Download Impact of biodiversity loss on production in complex marine food webs mitigated by prey-release

Impact of biodiversity loss on production in
complex marine food webs mitigated by
prey-release
Tak Fung, Keith D. Farnsworth, David G. Reid and Axel G. Rossberg
Fish is one of the most traded food commodities in the world, and provide a main source of
protein for over a billion people. However, many commercial fisheries are operating
unsustainably because of practices such as habitat destruction and overfishing, with large
impacts on ecosystem dynamics. There is thus a critical need for more informed fisheries
management, based on an explicit consideration of the ecosystem effects of fishing. In
particular, there is a need for greater understanding of how the amount of fish biomass
produced by a marine ecosystem changes with the number of species that have been lost,
due to overfishing and other unsustainable practices.
In our study, we used a realistically complex mathematical model of fished marine
ecosystems and found that as the fish diversity of complex marine food webs declines, the
remaining fish species initially resisted the change by compensating with an increase in
production, which helped to mitigate the decrease in total fish production. However, once the
biodiversity losses became too great and only about a third of the fish species in a food web
remained, a collapse ensued whereby production sharply declined with further species loss,
as the relatively small percentage of remaining species were unable to provide much
compensation. The initial compensation therefore masks a more serious non-linear decline
in fish production potential, providing a false sense of assurance until the biodiversity losses
become too great. Our findings show that it is vital to manage fisheries within the larger
ecological context and that action to halt species loss may avert unexpected sharp declines
in production, thereby helping to improve the world’s food security.
More specifically, we used the Population-Dynamical Matching Model (PDMM) to represent
marine food webs each with thousands of dynamically interacting species. This breakthrough
in modelling allows the representation of features such as prey-switching, where predators
preferentially target prey species in abundant supply in order to improve their chances of
survival, and gradual assembly of a model food web similar to the natural process. Such
detailed features encourage dynamic stability and coexistence of many model species, as
well as accurate representation of real food webs. We sequentially deleted fish species from
complex model marine food webs generated using the PDMM and after each deletion,
observed the dynamics of the remaining fish species and measured the change in total fish
production. In the future, we plan to use the PDMM to further investigate the relationships
between biodiversity and ecosystem functioning in order to allow for even more informed
management of fisheries.
------------------------------------------------------------------------------------------------------------------------The full paper can be accessed via:
http://www.nature.com/ncomms/2015/150323/ncomms7657/full/ncomms7657.html