A Simplified Population-Level Landscape Model Identifying Ecological Risk Drivers of Pesticide Applications, Part One: Case Study for Large Herbivorous Mammals

Abstract

Environmental risk assessment is a key process for the authorization of pesticides, and is subjected to continuous challenges and updates. Current approaches are based on standard scenarios and independent substance-crop assessments. This arrangement does not address the complexity of agricultural ecosystems with mammals feeding on different crops. This work presents a simplified model for regulatory use addressing landscape variability, co-exposure to several pesticides, and predicting the effect on population abundance. The focus is on terrestrial vertebrates and the aim is the identification of the key risk drivers impacting on mid-term population dynamics. The model is parameterized for EU assessments according to the European Food Safety Authority (EFSA) Guidance Document, but can be adapted to other regulatory schemes. The conceptual approach includes two modules: (a) the species population dynamics, and (b) the population impact of pesticide exposure. Population dynamics is modelled through daily survival and seasonal reproductions rates; which are modified in case of pesticide exposure. All variables, parameters, and functions can be modified. The model has been calibrated with ecological data for wild rabbits and brown hares and tested for two herbicides, glyphosate and bromoxynil, using validated toxicity data extracted from EFSA assessments. Results demonstrate that the information available for a regulatory assessment, according to current EU information requirements, is sufficient for predicting the impact and possible consequences at population dynamic levels. The model confirms that agroecological parameters play a key role when assessing the effect of pesticide exposure on population abundance. The integration of laboratory toxicity studies with this simplified landscape model allows for the identification of conditions leading to population vulnerability or resilience. An Annex includes a detailed assessment of the model characteristics according to the EFSA scheme on Good Modelling Practice.

Keywords: hare; landscape risk assessment; pesticides; population model; rabbit.

Figure A1

Representation of the conceptual model.

Figure 1

Replicability of total population dynamics (abundance) during a 1000 day period. Each color line represents the average of 50 replications per nest, each graphic presents results for 16 nests with identical properties. (A,B) Replicates (2 independent runs with same input values) for an initial number of 100 rabbits per nest. (C,D) Replicates (2 independent runs with same input values) for an initial number of 140 rabbits per nest.

Figure 2

Total population dynamics (abundance) for a period of 1000 days according to the initial number of individuals in the nest (from 30 to 200).

Figure 3

Replicability of total population dynamics during a 10,000 day period. Each line represents the average of 50 replications per nest, with identical properties and an initial number of 140 rabbits per nest.

Figure 4

Examples of abundance simulations for different reproduction and mortality conditions for nests with similar initial densities (140 rabbits per nest). (A): Reproductive seasons of 2, 3, 6, 9, or 12 months per year with similar adjusted annual reproduction rates. (B): Reproductive seasons of 2, 3, 6, 9, or 12 months per year with similar monthly reproduction rates. (C): Effects of different combinations for mortality and reproduction (Nest 1 default monthly values of 0.11 for mortality and 4.0 for reproduction with reproduction season of 6 months; Nest 2 rates of 0.22 for mortality and 8.0 for reproduction with reproduction season of 6 months; Nest 3 rates of 0.22 for mortality and 4.0 for reproduction with reproduction season of 12 months; Nest 4 rates of 0.22 for mortality and 4.0 for reproduction with reproduction season of 6 months; Nest 5 rates of 0.16 for mortality and 6.0 for reproduction with reproduction season of 6 months). (D): Effect of adding reproductive capacities to the subadult (A2) female group (reproduction rate for A2 of 4.0, 3.0, 2.0, and 0.0 for nests 1, 2, 3, and 4 respectively).

Figure 5

Relationship between daily exposure (A1), 12 days time-weighted average exposure (A2), the maximum monthly twaETA used for assessing mortality (B1) and reproductive (C1) effects, and the associated effects on the mortality (B2) and reproduction (C2) rates, following two applications of glyphosate on cereals at 4.0 kg/ha.

Figure 6

Relationship between daily exposure (A1), 5 days, time-weighted average exposure (A2), the maximum monthly twaETA used for assessing mortality (B1) and reproductive (C1) effects, and the associated effects on the mortality (B2) and reproduction (C2) rates, following one application of bromoxynil on cereals at 1.0 kg/ha.

Figure 7

Effect of bromoxynil on the evolution of rabbit abundance (total population number). Nest 1 control; Nest 2 treated 0.05 kg/ha; Nest 3 treated 0.1 kg/ha; Nest 4 treated 0.2 kg/ha. Each figure represents equivalent treatments at different time points (red vertical line) during the breeding season. (A): 15 days; (B): 30 days, (C): 90 days and (D): 120 days, after breading season initiation, respectively.

Figure 8

Effect of multiple applications of bromoxynil on the evolution of rabbit abundance (total population number). (A): One, two, or three applications summing 0.1 kg/ha. Nest 1 control; Nest 2 One application 0.1 kg/ha; Nest 3 two applications of 0.05 kg/ha; Nest 4 three applications of 0.033 kg/ha. (B): Effect of application time: Nest 1 control; Nest 2 One application 0.05 kg/ha; Nest 3 three applications of 0.05 kg/ha at 15 days intervals; Nest 4 three applications of 0.05 kg/ha at monthly intervals.