Lecture 5

Question 1

logistic growth rate formula

Answer 1

ΔN/Δt = rN[(K-N)/K]

ΔN/Δt = population growth rate
r = intrinsic growth rate
N = population size
K = carrying capacity

Question 2

the optimal strategy: growth vs. sexual maturity, and mortality risks

Answer 2

when mortality is high for all age groups…

• organisms that mature early have higher fitness as it increases their chances of reproducing before they die
• waiting too long to mature leads to death before reproducing (zero fitness)

when juvenile mortality is higher than adult mortality…

• organisms that mature late can become larger and have higher fitness through lifetime reproductive effects (more children overall)
• larger organisms are bigger and more competitive; they’re able to access more resources

Question 3

life history strategy

Answer 3

the overall pattern in average timing of events including…

• age and size at sexual maturity
• amount and timing of reproduction
• survival and mortality rates

Question 4

demography

Answer 4

study of factors that determine size and structure of populations through time

Question 5

population growth in an open system

Answer 5

open system = unlimited environment (dispersal exists)

N_t+1 = N_t + B_t + I_t - D_t - E_t

future population size = current population size + births + immigration - deaths - emigration

Question 6

age structure

Answer 6

the number of individuals alive at each age within a population

Question 7

increasing/decreasing population size

Answer 7

• immigration and births increase population size
• emigration and mortality decrease population size

Question 8

three types of survivorship curves

Answer 8

• Type I: most humans and other large mammals have a high probability of surviving to adulthood
• Type II: small mammals and birds have a constant mortality rate throughout their lifespan
• Type III: many fish, frogs, and plants have high early mortality rates, but high late survival rate

Question 9

three ecological characteristics that affect organisms’ optimal strategies

Answer 9

• abiotic conditions
• community composition
• resource availability

Question 10

population growth in an closed system

Answer 10

open system = isolated environment (dispersal doesn’t exist)

N_t+1 = N_t + B_t - D_t

future population size = current population size + births - deaths

Question 11

two types of population growth in closed systems

Answer 11

exponential growth and logistic growth

Question 12

population demography and offspring

Answer 12

the number of offspring produced varies with parent age/size

• e.g. France has slow reproductive rates, as most people are past their reproductive age (i.e. 40-70 years old)
• e.g. India has fast reproducitve rates, as most people are in their reproductive age (i.e. 20-30 years old)

Question 13

per capita growth rate (r)

Answer 13

• r = births - deaths
• r is a constant for a specific population; the number of individuals increases, but the per capita growth rate stays constant
• the higher the r, the faster the growth
• a.k.a. intrinsic growth rate

Question 14

opportunistic vs. equilibrial life history

Answer 14

• opportunistic species (r-strategists) are individuals with high fertility, grow quickly, mature early, and produce many small offspring (e.g. dandelions)
• equilibrium species (K-strategists) are individuals with high survivorship, grow slowly, mature late, invest energy into protection/survival/acquiring resources, and produce few large offspring (e.g. elephants)
• there is a continuum between these two extremes

Question 15

exponential growth

Answer 15

• density-independent; growth rate doesn’t depend on the number of individuals
• usually occurs when species colonize new habitats, or recolonize local habitats (usually not long-term)
• e.g. rabbits in Australia quickly became invasive, due to a lack of natural enemies

Question 16

per capita

Answer 16

per individual

Question 17

population growth

Answer 17

change in the number of individuals over time (ΔN/Δt)

Question 18

regular (population) cycles

Answer 18

• lagged responses between births and deaths due to population density can cause fluctuations around carrying capacity
• fluctuation severity depends on the size of the time lag

Question 19

exponential growth rate formula

Answer 19

ΔN/Δt = rN

ΔN/Δt = population growth rate
r = intrinsic growth rate
N = population size

Question 20

estimating future population size, using exponential growth

Answer 20

N_t = N₀e^rt

N_t = future population size
N₀ = current population size
r = intrinsic growth rate
t = time

Question 21

three tradeoffs in life history traits

Answer 21

• growth vs. reproduction
• early vs. late maturity
• few large vs. many small offspring

Question 22

carrying capacity (K)

Answer 22

the maximum number of individuals in a population that can be supported due to…

• food
• space
• water
• soil quality
• resting/nesting sites
• life history strategies

Question 23

logistic growth

Answer 23

• density-dependent; growth rate depends on the number of individuals, due to a lack of resources
• most populations show this type of growth
• growth slows as population size reaches carrying capacity
• e.g. rabbits in Australia quickly became invasive, due to a lack of natural enemies