BIOL_595: Demography and Population Growth (Exam 1)

what is demography?

the study of population statistics

what is a population?

• a group of conspecifics in a given place and time

• potential breeders

what is a cohort?

a group of conspecifics that join a population at the same time

what are the three age categories in a population?

1. pre-reproductive

2. reproductive

3. post-reproductive

what are the three types of age pyramids?

1. male vs. female

2. growing vs. declining

3. following a cohort

what three things do age pyramids allow us to do?

• look in the past

• project the future growth/decline of a population

• compare males to females

what would an age pyramid of a growing population look like?

• would have a wide base

• lots of births

what would an age pyramid of a declining population look like?

• would have a narrow base

• little births

how is mortality measured?

• crude death rate

• EX: number of deaths per 1,000 individuals per year

why is the crude death rate not very informative?

because not all individuals have the same risk of death

what is age-specific mortality?

• the PROPORTION of individuals alive at age x who do not survive to age x+1

• represented by mx

what is the equation for age-specific mortality?

mx = (nx - nx+1) / nx

what does x represent in the previous equation? n?

x: a given age group

n: the number of individuals within that given age group

what limits lifespans?

senescence

what two age groups have the highest mortality?

1. very young

2. very old

what is age-specific survival?

• the PROPORTION of individuals alive at age x who survive to age x+1

• represented by sx

what is the equation for sx?

sx = 1 - mx

what is survivorship?

• the PROPORTION of all individuals in an original cohort that survive to age x

• represented by lx

what is the equation for lx?

• lx = nx / n0

what is l0 always equal to?

1

what are the three types of survivorship curves?

1. type I

2. type II

3. type III

what goes on each axis of a survivorship curve graph?

x: total life span/age

y: lx on a log scale

what does a type I survivorship curve tell us?

• most of the population dies in old age

• typically common among social animals such as humans

what does a type II survivorship curve tell us?

• there is an equal probability of dying at each age

• usually typical of small mammals

what does a type III survivorship curve tell us?

• most of the population die very young, but those who do survive live until an old age

• commonly seen in invertebrates

what is Lx?

the proportion of individuals that survive to halfway between age x and age x+1

what equation do we use to determine Lx?

Lx = (lx + lx+1) / 2

what is Tx?

the sum of Lx from x to maximum x

what is ex?

• the age-specific life expectancy

• EX: if ex for a two year old is 1.5, that means that the average two year old is expected to leave 1.5 more years until they are 3.5

what is the equation for ex?

ex = Tx / lx

what are the two types of life tables?

1. cohort

2. time-specific

which life table is known as a dynamic life table?

cohort

which life table is known as a static life table?

time-specific

what is a cohort life table?

• a life table that follows a cohort from birth to last death

• allows us to measure demographic features accurately and directly

• can take an impossibly long time depending on the species

what is a time-specific life table?

• a table that includes data collected in a single season

• assumes birth rates and age specific mortalities are constant

• easier than cohort, but not as accurate

how is natality/fecundity measured?

• crude birth rate

• number of births per 1000 individuals per year

why is the crude birth rate not very informative?

not all individuals produce the same number of offspring

what is age-specific fecundity?

• the number of offspring per individual per year

• also the number of female offspring per female per year

• represented by bx

what is the net replacement rate?

• the number of individuals an individual will leave behind when they die; EX: R = 1… each individual will leave behind one by the time they die

• represented by R

what equation do we use to determine R?

Rx = the sum of lxbx

what are the two ways individuals can join a population?

1. birth

2. immigration

what are the two ways individuals can leave a population?

1. death

2. emigration

what type of generations does the exponential growth model deal with?

discrete generations

what are discrete generations?

individuals die after reproducing

what is the equation used to determine the number of individuals in a population at any given time using the exponential growth model?

• Nt = N0R^t

• N = total number of individuals

• t = time in generations/replacements

what is an example of a species who experiences discrete generations and exponential growth?

eastern tiger swallowtails

what type of growth does the exponential growth model deal with?

instantaneous growth

what is the equation for the instantaneous growth model?

• deltaN / deltat = rN

• deltaN / deltat is the growth rate

what is r in the previous equation?

• the intrinsic rate of natural increase

• instantaneous per capita birth and death rate

what shaped curve does an exponential growth model with instantaneous growth take?

j-curve

is a j-curve density independent or dependent?

• independent

• will grow by a rate of r, no matter the value of N

is the j-curve possible infinitely?

• no

• boom-bust model as resources run out

what is the equation for the logistic growth model?

deltaN / deltat = rN (K-N / K)

what does K represent in the previous equation?

the carrying capacity

what is carrying capacity?

the maximum sustainable population density

what shape is a logistic growth curve?

sigmoid/s curve

is the logistic growth model density independent or dependent?

density dependent

what does the logistic growth model predict when N approaches zero?

that the growth rate will be high

what does the logistic growth model predict when N is large?

the growth rate will be low

what does the logistic growth model predict when N > K?

• negative slope

• population decreases

what is the allee effect?

the minimum viable population density

is the allee effect part of the logistic model?

no

is the minimum viable population density a stable or unstable equilibrium?

• unstable

• below: extinction, above: carrying capacity

is the carrying capacity a stable or unstable equilibrium?

• stable

• below: will grow until reached, above: will decrease until reached

what is the difference between limited and limiting resources?

limited: finite

limiting: the resource that the carrying capacity is dependent on

what is the difference between inter and intra specific competition?

inter: between species

intra: within species

what are the two types of intraspecific competition?

1. scramble

2. interference

what is scramble competition?

• individuals gather as many resources as possible whilst they are available

what are the two subsets of interference competition?

1. social hierarchy

2. territoriality

provide an example of a species who participates in social hierarchy

chickens, lions, wolves

what is a territory?

• a defended area

• has exclusive access to certain resources

• cost vs. benefit to defense of the resources

what is a home range?

• the area in which an animal moves about

what is the relationship between a territory and a home range?

a territory is usually a subset of a home range

does territoriality evolve for the good of the species?

• no

• it is a selfish act

describe the probability of defense at a poor quality territory?

• low

• the cost of defense is not worth the poor quality resources

describe the probability of defense at an intermediate quality territory?

• very likely

• easy to monopolize

• benefits of defense outweigh costs

describe the probability of defense at a high quality territory?

• low

• difficult to monopolize

which type of competition is most likely in a rich quality environment?

scramble