biol 241 - reproduction/population growth

what is the ideal Eproduction?

unlimited resources to support maximal growth, long life, and unlimited continuous production of offspring

what is the life history theory?

every species has a pattern of growth and development, reproduction, and death shaped by natural selection

the environment affects life history traits by influencing energy budgets: amount of light, food choice, shelter, wind, precipitation

maximizing reproductive success involves trade-offs due to fixed energy budgets + selective pressures

can you maximize 2 life history traits silmultanesouly is they compete for a share of limited resources?

No, any gains by one trait will result in a loss by the other

What are life history traits?

• growth rate

• parental investment

• number of offspring (fecundity)

• frequency of reproduction (parity)

• size/age at sexual maturity

• size of offspring

• longevity/life expectancy (mortality rate)

parental investment - what is passive care

pre-birth energy expense

parental investment - what is active care

post-birth energy exposure

what does semelparity mean?

individuals of the same species can breed only once in its lifetime

what does iteroparity mean?

individual of the same species can breed more than once in its lifetime

life history strategies - what is r-selected?

low energy, high numbers

life history strategies - what is k-selected?

high energy, low numbers

what are r-selected species

• small adult/offspring size

• early sexual maturity

• semelparous

• high fecundity (number of offspring)

• low parental investment

• low juvenile survival

• short lifespan

what are k-selected species

• large adult/offspring size

• later sexual maturity

• iteroparous

• low fecundity

• high parental investment

• high juvenile survival

• long lifespan

what do life history tables tell us?

summarize info on age structure, size, history (reproductive) stage, and survivorship of a population

used to predict how a population will change over time

useful in managing: crops/livestock, conservation, pest/weed control

life history tables legend - what does x indicate

age

life history tables legend - what does nx indicate

number of females at each age (x)

life history tables legend - what does sx indicate

survival rate from one age to the next (sx= nt + 1/ nt)

life history tables legend - what does lx indicate

survivorship (fraction of original cohort still alive) lx = nt/no

life history tables legend - what does mx indicate

fecundity (avg number of female offspring each living female produces)

life history tables legend - what does Ro indicate

net reproductive rate (avg number of female offspring per female in cohort over the cohorts lifespan) Ro=∑(lx x mx)

What does Ro bigger, less or close to 1 signify

Ro> 1: population growing

Ro < 1: population decreasing

Ro = 1 = 0.95-1: population is steady

survivorship curves - type 1

high juvenile survival throughout lifespan

mortality at old age

survivorship curves - type 2

constant mortality throughout lifespan

survivorship curves - type 3

low juvenile survival throughout lifespan and then high survival

for this course, what is population size influenced by?

births and deaths

What formula can we use to study the change in total numbers of individuals in a population?

dN/dt = B-D

N = population size

t= time

B = # of births

D = # of deaths

what formulas can be used to track the per capita birth rate (b) and per capita death rate (d) in a population?

b = B/N, d = D/N

how can we use the per capita growth rate (r ) in a formula to predict population size changes?

r = b - d

what is the formula for calculating the change in population growth?

dN/dt = rN0

exponential model of population growth - under ideal conditions what would the per capita growth rate be for a population?

the per capita growth rate (r ) will be at a max, r = rmax = intrinsic rate of incresae

exponential model of population growth - in this model rmax is always….

positive and constant over time

exponential model of population growth - rmax varies by species, large vs small?

small organisms = large rmax

large organisms = small rmax

what formula should you use to calculate exponential growth?

Nt = N0(1+ rmax)^t

what limits population growht?

Ein, temperature, water, predators

most environments can only support a certain population size, this is referred to as…

carrying capacity (K)

what does the population size (N) being close to the carrying capacity (K) change?

the per capita growth rate

r is never going to be rmax

as the value N increases, the value of r does what?

decreases

when N=K what does r equal?

r=0

when N>K, what does r equal? when N<K?

when N>K, r<0

when N<K, r>0

as populations grow, death and birth rates do what?

death rates increase, birth rates decrease

r decreases as the population grows and reaches k

what is the formula for being influenced by the fraction of k available, rt=?

rt=rmax((K-Nt)/K)

to determine the size of a population growing logistically what formula do we use?

N_t+1 = nt(1+rt)^1