How the storage effect and the number of temporal niches affect biodiversity in stochastic and seasonal environments
Fig 4
Species richness (SR, upper panels) and Shannon’s entropy (SE, lower panels) vs. the rate in which new species are trying to invade the community, νN.
In all cases, when νN is small the diversity of a community and its evenness obey the same relationships as T in the previous section: global competition is better (for coexistence) than local due to the storage effect, and stochastic variations are worse than periodic variations. When the number of temporal niches is large, as in the Q = 30 case in panels (c) and (f), an increase of νN leads to an increase in the number of species, their different response buffers the effect of environmental variations and the results converge to the predictions of the neutral model (cyan dashed line). However, as the number of temporal niches decreases global competition puts a hurdle against invasion, as every invader must compete with niche-specialists. Therefore SR, and in particular SE, are much smaller for global competition if νN is large. A comparison between the case of Q = 10 [panels (b) and (e)] and Q = 3 [panels (a) and (d)] suggest that the crossover from the storage-dominated regime, where global competition is better, to the regime in which global competition acts to decrease biodiversity, occurs when the number of species is equal to the number of temporal niches. For all panels, parameters are: N = 10, 000, δ = 0.2 and γ = 0.4. SR and SE were monitored every generation and the results presented here reflect an average over the period between 6, 000 and 100, 000 generations. For the neutral model γ = 0 and δ is an irrelevant parameter.