Biology_Today_-_October_2016

Types of organisms

depending on

ability to tolerate

temperature

variations

Eurythermal organisms

Organisms which can tolerate a wide range of temperature variations, e.g., most mammals and birds, (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, e.g., polar bear, lizards, amphibians, plants, etc.

Types of organisms depending on ability to maintain body temperature

Homoiothermal

s Keep body temperature constant despite changes in ambient

temperature

s Also known as endothermal or warm blooded animals

s E.g., Birds, Mammals

Poikilothermal

s Body temperature varies with surrounding temperature

s Also known as ectothermal or cold blooded animals

s E.g., Reptiles, Amphibians

Adaptations to temperature

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

s Animals of colder areas have thick coat of hair, scales, feathers or subcutaneous fat to reduce loss of body heat.

s 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.

s Bergmann’s Rule: Warm blooded animals (birds, mammals) of colder areas are of larger size as compared to those of warmer

areas.

s Allen’s Rule: Extremities of mammals (ears, snout, tail, legs) of colder areas are shorter than those of warmer regions.

s Ransch’s Rule: Birds of colder areas have narrow wings as compared to those of warmer areas.

s Jordan’s Rule: Fish of cold water tend to have more vertebrae.

Effects of temperature

Growth
s Rate of growth increases with the increase in temperature upto an optimum level beyond which it begins to decline. E.g., eggs of Mackerel take
207 hours to hatch at 10°C and 5 hours to hatch at 21°C.
Reproduction
s 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.
Sex Ratio
s Daphnia produces only females at normal temperature. It produces both males and females at higher temperature.
Colouration
s Animals have a darker skin in warm and humid areas and lighter skin in arid cool areas.
Behaviour
s Ticks and certain snakes (e.g., Pit Viper) locate their warm blooded preys by body heat emitted by the latter.
Morphology
s In colder areas, the animal size generally increases while the extremities decrease.
Diurnal Thermoperiodicity Thermoperiodicity
Regular change in body
temperature that occurs
Temperature is high during the day and low during night. at specific time interval.
High day temperature favours photosynthesis while lower
night temperature stimulates growth and storage in plants.
It promotes seed germination in many plants and determines
the period of animal acitivity. For example, desert animals live
in burrows, during the hot daytime.

Different seasons of year have different temperatures. They favour

different aspects of plant and animal life or phenology. Seasonal

thermoperiodicity, therefore, controls flowering, fruiting, fruit

dispersal, leaf shedding, leaf bearing, seed germination, etc.

of plants. In animals, it determines growth, reproduction,

development, colouration and morphology.

Seasonal Thermoperiodicity