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Non-linear Effects of Pesticides on Food Web Dynamics epidemiology computer science Brian Thompson, Nhat Nguyen, Beth Lusczek, and Sanja Selakovic biophysics Collaboration facilitated by SFI Complex Systems Summer School 2014 ecology Motivation Related Work Net effects of pesticides on ecosystem (e.g. Stanton 1981, Yeates 1999) Pesticidal effects on species in isolation (e.g. Ingham 1984, Berthold 2002) Dynamics of bioenergetic flow (e.g. De Ruiter 1995, Säterberg 2013) Our Approach NET EFFECTS OF PESTICIDES DIRECT PESTICIDAL EFFECTS INTER-SPECIES INTERACTIONS Pesticide Model πΎ>0 πΎ<0 2 PESTICIDE π π₯ = β1 βπΎβ π₯ EQUATION 1+π πΎ = steepness of curve, specific to a given pesticide and species Bio-energetic Model (Lotka β Volterra) β’ Energy and matter flow from prey to predator Bio-energetic Model Consumers: πππ ππ = βππ ππ 1 β π π 1 β πππ ππ‘ ππ β πππ ππ ππ + ππ ππ πβ π πβ π INTER-SPECIES INTERACTION EQUATIONS Roots: πππ ππ = πΌπ ππ β ππ ππ 1 β π π 1 β πππ ππ‘ ππ Detritus: πππ = π π + ππ‘ πππ ππ ππ ππ ππ 1 β π π 1 β πβ π ππ πππ ππ β πππ ππ ππ πβ π + 1 β ππ πππ ππ ππ β πβ π πβ π,π πππ ππ ππ πβ π Data β’ Pesticide data: β Stanton, Allen, and Campion. βThe Effect of the Pesticide Carbofuran on Soil Organisms and Root and Shoot Production in Shortgrass Prairie,β 1981. β Carbofuran had a significant effect on bacteriophageous nematodes, phytophageous nematodes, and saprophytic fungi β’ Soil food web data: β Moore and De Ruiter. βEnergetic Food Webs: An Analysis of Real and Model Ecosystems,β 2012. β Observed biomasses, and parameter values for mortality rates, assimilation efficiency, production efficiency, predation coefficients, photosynthetic growth, and allochthonous material Soil Food Web Phytophagous Nematodes Collembolans Predaceous Mites Cryptostigmatic Mites Roots Saprophytic Fungi Noncryptostigmatic Mites Fungivorous Nematodes Enchytraeids Detritus Predaceous Collembolans Nematode Feeding Mites Predaceous Nematodes Bacteriophagous Nematodes Flagellates Bacteria Amoebae Bacteriophagous Mites (De Ruiter et al., 1993) Experiments Experiments Experiments Contributions β’ A new approach to studying the effects of pesticides on an ecosystem that integrates the findings from two bodies of literature β’ Mathematical model integrating pesticidal effects with food web dynamics β’ Simulations can inform policy decisions by helping us understand and anticipate the consequences of pesticide use Future Work β’ Effects of multiple pesticides on multiple species or functional groups β’ Model the consumption, decay, and inflow of pesticides in the system β Effects of species on pesticide concentration (e.g. roots of corn plants increase degradation of atrazine) β Bioaccumulation of pesticides β’ Do more extensive experiments to study sensitivity, stability, resilience, etc. in the presence of pesticides β’ Modeling of non-equilibrium dynamics Thank you! Special thanks to Miguel Fuentes, and to the staff and organizers of the SFI Complex Systems Summer School: Sander Bais, Juniper Lovato, and John Paul Gonzales
