Brian Thompson, Nhat Nguyen, Beth Lusczek, and Sanja Selakovic Non-linear Effects of Pesticides on Food Web Dynamics Collaboration facilitated by SFI Complex Systems Summer School 2014 computer science epidemiology ecology biophysics

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 DIRECT PESTICIDAL EFFECTS INTER-SPECIES INTERACTIONS NET EFFECTS OF PESTICIDES

Pesticide Model PESTICIDE EQUATION

Bio-energetic Model (Lotka – Volterra) Energy and matter flow from prey to predator

Consumers: Roots: Detritus: Bio-energetic Model INTER-SPECIES INTERACTION EQUATIONS

Pesticide data: – Stanton, Allen, and Campion. “The Effect of the Pesticide Carbofuran on Soil Organisms and Root and Shoot Production in Shortgrass Prairie,” – Carbofuran had a significant effect on bacteriophageous nematodes, phytophageous nematodes, and saprophytic fungi Soil food web data: – Moore and De Ruiter. “Energetic Food Webs: An Analysis of Real and Model Ecosystems,” – Observed biomasses, and parameter values for mortality rates, assimilation efficiency, production efficiency, predation coefficients, photosynthetic growth, and allochthonous material Data

Roots Detritus Phytophagous Nematodes Saprophytic Fungi Bacteria Collembolans Noncrypto- stigmatic Mites Cryptostigmatic Mites Fungivorous Nematodes Bacteriophagous Nematodes Bacteriophagous Enchytraeids Mites Flagellates Amoebae Predaceous Nematodes Predaceous Mites Predaceous Collembolans Nematode Feeding Mites (De Ruiter et al., 1993) Soil Food Web

Experiments

Contributions A new approach to studying the effects of pesticides on an ecosystem that integrates the findings from two bodies of literature Mathematical model integrating pesticidal effects with food web dynamics Simulations can inform policy decisions by helping us understand and anticipate the consequences of pesticide use

Future Work Effects of multiple pesticides on multiple species or functional groups Model the consumption, decay, and inflow of pesticides in the system – Effects of species on pesticide concentration (e.g. roots of corn plants increase degradation of atrazine) – Bioaccumulation of pesticides Do more extensive experiments to study sensitivity, stability, resilience, etc. in the presence of pesticides 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

Pesticide Model

Bio-energetic Model (Lotka – Volterra) Energy and matter flow from prey to predator Changes in death rates can lead to direct or indirect extinctions (Saterberg et al., Nature 2013)

Bio-energetic Model (Lotka – Volterra) Energy and matter flow from prey to predator Changes in death rates can lead to direct or indirect extinctions (Saterberg et al., Nature 2013)

Coupled Model pesticides species

Contributions Mathematical model integrating pesticidal effects with food web dynamics A new approach that addresses the shortcomings of existing literature – Isolation studies: hard to extrapolate to native environment – Field studies: analyze net effect but don’t describe mechanism Simulations can inform policy decisions by helping us understand and anticipate the consequences of pesticide use on the environment