© PSG and PDC, 2005
Last Update: February 11, 2008
Chapter 9 - Responding to conditions: environmental factors and gradients.
New books and papers | Websites
Chapter Outline :
- To understand the impact of environmental factors on species distribution we first need to appreciate the nature of the community;
- Environmental factors affect the distribution and abundance of all species;
- These factors are attributes which can vary in space and/or over periods of time;
- Although any physical factor can vary, in practice only a few key ones are significant in biogeography at the global and regional scale;
- Environmental factors rarely act singly and as a consequence, it is often difficult to distinguish which are the most important in any particular habitat;
- Environmental gradients occur in a wide range of situations in almost every type of habitat;
- Some gradients may be straightforward to interpret, such as changing light levels in woodlands or variations in soil moisture along transect leading down to a pond;
- Other gradients may reflect more complex matters such as varying pH or humus content, or the presence of toxic materials in the soil;
- There is a range of techniques that can be used to analyse gradients;
- Human
activities can modify the normal effects of environmental factors
or gradients.
| Author(s) | Title (and link) | Comment |
| O'Dea et al 2007 | Environmental change preceded Caribbean extinction by 2 million years | Extinction events are not single simple episodes but complex drawn-out series of events as shown here. |
| Jablonski, Roy and Valentine 2006 | Out
of the Tropics: Evolutionary Dynamics of the Latitudinal Diversity Gradient |
This study demonstrates that species spread out from the tropics and therefore loss of tropical species will have global implications |
| Groffman et al 2006 | Ecological
Thresholds: The Key to Successful Environmental Management or an Important Concept with No Practical Application? |
The concept of the threshold is key to explaining change and is something to be avoided in terms of management. However, the term is not well parameterised nor is it always capable of being used. This paper explores the notion behind it and the research needed to make it useful. |
| Holdaway and Sparrow 2006 | Assembly rules operating along a primary riverbed– grassland successional sequence | Assemblies and guilds are both controversial but evidence here suggests a need to factor in their impact when examining change in a system. |
| Willig and Bloch 2006 | Latitudinal gradients of species richness: a test of the geographic area hypothesis at two ecological scales | It is assumed that the greater areas in the tropics allows for greater biodiversity. This study of bats demonstrates that a strong gradient does exist, and at two scales, but area is not the main cause of variation. |
| Kromer et al 2005 | Diversity patterns of vascular epiphytes along an elevational gradient in the Andes | One example of an elevational gradient although the exact cause of the pattern is yet unknown with any accuracy. |
| Coudun and Gégout 2005 | Ecological
behaviour of herbaceous forest species along a pH gradient: a comparison between oceanic and semicontinental regions in northern France |
Larger studies on gradients are not that common and the effects are therefore not well known. This comprehensive study suggests more needs to be done as well as putting forward some useful ideas on impacts of gradients. |
| Kassen, Lllewellyn and Rainey 2004 | Ecological
constraints on diversification in a model adaptive radiation |
Experiments suggest that in some cases environmental gradients can affect adaptive radiation patterns. |
| Jacobsen 2004 | Contrasting patterns in local and zonal family richness of stream invertebrates along an Andean altitudinal gradient | Classic study of the variation of species richness with altitude but also showing how local variations might occur. |
| Kattan and Franco 2004 | Bird diversity along elevational gradients in the Andes of Colombia: area and mass effects | The simple idea of linear species change along a gradient is being found to be more complex at local scales. |
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