Unit 3 - Population

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
• i^^nfant 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)

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