Tritrophic interactions promote chamomile invasion in a biodiversity hotspot

Background/Question/Methods: Understanding the conditions that promote biological invasions is a critical step for developing successful management strategies. However, success of any given invasive species is affected by complex interactions among environmental factors that might change across habitats and regions, making broad generalizations uninformative for management. For many invasive species, we lack basic information about key attributes that promote invasion; analysis and documentation of these attributes is a challenging task for invasion ecologists. To successfully manage an invasive species we must understand the mechanisms behind its invasion process. Here, we report on a series of studies of the attributes that contribute to the invasiveness of the Eurasian annual forb stinking chamomile (Anthemis cotula) in the Kashmir Himalaya, India. The species often establishes virtual monocultures where diverse communities once flourished.

Results/Conclusions:  The results reveal that a protracted recruitment period aided by habitat disturbance and favorable moisture, temperature, light and nutrient regimes, and high population size even after seedling mortality, are the key demographic attributes contributing to the establishment and spread of this species. The germination ecology of the chamomile helps it synchronize its successful recruitment with favorable habitat conditions, thereby ensuring seedling survival, establishment, growth and fitness. An ecological trade-off in the life history of this species is clearly discernible, with individuals of pre-winter cohorts contributing to fecundity and those of post-winter cohorts ensuring the survival and continuance of the species in the invaded habitats. The inhibitory effect of the aqueous leaf leachate on its neighboring species indicate the allelopathic potential of this species. In addition to the myriad of traits that contribute to invasiveness of this species in Kashmir Himalaya, the tripartite interactions between a local herbivore and the AMF seem to be of paramount importance. The significant influence of mycorrhizal inoculation and herbivory, both in isolation and in combination, on invasiveness of A. cotula highlight how interactions of alien species with enemies, mutualists and competitors in the introduced range may jointly influence their invasive success and need to be understood in unison. The tripartite (herbivore-host-AM) interactions recorded in this study provide insights into the potential roles of top-down and bottom-up plant interactions in facilitating alien plant invasions.