6 Interaction of spatial and temporal scales
To have a full understanding of global biodiversity, we need to knit the roles of drivers with their impact across scales of time and space, as they often operate at the same time. Consider for example the impact of lightning causing a forest fire and decimating a rich diversity of reptiles. The fire event could happen within hours, but its impact could destroy the biodiversity of a large area at the landscape level, measured in tens of square kilometres.
In another context, climatic shift may occur gradually, perhaps over decades, to change the local forest biome to a desert and hence impacting an area encompassing tens of thousands of square kilometres – i.e. at the regional scale.
The key message here is the need to understand the time and space scales of environmental drivers and their impacts so that, when investigating environmental issues, cause and effect are considered at the appropriate scale. A hierarchical summary of drivers and impacts across scales of time and space is given in Table 1.
| Spatial scale | Dominant environmental variables | Temporal scale |
Local: within communities, within habitat patches ~0.1–10 km | Fine-scale biotic and abiotic interactions (e.g. habitat structure, disturbance by fires, storms) | ~1–100 years |
Landscape: between communities; turnover of species within a landscape ~10 km–100 km | Soils, altitude, peninsula effect | ~100–1000 years |
Regional: large geographical areas within continents ~100 km–1000 km | Radiation budget and water availability, area, latitude | Previous 10,000 years (i.e. since end of last glacial period) |
Continental: differences in species lineages and richness across continents ~1000–5000 km | Aridification events, Quaternary glaciation, interglacial cycles, mountain-building episodes (e.g. Tertiary uplift of the Andes) | Previous 1–10 million years |
Global: differences reflected in the biogeographical realms (e.g. distribution of mammal families between continents) ~5000–10000 km | Continental plate movements, sea-level change | Previous 10–100 million years |