Stability via Asynchrony in Drosophila Metapopulations with Low Migration Rates
Sutirth Dey and
Amitabh Joshi*
Evolutionary Biology Laboratory, Evolutionary & Organismal Biology Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O., Bangalore 560 064, India.
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Fig. 1. Experimental results. The P values indicate the significance level from the corresponding mixed-model analysis of variance. The inequalities denote the means that were found different at the 0.05 (*) or 0.01 (**) level of significance using Tukey's HSD test. CM, no migration; LMM, low levels of migration (10%); HMM, high levels of migration (30%). Error bars are SEM for four replicate metapopulations. (A) Mean fluctuation index (FI) of LMMs is lower than that of either CMs or HMMs, indicating higher constancy stability. (B) Mean FI of the subpopulations is highest in the LMMs, suggesting lower stability at that migration rate. (C) Mean subpopulation size of CMs is higher than for both LMMs and HMMs, which is unexpected. See text for possible explanations.
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Fig. 2. Mean (±SE) cross-correlation coefficients from the experimental data. (A) The means for all possible pairs of subpopulations are positive for CMs and HMMs, indicating synchrony between the subpopulations. (B) The mean nearest neighbor cross-correlation coefficient is significantly negative for the LMMs. This indicates that neighboring subpopulations are oscillating out of phase with each other, leading to the observed patterns of stability.
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Fig. 3. Simulation results averaged over 10 independent runs (error bars represent SEM). (A) Mean metapopulation FI values are lowest for LMMs and are similar for CMs and HMMs (compare Fig. 1A). (B) Mean subpopulation FI values are highest for LMMs (compare Fig. 1B). (C) The average subpopulation size of CMs is the lowest, contrary to the experimental findings (Fig. 1C). See text for a possible explanation.
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Fig. 4. Mean (±SE) cross-correlation coefficients from the simulations. (A) The average cross-correlation coefficient between all possible subpopulation pairs is close to zero for both CMs and LMMs. This indicates an overall lack of synchrony and contradicts the corresponding empirical observation for CMs (compare Fig. 2A). See text for a possible explanation. (B) The average cross-correlation coefficient between the nearest neighbors is negative for LMMs but is close to zero for CMs. This shows that although the LMM subpopulations were out of phase with each other, there was little synchrony among the CM subpopulations.
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