Allen’s rule and the Iberian lynx

July 25th, 2007 | by nick |

Leafing through a dictionary of zoology I came across a definition for Allen’s rule. It strikes me that this might apply to the lankiness of the Iberian lynx in comparison with its cousin the heftier Eurasian Lynx. (For size difference see below)

It states (from wikipedia) that:

“endotherms from colder climates usually have shorter limbs than the equivalent animals from warmer climates.The theory behind Allen’s Rule is that endothermic animals with the same volume may have differing surface areas, which will aid or impede their temperature regulation.”

“In cold climates, the greater the exposed surface area, the greater the loss of heat and therefore energy. Animals (including humans) in cold climates need to conserve as much energy as possible. A low surface area to volume ratio helps to conserve heat.

In warm climates, the opposite is true. An animal will overheat quickly if it has a low surface area to volume ratio. Therefore, animals in warm climates will have high surface area to volume ratios so as to help them lose heat.

In a nutshell, it simply means there is a ratio between body surface to body mass.”

Given that the Eurasian Lynx is much larger than the Iberian Lynx, also perhaps applicable is Bergmann’s Rule which “correlates environmental temperature with body mass in warm-blooded animals. It asserts that within a species, the body mass increases with latitude and colder climate. Among mammals and birds, individuals of a particular speciesin colder areas tend to have greater body mass than individuals in warmer areas. ” This is no doubt the case further north and when comparing areas with similar levels of rainfall, but also coming into play is the the extremely limiting factor of the Mediterranean summer drought, which also tends to reduce body size. There simply isn’t as much prey in the Mediterranean summer.

Top, a Eurasian Lynx, bottom Iberian lynx. Not sure if these pictures do justice to my idea.

Origin of the Iberian lynx and relation to Eurasian lynx.
The ancestors of both the Iberian lynx and the Spanish Imperial Eagle came originally from far to the East in the steppes of Asia Minor, and did not arrive in the Peninsula until one million years ago. The Iberian species separated from their Eurasian counterparts around one million years ago at the start of the Quaternary, when a series of intense ice ages swept across Eurasia. As the weather grew colder both south western populations were pushed into the Mediterranean in search of ground squirrels until they finally reached Iberia. With the cold, prey must have become scarce from Greece to Italy and the Eurasian imperial eagle and the lynx died out there. The populations which reached Iberia were saved by the presence of rabbits. The Eurasian lynx then moved back into Europe from Asia as the ices receded. To the north of Spain, the Eurasian Lynx was eliminated in Western Europe during the 18-19th centuries, but unlike its Iberian cousin its range is much greater, once extending from the Pyrenees to Siberia. (The Eurasian Lynx possibly existed in Spain and formed the northern boundary of the Iberian Lynx). Eurasian Lynx are still relatively common in parts of the ex-URSS which is enabling reintroduction programmes in Switzerland, France and Germany. A million years ago there was probably one species from Cadiz to Vladivostok. More on the Iberian Lynx