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The Influence of Hydrology and Associated Habitat Structure on Spatial and Temporal Patterns of Apple Snail Abundance and Recruitment

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Frequently-anticipated questions:

What does this data set describe?

The Influence of Hydrology and Associated Habitat Structure on Spatial and Temporal Patterns of Apple Snail Abundance and Recruitment
As the exclusive food of the endangered snail kite and prey to a variety of other wetland fauna, apple snails are generally recognized as a critical resource warranting monitoring in the context of the Greater Everglades ecosystem restoration. The overall goal of the project is to provide information to help predict the impact of changes in hydrology (and associated vegetation) to apple snail abundance following WCA-3A decompartmentalization.
This project is no longer funded by the USGS Greater Everglades Science Program: Place-Based Studies
  1. How should this data set be cited?

    Phil Darby Rob Bennetts, Unpublished Material, The Influence of Hydrology and Associated Habitat Structure on Spatial and Temporal Patterns of Apple Snail Abundance and Recruitment.

    Online Links:

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -81
    East_Bounding_Coordinate: -80.375
    North_Bounding_Coordinate: 26.375
    South_Bounding_Coordinate: 25.5
    Description_of_Geographic_Extent: wet prairie habitats in the Greater Everglades

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 02-Feb-2002
    Ending_Date: 31-Jan-2005
    Currentness_Reference: ground condition

  5. What is the general form of this data set?

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      Indirect_Spatial_Reference: WCA3

    2. What coordinate system is used to represent geographic features?

  7. How does the data set describe geographic features?

  8. What biological taxa does this data set concern?

    Taxonomic_Keyword_Thesaurus: none
    Taxonomic_Keywords: animals
    Taxonomic_Keywords: invertebrates
    Taxonomic_Keywords: single species
    U.S. Department of Agriculture - Agricultural Research Service (ARS)

    U.S. Department of Agriculture - Natural Resources Conservation Service (NRCS) Department of the Interior - U.S. Geological Survey Department of Commerce - National Oceanic and Atmospheric Administration (NOAA) Environmental Protection Agency (EPA) Smithsonian Institution - National Museum of Natural History (NMNH)

    Publication_Date: 2000
    Title: Integrated Taxonomic Information System (ITIS)
    Geospatial_Data_Presentation_Form: Database
    Retrieved from the Integrated Taxonomic Information System on-line database, <http://www.itis.gov>.
    Online_Linkage: <http://www.itis.gov>
    Snail abundance will be determined each year in five randomly selected wet prairie and five slough habitats using 1-m sq. throw traps.
    Estimates will be made of apple snail abundances in wet prairie habitats relative to slough habitats and in sites with foraging snail kites. Baseline seasonal apple snail egg production will be documented.
    General_Taxonomic_Coverage: Apple snails are identified to Species.
    Taxon_Rank_Name: Kingdom
    Taxon_Rank_Value: Animalia
    Applicable_Common_Name: Animals
    Taxon_Rank_Name: Phylum
    Taxon_Rank_Value: Mollusca
    Applicable_Common_Name: molluscs
    Applicable_Common_Name: mollusks
    Taxon_Rank_Name: Class
    Taxon_Rank_Value: Gastropoda
    Applicable_Common_Name: gastropods
    Applicable_Common_Name: snails
    Applicable_Common_Name: slugs
    Taxon_Rank_Name: Sub Class
    Taxon_Rank_Value: Prosobranchia
    Taxon_Rank_Name: Order
    Taxon_Rank_Value: Architaenioglossa
    Taxon_Rank_Name: Family
    Taxon_Rank_Value: Ampullariidae
    Taxon_Rank_Name: Genus
    Taxon_Rank_Value: Pomacea
    Taxon_Rank_Name: Species
    Taxon_Rank_Value: Pomacea paludosa
    Applicable_Common_Name: Florida apple snail

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

    • Phil Darby

  2. Who also contributed to the data set?

    Other project personnel include George Stewart and Don DeAngelis. Project personnel in FY 2003 include Jennifer DuPree and Jason Liddle.

  3. To whom should users address questions about the data?

    Phil Darby
    University of West Florida
    Department of Biology, University of West Florida

    11000 University Parkway
    Pensacola, FL 32514

    850 474-2647 (voice)
    850 474-2749 (FAX)

Why was the data set created?

The apple snail is an important performance measure in Comprehensive Everglades Restoration Plan (CERP) because it is the exclusive prey of the snail kite, and information on apple snail production and spatial distribution under different water management is essential for CERP evaluations.

The specific objectives for the project are as follows: 1) estimate apple snail abundance in wet prairie habitats (relatively short hydroperiod) relative to slough habitats (relatively longer hydroperiod) with potential linkages to snail kite foraging habitat selection; 2) estimate snail abundance in sites with foraging snail kites, and incorporate data from this study in to a larger coordinated effort to link snail kite habitat use and snail availability; and 3) document baseline seasonal apple snail egg production (not yet available in wetlands south of Lake Okeechobee) and assess the potential impacts of drying events on annual egg production.

How was the data set created?

  1. From what previous works were the data drawn?

  2. How were the data generated, processed, and modified?

    Date: Not complete (process 1 of 1)
    We will conduct a 3-year study in Water Conservation Area-3A (WCA3A) and Northeast Shark River Slough (NESRS)(if accessible). Based on 2002 results, we do not plan to access NESRS in 2003. The trends observed in 2002 show a strong effect due to habitat type. This is coupled with the fact that the sites are much drier than the other sites and therefore, we will be less likely to given permission to enter the area. We will sample additional sites in WCA3A. We will determine snail abundance each year in five randomly selected wet prairie (same 5 sites each year) and five slough habitats (same 5 sites each year) using 1-m sq. throw traps (approximately 50-70 throw traps in a 50 x 50 m area) per Darby et al. (1999). The throw trap data will be used to test the hypothesis that apple snail abundance is greater in wet prairie versus slough habitats. Site selection and classification will be based on habitat structure and the best available hydrologic information for the areas. The timing of all sampling will depend, in part, on hydrologic conditions and seasonal patterns in egg cluster production. Most throw trap sampling should be conducted from approximately February through April. Sites that are dry during this period will be sampled following reflooding (surviving snails emerge from aestivation within 24 h). Egg cluster surveys will provide data to avoid sampling during the period of greatest post reproductive mortality. Protocol modifications may be warranted to document unusual hydrologic events (e.g., extended or atypically timed dry downs or floods).

    We will characterize plant community composition (per cent species coverage for the area), substrate composition, plant stem density (1-m sq. quadrat samples, n=7) and periphyton abundance in all sampling sites. We will attempt to control for variation in all aforementioned habitat characteristics during sample site selection.

    Three wet prairie/slough habitats known to support foraging snail kites (locations provided from our own surveys or by the snail kite monitoring field crew; P.I., Wiley Kitchens, USGS-BRD) will also be sampled for snail abundance using throw traps. Comparisons to the randomly selected sites within a wetland unit will be made to see if kites forage in sites with relatively higher snail abundance. However, understanding how snail kites respond to apple snail abundance requires comparisons to foraging habitats spread throughout the snail kite’s range. Snail kites are highly nomadic, even in generally high-water years (Bennetts and Kitchens 2000), but no snail abundance data has been linked to kite movements. Data from this 3-year study will be examined as part of a coordinated effort via concurrent studies in the Loxahatchee N.W.R., Kissimmee Chain-of-Lakes, and potentially other areas in order to correlate snail abundance with snail kite habitat use. Such coordination enables us to increase our scope of inference across areas with a range of hydrologic regimes and varying substrate types (e.g., sand versus peat) and over a temporal and spatial scale relevant to the nomadic snail kites’ foraging range.

    Apple snail egg clusters provide critical information about the timing of the annual post-reproductive adult die off (Darby and Percival 2000). A 1m x 2.5m PVC quadrat will be flipped end over end 20 times in order to count egg clusters in each transect. Two egg cluster transects will be established in all of the aforementioned throw trap study sites (thus incorporating a hydrology effect) and sampled monthly from February - September each year (n=26 transects each month). Finally, 2 egg cluster transects will be established in each of 3 sites subject to frequent drying events and known to contain apple snails (e.g., portions of NESRS and northwestern WCA3A) in order to quantify recruitment losses related to drying events and/or potential resumption of oviposition after water levels rise following a dry down.

    Apple snail density data from an approximately 50 m x 50 m area tends to be distributed as a negative binomial (Darby et al. 1999). A likelihood ratio testing approach (per White and Bennetts 1996, see snail data in Darby et al. 1999) will be used to model apple snail density as a function of community type, substrate type, snail kite presence or absence (or possibly some index of foraging success or extent of kite use, if data were available) and time (+ interactions). Final model selection will be based on comparing Akaike's information criteria (AIC) values from a suite of candidate models (Burnham and Anderson 1998). We will evaluate a suite of candidate models that include each main effect separately as well as all possible combinations of interactions. Egg cluster counts will be analyzed using a generalized linear models approach as described in Darby and Percival (2000). The model for egg cluster production will include temperature, water level, community type, substrate type, and time (+ interactions) as independent variables. Final model selection will be based on an AIC approach as described above.

    Person who carried out this activity:

    Phil Darby
    University of West Florida
    Department of Biology, University of West Florida

    11000 University Parkway
    Pensacola, FL 32514

    850 474-2647 (voice)
    850 474-2749 (FAX)

  3. What similar or related data should the user be aware of?

    Bennetts, R. E. Kitchens, W. M., Dreitz, V., 2002, Influence of an extreme high water event on survival, reproduction, and distribution of snail kites in Florida, USA: Wetlands v. 22, no. 2, Society of Wetlands Scientists, McLean, VA.

    Burnham, K. P. Anderson, D. R., 1998, Model Selection and Influence: A Practical-Theoretic Approach: Springer-Verlag, New York, NY.

    Darby, P.C. Croop, J. D., Bennetts, R. E., , 1999, A comparison of sampling techniques for quantifying abundance of the Florida Apple Snail (Pomacea paludosa, SAY): Journal of Molluscan Studies 65, Malacological Society of London (Oxford University Press), Oxford, England, UK.

    Darby, P. C. Percival, H. F., 2000, Dry down tolerance of the Florida applesnail: effects of age and season: Final Report Research Work Order No. 182, U.S. Geological Survey, Gainesville, FL.

    White, G. C. Bennetts, R. E., 1996, Analysis of frequency count data using the negative binomial distribution: Ecology 77, Ecological Society of America, Washington, DC.

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?

  2. How accurate are the geographic locations?

  3. How accurate are the heights or depths?

  4. Where are the gaps in the data? What is missing?

    not available

  5. How consistent are the relationships among the observations, including topology?

    not applicable

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints: none
Project data are subject to change and are not citeable until reviewed and approved for official publication.

  1. Who distributes the data set? (Distributor 1 of 1)

    Phil Darby
    University of West Florida
    Department of Biology, University of West Florida

    11000 University Parkway
    Pensacola, FL 32514

    850 474-2647 (voice)
    850 474-2749 (FAX)

  2. What's the catalog number I need to order this data set?

    snail abundance data

  3. What legal disclaimers am I supposed to read?

    There are no explicit or implicit warrantees for the data.

  4. How can I download or order the data?

    • Availability in non-digital form:


    • Cost to order the data: none

    • Special instructions:

      Contact Phil Darby for data and information from this project

Who wrote the metadata?

Last modified: 23-Jan-2007
Metadata author:
Heather Henkel
U.S. Geological Survey
600 Fourth Street South
St. Petersburg, FL 33701

727 803-8747 ext 3028 (voice)
727 803-2030 (FAX)

Metadata standard:
Content Standard for Digital Geospatial Metadata Part 1: Biological Data Profile (FGDC-STD-001.1-1999)

This page is <https://sofia.usgs.gov/metadata/sflwww/darby_apple_snail.faq.html>

U.S. Department of the Interior, U.S. Geological Survey, Center for Coastal Geology
Comments and suggestions? Contact: Heather Henkel - Webmaster
Generated by mp version 2.8.18 on Tue Jan 23 03:54:31 2007