ecology ch 10

age structure

The number or proportion of individuals in each age group of a population.

survivorship curves

• Type I: Most individuals survive until old age. Examples: humans and Dall sheep.

• Type II: Individuals have an equal chance of dying at any age. Examples: many birds and small mammals.

• Type III: Most individuals die young; many offspring are produced with little parental care. Examples: plants that broadcast seeds and marine invertebrates with pelagic larvae.

cohort life tables

follow from birth to death

static life tables

when you cannot follow individuals from birth to death but can estimate their ages from physical remains

. skulls, horns, teeth, otoliths (fish scales)

exponential growth

Population grows rapidly when resources are unlimited.

• j shaped curve

• Equation: dN/dt = rN

intrinsic rate of increase

the instantaneous per-capita rate at which a population grows

• r = lnRo/t

• is the birth rate minus death rate per individual

doubling time

The time it takes for a population to double in size.

• equation: t = ln2/r

carrying capacity

(K): The maximum number of individuals an environment can support with its available resources.

time lag

τ: The delay between a change in population size and its effect on population growth.

logistic growth

growth slows as resources become limited and the population approaches carrying capacity

• S-shaped curve

intraspecific competition function

A function that reduces population growth as individuals of the same species compete for limited resources

density-independent regulation

Population growth is limited by external factors that do not depend on population density

• ex: weather

density-dependent regulation

Population growth is affected by population density

• ex: competition for resources increasing at high densities

lx

Age-specific survivorship

• equation: Nx/No

mx

age specific fecundity

• female offspring per female at age (x)

Ro

net reproductive rate

• equation: Σlxmx

T

generation time

• equation: t = Σxlxmx/Ro

finite rate of increase

yearly population growth rate

• equation: λ = Nt+1/Nt

which is less accurate, cohort or static life tables?

static life tables are less accurate because they assume rates remain constant.

What values of λ, R and λ, indicate growth?

when greater than 1

What values of λ, R and r indicate stability?

when equal to one

What values of λ, R and r indicate decline in population numbers?

when less than one

what are the assumptions of logistic growth?

closed population, constant K and r, linear density dependence, no interspecific competition, no time lags, same cohort.