Author: jungo-garcia.1

Why Pesticide-Induced Harm to Bats Disrupts Entire Ecosystems

Photo courtesy of Eric Kilby https://openverse.org/image/90cffaeb-e1b5-4f60-80a5-a8ea89c37c2e?q=bat%20eating%20fruit

Bats play a critical role in many ecosystems around the world. They have incredibly diverse eating habits that allow them to occupy different habitats and provide services that are vital to the health and balance of entire ecosystems. For example, fruit-eating bats disperse the seeds in their waste as they fly, nectar-eating bats pollinate plants and insect-eating bats contribute to insect control (Trust BC, 2024). They help pollinate our favorite fruits and they eat the insects that feed on us or our crops. Unfortunately, this relationship isn’t reciprocated. We as a species disrupt these ecosystem services by using pesticides that harm bats (Oliveira et al., 2020).

Pesticides are effective against their target species and help protect crops and livestock from pests (Oliveira et al., 2020). However, when pesticides are applied, they are dispersed through the air and water and they travel to regions that are far from the target site. They then come in contact with non-targeted species. For example, Dichlorodiphenyltrichloroethane (DDT) residues have previously been found in soil, surface water and air and in the tissues of fish, mammals and birds (Oliveira et al., 2020). Pesticide exposure can harm entire populations. The most well-known example is of eagles and their eggs. Eagles exposed to DDT produced eggs with thin shells which halted development of the chicks (US EPA, 2024). This caused population declines in eagles that landed them on the endangered species list.

Bats are exposed to pesticides through a number of mechanisms including contamination of food and water or through skin contact (Oliveira et al., 2020). Exposure to pesticides is mostly dependent on the bat’s feeding habits. Insect-eating bats are at highest risk because they eat agricultural pests that may be contaminated with pesticides. Fruit bats are the second highest at risk to exposure because they forage amongst plants applied with pesticides (Oliveira et al., 2020).

There are several classes of pesticides and their effects on bats differ. Organochlorine pesticides increase the metabolic rate of bats which reduce energy reserves (Oliveira et al., 2020). Reduced energy reserves mean that less energy is dedicated to important processes such as reproduction. This can cause bats to spend more time and energy foraging and puts them at higher risk of predation as well.

Neonicotinoids are another class of pesticides that harm bats. Imidacloprid, a neonicotinoid, interferes with the spatial memory of bats, affecting their echolocation (Hsiao et al., 2016). Chlorpyrifos, belonging to the organophosphate class of pesticides, impairs flight and movement of big brown bats and causes tremors (Eidels et al., 2016). Several organochlorine and pyrethroid insecticides are endocrine disruptors that can affect the reproductive success of bats (Oliveira et al., 2020). For example, fruit-eating bats exposed to a fungivore developed anatomical changes in their testes and epididymis, disrupting their normal reproductive function (Machado-Neves et al., 2018). 

Bats play important roles in the health and balance of their ecosystems. If we lose bats that contribute the most ecosystem services, many organisms that depend on these services for survival will be impacted, including us. Our food production would decrease and we may be exposed to more mosquito-borne diseases. We must advocate for all bat species and do our part to protect them.

References

Eidels RR, Sparks DW, Whitaker JO, Sprague CA (2016) Sub-lethal Effects of Chlorpyrifos on Big Brown Bats (Eptesicus fuscus). Arch Environ Contam Toxicol 71: 322–335.

Hsiao C-J, Lin C-L, Lin T-Y, Wang S-E, Wu C-H (2016) Imidacloprid toxicity impairs spatial memory of echolocation bats through neural apoptosis in hippocampal CA1 and medial entorhinal cortex areas. NeuroReport 27: 462.

Machado-Neves M, Neto MJO, Miranda DC, Souza ACF, Castro MM, Sertorio MN, Carvalho TF, Matta SLP, Freitas MB (2018) Dietary Exposure to Tebuconazole Affects Testicular and Epididymal Histomorphometry in Frugivorous Bats. Bull Environ Contam Toxicol 101: 197–204.

Oliveira JM, Destro ALF, Freitas MB, Oliveira LL (2020) How do pesticides affect bats? – A brief review of recent publications. Braz J Biol 81: 499–507.

Trust BC (2024) Bats as pollinators – Why bats matter. Bat Conservation Trust. https://www.bats.org.uk/about-bats/why-bats-matter/bats-as-pollinators (last accessed 3 April 2024).

US EPA O (2016) The Case of DDT: Revisiting the Impairment. https://www.epa.gov/caddis/case-ddt-revisiting-impairment (last accessed 3 April 2024).

The Impacts of Global Warming on the Common Toad

Common Toad. Photo Taken by Karamel. https://upload.wikimedia.org/wikipedia/commons/9/93/Common_Toad_%28Bufo_bufo%29.jpg

Over the last couple of decades, amphibians globally have experienced huge population declines that have resulted in the extinction of some species (AmphibiaWeb, 2017). Amphibians are ectothermic, meaning they cannot regulate their own body temperature. They instead rely on external sources like the sun to thermoregulate. This means that amphibians are particularly sensitive to changes in their environment. With global temperatures rising due to global warming, the summers are becoming longer and the winters are becoming shorter and milder (Reading, 2006). The hibernation periods of toads are disrupted in the process, leading to detrimental and even fatal health complications for toads. 

In a study on Common Toads, a widespread species in Europe, Jorgenson (1986) found that female toads who were given unlimited access to food during the winter and prevented from hibernating, grew slower and died at higher rates than female toads that hibernated. He also found that female toads reached reproductive age younger and at a smaller size than female toads that hibernated. A study conducted by Reading (2006) on the same species yielded the same results and found that mild winters caused female toads to reach breeding age at smaller sizes. This can be detrimental to toad populations because the amount of eggs a mother toad lays is dependent on how big she is. 

Amphibians have structures called fat bodies that allow them to store energy that can be used while they hibernate (Reading, 2006). When the winters are cold, metabolism slows down and energy usage is minimal. However, when the winters are only mild, the toad’s metabolism doesn’t slow down enough to minimize energy usage. The toads emerge hibernation with less energy availability and their body condition is decreased. In some cases, the toads’ energy reserves are depleted before they emerge from hibernation and they die in the process (Reading, 2006). 

Unfortunately, global mean temperatures are expected to rise by 1-7 in the coming years (IPCC, 2001). The Common Toad and other amphibian species populations will likely face more challenges as temperatures continue to rise. In order to help these species see the future, we can continue to study them and their physiological limitations further. Although amphibians may not seem important enough to preserve, we must remember that they help control mosquito populations that can reduce our risk of disease exposure (Morris, 2020).

References

AmphibiaWeb: Worldwide Amphibian Declines (2024). https://amphibiaweb.org/declines/ (last accessed 12 February 2024).

External and internal control of patterns of feeding, growth and gonadal function in a temperate zone anuran, the toad Bufo bufo – Jørgensen – 1986 – Journal of Zoology – Wiley Online Library (2024). https://zslpublications.onlinelibrary.wiley.com/doi/abs/10.1111/j.1469-7998.1986.tb03631.x?casa_token=mZ2kbsVtPwQAAAAA:WkOXqMUoUJ2XXl-546g0FEczyBwOPNJxCTVoN7fRJk5ghTBgPCo6SseiegGljrfTahwqCbLqSivC4bM (last accessed 12 February 2024).

Kerlin KE (2020) Amphibian Declines Affect Human Health. UC Davis. https://www.ucdavis.edu/climate/what-can-i-do/amphibian-declines-affect-human-health (last accessed 12 February 2024).

Reading CJ (2007) Linking global warming to amphibian declines through its effects on female body condition and survivorship. Oecologia 151: 125–131.

Watson RT, Albritton DL, Intergovernmental Panel on Climate Change, Intergovernmental Panel on Climate Change, Intergovernmental Panel on Climate Change, eds. (2001) Climate Change 2001: Synthesis Report. Cambridge University Press, Cambridge ; New York.