10 population changes Flashcards
Populations undergo changes
➢ Natality and Mortality (greater effect)
➢ Immigration and Emigration
Absolute natality rate
B = Nn/t. the number of new
individuals produced in a population by the time
Specific natality rate
b = Nn/Nt the number of new individuals produced
per unit of population per unit of time
Mortality
is expressed as a loss of individuals per unit
time, the mortality rate
what is a life table
a systematic picture of a population
what is Survivorship Curves
the number of individuals in the population which survive
(y-axis) against age (x-axis)
Curve A:the population mortality rate is low until the end of the life span/large animals
Curve B: experience high mortality rates in their young stages but lower levels of mortality in their adult stages/small animals
Curve C: high mortality during the young stages/oysters,shellfish
how does population changes
Natality rate > Mortality rate = Population
increase
Natality rate < Mortality rate = Population
decreases
Natality rate = Mortality rate = Population size
unchanged
A population’s growth rate
ΔN/Δt
ΔN = Change from the initial number of individuals in the population
Δt = time period during the change
A population’s growth rate
ΔN/Δt
ΔN = Change from the initial number of individuals in the population
Δt = time period during the change
instantaneous rate
rN = dN/dt
N = number of individuals alive at any point in time
r = rate of change per individua
When the rate of change per individual (r) of the
population is related solely to natality (b = r)
bN = dNn/dt
When mortality occurs
dN/dt = bN - dN
what is Migration
seasonal movements involves travelling from one habitat type to another, it is an adaptive response to the seasonal variation of resources, migrants take advantage of favorable food and weather conditions offered in certain areas during very limited time periods.Phusiological changes during migration include fat store and minimize weight and maximize flight efficiency
examples of migration
*Southern right whales migrate from their feeding areas in the
Antarctic to temperate breeding areas, Their migration is entirely fuelled by fat accumulated during their four-month stay in the icy Southern Ocean of Antarctica
*Young salmon migrate to the ocean to take advantage of the great abundance of food and high potential for growth available there
