parasites as ecosystem engineers

Diverse effects of parasites in ecosystems 

Community ecologists generally recognize the importance of species – such as pollinators – that have clear positive effects within ecosystems. However, parasites – usually regarded in terms of their detrimental effects on the individuals they infect – can also have positive impacts on other species in the community. We now recognize that parasites influence species coexistence and extirpation by altering competition, predation, and herbivory, and that these effects can, in turn, influence ecosystem properties. Parasites and pathogens act as ecosystem engineers, alter energy budgets and nutrient cycling, and influence biodiversity.

Effects of parasites on network structure. (a) Connectivity measures the proportion of possible trophic links that are realized in the food web. Adding parasites to the web can boost connectivity substantially if all the realized links (parasite–parasite, parasite–predator, and host–parasite links) are included. In this example, including parasites (in red) more than doubles the number of links in a simple network, even though parasite species number only half those of free-living species (basal resource species: green; herbivores: blue; predators: black). Provided these interactions are generally weak, increased connectivity increases community resilience by increasing dynamic stability. (b) Nestedness describes how consumer–resource links are organized in a network. Well-nested
communities have a core of strongly interacting species (shaded) around which other, less connected species associate, so generalist consumers use strongly and weakly connected resources, and specialists tend to consume the dominant, well-connected resource species. Well-nested webs tend to be less vulnerable to secondary extinction, and food webs involving parasites tend to be strongly nested.


Melanie J Hatcher , Jaimie TA Dick , Alison M Dunn (2012)
 https://fdocuments.in/document/diverse-effects-of-parasites-in-ecosystems-linking-interdependent-processes.html
 https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/110016