The Ecological Role of Mesopredators

 

Mesopredators Collage

 

Site Contents:

Background Information

Study Objectives

Study Approach

Conservation Implications

Education and Outreach

Publications

Graduate Students

 

BACKGROUND INFORMATION

Until approximately 25 years ago, mammalian predators were actively pursued by hunters and trappers for both sport and economic gain.  However, fur prices have fallen precipitously, and the popularity of sport hunting and trapping has declined dramatically.  The effects of reduced fur prices and the associated reduction in predator harvest have raised concern that many mid-sized mammalian predators (mesopredators) may become overabundant and exert excessive pressure on their prey populations. 

Traditional Quail Hunt

It is generally accepted that the existing predator community in the southeastern U.S. has been altered by a number of factors such as, the elimination of top carnivores (e.g., cougars and red wolves), the reduction of sport hunting and trapping of mesopredators, and changes in the landscape that favor certain predators.  These landscape changes often concentrate prey species rendering them even more susceptible to predation.

Gopher Tortiose


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The altered predator community may affect both game and non-game wildlife.  In Georgia, some mammalian predators can be legally harvested for predator management objectives.  Although some studies have shown that removal of predators can result in increases in populations of certain prey species, there are other studies suggesting that reduction of predator populations has no positive impact on their prey.  Thus, the impacts of predator removal on the overall wildlife community are unknown and often debated.

Blue Male Grosbeak

 

STUDY OBJECTIVES

Virtually all management decisions are based on weighing the relative benefits of management against costs of implementation.   Historically, there has been a tendency to study predation from a single species perspective.  In so doing, it becomes difficult, if not impossible, to fully evaluate the costs and benefits of managing the process of predation; thus, there is a need to holistically examine the role of predators in today’s ecosystems. 

Food Web


Our primary goals are to determine the effect of mesopredator control on prey populations and to identify and quantify the trade-offs associated with a mesopredator control program.  To accomplish this task we must increase our understanding of the ecological role of mesopredators.  Therefore, the objectives of this long-term project are to:

  1. Quantify effects of mesopredators on avian and gopher tortoise nest success and small mammal populations and communities.
  2. Quantify the relationship between nest success and densities of small mammals, raptors, corvids, and snakes.
  3. Determine whether removal of mammalian predators results in a change in the vegetation community.
  4. Estimate habitat needs and factors affecting habitat use select predators.
  5. Determine the ecological roles of select predators within our study system.
  6. Ultimately, provide predator management options that are based on the wildlife community as a whole, as opposed to single species management.

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STUDY APPROACH

Removal of predators or groups of predators, results in a prey response that occurs along a continuum.  At one end of the continuum, there is a one-to-one response, (e.g., a 10% reduction in a predator population brings about a 10% decrease in predation by that particular predator species).  At the other end of the continuum, a decrease in predator abundance results in a drastic increase in predation rates.

Prey Response Continuum

In a natural system, it would be unlikely for a prey response to predator removal to occur on either end of the continuum.  Instead, prey response to predator reduction can be expected to fall between these two extremes, with the observed response being influenced by several factors. If prey response is sufficiently far to the left, then predator removal may be viewed as a viable management practice.  However, as prey response progresses along the continuum, predator removal becomes less cost effective as a management practice and may actually become detrimental.  

 

The decision, then, as to whether predator removal is a viable management practice depends on where the response in prey population occurs along this continuum.  This response must also be weighed against both the financial and ecological costs of the removal before reaching a management decision.  The financial costs of control efforts will vary, yet they are easily measured, and decisions concerning the financial viability of control can be made.  Ecological costs of predator control are not easily measured and should play a major role in making a decision concerning the implementation of a predator control program.  To help measure the costs and benefits of predators, predation management, and predator control, we have taken the following research approach.

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Predator Exclosure Experiment

We initiated a field experiment in which mesopredators, which can legally be harvested in Georgia, are excluded from four large (approximately 100 ac) areas.   We constructed exclosures with 2 x 4 in woven wire fences . Fencing    After Prescribed Fire

At the top, middle, and bottom of the fence we placed electrical wires to discourage animals from digging under or climbing over the fence.  We turned the fences off, opened the gates, and applied prescribed fire to each of the exclosures.  We also burned 4 unfenced control sites to use for experimental comparison. 

Predator trapEnclosure Areas

Following the prescribed fire, we turned on the electric fences and shut the gates of the exclosures.  We then trapped inside the exclosures to remove any remaining predators.  Thus, our study has 4 sites where predator numbers were greatly reduced and 4 sites where predators are at normal densities for our study area. 

 

Fire Ant Video

Fire ants were the number one predator of shrub and ground nesting birds during our study.  This video shows a Northern Cardinal nest with 2 eggs and 1 nestling.  The nestling is being attacked and killed by fire ants.  A male Northern Cardinal removes the nestling that has been killed by fire ants. 

 

Snake Predation Video

Snakes, as a group, are among the top three predators of shrub nesting and ground nesting birds in our study.  However, if you break up ‘snakes’ into individual species destroying a nest, there is no one snake species that we would consider a major nest predator of shrub nesting and ground nesting birds.  This is a video of a Northern Cardinal nest with 2 nestlings.  The nestlings are consumed by a gray snake.

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Tortoise

This arrangement permits comparison of predator impacts on a variety of prey species.  Specifically, this study allows us to evaluate the effects of predators on nest success of birds and gopher tortoises, small mammal communities , deer , rabbit , and snake densities.

Small Mammals of Ichauway

 

 

Buck and Rabbit

 

Snake Collage

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Radio Telemetry

We have studied movement patterns and habitat associations of bobcat, raccoon, gray fox, red-tailed hawk, armadillo, king snake, eastern coachwhip, eastern diamondback rattlesnake, and Florida pine snake.  We plan to initiate work with great-horned owls later this year.  Each of these species fills a unique predator niche on our study site, and through better understanding the habitat needs of these species, we hope to better understand how habitat management can be used to manage the likelihood that a predator comes into contact with a given prey, ultimately providing habitat management recommendations that can reduce predation on select prey species.

Radio Tagging

To reduce predation rates through manipulation of habitats, we must also have an understanding of the habitat needs of prey species.  Therefore, we have also radio-tagged select species including cotton rats (the most consumed prey species on our study site) and white-tailed deer.

 

Predator diet analysis

We systematically search for scat of bobcat and coyote throughout the study area.  ScatScats are dried, washed, and then examined to determine the diets of these two top mammalian predators.  This information will be used to develop models that estimate the number of prey items taken by these predators during a year.  Particular emphasis will be placed on consumption of bobwhite quail and deer by these two predators.

 

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CONSERVATION IMPLICATIONS

There is a need to better understand the predation process, which will ultimately inform managers about cost-effective management strategies to retain economic values of game species, while also protecting the unique biodiversity (including rare and keystone species) of the ecosystem.  The focus of this research is on determining the effectiveness of mesopredator removal as well as on identifying the effectiveness of habitat management strategies, such as prescribed fire and hardwood removal on managing predators.
Jones Center staff work with state agencies, private landowners, and land managers who are interested in predators and the predation process.  Our research results are presented to various user groups in an attempt to aid managers in meeting management objectives for their land. 

 

EDUCATION AND OUTREACH

Our research results are incorporated into a variety of presentations to both professional and civic groups. Additionally, results are presented to a variety of groups during short courses, college classes, and landowner field days.  These courses emphasize topics ranging from wildlife sampling techniques, to predator ecology, and habitat management.  We also host a predation management workshop every other year with approximately 50 landowners in attendance.

Wildlife Techniques

Wildlife ImageThe wildlife techniques Maymester course focuses on providing hands-on experiences for future wildlife biologists, wildlife managers, and educators. The primary focus of the course involves capture and handling of diverse wildlife species as well as various methods of indexing wildlife populations and communities. Learn More...

Private Landowner Outreach

Private Landowners Field DayMany of the finest examples of the longleaf pine/wiregrass ecosystem are found on lands in private ownership. Stewardship and management of these lands based on sound science is critical to their conservation. The Jones Center's education and outreach programs provide information to conservation-oriented longleaf pine land owners and managers in order to further their stewardship efforts. Learn more...

EERA - Programs for Educators

EERA ImageAlthough the Center does not work directly with K – 12 students, we recognize the importance of impacting this age group for the future of conservation in the region. To accomplish this, as well as to foster healthy public relations in our surrounding communities, we dedicate a significant amount of time annually to schoolteacher training.  These efforts have increased public awareness of the Center among people in the region, contributed to professional development of educators in an underserved part of the state, and helped to institutionalize educational efforts related to the region’s rich natural resources in local school systems. Our flagship project in this category is the Environmental Education Research Academy EERA. Learn more...


           

PUBLICATIONS

Click here for a list of our current publications.Publications

 

GRADUATE STUDENTS

Click here for the Graduate Students List Graduate Students

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