Introduction

Coryi Foundation, Inc. is a non-profit scientific organization studying bobcat (Lynx rufus) population viability in intensely developed landscapes east of the St. Johns River. This is done, in part, by radio-collaring and monitoring bobcats to assess status and document movements through corridors. Based on its findings, the Foundation develops recommendations for the preservation of wildlife corridors and larger habitat areas to which they connect. The end goal of this effort is to insure the long-term persistence of bobcats in intensely developed counties like Brevard. This paper discusses the potential threat to local persistence and briefly presents generalized solutions that will avert this threat.

Though the bobcat is not a listed species, there is the potential for its local loss in mainland Brevard County. Development is enveloping and eliminating preferred bobcat habitat as shown in Figure 1. Of all the land that exists between the St. Johns River and the Indian River Lagoon, 50% is developed. Another 25% consists of non-forested wetlands, specifically freshwater marsh, shrub wetlands, and wet prairie - types avoided by bobcats. These types are generally too wet for denning, lack sufficient numbers of preferred prey, and degrade the health of individuals. The bulk of these avoided habitats exist in the St. Johns River floodplain wetland system, toward which development is pushing and which is quickly becoming the last natural area of appreciable size. The remaining 25% constitutes the only amount available as preferred bobcat habitat and consists of wetland forests and development-vulnerable upland types. These include pine flatwoods, upland hardwoods, upland brush stages, and mixed forest wetland. These types possess sufficient prey (rabbits and rodent) and suitable denning cover.

The remaining preferred 25% is extremely limited for bobcats. Bobcats are wide-ranging and solitary. Males and females defend territories that average 4800 and 2900 acres, respectively. Both sexes do not allow other adults of the same sex to occupy their ranges. These conditions dictate that populations require extensive tracts of land. In order to be free of the extinction-yielding effects associated with small populations, a population requires at least 200 adults. For bobcats, this equates to about 291,000 acres, far more than all the land available between Mims and Melbourne.

This limitation of space is significant if development reaches 100% saturation from the floodplain to the Indian River lagoon at several constricting locations. These locations include Mims, Port St. John, Lake Poinsett, and Melbourne. The net effect of this could be the creation of small and isolated population cores. Potential cores are depicted in Figure 1 as the Titusville, Cocoa, and Viera cores.

As an example, if the Mims and Melbourne were to become fully developed from river to river, the population within would likely be isolated and have available to it only 50,964 acres of preferred habitat. This would limit the number of adults to no more than 75 individuals. This population would be far smaller than that required for long-term persistence. If, in addition, the Port St. John and Lake Poinsett constrictions were fully developed, the three cores above would have anywhere from 14 to 30 adults each. [Note: Isolation occurs because, additionally, the St. Johns River floodplain (wide channels and hostile wetlands) effectively prevents movement into the area from the west.]

Under the above isolation scenarios, a number of events will likely occur. Inbreeding rates will increase in the small populations and lead to a reduction in genetic diversity. Loss of genetic diversity can limit a population’s ability to respond to changes in the environment. Inbreeding depression can allow the expression of harmful genes that reduce immunity to diseases, lower reproductive success, and induce life-threatening physical impairments. Furthermore, small populations are more susceptible to epidemics and catastrophes such as fires or hurricanes. Because of isolation, individuals will not be able to move into an isolate to replenish losses that arise from mortalities. Additionally, the gene flow that is needed to offset the effects of inbreeding will not occur. These events typically lead to extinction. Thus, bobcats from Mims to Melbourne could disappear. Furthermore, river to river development would likely isolate all bobcats east of the St. Johns River all the way to Jacksonville. This is because the St. Johns River proceeds all the way to Jacksonville where it empties into the Atlantic Ocean. Such could set the stage for future extirpation on a regional scale.

General Solution to Avert Local Extirpation

To prevent isolation and allow for a large continuous population that is less vulnerable to local extinction, corridors need to be retained, especially at the above mentioned constrictions. Corridors are linear habitats that facilitate successful movement by adult breeders and dispersing juveniles between population cores. They promote the gene flow required to offset inbreeding effects and help replenish individuals. A corridor that promotes successful movement mostly consists of preferred habitats, possesses minimal impediments like highways, is sufficiently wide, and is the shortest possible route between cores. Furthermore, large blocks of habitat (cores) need to be retained to allow the existence of resident adults. These are generally the areas at which corridors terminate. Cores also provide important temporary use areas for dispersing juveniles. Because juveniles can disperse as far as 100 miles, the long and linear shape of the county mandates that intermediate cores exist. Thus, conservation efforts involving bobcats must include a network of cores and corridors. These efforts can be accomplished via linear parks and by the preservation of other linear habitats that connect existing public lands on a landscape scale. The Foundation develops conservation plans that incorporate such a structure and that are made available to local agencies and conservation entities.

The bobcat is the only large Florida carnivore remaining at population status in Brevard County. If bobcats disappear from this area, it will lose yet one more component of the food web and its old wild Florida heritage. It must be decided if we can afford this loss. The bobcat is a keystone species. This means that its presence determines what other species exist in the food web, as well as their abundance’s. Its absence as a keystone predator can cause prey populations (rabbit and rodent) to increase, over-forage and deplete their own food sources. This food depletion can increase competition between species that use the same foods. Some species may dominate the dwindling food supply and cause others to disappear. Thus, bobcats help maintain natural balance and their loss can induce the loss of other species. The bobcat is also an umbrella species. Because bobcats need lots of forested land, efforts to maintain them automatically umbrella the preservation of the many other species that need less land, without duplicated cost. Finally, people benefit from their presence. As a symbol of old Florida that enhances the aesthetic quality of an area, its exciting to see a bobcat and habitat protection provides natural areas for people to enjoy and travel back in time.

This non-referenced paper is a draft of a version that will be published in a professional journal. I do not forfeit any copyrights or publishing rights that belong to the eventual publisher or myself.