Unit 5 - Demography Flashcards
demoraphy
the study of the growth rate, age structure, and other characteristics of pop. Ecologists use demographic analysis to predict the growth of a pop
Factors that affect pop growth (4)
1) birth rate (natality)
2) death rate (mortality)
3) movement into a pop
(immigration)
4) movement out of a pop (emigration)
Life Tables
causes of death
every species has a characteristic lifespan
+ Individuals may die from starvation, disease, predation, or inability to find a suitable habit
Demograhers
collect data by monitoring a cohort for their survival until death
Mortality Rate
+ two was it is observed
the number of deaths in a pop per unit of time; observed in 2 ways
- age-specific morality
- age-specific survivorship
age-specific mortality
the proportion of individuals that were alive at the start of an age interval but died during the age interval
age-specific survivorship
the proportion of individuals that were alive at the start of an age interval and survived until the start of the next age interval
age-specific mortality rate equations =
number that died during the interval / number alive at the start of the interval
age-specific survivorship equation =
number still alive at the end of the interval / number alive at the start of the interval
sume of ASM and ASS must equal=
1
Life Tables summarizes…
the proportion of the cohort that survived to a particular (identifies the probability that any randomly selected newborn will still be alive at this age)
probability of being alive as a specific age equation =
number alive at the start of the age interval / number alive at the start of initial age interval
Survivorship curves
- life tables used to see how diff species can survive hardship
- date is expressed graphically using SC showing survival of an individual over lifespan
- three types 1,2, and 3
type 1
relatively flat at the start, reflecting a low death rate in the early and middle years, followed by a steep drop as the death rate increases for the older age group
type 1 typically found in?
LARGE animals that produce few young (take care of their young = reduced juvenile death)
and have a long gestation period
ie. deer, moose, humans
type 2
relatively constant rate of death in all age groups. steadily declining survivorship. constant probability of death from predation, disease, and starvation.
- short gestation period
- feed on type 3 but r prayed on by type 1
ie. lizards, songbirds, small mammals
type 3
rapid drop at the start = a very high death rate early in life and then flattens out as the death rate declines for the few individuals who surivive critical stage
- make large amounts of offspring
ie. plants, insects, fish
Fecundity
is the potential for a species to produce offspring in a lifetime
- highly dependent on environment conditions
plenty of food or best climate=?
higher rates of reproduction
little food and prediators=?
decreased rates of repoduction
example of fecundity
horseshoe crab lay 100 of thousands of eggs a year vs asian elephants produces 4 offspring during 60 life spam
generation time
the average time between the birth of an organism and the birth of its offspring
small body size (generation time)
v short generation time bc the individuals reach maturity very quickly ie. E. coli
large body size (generation time)
later reproductive maturity w a longer generation time
ie. humans or whales
sex ratio
is the relative proportion of male and females in a pop
in general number of females has a greater impact then males
- females make offspring
- one male can mate w many females
elephant seals
mature bulls fight for dominance. the few who win inseminate 100+ females so greater number of females in pop size.
goose/swans
50/50
= lifelong pairs mate for life therefore both females and males influence reproduction
high fecundity in intermediate age
high in humans
- younger individuals have not yet reached sexual maturity, and older individuals are past their reproductive prime. but fecundity increases steadily with age in some plants and animals
high fecundity in animals
high = animals w many offsprings and normally do little to care for offspring
ie. turtle lay 100 eggs and immediately leave offspring hatch and fend for themselves
low fecundity in animals
animals w few offspring r often v proactive of offspring
ie. black bears stay w cubs aprox. 27
changes in pop size
birth, death, immigration, emigration numbers can be used to determine the change in the size of pop in a given period of time
population change equation =
(birth + immirgration) - (deaths + emigration)
pop sizes determined by
four things
changes in the number of individuals that immigrate , emigrate, born or die
natality and immigration =
to mortality and emigration then pop size will remain stable
if natality and immigration exceed mortality and emigration
there is a pop growth
if mortality and emigration greater then natality and immigration
pop decline
