4 How apparently non-mobile organisms adapt to environmental change

4.1 Introduction

In the unit so far we have looked at relatively mobile species; that is, species where individual organisms can move about and, therefore, have the potential to react to changing environments by shifting location. We also saw that even for apparently mobile species like birds this is not always straightforward.

In this section we are going to consider the effects of changing environmental conditions on non-mobile species. We use the term non-mobile species where individual organisms stay in the same place. The use of the term organism reminds us that we are talking at the level of an individual; we are not talking about the species as a whole or an ecosystem.

Even apparently non-mobile species can migrate. They do so by dispersing seed, or spores in the case of fungi. Indeed, fungal spores can travel thousands of kilometres, and many of those who study food plants are gravely concerned about the effects that the arrival of new plant pathogens will have on UK food security.

Non-mobile species react much more slowly to environmental change. If changes in the environment are gradual then the range of a non-mobile species gradually expands or contracts to account for those changes. Seeds are dispersed and if they fall on favourable conditions they grow. If environmental changes are only short term or are very gradual, then the long time scales (especially in relation to woodland) involved in the dispersal of that non-mobile are of little consequence.

The problem occurs when environment changes happen relatively quickly and are part of a sustained pattern of environmental change. Non-mobile species like plants, especially those with long life cycles (slow growing and slow to mature trees), cannot adapt to rapid and sustained changes in environmental conditions. This issue is likely to be exaggerated in species that only disperse seeds over relatively short distances or where the habitat is fragmented.