Question

1. Many factors must be considered when attempting to predict the energetic needs of organisms - a primary goal of ecology. Below are two factors that must be considered. Compare and contrast how and why each effects the basal/standard energetic needs of endothermic regulators (homeotherms) and ectothermic conformers (poikilotherms)– feel free to draw and paste in a graph(s) but be sure to reference them and explain what they mean in text (40 points).

1. Body size

2. Environmental temperature

c. Explain how and why the effect of body size on energetic demands may affect the ability of individuals of different sizes (small and large) to cope with a shifting thermal environment in the face of climate change.

Answer 1

Energy requirements

Homeothermic animals (warm blooded) are able to maintain their body temperature at a constant. For maintaining their homeothermy consumes about 90% of the energy intake of the animals. otherside, Poikilothermic (cold blooded) animals are not able to maintain their body temperature at a constant level. In these organisms, the body temperature fluctuates with changes in the environmental temperature. Poikilotherms have low metabolic rates and high thermal conductance which controlled by environmental.

Endotherms (in Greek endo means ‘within’ and therme means ‘heat’) regulate their temperature by the production of heat within their own bodies, and ectotherms (in Greek ecto means ‘outside’ and therme means ‘heat’) depends on external sources of heat.

Environmental temperature and body size

The Effect of temperature is size dependent. Small animals have more surface area and relatively less metabolically active tissue to generate heat. Thats why, a small animal, when faced with cold, lose heat more rapidly than a larger animal. If small animal attempted to generate heat to offset the heat loss and maintain body temperature, it would require a relatively higher rate of energy generation. On the othe side, large animals have relatively small surface areas and cool slowly if placed in a cold environment.

According to Bergmann’s rule individuals of species in cooler climates tend to be larger than those in warmer climates. This relationship derives primarily because bodies with larger volumes have small surface area-to-volume ratio. Because heat loss relates to surface area, larger bodies can retain heat more efficiently in cooler climates, whereas smaller bodies (large surface area-to-volume ratio) can eliminate heat more efficiently in warmer climates.

According to Allen’s rule, endothermic animals from colder climates tend to have shorter extremities or appendages (e.g. ears and tail) than closely related species from warmer climates (shorter extremities dissipate less heat). And according to Hesse’s rule (also known as the heart–weight rule) which states that species inhabiting colder climates have a larger heart in relation to body weight than closely related species inhabiting warmer climates.

Kleiber’s law suggests a relationship between the resting metabolic energy requirement per unit mass (B/M) and the total body mass (M) (shown by figure)