The History of the Coyote (Canis latrans) Hybridization and Impacts on Ecosystems in the Appalachian Region
Many large predators have a great impact on a given ecosystem and can influence every trophic level through a top-down effect (Gompper 2002). The coyote is one of the most adaptable predators in North America because of its variability in diet and ability to thrive in areas developed by humans (Gompper 2002). There are many debates surrounding this species. Due to its large and increasing population in the Eastern United States, coyotes also influence the genetic makeup of other canid species (Allendorf et al. 2001). One of the most studied relationships between two canid species is the eastern coyote and the red wolf. The scope and capability of genetic analysis has expanded greatly over the last 50 years due to DNA markers while we used to rely solely on morphological features to classify species. Because of the relatively recent developments in the filed of genetics, there have been many studies on the genetic diversity of related species that focus on defining what hybridization is. The majority of these studies on hybridization focus on if a hybrid can become a new species or is it merely just genetic swapping between to different species that occurs (Allendorf et al. 2001). The question that will be addressed is, “what implications do today’s developments of hybridization of coyotes have on the future of the species and the ecosystems in which it occurs?”
Hybridization has become more and more common since anthropogenic changes have started to have a wider impact on wildlife. It is a very complex process that often results in the extinction of a species. Hybridization is most commonly known for occurring in plants, but it has been more recently known to occur and have a large impact on animal evolution as well because of technological advances in genetic analysis (Allendorf et al. 2001). As stated, current anthropogenic changes have led to an increase in hybridization among wildlife. The three main ways humans can help cause hybridization between species are introduction of species, fragmentation, and habitat modification, although in the case of the red wolf and coyotes, the main reason for hybridization came from hunting by humans (Allendorf et al. 2001). Habitat fragmentation occurs when habitat is broken apart due to human practices such as agriculture. These practices cause hybridization by significantly lowering population numbers. When a population of a species reaches levels that are too low to replace themselves in future generations, the species is forced to mate with similar species, which often results in the extinction of one or both species.
To decide how coyote hybridization can affect future ecosystems, we can look at the history of hybridization among these species and the controversy surrounding them. A species that has played a large part in the genetic hybridization of the coyote, specifically in the eastern United States, is the red wolf. The red wolf used to have a range from Texas to most of the east coast, but now are being reintroduced in select areas of the eastern United States. During the 20th century, the red wolf was highly persecuted due to the specie’s effect on livestock and a growing population of coyotes (Hinton et al. 2013). They were then forced to mate and hybridize with coyotes due to their inability to maintain a sustainable population. Red wolves were known to be able to cross with coyotes before the advent of molecular genetics due to skull measurements but did not rely this heavily on the other species (Allendorf et al. 2001). By the mid-sixties, we relied less on morphological features to determine genetic similarities and were able to make more accurate assumptions based on molecular genetic markers. This led to the ability to more accurately identify the genetic changes that species go through over time.
Because of the increase of hybridization, many were concerned that the remaining population of red wolves would be assimilated into the genome of the coyote and cease to exist as their own species. In the early stages of the Endangered Species Act, hybrids were not protected because it was thought that protecting them would lessen the chance of the previously listed specie’s survival (Hinton et al. 2013). Further developments in the field of genetic introgression led to this stance being changed, which prompted the creation off the Red Wolf Recovery Program by the United States Fish and Wildlife Services. This program allowed wolves to be captured in Texas and Louisiana and moved to North Carolina (Hinton et al. 2013). These wolves represented the last of the red wolf genome and have been used to expand the population enough for an eventual release back into the wild. In 1991, 37 red wolves were reintroduced into the Great Smoky Mountains National Park in Tennessee (Hinton et al. 2013). Knowing how the two species interact once the red wolf is reintroduced is very important for success of future management techniques. When reintroducing the red wolves back into the wild, one of the main concerns was the introgression of the red wolf genome into that of the coyote. (Hinton et al. 2013). This was very challenging for conservationists given that coyotes are very resilient and can withstand efforts of eradication. The recovery program was a success overall because it prevented the extinction and complete assimilation of the red wolf genes into that of the surrounding coyote populations. (Hinton et al. 2013).
As a top-down predator, coyotes influence a wide variety of species in their respective ecosystems. (Hinton et al. 2013). Interference competition between coyotes and smaller predators can cause a cascade which can affect wildlife species such as waterfowl, songbirds, and rodents (Gompper 2002). By using the correct management techniques, wildlife biologists can use coyote populations a tool to increase or decrease populations of species such as waterfowl (Gompper 2002). This can be very challenging due to the question of whether the prey populations are being controlled by compensatory means or by both compensatory as well as additive caused by coyotes. (Gompper 2002).
Since the expansion of the eastern coyote is a relatively recent development in wildlife biology, there are many ongoing studies by biologists throughout the country. Besides those studying these populations from an ecological standpoint, who are primarily concerned with how coyotes are impacting species in lower trophic levels, there is also much interest from the evolutionary side of biology as well. One of the most commonly studied coyote-prey relationships in the southeastern United States is the one between coyotes and white-tailed deer. The population of white-tailed deer in the region is very large and has presented problems for wildlife managers. Because of increases in coyote populations, the effects of these increases must be known in order to successfully implement the correct management techniques.
From 2006 to 2009, Kilgo, et. al studied the impacts of coyotes on fawn survival rates at the United States Department of Energy’s Savannah River Site in South Carolina. White-tailed deer populations had been previously declining in the area, so it was crucial to know the causes in order to continue to correctly manage the population, even though this decrease of deer was looked at as a positive due to the problems of deer over-population (Kilgo et al. 2012). Coyotes were not found throughout the state until the 1990s, so there is still limited data on the impact they can have on species such as deer in the specific region. (Kilgo et al. 2012). Conductors of this study were able to measure juvenile survival rates of deer by using vaginal implant transmitters which allowed for the capture of neonates after birth. Using the transmitters, the neonates were monitored until the age of 16 weeks, and when mortalities occurred the cause of death was then determined as accurately as possible based on DNA identification of predator species. Among the neonates that were monitored, there were 70 fatalities and 37%-80% of them were found to be from coyotes, while bobcats made up the other fatalities from predation. The study concluded that while it is likely that coyotes have an impact on neonate survival rates of white-tailed deer, more data is required to accurately quantify the overall effect on the populations in the region. (Kilgo et al. 2012).
There have been many studies conducted on coyote hybridization as well as numerous ongoing studies. One technique that has seen success in recognizing hybrid species is the mitochondrial DNA sequencing of scat samples. In 2008, Bohling and Waits collected a total of 614 scat samples in 22 counties in northeastern North Carolina. Out of these, 250 were assigned to canids by mtDNA sequencing. The study found that even though there was a small percentage of the samples that proved to be from hybrids, the conclusion was that red wolf hybridization in the area was minimal (Bohling et al. 2017). The results of the study stated that the coyote/red wolf hybrid makes up a relatively small percentage of the overall population of the canids in the limited area included in the study (Bohling et al. 2017). There were two reasons discussed of why such low numbers of hybridization were obtained. First, it was proposed that the dispersal of the red wolf was not as wide as first hypothesized, most likely due to high mortality rates. 36% of the annual mortalities reported for the red wolf were caused by gun shots or vehicle collisions. This means that red wolves do not have the opportunity to mate with coyotes due to the inability to successfully disperse into the territory dominated by the coyote. The second reason is that because of the number of successfully dispersing red wolves is so small, any wolf that is able to mate with a coyote will not make much of a difference in the DNA of the coyote population and will be swamped and un-detectible by mtDNA analysis. The final conclusions of this study found that there is evidence of candid hybridization in the area of study. (Bohling et al. 2017). These hybridizations included coyote-dog crosses and back-crosses, as well grey wolf-coyote crosses. The author cites the large dispersal distance of the gray wolf as the reason for this. (Bohling et al. 2017).
There are still many questions and debates involved with the future predictions of the coyote in the region. Wildlife biologists are still finding wider implications of genetic analysis and more efficient techniques of classifying organisms. Since we now rely on genetics to classify organisms instead of the physical appearance of the organism, we will be able to see more accurately the distinction between species. As coyotes extend their range further and further into more developed areas and are able to permanently adapt to their new habitat, the possibility of dog-coyote hybrids grows more likely. (Gompper 2002). Also, direct contact of coyotes with humans will become more common which will present knew challenges in conservation. (Gompper 2002). Since the coyote has become one of the top predators of the region, there will be many further developments of the ecosystems of the region in the field of conservation biology.
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