Oversimplified – Deforestation cuts down spider species

Featured Image Caption: Forests are home to many species of spiders and are at risk of extinction when the forest is disturbed (Image Source: “Web” by YLev is licensed under CC BY 2.0.).

Reference: Munévar, A., Cardoso, P., & Zurita, G. A. (2022) From forest to forestry: Reassembly of spider communities after native forest replacement by pine monoculture. Ecological Entomology, 47(3), 400-410. https://doi.org/10.1111/een.13125

Simple Is Not Always Better

Making complex things and ideas simpler certainly has its perks in specific contexts. For instance, simplifying challenging problems can encourage learning and understanding when teaching math to children. The very goals of this platform are built on making complex research studies more approachable. On the other hand, converting complex, chaotic environments into simple and organized patches by reducing the diversity of plants can create severe problems for the animals that live there. For example, a forest – with its many layers of vegetation stretching from the forest floor to the tree canopy – supports diverse wildlife. When humans clear the forest to make room for agricultural fields, livestock, and tree farms, we rapidly and crucially change the conditions that native animals rely on.

Across the world, diverse and complex forests are being converted into uniform and simple habitats like the pine farm shown here (Image Source: left – “Skyrail Rainforest 2” by ozjimbob is licensed under CC BY-NC 2.0; right – “Managed Tree Plantations” by John A. Kelley).

The Atlantic Forest runs along the Atlantic coast of South America. A once large, continuous stretch of woodland, this forest has been diminished and fragmented by over 85% to make way for pine tree farms to produce paper. The diverse forest kept cool and damp by the dense towering trees is cleared with nothing in its place except organized rows of pine trees offering little relief from the sun’s hot beams. This forest has been designated as a hotspot for biodiversity, meaning that it is one of the most vital but threatened ecosystems on the planet. Spiders are one of the many types of animals that the forest supports that are threatened by its disappearance.  

Pines Cause Declines
The Atlantic Forest (in green) is a stretch of woodland in South America. The study was completed in the Atlantic Forest in Argentina (Image Source: “Mata Atlântica em Foz do Iguaçu/ Atlantic rainforest at Iguaçu falls” by Luísa Mota; inset – “Alto Paraná Atlantic Forest” by Miguelrangeljr).

 Despite their small stature, spiders are crucial for ecosystems by keeping insect populations in check, including some that we consider pests. Where there are lots of spiders, there is likely to be lots of insects for spiders to eat, indicating that the environment is healthy and productive. Conversely, the environment may be unfavorable for animals if the number of spiders drops. There are over 49,000 known species of spiders and they play diverse roles in each ecosystem. Dr. Ana Munévar, with a team of researchers, used the number of spider species to assess the health of the Atlantic Forest as it is cleared for pine farms. The team collected spiders in the Atlantic Forest and pine farms of different ages.

As the forest’s dense trees began to disappear, so did over a third of the 126 spider species originally found at study sites in the Atlantic Forest. Even a decade following the disturbance was not enough time to restore the once-booming spider population. Many of the spider species that remained on the farms differed from those initially found in the forest, having replaced the native spiders. Spiders that inhabited the young pine farms were larger, more likely to be active throughout the day and night, and not picky about their food – all traits that may have helped them deal with the rapid changes. The researchers found that the drop in complexity, tree density, and humidity seem to be at the root of the loss.  

Keeping It Complex
The most common spider in the Atlantic Forest was Thwaitesia affinis (top, close relative pictured). Aillutticus nitens (left) and Miagrammopes guttatus (right, close relative pictured) were the most common in young and old pine farms, respectively (Image Source: top – “Theridiidae > Thwaitesia argentiopunctata?” by Robert Whyte; left – “Sitticini” by Maddison et al. 2020), right – “Miagrammopes – gathering a bundle of silk to post-tension the strand” by spiderman (Frank) is licensed under CC BY-SA 2.0.).

Simplifying the complex Atlantic Forest into orderly rows of pine trees caused a severe drop in spiders, leading many to disappear entirely from the area. The extreme disturbance of clearing out trees did attract some new species to the site, especially ones that are experts in dealing with change. Such a disruption can change the environmental conditions and reduce the number of prey available. Thus, spiders that are tolerant of the warm, dry habitats and are not choosy of their food are more likely to thrive. While the environmental changes seemed to play a significant role in the loss of the spider species, the researchers suggest that competition between species for the limited prey might have also driven out some species.

In addition to being significant contributors to the ecosystem, spiders also helped researchers uncover how deforestation changes animal communities. Although this study took place in the Atlantic Forest, natural habitat is being cleared worldwide to be converted for agriculture and livestock. If this pattern continues, animals that are vital to their habitats will disappear entirely. By reducing, reusing, and recycling the products we buy, we can help stop the clearing of the forests before it is too late.

Making complex problems simpler can be helpful for learning math, but simplifying complex environments only subtracts from the rich diversity we have on this planet.

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Brandi Pessman

I am a fifth-year Ph.D. student at the University of Nebraska-Lincoln in the School of Biological Sciences. Growing up on a farm in a small town in Illinois, I developed an early love for animals and a fascination with their behaviors. When I was younger, however, it never crossed my mind that I would be using spiders to investigate how human presence affects animal behavior, but I am loving every second of it. Studying the behaviors of animals can tell us a lot about the role that we play in their survival (or death), which is becoming increasingly important as human populations continue to grow. When I am not studying spiders, I enjoy playing with my cat or being outdoors!

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