The Effects of Minor Ecological Factors on the Breeding Season

Abstract

The actual height at which an animal lives does not in itself cause variation in the breeding season, but a number of other ecological factors vary considerably with height, and thus can affect breeding phenomena. It is a pity that so little is known about the exact effect of increasing height on other environmental variables. At extreme heights the effect of reduced oxygen concentration in the atmosphere is well known, but we know little of the changes in variables other than temperature or oxygen. The altitude itself may not be so important as the aspect of the region under consideration, as this will alter the light regime (if the aspect is other than due east-west) and will also affect the rainfall and possibly nutrition available to mountain species. A common feature of many mountain-dwelling large mammals is a vertical seasonal migration pattern, so that the effects of the altitude itself will need to be considered in the light of these movements. Thus it will be appreciated that the breeding pattern of mammals will vary according to the altitude, but this is due to a combination of individual ecological factors which are usually not separable as to their individual action. The interested reader is referred to a paper by Roberts, Hock, and Smith (1966) which analyses the metabolic responses of deermice (Peromycus maniculaws) to temperature and altitude.