Population Ecology of the Jefferson salamander, Ambystoma jeffersonianum, in Illinois

Sarabeth Klueh and Stephen J. Mullin

Department of Biological Sciences, Eastern Illinois University

Abstract

Amphibian populations utilizing small isolated wetlands are often small in size, have little to no contact with other populations, and are susceptible to stochastic extinction processes. The persistence of such populations can only be ascertained by obtaining data that allow the prediction of the population’s growth, trajectory, and capacity to achieve a sustainable size. The Jefferson salamander, Ambystoma jeffersonianum, is a state-threatened species, occurring at fewer than 15 ponds within Illinois. Individuals at a pond in the east-central part of the state are captured using a drift fence-pitfall trap array, then sexed, measured for SVL, and marked using a unique combination of toe clips. Also obtained are the number of egg masses, average percentage of successfully hatched eggs, and number of juveniles leaving the pond. All data is then entered into a life history table and used to develop a population model. Information obtained from the model will be used to determine which life history stage is critical to the survival of the population, and it will allow management efforts to focus on mechanisms that are most likely to cause declines.
 

Introduction

Habitat destruction and forest fragmentation have led to the isolation of small habitat fragments. Populations inhabiting these areas are typically small and are susceptible to stochastic extinction processes³, especially if they exist at the edge of the species’ known distribution.  Isolated populations of Ambystoma jeffersonianum breed at fewer than 15 ponds in east central Illinois⁴. This study provides information on a population at Lincoln Trail State Recreation Area (LTSRA, Figure 1; Clark County, Illinois).  A population model will be used to assess the stability of the population as well as suggest any needed conservation measures^1,2.

Questions

• How many individuals are in the population?

• How stable is the population?

• What conservation efforts (if any) need to be made?

Methods

We constructed a drift-fence pitfall trap array around a pond at Lincoln Trail State Recreation Area (Figure 2).  We measured, sexed, and toe-clipped all individuals entering or leaving the breeding pond during the 2004 and 2005 breeding seasons.  We counted all egg masses, and determined the average number of eggs per mass, the hatching success of each mass, and therefore, the number of larvae produced per season.  We entered all demographic data into a life history table and developed a stage-based population model¹.

Results

In 2004, we recorded 104 marked Ambystoma jeffersonianum (68 females and 32 males)

We counted 487 egg masses

We determined that there were 6750 larvae

We recorded 4 marked juveniles

In 2005, we recorded 84 marked Ambystoma jeffersonianum (47 females and 37 males)

We counted 393 egg masses

We determined that there were 5447 larvae

No juveniles were recorded

In 2004 and 2005, the breeding pond dried before larval development was complete

We recorded an average of 18 eggs per mass

Females laid an average of 7 egg masses (129 eggs)

Eggs had a 77% survival rate to hatching

Management Options

• Initial emphasis should be placed on enhancing larval survivorship.

• We recommend that the breeding pond at LTSRA be excavated in order to provide a water depth that allows all larvae to complete metamorphosis.

Literature Cited

1. Akcakaya et al. 1999. Applied Population Ecology. Sinauer Assoc, Inc.
2. Biek et al. 2002. Conservat. Biol. 16:728-734.
3. Caughley and Gunn. 1996. Conservation Biology in Theory and Practice. Blackwell Science.
4. IDNR. 2003. Endangered and Threatened Species– Strategic Recovery Outline. Springfield, Illinois.

Acknowledgements

Funding for this research was provided in part by the Illinois Department of Natural Resources Wildlife Preservation Fund and the Eastern Illinois University Council on Faculty Research. We thank the staff of LTSRA. L. Walston, C. Foster, J. Florey, and M. Sikich for their assistance in the field. Specimens were collected under IDNR permit # 0946 and # 03-16S.