Authors: Allison Schwarz, Pre-veterinary Science major; Fanula Karanxha, Biochemistry and Molecular Biology major; Sarah Spaulding, Natural Resource Conservation major
A decade ago, on a trip to the Alligator River National Wildlife Refuge along the eastern coast North Carolina, you could spot a 50-80 pound, majestic canine with a distinctive red hue in its fur (Defenders of Wildlife, 2018; Schweig, 2016). At nightfall, their golden eyes could be seen from a distance and their haunting howls could be heard for miles. These elusive creatures are a distant relative of our faithful companions, the dog, but are now critically endangered and one of the rarest sights to see (Fears, 2018). Today, less than 50 animals remain and they can only be found in the 150,000 acres of the Refuge (Fears, 2018, para. 6). These creatures are the iconic American red wolf.
Thousands of people visit national parks and animal refuges each year with the hope of encountering wildlife while exploring nature, with over 1,000 visitors attending the red wolf howlings offered in the Alligator River Refuge each year (USFWS, 2016, para. 1). The red wolf populations were originally living in coastal habitats of Eastern Texas and Western Louisiana and expanded throughout much of the eastern United States, ranging from the Atlantic Ocean to central Texas and as far north as Pennsylvania (Hinton, Chamberlain, & Rabon Jr., 2013; Schweig, 2016). However, during the colonial period from the 1700s to the 1900s, European settlers hunted and displaced many wolves out of their territory in order to develop the land, protect their livestock, and to use the red wolves’ prey as their own food source (Levy, 2012; Beeland, 2012). An increase in the number of government-supported eradication campaigns in support of agricultural and livestock interests occured up until the 1970’s, when a change in American societal beliefs resulted in the Endangered Species Act (ESA) becoming a federal law in 1973 (Hinton et al., 2013).
The passing of the Endangered Species Act provided great hope for the red wolves. The ESA provides funding for the conservation and reintroduction programs of endangered and threatened species utilized all across the world. The red wolves became listed as an endangered species in 1967 but their first recovery plan did not begin until 1973 after the ESA was implemented. The Red Wolf Recovery Program aimed to increase red wolf populations in order to reach a stage where red wolves inhabited their ecological niche and naturally excluded coyotes and/or hybrids from the area through competition and strife (Murray, Bastille-Rousseau, Adams & Waits, 2015). An ecological niche is defined as the function, habitat, and resources of an organism necessary for its survival (Sharov, 1997). The program took red wolves from the few areas they were left and put them into Alligator River National Wildlife Refuge in North Carolina. At first it was successful and was able to bring a population of 12 wolves in 1973 up to 225 wolves in 2008 (Fear, 2018, para. 6). However, the recovery program was unable to stabilize the red wolf populations.
A massive population decline began almost a decade ago due to an influx of coyotes into the refuge area, leaving only around 50-75 red wolves (Kerns, 2013, para. 9). The wolves were originally released into the refuge under the impression that there were no coyotes in the area. But with the low numbers of wolves, compared to the coyote population, coyotes were able to settle in the same area as wolves increasing the competition for resources such as food, space and mates. Coyotes thrived and expanded their range over the past 150 years due to their masterful adaptation skills, as shown in Figure 1 (Ellington, 2015, p.10). Coyotes survived by exploiting the influence of human activity in the environment, such as feeding on livestock and scavenging waste, which red wolves did not do (McVey et al., 2013, p. 1141-1142). As the coyotes expanded into the red wolf recovery area, they stole valuable resources from the vulnerable red wolf populations and ultimately leading to a decline in red wolf numbers.
Figure 1. The historic (prior to European colonization) range of coyotes (Canis latrans), current distribution, and where hybridization is occurring in North America (Ellington, 2015, p. 10).
Although red wolves and coyotes are two separate species, they are closely related evolutionarily and therefore occupy the same ecological niche, meaning they rely on the same resources. Using fecal DNA analysis in North Carolina, researchers showed that red wolves and coyotes have similar diets in an overlapping range, indicating competition (McVey et al., 2013). According to the competitive exclusion principle, when two species compete for the same limiting resource they cannot coexist at constant population values and if one species has even the slightest advantage over the other, the one with the advantage will dominate in the long term (Hardin, 1960). In the case of red wolves and coyotes, the red wolves would be the ones at the disadvantage due to their small population size and the the coyotes’ versatility and adaptability. Although this is not the main driving force of red wolf population decline, it indirectly affects red wolf populations because they do not have the resources to grow their population to overcome the coyotes in the area..
Furthermore, the coyotes flourished due to their ability to breed more quickly than red wolves (Levy, 2012). Coyotes have a litter size (the number of offspring produced at one birth by an animal) of four to seven pups per breeding pair while only one red wolf breeding pair, the alpha male and female, have a litter of two to eight pups a year (Defenders of Wildlife, 2018, para. 7-11). This allows the coyotes to increase their population much faster than red wolves which reduces the resources available for both species. Currently, coyote populations increase by about 25,000 to 35,000 per year (Kozak, 2016, para. 50) and the red wolf populations are declining (Fears, 2018).
The driving force of the red wolf population decline is interbreeding between the coyotes and the red wolves. Coyote and red wolf hybridization, or interbreeding, reduces the genetic purity of red wolves and poses the greatest threat to red wolf recovery (USFWS, 2016). Due to a limited amount of space in the recovery area, red wolves often mate with coyotes producing fertile hybrid offspring. This occurs because any canine species can breed and produce reproductively competent offspring with another canine species (Kozak, 2016, para. 35). Interbreeding between red wolves and coyotes or hybrids causes a loss of genetic purity and diversity through a process known as gene introgression. Gene introgression is the exchange of genes between species due to hybridization. Gene introgression works in a similar way to mixing paint. If you have blue and yellow paint, and you mix them, you get a new and unique green paint. No matter how much yellow or blue paint you add to the mixture, you can never get back to just blue or yellow without starting over. Currently, red wolf hybrid DNA is only 25% red wolf and 75% coyote on average (Fears, 2018, para. 49), and it is predicted that interbreeding between red wolves and coyotes will increase from 21% to 59% over the next 25 years (Fredrickson & Hedrick, 2006, p. 1279) furthering the loss of red wolf genes. A dramatic decrease in genetic purity could make the red wolves ineligible for government funded protection (Fears, 2018).
Without doubt, the biggest driving force of interbreeding in a red-wolf coyote system is the female red wolves. Female wolves select mates from the more common species (Bohling & Waits, 2011; Bohling & Waits, 2015; Wirtz, 1999) and since male coyotes are more common than male red wolves, there are more opportunities for interbreeding between male coyotes and female red wolves. Female red wolves are involved in 90% of all hybridization events (Bohling & Waits, 2015, p. 113). From 2001 to 2013, there were 30 hybrid litters, and in 27 out of the 30 litters, the red wolf parent of the hybrid litter was a female (Bohling & Waits, 2015, p. 112.). These studies all suggest that female red wolves are the biggest driving force of hybridization, thus something needs to be done to prevent female red wolves from choosing coyotes as mates.
In addition, the immediate effects of red wolf and coyote interbreeding also poses one of the greatest threats to their recovery. Interbreeding with coyotes results in a decrease in body size and gives the hybrid wolves a physical appearance that resembles coyotes (Murray et al., 2015; Brzeski, Rabon, Chamberlain, Waits & Taylor, 2014). Human error by hunters and farmers resulted in 25% of red wolf deaths from 1999-2014 (Murray et al., 2015, p. 341). Hunters and farmers often hunt coyotes that prey on their livestock or the deer they are trying to hunt. Red wolves are illegal to hunt on the refuge but coyotes are not so mistaken identity is the only legal way of killing a red wolf. On average, six to eight red wolves are killed each year due to mistaken identity, and gunshot mortality may be compounded if shooting deaths among adult wolves leads to pup starvation or pack breakdown and dispersal if the killed wolf was the alpha male or female of the pack (Beeland, 2012; Murray et al., 2015, p. 342). Gunshot mortality is 6-7% more prevalent than any other cause of death for the red wolves (Hinton, White, Rabon Jr & Chamberlain, 2017, p. 424). Of the fifty red wolf deaths between 2013 and 2016, only 24% were from natural causes, the rest being human-related (USFWS, 2016, Table 1). These types of killings pose the greatest threat to recovery since it limits population growth (Bohling & Waits, 2011; Bohling & Waits, 2015; Fears, 2018; Hinton et al., 2017).
In order to alleviate interbreeding and protect the reintroduced red wolf population from coyote invasion in the recovery area, the U.S. Fish and Wildlife Service has implemented a sterilization program for coyotes (Beeland, 2012). Sterilization of coyotes can gradually reduce interbreeding and the loss of genetic purity without creating an immediate loss to the ecosystem. Sterilized animals would remain in the refuge and allow social structures and territories to be maintained until the red wolves can effectively take over the area. Ultimately, sterilization is a method that allows territorial space to be held until that animal can be replaced naturally. Sterile “placeholder” coyotes are naturally replaced when the larger red wolves displace or kill the coyote (USFWS, 2016, para. 4). With the introduction of these programs, the sterilized ‘placeholder’ coyotes and hybrids began to be displaced or killed by red wolves with 37% of the coyote/hybrid displacements resulting in red wolf occupancy (Gese & Terletzky, 2015, p. 11). The majority of displacements occurred between male coyotes and male red wolves (Gese & Terletzky, 2015, p. 14). This phenomenon increases the range of male red wolves and can increase breeding opportunities for the red wolves since sterile coyotes are more likely to disperse than intact coyotes (Bromley & Gese, 2001, p. 391).
Similarly, sterilization programs for feral cats have reduced the overall cat population by 66% over four years in the most humane way possible (Levy, Gale & Gale, 2003, p. 42). Vasectomy (removal of the vas deferens) and hysterectomy (removal of the uterus) is the most effective method of sterilization (McCarthy, Levine, & Reed, 2013, p. 502). However, this process can cost about $560 per coyote (Bromley & Gese, 2001, p. 391). A more cost effective method is a one time non-transferable chemical contraceptive injection that blocks the production of hormones necessary for sperm production (MacGregor, Perkins, Asa & Skinner., 2013, p. S4). Thus, targeting only male coyotes and hybrids utilizing a chemical contraceptive can help control male coyote and female red wolf hybridization with a significantly smaller cost.
By utilizing this program on the coyote populations present in the refuge and its surroundings, the red wolves can re-establish their population in the area and eventually be able to sustain themselves and expand without additional funding. By including the surrounding areas in addition to the refuge area, we can prevent the coyotes from returning to the area for a longer period of time. Once the red wolf population is stabilized in the refuge, they will naturally exclude coyotes from the area. Dave Mech, a wolf biologist, states that sterilization is a “useful and effective technique of reducing introgression of coyote genes into red wolf populations” (Augliere, 2015, para. 5). By reducing the hybridization between male coyotes and female red wolves through sterilization of male coyotes, the wolves will regain their distinct body size and appearance, avoid coyote mistaken deaths, and have access to more resources giving them an opportunity for population growth. Therefore in order to prevent the tragic loss of genetic purity of the red wolf, government funding needs to shift to help control the male coyote populations through sterilization in the current refuge area.
Although some people may view the red wolf as a pest and not understand why we should invest money and time into their recovery and expand their population, large carnivores, such as the red wolf, are important in the ecosystem and help maintain biodiversity. The proper function and resilience of the ecosystem is essential because human resource demands are increasing. Predators, like red wolves, increase ecosystem productivity by controlling prey species populations (Ripple et al., 2014, p. 151, 4). This is important because most prey species are herbivores and feed on vegetation and crops. Increased prey species results in decreased plant diversity and decreased resources (Ripple et al., 2014). Low survival rates of red wolves threatens the predator-related roles in an ecosystem and in turn decreases the biodiversity of wildlife and ecosystem efficiency.
In addition, red wolves also possess an economic benefit to the public. Red wolves draw in millions of dollars to local economies through ecotourism and there is potential increase in that number by restoring the red wolf populations (Wheeler et al., 2008, p. 4). A unique advantage of red wolves as a major tourism attraction is that they exist nowhere else in the world except North Carolina. A study conducted on whether people would be interested in visiting the Red Wolf Center in North Carolina to learn more about the red wolf recovery program, habitat, food sources, and to simply see live red wolves, showed that 89% of the refuge’s visitors interviewed were interested in visiting the Red Wolf Center, and 76% of these visitors are willing to pay $5 for admission (Lash & Black., 2005, p. 50). In order to predict the economic benefits of red wolves, calculations to showed a potential future revenue of $182,400 over a twelve-week period, bringing an overall $1 million to the Red Wolf Center in the summer (Lash & Black, 2005, p. 50). Although this is an estimated revenue, even with a small percentage of visitors to the Red Wolf Center and other ecotourism activities, it would not only benefit local businesses but it would also effectively educate and communicate to the public the importance and benefits of the red wolf population.
Unlike red wolves, coyotes do not have an economic benefit. In fact, coyotes are responsible for numerous agricultural losses each year. Coyotes affect farmers the most because they are the most common predator of livestock and they also consume watermelons and other fruit crops causing a loss of over $40 million in 2010 (ICWDM, 2015; Mitchell, Jaeger & Barrett, 2004, p. 1210). This is an increase of $34 million from the $6 million in agricultural losses in 2008 (Rashford, Grant & Strauch, 2008, p. 25). Breeding coyotes also killed more prey due to their increased nutritional needs (Bromley & Gese, 2001, p. 391), thus the sterilized coyotes showed a decrease in sheep predation which could be beneficial to farmers and their decreased prey consumption will allow more resources for the red wolf populations.
Some may think the simplest solution would be to shoot the coyotes to remove them. However, lethal control, such as shooting, are ineffective for long-term management (MacGregor et al., 2013, p. S4). The immediate massive loss of a predator species could cause the ecosystem to crash (Ripple et al., 2014) and poses all of the same threats as the extinction of red wolves. It is also possible that more red wolves would be shot during the process due to similar physical appearances, and many hunters are not skilled enough to distinguish the two species. Sterilization allows for the animals to be examined fully before alterations are performed therefore protecting the red wolves from being sterilized or killed by mistake.
While sterilization programs for the red wolf-coyote system have proven to be successful, they have only been implemented in a small portion of the refuge in North Carolina. Therefore, sterilization programs must expand across the entire refuge area and the surrounding area to prevent hybridization driven by female red wolf choice, and male sterilization alone can provide the desired effect by limiting the number of both hybrid and coyote offspring. Continuing coyote sterilization can improve the survivability and reproductivity of the red wolves and prevent their extinction by allowing their range to expand and providing them with more resources. By implementing either surgical or chemical sterilization, red wolves can return to breeding within their own species, preventing gene introgression and regaining their distinctive appearance, and allowing their population to grow and thrive once again.
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