The impact of human activity on the sensory environment is undeniable. This can have drastic impacts on interspecific communication. In this article, I will explore how human activity can influence one of the most ecologically important examples of interspecific communication: Plant-pollinator interactions.
The impact which human activity has on the local sensory environment is undeniable. One need only compare the quiet tranquillity of a forest to the hustle and bustle of the inner city and the difference becomes stark. It is important that we understand the effects of this noise on animal behaviour as it can lead to perturbations in activity patterns (Bunkley et al. 2015) and communication disruptions (Díaz et al. 2011).
An example of communication that can be affected by human activity and vital to the local ecosystem is the interspecific communication between plants and their pollinators. This communication is mediated by flowers which act as “billboards” advertising a high-energy reward for any nectar feeders in the area using signals of multiple different modalities (Raguso 2004). These signals are integral to the plant’s success as they draw in the pollinators and any changes to them can alter their effectiveness and thus affect the plant’s fitness.
The aspect of this signal that we, as humans, are most familiar with is the visual component. Flowers showcase a dazzling array of beautiful colours to attract pollinators, it is hard to believe that humans can impact how they are perceived, but we do, and the way we do so is very straightforward. You see, areas, where humans live, are often illuminated at night to improve the safety and well-being of the inhabitants, the effects of artificial light at night are numerous and are currently the subject of a lot of research, but how does this link to pollination? A recent study showed that artificial light at night can affect the ability of a nocturnal pollinator, the elephant hawkmoth (Deilephila elpenor), to distinguish between the colour of flowers and leaves (Briolat et al. 2021). The researchers discovered that this effect isn’t very straightforward because, while some sources of light, such as white LEDs, may enhance the perceived chromatic contrast between flowers and leaves compared to when they are viewed under the moonlight, others, such as low-pressure sodium lamps, reduce it to the point where the colours of the flowers and leaves can become indistinguishable to the moth (Briolat et al. 2021). To further complicate matters, some sources of light, such as phosphor-converted amber LEDs, can either increase or decrease chromatic contrast depending on how strong the light is (Briolat et al. 2021).
However, artificial light at night may not just affect visual signals. When a team of researchers found that diurnal communities of pollinators can be affected by artificial light at night, they proposed several explanations for what was causing these changes (Giavi et al. 2021). One particularly interesting hypothesis they came up with is that it could affect the olfactory signals from the flowers (Giavi et al. 2021). They reasoned that because artificial light at night can affect the physiology of plants including the timing of various processes (Bennie et al. 2016) and scent production in day-flowering plants follows a diel rhythm (24-hour cycles which are influenced by the cycle of day and night) (Bloch et al. 2017), artificial light at night may alter the rhythm of scent emission of the flowers and this may, in turn, affect the behaviour of the pollinators (Giavi et al. 2021).
Sometimes, human activity can even affect communication channels we can’t perceive. Around 10 years, bumblebees were discovered to have the ability to detect and respond to the electric fields of flowers (Clarke et al. 2013). Since then, it has been shown that other pollinators, such as hoverflies, also share this ability (Khan et al. 2021). These studies have highlighted the importance of electrical ecology in plant-pollinator interactions, however, even this can be disrupted by human activity. A recent study showed that synthetic fertilizers, as well as a neonicotinoid pesticide (imidacloprid), alter the electrostatic properties of flowers (Hunting et al. 2022). They also found that while the application of these chemicals did not alter the visual signals of the flower nor did the scent of these chemicals repel the bees when flowers had their electric fields altered by an amount comparable to the change caused by the application of fertilizers, they received fewer visits than unaltered flowers (Hunting et al. 2022). This suggested that bees can detect the differences in floral electric fields caused by the application of these chemicals and that these differences made flowers less attractive to them (Hunting et al. 2022).
Together, these studies emphasise that human activity can often have far-reaching and often unexpected effects on the lives of animals in the local area and that much more research needs to be carried out to fully understand the impact we are having and to find ways of reducing these effects.
Article written by Matthew Wheelwright
Published & edited by Janire Castellano
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