAR RESPIRATION
        6H₂O + 6CO₂ + SUN ⇨ C₆H₁₂O₆ + 6O₂
  - FROM SPECIES TO ECOSYSTEMS
    - SPECIES
      - POPULATION
        COMMUNITY
        ECOSYSTEM
        composed of a biological community and its physical environment
        TROPHIC LEVELS
        composed of all organisms that feed at a particular link in a food chain
        PRODUCERS and PRIMARY, SECONDARY, TERTIARY, QUATERNARY CONSUMERS
        PRIMARY PRODUCERS (AUTOTROPHS)
        require energy source (SUN) and inorganic nutrients to produce organic food molecules (photosynthesis)
        green plants, algae, cyanobacteria
        CONSUMERS (HETEROTROPHS)
        need to ingest organic nutrients from external source
        herbivores, carnivores, omnivores
        PARASITES, SCAVENGERS, and DECOMPOSERS
        SCAVENGERS
        DETRITIVORES
        DECOMPOSERS
        complete final breakdown and recycling of organic materials ex. fungi, bacteria
        consume litter, debris, feces ex. ants, beetle
        cleans up dead carcasses ex. jackals, vultures
        all of the populations of organisms living and interacting in a particular area
        all members of a species living in a given area at the same time
      - all organisms of the same kind that can successfully breed and produce viable, fertile offspring
    - ENERGY FLOW AND CHEMICAL CYCLING IN ECOSYSTEMS
      - energy ENTERS ecosystem as SUNLIGHT and ABSORBED by PRODUCERS
        chemicals enter when producers take in inorganic nutrients
        producers make organic NUTRIENTS for themselves and ALL organisms in the ecosystem
        CONSUMERS GAIN nutrients and energy from EATING PRODUCERS, directly (HERBIVORES), indirectly (CARNIVORES)
        some ENERGY is RELEASED at each level to the environment in the form of HEAT and WASTE products
      - ECOLOGICAL PYRAMIDS
        broad base of primary PRODUCERS, and fewer CONSUMERS in higher trophic levels
        only 10% of energy of one trophic level is availble for another
    - BIOGEOCHEMICAL CYCLES AND LIFE PROCESSES
      - NITROGEN CYCLE
        CARBON CYCLE
        HYDROLOGIC CYCLE
        H₂O EVAPORATES ⇨ H₂O CONDENSES ⇨ H₂O PRECIPITATES
        PHOSPHORUS CYCLE
        phosphorus moves from ROCKS on LAND TO OCEANS thru WEATHERING; causes erosion
        gets trapped into sediments ⇨ phosphorus moves back onto land following a geological upheavel ⇨ producers take in inorganic phosphorus, incoporate it into prganic molecules ⇨ plants pass it to consumers
        HUMAN ACTIVITIES
        phosphate is a limiting inorganic nutrients for plants
        PHOSPHATES are used in FERTILIZERS, ANIMAL FEEDS, DETERGENTS
        excess phosphates in water supplies leads to EUTROPHICATION
        algal blooms decrease oxygen and can lead to massive aquatic organism degradation
        begins with PHOTOSYNTHETIC ORGANISMS taking CO₂ from air and CHANGING its FORM (CARBON FIXATION)
        CARBON is CHANGED from gaseous CO₂ to less mobile ORGANIC MOLECULES like sugar ( C₆H₁₂O₆)
        SUGAR molecules are ABSORBED and made AVAILABLE to cells for CELLULAR RESPIRATION or production of more complex biomolecules
        photosynthesis TAKES up carbon dioxide from the atmosphere, cellular respiration RETURNS it to the ATMOSPHERE
        RESERVOIRS OF CARBON:
        dead organisms, fossil fuels, shells, limestones
        CARBON RECYCLING TAKES LONG TIME
        SULFUR CYCLE
        most of earths sulfur is tied up underground in rocks and minerals
        weathering, emissions from deep floor vents, volcanic eruptions release inorganic sulfur into air and water
        living organisms, especially bacteria, also sequester sulfur in biogenic deposits or release it into the environment
        HUMAN ACTIVITIES
        release large quantities of sulfur by burning fossil fuels; emits SULFUR DIOXIDE (SO₂) contributes to ACID RAIN; ACID RAIN DAMAGES ECOSYSTEMS and statues
        NITROGEN gas makes up ~ 78% of ATMOSPHERE
        PLANTS CANNOT USE NITROGEN GAS
        PLANTS acquire nitrogen via NITROGEN-FIXING BACTERIA that live in and around their ROOTS
        the bacteria will COMBINE N₂ with HYDROGEN to make ammonia NH₃ and ammonium (NH₄ᐩ)
        consumers ingest nitrogen from their diet to produce proteins and nucleic acids
        HUMAN ACTIVITIES AFFECT NITROGEN CYCLE
        nitrogen is added to FERTILIZERS; RUNOFF contains nitrogen; leads to EUTROPHICATION
        BURNING FOSSIL FUELS release NITRUS OXIDE (N₂O) a GREENHOUSE GAS
        NITROGEN FIXATION:
        conversion of nitrogen to ammonium ions (N₂) ⇨ (NH₄ᐩ)
        NITRIFICATION
        production of nitrates (NO₂) which plants can use
        nitrogen gas converted to nitrate in atmosphere by lighting
        ammonium in soil converts to nitrate via nitrogen fixing bacteria
        plant CELLS ABSORB NITRATES, use them to BUILD PROTEINS
        DENTRIFICATION
        conversion of nitrate back to nitrogen gas via dentrifying bacteria
        nitrogen REENTERS ENVIRONMENT thru the death of organisms
        fungi and bacteria DECOMPOSE DEAD organisms, which RELEASES AMMONIA and AMMONIUM IONS for NITRATE FORMATION
        NITROGEN FIXATION ⇨ NITRIFICATION ⇨ ASSIMILATION ⇨ AMMONIFICATION ⇨ DENTRIFICATION
- CHAPTER 3 : Evolution, Species Interactions, and Biological Communities
  - EVOLUTION LEADS TO DIVERSITY
    - NATURAL SELECTION AND ADAPTATION
      - ADAPTATION
        the acquisition of traits that allow a species to survive in its environment
        NATURAL SELECTION
        occurs when the fittest individuals are passing traits on to the next generation while those with less adaptive traits reproduce less successfully
        FITNESS
        REPRODUCTIVE SUCCESS
        MUTATIONS
        changes to the DNA
    - LIMITING FACTORS INFLUENCE SPECIES DISTRIBUTIONS
      - organisms physiology and behaviour allow them to survive in certain environments
        critical limiting factors keep an organism from expanding everywhere
        SELECTION PRESSURES
        temperature, moisture, nutrient supply, soil and water chemistry, living space
        TOLERANCE LIMITS
        each environmental factor has minimum to maximum levels, species cannot survive and/or unable to reproduce
        tolerance limit can be shown via tolerance curve; when out of optimum range, species experience stress
    - HABITAT VS ECOLOGICAL NICHE
      - ECOLOGICAL NICHE
        GENERALISTS
        SPECIALISTS
        species which have a narrow ecological niche
        COMPETITIVE EXCLUSION PRINCIPLE
        no two species can occupy the same ecological niche at the same time if resources are limited; leads to total exclusion
        RESOURCE OF PARTITIONING
        differences in way resource is utilized; decreases competition between two species, use different parts of the same resource and coexist within habitat
        species that tolerate a wide range of conditions and exploit a wide range of resources
        role played by organism, and the set of environmental factors and determine its distribution
        endemic species occur in one area
        SPECIATION LEADS TO SPECIES DIVERSITY
        SPECIATION
        development of new species
        ALLOPATRIC SPECIATION
        SYMPATRIC SPECIATION
        occurs within one geographical area due to behavioural isolation
        occurs when populations are geographically separated
      - TAXONOMY DESCRIBES RELATIONSHIPS AMONG SPECIES
        DOMAINS: bacteria, archaea, eukarya; kingdoms of eukarya: animals, plants, fungi, protists
      - COMPETITION LEADS TO RESOURCE ALLOCATION
        INTRASPECIFIC
        INTERSPECIFIC
        competition between members of different species
        competition among members of same species
    - COMMUNITY DIVERSITY
      - ABUNDANCE
        DIVERSITY
        # of different species in an area, # per unit in area
        communities with high diversity often have few individuals of any one species
        most communities contain a few common species and many rarer ones
        RESILIENCE SEEMS RELATED TO COMPLEXITY
        COMPLEXITY
        # of trophic levels in a community, # of species at each level
        complex interconnected community might have many trophic levels and groups of species performing the same functions
        in most cases the more complexity a community possesses, the more resilient it is when disturbance strikes
        COMPLEXITY AND BIODIVERSITY IS A GOOD THING
        PRODUCTIVITY VARIES IN ECOSYSTEMS
        PRIMARY PRODUCTIVITY
        production of biomass by photosynthesis
        produces biomass by converting solar energy into chemical energy
        depends on light levels, temperatures, moisture, and nutrient availability
        varies dramatically among different ecosystem types
        expressed as units of biomass or energy per unit area per year
        biomass accumulates at different rates in different ecosystems
        # of individuals of a particular species in an area; density measure
      - PATTERNS PRODUCE COMMUNITY STRUCTURE
        UNIFORM DISTRIBUTION
        RANDOM DISTRIBUTION
        CLUMPED DISTRIBUTION
        species clumps together for protection, mutual assistance or reproduction; common; forms a herd ex. fish, buffalo
        individuals live where ever resources are available; chain events allow them to settle ex. trees, flowers
        often arises from competition and territoriality ex. penguins, seabirds
      - COMMUNITIES ARE DYNAMIC AND CHANGE OVER TIME
        ECOLOGICAL SUCCESSION
        change in communitys composition over time that is directional and follows a continuous pattern of extinction and colonization by new species
        PRIMARY SUCCESSION
        establishment of plant community in a newly formed area where there is no soils; rocky volcanoes, mountains
        PIONEER SPECIES
        first plants to colonize bare substrate; lichens and mosses
        SECONDARY SUCCESSION
        the return of a community to its natural vegetation following a disturbance
        TYPES OF DISTURBANCES:
        agricultural, forest fire, natural disasters, human disturbances
        end stage of succession depends on biome; takes 150+ years
        grasses ➜ low shrubs ➜ high shrubs ➜ shrub/tree mix ➜ low trees ➜ high trees
        SUCCESSION WILL REACH CLIMAX COMMUNITY
        CLIMAX COMMUNITY
        end stage of succession ex. temperate deciduous forest
  - SPECIES INTERACTIONS
    - interactions with other species causes species to evolve i.e. competition, predation
      - PREDATION AFFECTS SPECIES RELATIONSHIPS
        PREDATORS
        HERBIVORES, CARNIVORES, OMNIVORES
        PREDATION LEADS TO ADAPTATION
        COEVOLUTION; predators and prey entwined
        species with chemical defense often display distinct colouration and patterns to warn enemies
        prey camouflage; species display forms, colours, patterns that help them hide
        SYMBIOTIC RELATIONSHIPS
        SYMBIOSIS
        close interaction between members of two or more species; can enhance survival of one or two species
        MUTUALISM
        COMMENSALISM
        PARASITISM
        parasite derives nourishment from host ex. mosquito
        one species benefits ex. clownfish and anemones
        both species benefit ex. bee and flower
    - POPULATION GROWTH
      - PATTERNS OF POPULATION GROWTH
        BIOTIC POTENTIAL
        unrestrained biological reproduction of an organism
        FACTORS THAT INFLUENCE BIOTIC POTENTIAL:
        average # of offspring per reproduction
        chances of survival until age of reproduction
        age of first reproduction
        how often each individual reproduces
        INHERENT RATE OF REPRODUCTION INFLUENCES POPULATION SIZE
        CARRYING CAPACITY LIMITS GROWTH
        CARRYING CAPACITY
        # or biomass of organisms that can be supported in an area
        *suggests limit
        resources become limited, death rates rise, population crashes
        LIMITS TO POPULATION SIZE
        DENSITY-DEPENDENT FACTORS
        affected by population size
        food shortage, disease, parasites, predation
        DENSITY-INDEPENDENT FACTORS
        limits population that are nonbiological and are often result of acts of nature
        flood, fire, pesticides, climate and temperature change, habitat destruction, drought
        PATTERNS OF POPULATION GROWTH
        SURVIVORSHIP GROWTH CURVE
        assume all individuals are identical; in real life individuals are different life stages
        plot # of individuals surviving over time gives survivorship curve
        COHORT
        a group of individuals born at the same time
        TYPE 1
        TYPE 2
        TYPE 3
        most individuals die early (young), low rates of death for those who survive; species produces lots of offspring ex. insects, sea turtles
        individuals that die consistently overtime; uniform rate ex. songbirds, reptiles
        most individuals survive until old age ex. humans, elephants
      - EXPONENTIAL PATTERN OF POPULATION GROWTH
        J-SHAPED CURVE
        LAG PHASE
        growth small because population small
        EXPONENTIAL GROWTH PHASE
        growth accelerating, population exhibits biotic potential
        *usually CANNOT continue long due to environmental constraints i.e. physical space, food, water
        LOGISTIC PATTERN OF POPULATION GROWTH
        S-SHAPED CURVE
        intensity of environmental resistance increases as population grows larger
        population growth slows, levels off as it reaches carrying capacity
        *more typical
        R-SELECTED and K-SELECTED SPECIES
        R-SELECTED SPECIES
        K-SELECTED SPECIES
        organisms reproduce conservatively with longer generation times, late sexual maturity, fewer offspring; adapted for slower growth conditions near carrying capacity (k) of their environment ex. humans, elephants
        specialists, predators
        organisms adapted to employ a high reproductive rate and growth (r) to secure a place in its environment ex. mice, dandelions
        generalists, prey
  - Chapter 4: Human Populations
    - PAST AND CURRENT POPULATION GROWTH ARE VERY DIFFERENT
      - EVERY SECOND on earth 4 to 5 HUMANS are BORN, whilst 1 to 2 HUMANS DIE
        in 2011 we reached 7 BILLION PEOPLE
        as of FEBRUARY 7, 2022, we have approx. 7,925,598,275 PEOPLE
        the most recent BILLION happened in 12 YEARS
        human population is growing 1.1% per year
        HIGHEST POPULATION DENSITY:
        United States, Europe, India, China, South East Asia
        COUNTRIES WITH LARGEST POPULATION:
        China and India
        CALCULATE IMPACT - IPAT FORMULA
        impact = population x affluence x technology
        ECOLOGICAL FOOTPRINT
        a single # that estimates the relative amount of productive land required to support human population
        i.e. forests/grasslands store carbon, protect watersheds, purify water, wildlife habitats
      - HUMAN POPULATION GREW SLOWLY UNTIL RECENTLY
        before agriculture, humans were nomadic
        agriculture evolution = human population growth
        HUMAN POPULATION INCREASES ARE RELATIVELY RECENT
        human populations began to reproduce rapidly about A.D. 1600
        it took 156 years to get to 3 billion in 1960
        # of humans tripled during 20th century
        DOES ENVIRONMENT OR CULTURE CONTROL HUMAN POPULATION GROWTH?
        1798, Malthus hypothesized humans would outstrip supplies and collapse
        Karl Marx, population growth resulted from poverty, resource depletion, pollution
        TECHNOLOGY INCREASES CARRYING CAPACITY FOR HUMANS
        surpassed earths carry capacity; or approaching
        earth is estimated to only handle 10-12 billion
        Malthus did not account for scientific and technological advances
        progress in agriculture, engineer, info, commerce, medicine, sanitation enabled there to x 1,000 more people than 10,000 years ago
      - FERTILITY IS INFLUENCED BY CULTURE
        PRONATALIST PRESSURES
        factors that increase peoples desire to have babies
        lesser countries have child labour, society also needs to replace people
        EDUCATION AND INCOME AFFECT THE DESIRE FOR CHILDREN
        HIGHLY DEVELOPED COUNTRIES
        DEVELOPING COUNTRIES
        feeding and clothing is minimally expensive, adding one more child is negligible compared to the costs in developed countries
        higher education and personal freedom affect women to not have children
        desire to spend money and time on other priorities, limits # of children
        DEMOGRAPHIC TRANSITION CAN LEAD TO STABLE POPULATION SIZE
        DEMOGRAPHIC TRANSITION
        a typical pattern of falling death rates and birth rates due to improved living conditions that usually accompanies economic development
        THE DEMOGRAPHIC TRANSITION MODEL
        STAGE 1
        STAGE 2
        STAGE 3
        STAGE 4
        represents conditions in developed countries, where the transition is complete and both birth and death rates are low
        populations grow rapidly when death rates have already fallen but birth rates remain high
        economic development brings better jobs, medicare, sanitation; generally improved standard of living, and death rates often fall very rapidly
        economic and social conditions change mortality and births; represent conditions in premodern society
        MANY COUNTRIES ARE IN DEMOGRAPHIC TRANSITION
        some demographers claim that a demographic transition already is in progress in most developing nations
        they believe that lag between falling death and birth rates may hide this for a time but the world populations should stabalize by 2100
        IMPROVING WOMENS LIVES HELP REDUCE BIRTH RATES
        responsible economic development, education, womens rights, high-quality health care
        FAMILY PLANNING GIVES US CHOICES
        FAMILY PLANNING
        allows couples to determine the # and spacing of their children
        BIRTH CONTROL
        any method used to reduce births including celibacy, delayed marriage, contraception, and methods that prevent embryo implantation
    - MANY FACTORS DETERMINE POPULATION GROWTH
      - DEMOGRAPHY
        vital statistics about people, such as births, deaths, where they live, and total population in size
        FACTORS AFFECTING POPULATION GROWTH
        average age of population (some skewed, old or young)
        varies among cultures and at different times
        mortality offsets births
        life expectancy is rising worldwide
        living longer has profound social limitations
        TOTAL FERTILITY RATE IS IMPACTED BY CULTURE
        TOTAL FERTILITY RATE
        # of children born to an average woman in population during her entire reproductive life
        RATE VARIES DEPENDS ON:
        education, access to modern health care, and religious practices
        WORLD FERTILITY RATES ARE DECLINING
        ZERO POPULATION GROWTH (ZPG) occurs when births and immigration = deaths emigration
        takes several generations of replacement - level fertility to reach ZPG
        fertility rates have declined dramatically in most regions of the world over the past 50 years
        while the world still has an AVERAGE FERTILITY RATE OF 2.6, growth rates are now lower than at any time since World War II
        LIFE EXPECTANCY IS RISING WORLDWIDE
        LIFE SPAN
        LIFE EXPECTANCY
        average age that newborn infant can expect to attain in any given society
        life expectancy is related to income
        oldest age to which a species is known to survive
        LIVING LONGER HAS PROFOUND SOCIAL IMPLICATIONS
        AGE CLASS HISTOGRAMS
        shows differences between different ages of people in population and illustrate the social implications of population growth
        DEPENDENCY RATIO
        # of nonworking compared with working individuals in a population
        in Niger each working person supports a high # of children
        in US a declining working population is now supporting a growing # of retired persons
        by prereproductive, reproductive, postreproductive

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