Explaining the coexistence of large number of plant species pose a central problem in community ecology. The Janzen-Connell hypothesis proposes that seedling occurring at high conspecific density suffers greater attack from specialist natural enemies (insect herbivore and fungal pathogens). The process disproportionately reduces population of abundant species and maintains host plant species coexistence. An important assumption of this mechanism is that natural enemies are host specific and the simulations suggest the number of stably coexisting host species increases with the specificity of their natural enemies. However, increased host-specificity also increases the risk of stochastic extinction of pathogen species that will release host species from regulation to become monodominant. Thus while high host specificity can lead to stably coexisting period for a short period of time, it may also reduce the longer-term stability of the overall community of hosts and natural enemies. We developed models that considered the population dynamics of host plants and their pathogen jointly. We used these models to examine the relationship between the pathogen host specificity and the long term stable coexistence of the hosts.
Results/Conclusions
Our models suggest long term coexistence will be possible under a range of pathogen host specificity, and high host specificity does not translate into longer term stable coexistence of the community of host plant and their pathogen. Both diversity and stability can be affected by the pathogen traits. It is important to consider the pathogen dynamics while investigating coexistence and stability as it can change the community dynamics.