Overpopulation of Canis Latrans (coyote) in the Southeast and its Affect on Canis Rufus (red wolf) Conservation Olivia Cobb Abstract: Concerns: What effects

  • View
    216

  • Download
    4

Embed Size (px)

Transcript

  • Overpopulation of Canis Latrans (coyote) in the Southeast and its Affect on Canis Rufus (red wolf) Conservation Olivia CobbAbstract:Concerns: What effects to coyotes have on red wolf conservation efforts? What are the options for reducing coyote populations to a manageable level? Will there be detrimental affects on prey populations with the addition of another large predator? Red wolves were inhabitants of the southeast until near extinction in the 1970s. During this time less than 100 red wolves remained wild and only in Texas. This species has only recently been restored to part of their natural habitat on a wildlife refuge in North Carolina where they have met a new threat, the coyote. Coyote populations began widespread expansion into North Carolina in the early 1990s, just as the red wolves were released back into the wild. Hybridization rates between these two species threaten pure red wolf genetics, especially since hybrids are able to backcross with both parent species. Coyotes also threaten red wolves by threatening their historical niche as a deer predator in this region. Deer populations in the southeast have declined 36% between 1997 and 2006 with the spread of coyote populations, reducing availability of a main source of food for red wolves. Methods for controlling coyotes and hybrids have been explored including lethal methods and sterilization, though lethal methods may be opposed by portions of the general public. Success of these methods must also be taken into account and research shows that sterilization may be the best option for reducing coyote populations quickly and keeping numbers low up to 5 years after administration. Sterilization of hybrids should be approached with discernment to avoid losing valuable genetics held by some hybrids. There is no easy solution for correcting impacts coyotes have already had on red wolf conservation, but steps may be taken to prevent further damage.Key Words: Coyote, Red Wolf, Hybrid, Population, ControlIntroduction: English settlement of the United States began on the east coast during the 1600s. Colonization of the Midwest and western Us followed between the 1700s and early 1900s. These permanent settlements meant deforestation, land clearing, farms and livestock production, and extensive hunting of red wolves. Red wolves traditionally ranged from Texas to Pennsylvania while coyotes were limited to western states. The expansion of humans into coyote territory caused an eastward movement by coyote populations. Red wolves were drastically reduced in numbers by hunting efforts as the coyotes moved into their territory, leading to breeding between these populations. By 1973 only 100 red wolves existed in the wild (Allendorf et al. 2001). Over the next 7 years red wolves were captured to begin a conservation program. The hybridization with coyotes left only 10% of the population pure and only14 wolves were used to begin todays population (Frederickson and Hendrick 2006). In the 1980s, a new population of red wolves was released into the wild on the Alligator River Wildlife Refuge in North Carolina (figure 1). This location was originally chosen because it was free of coyotes, but by 1990 coyotes were documented in this area, along with hybridization (Miller et al. 2003).

    Figure 4: Current distribution of Red Wolves (including Alligator River)Thomas and Summer, 2006Red Wolf Biology: Canis Rufus (red wolves) are name for their cinnamon brown fur. Red wolves also have distinguishing black marks along their spine and tail. Their body size can range from 53-62 lbs. on average, an intermediate between coyotes and gray wolves. Red wolves live in packs with an alpha pair and their offspring from the two previous years. Red wolves are also very territorial and may chase away or kill invading small predators (Sillero-Zubiri et al. 2004). Diet can vary depending on location. In the southeastern U.S. red wolves typically prey on rabbits, raccoons, rodents and deer. Red wolves typically have a home range of 27-255 km (the city of Clemson is 20 km) and may bear between 1 and 8 offspring per litter with only one litter per pack each year (Roth et al., 2008).(U.S. Fish and Wildlife Service, 2006)Coyote Biology: Canis latrans (coyotes) range in color from grey to rusty brown and may also have black coloration along their body. Coyotes are smaller than red wolves, averaging between 30 and 36 lbs. Coyotes may live in packs with an alpha pair or as transients wandering between territories (Macdonald and Sillero-Zubiri, 2004). Similar to red wolves, coyotes average 6 pups per litter but their reproductive rates are actually higher because more females are involved in breeding each year. Coyotes are also territorial but are much less aggressive than red wolves and only require 2-20 km for their home range. Coyotes are opportunists and will eat a variety of foods including berries, insects, rodents, rabbits, deer, or even human made foods (Roth et al., 2008).(Thomas and Summer,2009)Ecological Niche: A species ecological niche is its job or role in the ecosystem. This system is based on competition and has led to genetic evolution of species. There may be specialists, such as red wolves, which require specific habitat and food or generalists, such as coyotes, which are much more adaptive to changes. Two species cannot fill the same niche. In a case such as with red wolves and coyotes one species must either be displaced or eliminated in a specific habitat (Bolen and Robinson, 2003).Hybridization: Hybridization is the process of breeding between two species. This is a natural occurrence and has been important in genetic evolution. Unfortunately, it can have detrimental affects on endangered species, especially those interacting with a species of significantly larger population size (Allendorf et al., 2001). Hybridization is worsened with introgression, meaning the hybrid offspring are not only fertile they may also breed with both of the parent species. This can lead to the elimination of an endangered species within only a few generations (Frederickson and Hendrick, 2006). The 1960s creation of Polymerase Chain Reaction (PCR) has made the detection of hybrids significantly easier. Hybrids can also be distinguished between first generation (cross between parent species) and those which have undergone introgression (Allendorf et al., 2001). Pure populations of red wolves are able to maintain 90% of their genetics only if hybridization rates are less than 1.7% (1 in 59 litters). Rates in 2004 were estimated to be 15% or higher, which could lead to elimination of pure red wolf genetics within 12-24 years (Macdonald and Sillero-Zubiri, 2004). Scientists and conservationists agree that hybrid and coyote populations need to be controlled. The methods and extent of control, though, are debated. Possible methods include euthanasia or sterilization of coyotes and hybrids. Many scientists urge that these be undertaken with caution to prevent the removal of useful red wolf genetics from the hybrid population (Kyle et al., 2008).Accuracy of Pedigree-Based Assignment Tests: In 2003, Miller et al. conducted a study to determine the accuracy of pedigree-based assignment tests in differentiating pure populations and different hybrids as well as if differentiating which hybrids are removed from a population has an affect on red wolf population genetics. The test was conducted for populations with either high or low levels of introgression under the following conditions: initial (current conservation conditions), perfect, using coyote private allele (CPA) test, likelihood ratio (LR) test, and a mixed test. The CPA test looked for alleles only found in the coyote population when comparing hybrids. The LR test compared hybrids against known alleles for both pure parent species, and a mixed test used both LR and CPA. Each subject was placed into 1 of six categories: pure red wolf (RW), pure coyote (Coy), red wolf, red wolf, or red wolf. When removing hybrids three methods or removal criteria (RC) were used: 1. RW only were allowed to return.2. RW or RW & cross were allowed to return. 3. RW, RW & cross, and red wolves were allowed to return. Results showed that RC 1 had the highest risk of genetic loss for red wolf populations, RC 3 had the lowest population decline, but highest risk of diluting pure red wolf genetics. RC 2 proved to be the best option for maintaining red wolf genetics without allowing for further dilution. This study solidified the idea that hybrids may in fact be useful in maintaining some pure red wolf genetics if chosen selectively to return to the wild population (Miller et al., 2003).Dynamics of Hybridization and Introgression: Frederickson and Hendrick in 2006 studied N.C. red wolf populations using a simulation to determine if sterilization of hybrids helped pure red wolf populations and how intensive these efforts should be. During the study sterilization was used in low levels (when >40% of mating pairs led to hybridization) or high levels (when >10% of mating pairs led to hybridization. The study concluded that sterilization of hybrids was a viable option over the short term (25-50 years). Chances of extinction were reduced from 79% to 16.8% in year 50 with high levels of sterilization of hybrids (Frederickson and Hendrick, 2006).Sterilization vs. Lethal Control in Coyote Populations: Coyotes first appeared in S.C. in 1980 and have since grown exponentially in population numbers, over 25,000 were harvest in 2008 by deer hunters alone. Methods of control, especially lethal methods, are controversial among scientists and the public. Conner et al., 2008 conducted a study to compare lethal control methods to sterilization in coyote populations. Each of these methods was tested in either spatially random locations (non-adjacent habitat areas) or spatially clumped (adjacent habitat areas). Results showed that lethal methods