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Project Work Plan
Department of Interior USGS GE PES and ENP CESI
Fiscal Year 2006 Study Work Plan
Title: Use of Amphibian Communities as Indicators of Restoration Success
Overview & Objective(s): Declines in amphibian populations have been documented by scientists worldwide from many regions and habitat types. No single cause for declines has been demonstrated, but stressors like acid precipitation, environmental contaminants, the introduction of exotic predators, disease agents, parasites, and the effects of ultraviolet radiation have all been suggested. Because of their susceptibility to these and other stressors, amphibians are important as indicators of ecosystem health. Amphibians are present in all habitats and under all hydrologic regimes in the Everglades. The species present and the occupancy rate of a given species differ greatly across those gradients. These differences are due to hydropattern, vegetation, and other environmental factors. The combination of species composition and proportion of each habitat occupied at a given time form unique communities defined by those environmental factors. Therefore, if these communities can be reliably defined and measured, Everglades restoration success can be evaluated, restoration targets can be established, and restoration alternatives can be compared. This study will develop methodologies for defining and measuring the membership and area occupancy of amphibian communities. Further, we will investigate the relationship of occupancy of amphibians with hydroperiod and other environmental factors. Finally, we will provide a method for measuring restoration success based on these communities. Our objectives include:
Specific Relevance to Major Unanswered Questions and Information Needs Identified:
Status: We continue to use data previously collected from Everglades National Park to develop methods for defining amphibian communities using the Proportion Area Occupied (PAO) model and multivariate statistical techniques (see Fact Sheet 2004-3106). In Everglades National Park and adjacent Water Conservation Areas 3A and 3B, we have now completed fieldwork for a large scale study to determine the PAO by each amphibian species across habitats defined by hydropattern. The PAO method estimates the abundance of sites at which each species occurs based on the capture results of several visits to each site. This method takes into account that some species are more difficult to detect, given that they are present, than others. This sampling is done along a hydrologic gradient from very long hydroperiod sloughs to the extremely short hydroperiod rocky glades of eastern Everglades National Park. We have completed sampling including call count, visual encounter surveys, PVC refugia captures, and trapping in over 20 sites.
Recent Products: We have completed Fact Sheet 2004-3106 and have presented our initial findings and models to national and international conferences (presentations and posters). In 2005, 1 peer-reviewed journal article, 2 USGS open-file reports, and 1 book chapter were published. We also gave several presentations at National and International Meetings and 2 additional manuscripts were submitted to peer-reviewed journals.
Planned Products: We are presenting the results of this work at national and international conferences. We have 1 manuscript under preparation for publication in a peer-reviewed journal. We plan to complete further peer-reviewed manuscripts on the study upon completion and provide the monitoring program and simulation models to CERP managers.
Title of Task 1: Use of Amphibian
Communities as Indicators of Restoration Success
Task Summary and Objectives: Declines in amphibian populations have been documented by scientists worldwide from many regions and habitat types. No single cause for declines has been demonstrated, but stressors like acid precipitation, environmental contaminants, the introduction of exotic predators, disease agents, parasites, and the effects of ultraviolet radiation have all been suggested. Because of their susceptibility to these and other stressors, amphibians are important as indicators of ecosystem health. Amphibians are present in all habitats and under all hydrologic regimes in the Everglades. The species present and the occupancy rate of a given species differ greatly across those gradients. These differences are due to hydropattern, vegetation, and other environmental factors. The combination of species composition and proportion of each habitat occupied at a given time form unique communities defined by those environmental factors. Therefore, if these communities can be reliably defined and measured, Everglades restoration success can be evaluated, restoration targets can be established, and restoration alternatives can be compared. This study will develop methodologies for defining and measuring the membership and area occupancy of amphibian communities. Further, we will investigate the relationship of occupancy of amphibians with hydroperiod and other environmental factors. Finally, we will provide a method for measuring restoration success based on these communities. The importance of amphibian communities to Everglades restoration has been recognized and listed as critical priority research needs (see USGS Ecological Modeling Workshop and the DOI Science Plan in Support of Greater Everglades Ecosystem Restoration).
We will use established sampling methodologies such as PVC refugia trapping to investigate amphibian occupancy rates, develop new methods for sampling across hydroperiod gradients (drift fence arrays, PVC arrays), and use newly developed statistical techniques to estimate the proportion of area occupied by and to define amphibian communities. Our objectives include:
Work to be undertaken during the proposal year and a description of the methods and procedures:
During FY06, we will concentrate our work on:
Duellman and Schwartz (1958) produced the first scientific survey of the amphibians of south Florida. This work serves as an excellent reference for the historical distribution of many species before the extensive habitat loss in south Florida during the second half of the 20th century. Meshaka et al. (2000) produced a species list of the herpetofauna for ENP, but little information about the habitat associations and population status of the species was contained in that report. Dalrymple (1988) provided a good description of the herpetofauna of the Long Pine Key area in ENP, but no attempt has been made to sample amphibians throughout the Everglades.
We used 2 primary methods to accomplish the objectives of the project:
Proportion area occupied by a species (Field work FY04-FY05, Analysis FY06).-- One problem with many of the methods used to sample amphibians is the lack of any control of the myriad environmental factors that affect the behavior and activity of the animals. Abiotic factors like temperature, humidity and hydrology as well as biotic factors like the presence of predators or conspecifics can affect the observability of amphibians. The observability of species' population is a function of the population size, the behavior of the individuals, and the ability of the observer to locate the animals in the particular habitat. Many monitoring programs simply count animals and do not control for this observability or capture probability (p). Therefore, comparisons over time or space are not possible or are biased. If the monitoring program can assume the cost of marking individual animals, then p can be determined and population size or density determined (standard mark-recapture methods, see Williams, et al. 2002). However, this would be cost prohibitive in a monitoring program for all amphibian species throughout the Everglades. MacKenzie, et al. (2002) has developed a novel approach to this problem. Rather than mark the individual, we "mark" the species. Therefore, presence/absence data from several plots within a habitat (or along a hydroperiod gradient in our study) provided an estimate of p and will allow estimation of the proportion of a stratum occupied by a given species at a given time.
Sampling units were chosen randomly within each stratum. Within Everglades National Park these were along the Main Park Road and Context Road. We chose 5 permanent sites along each road accessed by foot. The sites were located within 300 to 900 feet of the road. In Water Conservation Area 3A, we selected 5 permanent sites in each stratum along a North-South transect from I75 to SR41. Each stratum was defined by the hydroperiod observed from existing hydrologic data and habitat type as defined by existing GIS vegetation layers. Sites were visited twice biweekly, April through September. Further sites in each stratum were visited twice during the study to provide further information on a broader geographic scale.
Our standardized sampling unit was a circular plot of 20m radius. Plots were sampled after dark to increase the probability of observing nocturnal amphibians. At each plot 2-3 person crews began by listening for anuran vocalizations for 10 minutes. The abundance of each species was categorized as: no frogs calling, one frog calling, 2-5 calling, 6-10 calling, >10 calling, or large chorus. The intensity of the vocalizations were categorized as: no frogs calling, occasional, frequent, or continuous. After the vocalization survey, we performed a 30-minute visual encounter survey (VES) in each plot. During this time, all individual amphibians observed were identified to species and captured if possible. We recorded the species, categorized the age (egg, larvae, juvenile, sub-adult, or adult), measured and recorded the snout-to-vent length and recorded the sex when possible. The animal was released at the original capture site. We also recorded the substrate and perch height of the animal. A University of Florida Institutional Animal Care and Use Committee approval was obtained for animal capture. In addition to VES, we used funnel traps to attempt to capture aquatic amphibians. We also recorded several ancillary variables at each plot (air temperature, relative humidity, presence of water, water temperature, wind speed, cloud cover).
In addition, 20-1m tall, 5 cm diameter PVC removable pipes were installed in each site for refugia of treefrog species. During each visit, animals were removed from the pipe for identification and measurement as outlined above. All animals were released into the original PVC refugia. All PVC was removed at the end of the study.
At 10 sites in ENP (5 along Context Road and 5 along Main Park Road) we installed 20m of drift fence for capture of aquatic salamanders. The drift fence consisted of removable erosion control fence with a funnel trap incorporated at each end. The fence was arrayed as 4 separate 5-m fences in a grid around the center of the site. Traps were placed along the fence for 5 consecutive days once per month during May through October. The traps were checked each day in the morning to minimize heat stress on captured animals. Animals were measured as outlined above and released at the capture site. All traps and drift fences were removed during non-capture periods and at the end of the study.
Analysis during FY06. - Individual species capture histories (matrix of presence/absence of each species at a sampling period and plot) and corresponding covariates (habitat, hydroperiod, temperature, humidity) will be assembled. We will then estimate the proportion of each stratum occupied by a species and the capture probability (using MLE and the logistic regression for covariates; MacKenzie et al. 2002). The best model will minimize AIC and adequately estimate the parameters in the model (the candidate model list will be developed a priori based on ecological knowledge and will not include all possible combinations). We can then use these estimates to construct appropriate communities for each stratum (see proportion of area occupied by a community below).
Proportion area occupied by a community (FY06). - Given that species occupancy rates differ across hydroperiod gradients and that hydrology is the controlling factor of this difference (see above), we can begin to construct "communities." In Figure 1 below (letters represent species, the size of the circle represents PAO, numbers represent hydroperiod), we can see that in short hydroperiod sites, species A and D dominate. However, as we move to longer hydroperiod sites, other species emerge as the dominate species in the community. This pattern of species composition and PAO forms the set of "communities" along the hydroperiod gradient.
We have seen this pattern begins to emerge in preliminary data from the Everglades (Table 1).
At present, the method for defining and then predicting community composition and PAO is not complete. This study will develop this methodology for the Everglades.
Index of Biological Integrity (FY06). -- Indices of biological integrity (IBI) were originally developed to assess conditions of riverine systems (Karr 1991, 1993) and also have been developed successfully for use in terrestrial environments (O'Connell et al. 1998). The basic premise of IBI's is that a range of conditions of ecological integrity can be defined based on the structure and composition of a selected biological community (e.g. amphibians, fish, birds, macroinvertebrates). The concept of biological integrity provides an ecologically-based framework in which species-assemblage data can be ranked in a manner that is more informative than traditional measures such as richness and diversity (Karr and Dudley 1981, Brooks et al. 1998). Therefore, the final step in this project will be to develop an amphibian community index (ACI) for evaluating the success of restoration and management of Greater Everglades Ecosystems. The ACI will be modeled after previously developed IBI's (Cronquist and Brooks 1991, Karr 1991,1993, Books et al. 1998, O'Connell et al. 1998). Essentially, we will use the PAO of communities estimated above to index or define the integrity of a given stratum. As restoration proceeds, we can use changes in the index to make informed management decisions and to measure success. Further, we can use the pattern of these communities based on hydopattern to develop restoration targets and to compare alternatives. By providing a reliable and repeatable measure of ecological quality an ACI will help managers reach scientifically defensible decisions (Brooks et al. 1998).
Work to be undertaken during future FY's and proposed funding:
This project is scheduled to end in FY06.
Boughton, R. G., J. Staiger, and R. Franz. 2000. Use of PVC pipe refugia as a sampling technique for hylid treefrogs. American Midland Naturalist 144: 168-177.
Brooks, R.P., O'Connell, T.J., Wardrop, D.H., and Jackson, L.E.: 1998, "Towards a Regional Index of Biological Integrity: The Example for Forested Riparian Systems," Environmental Monitoring and Assessment, 51, 131-143.
Croonquist, M.J. and Brooks, R.P.: 1991, "Use of avian and mammalian guilds as indicators of cumulative impacts in riparian-wetland areas," Environmental Management 15, 701-714.
Dalrymple, G. H. 1988. The herpetofauna of Long Pine Key, Everglades National Park, in relation to vegetation and hydrology. Pp 72-86 In: Szaro, R. C., K. E. Stevenson, and D. R. Patton, eds. The management of amphibians, reptiles and small mammals in North America. U.S. Dept. of Agriculture, U.S. Forest Service Symposium, Gen. Tech. Rept. RM-166, Flagstaff, AZ.
Donnelly, M. A., C. Guyer, J. E. Juterbock, and R. A. Alford. 1994. Techniques for marking amphibians. In Heyer, W. R., M. A. Donnelly, R. W. McDiarmid, L. C. Hayek, and M. S. Foster, editors. Measuring and monitoring biological diversity: Standard methods for amphibians. Smithsonian Institution. Washington, D.C.
Duellman, W.E. and A. Schwartz. 1958. Amphibians and reptiles of southern Florida. Bull. Florida State Mus., no. 3.
Enge, K. M. 1997. A standardized protocol for drift-fence surveys. Florida Game and Fresh Water Fish Commission Technical Report No. 14. Tallahassee. 69 pp.
Karr, J.R. : 1991, "Biological integrity: a long-neglected aspect of water resource management," Ecological Applications 1, 66-84.
Karr, J.R. : 1993, "Defining and assessing ecological integrity: beyond water quality," Enironmental Toxicology and Chemistry 12, 1521-1531.
Karr, J.R. and Dudley, D.R. : 1981, "Ecological perspective on water quality goals," Environmental Management 5, 55-68.
MacKenzie, D.I., J.D. Nichols, G.B. Lachman, S. Droege, J.A. Royle, and C.A. Langtimm. 2002. Estimating site occupancy rates when detection probabilities are less than one, Ecology. In Press.
Meshaka, W.E., W.F. Loftus, and T. Steiner. 2000. The Herpetofauna of Everglades National Park. Florida Scientist 63(2): 84-103.
O'Connell, T. J., Jackson, L.E., and Brooks, R.P. : 1998, "A Bird Community Index of Biotic Integrity for the Mid-Atlantic Highlands," Environmental Monitoring and Assessment, 51, 145-156.
Williams, B.K., J.D. Nichols, and M.J. Conroy. 2002. Analysis and management of animal populations. Academic Press, London. 817 pp.
Specific Task Product(s):
U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 04 September, 2013 @ 02:09 PM(KP)
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