APES Unit 3: Populations

specialist species

Species with a narrow ecological niche. They may be able to live in only one type of habitat, tolerate only a narrow range of climatic and other environmental conditions, or use only one type or a few types of food. (EX: panda)

generalist species

species with a broad ecological niche, larger range of tolerance, less prone to extinction, more likely to be invasive, broad food requirements (EX: racoons, mice)

k-selected species

Species that produce a few, often fairly large offspring but invest a great deal of time and energy to ensure that most of those offspring reach reproductive age. More likely to be disrupted by environmental change or invasive species due to slow population growth rate. (EX: mammals, birds)

r-selected species

Species that reproduce early in their life span and produce large numbers of usually small and short-lived offspring in a short period. Better suited for rapidly changing environmental conditions due to high population growth rate (EX: insects, fish, plants)

survivorship curve

line that shows survival rate of a cohort (group of same-aged individuals) in a population from birth to death (faster drop in line = quicker die-off of individuals)

Type 1 survivorship curve

• a pattern of survival over time in which there is high survival throughout most of the life span, but then individuals start to die in large numbers as they approach old age - mostly k-selected species (mammals)

type 2 survivorship curve

a pattern of survival over time in which there is a relatively constant decline in survivorship throughout most of the life span (species between r and k selected)

type 3 survivorship curve

• a pattern of survival over time in which there is low survivorship early in life with few individuals reaching adulthood due to no parental care - mostly r-selected species

carrying capacity (k)

the maximum number of individuals in a population that can be supported in a particular habitat over a sustained period of time (based on limiting resources)

limiting resources

determines the highest population size an ecosystem can support (EX: food, water, habitat)

overshoot

when a population briefly exceeds carrying capacity (consequence = resource depletion)

die-off

sharp decrease in pop. size when resource depletion (overshoot) leads to many individuals dying

population size (N)

total number of individuals in a given area at a given time (larger = safer for population decline)

population density

Number of individuals per unit area (high _____ = higher competition, possibility of disease outbreak, possibility of resource depletion)

population distribution

how individuals within a population are distributed with respect to one another (random, uniform, and clumped)

random distribution

organisms arranged in no particular pattern (EX: trees)

uniform distribution

Distribution where populations are spaced evenly (EX: territorial animals)

clumped distribution

individuals are found in groups or patches within the habitat (EX: herd/group animals)

sex ratio

• the ratio of males to females in a population - closer to 50:50, the more ideal for breeding (usually) - die-off or bottleneck event can lead to skewed sex-ratio limiting population growth

biotic potential

• the potential growth of a population if it could grow in perfect conditions with no limiting factors - also called, "intrinsic rate of increase (r)" - may occur initially, but limiting resources slow growth, and eventually limit population to carrying capacity - exponential growth

density-dependent factors

• limiting factor that depends on population size - tend to be biotic, have strong influence when the number of organisms per unit of area reach a certain level

density-independent factors

• limiting factor that affects all populations in similar ways, regardless of population size - tend to be abiotic, have an effect on all populations, regardless of size or density - EX: natural disease

logistic growth

Growth pattern in which a population's growth rate slows or stops following a period of exponential growth

age cohorts

groups of people categorized by age range

Total Fertility Rate (TFR)

• The average number of children a woman will have throughout her childbearing years. - developing nations = >2.1 - developed nations = <2.1

replacement level fertility

the total fertility rate required to offset the average number of deaths in a population in order to maintain the current population size (approximately 2.1)

Infant Mortality Rate (IMR)

• The total number of deaths in a year among infants under 1 year old for every 1,000 live births in a society. - high ____ = high TFR

Malthusian Theory

focuses on how the exponential growth of a population can outpace growth of the food supply and lead to social degradation and disorder

population growth rate

explains how fast a given population grows

Crude Birth Rate (CBR)

The total number of live births in a year for every 1,000 people alive in the society.

Crude Death Rate (CDR)

The total number of deaths in a year for every 1,000 people alive in the society.

doubling time

The number of years needed to double a population, assuming a constant rate of natural increase.

industrialization

the process of economic and social transition from an agrarian (farming) economy to an industrial one (manufacturing based)

Stage 1 of Demographic Transition Model

low growth - high birth rate, high death rate, (birth and death rate cancel each other out), and low population growth

Stage 2 of the Demographic Transition Model

high growth - high birth rate, falling death rate, high population growth (society: from agricultural to urbanized, raising quality of life)

Stage 3 of the Demographic Transition Model

moderate growth - falling birth rate, low death rate, steady population growth (urbanized and more industrialized families have less children)

Stage 4 of the Demographic Transition Model

low/stationary growth - (SPL) low birth rate, low death rate, steady/stationary population growth

population density formula

population/area

crude birth rate formula

(births/total population) x 1000

crude death rate formula

(Deaths/Total Population) x 1000

population growth rate formula

((births - deaths)/ total population) x 100 OR (CBR/CDR)/10

doubling time formula

70/growth rate %

future population formula

(initial population) x (growth rate)^years