My interpretation of this Chinese study is that street lighting can make the leaves of urban trees lining streets tougher which makes them harder for insects to eat or too tough to eat. As insects are near the bottom of the food chain for many carnivorous species, street lighting may impact the biodiversity of a region. Artificial light has increased levels of nighttime brightness by almost 10% which also disrupts body clocks.
The researchers found that leaves were more likely to be uneaten near artificial light and eaten away from artificial light. Artificial light is ‘light pollution’ despite its necessity in the urban environment. See below for the reason why leaves become tougher.
Insects at bottom of food chain
Insects are generally towards the bottom of the food chain (one up from the bottom) for many carnivorous animals. Here are some key points about the role of insects in food chains:
- Insects are a primary food source for a wide variety of carnivores, including birds, small mammals, reptiles, amphibians, and other insects.
- Due to their small size, abundance, and ability to reproduce rapidly, insects provide an important and readily available source of nutrition for larger predators.
- Many carnivorous animals, such as frogs, lizards, spiders, and some small mammals, have specialized adaptations like long tongues or keen eyesight that allow them to effectively hunt and consume insects.
- Insects occupy the lower trophic levels of food chains, serving as the prey for higher-level carnivores. This makes them a critical link in the transfer of energy and nutrients through ecosystems.
- In some environments, insects can make up the majority of the biomass and are the main source of food for many vertebrate predators, positioning them firmly at the bottom of those particular food webs.
So in summary, yes, insects are a foundational food source for numerous carnivorous organisms and occupy a bottom-rung position in many food chains and food webs across different ecosystems.
Through a paired design and extensive field investigation, we demonstrated that ALAN [Artificial Light at Night] can enhance leaf toughness while concurrently reducing leaf herbivory levels [consumption of plant material by animals] in two of the most common street tree species in Beijing, China. Furthermore, ALAN had species-specific effects on leaf nutritional contents and defensive traits. – Study: Artificial light at night decreases leaf herbivory in typical urban areas. Lead author: Yu Cao. Conducted in China
Link to study: https://doi.org/10.3389/fpls.2024.1392262 – opens new page/tab.
The researchers studied 180 trees around roads in Beijing that were illuminated by streetlights; measured how much light each tree was getting and then studying almost 5,500 leaves for their different properties.
Although I have summarised, in my words, the study in the first paragraph, I will add some more detail here. Chinese scientists have said that their findings warn that food chains might be upended by artificial lighting. It has increased by almost 10% and for plants which depend on light for photosynthesis its effects could be profound.
The scientists concluded that their findings “illustrate that ALAN can significantly alter some key functional traits and ecological processes (nutrient cycling, energy flow). In general, we suggest that high ALAN intensity will be detrimental to the energy flow from urban plants to hire tropic levels, posing a potential threat to the maintenance of biodiversity (e.g., arthropod diversity, bird diversity) in urban ecosystems.”
My interpretation of the phrase “energy flow” is the food chain. Energy passing from the consumption of insects and then to animals higher up the food chain. The food chain starts with plants and insects are the second level in that food chain and they are eaten by birds so they are the third level in that food chain. Any other predator which eats birds such as feral cats would be the fourth level in that food chain and so on.
RELATED: 50 trees ‘butchered’ by a local authority
Reason why leaves become tougher and the input of AI on circadian rhythms
There is an ecological reason why artificial light can make tree leaves tougher:
The presence of artificial light at night can have an impact on the physiology and chemistry of tree leaves. This is due to a phenomenon called “night lighting” or “light pollution.”
When trees are exposed to artificial light at night, it can disrupt their natural circadian rhythms and light/dark cycles. This confuses the trees and affects various physiological processes, including leaf development.
Specifically, artificial light at night can:
- Increase production of defensive compounds: The leaves will produce more structural carbohydrates, lignin, and other defensive chemicals in response to the perceived threat of herbivory during the “wrong” time of day.
- Thicken leaf cuticles: The waxy outer layer of the leaves (the cuticle) becomes thicker and more impermeable to help protect against potential herbivores.
- Increase leaf toughness: The leaves become physically tougher, with smaller, more densely packed cells and a higher concentration of structural compounds like cellulose.
These changes make the leaves less palatable and more difficult for herbivorous insects and animals to consume. It’s the tree’s way of adapting its leaf physiology to the disruption caused by artificial light.
So in summary, the artificial light exposure tricks the trees into thinking they need to fortify their leaves against nighttime threats, resulting in tougher, more defensive foliage.
My thanks to AI bot Poe for the above section.
