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Neutrality and the response of rare species to environmental variance.

Benedetti-Cecchi L, Bertocci I, Vaselli S, Maggi E, Bulleri F - PLoS ONE (2008)

Bottom Line: A field experiment was performed to examine whether assemblages responded neutrally or non-neutrally to changes in temporal variance of disturbance.The experimental results did not reject neutrality, but identified a positive effect of intermediate levels of environmental heterogeneity on the abundance of rare species.This effect translated into a marked decrease in the characteristic time scale of species turnover, highlighting the role of rare species in driving assemblage dynamics in fluctuating environments.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Biologia, Università di Pisa, Pisa, Italy. lbenedetti@biologia.unipi.it

ABSTRACT
Neutral models and differential responses of species to environmental heterogeneity offer complementary explanations of species abundance distribution and dynamics. Under what circumstances one model prevails over the other is still a matter of debate. We show that the decay of similarity over time in rocky seashore assemblages of algae and invertebrates sampled over a period of 16 years was consistent with the predictions of a stochastic model of ecological drift at time scales larger than 2 years, but not at time scales between 3 and 24 months when similarity was quantified with an index that reflected changes in abundance of rare species. A field experiment was performed to examine whether assemblages responded neutrally or non-neutrally to changes in temporal variance of disturbance. The experimental results did not reject neutrality, but identified a positive effect of intermediate levels of environmental heterogeneity on the abundance of rare species. This effect translated into a marked decrease in the characteristic time scale of species turnover, highlighting the role of rare species in driving assemblage dynamics in fluctuating environments.

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Mean species abundances (±1 s.e.m., n = 18) in Low Variance (horizontal axis) and Medium Variance (vertical axis) treatments.The inset shows an increase in abundance of rare species (mean abundances in the range 0.1–10) associated with enhanced temporal variance of disturbance; cc: Cystoseira compressa; nh: Nemalion helmintoides; pp: Padina pavonica; ss: Spirorbis sp.; vt: Vermetus triqueter.
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pone-0002777-g003: Mean species abundances (±1 s.e.m., n = 18) in Low Variance (horizontal axis) and Medium Variance (vertical axis) treatments.The inset shows an increase in abundance of rare species (mean abundances in the range 0.1–10) associated with enhanced temporal variance of disturbance; cc: Cystoseira compressa; nh: Nemalion helmintoides; pp: Padina pavonica; ss: Spirorbis sp.; vt: Vermetus triqueter.

Mentions: Inspection of the rank-abundance curves (Figure 2), however, showed that assemblages in Control and LV conditions had a tail of rare species, represented by singletons, whilst assemblages in MV and HV treatments lacked singletons. Rare species disappeared from HV plots, which had lower species richness compared to the other treatments. In contrast, singletons were missing in the MV condition because rare species entered higher abundance classes under intermediate levels of temporal variance of disturbance. This was the case for 5 of the 29 species (17.2%) in the MV treatment, which were either unobserved or had a lower rank in the LV treatment (Figure 3).


Neutrality and the response of rare species to environmental variance.

Benedetti-Cecchi L, Bertocci I, Vaselli S, Maggi E, Bulleri F - PLoS ONE (2008)

Mean species abundances (±1 s.e.m., n = 18) in Low Variance (horizontal axis) and Medium Variance (vertical axis) treatments.The inset shows an increase in abundance of rare species (mean abundances in the range 0.1–10) associated with enhanced temporal variance of disturbance; cc: Cystoseira compressa; nh: Nemalion helmintoides; pp: Padina pavonica; ss: Spirorbis sp.; vt: Vermetus triqueter.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2481292&req=5

pone-0002777-g003: Mean species abundances (±1 s.e.m., n = 18) in Low Variance (horizontal axis) and Medium Variance (vertical axis) treatments.The inset shows an increase in abundance of rare species (mean abundances in the range 0.1–10) associated with enhanced temporal variance of disturbance; cc: Cystoseira compressa; nh: Nemalion helmintoides; pp: Padina pavonica; ss: Spirorbis sp.; vt: Vermetus triqueter.
Mentions: Inspection of the rank-abundance curves (Figure 2), however, showed that assemblages in Control and LV conditions had a tail of rare species, represented by singletons, whilst assemblages in MV and HV treatments lacked singletons. Rare species disappeared from HV plots, which had lower species richness compared to the other treatments. In contrast, singletons were missing in the MV condition because rare species entered higher abundance classes under intermediate levels of temporal variance of disturbance. This was the case for 5 of the 29 species (17.2%) in the MV treatment, which were either unobserved or had a lower rank in the LV treatment (Figure 3).

Bottom Line: A field experiment was performed to examine whether assemblages responded neutrally or non-neutrally to changes in temporal variance of disturbance.The experimental results did not reject neutrality, but identified a positive effect of intermediate levels of environmental heterogeneity on the abundance of rare species.This effect translated into a marked decrease in the characteristic time scale of species turnover, highlighting the role of rare species in driving assemblage dynamics in fluctuating environments.

View Article: PubMed Central - PubMed

Affiliation: Dipartimento di Biologia, Università di Pisa, Pisa, Italy. lbenedetti@biologia.unipi.it

ABSTRACT
Neutral models and differential responses of species to environmental heterogeneity offer complementary explanations of species abundance distribution and dynamics. Under what circumstances one model prevails over the other is still a matter of debate. We show that the decay of similarity over time in rocky seashore assemblages of algae and invertebrates sampled over a period of 16 years was consistent with the predictions of a stochastic model of ecological drift at time scales larger than 2 years, but not at time scales between 3 and 24 months when similarity was quantified with an index that reflected changes in abundance of rare species. A field experiment was performed to examine whether assemblages responded neutrally or non-neutrally to changes in temporal variance of disturbance. The experimental results did not reject neutrality, but identified a positive effect of intermediate levels of environmental heterogeneity on the abundance of rare species. This effect translated into a marked decrease in the characteristic time scale of species turnover, highlighting the role of rare species in driving assemblage dynamics in fluctuating environments.

Show MeSH
Related in: MedlinePlus