Chap 9 Population Growth

population growth

describes how the number of individuals in a population changes over time

individuals are added to a population through

births and immigration

individuals leave the population through

deaths and emigration.

open population has

immigration and emigration

closed population

does not have (or has a very low level of) immigration and emigration that doesn't influence population growth

N

the number of individuals in a population

t

time

Nt

number of individuals in the population at a given time (t)

if the initial population size is 100 at time zero (day zero t= 0)

N0= 100

- If N

Exponential population growth model

dN/dt = rN

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- r = instantaneous per capita rate growth (intrinsic to population)

- differential equation can integrated and the resulting equation can be used to predict population size under conditions of exponential growth at any value of t

- can insert value t = 1 day, 1 year, or 1 sec

Nt = N0ert

N0 = initial population size at t = 0

e = base of the natural logarithm, approximately 2.72

- r = intrinsic rate of

growth of the

population

when r= 0 aht is the relationship between b and d? what happens to the size of the population?

ert =e0 =1

- so Nt= no... b=d

population growth is zero

exponential growth results in

in a continuously accelerating or decelerating rate of population growth as a function of population size.

populations that show positive exponential growth generally

- live in favorable environments

- are at low population densities

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these conditions are present during the process of colonization and establishment in new environments

a population is declinging when deaths exceed births

r<0

why are small populations more vulnerable to extinction

- loss of genetic variability

- deaths of small # of reproductive individuals can have large (negative) consequences

extreme environmental events can increase mortality rates and reproduce population size

- drought

- flood

- heat waves

- cold snaps

if environmental conditions exceed the bounds of tolerance for the species, an extreme event could lead to extinction.

changes in regional and global climate

A severe resource shortage

caused by either extreme environmental conditions or overpopulation, can lead to a population decline

- extinction is possible if the resource base does not recover in time for survivors to reproduce

invasive species can cause

population declines

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EX:

- reindeer on St. Paul island

- overgrazed the island severely

- herd size dropped from 2000 in 1938 to 8 in 1950

- such a population may recover or it may go extinct

what is the major way that humans impact population or species level extinctions

- habitat destruction

- pollution

- hunting

- invasive species

- climate change

human lands use changes the environment

leads to decliine in available habitat for many species

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types of land use include:

- habitat destruction

- pollution

- hunting

- invasive species

- climate change

Dams affect the characteristics of the water

- flow rate

- temperature

- oxygen levels

- sediment transport

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have a negative impact on species that migrate, reducing their ability to move upstream