Chapter 6: Population Dynamics
population growth
rate - fig p 130
exponential growth grows at a constant rate J curve can determine a doubling time (4% annual
growth doubles population every 175 years)
arithmetic growth grows by a constant amount rate decreases over time
biological reproduction
exponential
offspring can reproduce at the same rate as parents
biotic potentialmaximum reproductive rateactual rate limited by other factors
carrying capacity
population limit
environmental resistance
growth patterns/strategiesoscillations - fig p 131 overshoot & dieback irruptive/Malthusian growth regular or irregular
logistic growth - fig p 132 constantly changing rate S-curve little resistance - exponential growth rate increasing resistance - slows growth rate
chaotic (variation of oscillation) natural fluctations may include catastophic changes no apparent mathematical pattern not necessarily random
reproductive strategy
table p132externally controlled many offspring rapid growth low trophic level little parental care/effort
intrinsically controlled few offspring slow growth high trophic level much parental care/effort
factors that effect population sizenatality: production of new individuals fecundity - ability to reproduce fertility - number of offspring produced
immigration & emigrationmortality death rate survivorship - curves - fig p 135 life expectancy - probabale life span for an individual at a certain age life span - maximum possible age
age structure histograms - fig p 135 patterns (expanding, stable, diminishing)
factors that effect population growth
extrinsic vs intrinsic
biotic vs abiotic
density dependent vs independent
may be positive or negative
pop. growth factors
density independent usually abiotic weather, climate catastrophes
fires volcanoes weather
density dependent usually biotic interspecific
predator-prey parasitism competition for resources mutualism and
commensalism intraspecific
competition for resources - individuals of a
species inhabit the same niche
mates territoriality
crowding stress shock too much competition
Human Population - fig p 144low population with respect to most speciesearly controls on size disease famine war culture
after 1600 international commerce international communication ag development power supplies medicine hygiene
Limits to growth - fig p 145Malthusian human population growth > growth rate of food supply stabilizing factors
disease & famine reduced birth rate (late marriage, no kids until you can afford them)
however: most people are too lazy/immoral to regulate birthrates voluntarily
don’t help the poor overpopulation is a cause
Marx social injustice is the problem people will regulate themselves given the opportunity and fair share poverty & overpopulation are consequences
open questions
WHAT IS THE MAXIMUM CAPACITY???What is the relationship of population growth, poverty, and env. degradation?What are the effects of technology?What are the benefits of more people?Was Malthus correct? Marx? neither? both?
Demographicsmeasurement of peopletotal populationnever actually countedappx. 6 billion top 10: China, India, US, Indonesia, Brazil,
Pakistan, Russia, Bangladesh, Nigeria, Mexico,
densitypeople per mi2 - map p 148
Population growth
natural rate = births - deaths
total rate = (births + immigration) - (deaths + emigration)
Fertility
crude birthrate - births per year per 1000total fertility rate - # of children born to an avg. women during her reproductive years highest - Ivory Coast – 7.5 lowest Italy – 1.3
birthrates for men??? - not countedzero population growth replacement rate a bit more than 2 per couple
mortalitymortality rate - deaths per 1000 per yearlife span max possible age 122?
expectancy average age a newborn can expect to attain increases as you age has risen dramatically responsible for population increase related to affluence (fig p. 151) implications - age structure - fig p 152
young support old if the bottom of the histogram thins…?
emigration & immigration
culturaleconomicdisease faminewarslaverypolitical
Controlling growth (or not)fig p 154pronatalist pleasure pride comfort economic support high infant mortality status
of men of women
culture replacement
reduction education economic status personal freedom work/career income/household budget status of women family planning
negative population growth
more resources per person less people to run the system
demographic transition
fig p. 156pattern high death and birth rates death rates drop birth rates follow later population size increases during the transition
current outlooks in transition, soon to be out stuck in transition transition will end when resources are equitably
distributed
future population
figs. p. 162 and 163
will stabilize in the next 100 years???
6 to 16 billion
What is the Carrying Capacity???
Human nutrition
needs minimum: 2000 to
2200 calories/day up to: 6000 to 7000
calories/day
problems undernourished
< 90% of minimum serious < 80% of minimum
overnourished malnourished: not enough of
the right things protein carbohydrates lipids and oils minerals vitamins
Food resourcescropsgrains tubers fruits & veggiessugar
animalsmeat & milkpoultry fish & seafood
Limited to a few (10-20) primary food sources!
Meat, milk, seafoodhigh in protein and nutrients and fatscrop useU.S.: 90% of grain is used to feed
livestock16kg of grain yields 1 kg of edible beef
overgrazingoverfishinghigh on the food pyramid!
new food sources
plantsregionalwild: hearty
“blue revolution”fish farmingfish ranching
world hungertypesfamine: short-term, severe shortagechronic shortages: under- and mal-nutrition
causesenvironmental conditionsfood distribution
politicseconomics
world food supply
how many people can be supported?
what is sustainable?
soil
regolith (weathered parent material)
organic material
water
air
soil formation
parent material is weatheredwaterbiological
material moves downward, creating layers (horizons)
rate: best is 1 mm/yr
soil horizons
figure, p. 245
layers
top soil is O & E
soil use
must consider climate
production landcrops or grazingdecreasing in developed worldincreasing in developing areas
soil degradation
erosion (7.4 million acres/yr are ruined)
desertification
conversion to non-ag
pollution
impoverishment (loss of fertility)
soil degradationcausesovergrazing – 35%deforestation – 30%cultivation – 28%overexploitation – 7%industrialization – 1%
mechanisms (graph p. 247)water erosionwind erosionchemicalphysical
soil degradation
solutionscontour tillingstrip croppingterracingground covertill reduction
agricultural resourceswaterrainfallirrigation (70% of water use)
fertilizersupplement natural cyclesinorganic, organicuse vs yield
energy (fig p 250)diversity
green revolutionchangesmore land in productiongeneticsfertilizerpesticides
benefit: greater yield/acredownsidesmall operators outreduction in diversityconcerns about bioengineering
sustainable agriculture
soil conservationlow input & low impactlower yieldecologically soundland reformreal pricingwomen’s rights
Pests
unwantedinterferingdestructive
plants or animals or fungi
pest control
biocideherbicideinsecticidefungicidenematociderodenticide
early methods
saltsmokeplantsinorganics (S, As, Hg)culturalalcoholspicespredators
modern methods
inorganicsnaturla organicsfumigantschlorinated hydrocarbonsorganophosphatescarbamatesmicrobial agentspredators and parasites
effectsgooddisease controlcrop protection
badnon-target speciesresistance and
resurgencepredator losspersistancemobilitybioaccumulationhuman health effects
alternativescrop rotationcultivationflooding/burningattract predatorsadjust planting timesavoid monoculturerepellant plantsgenetics/bioengineeringsterilizationintegrated pest management