3.2 The relevance of longitude, latitude and altitude

The examples we have looked at so far have alluded to a relationship between the range of a species and changing environmental conditions associated with changing geography, particularly latitude (movements of species south and north). Longitude (movements east and west) and altitude (height above sea level) also play a role.

We can see that there is a relationship between latitude and altitude. The early American ecologist Hopkins developed a rough and ready rule that, for every degree of latitude and every 100–130 m in altitude, spring events are delayed by about 3–4 days.

As temperatures increase, sub-Arctic and upland habitats (on which grouse, for example, are dependent) will move further north and up the hills. If temperatures continue to increase, then these habitats will literally disappear off the top of the mountains.

Even if temperature stabilises, these populations are still vulnerable. I want to illustrate why this is the case by introducing some new terms: fragmentation, resistance and resilience.