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)