I am wondering - How does species diversity change along the successional sequence?
For example, as attached in the figure, Shannon's Diversity Index increases during early stage of succession (say 15-25 years), then at an intermediate stage (say around 50 years) drops, and rise again during 50 - 70 years of succession but again drops after 70 years of succession.
Please have a look at this link and PDF attachment.
https://www.researchgate.net/publication/222689681_Species_composition_similarity_and_diversity_in_three_successional_stages_of_a_seasonally_dry_tropical_forest
Article Species composition, similarity and diversity in three succe...
Hi Sawaid
There is a bunch of literature on this topic. Here there are some suggestions for the tropical forest case (and references therein):
http://press.uchicago.edu/ucp/books/book/chicago/S/bo17407876.html
http://dx.doi.org/10.1098/rspb.2013.2236
http://dx.plos.org/10.1371/journal.pone.0082433
Also, I would suggest than rather than using first a "complex" index like Shannon diversity (which accounts for both species richness and relative abundances), use first an index for the number of species only, or use Hill numbers (0D is species richness, 1D~Shannon, 2D~ Simpson).
The general trend as succession theory says diversity increases as succession proceeds. But the examples you and Dr. Arvind show say something different. The change in values might have different causes otherwise climax stage will not achieved. Now a day, Clementsian's climax concept is questioned and random colonization model is accepted by many authors specially those who are working in non-equilibrium dry land areas. So, I think depending on the climatic condition, the values may fluctuate, otherwise it will increase as succession proceeds.
Regards
Hi Dr. Arvind,
If a numerical dominant species is present and increase it's abundance along successional sequence, Shannon's diversity index may give low values even though the number of species increases.
Kind regards
We have always do differentiate species richness and heterogeneity, thus calculating different indices.
For species richness I propose the Chao 1 Index that gives you an exact number number of the expeced Maximum species number.
For heterogeneity measures, both the Shannon and Simpson index depend on the species number in the samples, thus better measures are the eveness measures. (Pilou or Buzas and Gibson).
Then look, if in both measures (species richness and heterogeneity) the trends are detectable.
The fluctuations you observe might possibly be within the natural imprecision of H'. The plot by itself is only partially informative without further information such as what species group has been targeted (plants? invertebrates? birds?), how many samples went into each data point, and what was the size and type of sampling, among other factors.
H' is particularly sensitive to rare species, e.g. initial (transient) colonist that might artificially push up its value or late-successional invaders that might bring it down, as Massimiliano's answer implies. Francisco's and Johann's advices are sound--look for other measurements of richness and, above all, make sure the sampling procedure is not penalizing older growth (e.g. if target was plants of all sizes, a less-than-optimal sample size may penalize older stands by lowering the counts of larger trees). Dr. Ahmed's point also holds if the plot is far from climax--the last point, with large variance, might represent a non-equilibrium patch.
Regards
I agree with indications reported in the other replies. I would also suggest to investigate various diversity indices (e.g. combining species and functional metrics, if doable) within- and among- different life history traits/strategies across the successional gradient. You may obtain a more complex picture of the system dynamics.
Regards
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