There is an urgent need to mitigate “sensory pollution” (night lighting, noise, etc.) that disturb wild flora and fauna, according to our partner The Conversation.
The impacts of this pollution are however very complex to assess because they vary according to the species (and even the individuals) and are not very visible in the short term.
The analysis of this phenomenon was carried out by Michel Renou, research director in insect biology at INRAE.
The human species is a noisy neighbor who leaves the light on all night and releases many odorous chemicals into the environment.
Even non-toxic, these productions interfere with the sensory and cognitive processes that allow organisms to communicate, to exploit their environment, or to avoid predators.
These attacks on ecosystems are called "sensory pollution" to emphasize that they are exerted through the senses and have the main effect of modifying behavior.
Sensory pollution is very varied;
one of its best-known forms concerns the night-time lighting of urban areas, which disrupts the natural cycles of day-night alternation.
How does this sensory pollution act precisely on wild fauna and flora?
What can be done to alleviate it?
Light pollution emitted by the city of Salt Lake City, United States © Makelessnoise / Flickr
Sensory and cognitive mechanisms
Four mechanisms come into play here.
There is first of all the emission of human origin (called “anthropogenic”), wrongly recognized by the animal as a natural signal and which could deceive the organism.
Dragonflies, for example, are attracted to polarized light reflected from the water surface of ponds in which they lay eggs. But the smooth and dark artificial surfaces of car bodies, paved roads, glass facades, black plastic films used in agriculture, or solar panels, also polarize sunlight and appear like so many bodies of water in the eyes of dragonflies. Many stop there to lay eggs and end up perishing without securing their offspring. The source of pollution acts here as an "ecological trap" attracting organisms to an environment of mediocre value.
The second mechanism concerns situations in which natural signals, such as the light of the stars, are used by animals to orient themselves during their migratory movements or to change habitat; artificial sources of similar stimuli confuse them. The frequent nocturnal lighting on the shores will thus disrupt the search for nesting sites in sea turtles and hinder the return to the sea of the young after their hatching.
The third mechanism corresponds to “masking”: this is the case when sensory pollution, often of greater intensity than that of natural signals, prevents their perception.
The light of large metropolises diffuses in the sky well beyond inhabited areas and obscures the sight of the stars from species migrating at night.
The urban noise, chronic, covers the songs of the birds.
Singing insects themselves are sensitive to human-made sounds.
Repulsive odors can deter an animal from exploiting an otherwise favorable habitat.
Last mechanism: sensory pollution can distract the animal's attention.
It creates habituation by its consistency and intensity, and can thus reduce its level of vigilance and its rate of response to danger signals, for example the presence of predators.
All circles are concerned
Sensory pollution affects all the senses;
all environments, whether terrestrial, freshwater, or marine, are affected.
If vision primarily concerns nocturnal species, we have seen that sources of polarized light deceive diurnal aquatic insects;
plastic waste floating in the oceans is mistaken for prey.
The intense noises generated by traffic routes, land or sea, disturb the hearing of land or aquatic organisms.
The chemical senses are also very stressed by emissions of volatile organic compounds of anthropogenic origin (AVOCs) or organic compounds soluble in water.
Plastic waste is a major source of pollution for the oceans © Marcos André / PxHere
A form of sensory pollution can also affect a mode of communication relating to another direction: the emission of sex pheromones by certain insects is disturbed by night lighting.
Certain air pollutants, such as ozone and nitrogen oxides, disrupt pollination by destroying the constituents of floral aromas.
Odor pollution spreads very easily from anthropized areas where it is produced to environments less affected by artificialization.
Disturbances can affect an entire territory and modify the whole of a sensory landscape as in the case of fragrant landscapes,
odorscapes
.
From the individual to the entire ecosystem
Sensory pollution concerns all levels of living things.
Each individual must collect information in his environment to move there in safety, to find his way there, or to identify a food source.
The correct perception of this information is essential to its survival.
Intense stimuli are a source of stress which in the medium term affects his physiological state.
At the species level, sensory pollution disrupts the encounter of sexes, courtship behavior and reproduction.
Birds are very sensitive to sensory pollution © John Doe / PxHere
During their nesting period, birds are thus very sensitive to disturbance and abandon the nest if their environment is too disturbed.
Organisms, from simple bacteria to mammals, are in constant interaction with one another, in particular maintaining mutualistic or symbiotic relationships.
For this information must constantly circulate between the levels of the food chain and the disturbance of a single trophic level has cascading effects in the ecosystem.
Finally, sensory pollution constitutes a force of selection which acts on biodiversity.
The most resilient species change the way they communicate, for example by changing the intensity or frequency of their sound productions.
But the less tolerant species are gradually eliminated.
On the contrary, the development of undesirable species can be favored.
It is yet another aggression which insidiously hits already weakened ecosystems.
Our own living environment can be directly affected by the confusion between ecological signals and anthropogenic emissions.
Some attacks of the giant Asian hornet have been attributed to the proximity of the composition of cosmetics to its alarm pheromone.
The puzzle of impact assessment
Ethologists and environmentalists are aware of the insidious effects of sensory pollution and many studies have been published on invertebrates, vertebrates, or plants.
In humans, air pollution affects olfaction.
But we are far from understanding everything.
First of all because each species has its own sensory universe and therefore does not react to the same stimuli. Only certain wavelengths of the spectrum, or the range of molecules defining the olfactolome, pass the filter of sensory receptors. Therefore it is quite understandable that there is a certain anthropocentrism.
We are therefore much more sensitive to the effects of noise generated by transport, or to odor nuisance from factory farms or waste treatment sites.
The notion of bad odors is however quite relative if we refer to the preferences of a coprophagous insect very interested in faecal odors!
What is referred to as "valence" in psychophysiology, ie the positive or negative rating given to a stimulus by the animal, varies between species, or even between individuals.
The assessment of impacts is very complex, as the effects are not very visible in the short term and the sensitivity varies between species and even individuals.
In humans, air pollution affects olfaction © Geralt / Pixabay
It is certain that in terms of environmental damage we prioritize actions by targeting forms of pollution causing clearly visible organic symptoms, or even mortality, in a wide spectrum of organisms.
Measuring stress or evaluating behavioral discomfort in a wild species remains difficult.
How to fight against these light, sound and chemical nuisances?
First of all, it is effective to limit the volume of emissions.
It is thus possible to reduce the light intensity of the lighting, use directional spotlights, treat effluents, and finally install noise reduction devices.
Changing the nature of the emissions according to the sensitivity of the organisms can eliminate the nuisance.
Changing the wavelength of lighting, for example, decreases its attractiveness.
Land use planning must be planned in such a way as to spare zones preserved from sensory pollution, as is done to constitute the white and black networks in terms of noise and light pollution.
This landscape engineering could be generalized to other modalities such as olfaction.
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Many other sources of sensory pollution at the origin of inappropriate behavior still need to be better identified.
Plastic residues, for example, become loaded with odors that make them appetizing for small or large predators.
Sensory pollution remains difficult to assess and it is often necessary to change point of view to judge the impact of human activity on a species whose sensory universe is foreign to us.
We must therefore encourage the development of sensory ecology, preferably in the field, in order to improve our ability to carry out sensory diagnostics of natural spaces.
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This analysis was written by Michel Renou, research director in insect biology at the National Research Institute for Agriculture, Food and the Environment (INRAE).
The original article was published on The Conversation website.
Declaration of interests
Michel Renou received funding from the ANR within the framework of the Odorscape project.
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