Biology subjects

Pande, J.

Publications and source records attributed to Pande, J..

3 recordsLinked to original sources

bioRxiv2021

Quantifying invasibility

Invasibility, the chance of a population to grow from rarity and to establish a large-abundance colony, plays a fundamental role in population genetics, ecology, and evolution. For many decades, the mean growth rate when rare has been employed as an invasion criterion. Recent analyses have shown that this criterion fails as a quantitative metric for invasibility, with its magnitude sometimes even increasing while the invasibility decreases. Here we employ a new large-deviations (Wentzel-Kramers-Brillouin, WKB) approach and derive a novel and easy-to-use formula for the chance of invasion in terms of the mean growth rate and its variance. We also explain how to extract the required parameters from abundance time series. The efficacy of the formula, including its accompanying data analysis technique, is demonstrated using synthetic and empirically-calibrated time series from a few canonical models.

ecology↗

bioRxiv2021

Stochasticity-induced stabilization weakens in diverse communities.

Environmental stochasticity and the temporal variations of demographic rates associated with it are ubiquitous in nature. The ability of these fluctuations to stabilize a coexistence state of competing populations (sometimes known as the storage effect) is a counterintuitive feature that has aroused much interest. Here we consider the performance of environmental stochasticity as a stabilizer in diverse communities. We review the results of previous studies which suggest that the stabilizing effects of stochasticity weaken as the number of species increases, provide a systematic numerical exploration of the phenomenon and identify the relevant parameter regimes. Of particular importance is the ratio between the dwell time of the environment and the generation time: we show that stochasticity promotes diversity only when this ratio is smaller than the inverse of the fundamental biodiversity parameter. In an opposite regime, when stochasticity impedes coexistence and lowers the species richness, its effect is determined by the ratio between the strength of environmental variations and the rate at which new types are added to the community via speciation, mutation or immigration.

ecology↗

bioRxiv2019

Mean growth rate when rare is not a reliable metric for persistence of species

The coexistence of many species within ecological communities poses a long-standing theoretical puzzle. Modern coexistence theory (MCT) and related techniques explore this phenomenon by examining the chance of a species population growing from rarity in the presence of all other species. The mean growth rate when rare, [E][r], is used in MCT as a metric that measures persistence properties (like invasibility or time to extinction) of a population. Here we critique this reliance on [E][r] and show that it fails to capture the effect of random abundance variations on persistence properties. The problem becomes particularly severe when an increase in the amplitude of stochastic temporal environmental variations leads to an increase in [E][r], since at the same time it enhances random abundance fluctuations and the two effects are inherently intertwined. In this case, the chance of invasion and the mean extinction time of a population may even go down as [E][r] increases.

ecology↗