Guest essay by Eric Worrall
A climate scientist doing fieldwork has made the shocking discovery that, contrary to predictions, the Earth’s ecosystems might have some capacity for self regulation.
CLIMATE CHANGE MAKES SPIDERS BIGGER — AND THAT’S A GOOD THING
BY THERESA MACHEMER 24 JULY 2018
High temperatures make arctic wolf spiders ditch their favorite food, indirectly helping the environment.
THE ARCTIC TUNDRA is teeming with predators, just not the ones you might expect: By biomass, arctic wolf spiders outweigh arctic wolves by at least 80-to-1.
The eye-popping calculation, published today in PNAS by National Geographic explorer Amanda Koltz, could shape our understanding of how the Arctic will respond to future climate change.
Her study reveals that at increased temperatures and population densities, arctic wolf spiders change their eating habits, starting an ecosystem-wide cascade that could change how quickly melting permafrost decomposes.
In higher temperatures, decomposition occurs more quickly and wolf spiders are more active, so Koltz expected that when her mini-ecosystems got warmer, their wolf spiders would drastically reduce the springtail population. But Koltz found just the opposite.
In plots with more spiders, the spiders actually ate fewer springtails. These larger springtail populations then ate more fungus, which lowered the rate of decomposition. Among the hotter plots, the one with more spiders decomposed less than plots with almost no spiders. In a way, the spiders are helping to fight climate change in the arctic tundra.
The unexpected find has drawn praise from experts. “The novelty of Dr. Koltz’s paper is that it shows not only is [climate change] having direct impacts on these important ground dwelling animals but also on the complex ecological interactions between species on the tundra,” Joseph Bowden, an entomologist with the Canadian Forest Service who was not involved with Koltz’s research, says by email.
The abstract of the paper;
Warming reverses top-down effects of predators on belowground ecosystem function in Arctic tundra
Amanda M. Koltz, Aimée T. Classen, and Justin P. Wright
PNAS July 23, 2018. 201808754; published ahead of print July 23, 2018. https://doi.org/10.1073/pnas.1808754115
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Edited by Alan Hastings, University of California, Davis, CA, and approved June 12, 2018 (received for review May 21, 2018)
Predators can disproportionately impact the structure and function of ecosystems relative to their biomass. These effects may be exacerbated under warming in ecosystems like the Arctic, where the number and diversity of predators are low and small shifts in community interactions can alter carbon cycle feedbacks. Here, we show that warming alters the effects of wolf spiders, a dominant tundra predator, on belowground litter decomposition. Specifically, while high densities of wolf spiders result in faster litter decomposition under ambient temperatures, they result, instead, in slower decomposition under warming. Higher spider densities are also associated with elevated levels of available soil nitrogen, potentially benefiting plant production. Changes in decomposition rates under increased wolf spider densities are accompanied by trends toward fewer fungivorous Collembola under ambient temperatures and more Collembola under warming, suggesting that Collembola mediate the indirect effects of wolf spiders on decomposition. The unexpected reversal of wolf spider effects on Collembola and decomposition suggest that in some cases, warming does not simply alter the strength of top-down effects but, instead, induces a different trophic cascade altogether. Our results indicate that climate change-induced effects on predators can cascade through other trophic levels, alter critical ecosystem functions, and potentially lead to climate feedbacks with important global implications. Moreover, given the expected increase in wolf spider densities with climate change, our findings suggest that the observed cascading effects of this common predator on detrital processes could potentially buffer concurrent changes in decomposition rates.
Read more (paywalled): http://www.pnas.org/content/early/2018/07/17/1808754115
Some of the more amusingly simplistic climate predictions are claims that we’ll all be overrun with pest species like ticks and mosquitoes if the world warms.
Living on the edge of the tropics I’ve learned something that people who make such predictions obviously have not – warm climates also support an abundance of predators, which usually keep the pest species under control.
More food more consumers, everything tends to balance.