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Top Predators: What Wolves and Wolf Spiders Have in Common


Wednesday, June 18, 2014, by Heather Clendenin
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People understand ripples: you throw a stone into the middle of a pond, and the effects of that action carry on far past where the stone broke the surface of the water. For me, studying ecology has always been somewhat analogous to watching ripples on a pond: the members of an ecosystem respond to each other through their various relationships, and what affects some members directly can carry over to indirectly affect others.

[Heather collecting soil for use in her group project on soil processes and climate change.]At Harvard Forest, the research I'm participating in is looking at the "ripples" that may pass through food webs as climate change brings about warmer temperatures. In particular, we're looking at the soil food web, with wolf spiders as a toppredator.

Yes, we're studying "dirt" and spiders.

Outside of the world of ecology, it seems that these two subjects either receive little attention or are unfortunately maligned.

For instance, not much thought tends to be given to the interspecies-drama taking place in the earth beneath our feet, but a short glimpse of this complex little world beneath a microscope should be enough to convince the casual observer that there's more to it than it may otherwise seem. Just like any other ecosystem, there are predators, prey, decomposers, et cetera, but scaled way, way down (and thank goodness—I wouldn't want to encounter a pseudoscorpion if it were the size of a mammal). As it stands, this overlooked but ubiquitous ecosystem releases ten times the amount of carbon dioxide (CO2) than that released by human activity; pretty important to consider with climate change looming.

[A drawing in ink of the face of a wolf spider; drawing by Heather Clendenin.]And spiders, while being some of my personal favorite creatures, are not known to inspire warm and fuzzy feelings among the general public. I'm grateful for every pest insect they keep me from having to deal with, but their role as a top predator in the soil food web is also worth appreciation in its own right. Top predators have been known to do incredible things in ecosystems beyond what simple intuition might predict. Perhaps the most well-known example of the impact of a top predator has been seen in Yellowstone, where the re-release introduction of wolves has reverberated throughout the park, impacting not only their prey species, but the plants their prey fed upon. Streamside vegetation and trees regrew, allowing water quality to improve, and ushering the return of beaver and songbirds into the area (for more information, check out George Monbiot's TED Talk, How Wolves Can Alter the Course of Rivers:
http://blog.ted.com/2014/02/18/video-how-wolves-can-alter-the-course-of-rivers/).

My team will study similar ripples carrying through the soil ecosystem, starting with our own humble top predator, the wolf spider.

[Laura and Audrey moving the buckets containing soil and microbes that will become our mesocosms.]We've constructed mini-ecosystems from the bottom-up, ultimately looking to see how increases in temperature and either the presence or absence of our predators will affect the already high rate of the release of CO2 from the soil.

However, here is where the "ripple" analogy breaks down. Whereas ripples in water gradually attenuate and disappear as they spread, what we may see may not be as simple as ripples. What we may see could be a positive feedback response where more CO2 is released as temperatures increase. Invertebrates increase activity with temperature, and from wolf spiders down to the soil microbes, increased activity can mean increased CO2. And increased CO2 means—you guessed it—increased temperature.

It makes it seem awfully important to pay attention to dirt and spiders. 

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