Lecture 5

Question 1

increasing/decreasing population size

Answer 1

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

Question 2

population growth in an open system

Answer 2

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 3

population growth in an closed system

Answer 3

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 4

population growth

Answer 4

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

Question 5

two types of population growth in closed systems

Answer 5

exponential growth and logistic growth

Question 6

exponential growth

Answer 6

• density-independent; growth rate doesn’t depend on the number of indivudals
• 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 7

per capita

Answer 7

per individual

Question 8

per capita growth rate (r)

Answer 8

• 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 9

exponential growth rate formula

Answer 9

ΔN/Δt = rN

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

Question 10

estimating future population size, using exponential growth

Answer 10

N_t = N₀e^rt

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

Question 11

logistic growth

Answer 11

• density-dependent; growth rate depends on the number of indivudals, 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

Question 12

carrying capacity (K)

Answer 12

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 13

logistic growth rate formula

Answer 13

ΔN/Δt = rN[(K-N)/K]

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

Question 14

regular (population) cycles

Answer 14

• 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 15

demography

Answer 15

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

Question 16

age structure

Answer 16

the number of individuals alive at each age within a population

Question 17

population demography and offspring

Answer 17

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 18

three types of survivorship curves

Answer 18

• 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 19

life history strategy

Answer 19

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 20

three tradeoffs in life history traits

Answer 20

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

Question 21

three ecological characteristics that affect organisms’ optimal strategies

Answer 21

• abiotic conditions
• community composition
• resource availability

Question 22

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

Answer 22

when mortality is high for all age groups…

• organisms that mature early have higher fitness if 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 23

opportunistic vs. equilibrial life history

Answer 23

• 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