Biology Today - February 2018

Abiotic Factors

1. Temperature

• It is the degree of hotness or coldness of a substance. It ranges from subzero levels in polar areas and high altitudes to
  more than 50°C in tropical deserts in summer.


• Changes in temperature are influenced by latitude, altitude, topography and vegetation.


• Most organisms survive a temperature range of 0° to 40°C.


• However, certain bacteria and blue green algae live in hot springs having a temperature range of 60° to 90°C.


• Temperature has a direct effect on the working of enzymes. Through enzymes, it influences basal metabolism, activity and other

physiological functions of the organism.

Growth

• Rate of growth increases with the increase in temperature upto an optimum
  level beyond which it begins to decline. (J, eggs of Mackerel take 207 hours
  to hatch at 10°C and 5 hours to hatch at 21°C.

Colouration

• Animals have a darker skin in warm and
  humid areas and lighter skin in arid cool
  areas.

Reproduction

• Maturation of gonads and formation of gametes are controlled by temperature.
  In grasshopper, increase in temperature from 22°C to 32°C increases egg
  laying by 20-30 times. Beyond the optimum level, fecundity declines.

Behaviour

• Ticks and certain snakes (HJ, Pit Viper)
  locate their warm blooded preys by body
  heat emitted by the latter.

Sex Ratio

• 'DSKQLD produces only females at normal temperature. It produces both
  males and females at higher temperature.

Morphology

• In colder areas, the animal size generally
  Various effects of temperature areincreases while the extremities decrease.

Types of organisms

depending on

ability to tolerate

temperature

variations

Eurythermal organisms

Organisms which can tolerate a wide range of temperature variations, HJ, most mammals and birds, $UWHPHVLD

WULGHQWDWD plants of Family Asteraceae.

Stenothermal organisms

Organisms which live within narrow range of temperature because of their requirement of nearly constant temperature

throughout the year, HJ, polar bear, lizards, amphibians, plants, etc.

Types of organisms depending on ability to maintain body temperature

Poikilothermal

• Body temperature varies with surrounding temperature


• Also known as ectothermal or cold blooded animals


• (J, reptiles, amphibians

Homoiothermal

• Keep body temperature constant despite changes in ambient temperature


• Also known as endothermal or warm blooded animals


• (J, birds, mammals

Adaptations to temperature

• Plants have various adaptations, such as hair, thick covering, mucilage, thick leaves to reduce transpiration and retain water.


• Animals of colder areas have thick coat of hair, scales, feathers or subcutaneous fat to reduce loss of body heat.
  
  
  • Gloger’s Rule: In warm blooded animals, including humans, pigmentation is little in colder areas, yellow brown to red
    in arid climates and black in humid hot areas.
  
  
  • Bergmann’s Rule: Warm blooded animals (birds, mammals) of colder areas are of larger size as compared to those of warmer areas.
  
  
  • Allen’s Rule: Extremities of mammals (ears, snout, tail, legs) of colder areas are shorter than those of warmer regions.
  
  
  • Rensch’s Rule: Birds of colder areas have narrow wings as compared to those of warmer areas.
  
  
  • Jordan’s Rule: Fish of cold water tend to have more vertebrae.