Rise of Mesopredators in Eastern Forest
Abstract:
Mesopredators are classified as mid-ranking predator’s in the trophic level that prey on smaller animals; such as coyotes, raccoons, opossums, and skunks. Traditionally wolves, or pumas, were the apex predator in the Eastern Forest range, and would dominate coyotes, and lesser mesopredators, in both food competition and home ranges. However, recent studies have shown that the release of mesopredators such as coyotes, raccoons, skunks, and opossums has been on a rise; due to the migration and decimation of common apex predators largely through human interaction. Research in regards to the effects of home-range and population abundance of both the mesopredators and prey in the Eastern Forest demonstrate the emergence of a new food cycle and the impact of forest fragmentation and human intervention.
Introduction:
Mesopredator abundance has altered the biodiversity of the North American Eastern Forest ranging from Florida to southern Canada, with the removal of natural apex predators, mesopredators have been released from their traditional roles as secondary-predators, allowing trophic cascade, a chain of effects moving down the food chain, to occur. Mesopredators are classified as a mid-ranking predator in the trophic pyramid that preys on smaller animals; examples include coyotes, raccoons, opossums, and skunks. Apex predators, like wolves and pumas, are at the top of the trophic level with no competition in the food chain.
Mesopredators and apex predators have some similarities. For example, wolves and coyotes are both in the Canidae family, have similar social organizations in the food chain, and are perceived to be a threat to livestock. However, apex predators will always be top predators (Tremblay 2021). Wolves and coyotes share similar lifestyles as they are both carnivores and are considered generalist species. Traditionally wolves will dominate coyotes in competition for food.
Studies have shown that the release of mesopredators such as coyotes, raccoons, and opossums has been on a rise; following the decimation of apex predators in the Eastern Forest ranging from Florida to southern Canada. There are studies that argue this release suggesting that since coyotes act as a top predator, this would have a positive effect on songbird populations (Cove et al. 2012) . Consequences could also arise because states would have problems with smaller predators and some could become a nuisance, with getting in trash bins or becoming a problem of spreading disease to domesticated animals (Owen et al. 2015). Some of the key aspects that I will be covering include why top predators have heavily decreased in population from the Eastern Forest, the positive and negative impacts on human and natural communities, including tropic cascades, as well as the trapping and harvesting of mesopredators, and habitat restoration.
Historical Review:
Long before humans began to settle in the North American Eastern Forest, apex predators roamed the lands. The first predator species to be discovered in the Eastern Deciduous Forest were red and gray wolves (Shea 2019). Holding the top predator title wolves were the most common in the Eastern Forest because of the richness of habitat and food resources. With wolves and coyotes being species from the same family, they are classified as generalist species and therefore are always in competition for food (Pierce 2021). Being a generalist species, meaning not having one particular diet, this became a problem for settlers coming to America.
When European settlers arrived in America, agriculture and livestock plantations were created starting the process we know today as forest fragmentation (Shea 2019). With the increase of settlers this became an issue as more forests were being cut down and wildlife began to disappear, forcing wolves to rely more on livestock owned by settlers (Shea 2019). Additionally, pumas, another native apex predator at this time began to take down livestock like the wolves, causing widespread bounties on both species, (Shea 2019).
With the decimation of top predators came a rise in mesopredator release, this is when a top predator is removed from a habitat either by humans or habitat loss, causing the next trophic level population to increase. For this ecological succession it would be the release of the next predator in line, the coyote. “It is clear that the coyote has been able to expand dramatically through the ranges of other Cani. spp. Despite anthropogenic persecution and probably will continue to dominate the eastern United Stated as its principal mammalian predator,” (Bozarth et al. 2011).
Ecology is understanding the factors that shape our distributional limits within a species. Roles in biotic interactions, such as predation and competition, in determining range boundaries remains poorly understood, even though these interactions can have a strong effect on the species populations. There is an additional need to examine how biotic factors limit species distribution across ranges of habitats that have different levels of stressors such as habitat loss, human modifications to land and disruptions of forest, as well as a decline or increase of apex consumers (Newsome et al. 2017).
Field studies, conducted in the article “Use of Camera Traps to Examine the Mesopredator Release Hypothesis in a Fragmented Midwestern Landscape” by MV Cove and associates, suggest that the mesopredator release hypothesis (MRH), would be the reason that the generalist mesopredators would now become abundant. This would also cause the release of raccoons and opossums and allow for an up-rise in other neighboring species. Stanley Gehrt and William Clark further explored the MRH, in “Raccoons, Coyotes, and Reflections on the Mesopredator Release Hypothesis”, they argued that with the coyote population beginning to act as the apex predator in the Eastern Forest there would be a positive effect on the abundance of wildlife within the fragmented forest.
The neighboring species to both apex predators and mesopredators are referred to as edge species. Edge species are animals that live in the ecotone region between two habitats. Due to these edge species, mesopredators tend to thrive in fragmented forest. Articles by (Cove et al. 2012), (Owen et al. 2015), and (Kays et al. 2008), explained that in all study areas of the Eastern Forest that they used, top predators sometimes used these ecotones alongside coyotes, their usage and inclusion in the overall data was tracked for their zones of predation showing their overlap between predators. Even with the addition of top predators, all three studies were able to collect significant data in regards to mesopredator predation zones and impacts. The study conducted by (Owen et al. 2015) selected areas with healthy rich forest, and monitored 42 adult raccoons. Of those 42, 13 females were monitored for their seasonal home ranges as well as 17 males. The data showed changes in the home range from 2001 to 2002 with ranges increasing in size due to lack of predation from coyotes.
The abundance of racoons cited in Owens' study had negatively impacted migratory birds, as well as had a negative impact on humans and other wildlife through the spreading of diseases and bacteria. Due to the MRH with coyotes having significantly broader ranges without competition with wolves, smaller mesopredators like raccoons and opossums are becoming abundant in numbers and as a generalist species their populations are flourishing, telemetry studies have shown that there is little to no avoidance of racoons in areas frequently used by coyotes. One of the positive impacts of racoons being the top mesopredator in a homerange is the increase of the songbird and migratory bird populations; however, one of the negatives is the depletion of ground nesting bird populations like Killdeer, Virginia Rail, some types of waterfowl, turkey, grouse, and Whip-Poor-Wills (Cove et al. 2012).
Another edge species impacted by the mesopredator changes are the white-tail deer. Two studies conducted by (Bragina et al. 2019) and (Chitwood et al. 2014) expanded on the relationship between coyotes and predation on white-tail deer. Chitwood’s study, “Confirmation of Coyote Predation on Adult Female White-Tail Deer in the Southeastern United States'', found that female deer may have succumbed to higher predation from coyotes due to their gestation periods as well as their care patterns for neonates. These mortalities were higher than vehicular incidents and hunter harvest, with most predation occuring along the forest edge specifically in places often used for bedding, escape or that offered partial cover. Bragina’s study, “Effects on white-tailed deer following eastern coyote colonization”, studied first historical patterns from the 1940s to present day, then estimated local coyote distribution and abundance.
Trends from 1981-2014 in 384 counties of six eastern states in the United States found that local studies provided contradictory evidence as to the extent of overall coyote predation and its over arching effect on the white-tail deer population, often in regards to neonate and fawn survival rates. Chitwood (2014) found that there were some small scale declines locally in the population of white-tail deer, related to predation, however, that finding was not supported by Bragina on larger scales. (Bragina et al. 2019) discovered that there was a negative association between colonization of coyotes and the white-tailed deer population, instead they found that there was a consistent rise in abundance of both species following the removal of apex predators (wolves and pumas) from the food chain.
There are positive and negative outcomes to having coyotes as a generalist top species. (Cove et al. 2012), theorized there are varying outcomes to considering coyotes as a generalist top species or as the new Apex predator within the Eastern Forest. (Kays et al. 2008), wrote “Landscape Ecology of Eastern Coyotes Based on Large-Scale Estimates of Abundance”, which theorized that with an overabundance of lesser mesopredators such as raccoons, opossums, and skunks there would be a negative impact on the habitat and population of migratory songbirds. In return, this could lead to an increase in overall predation of songbirds because there would be limited to no competition between the new Apex predator and lesser mesopredator. (Cove et al. 2012), discusses how the presence of coyotes could have a beneficial outcome for ground nesting birds, because coyotes would control the population of lesser mesopredators such as raccoons. In the same study it suggested that there were no killings of these lesser mesopredators by coyotes which supports the assumption of the generalist nature within the MRH.
Problems with Mesopredator Overpopulation:
Lesser mesopredators, such as opossums, raccoons, and skunks, have had a major impact on the biodiversity of bird species found in Eastern Forest as well as the native herpetofauna. Reptiles and amphibians are classified as herpetofauna (Cove etal. 2012). Raccoons as a generalist species are highly opportunistic hunters that prefer to eat consistent prey such as mice, bird eggs and herpetofauna. With coyotes no longer constantly preying as on lesser mesopredators, the population of raccoons and possums increases to almost overpopulation for their home range. An overabundance of these species allows them to have the opportunity to prey more on small shrub birds who make their nest on the ground or near the forest floor. This also gives these opportunistic species a constant resource of food that could illustrate the boom and bust cycle, where predator abundance may drive the supply of prey down.
With an abundance of mesopredators as their population starts to grow they require larger quantities of prey to feed on. Which inturn affects prey animals because they then are unable prey animals because they then are unable to replace their population quantity prior to the change in predation behavior.
The mesopredator overpopulation could also become a nuisance problem for humans (Owens et al. 2015). Humans litter and leave trash out in open areas, often where opportunistic mesopredator species can take advantage by learning that there is a potential for food where humans reside. They begin to make homes in or around the human population, often getting into trash, or becoming roadkill which can cause vehicular damage. Raccoons have the distinction of being found cute by some, however they are also known to carry rabies which is a deadly disease that causes confusion and disorientation to the infected animal. For instance, if a domesticated animal or pet was to be bitten by a mesopredator with rabies it would then contract the disease and need immediate medical attention. Rabies can spread across species causing cross-contamination bacterial strains. Researchers have discovered that the spread of diseases and outbreaks have been focused on urban area research where forest fragmentation has occurred and the mesopredator have reached nuisance status (Owen et al. 2015).
Problems can arise as well with interactions between coyotes and livestock belonging to European settlers was lost to wolf predation. With the rise of the coyote as the pseudo apex predator, livestock once more has become a focus food group, Matthew Gompper’s study from 2002, titled “Top Carnivores in the Suburbs? Ecological and Conservation Issues Raised by Colonization of North Eastern North America by Coyotes : The Expansion of the Coyote’s Geographical Range May Broadly Influence Community Structure, and Rising Coyote Densities in the Suburbs May Alter How the General Public Views Wildlife”, found that increased predation of livestock and domesticated animals by coyotes has increased the fear of attacks against humans.
Potential Solutions:
Lethal mesopredator control has been used as a means of conservation, ecosystem stability and to keep lesser mesopredator populations in balance. However it is considered highly controversial because studies were not conducted before or during the use of lethal control, meaning scientists potentially don’t have a true representation of the outward impacts of wholesale lethal control with species such as coyotes (Conner, 2015). Mastro’s study “Life History and Ecology in the Mid-Atlantic States: A Summary of Scientific Literature” suggests that trapping and removal could be a solution to the overabundance of mesopredators and coyotes. Trapping can be dangerous if whomever is removing them does not know the correct techniques and approach to properly remove them. Knowing the correct way to approach a coyote when it’s in an overwhelmed situation would be beneficial so that you do not run the risk of getting bit, or the animal further hurting itself.
Research from Conner and Morris (2015), informs us that removal studies have documented long term reductions in mesopredator abundance as a result of lethal control efforts, but these declines were normally because of habitat loss and deforestation. They analyzed published mesopredator data to determine if overall mesopredator removal rates changed over time. They found that many of the world’s larger predators are declining due to land use change and human conflicts (for example war-torn regions), this loss of predators ultimately cascades down causing ripples within the ecosystem. However, they also found that some mesopredator populations flourished in areas that had been modified by humans.
Bounties have been considered to be another solution to solving the abundance of nuisance species in an area. Researchers have found that there was a number of harvesting in Pennsylvania, Virginia, and North Carolina from state agencies in recent years (Mastro 2011). If bounties are set, and hunters or trappers know there is a reward behind them they are incentivized to help control the species population of mesopredators (Shea, 2019).
Leaving trash cans accessible may bring in nuisance animals as well. When one raccoon finds an easy resource for food, it often will lead more raccoons to the site and thus cause nuisance species. As a generalist species they will find or attempt to reach an accessible food source that requires little to no effort. Both Hernandez (2016) and Gehrt (2003) found that tuna, corn and any kind of pungent scent attracts these animals and they will congregate wherever the food resource is.
Habitat restoration is the manipulation of the physical, chemical or biological characteristics of a habitat where living and nonliving organisms live and has the potential to play a large role in mitigation of nuisance species. Habitat restoration acts as an all-time solution to an ecosystem because with a mature forest this more prey species and food for an array of species are attracted to the stable habitat and plentiful resources (Owens et al. 2015). As humans work to restore the natural state of forest, edge species as well as regular prey animals would have restored hiding, living, and mating locations. Not only would edges be positive modified, but interior forest, defined as the center of a forest surrounded by an edge, which is a crucial attribute for prey animals (such as music, rabbits, and ground nesting bird species), these forest are especially important because they act as extended shelter for prey animals as well as provide fauna. The overpopulation of raccoons, could be minimized along with other mesopredators (coyotes, pumas, raccoons, skunks, and opossum), by the reintroduction of apex predators back into their once natural ecosystems.
The reintroduction of Apex predators across most of the Eastern Forest could have both a positive and negative effect on the diverse ecosystems and human elements that regularly interact with those forests. Some of the positive effects for reintroduction of apex predators include the potential population control of the abundance of coyotes as well as a control of the deer population. Having top predators, such as wolves or pumas back in the Eastern Forest, would force coyotes to once more rely on raccoon predation, which would have a declining effect on both the raccoon population overall and the raccoon population's ability to become a nuisance to humans. Negatives of the reintroduction of Apex predators include the impact to humans. People who utilize the land and areas around forest would need to be more careful when traveling near or through heavily wooded areas. Hunters and trappers would also have to modify their behaviors when it comes to how they move through the woods, and what prey animals they regularly take down and in what quantities they are allowed to deplete season to season. For farmers the fear that livestock predation would rise again is always there. Collectively research suggests that the anthropogenic (human) lifestyle that the human species adapts their thinking and behaviors to work around the apex predators in question with reintroduction.
Conclusion:
By discussing the rise of mesopredators and how the release of mid-ranking predators [] it will give more insight on whether it is beneficial or inadequate for the ecosystem. Apex predators have been valuable to many ranges of forest dating back to prehistoric times but caused controversial problems for early European settlers in America due to livestock depletion. These complications resulted in bounties being placed upon these species and the apex predators either being decimated in eastern forest or forced to migrate to avoid human harvesting and trapping, which in return released the control on mesopredators such as coyotes allowing the trophic levels within the food chain to shift and realign. With active mesopredator release, coyotes have no active competition in the Eastern Forest for larger game prey and have begun to expand their range further north. Lesser mesopredator overpopulation has thrived with the release of coyotes, providing traditional prey organisms to repopulate, the relationship between the two is connected and shows the boom and bust model.