Population attributes:

  • Population: a group of individual living in a well defined geographical area, share or compete for similar resources, potentially interbreed.
  • Birth rate and death rate refers to per capita births and deaths respectively.
  • Another attribute is sex ratio. The ratio between male female in a population.
  • If the age distribution is plotted for a population the resulting structure is called age pyramid.
  • The shape of the pyramids reflects the growth status of the population like growing, stable or declining.
  • The population size is more technically called as population density.

Methods for measurement of population density:

·         Counting the number

·         Percent cover

·         Biomass.

·         Pug marks and foecal pellets for tiger census

Population growth:

  • The size of the population changes depending on food availability, predation pressure and reduce weather.
  • Population size fluctuated due to changes in four basic processes, two of which (Natality and immigration) contribute an increase in population density and two (mortality and emigration) to a decrease.


  • Natality: number of birth in given period in the population.
  • Mortality: number of deaths in the population in a given period of time.
  • Immigration: is the number of individuals of same species that have come into the habitat from elsewhere during a given period of time.
  • Emigration: number of individuals of the population who left the habitat and gone elsewhere during a given time period.
  •   If  ‘N’  is  the  population  density  at  time  ‘t’,  then  its  density  at  time  t  +  1  is  :

Where B = the number of births
I = the number of immigrants
D = the number of deaths
E = the number of Emigrants.
N = Population Density
r = Intrinsic rate of natural increase
t = Time period
K  =  Carrying  capacity  (The  maximum  population  size  that  an  environment  can  sustain)

Exponential growth:

  • The Exponential growth equation is  Nt = N0ert
  • Nt  =  Population  density  after  time  t
  • N0  =  Population  density  at  time  zero
  • r  =  intrinsic  rate  of  natural  increase
  • e  =  the  base  of  natural  logarithms  (2.71828)


Exponential growth (‘J’ shape curve is obtained).
*    When resources are not limiting the growth.
*   Any  species  growth  exponentially  under  unlimited  resources  conditions  can  reach enormous  population  densities  in  a  short  time.
*    Growth is not so realistic.
Logistic growth model

  • Verhulst-Pearl  Logistic  Growth  is  described  by  the  following  equations 
  • dN/dt  =  rN  (K–N  /  N)
  • Where  N  =  Population  density  at  time  t
  • r  =  Intrinsic  rate  of  natural  increase
  • K  =  Carrying  capacity

Logistic Growth (Sigmoid curve is obtained)


  • When responses are limiting the Growth.
  • Resources  for  growth  for  most  animal  populations  are  finite  and  become  limiting.
  • The logistic growth model is a more realistic one.


  • Adaptation: is any attribute of the organism (morphological, physiological, and behavioral) that enables the organism to survive and reproduce in its habitat.

Adaptation of animal in desert:

  • Kangaroo rat meets their water requirement from oxidation of fat.
  • Excrete very concentrate urine to conserve water.

Adaptation of plant in desert (xerophytes)

  • Thick cuticle on their leaf surfaces.
  • Sunken stomata, both to reduce transpiration.
  • Have special photosynthetic pathway (CAM), stomata closed during day time and remained open during night.
  • Opuntia has no leaf- they are reduced to spines.
  • Photosynthesis takes place in flat green stems.


Adaptation of animal in cold climate:

  • Allen’s Rule: mammals from colder climates generally have shorter ears and limbs to minimize heat loss.
  • Seals of polar aquatic seas have a thick layer of fat called blubber below their skin that acts as insulator and reduces loss of body heat.


Adaptation in high altitude:

  • A person move to high altitude (>3,500 meter), develop altitude sickness.
  • Symptoms developed are nausea, fatigue and heart palpitations.
  • This is due to low atmospheric pressure of high altitudes; the body does not get enough oxygen.


How the bodies solve the problem?

  • The body compensates low oxygen availability by increasing red blood cell production.
  • The body compensates decreasing binding capacity of hemoglobin with oxygen by increasing rate of breathing.

Behavioral adaptation:

  • Desert lizards are conformer hence they cope with the stressful environment by behavioral adaptations:
    • They bask in the sun and absorb heat when their body temperature drops below the comfort zone in winter.
    • Move to shade when the ambient temperature starts increasing.
    • Some species burrowing into the soil to hide and escape from the above-ground heat.

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