A temporal perspective of weed species abundance distribution

Póster presentado en el 4th Workshop of the European Weed Science Society (EWRS) working group Weeds and Biodiversity, celebrado en Dijon (Francia) del 28 de febrero al 2 de marzo de 2011.

We could gain further insight in how different management procedures affect weed community structure attending to the abundance distribution of species from a temporal perspective. Here we show that arable plant communities can be separated in two groups of species, core and occasional, attending to their persistence in the record and that the commonness of each species is related to their permanence. It has been proposed that each group of species follows a different distribution and that the overlay of both leads to the general observed pattern of species distribution in an assemblage. The abundance of core species would be log-normal distributed whereas the abundance of occasional species would follow a log-series distribution. Here we apply a previously employed methodology (Magurran and Henderson 2003) to separate core and occasional weed species is not an artifact. We used data from a long term experiment in which three different tillage systems were compared. We pooled data from the three systems and calculated for each year the value of Simpson’s diversity index (D) in progressively larger subsets of the data: from a subset in which only species present in =8 years were included to a subset in which species present in = 19 years were incorporated. For each subset we related the value of D to the number of years of the data. D remains constant when species are distributed according to the log series distribution, whereas the index increases if data follow a log normal distribution. Also, we calculated the variance to mean ratio for each species and related it to the number of years that each species appeared on the record. The variance to mean ratio is not significantly different from one in those species following a Poisson distribution. Our results show that only ten of the 45 species recorded in the experiment could be considered core species. Although the distinction between both groups is commonly done by researches when eliminating rare species from analyses, it is useful to formally divide both groups to test the nature of the processes that structure the abundances of species.

Peer Reviewed