This study used GIS to map waterways, the Everglades boundary, and single-family homes in Dade County, Florida in order to assess risks from the invasive spectacled caiman. The analysis found that 14% of waterways are within 2 miles of the Everglades and 4.6% intersect it, representing potential pathways for caiman to migrate into the ecologically sensitive wetland. Additionally, a significant portion of homes are near waterways, indicating danger zones where people could encounter caimans. The map produced will help focus future management efforts on controlling the caiman population before it becomes established within the Everglades.
This is an overview of my MS in Sustainability thesis project. It is a baseline structural investigation of connectivity within the exurban construct using Delaware, Ohio as a case study. Delaware was chosen because it exhibits exurban characteristics with landscape typologies that span the urban to rural continuum and because the area is under intense development pressure from the large urban area of Columbus, Ohio 10 miles to the south.
This is an overview of my MS in Sustainability thesis project. It is a baseline structural investigation of connectivity within the exurban construct using Delaware, Ohio as a case study. Delaware was chosen because it exhibits exurban characteristics with landscape typologies that span the urban to rural continuum and because the area is under intense development pressure from the large urban area of Columbus, Ohio 10 miles to the south.
Some of the coolest imagery around is lidar derived. Such is the case with the bare earth images produced from Continental Mapping's work in the Yukon Delta Wildlife Refuge.
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A Study of Dade County, Florida: In Regards to the Spectacled Caiman
(Caiman crocodilus)
By Teonia Manley
Introduction:
Dade County, Florida is well known for its problems with many invasive species. These
issues can be particularly problematic due to part of the Everglades lying within Dade County.
The Everglades is a very unique environment because of its subtropical climate and wetland
ecosystem. The area is susceptible to invasion because it is surrounded by urban and agricultural
habitats and has had significant disturbance caused by human activities (Everglades Invasive
Reptile and Amphibian Monitoring Program, n.d.; Everglades - National Wildlife Federation,
n.d.).
One such invasive species is the Spectacled Caiman (Caiman crocodilus). It was first
discovered in Dade County in the late 1950s and established a breeding population there in the
1970s. Efforts have been made in Dade County to extirpate the species, but there has been little
success (Nonnatives-Spectacled Caiman, n.d.). There is a concern that if the population
continues to grow and migrate the caiman could eventually establish itself in the Everglades. If
this occurs it will be extremely difficult if not impossible to remove them.
The purpose of the study is to provide some basic information on key areas of concern
and to ultimately provide a map for future work with the spectacled caiman. Due to the
spectacled caimans preference for canals in the area as well as an ability to habitat any riverine
habitat, one portion of the study focuses on the canals and waterways of the county. It examines
the proximity of these potential habitats to the Everglades. Another portion of the study focuses
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on the proximity of single family homes to the canals and waterways. It allows for assessment of
possible danger zones where people could be in danger of coming in contact with this potentially
dangerous species.
Ultimately, the purpose of this study is to provide a map that will be useful in future work
with the spectacled caiman. GIS provides a useful set of tools that can be very helpful in efforts
to extirpate or study the species. For example, GPS locations could be added to the map and then
spatial analysis could be preformed over a period of time to determine population growth and
migration. This information could also be used to perform a risk assessment in regards to the
spectacled caiman migrating into the Everglades, and provide a timeline to scientists and
government officials on how long they have to remove the species before it is too late. It can
also indicate possible trouble areas to focus on if funding is an issue. Another example, is
research on the reproduction of the species. Spectacled caimans sexes are determine by
temperature. GPS locations of nesting areas can be added to the map as well as average
temperature readings. These can be used to predict sex ratios and allow scientist to predict the
trend of population growth based on sex and how reproduction can be affected by such sex
ratios. Finally, the map could be useful for other invasive species as well as it includes basic
information that can be applied to a wide array of studies.
Methods:
I began the project by downloading the base layer of Dade County. I retrieved the file
package for the County Outline Boundary from miamidade.gov self service GIS database
(http://arcgisinter.miamidade.gov/GISSelfServices/GeographicData/MDGeographicData.html).
The package included six files in DWG format. All files in the database are in US Feet, North
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American Datum 1983 (NAD83), State Plane Coordinate System Florida East (FIPS Zone 0901).
All future layers are projected into this coordinate system.
I next downloaded a shapefile (enp_boundary_line.shp) for the Everglades National Park
from the Florida Coastal Everglades Long Term Ecological Research webpage
(http://fce.lternet.edu/data/GIS/?layer=enp). This file comes in a different projection (UTM,
Zone 17, WGS84) and had to be re-projected.
With both files added to the map I then preformed an intersect with the shapefile and the
polygon layer from the county outline package. Once the intersect was performed I removed the
shapefile layer of the Everglades and finished with a map of Dade County showing where the
Everglades intersects it.
To provide a more put together look of the Everglades boundary I drew in its left
boundary. I did this by beginning an editing session with the intersect file and choose to use line
and trace with snapping activated. I traced the outer left boundary of the county that the
Everglades intersected and finished by merging the line segment to the Everglades intersect.
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I then added a layer for canals obtained from the USGS (http://sofia.usgs.gov/
publications/circular/1275/gisdata.html). This came as a zip file with layers for canals in
Southern Florida from 1920s-1990s, each file encompassing ten years. These files came in a .adf
extension, which I believe is the Arc/Info Binary Grid format. I only used the files for 1990.
The layer covered all of Southern Florida, so I performed another intersect with the county
boundary and resulted in only the canals and waterways for Dade County.
With those steps done the map was then ready for the first analysis. I carried out a couple
select by locations between the canals and waterways layer (target layer) and the Everlgades
boundary layer (source layer). I did two querys one for all canals and waterways within 2 miles
of the boundary and another for all canals and waterways that intersect the boundary. I
arbitrarily chose two miles, because I was unable to find information on how far the spectacled
caiman could travel. I chose a 2 mile distance on the understanding that caimans can travel rather
quickly in water. I applied a reference number in the attribute table for the canals and waterways
for each set of results. These reference numbers where then used to perform a dissolve on the
Canals and Waterways layer. I used the reference numbers as the field for the dissolve so that all
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canals and waterways were placed into three groups based on there reference number. I also
added the Sum statistic function for the length field. I used this statistic to then calculate what
percent of the total length each query was attributed to. Then I produced a pie chart using the
new disolve layer. The new disolve layer was also used for the symbology. The map was
finished by adding color to the base layer, a boundary symbology to the Everglades and the final
colors to the canals and waterways.
The next part of the study focuses on single family homes in Dade County and their
proximity to the canals and waterways. I began this by adding an additional data frame and
copying over the Everglades boundary layer, the Dade County layer, and the canals and
waterway layer. I removed the symbology on the canals and waterways making it all one color
and size, so it does not distract from the house information. I then downloaded data from
miamidade.gov on single family homes. This came as a file package as well
(smallbuildings2005.dwg), which contained information on small buildings determined to be
single family homes during an aerial survey.
The layer was then used in set of select by location queries. I also arbitrarily chose the
numbers for these selection. I used the assumption that the caiman could not travel to far without
tiring easily; therefore, I used measurments in feet insead of miles. The queries were for houses
within 500 feet and 50 feet of the canals and waterways. The target layer was the single family
homes and the source layer the canals and waterways. Unfortunately, changes could not be
made to the attribute tables for reference numbers. I could neither edit a previously made field
nor add a new field. I made a new layer from each selection so it could be represented. I used the
total (# out of # selected) located on the base of the attribute tables to get the numbers for how
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many houses were in each selection. These numbers were then used to calculate percentages.
Each house was then represented by a house symbol and color coordinated with its distance. I
made each house layer 40% transparent to make them easier to differentiate.
A third map was produced to provide a visual reference of Dade County's location in
Southern Florida. I added an additional data frame and downloaded a layer from the Florida
Coastal Everglades Long Term Ecological Research webpage (http://fce.lternet.edu/
data/GIS/?layer=enp). The file is a shapefile, polygon layer of the boundaries of counties in
Florida (COUNTYSHORE_AREAS.shp). I performed and attribute query for all counties named
Dade. I found there were several entries that matched. I then went to the symbology tab and used
the unique values option to mark all entries that were named Dade the color mars red.
I finished by placing all data frames in the final map. Legends for the Canals and
Waterways frame and the Single Family Homes frame were added. Scale bars were also added to
the previous frames. I added a picture of the spectacled caiman as well to provide a finished
appearance.
Results:
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The total length of all canals and waterways in Dade County is 196.568 miles. This was
determined from the sum value in the disolve layer that represented all canals and waterways.
The total length of canals and waterways within 2 miles of the Everglades was 27.562 miles.
This accounted for 14.02% of the total length of all canals and waterways. Canals and waterways
that intersect the Everglades was 9.049 miles, which is 4.6% of the total length of all canals and
waterways. While neither percentage was very high it is still enough to be disconcerting. 18.62%
of the canals and waterways offer a higher than usual possibilty for the spectacled caiman to
migrate into the Everglades. The dark blue in the pie chart below represents all canals and
waterways more than 2 miles from the Everglades. The lighter blue, second largest slice,
represents all canals and waterways within 2 miles of the Everglades. Finally, the greenish-blue
and smallest slice represents the canals and waterways that intersect the Everglades.
Total Length (ft)
1,005,587.74
270,513.617
47,778.488
Length of Canals and Waterways
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There was 394,817 single family homes in Dade County in 2005. About 1.02% of those
homes are within 50 feet of canals and waterways. Therefore, 4,044 single family homes lay
within a high risk zone for coming into contact with possible spectacled caiman habitats. Homes
that are within 500 feet account for 9.5% of all single family homes. While contact is still
possible for the inhabitants of these 37,550 homes, it is not nearly as likely as those within 50
feet.
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Discussion:
A few recommendations can be made based upon the results; however, they would be
more credible if actual migration distance and time was found for the spectacled caiman. For
instance, areas of the canals and waterways within 50 feet of the single family homes should be
checked routinely for the presence of the spectacled caiman. If any efforts are made to remove
the spectacled caiman it should be done in the portions of the canals marked within 2 miles of the
Everglades.
Data Sources:
Miamiedade.gov:
http://arcgisinter.miamidade.gov/GISSelfServices/GeographicData/MDGeographicData.html
Florida Coastal Everglades Long Term Ecological Research:
http://fce.lternet.edu/data/GIS/?layer=enp
USGS:
http://sofia.usgs.gov/ publications/circular/1275/gisdata.html
Cited References:
Everglades - National Wildlife Federation. (n.d.). Home - National Wildlife Federation.
Retrieved December 6, 2011, from http://www.nwf.org/Wildlife/Wild-
Places/Everglades.aspx
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Everglades Invasive Reptile and Amphibian Monitoring Program. (n.d.). The Croc Docs.
Retrieved December 6, 2011, from http://crocdoc.ifas.ufl.edu/projects/eiramp/
Nonnatives - Spectacled Caiman. (n.d.). Florida Fish and Wildlife Conservation Commission.
Retrieved December 6, 2011, from
http://myfwc.com/wildlifehabitats/nonnatives/reptiles/spectacled-caiman/
