A brief history of conservation
The Florida panther (Puma concolor coryi) represents the last subspecies of puma occurring in the eastern United States. It consists of a single, small, relictual subpopulation of the wide-ranging puma (Puma concolor) in southern Florida and has been of great concern to conservationists since 1958, when the Florida Fish and Wildlife Conservation Commission (FWC) declared the panther a protected species, well before the establishment of the 1973 Endangered Species Act (Maehr, 1997). The current range of the Florida panther is thought to represent a miniscule 5% of its past territory (Maehr, 1997). In 1967 many believed the Florida panther to be extinct, however sightings of wild panthers started emerging in the early 1970s, and by 1976 actual recovery efforts began. Initial estimates of the panther’s population size were difficult to attain, but they were definitely rare. After more data was compiled, it suggested that the population consisted of fewer than 30 individuals (Nowak and McBride, 1973). Initial proposals for panther recovery were to capture individuals for a captive-breeding program; panthers were captured, but the program never came to fruition because it was abandoned for the expediency of introducing individuals from an extant neighboring population, which began in 1995 with the introduction of 8 female Texas panthers to the Florida population.
Reasoning for the introduction of Texas panthers was not solely that of practicality, but for the purpose of genetic augmentation of the Florida population. As a result of such a recent population bottleneck, the genetic diversity of the Florida panther has been depleted. Homozygocity in Florida panthers is high, and microsatellite variation has been shown to be astonishingly low. That this genetic condition of the panthers is recent is patently obvious, as Florida museum specimens indicate much higher genetic variation than current levels (Culver et al, 2000). Not all researchers are on the same page regarding the necessity of genetic augmentation, however, and much controversy surrounds this issue still today. The main voice in opposition to measures involving permanent genetic augmentation is that of David S. Maehr, who expressed concern for the program before and after its implementation.
Maehr’s initial criticisms of genetic restoration took place while the program was still in its infancy. He argues that the program is more of a “quick fix” and calls for an alternate approach that encompasses many more aspects of Florida panther ecology. Maehr has suggested that Florida panthers are forest obligates, a claim that was initially unsupported and criticized, yet has been subsequently supported in further studies (Land et al, 2008). This being the case, there is no doubt that habitat loss via deforestation has been the biggest influence regarding Florida panther endangerment.
After the genetic augmentation had run its course for seven years, a wealth of new data became available to assess the success of the program. Maehr’s position had not changed much, and he offered even more criticism of the approach in light of new findings, which he was able to condense into four complaints (Maehr and Lacy, 2002), and which I have further condensed into three:
- That the eight adult female Texas pumas had been introduced during a period of population stability for the Florida panther, and this may have pushed the population to post-saturation levels.
- The problem of genetic swamping. The initial plan of an introgression level of genetic descent from Texas pumas was 20%. This number had been reached ahead of schedule, in 2000, and as of 2002 (the time of Maehr’s criticism) was at 24.5%. The genetic restoration, according to Maehr, appears to have been “too successful” and is “leading to a pedigree dominated by cats of Texas origin. . .” which is “counter to recovery objectives for the Florida subspecies.”
- Many scientists seem overly satisfied with the results thus far, but these successes are only short-term, and may “distract from making progress in the area of landscape planning and conservation essential for long-term panther survival and recovery.”
Though compelling Maehr’s arguments may be, many scientists have taken him to task on his assessment of the stability and robustness of the panther population prior to genetic restoration efforts. An example of one such rebuke can be found in Beier et al, 2006, which is a rather pugilistic refutation of many of Maehr’s scientific inferences regarding the Florida panther. The details of the exchange are fascinating and worth looking into, but further treatment of the controversy will not be given here. Let it be known that today, after decades of conservation effort marred with controversy, the population currently sits at an estimated 160 individuals.
The current predicament of the Florida panther today is dismal, but how did this once wide-ranging animal end up in such dire straits, restricted to only a tiny fragment of its original range? In order to explain this, the evolutionary history of the puma lineage must be put into context with the geological history of the surface of the globe. The start of this treatment takes place 30 million years ago, at the origin of what we would identify as true cats.
Current puma distribution is the result of a long and complex history. It is only now becoming possible, with the accumulation of hard physical evidence from the fossil record and the advent of new technology that allows genetics to offer valuable new insight and inference, to illuminate the past of this organism that today spans myriad ecological zones from North America to South America. Reconstructing the evolution of felids has proven quite difficult. Cats, being highly mobile, generally span large ranges that often overlap with other species of cat, making comparison between the fossil record and current geographical distributions a rather arduous task.
Cat-like carnivores (Feliformia) diverged from the dog-like carnivores (Caniformia) in the Old World, Eurasia, approximately 55 million years ago (MYA) (O’Brien and Johnson, 2005). This group is represented today in cats, hyenas, mongoose, and civets. Around 35 MYA there began a radiation of saber-toothed cats, but modern cats (Felidae) seem to have arisen 10-11 MYA and are now represented in 37 living species. Molecular analyses of these extant 37 species have identified 8 strongly supported, distinct lineages (Culver et al, 2006). The genus Panthera, also known as the roaring cats, arose 10.2 MYA, and remained in Asia, while some (leopards and lions) eventually migrated to Africa, and jaguars spread to the Americas via the Bering land bridge 8 MYA. This American group subsequently radiated into many lineages including ocelots, lynx, pumas, leopard cats, and domestic cats, and in that order (Johnson et al, 2006). It was in the late Miocene that the puma lineage split, forming two sister taxa (modern pumas + jaguarundi) with the cheetah (Acinonyx jubatus) being basal. The cheetah then died off in North America, coincidental with other large fauna, after having migrated back to Asia and ultimately Africa, where it now resides.
We now have the puma lineage in North America, where its fossil record is also found. Ignoring the jaguaroundi (Puma yagouaroundi), modern pumas (Puma concolor) have a fossil record 300,000 years old. The fossil record is near nonexistent in South America, which is to be expected if North American pumas have a North American origin, and South American populations represent a recent migration through Panama during the Great American Interchange, 2-4 MYA, when South America became contiguous with Central and North America. This assumed migratory trajectory predicts that South American pumas should have the least amount of genetic diversity, since only a subset of North American individuals would have migrated through Panama, taking with them only a subset of the genetic diversity of the North American population. However, recent molecular studies have shown that this doesn’t appear to be the case. Instead, pumas from eastern South America displayed the highest genetic diversity, with this diversity steadily decreasing to the north (Culver et al, 2006).
Melanie Culver and Carlos Driscoll, graduate students at the time, were the discoverers of this counterintuitive pattern of genetic diversity among North and South American puma populations. Culver and Driscoll analyzed several mtDNA genes as well as 10 microsatellites in order to test whether or not there was a genetic basis regarding the 32 named subspecies of P. concolor. Their study narrowed this number to just 6 discernable subspecies, but also revealed that all puma genetic diversity is derived from five subspecies South of Mexico, and that pumas North of Mexico had up to 50-fold less genetic diversity than those in South America. This data is indicative of a recent genetic bottleneck of a species migrating northward. But pumas have a fossil record in North America, and no scenario had been put forward that could possibly explain how pumas could have arisen in South America first. How are we to explain this paradox?
Driscoll and Culver expanded their study to include 85 microsatellites and were able to approximate the North American puma’s population bottleneck. O’Brian and Johnson summarize Driscoll and Culver’s findings thus:
The North American puma microsatellite variance was virtually indistinguishable from the variance of the same loci in African cheetahs, indicating that cheetahs in Africa and pumas in North America both experienced a near-extinction event at the same time, 10,000–12,000 years ago and in the same place, North America. Puma fossils much older than this period prove pumas were present in North America earlier, so it seems that whatever eliminated the cheetahs, sabertooths, mastodons, and American lions from North America also extirpated the pumas.
If North American pumas met the same fate of many other large North American fauna, then the seemingly paradoxical genetic variation suddenly makes sense; North America was re-colonized by South American pumas after their North American progenitors were eliminated. Subsequent studies have corroborated this north-south difference in genetic diversity using populations in the western United States (McRae et al, 2005). As mentioned earlier, the Florida Panther population suffers from severe inbreeding depression. This south-to-north re-colonization represents one of many genetic constriction events responsible for its current condition. Now that we have pumas in North America (again!) we must discuss how their once cosmopolitan range in North America became disjunct, leaving the Florida panther in a region representing only 5% of its original home range.
Pumas in North America
Pumas, upon radiating back into North America, expanded their range and quickly attained a cosmopolitan distribution. Pumas occupy and obtain land based on a land-tenure system, and adolescents generally radiate away from their natal grounds to establish their own territory. During re-colonization of North America, northern ranges were vacant, while southern territories were more densely occupied (O’Brien and Johnson, 2005; Pierce et al, 1999). Other types of behavioral reinforcement, such as their ability to switch between a wide variety of survival strategies (i.e., adopting specialist, generalist, and optimal foraging regimens as well tracking large, mobile prey) contributed to the quick repopulation of North America (Branch et al, 1996).
Pumas in North America generally take fewer, larger prey than their South American relatives. This is likely due to differences in the distribution of different sized prey, but may also be due to the fact that South American pumas live sympatrically with larger jaguars, which take the majority of large prey (Branch et al, 1996). This relief from competition with the jaguar may also account for the vast range of the North American puma. But what, then, led to the eastern rarity and disjunct distribution of pumas we see today in North America?
The disjunct distribution of North American pumas can be summarized in two words—habitat loss. Ever since the European colonization of America two centuries ago, human encroachment on puma habitat has been steadily increasing. Indeed, the eastern panther has been extirpated across the vast majority of its home range, leaving only a small relictual population in southern Florida (the Florida panther). The remainder of puma territory in North America is faced with the threat of continual human development. This winnowing down of puma habitat, and consequently its range, robs the puma of sufficient gene flow required to maintain robust populations. The Florida panther is a prime example of a population whose range had been so severely diminished that genetic abnormalities such as a high incidence of sperm abnormalities (90%), cryptorchidism (the failure of one or more testes to descend into the scrotum) (80%), congenital heart defects, and high loads of infectious disease are quite common (Roelke et al, 1993).
Pumas in Florida
The Florida panther is the last remaining population in eastern North America. Their history is fraught with genetic bottlenecks resulting in their truly impoverished state today. The first major genetic bottleneck took place 10-12 KYA when South American pumas repopulated North America. The second trim of genetic information took place in the 19th Century during periods of rapid human encroachment, and yet a third occurred in the early 1900s when genetic flow between it and Texas panther was severed (Florida, 2007). The current habitat of the Florida panther is confining; it cannot expand north due to the presence of many obstacles including Caloosahatchee River, a swath void of forest along the southern rim of Lake Okeechobee, as well as lands used for human agricultural needs (Maehr, 1997a). Being a forest obligate, the Florida panther faces even harder times as Florida forests become more and more sparse and fragmented.
Apart from purely abiotic, physical barriers restricting panther mobility, other human behaviors, such as the use of off-road vehicles (ORVs) and hunting, also contribute to panther isolation and range restriction. Florida panther habitat—forests—are become increasingly fragmented due to the presence of circuitous trails for ORVs (Janis and Clark, 2002). Panthers have been shown to avoid ORV trails, which are generally used by hunters of white tailed deer during the hunting season. Though a study has shown that panthers avoid ORV trails during the hunting season more than other periods, it is not completely clear whether panthers are directly avoiding the hunters and vehicles themselves, or whether deer are avoiding these areas and panthers are simply tracking the deer, a major food source (Janis and Clark, 2002). Either way, panthers are showing avoidance of these trails, either directly or indirectly, due to human activity. As the human population continues to grow in southern Florida, it will only exacerbate current unfavorable conditions for panther conservation.
The current state of the Florida panther
In reading many popular accounts of the Florida panther recovery program, one gets the overall feeling that genetic supplementation has been a success; the population of panthers shot up from around 30 individuals to an estimated 160 today. The introduced Texas panthers have been removed after having reached pre-defined goals in genetic diversity, and they appear to be doing very well compared to their condition in the past few centuries. Many scientists, however, are not celebrating, and feel that this apparent victory is just a short-term illusion, distracting people away from what true victory entails—long term genetic stability.
This type of stability can only come about if conservationists are able to suppress the prevalence of the factors that led to the Florida panther crisis in the first place—habitat loss. Without incorporating substantial efforts to acquire new and protect current panther habitat, no amount of genetic reinforcement will be sufficient to maintain a healthy population. The focus on genetic manipulation, as some see it, completely “sidesteps the issue of disappearing forest cover” (Maehr, 1997). Many have called for a “holistic approach” that approaches conservation from multiple angles such as demographics, land management, and reintroduction of panthers in to apparently vacant, suitable panther habitat. Since males have been found to disperse farther than females from their home range, they are thought to be the most important factor in nuclear gene flow (Sweanor et al, 2000). If the Florida panther could consist of multiple subpopulations, this natural mechanism for genetic exchange would be put in place and reduce the incidences of inbreeding (Belden, 1988). But would it even be possible to create a second panther population in order for this to occur?
Future conservation prospects
A study performed by David Maehr and John Cox at the University of Kentucky suggests that panther habitat exists in northern Florida, and that dispersing males would probably be able to get there if the in-between habitat could be conserved for this purpose (Maehr and Cox, 1995). North of the Caloosahatchee river exists forested habitat, currently unoccupied by panthers, which seems suitable to reintroduction. Little is known about how robust the corridors are connecting southern habitat with this potentially useful northern habitat, but increased road construction, urban development, and deforestation makes obtaining such lands for panther conservation all the more urgent (Maehr and Cox, 1995).
By many estimates, Florida panthers are currently above carrying capacity. The genetic fortification delivered to the population in recent times is likely temporary since, as population numbers drop, genetic drift becomes a serious problem. Inbreeding seems inevitable for the Florida population unless the range could somehow be expanded to support several hundred individuals. Conservationists face many battles with private land owners. Indeed, prime panther habitat is also desirable to people as well, creating serious conflict between conservationists and land developers. At the moment, Florida panther numbers are high (around 160 individuals), but maverick land purchases are needed in order to ensure the future survival of the panthers.
The isolated Florida population may represent a sad ending to a long and eventful history. Long term prospects do not look too bright, but potentially analogous success stories exist, such as the elephant seal, which has made a dramatic recovery from the brink of extinction. Estimates in the early 1900s suggested that only 20 individuals existed, yet conservation efforts have worked, and the elephant seal now occupies an increasingly wide range along the coast of California, with a current population estimate of 175,000! Perhaps the Florida panther will respond similarly with prolonged conservation efforts. Only time will tell for this critically endangered cat.
- Beier, P. 2006. Evaluating Scientific Inferences about the Florida Panther. The Journal of Wildlife Management 70(1):236-245.
- Belden, R. C. 1988. Panther habitat use in southern Florida. Journal of Wildlife Management 52:660-663.
- Branch, L. C., et al. 1996. Response of pumas to a population decline of the plains vizcacha. Journal of Mammalogy 77(4):1132-1140.
- Cox, J. J., et al. 2006. Florida Panther Habitat Use: New Approach to an Old Problem. The Journal of Wildlife Management 70(6):1778-1785.
- Culver et al. 2000. Genomic Ancestry of the American Puma (Puma concolor). The American Genetic Assosciation 91:186-197.
- Florida Panther and the Genetic Restoration Program. U.S. Fish and Wildlife Service. Retrieved 2007-01-30.
- Janis, M. W., and Clark, J. D. 2002. Responses of Florida panthers to recreational deer and hog hunting. Journal of Wildlife Management 66(3):839-848.
- Johnson, W. E. 2006. The Late Miocene Radiation of Modern Felidae: A Genetic Assessment. Science 311 (5757): 73–77.
- Land, D. E., et al. 2008. Florida Panther Habitat Selection Analysis of Concurrent GPS and VHF Telemetry Data. The Journal of Wildlife Management 72(3):633-639.
- Maehr, D. S., and J. A Cox. 1995. Landscape features and panthers in Florida. Conservation Biology 9:1008-1019.
- Maehr, D. S. 1997a. The Florida Panther: life and death of a vanishing carnivore. Island, Washington, D.C., USA.
- Maehr, D. S., and Lacy, R. C. 2002. In My Opinion: Avoiding the lurking pitfalls in Florida panther recovery. Wildlife Society Bulletin 30(3):971-978.
- McRae, B. H. 2005. Habitat barriers limit gene flow and illuminate historical events in a wide-ranging carnivore, the American puma. Molecular Ecology 14:1965-1967.
- O’Brian, S. J., and Johnson, W. E. 2005. Big Cat Genomics. Ann. Rev. Genomics Hum. Genet. 6:409-29.
- Pierce et al. 1999. Migratory Patterns of Mountain Lions: Implications for Social Regulation and Conservation. Journal of Mammalogy 80(3):986-992.
- Roelke, M. E., et al. 1993. The consequences of demographic reduction and genetic depletion in the endangered Florida panther. Curr. Biol. 3:340-50.
- Sweanor, Linda. 2000. Cougar Dispersal Patterns, Metapopulation Dynamics, and Conservation. Conservation Biology 14(3): 798–808.