Organisms and Populations

SYNOPSIS

• Ecology is a branch of biology which deals with the inter-relationships among organisms and interactions between organisms and their environment.
  
  
• Homeostasis is a self-regulatory mechanism to maintain the internal environment constant despite changes in the external environment.
  
  
• Regulators are organisms which maintain their homeostasis by physiological means to ensure constant body temperature and osmotic concentration irrespective of the fluctuations in the external environment; for example, birds and mammals.
  
  
• Conformers are organisms which cannot maintain a constant internal environment; for example, fish and reptiles.
  
  
• Adaptation is the development of certain features in an organism in response to a particular environment which may improve its chances of survival and reproduction in the habitat.
  
  
• Differences between Hibernation and Aestivation
  
  
  

• Population is defined as a group of organisms of the same kind at a particular time which occupy a particular space.

• Population density is defined as the number of individuals present in a unit area at a given time.

• Factors Affecting Population Density
  
  
  

• Natality is the increase in the number of individuals in a population under the given environmental conditions.

   

• Mortality is the loss of individuals due to death in a population under the given environmental conditions.

• Age Pyramids for Human Population
  
  
  

• Population growth can be measured as an increase in the size of a population over a period of time.
  

• Population exhibits a characteristic pattern of increase known as the population growth curve.

• Exponential (J-shaped) growth curve: When the resources are not limiting the growth, the plot is exponential (curve a).

• Logistic (S-shaped) growth curve: When responses are limiting the growth, the plot is logistic (curve b).

• The interaction of populations of two or more different species is known as population interaction.
  
  
  

• Gauss gave the competitive exclusion principle which states that two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually.