Metapopulation modelling of threatened plants to assess conservation status and determine minimum viable population size

Abstract

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, popu-lation viability analysis, and analysis of impact of dis-turbance on the metapopulation were undertaken. The metapopulation had 11 populations of which sev-en 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) represent-ing the disturbed condition, and alternate model (M2) representing the undisturbed condition for three dis-tinct layers of P. polyphylla populations, i.e. CF, FF in isolation, and collectively as metapopulation. The out-puts 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 fecun-dity in both the models. Stochastic simulations re-vealed an extinction risk of >10% in 100 years in M1 scenario, which put the species under vulnerable cate-gory. The extinction risk of metapopulation signifi-cantly varied between the two models (M1=0.85; M2=0.42), conforming the hypothesis that dis-turbance and forest fragmentation have detrimental effect on the persistence of P. polyphylla. Recovery of species was most promising when reproductive indi-viduals were introduced to the M2 model. Thus, both in-troduction of individuals in the field and protection of the populations with emphasis on the reproductive sub-set would result in achieving minimum viable popula-tion size or low threat status of the species.