What matters most - role of environment, arrival order and population fitness in invaded community assembly.
High population fitness and early arrival in the community give exotic plants a competitive advantage over the natives in a novel environment. These processes are often influenced by environmental heterogeneity like habitat disturbance and seasonal impacts. These effects were experimentally investigated in this study with the hypothesis that environmental factors, arrival order and physiological fitness of the invading species determine the fate of the community assembly. Controlled regeneration experiments were conducted in a disturbed and undisturbed plot during the winter and monsoon periods. At a weekly interval, above ground biomass data of the invasive Mikania micrantha and the native species were collected for twenty weeks from the undisturbed plot in the winter and from the disturbed plot in both the seasons. Relative growth rate and carrying capacity were estimated using a logistic growth model and used as fitness metrics for the invasive and native species. During the winter season, priority effects were weakened. M. micrantha was late-arriving species but became community dominant due to the higher growth rate in the undisturbed habitat, whereas its stable growth rate and habitat disturbance reduced fitness of the native species in the disturbed habitat. Seasonal priority effect was established in monsoon when M. micrantha was the early-arriving species and due to seasonal influence on its rapid growth, it became a driver of community change leading to the regrowth failure of the annual species in the community. Based on the revegetation pattern in the experimental sites, season-specific management strategies and continuous monitoring were recommended for this invasive plant.