Fear is an essential factor in survival for both humans and animals (Sacks, 2011). Without it, we lose our ability to assess risk and make decisions that keep us out of danger (Sacks, 2011). A part of the brain called the amygdala is responsible for processing fear (Brocke et al., 2010). The Gleb Shumyatsky Research Group at Rutgers University Department of Genetics used that information to conduct a study on mice and discovered an important correlation while analyzing the molecular and cellular analysis of fear and memory (2005). The stathmin gene (STMN1) is only active in the amygdala, and in this gene's absence in mice there was a significant deficiency of learned and innate fear behavior (Shumyatsky et al., 2005; Martel et al., 2011). In a study done at the National University of Ireland Galway, researchers found that when the STMN1 gene was removed from English Springer Spaniels the dogs showed significantly less fear behaviors, similar to those observed in mice. (Ding et al., 2016). A different research group wanted to test these findings on humans. Their research revealed evidence supporting that the STMN1 gene affects the fear responses in humans comparable to the effects found in other animals (Brocke et al., 2010). Although species may respond to fear in different ways, it would appear that fear may be processed in a similar manner across species. We will be looking at two different species fear of predation in urban and rural landscapes, how they communicate this fear and whether this fear is processed genetically in a similar manner.
One of the species we will be studying is the fox squirrel. Fox squirrels, or Sciurus niger, are one of the common tree squirrels native to the eastern and mid-United states (McCleery et al., 2007). The fox squirrels are diurnal creatures that nest in deciduous forests (Koprowski, 1994 ). They prefer an open woody habitat to an overgrown forest, making parks and grassy areas within urban environments an acceptable habitat (Linzey et al., 2008; McCleery et al., 2007). Having some trees around is ideal, as the species will use them for shelter, nesting and escaping predators, making the squirrels arboreal creatures (Koprowski, 1994). The most common predators of the fox squirrels are hawks, snakes, owls, foxes and other mammals that feed on small vertebrates (Koprowski, 1994). According to a study done at the University of Montana, Erick Greene observed that the squirrels in rural environments were reactive to their surrounding and different predatory threats (Greene and Meagher, 1998). These small mammals are extremely agile and fast, climbing trees to escape predators (Greene and Meagher, 1998; Koprowski, 1994). In undisturbed or rural habitats fox squirrels were observed to also emit threat specific alarm calls to alert other squirrels in the area to potential dangers (Greene and Meagher, 1998). Other alarm behaviors of the fox squirrel include: chattering teeth, scanning the area, running away, freezing in a low or upright position, aggressive tail wagging and laying down flat (Mccleery, 2009). Predatory responses, like the ones listed above, are crucial for survival in both rural and urban habitats.
Similar to fox squirrels, humans living in rural areas have greater exposure to their natural predators, than the humans living in more urbanized landscapes. The most common of these predators include cougars, bears and coyotes (Lowry and Wong, 2013). Although exposure to predators may be greater for people living in rural areas, many people living in urban areas vacation and explore the United States' many national lands (Penteriani et al., 2016). Almost half of all reported animal attacks in the United States are due to risky behaviors demonstrated by humans and their lack of predatory knowledge (Penteriani et al., 2016). A recent trend displaying this risky behavior are the people who visit Lake Tahoe, California to take "selfies" with the wild bears of the area. If this unsafe behavior does not stop, the United States Forest Service officials have threatened to shut the park down (Herron, 2014). People in rural environments are more aware of these predators and know how to handle the situation when faced with one of these animals (Kallen, 2016). That does not appear to be the case for the people who reside in urban environments.
The desensitization of humans to predatory threats can be attributed to the stathmin gene, which may have caused them to learn not to actively fear their predators (Brocke et al., 2009). A similar phenomenon, known as habituation, can be observed in fox squirrels in an urban environment. Habituation is defined as a learned behavior, caused by multiple encounters with the same stimulus, which enables an individual to respond in a manner evading unnecessary exertion of energy when there is no benefit in responding to recurring stimulation (Rankin et al., 2008; Blumstein, 2016). As a result habitation leads to variation in tolerances among individuals of a species to different stimulations based on their surrounding environments (Samia et al., 2015; Blumstein, 2016). The notion that fox squirrels are affected by habituation is supported by a study conducted at Texas A&M University by Robert A. Mccleery. The study found that, when exposed to the vocalizations of both red-tailed hawks and coyotes, fox squirrels in an urban location responded with a meaningfully lowered amount of observed anti-predator behaviors than fox squirrels in a rural setting (Mccleery, 2009). Therefore, we hypothesized fox squirrels in an urban environment have become desensitized to their natural predators. Similarly, we hypothesized humans in an urban environment have become desensitized to their natural predators. Due to the potential of fear desensitization being comparable in both species, we hypothesized that rural fox squirrels and rural humans will react to natural predators in a similar manner to one another. This has led us to conclude that the same may be true for an urban environment as well. Thus, we hypothesized urban fox squirrels and urban humans will react to natural predators in a similar manner to one another.
To test for desensitization of fear in fox squirrels and humans, we designed a playback experiment to observe the reactions of both species in response to predator and non-predator playback calls. In a previously published playback study, Robert Mccleery observed the behaviors of fox squirrels in an urban, suburban, and rural setting to determine if different environments affected anti-predator behaviors (Mccleery, 2009). We wanted to compare the reactions of both fox squirrels and humans in the extreme ends of the urban-rural gradient. Our experiment took place at two different locations, one rural and one urban, both located on the campus of Michigan State University. The location chosen for our urban site was a section of the river trail located directly south of the main campus library. This part of campus had high amounts of daily activity from both squirrels and humans, causing the two species to interact more than they would have in a rural location. The location that was chosen for our rural site was the Baker Woodlot. This location was considered an undisturbed forest environment. The squirrels living in the woodlot were less likely to encounter human interaction in a typical day than the one that resided near the center of MSU campus. Each location was tested 4 times per species, resulting in a total of 16 sampling visits.
Upon arrival at each site, a JBL Charge 2 Bluetooth speaker was placed next to a tree located 5 to 10 feet away from where we were sitting in all experiments. This was done because we wanted to be sure that the fox squirrels and humans observed were reacting to the playback calls and not to our presence. During the squirrel portion of the experiment, we waited at each site for 20 minutes before starting the playback calls. This allowed the squirrels to become accustomed to our presence. The majority of students found in the area were just passing through and there would be new individuals present every few minutes, causing a waiting period to be unnecessary in the human portion of the experiment. In each experiment, all sounds were played at the maximum volume of the speaker (approximately 95 decibels). For all experiments, one member of our group was tasked with recording video data with a GoPro and iPhone camera. A second member of our group was in charge of maintaining consistency with the playback calls and sequences across all trials. The playback sequences will be discussed in more detail later. The remaining two members of our group recorded the behaviors of each species on observational data sheets. The observational data sheets documented the date, time, location, playback sequence number, and reactions observed in response to each playback call.
The reactions that were considered anti-predator behaviors in the squirrel experiment were chosen based on a study done by Robert Mccleery. They include: chattering teeth, scanning, running away, freezing or becoming immobilized on the ground (meaning that at least three limbs were in contact with the ground), freezing or becoming immobilized upright (meaning only two limbs are in contact with the ground), wagging tail aggressively, laying down, other behaviors or no change in behavior (Mccleery, 2009). The reactions that were considered anti-predator behaviors in the human experiment were chosen based on a study done by Thornton and Quinn. They include: hiding, threatening to yell or attack, yelling or screaming, attacking, running away, looking for a weapon, freezing or becoming immobilized, begging or negotiating, investigating, other behaviors or no change in behavior (Thornton and Quinn, 2009).
Both predator and non-predator playback calls were used to test the anti-predator behavioral responses of fox squirrels and humans. In the fox squirrel experiment we selected two predators of the fox squirrel: the great-horned owl and the red fox. These sounds were taken from The Cornell Lab of Ornithology and the online magazine Water and Woods, respectively. We used a blue jay call as a non-predator control, also taken from the Cornell Lab of Ornithology. The blue jay call is a negative control because the blue jay is a prominent non-predator species found on the Michigan State campus. Therefore, the squirrels were well acquainted with that call and had no reason to respond to it with anti-predator behaviors. In the human experiment, we selected two large carnivores that were common predators of humans, the grizzly bear and the mountain lion (cougar) (Penteriani, 2016). These calls were both taken from the online magazine Water and Woods. We used a mallard duck call, taken from the Cornell Lab of Ornithology, as a non-predator control. The mallard duck served as a negative control because they do not threaten humans and they had a strong presence on the campus.
Four different sequences of playback calls were used for both the human and fox squirrel experiments. This totals to eight different sequences. This first visit of both locations in the fox squirrel experiment would use the first sequence made up of predator and non-predator calls associated with the fox squirrel. The same procedure was used with the sequences associated with the human experiments. Each sequence was created with each call played three times for 30 seconds per playback, totaling in 9 calls per sequence. We randomly generated the playback sequences to ensure the playback order did not affect the results and to help distinguish what visit and site the data had been collected from. In the squirrel experiments, we included five minutes of white noise between each call in order to allow the squirrels time to return to their normal behavior. This was done because we had no way of knowing if we were observing the same squirrel or a different one, as marking the squirrels for identification was not within the scope of our experiment. We decided that five minutes would be sufficient time based upon Robert Mccleery's study (Mccleery, 2009). There was no white noise added in-between the animal calls for the human portion of the experiment, because we could be sure that different humans were being observed for each call.
Once all data was collected, we used both a one-tailed and two-tailed independent sample t-test to determine if our results were considered significant or not. For these statistical tests we formed a null hypothesis and an experimental hypothesis. In the one-tailed test, the null hypothesis stated that on average, location had no effect on anti-predatory behaviors. The experimental hypothesis stated that on average, an urban environment decreased anti-predator behaviors. The mean values of reactions observed in response to a predator call in an urban location were compared to the mean values of reactions in a rural location. In order to do this comparison we determined that the locations were our independent variables and the anti-predator behaviors observed was the dependent variable. In the two-tailed test, the null hypothesis stated that on average, different species will react with different levels of anti-predator behaviors in the same environment. The experimental hypothesis stated that different species will react with similar levels of anti-predator behaviors in the same environment. The mean values of reactions observed in response to a predator call in humans were compared to the mean values of reactions in squirrels. In order to do this comparison we determined that the types of species were our independent variables and the anti-predator behaviors observed was the dependent variable. The test resulted in a p-value that was used to determine the significance of our findings. If the p-value equaled less than the commonly accepted value of 0.05, our results were considered significant.
To test the first hypothesis, we compared the anti-predator behavioral responses of fox squirrels to their natural predators in an urban environment with those in a rural environment, as depicted in Figure 1. To analyze the significance, we used a one-tailed independent sample t-test. We found there was a significant difference in the anti-predator responses of urban fox squirrels (M = 3.75, SD = 0.87) to rural fox squirrels (M = 8.25, SD = 0.87); t = -7.30, p = 0.00016. Another one-tailed independent-sample t-test was used to compare the lack of anti-predator responses of fox squirrels in the urban environment to those in the rural environment. Our findings showed that there was a significant difference in the lack of anti-predator responses to the playback calls of the urban fox squirrels (M = 10.50, SD = 4.18) to rural fox squirrels (M = 1.63, SD = 0.82); t = 4.20, p = 0.0029.
We compared the anti-predator behavioral responses of humans to their natural predators in an urban environment with those in a rural environment to test our second hypothesis, as depicted in Figure 2. To analyze the significance, we used a one-tailed independent sample t-test. We found there was a significant difference between the anti-predator responses of the humans in the urban location (M = 3.63, SD = 0.75) and those of the humans in the rural location (M = 8.63, SD = 0.75); t = -9.43, p = 0.000040. Another one-tailed independent-sample t-test was used to differentiate between the lack of anti-predator responses of urban humans to rural humans. There was a significant difference between the lack of responses in urban humans (M = 12.13, SD = 4.18) to those in rural humans (M = 3.75 , SD = 1.71); t = 4.84, p = 0.0014.
To test our third hypothesis, we then compared the anti-predator responses of rural fox squirrels and rural humans, as depicted in Figure 3. To analyze the significance, we used a two-tailed independent sample t-test. Our results showed there was not a significant difference between rural anti-predator responses in fox squirrels (M = 8.25, SD = 0.87) and in rural humans (M = 8.63, SD = 0.75); t = -0.65, p = 0.54. Another two-tailed independent-sample t-test was used to analyze the significance between the lack of anti-predator responses of rural fox squirrels and rural humans. The results showed that there was not a significant difference between the lack of anti-predator responses in rural fox squirrels (M = 1.63, SD = 0.82) and rural humans (M = 3.75, SD = 1.71); t = -0.65, p = 0.54.
To test our fourth hypothesis, we then compared the anti-predator responses of urban fox squirrels and urban humans, as depicted in Figure 4. To analyze the significance, we used a two-tailed independent sample t-test. We found there was not a significant difference between the anti-predator responses urban fox squirrels (M = 3.75, SD = 0.87) and urban humans (M = 3.63, SD = 0.75); t = 0.22, p = 0.84. Another two-tailed t-test was used in order to compare the lack of anti-predator responses in urban fox squirrels and in urban humans. Again, our results showed that there was not a significant difference between the lack of anti-predator responses in urban fox squirrels (M = 10.50, SD = 4.18) to those in urban humans (M = 12.13, SD = 4.18); t = 0.22, p = 0.84.
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