Are Pesticides the Primary Cause of Species Decline in North America?

Popular culture suggests as much; however, a systematic review of the evidence indicates otherwise. A recent publication evaluated the primary, secondary, tertiary, quaternary, and quinary contributors to terrestrial plant decline in the United States and Canada based primarily on U.S. Fish and Wildlife (USFWS) recovery plans for 938 “listed” (threatened and endangered) species, as well as 206 species listed as being of special concern by the Government of Canada.

What was the primary driver you ask? Wait for it…invasive species, accounting for ~43% of the total in the U.S., followed by habitat alteration (~26%) and development (~23%). In Canada, habitat alteration was the primary driver, followed by development and non-native species. But what about pesticides? Herbicides or insecticides were identified as the primary or secondary driver of decline for a total of 12 listed plants species in the U.S. (~1.3%) and 2 species in Canada (~1%).

Herbicides, insecticides, or pesticides were identified as a driver of any importance (primary to quinary) for a total of 46 listed plant species in the U.S. and 10 species in Canada. Clearly, factors other than the application of pesticides pose much greater risks to the health and viability of listed plant species. This analysis is part of a four-publication series intended to provide context regarding the dominant causal factors influencing species decline in North America.

Context matters. Pesticides have a contentious origin, plausible biological relevance, and an easily exploited legal construct in the U.S. (e.g., citizen suit provisions) making them an easy target for litigious opportunism. However, being an easy target does not mean pesticides are the right target. Granted, it is difficult to sue the Spanish conquistador Hernando de Soto for having introduced feral hogs to Florida in 1539 for example, or John Rolfe for introducing a new variety of tobacco in1612, or Mother Nature for pathogen outbreaks, droughts, and floods.

The unintended consequences of promoting a narrative and sensationalizing a micro-scale contributor to a macro-scale issue include lack of public awareness regarding the primary drivers of species decline, missed opportunity to proactively address them, and potential misallocation of resources. In effect, metaphorically, we will miss the conservation opportunity of the forest for the counterfactual narrative of the trees.

Many thanks to my co-authors Julie Anderson and Ryan Prosser for realizing these analyses over the past several years and Daniel Perkins for creating the artwork.