Ecologists have long understood the intermediate disturbance hypothesis, which explains that moderate levels of agitation can maximize biodiversity in a particular environment. However, a study by Xavier Santos and Marc Cheylan has introduced evidence to the contrary, showing that beta diversity of reptilians decreases in areas of repeated exposure to fires.
The areas studied were categorized as unburnt, once burnt, and repeatedly burnt based on the exposure to fire over the past 51 years. The disturbance provided by the fire, which would typically be expected to improve diversity, actually caused the number of reptilian species to decrease.
This decrease in biodiversity is attributed to the severity of the fires occurring, as well as the longevity of the flora and fauna in the Mediterranean environment studied and the lack of speed involved in replenishing the plant life. Presumably, in an area with quickly reproducing organisms, natural fires could be refreshing, providing a new basis for growth.
In addition to the diversity of species, individual reptile species in each area were studied based on characteristics such as longevity, feeding patterns, and thermal flexibility.
The authors note that “fire acts as an environmental filter, selecting the traits most suitable to fire and post-fire conditions,” and indeed differences in the aforementioned characteristics emerged in post-fire habitats, compared to the original state, in the form of dominant species that gained precedence only after the effects of fires.
Traits that appear to be favorable for surviving repeated fires include increased tolerance for thermal variation, increased tendency to be insectivorous, and the tendency to have shorter lifespans.
These traits are understandable in view of the changing environment. Species with longer lifespans and more development time before reproductive age require more time to adapt to a changing environment, which is disadvantageous in the areas with more frequent fires.
The expansion of thermal preferences applies when the canopy is reduced by fires and more sunlight reaches the level of the reptilians. Species with higher sensitivity to thermal radiation experience decreased ability to thrive in the more open forest.
Preference for insects is logical considering the changes in the quantity and identity of local plant populations following traumatic fire.
Depending on where and how intensely fires occur in Mediterranean ecosystems, either a positive or negative product could result.
If fires continually occur in different areas, beta diversity will be decreased overall, as shown by the sampling of habitats in this study. However, if fires occur in one area repeatedly, beta diversity for the region can be improved, as shown by the significant variance in traits between reptilians in unburnt and repeatedly burnt areas.
The results can be extended to understanding the outcomes of environmental disturbance for reptilians in other areas with similar organismal composition.
An understanding of the effects of fires, both manmade and natural, is important to developing knowledge about the functional and taxonomic adaptations made by certain species.
By examining the patterns exhibited by the Mediterranean reptilians in addition to other studies on reaction to disturbance, it is increasingly possible to predict how species will respond to mild, moderate, or even catastrophic changes to their living environments.
With such an understanding, humans can advance their ability to minimize impact on the environment and preserve species that may not be so lucky to adapt the most advantageous traits.
Xavier Santos, Marc Cheylan, Taxonomic and functional response of a Mediterranean reptile assemblage to a repeated fire regime, Biological Conservation, Volume 168, December 2013, Pages 90-98, ISSN 0006-3207 (http://www.sciencedirect.com/science/article/pii/S0006320713003170)
Photo by Alexandre Roux (http://www.flickr.com/photos/30142279@N07/8996686596/in/photostream/)