Richard A. Seigel

Phenotypic Plasticity in Reproductive Traits: Evidence from a Viviparous Snake

A number of recent studies have indicated that life history characteristics (e.g., number of offspring, offspring size, age at sexual maturity) are strongly affected by proximate environmental factors such as prey availability. Evaluating this phenotypic plasticity will be crucial to a complete understanding of the evolution of life history traits, because the occurrence of such variability casts doubt on the common assumption that the values of life history characteristics expressed in nature are the outcome of long-term natural selection. In this study, we manipulated the diets of a captive-bred colony of the viviparous snake Thamnophis marcianus to determine to what degree the reproductive characteristics of this species were determined by food intake. We found that both number of offspring and clutch mass were significantly affected by prey availability, but that relative clutch mass and offspring size were fixed relative to diet. Our data suggest that like other organisms, T. marcianus shows a gradient in phenotypic plasticity, with some traits more canalized than others. Therefore, intraspecific comparisons of life history characteristics should not be made without information on which traits are subject to phenotypic plasticity.

Stochastic variation in reproductive success of a rare frog, Rana sevosa: implications for conservation and for monitoring amphibian populations

Abstract Although amphibian populations are thought to be declining in many parts of the world, detailed information on populations in decline are often not available. From 1988 to 2001, we studied temporal variation in the reproductive biology of the only known population of dusky gopher frogs, Rana sevosa Goin and Netting. We found high annual variation in reproductive effort, mortality at the egg and larval stages, and hydroperiod length. No overall trends were apparent in terms of either number of egg masses deposited or in reproductive success, as we found extensive variation among years in the number of egg masses deposited, a high rate of reproductive failure, and no consistent relationship between the number of females present, the number of eggs deposited, and the number of metamorphs emerging. Given the complete isolation of this population from other gopher frogs and the high rate of reproductive failure, the probability of extinction of this population appears to be quite high (0.125–0.316).

Reproductive and Nesting Ecology of the Yellow-Blotched Map Turtle, Graptemys flavimaculata: Implications for Conservation and Management

Abstract We studied the reproductive and nesting ecology of the Yellow-Blotched Map Turtle (Graptemys flavimaculata) from 1993–1994 and from 1996–1997 on the Pascagoula River in southeastern Mississippi. This species has undergone a recent decline leading to its listing as Threatened under the U.S. Endangered Species Act. We found three distinctive features of the biology of this population: a relatively low reproductive frequency compared with most other map turtles (maximum of 1.16 clutches/female), a very high level of nest mortality caused by river flooding and fish crow predation (90% mortality in some years), and an unexpectedly high level of nesting in shaded areas along the riverbank, perhaps in response to human disturbance on and near sandbars. Our data suggest that, in the absence of extraordinarily high adult survival, this population will decline because of low recruitment. We suggest a series of specific strategies to reverse these declines, including better law enforcement to protect adult turtles, public education, and possibly, protection of nests on the nesting beaches.

Annual Variation in the Population Ecology of the Endangered Gopher Frog, Rana sevosa Goin and Netting

Abstract We studied variation in the population ecology of dusky gopher frogs, Rana sevosa Goin and Netting, in southern Mississippi from 1996–2001. Specifically, we measured adult size structure, adult survivorship, residency length within the pond, and juvenile recruitment using a drift fence that completely enclosed the study pond. Population size structure shifted among years because of lack of recruitment in previous years, adult mortality, and differential age at maturity. Age at maturity was 6–8 months for males and 24–36 months for females. Annual survival ranged from 65 to 92%; however, the rate at which adults returned to breed among years was low (16–22%). The average number of seasons that adults bred was 1.2, although nine individuals bred in 3–5 seasons. Our data suggest that R. sevosa has high population turnover among years and that most adults live less than 7 yr. Because of the low rate of return of adults among years and complete isolation of the population, the viability of the population is contingent on consistent recruitment of juveniles with minimal years of reproductive failure.

Swine Flu or 1918 Pandemic? Upper Respiratory Tract Disease and the Sudden Mortality of Gopher Tortoises (Gopherus polyphemus) on a Protected Habitat in Florida

Abstract Although Upper Respiratory Tract Disease (URTD) has been recognized as a potentially serious problem threatening the viability of gopher tortoises, little is known about the impact of this disease on tortoise populations in the wild, and some researchers regard the disease as relatively benign. We monitored the impact of URTD on gopher tortoises at the Kennedy Space Center, Florida, and found a striking increase in the proportion of tortoises showing signs of URTD between 1995–2000. We also documented a sudden increase in the number of tortoises found dead at the site, starting in 1998 and continuing through 2001. Based on condition and position of dead tortoises, we strongly suspect that URTD was the cause of death. Sex ratios and body sizes of tortoises found dead were not distinguishable from samples of living tortoises, indicating that mortality was not confined to a single gender or age class. Combined with recent reports of large-scale mortality of tortoises from other sites in Florida, we suggest that URTD is not benign but may instead have a substantial impact on tortoise populations. If so, the “protected lands paradigm” that many resource managers rely on to conserve tortoise populations may be violated, suggesting that more active management measures are needed.

Changes in a population of an endangered rattlesnake Sistrurus catenatus following a severe flood

Abstract We studied changes in the abundance, population structure, and reproductive traits of an endangered rattlesnake Sistrurus catenatus between 1979–1983 and 1993–1995. This population was subjected to an extensive flood during the summer of 1993, the most severe flood in northern Missouri in at least 100 years. The abundance of rattlesnakes had not changed substantially since the initial studies in the 1980s, but sex ratio, population structure, and body condition differed significantly. Most of these changes can be attributed to the 1993 flood, which severely damaged the habitat for the snakes and may have reduced prey availability. Data collected in 1995–1996 suggest that both the habitat and the massasauga population are recovering from the 1993 flood. Monitoring programs for endangered species should collect data not just on changes in abundance, but changes in underlying population characteristics as well.

The Management of Amphibian and Reptile Populations: Species Priorities and Methodological and Theoretical Constraints

Many reptile and amphibian populations either are pests, are harvested, or are declining towards extinction; however, relatively few are managed. This neglect can be traced to many causes, chief of which is the lack of sympathy that many people have for reptiles and amphibians, especially life-threatening forms such as large or poisonous snakes and large crocodilians. A few reptiles and amphibians are pests, especially some introduced forms such as the brown tree snake (Boiga irregularis) on Guam and the cane toad (Bufo marinus) in many tropical areas. Many reptiles and amphibians are on the U. S. list of endangered and threatened species because of uncontrolled harvest and habitat degradation. International trade in amphibian and reptilian products amounts to hundreds of millions of U. S. dollars annually. Management priorities are often set by nonbiological criteria, such as economic importance and the size and appeal of the animal. Sea turtles and crocodilians receive the most attention. However, priorities set in this manner ignore economically less valuable and less glamorous species that may become endangered by neglect. Common management measures include the protection of species from illegal exploitation, the establishment of harvest quotas, and the captive rearing of endangered species. Management protocols are often hastily implemented without adequate testing for effectiveness. As a group, crocodilians are probably the most effectively managed reptiles. By partially controlling the international market, illegal harvest has been greatly reduced and many formerly threatened populations are recovering. Legal harvest and ranching projects provide the impetus (and often the funds) for high priorities being placed on the research and management of crocodilians. Placing a value on wild crocodilian populations helps conserve wetlands for the benefit of other species of wildlife. Sea turtles are also the recipients of massive management efforts. However, positive results are not easily demonstrated. The huge effort in saving eggs and hatchlings on sea turtle beaches seems to be largely misplaced; long-lived, highly fecund species such as sea turtles are most effectively managed by controlling the mortality of large juveniles and adults. Recently, the reduction of mortality in Kemp’s ridley turtle (Lepidochelys kempi) resulting from the killing of nesting females and drowning in shrimp nets seems to have reversed the plunge towards the extinction of the world’s rarest sea turtle. Management-oriented research on reptiles and amphibians is unevenly distributed among taxa. Crocodilians and sea turtles are the subjects of much research, but reliability of much of it is difficult to judge as it does not undergo the peer-review process of scientific literature. Research is especially needed to identify the critical life stages of sea turtles, in order to better direct management. Because of their ecothermic physiology, the life history and ecology of amphibians and reptiles often differ markedly from those of traditionally managed game species. Amphibians and reptiles can survive long periods without food, have extended periods of inactivity (often including long periods of hibernation), and exhibit strong seasonal changes in habitat utilization. When compared to endotherms, amphibians and reptiles have low rates of parental care and viviparity, high rates of neonate mortality, low frequencies of reproduction, extended age at sexual maturity, and long generation times. These traits suggest that appropriate management of amphibians and reptiles should focus more on protecting subadults and adults than protecting juveniles and neonates. However, most current management practices protect juveniles and neonates, and allow adults to be harvested. Many reptiles and amphibians are difficult to study and require specialized techniques. There is a need for standardized monitoring techniques to allow comparison of different studies and years. Herpetologists could more often choose their organisms and design their studies to better meet the informational needs of wildlife managers. Wildlife management training needs to include reptiles and amphibians, along with birds and mammals, so that managers in the future will consider all taxa in their plans.

VARIATION IN HATCHLING TORTOISE SURVIVORSHIP AT THREE GEOGRAPHIC LOCALITIES

Survivorship of hatchling chelonians is low in many instances, although few investigators have intensively studied the immature life stages. We used radio telemetry to assess hatchling gopher tortoise (Gopherus polyphemus) survivorship in central Florida (n = 20), and compare our results to previously published studies in north Florida and Mississippi. At our site tortoise predation was extremely high, and no hatchlings lived over 335 days. Average lifespan was consistent among clutches, and the highest mortality occurred within one month of hatching. Major predators included mammals and snakes. Our results are similar to published data from north Florida (n = 20) and Mississippi (n = 45), although hatchlings in north Florida survived the longest. However, all tortoises (n = 85) in each study died many years before reaching sexual maturity due to predation. Hatchling predators varied by site, but mammals were the major predator at all three sites. We discuss the population-level consequences of high mortality in the younger life stages and several hypotheses associated with population stability. Although hatchling mortality was extremely high, long-term data from our central Florida site show that immature animals are captured on a regular basis. The most likely explanation for this apparent contradiction is that true hatchling survival levels are above zero, but are too low to be accurately detected with the current sample sizes. Therefore, long-term mark-recapture studies focusing on hatchling and juvenile animals are necessary to determine whether recruitment is sufficient to maintain current population sizes, or if populations are declining slowly.

Third Workshop on the Ecology, Status, and Conservation of Diamondback Terrapins (Malaclemys terrapin): Results and Recommendations

The Third Workshop on the Ecology, Status, and Conservation of Diamondback Terrapins (Malaclemys terrapin) was held in Jacksonville, Florida, on 17–19 September 2004. The workshop was sponsored by the University of North Florida and the Florida Turtle Conservation Trust. Sixty-six individuals from academic, scientific, regulatory, and private institutions/organizations met to discuss recent research findings and conservation concerns related to this ecologically significant coastal wetland species. All 16 states within the range of the species were represented. Eighteen papers were presented in sessions on ecology, conservation concerns, environmental education, and status; 13 posters were presented in a separate session. Abstracts can be viewed at http://www. dtwg.org. This conservation meeting built upon the accomplishments of 2 earlier workshops. The first workshop was held in August 1994 in response to reports of potential declines of diamondback terrapin (Malaclemys terrapin) populations in several locations within its range. That workshop provided an opportunity to share data on terrapin biology and status, and to produce specific recommendations for action by local, state, and federal management agencies. A result of the workshop was the publication of a paper identifying the threats and steps needed to conserve the species (Seigel and Gibbons 1995). The second workshop in the series was held in October 2000 and provided a welcome opportunity to share new research findings and discuss conservation concerns.

Occurrence of Upper Respiratory Tract Disease in Gopher Tortoise Populations in Florida and Mississippi

We studied the occurrence of exposure to Upper Respiratory Tract Disease (URTD) in gopher tortoises (Gopherus polyphemus) at protected sites in southern Mississippi (Marion County Wildlife Man- agement Area (MCWMA)) and east-central Florida (Kennedy Space Center (KSC)). Based on antibody as- says, exposure to URTD was very common in both populations, with combined positive and suspect results ranging from 60% (KSC) to 100% (MCWMA). At KSC, males were significantly more likely to show positive or suspect results than were females. Tortoises with active signs of URTD were seen at KSC but not at MCWMA. Our data do not support the hypothesis that exposure to URTD is associated with human dis- turbance or habitat destruction; several sites that had good habitat conditions and little disturbance by humans had high rates of URTD, whereas some sites with high levels of disturbance had low rates of URTD.