My long-term research interests have focused on the effects of environmental stressors (acid rain, exotic species, turbidity associated with sediments, eutrophication and
herbicides) on aquatic food webs. I am interested in food web interactions and how
environmental stressors can affect such interactions. My research integrates field and lab experiments and comparative field studies. Within this general framework, I have successfully maintained continuous external funding for the following lines of research.
1. Factors affecting food web efficiency:
Food Chain Efficiency (FCE; the proportion of primary production that results in production of the top predator) is a very important ecosystem function that can be affected by autotroph quantity and composition, traits that are linked to the availability of light and nutrients. It is well known that variability in algal carbon and nutrient stoichiometry, fatty acid composition, and digestion resistance can limit the production of herbivores that consume these autotrophs. However, little is known about how constraints at the autotroph-herbivore link propagate to upper trophic levels. Using the mesocosm facility at Miami Ecological Research Center, we have tested the interactive effect of light and nutrients on FCE in two and three trophic level food chains and in pelagic and benthic food webs. These studies show that light and nutrients, via effects on algal quality, can constrain energy flow to upper trophic levels, i.e., carnivores. Currently, my lab is investigating the generality of interactive effects of light and nutrients in FCE. We are interested on how predator identity in terms of nutrient requirements (among-species comparison) and ontogeny (among-species comparison) mediates the effects of light and nutrients on FCE. We also have examined the carryover effects and resulting changes in FCE under different light, phosphorus, and N:P supply ratios (within-species comparison).
2. Factors regulating reservoir food webs:
My lab has collaborated in a long-term study focusing on the factors regulating reservoir food webs, particularly the roles of watersheds and an omnivorous fish (gizzard
shad) on these ecosystems. We have analyzed the long-term dynamics of zooplankton communities in Acton Lake and larval fish-zooplankton interactions. Gizzard shad is a widespread omnivorous fish in reservoirs, especially those in agriculturally dominated areas, suggesting a linkage between land use practices and food web dynamics in reservoirs. My long-term data set on zooplankton and larval gizzard shad, in addition to the limnological and hydrological data accumulated by my colleagues (MJ Vanni and WH Renwick), has allowed us to study the response of a reservoir ecosystem to declining nutrient and detritus inputs from the watershed due to improvements in agricultural practices. These improvements have caused substantial declines in phosphorus and suspended sediment inputs to Acton Lake over the last 15 years. Mean phytoplankton biomass (chlorophyll) has increased during this period, apparently due todecreased light limitation resulting from decreased sediment inputs. Our results suggest that in spite of high turnover rates, zooplankton responses to changes in agricultural subsidies lagged behind those of primary producers.
- Dickman, EM, JM Newell, MJ González, and MJ Vanni. 2008. Light, nutrients, and food chain length constrain planktonic energy transfer efficiency across multiple trophic levels. Proceedings of the National Academy of Science 105: 18408-18412
- Pilati, A, MJ Vanni, MJ González and AM Gaulke. 2009. The effect of agricultural subsidies of nutrients and detritus on a detritivorous fish population. Ecological Applications 19: 942-960.
- González, MJ, LB Knoll, and MJ Vanni. 2010. Differential effects of elevated nutrient and sediment inputs on survival, growth and biomass of a common larval fish species. Freshwater Biology 55: 654-669.
- Mette EM, MJ Vanni, JM Newell**, and MJ González. 2011. Phytoplankton communities and stoichiometry are interactively affected by light, nutrients, and fish. Limnology and Oceanography 56: 1959-1975.
- Stoeckel, JA, J Morris, E Ames, MJ. Vanni, WH Renwick, and MJ González. 2012. Exposure times to the spring herbicide flush along a stream-reservoir system. Journal of the American Water Resources Association 48:616-634.