S1 E5: Predator Ecology with Aaron Wirsing

Aaron Wirsing is an ecologist with the School of Environmental and Forest Sciences studying predator-prey interactions.

On this episode of FieldSound, Wirsing discusses his research in both terrestrial and aquatic systems, the ways that top predators, such as grey wolves and tiger sharks, shape their ecosystems and how humans affect predator-prey interactions through processes such as urbanization and climate change.

The Predator Ecology Lab seeks to help better understand how predators influence their surroundings by interacting with their prey and seeks solutions to the challenges of large carnivore conservation & management in the changing world.

https://www.predatorecology.com/

Aaron Wirsing’s research has received support from the Seeley Fund for Ocean Research on Tetiaroa to establish and maintain a marine laboratory on the Tetiaroa atoll, the Save Our Seas Foundation and the Disney Wildlife Conservation Fund.

https://environment.uw.edu/podcast

Transcript

00;00;00;03 - 00;00;14;01
Aaron Wirsing
It is difficult to ask questions about anything in ecology, about interactions and their outcomes for ecosystems without explicitly factoring in people. Because our influence is so pervasive.

00;00;17;16 - 00;00;22;00
Sarah Smith
From the University of Washington College of the Environment, this is FieldSound.

00;00;23;01 - 00;00;24;22
Aaron Wirsing


00;00;35;23 - 00;01;07;18
Sarah Smith
When you think of the wild, where does your mind go? I tend to think of the American West wild rivers running through rugged landscapes, wide open spaces, rolling hills ringed by snowcapped peaks. A vast mountain ranges, the sounds of the desert at sunset, a harsh and beautiful landscape coming to life as the sun goes down or waves crashing on the worn rocks and geologic formations of the Pacific coastline.

00;01;09;01 - 00;01;11;17
Sarah Smith
Beautiful and dangerous and mesmerizing.

00;01;14;11 - 00;01;29;14
Sarah Smith
We live in the age of the Anthropocene. The world's human population has swelled 8 billion and growing. Our world is changing. Wild places are fewer and farther between.

00;01;33;16 - 00;01;48;23
Sarah Smith
The work of scientists like Aaron Wirsing exists in wild places, forcing studies, predator prey interactions, seeking a better understanding of how predators influence their surroundings by looking at their interactions with one another and the prey.

00;01;51;09 - 00;02;11;01
Aaron Wirsing
I'm Aaron Wirsing and a professor of wildlife science in the School, Environmental and Forest Sciences, and also the principal investigator of the Predator Ecology Lab, where my students, postdocs and I explore a wide range of questions pertaining to the behavior of the ecology and the conservation of large predators in terrestrial and marine environments.

00;02;12;00 - 00;02;28;17
Sarah Smith
Fieldwork, by its very nature, cultivates connection to the wild, working as a field ecologist. The experience of putting yourself in the wild environments where these predator prey interactions occur means Wirsing is essentially able to put himself in the shoes of the animals he studies.

00;02;29;08 - 00;02;49;04
Aaron Wirsing
The first time I really did that extensively was probably when I was a master's student at University of Idaho. I was studying snowshoe hares, not dangerous predators, fluffy bunnies. But the great thing about Snowshoe Harris, is they're sort of the ultimate vocal species if you're interested in predation, because everything out there in the woods is trying to eat them.

00;02;49;24 - 00;03;20;20
Aaron Wirsing
And so at the time, I was really interested in how various predators from bobcats to coyotes to large weasels like Martin and Fisher were targeting snowshoe hares and the impacts that had on snowshoe hare populations in Idaho. But that meant I was out catching and tagging and tracking the survival of snowshoe hares in the Bitterroot Mountains, which are part of the Selway Bitterroot Wilderness, one of the largest unbroken tracks of wilderness in the lower 48 states.

00;03;21;12 - 00;03;37;12
Aaron Wirsing
It was an area that at the time, in the late nineties and early 2000s was being recolonize by wolves, and it was filled with black bears and mountain lions. The process was basically going out at the end of the day at twilight and setting snowshoe hare traps out and then checking them in the morning to see what you got.

00;03;37;12 - 00;03;58;21
Aaron Wirsing
And that meant being in the woods, often alone in low light situations that I bumped into bears in particular quite a lot. I was working in dense forest, so I had to cut trails in the woods. The bears loved my trails and they were 50 meters apart, so I'd be walking up one and 50 meters over. I could hear the bear walking down my trail.

00;03;58;21 - 00;04;24;08
Aaron Wirsing
And so I had to get used to basically sharing the environment with bears under those circumstances. And generally speaking, black bears aren't dangerous. But I also knew that there are rare occasions when they can be. And I had one especially frightening instance, really at the tail end of my fieldwork as a master's student. I was on one of my study areas and I was walking along one of my trails and I just got this sense that something wasn't quite right.

00;04;24;08 - 00;04;44;09
Aaron Wirsing
And I looked up and there was a very large black bear, probably 50, 100 feet away, looking right at me. And I had been used during those encounters to seeing them just run away because they're typically very frightened of people. But in this instance, it looked at me and it actually and so I yelled out just to make myself known, assuming it would leave.

00;04;44;10 - 00;05;08;15
Aaron Wirsing
It didn't. Instead, it stood up on its hind legs. It was way bigger than I was, and I'm a pretty big person. And so the hair just stood up in the back of my neck and it looked at me for a little bit and then it dropped back down on all fours and started walking toward me. And I got the sense right then and there that I there was a possibility that I might have to defend myself because the rule with black bears is if it does attack you, you have to fight back.

00;05;09;07 - 00;05;47;21
Aaron Wirsing
Unlike brown bears, which are typically just looking to neutralize a threat, so you would defend yourself. So I just slowly backed away and I decided if the bear wouldn't leave, maybe I would like to diffuse the situation. And happily, that's what happened. It didn't follow me any farther. But again, there was that moment of engagement. When you're in field situations like that, working with large predators, or at least in systems where you might meet one, the fear is not that they're there, but that you might end up in a situation where there is that engagement, where you see it, it sees you, it's an interaction and that kind of links back to my science because

00;05;47;21 - 00;06;09;16
Aaron Wirsing
it's actually, I think the fact that that those circumstances resonate so much with me and can be so intense also to explain why I'm so excited because that's the focus of my research is those predator prey interactions which are frightening, and how to both the predator and the prey animals sort of cope with those situations, right? What do the predators do to ensure they make a catch?

00;06;09;27 - 00;06;12;03
Aaron Wirsing
What do the prey animals do to ensure they get away?

00;06;14;08 - 00;06;25;24
Sarah Smith
So what sets field ecology apart from other sciences? Patience, adaptability, observation, readiness.

00;06;27;13 - 00;06;50;26
Aaron Wirsing
So one of the sort of fundamental precepts of the scientific process is that if you have a question you want to answer, you try to control the circumstances as much as possible so you can target whatever causal factor relationship you're interested in. And we typically do that in laboratory experiments where some kind of manipulative experiment where we control every other factor except the one that we're manipulating.

00;06;51;08 - 00;07;17;08
Aaron Wirsing
But you can't often do that in open field situations where you're studying wide roaming cryptic species that aren't very numerous, that might be rare, threatened, protected, difficult to capture, dangerous to capture, Right. And so instead, you have to look for opportunities. Basically, you have your questions in mind and you have the answers to those quite possible answers to those questions.

00;07;17;08 - 00;07;38;14
Aaron Wirsing
Which are your hypotheses? To test those hypotheses, you have to sort of wait for nature to actually provide you with an opportunity to do what's called a pseudo or natural experiment. Basically, you have to look for variability in the right set of circumstances in nature where the thing you're interested in is changing where at while everything else remains roughly the same.

00;07;39;02 - 00;08;04;25
Aaron Wirsing
And so some examples of that as when I was a Ph.D. student, I participated in a long running study of the ecological role of Tiger sharks in a coastal seagrass ecosystem called Shark Bay in Western Australia. And the really the challenging thing about that system is it's a 13,000 square kilometer bay that is remarkable because it houses the world's largest and most diverse beds of seagrasses.

00;08;05;01 - 00;08;29;14
Aaron Wirsing
It's truly the seagrass Serengeti. I think it's every bit as exciting as the Great Barrier Reef, but it doesn't get the publicity. But you can't manipulate it, not at a scale it's relevant to tiger sharks, which are oceanic voyagers that make trips, for example, between Western Australia and South Africa. You can't manipulate that system. So how do you know what the sharks are doing with a nice thing about Shark Bay is.

00;08;29;23 - 00;09;03;10
Aaron Wirsing
My colleagues and I discovered early on that sharks aren't always in the system and in fact their numbers in the system fluctuate in a very predictable way. They tend to be quite numerous in the warm season, less numerous in the cold season, but month to month there's also a fair bit of variability. And so in tracking that variability in tiger shark numbers, what we're able to do is basically create an index of how much need there was to be safe for animals that they target as food, dugong, sea cows, sea turtles, sea snakes, cormorants, bottlenose dolphins, things like that.

00;09;03;10 - 00;09;31;13
Aaron Wirsing
We studied the behavior of a suite of these potential prey animals in relation to sort of ambient fluctuations in tiger shark numbers, which again corresponded to what I call the need for defensive investment. B, the idea was if tiger shark predation risk is important to these animals, then why tiger sharks are absent. They should relax. They should worry about other concerns like reproduction and feeding on whatever their food sources like fish or seagrass.

00;09;31;22 - 00;10;01;20
Aaron Wirsing
And as tiger shark abundance goes up, they should switch from doing those things to taking preventative actions to make sure they don't end up getting eaten by tiger sharks. Because the fundamental rule when you study what's called the ecology of fear or how animals respond to the prospect of predation, you would expect almost every animal that's out there, unless it has a very short life, basically, if it has any future reproductive prospects when there's a need for defensive investment, they should pay heed to that.

00;10;01;25 - 00;10;26;27
Aaron Wirsing
And that's exactly what we saw, basically in a very predictable manner as tiger shark abundance went up, the all those other animals, like dugongs and sea turtles, started abandoning their favorite foraging grounds. They started resting in different areas. They altered their grouping patterns, they altered their activity cycle, becoming more vigilant or apprehensive in ways that totally corresponded with the ambient abundance of tiger sharks that weren't explained by other factors.

00;10;26;27 - 00;10;50;07
Aaron Wirsing
So that was a classic natural experiment that we could not have conducted if tiger sharks had always been there. Another great opportunity was when I started my position here at the University of Washington in 2008. At that very moment, the very first gray wolf pack was discovered in Washington. The lookout pack in the metal valley after wolves had been absent for about 70, 80 years.

00;10;52;15 - 00;11;17;13
Aaron Wirsing
Here was another ecological opportunity where you have prey animals for gray wolves, mule deer, elk, moose, white tailed deer that had existed for about 80 years with no wolves. And now wolves were coming back into the state, but their distribution was patchy. They had recolonize some areas and not others. So I left on that opportunity and established a series of study sites, some that were occupied by wolves, some that weren't.

00;11;17;22 - 00;11;41;05
Aaron Wirsing
All of which were otherwise similar in terms of topography and forest cover and things like that. And then my students and I asked, Is there anything different about deer behavior in the areas with wolves that would be an indicator that the deer did care about not being eaten by wolves? And the answer was yes, quite dramatically that we observed differences in spatial distribution patterns, daily activity.

00;11;41;14 - 00;12;08;16
Aaron Wirsing
When I started that wolf study, I just ported over all the understanding that we had developed from about 20 years in Shark Bay, about our understanding of how Tiger sharks affected different prey species and used it to make predictions about how deer respond to wolves. And that marine tiger shark model worked really, really well at predicting not just that deer respond to wolves, but that different deer species would respond differently.

00;12;09;10 - 00;12;39;17
Aaron Wirsing
And that was exactly the same thing that we had seen in shark bait. Basically, prey animals responded in ways that were predicted by whatever decision favored their probability of getting away, where they sprinter's, where they Hightower's where they fighters. And so that's become a major theme of my research program now is not just documenting that prey or afraid of predators, but anticipating exactly how they will respond and using the traits of the prey species to make those predictions.

00;12;41;13 - 00;12;49;08
Sarah Smith
In talking with Wirsing, a question came to mind repeatedly Is there any wild left untouched by humans?

00;12;49;29 - 00;13;20;18
Aaron Wirsing
That is sort of the key question now that we're in ostensibly the Anthropocene, right? The era of pervasive human influence. Not only do people heavily modify the landscape, but they can modify traits of both the prey and predators, including other top predators like wolves. It is difficult to ask questions about anything in ecology, about interactions and their outcomes for ecosystems without explicitly factoring in people because our influence is so pervasive.

00;13;22;29 - 00;13;47;18
Sarah Smith
Human impacts on the environment are nearly impossible to separate from field ecology. Perceptions of a threat and wild animals changes their behavior. The term Anthropocene describes the geological period marked by human impact on global environmental systems and the geologic record. Anthropocene more broadly applies to humanity's massive impact on the natural environment.

00;13;48;16 - 00;14;25;11
Aaron Wirsing
These debates are so challenging because you sort of you have these opposing forces which are all have validity. So in in the case of parks and protected areas and beautiful areas that people want to visit, on the one hand are considerations like we have a problem with people becoming disconnected with nature, right? As we become increasingly urbanized and young people grow up without any connection to nature, basically they don't miss what they're not even aware of, which becomes a major conservation issue and contributes to global biodiversity loss.

00;14;25;11 - 00;14;44;29
Aaron Wirsing
But the opposite end of the spectrum is there are so many of us now, what did we just crest 8 billion? And we also have, when we are given the opportunity and insatiable appetite for connecting with nature. But that sort of sets up the love it to death. Problem is, right, we have these beautiful areas, but what's happening?

00;14;44;29 - 00;15;08;05
Aaron Wirsing
What are we seeing now in national parks but reservation systems and caps on usage because their can and this this applies to all forms of recreation, eco tourism. There can be too much of a good thing and there are too many of us from it from an ecological perspective, we can't all be everywhere tromping all over everything because it doesn't leave much room for the rest of the wild.

00;15;08;23 - 00;15;26;17
Aaron Wirsing
So those are those are two really challenging forces and there aren't easy answers to how we reconcile that. But again, you know, research on these non consumptive effects is just a reminder to us that, again, even if we have the best of intentions, if too many of us show up in a place we can cause the animals to vacate forever.

00;15;37;10 - 00;15;57;04
Sarah Smith
The Yellowstone wolves were once considered vermin. The government put bounties out to eradicate them. In the twenties, and the food web fell apart in the sixties and seventies. Conservation biologists brought attention to this issue. Then in the nineties, wolves returned to Yellowstone.

00;15;57;19 - 00;16;05;03
Aaron Wirsing
Used.

00;16;05;23 - 00;16;17;17
Sarah Smith
As predators. Wolves keep a cap on the abundance of their prey, and they help maintain balance in the food web. Yellowstone wolves are a great example to learn from, but they're a bit of an anomaly.

00;16;18;06 - 00;16;41;15
Aaron Wirsing
Wolves were reintroduced into Yellowstone in 1995 and 1996. They were repatriated to a national park where human influence was fairly minimal, at least critical human influences that would be deleterious to wolves. And of course, the Wolf project that precipitated at that time has I would say, has been, you know, the most revealing long term study of wolves anywhere in the world.

00;16;41;15 - 00;17;09;16
Aaron Wirsing
And as it has generated information, it is not just taught us a lot about wolves, but I think it is completely reframe the debate about predators and as globally changed debates about the roles predators play. When I was on sabbatical and and in Australia both earlier this year and back in 2016, I was amazing how in that country the discussion about dingoes, are they a pest animal or are they a key top predator?

00;17;09;19 - 00;17;35;10
Aaron Wirsing
Was being informed by what had been found in Yellowstone. All of that information has been gleaned from a national park. That sort of an anomalous postage stamp embedded in a landscape where humans dominate. So there are real questions about it's not that that anything found out about wolves in Yellowstone is illegitimate. In fact, it may be the most legitimate because it's a it's maybe more of a reference point for the way things used to be.

00;17;35;29 - 00;18;03;17
Aaron Wirsing
But there are questions about the applicability of what we've learned about wolves in Yellowstone to other systems where humans are a major ecosystem player. And so what's really, I think, what's an exciting research frontier that we have the ability to explore in places like Washington is what is the role of wolves not in a protected area like Yellowstone, but in what we call a managed or anthropogenic or human dominated landscape of eastern Washington, which they're pouring into now.

00;18;04;03 - 00;18;35;26
Aaron Wirsing
And the suspicion is it might be fundamentally different because of all the different ways that humans can influence wolves. And if humans influence wolves and humans might indirectly influence the relationship between wolves and a host of other species. That area is is fairly new. But there is evidence accumulating, including out of some of my own work that when you put big predators like wolves in a human dominated system, their impact is really different because they tend to be less numerous, more patchouli distributed and they're afraid of us.

00;18;36;22 - 00;19;04;05
Aaron Wirsing
So they're not just impacting prey, they're responding to us. Right. So it totally repositions them in the food web. And I think in many cases for a variety of different reasons, our presence in our activities can short circuit what would be I don't want to say normal, but you know what would be interactions more typical of of situations where humans have a light footprint and Washington is just the ultimate system for doing that.

00;19;04;14 - 00;19;22;12
Aaron Wirsing
Not only because we have large predators colonizing human landscapes, but also in western Washington, because Seattle has this phenomenal urbanization gradient, right, where people are kind of pouring into wilderness areas, too. And so there are lots of opportunities right in our own backyard to explore how human presence shapes predator ecology.

00;19;26;15 - 00;19;28;07
Sarah Smith
So what keeps Aaron Wirsing going?

00;19;29;07 - 00;19;56;03
Aaron Wirsing
Earlier we were talking about really I mean, the reason I do this is really because I still just have this childlike excitement about predation. I was just utterly fascinated with them when I was a three or four year old, and I still am. And so that passion is what continues to motivate. And so from the first lecture of all the underage undergrad classes, I do really emphasizes that we mustn't forget animals are exciting, right?

00;19;56;03 - 00;20;25;08
Aaron Wirsing
Why are we doing this? Why are we in these classes? Why do we want to protect these animals? Because they're absolutely fascinating, Right? And to be in this business, to be a scientist because so much of it is laborious, you have to be absolutely driven and motivated by excitement about the subject material. And so really what I mostly try to convey in my classes is just how amazing animals are, how excited I still am about wildlife.

00;20;25;08 - 00;20;50;01
Aaron Wirsing
If I if I teach the students nothing, but managed to just convey a little bit of that and amplify what is often already there, their excitement about animals that I will have considered myself successful. Ultimately, I like the classes to be a fusion of the scientific method, but more importantly with that excitement, if you can put those two things together, then you'll be a good scientist.

00;20;55;03 - 00;21;24;19
Sarah Smith
A special thanks to our guest Aaron. Wirsing. You can learn more about Wirsing’s research and the University of Washington College of the Environment by clicking the links in this episode description or by visiting our website, Environment.UW.edu. From all of us at FieldSound. Thanks for listening.