Brian Thompson, Nhat Nguyen,Beth Lusczek, and Sanja Selakovic
Non-linear Effectsof Pesticides on
Food Web Dynamics
Collaboration facilitated by SFIComplex Systems Summer School 2014
computer science epidemiology
ecologybiophysics
Motivation
Related WorkNet 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, Sรคterberg 2013)
Our Approach
DIRECT PESTICIDALEFFECTS
INTER-SPECIESINTERACTIONS
NET EFFECTS OF PESTICIDES
Pesticide Model
= steepness of curve, specific to a given
pesticide and species
๐ (๐ฅ )= 2
1+๐โ๐พโ ๐ฅโ1PESTICIDE
EQUATION
๐พ>0
๐พ<0
Bio-energetic Model(Lotka โ Volterra)
โข Energy and matter flow from prey to predator
๐ ๐ ๐
๐๐ก=โ๐๐ ๐ ๐(1โ๐ ๐ (1โ ๐๐
๐ ๐๐๐๐ ))โโ๐โ ๐ ๐ ๐๐ ๐๐ ๐ ๐+๐๐๐๐โ
๐ โ ๐
๐ ๐๐ ๐ ๐๐ ๐
๐ ๐ ๐
๐๐ก= ๐ผ๐ ๐ ๐โ๐๐ ๐ ๐(1โ๐ ๐ (1โ ๐ ๐
๐ ๐๐๐๐ ))โโ๐โ ๐ ๐ ๐๐ ๐๐ ๐ ๐
๐ ๐ ๐
๐๐ก=๐ ๐+โ
๐ โ ๐
๐ ๐ ๐ ๐ (1โ๐ ๐ (1โ ๐ ๐
๐ ๐๐๐๐ ))+โ๐ โ ๐ โ๐โ ๐ , ๐ (1โ๐ ๐ )๐๐ ๐ ๐ ๐ ๐๐โโ
๐โ ๐
๐ ๐๐ ๐๐ ๐ ๐
Consumers:
Roots:
Detritus:
Bio-energetic Model
INTER-SPECIESINTERACTIONEQUATIONS
โข Pesticide data:โ Stanton, Allen, and Campion. โThe Effect of the Pesticide Carbofuran on
Soil Organisms and Root and Shoot Production in Shortgrass Prairie,โ 1981.โ Carbofuran had a significant effect on bacteriophageous nematodes,
phytophageous nematodes, and saprophytic fungi
โข Soil food web data:โ Moore and De Ruiter. โEnergetic Food Webs: An Analysis of Real and Model
Ecosystems,โ 2012.โ Observed biomasses, and parameter values for mortality rates,
assimilation efficiency, production efficiency, predation coefficients, photosynthetic growth, and allochthonous material
Data
Roots
Detritus
PhytophagousNematodes
SaprophyticFungi
Bacteria
Collembolans
Noncrypto-stigmatic Mites
CryptostigmaticMites
FungivorousNematodes
Bacteriophagous
NematodesBacteriophagous
Enchytraeids
Mites
Flagellates
Amoebae
PredaceousNematodes
PredaceousMites
PredaceousCollembolans
NematodeFeeding Mites
(De Ruiter et al., 1993)
Soil Food Web
Experiments
Experiments
Experiments
Contributions
โข A new approach to studying the effects of pesticides on an ecosystem that integrates the findings from two bodies of literature
โข Mathematical model integrating pesticidal effects with food web dynamics
โข Simulations can inform policy decisions by helping us understand and anticipate the consequences of pesticide use
Future Work
โข Effects of multiple pesticides on multiple species or functional groups
โข Model the consumption, decay, and inflow of pesticides in the systemโ Effects of species on pesticide concentration (e.g. roots of
corn plants increase degradation of atrazine)
โ Bioaccumulation of pesticides
โข Do more extensive experiments to study sensitivity, stability, resilience, etc. in the presence of pesticides
โข 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