3.1 Generalist & Specialist Species

• some species (generalist feeders) adapt to environmental changes better than other species (specialist feeders)

• generalist species: thrive in dynamic environments; can adapt well (broad niche)

  • can live in a variety of environments

  • broad range of ecological tolerance (no specific diet or habitat)

  • usually known for being invasive species

    • ex. raccoons, mule deers, rats, bald eagles

• specialist species: thrive in stable environments; easily struggle or succumb to changes in habitat (narrow niche)

  • only live in specific conditions

  • narrow range of ecological tolerance (limited diet, conditions, and habitat)

    • ex. giant pandas, mountains gorillas, osprey

3.2 K-Selected & r-Selected Species

• K-selected species: large, quality > quantity in offspring, long life spans, late maturation can reproduce multiple times, specialists, large body types, strong competition in their particular environments

  • high levels of competition for resources in the habitat

  • more prone to the colonization of invasive species

  • can maintain the population at carrying capacity (adjusting population to utilize resources efficiently)

    • ex. giant pandas, elephants

• r-selected species: small, quantity > quality in offspring, early maturation, reproduce only once, generalists

  • low competition for resources in the habitat

  • prone to overpopulation by exceeding the carrying capacity

  • can experience population dieback due to overpopulation

    • ex. mosquitos, invasive species

• biotic potential: max ideal reproductive rate of a population (measurement of growth capacity in populations)

  • ex. 1-2 cubs for giant pandas

• many species have characteristics of both K-selected and r-selected species

  • ex. osprey, frogs, sea turtles

3.3 Survivorship Curves

• survivorship curve: displays the relative survival rates of a group of same-age individuals in a population

  • x-axis: max lifespan of organisms from birth to death

  • y-axis: percent of surviving organisms in a population (logarithmically)

Types of Survivorship Curves

• Type I: late loss

  • a large number of the population survives throughout their lifespan, reaching old age

  • dies at the end of their lifespan

  • adequate care → increasing chances of survival to maturation

  • represents many K-selected species

    • ex. mountain gorillas

• Type II: constant loss

  • death rate constant from birth to death

  • organisms die throughout their lifespan

    • ex. birds, squirrels

• Type III: early loss

  • surviving rate drops immediately after birth; few organisms survive to adulthood

  • little to no care → high infant mortality

  • represents many r-selected species

    • ex. monarch butterflies

3.4 Carrying Capacity

• >= carrying capacity → resource depletion → famine, disease, and conflict

• carrying capacity: max number of organisms the environment can support without resource degradation

  • represented as a horizontal dotted line at the top of the graph labeled K

• population dieback: decrease in population as a result of resource degradation caused by overpopulation in species

  • exceeding carrying capacity → population dieback → within carrying capacity

    • ex. reindeer of st. matthew island

3.5 Population Growth and Resource Availability

• environmental resistance: factors that limit population growth

  • emerges after the population goes over carrying capacity

• exponential growth = unlimited resources

  • occurs in all populations below carrying capacity (competition does not greatly affect population growth)

• logistic growth = limited resources

  • occurs in populations at or above carrying capacity when competition is a dependent variable

• fecundity: ability to produce offspring

  • including factors such as maturation age, reproductive rate, biotic potential, and reproductive strategy

Types of Environmental Resistance Factors

• density-dependent resistance factors: biotic, affects organisms when population density is high

  • ex. competition, predation, parasitism

• density-independent resistance factors: abiotic, affects all populations regardless of size or density

  • ex. natural disasters or droughts

3.6 Age Structure Diagrams

• another name for population pyramid

  • shows the distribution of ages in a population divided by males and females

  • shapes represent trends within the population

• x-axis: # of individuals (left side male right side female)

• y-axis: center of the diagram showing age groups

  • reproductive: 0-14 years

  • reproductive: 15-45 years

  • post-reproductive: 46-100+ years

• higher proportion of young people = rapid population growth (bottom heavy)

  • wide base, pyramid shape

  • indicates developing nation

    • ex. india, brazil, nigeria, mexico

• higher proportion of middle-aged people: stable population growth (middle heavy)

  • rectangular shape

  • similar percentages throughout all age groups

  • indicates more developed nations

    • ex. united states, sweden, canada, austrailia

• higher proportion of elder people: declining population growth (top heavy)

  • inverted pyramid shape

  • many people in the post-reproductive stage

  • more economic and social development, higher education common

  • long-term impact on social services

    • ex. japan, germany, italy, russia

3.7 Total Fertility Rate

• TFR: avg # of children a woman has during her childbearing years (15-49)

  • been lowering in recent years depending on the country

    • ex. world avg = 2.5

• developing countries: TFR > 2.1

  • rapid population growth

    • ex. niger, congo, uganda

• developed countries: TFR <= 2.1

  • stable/declining population growth

    • ex. united states, japan, united kingdom

Societal Factors

• age of first pregnancy

• educational opportunities for women

• family planning resources

• governmental regulations

• access to healthcare resources

3.8 Human Population Dynamics

• thomas malthus → all populations have a carrying capacity

• humans are limited by density-independent & density-dependent factors

  • density-independent factors: affects population regardless of size or density

    • ex. storms, fire, heat waves, droughts

  • density-dependent factors: affects population based on size or density

  • arises during overshoot and dieback → decreasing overpopulation

    • ex. disease transmission, territory size, food availability, access to clean air and water

• doubling time: the amount of time a population takes to double at a constant growth rate

  • calculated using rule of 70

    • rule of 70: 70/r = doubling time

    • r = growth rate of population (%)

Environmental Problems

• density-independent factors

  • hurricanes → drop in population due to property damage, economic loss, and better opportunities elsewhere

• more years a woman is in school = lower TFR

Societal Factors

• birth rates:

  • high rate = rapid population growth

  • low rate = slow population growth

• death rates:

  • high rate = slow population growth

  • low rate = rapid population growth

• education of women:

  • high rate = slow population growth

  • low rate = rapid population growth

• infant mortality:

  • high rate = slow population growth

  • low rate = rapid population growth

• age of marriage:

  • early - rapid population growth

  • late - slow population growth

• nutrition:

  • better = rapid population growth

  • worse = slow population growth

3.9 Demographic Transition

• demographic transition: model that shows trends in CBR, CDR, and total population

  • derived from historical data

  • moving towards industrialization from agricultural-based economies

  • development shown in 4 stages

• Stage 1: high infant mortality, child labor → low growth (preindustrial)

• Stage 2: improved resources → very high growth (transitional)

  • the gap between birth and death rate widens

  • less developed countries (LDC)

• Stage 3: high education amongst women, low infant mortality → slower growth (industrial)

  • less developed countries (LDC)

  • birth and death rate are almost equal

• Stage 4: stage 3 + aging population + tax burdens for senior citizen care → zero or negative growth (post-industrial)

  • more developed countries (MDC)