Metapopulation Modelling of Threatened Plants to Assess Conservation Status and Determine Minimum Viable Population Size

Use of metapopulation modelling in conservation of threatened plants has been demonstrated in this article taking Paris polyphylla Smith as an example. The metapopulation data collected from Sikkim Himalaya over a period of four years were analysed using RAMAS Metapop 5.0 software. Demographic projection, assessment of extinction probability, population viability analysis, and analysis of impact of disturbance on the metapopulation were undertaken. The metapopulation had 11 populations of which seven were in continuous forest (CF) and four were in forest fragments (FF). All the analyses were done in two model scenarios, viz. base-model (M1) representing the disturbed condition, and alternate model (M2) representing the undisturbed condition for three distinct layers of P. polyphylla populations, i.e. CF, FF in isolation, and collectively as metapopulation. The outputs of the deterministic population models in respect of CF and FF populations revealed that both the populations had contribution of growth and survival of plants to such decline was greater than the fecundity in both the models. Stochastic simulations revealed an extinction risk of >10% in 100 years in M1 scenario, which put the species under vulnerable category. The extinction risk of metapopulation significantly varied between the two models (M1 = 0.85; M2 = 0.42), conforming the hypothesis that disturbance and forest fragmentation have detrimental effect on the persistence of P. polyphylla. Recovery of species was most promising when reproductive individuals were introduced to the M2 model. Thus, both introduction of individuals in the field and protection of the populations with emphasis on the reproductive subset would result in achieving minimum viable population size or low threat status of the species.