When their surroundings dry out, insects that have evolved to live in permanently damp settings, like tropical rainforests, typically don’t fare well. According to recent research that was released on Wednesday, they might both dislike heavy rain.
A comprehensive five-year research project in Peru found that short periods of both drought and high precipitation led to a 50% drop in arthropod biomass. The results of one of just a handful of such studies carried out in the tropics imply that terrestrial arthropods, which include insects and spiders, will be more vulnerable to climate change than previously thought.
According to Felicity Newell, a postdoctoral associate and former doctoral student with the Florida Museum of Natural History, “Most of the time when we think about climate change, we think about warming temperatures, but rainfall patterns will also change, which is something insects seem to be especially sensitive to.” We can see that excessive rainfall can be harmful over relatively short durations.
A new level of the insect apocalypse has been reached.
Against the unsettling backdrop of population decrease, the discovery of a Goldilocks preference for the ideal amount of water makes its debut. Over the past 20 years, many studies have shown that insects are dying out and going extinct on every continent except Antarctica. Some people have called this trend the “insect apocalypse.”
These findings present a sharp but unfinished picture. The majority of this research has been conducted in densely populated temperate regions, whereas the tropics, which have the most biodiverse ecosystems on the planet, have received far less attention.
Because the tropics are home to half of the world’s insect variety, very little is known about the majority of insect species that are in danger of extinction. This imbalance makes it very hard to figure out how insects will react to the complicated issue of climate change.
“Abiotic elements like temperature and rainfall have a large impact on many things, which is one of the major concerns. They have the power to affect both the development of new leaves and the arthropods that consume them. It’s challenging to tell the two apart in temperate systems because they’re frequently highly coordinated, “Newell remarked.”
The seasons move in close lockstep in temperate zones. In the spring and summer, life is active and abundant; in the fall and winter, it is quiet and dormant. The annual fluctuations are less pronounced close to the equator. Despite the fact that the wet and dry seasons and constant temperatures allow plants to retain their leaves and tropical ecosystems to be active year-round.
Any significant rise or fall in insect populations in the presence of a steady supply of plant food is more likely the result of shifting climatic conditions. Scientists like Newell who want to find out how climate change might affect insect populations can do their best research in the tropics.
For unknown reasons, insects drop in wet environments.
Between 2015 and 2019, Newell and his co-author Ian Ausprey put in a total of two and a half years of fieldwork in the northern Peruvian Andes. They lived and worked alongside the villagers nearby, gathering insects in areas that were more than 4,500 feet above sea level many times a year. They gathered more than 48,000 insects in all, which they compared to annual rainfall and temperature records.
They anticipated that a close relationship would exist between insect abundance and plant development. The creation of new, supple leaves, which are preferred by herbivorous insects, correlates with the start of the rainy season, even though most trees and shrubs in the tropics don’t lose their leaves. They didn’t discover this, though. According to satellite data and visual field observations, the burst of vibrant green growth had a negligible impact on insect biomass.
Instead, rainfall was the best predictor of how many insects you might find in a given location.
According to Newell, after three months of dry weather but also after three months of very wet weather, arthropod biomass declined. When there was an average amount of rain, “biomass grew, creating a dynamic balance between too wet and too dry.”
By trying to identify the precise process causing the decreases, Newell and Ausprey went a step further. On field-collected insects, they experimented with desiccation. Most of their specimens struggled to adapt to even a slight drop in humidity. Small insects are particularly susceptible to drying out because of their higher surface-to-volume ratio.
However, scientists are baffled as to why wetter-than-average conditions are an issue. Theories range from shortened foraging times brought on by more frequent storms to the actual harm that raindrops inflict on little insects. Another idea is that the colder temperatures caused by the long-lasting cloud cover might stop insects from growing and developing.
According to one theory, there are more fungal spores present during the rainy season, which would increase the prevalence of entomopathogenic fungi. In tropical settings, these insect-preying fungi are common. Infection frequently causes the insect host to die, but only after their behavior has been drastically changed to enable the best spore distribution for the next batch, as is the case with zombie ants.
For whatever reason, the authors are concerned about what their findings might mean for insects and the animals that depend on them in a world that is quickly warming. They also created a predictive model that could aid in unraveling the “black box” of ecosystem function and response by fusing their field data with 50 years of regional rainfall data. Their model says that insects will be among the first species to change if the climate continues to get worse and become dangerously out of balance.
“The variety and significance of insects are enormous. “They serve as a source of food for many birds and mammals, and they perform the ecological functions of pollination and decomposition,” Newell remarked. Our forecast model shows that insects respond to extremes in rainfall, but it’s still not clear how they’ll respond to a changing climate in the long run.
