Unit 3: Populations

Notes

Population description

• Population density: number of individuals of a population that inhabit a certain unit of land/water area

• Population dispersion: how individuals of a population are spaced within a region

• Random

• position of each individual is not determined/influenced by the other members of the population

• Relatively uncommon

• Clumping

• Most common dispersion pattern

• Individuals flock together (ex. avoid predation, migration groups)

• Uniform

• Uniformly spaced throughout their geographic region

• Often the result of competition for resources in an ecosystem

Population growth

• Biotic potential: amount the population would grow it there were unlimited resources in its environment

• Carrying capacity (K): max pop size that can be sustainably supported by the available resources in the region

• Exponential growth

• Aka J curve

• Ex. bacteria grows exponentially

• Logistic growth

• Aka S curve

• Initial burst in population → growth rate generally drops → curve flattens into S

• Rule of 70

• Predict long term population growth rates

• The time it takes for a pop to double can be approx by dividing 70 by the current growth rate of the population

• r-selected organisms

• Reproduce early in life

• High capacity for reproductive growth

• Ex. bacteria, algae, protozoa

• little/no care given to offspring → due to sheer numbers of offspring in the population, enough of the offspring will survive to enable the population to continue

• K-selected organisms

• Reproduce later in life, produce fewer offspring, devote sig time and energy to the nurturing of their offspring

• Imp to preserve as many members of the offspring as possible bc they produce so few

• Ex. humans, lions, cows

• Density dependent factors: changes population’s size based on density

• Ex increased predation (more members of the population to attract predators); competition for food or shelter; disease (spreads more rapidly in overcrowded pop); buildup of toxic materials

• Density independent factors: change pop size regardless of pop size

• Ex. fire, storms, earthquakes, natural disasters

Population cycles

• Boom and bust cycle

• Common among r-strategists

• Rapid increase in the population and then an equally rapid drop off

• Rapid changes linked to predictable cycles in env (temp, nutrient availability)

• When conditions are good for growth, pop incr rapidly → when conditions worsened, umbers rapidly decr

• Predator-prey cycle

• Incr reproduction of prey means that predators have plenty of food, pop incr rapidly

• Next year, less prey means predator pop also decr

• Predator population rises after prey population does because the prey population has to have time to build up fairly high levels before the predators can find enough to eat

• When there is enough good, reproducing predators have enough energy to give birth and feed their offspring → predator pop incr

Human populations

• Actual growth rate (%) = (birth rate - death rate) / 10

• Crude birth rate = number of live births per 1000 members of the pop in a year

• Crude death rate = number of live deaths per 1000 members of the pop in a year

• Emigration: movement of people out of a pop

• Immigration: movement of people into a pop

• Replacement birth rate: number of children a couple must have in order to replace themselves in a pop

• Factors that affect total fertility rates in a pop

• Availability of birth control

• Demand for children in the labor force

• Base level of edu for women

• Existence of public and/or private retirement sys

• Population religious beliefs, culture, traditions (for/against reproduction)

• Age structure pyramids

• 0-14: pre-reproductive

• Majority here: pop increase in size as time goes by

• 15-44: reproductive

• 45+: post-reproductive

• Majority here: pop size decreases in the future bc mot are incapable of reproducing

• Life expectancy

• Fertility rate

Demographic transition model

• Used to predict population trends based on birth and death rates of pop

• Demographic transition: when pop moves from first state to the second state

States

1. Pre-industrial state

1. Population exhibits slow rate of growth

2. Harsh living conditions- high birth rate and high death rate

3. Environmental resistance: conditions that slow a pop growth (ex. harsh living conditions)

2. Transitional state

1. Birth rates high

2. Due to better good, water, and HC, death rates are lower

3. Rapid pop growth

3. Industrial state

1. Pop growth state is still fairly high

2. Birth rate drops → similar to death rate

3. Many dev countries are currently in this state

4. Postindustrial state

1. Pop approaches and reaches a zero growth rate

2. Pop can drop below zero growth rate (RUS, S AFR, JAP)

Humans on earth

Increase pop

• Improved nutrition, availability of clean water, newly implemented sys for sanitary waste disposal, better medical care

• Increase in food production

• Almost half of earth’s land surface is devoted to producing food for humans

• 12 % farms

• 11% forests planted by humans

• 26% grazing livestock

• Bad MPX: erosion, chemical residues

• Deficiency of housing or habitable areas for incr population

• Homeless

• Homes in completely undev areas (no water/elec; no stable durable housing)

Resources

• Macronutrients: nutrients needed in large amounts (proteins, carbs, fat)

• Micronutrients: nutrients needed in smaller amounts (vitamins, iron, minerals)

• Hunger: insufficient calories taken in to replace those being expended

• Malnutrition: poor nutrition that results from an insufficient or poorly balanced diet (lack essential vitamins and other components)

• Undernourished: not receiving sufficient resources

• Urban sprawl: emigration of ppl out of the city and into suburbs

• Urban areas grow too large and become too dense → providing water to all citizens becomes difficult

• Strain on water supply, more ppl = more water use → newly crowded areas lead to water shortage → restrictions on water usage

Sustainability

• Transportation

• Encouraged to use mass transit or carpools rather than drive separately (fewer cars decr air pollution from automobiles and results to less congestion)

• Green modes of transpo: bikes, moto scooters, electric bikes

• Larger cities: build subway systems (very expensive to dev; only cost eff when they’re enough ppl who will pay to use them)

• Large/small cities: city buses → less expensive than subways to create and maintain; contribute to road congestion but decr congestion by having more ppl per vehicle

• Rapid-rail/light rail sys: magnetic levitation → suspended above a track, train moves along by strong attractive and repulsive magnetic forces

• Cities

• Boulder, colorado

• Forward-thinking green policies

• Bike paths cover the city → cyclists move freely from one area of the comm to another

• Buses move around the city and in’n’out of denver and surrounding comm → ppl commute w/o using cars

• Strong recycling programs help decr amount of material added to landfills

• Open spaces that can be used by city pop for rec

• Curitiba, brazil

• Mass transport sys (bike paths, pedestrian walkways)

• Recycling programs, job training, HC, env edu provided for citizens

• Portland, oregan

• Statewide zoning policies and restrictive growth policies for urban areas

• City developers encouraged to invest in est neighborhoods rather than dev undisturbed areas

• Est Metro (regional body that deals with land use, city planning, and dev of natural areas)

• Light rail sys developed

• Ecological footprint

• Env impact of a pop

• Amount of earth’s surface that's necessary to supply the needs of and dispose of the waste of a particular population

• Affluent pop have a much higher eco footprint than non-affluent ones

• I = P • A • T

• I = total mpx

• P = pop size

• A = affluence

• T = level of tech