Trophic transfer of pesticides: The fine line between predator–prey regulation and pesticide–pest regulation

Abstract

Understanding pesticide impacts on populations of target/non‐target species and communities is a challenge to applied ecology. When predators that otherwise regulate pest densities ingest prey contaminated with pesticides, this can suppress predator populations by secondary poisoning. It is, however, unknown how species relationships and protocols of treatments (e.g. anticoagulant rodenticide [AR]) interact to affect pest regulation. To tackle this issue, we modelled a heuristic non‐spatialized system including montane water voles, specialist vole predators (stoats, weasels) and a generalist predator (red fox) which consumes voles, mustelids and other prey. By carrying out a broad‐range sensitivity analysis on poorly known toxicological parameters, we explored the impact of five farmer functional responses (defined by both AR quantity and threshold vole density above which AR spreading is prohibited) on predator–prey interactions, AR transfer across the trophic chain and population effects. Spreading AR to maintain low vole densities suppressed mustelid and fox populations, leading to vole population dynamics being entirely regulated by AR use. Such vole‐suppression treatment regimes inhibited predation ecosystem services and promoted pesticide dependence. Keeping vole density below acceptable bounds by spreading AR while maintaining sufficient voles as prey resources led to less AR being applied and extended periods without AR in the environment, benefiting predators while avoiding episodes with high vole density. This may meet farm production interests while minimizing the impact on mustelid and fox populations and associated ecosystem processes. These alternating phases of mustelids and farmer regulation highlight the consequence of intraguild relationship where mustelids may rescue foxes from poisoning. Both global and wide‐range sensitivity analysis illustrate the tightrope between predator–prey regulation and pesticide–pest regulation. Synthesis and applications. Different pesticide protocols lead to a rich variety of predator–prey dynamics in agro‐ecosystems. Our model reveals the need to maintain refuges with sufficient non‐poisoned voles for sustaining specialist mustelids, to conserve the predator community given the potential of secondary poisoning with rodenticides. We suggest that long periods without pesticide treatment are essential to maintain predator populations, and that practices of pesticides use that attempt to permanently suppress a pest over a large scale are counterproductive.

Weasel exposure to the anticoagulant rodenticide bromadiolone in agrarian landscapes of southwestern Europe

“…In any case, we found that weasels in Spain have been exposed to bromadiolone as in northern and central Europe (Elmeros et al, 2011;Fernandez-de-Simon et al, 2019;Koivisto et al, 2018;McDonald et al, 1998). Bromadiolone and another AR (brodifacoum) could eventually have produced population declines of small mustelids, as it has been observed empirically in France and New Zealand (Brown et al, 1998;Fernandez-de-Simon et al, 2019;Murphy et al, 1998) and also suggested by a biomathematics modelling approach in the French study context (Baudrot et al, 2020). In north-east Spain, weasel declines have also been recorded during the last several decades, although the factors potentially explaining such declines are not completely known (Torre et al, 2018).…”

Crop damage by vertebrates in Latin America: current knowledge and potential future management directions

“…Similarly, bird species that roost in large groups, such as Dickcissels ( Spiza americana ), can be killed in great numbers when their nesting sites or watering holes are poisoned ( Basili & Temple, 1999 ). Furthermore, poisons can have severe consequences for carnivores and scavengers that feed on the carcasses of poisoned animals ( Baudrot et al, 2020 ; Kalaivanan et al, 2011 ). In addition to the dangers that chemical pesticides pose to the environment, they can also pose a serious threat to the health of human workers and consumers ( Rani et al, 2021 ).…”

“…Such extinctions may have far-reaching effects on the ecosystem if the species is an essential part of the food web or plays important ecological roles, such as seed dispersal, with their disappearance causing cascading effects on the community ( Castillo-López et al, 2017 ). Furthermore, the use of poison to kill crop-damaging vertebrates can have severe consequences not only for the target species ( Lima et al, 2019 ), but also for other animals that may consume them, such as predators or scavengers ( Baudrot et al, 2020 ; Kalaivanan et al, 2011 ), and affect the health of human communities and cause social conflicts ( Rani et al, 2021 ). Thus, there is a need to find alternative, non-lethal crop protection techniques that can effectively protect crops while preserving the consumer vertebrate species that damage them.…”

Blood biomarkers in white stork (Ciconia ciconia) nestlings show different responses in several areas of Croatia

“…With the use of pesticides in continental Croatia (Romić et al, 2015), for example, organophosphate (OP) and carbamate (CB), insecticides which are extensively used to control pests and disease vectors at agricultural lands (Hill, 2002), there is a high possibility for pesticide exposure. Apex predators, such as white storks, could ingest contaminated prey and subsequently suffer secondary poisoning (Baudrot et al, 2020). As their nestlings reside in the nest and are completely dependent on the local food sources foraged by their parents, they are suitable bioindicators and sentinels of contaminants in the local environment (Blázquez et al, 2006; Lewis & Pomeroy., 2017).…”