Download Ecology of Native and Exotic Anolis lizards in Southern Florida.

A Survey of Native and Introduced Anolis in
Southern Florida
Christine Hwang1, Eric Rackear2, Khary Alexander3,
Prince Vargas3, Villardie Latortue4
Westminster Christian School1, South Miami Middle Community School2,
Allapattah Middle School3, North Miami Middle School4
Abstract
This summer we performed a survey of native and introduced Anolis lizards in several
localities within Miami-Dade County. Our main purposes were (1) to see if the
population of A. carolinensis has changed since a 2005 Research in Ecology survey, (2)
to see if the introduced species are having a negative impact on A. carolinensis, and (3) to
see if there were any Anolis population differences between native and artificial habitats.
To carry out our study we used 100-meter transects in several native and artificial
habitats. We counted anoles along each transect and identified them according to species.
We also ran an analysis to see if our sampling methods were affected by differing
weather conditions during the transects. We found that the A. carolinensis encounter
rates were variable across 6 habitats: statistically unchanged in three of them,
significantly decreased in one, and significantly increased in two. We found that A.
sagrei, an introduced species with significant niche overlap to the native species, is far
more abundant than A. carolinensis in both the native and artificial habitats surveyed.
We also found that A. equestris was most abundant where smaller anoles were also
highly abundant and that A. distichus was most abundant along a street with old trees
with large trunks. We found no statistically significant difference in Anolis counts
between sunny and overcast days, supporting the sampling method we employed.
Introduction
Over 50,000 species of plants and animals have been introduced into North
America (Pimentel, 2003) and upwards of 15% of those species can be classified as
invasive in that they could potentially harm or have caused serious harm to native species
and/or ecosystems (Simberloff, 1996). Invasive species can cause serious economic
damage as well; one study estimates that between 1906 and 1991, 97 billion dollars in
damage was caused by 79 invasive species of plants and animals (OTA, 1993). Modern
costs have skyrocketed from there. Invasive species now cost the United States billions
of dollars a year in control measures and damages (Pimentel, 2003). We define
“introduced species” as a species intentionally or accidentally released into a habitat
outside of its native range. We define “invasive species” as a species that is established
outside of its native range and is reproducing to a degree whereby it may negatively
impact native species or ecosystems.
Florida offers a wide range of habitats and a relatively mild climate, potentially
facilitating the introduction process for tropical and subtropical species. In addition,
Miami has been a major gateway into the United States for plants and animals and the
volume of cargo passing through these ports into the U.S. increases yearly. These
combined forces add to the potential for introduction (Pimentel, 2003). In fact, there
have been numerous introductions of reptiles and amphibians into Florida, many of
which are believed to have damaged native species and ecosystems (Wilson and Porras,
1983). Among these introductions have been lizards of the genus Anolis (Wilson and
Porras, 1983; Ashton and Ashton, 1985).
South Florida is home to one native species of anole, A. carolinensis (Ashton and
Ashton, 1985). There are at least 10 species of Anolis introduced to Florida via various
pathways (FFWCC, 2006). At least three of these ten species are potentially important in
impacting the native anole in S. Florida: the bark anole, A. distichus, the Cuban Knight
anole, A. equistris, and the brown anole, A. sagrei. The bark anole was introduced to
Florida from the Bahamas and was first observed in 1946 (FFWCC, 2006). The Cuban
Knight anole was first observed in 1952 on the University of Miami campus, where it
was allagedly introduced there by students; it is originally from Cuba (Wilson and Porras,
1983). The brown anole has a wide distribution on Caribbean islands (Ashton and
Ashton, 1985) and was first observed in S. Florida in 1887 (Wilson and Porras, 1983).
The mix of anoles now living in S. Florida is a dynamic one. There is ample
evidence to suggest that these species are interacting with one another. For example,
both A. equistris and A. sagrei have been observed preying on smaller anoles, including
the native A. carolinensis (Wilson and Porras, 1983; Ashton and Ashton, 1985). Gerber
and Echternacht (2000) provided evidence for competition between A. carolinensis and
introduced anoles. Salzburg (1984) demonstrated that introduced anoles were competing
with one another. Roughgarden (1995) suggests that species with more niche overlap
will directly compete, with one species dominating and another ultimately disappearing
from the habitat. The introduced A. sagrei and the native A. carolinensis are roughly the
same size, inhabit the same positions in the environment, and feed on similarly sized food
items (Wilson and Porras, 1983; Ashton and Ashton, 1985). We will focus some of our
comparisons on these two species.
In 2005, the Research in Ecology at the University of Miami had one group
survey various habitats for anoles in S. Florida. The aim of this group was to look for
evidence that the native anole was being impacted by introduced anoles (Honorat et al.,
2005). We decided to resurvey many of their localities and look for further evidence of
an impact on the native anole by introduced anoles. We began our work by asking the
following questions:
(1) Were there significant changes in the A. carolinensis population?
(2) Are there more A. sagrei than A. carolinensis in artificial habitats?
(3) Are there more A. carolinenesis than A. sagrei in natural habitats?
(4) Is there a difference with finding anoles with overcast vs. sunny days?
We produced the following null hypotheses:
(1) There will be no difference between A. carolinensis counts between 2005 and
2006.
(2) There will be no difference between counts of A. sagrei and A. carolinensis in
artificial habitats.
(3) There will be no difference between counts of A. sagrei and A. carolinensis in
native habitats.
(4) There will be no difference in Anolis counts between sunny and overcast days
in similar habitats.
Methods & Materials
On the first day, we caught anoles using a noose which was attached to a fishing
rod. We then learned how to identify the anoles using the color of their dewlap, size,
shape of their head, location in the habitat, and behavior. The main characteristics of A.
carolensis are their green or brown color, pointed snout, and a reddish – purple dewlap
(Ashton and Ashton, 1985). The main characteristics of A. sagrei are their brown and
dotted skin, wide head, and red with white spotted dewlap (Ashton and Ashton, 1985).
Anolis distichus is small in size, usually spotted near the crown of the trees, and has a
light green or yellow dewlap, and it usually runs upward if something suspicious comes
near it (Ashton and Ashton, 1985). A. equistris is usually one foot in length, usually high
in a tree, and bright green with yellow spots (Ashton and Ashton, 1985).
We either drove or walked to a designated location and split up into two groups,
which consisted of two students each. Each group would establish a 100-meter transect
using two 50 meter tapes. A transect is a path along which one records and/or counts
occurrences of a phenomenon of study, in this case, Anolis lizards. A fifth team member
acted as timekeeper and recorder of data. Each group would move from one 5-meter
interval to the next along the transect and look for and identify anoles. After each twominute observation, we would tell the recorder what species and how many of that
species we had found at a particular interval. Because each transect was 100 meters in
length, we stopped twenty times to take observations per transect.
After each transect, we would calculate the encounter rate of each species of anole
at an area. We divided the number of stops where a given species was observed by the
total number of stops possible in a transect (20). Chi–square analyses and the 2–way
ANOVA were performed using Statview 5.0.
RESULTS
We sampled 10 different sites: (1) University of Miami (near Physics Building),
(2) UM (near Memorial Building), (3) Urbino Street, (4) Barracoa Street, (5) Ancona
Street , (6) Lenny & Penny Thompson Park , (7) Barnes Park, (8) Tropical Park (natural),
(9) Tropical Park (Australian pine), (10) Mathesson Hammock Park. We did a total of 25
transects, 13 in artificial sites and 12 in natural sites. We calculates percentages for
anoles encountered per locality and found the greatest percentage of anoles at Barnes
Park (31%) (Fig.1).
We found a total of 624 anoles. This included 41 A. carolinensis, 467 A. sagrei,
94 A. distichus, and 22 A. equestris. We calculated encounter rates by dividing the
number of intervals at which anoles of each species were observed by the total possible
number of encounters per transect (20). The highest encounter rate for A. carolinensis
was at Mathesson Hammock Park (0.15) and the lowest was at the Memorial Building at
University of Miami (0) (see Table 2). The highest rate of encounter of A. sagrei was at
Mathesson Hammock Park (0.95) and the lowest was at the University of Miami
Memorial Building (0.075). We found 24 A. carolinensis, 185 A. sagrei, 31 A. distichus,
and 4 A. equestris in natural habitats. We found 17 A. carolinensis, 282 A.sagrei, 63 A.
distichus, and 18 A. equestris in an artificial habitat.
We tested the null hypothesis that there would be no difference in counts of the
native anole, A. carolinensis, between the 2005 and 2006 Research in Ecology anole
surveys. The results of our Chi-square analyses suggests that counts between years are
dynamic across the six localities examined (Table 1 and 2). Three localities had no
significant change in counts between 2005 and 2006. At one locality (Barracoa Street) a
significant decrease was observed (χ2 = 17.64, df = 1 p<.005). At the final two localities
(Larry and Penny Thompson Park and Barnes Park) significant increases were observed
(χ2 = 5.44, 10.28, .01<p<.025). Next, we tested the null hypothesis that there would be no
difference in counts between A. sagrei and A. carolinensis in artificial habitats. The
results of our Chi-square analysis indicate that there are significantly more A. sagrei than
A. carolinensis in artificial habitats (χ2 = 266.97, df = 1, p<.005) (Fig. 2). Further, we
tested the null hypothesis that there would be no difference between A. sagrei and A.
carolinensis in native habitats. The results of our Chi-square analysis indicate that there
are significantly more of the introduced A. sagrei than the native A. carolinensis in native
habitats surveyed (χ2 = 124.02, df = 1, p <.005) (Fig. 2). Finally we tested the null
hypothesis that there would be no difference between anole counts on sunny vs. overcast
days. The result of our two-way ANOVA indicates that there were not significantly
different counts recorded across the two weather conditions (Table 3).
DISCUSSION
From 2005 to 2006, our study results are inconclusive with regard to changes in
the populations of A. carolinensis. We did observe significant changes in counts at three
of six localities; however, one change was a decrease and two were increases. This study
is comprised of two summers of data and only compares six localities. We recommend
resampling these locations through a greater period of time. We also recommend
increasing the number of localities across which A. carolinensis population can be
compared. A larger data set through several more years might enable a more conclusive
statement regarding trends in the native anole’s populations. It is interesting to note that
the two significant population increases that we detected occurred in native habitats
(Larry and Penny Thompson Park and Barnes Park) whereas the one decrease (Barracoa
Street) is an artificial habitat (see Figure 1). While A. sagrei and A. carolinensis
experience considerable niche overlap based on the “formula’ provided by Roughgarden
(1995), it is important to note that one of the greatest encounter rates we recorded for A.
sagrei was along Barracoa Street (0.625). If populations of A. sagrei are increasing at
this locality, it could account for a decrease in the resident A. carolinensis population.
This may be a trend worthy of future attention.
The 2005 summer Research in Ecology group (Honorat et at. 2005) found a
negative correlation between the presence of A. sagrei and A. carolinensis. Our findings
support their conclusions in both native and artificial habitats. Both years’ studies
support Roughgarden’s (1995) arguments in that species with considerable niche overlap
will directly compete and one will decline. We recommend that future studies focus on
this relationship, perhaps through the use of controlled removal experiments.
We predicted at the outset of our study that we would find more A. carolinensis in
native habitats. In fact, our greatest encounter rate (0.125) for the species occurred in
native habitat within Barnes Park (see Figure 2). Our findings suggest that A. sagrei is
successful throughout the habitats sampled; we only had one example of any other
species of anole with a greater encounter rate. According to Ashton and Ashton (1985) A.
distichus inhabits larger trees with trunks of larger diameter. Our greatest encounter rate
with this species took place along Barracoa Street which has numerous older trees with
large trunk diameters. Wilson and Porras (1983) and Ashton and Ashton (1985) indicate
that A. equestris prey on smaller anoles. Our findings support this relationship in that
greatest encounter rate we recorded for A. equestris took place along Urbino Street. Also
recorded along Urbino Street were some of the greatest encounter rates for A.
carolinensis, A. distichus, and A. sagrei, all potential prey items. The high encounter rate
with A. equestris in Tropical Park in the Australian Pine grove might reflect the fact that
spotting lizards on the barren trunks of those trees was easier than the more foliated and
complex habitats elsewhere in the study.
Finally, we wanted to test our sampling methods and check to see if our anole
counts differ between sunny and overcast days. Our findings confirm that there are not
significantly different counts between sunny and overcast days.
Figures and Tables
Table 1. Anolis carolinensis counts for each location surveyed from 2005-2006 along
with statistical significance of change observed.
Location
A.
carolinensis
counts 2005
A.
carolinensis
counts 2006
χ2
P value
UM Campus
Barracoa St.
5
23
2
2
1.3
17.6
.25 < p < 5
p < .005
Ancona St.
Larry & Penny
Thompson
Park
Barnes Park
5
1
3
8
.5
5.4
1
13
10.3
p < .005
Tropical Park
4
3
.14
.5 < p < 75
Condition
Not significant
Significant
decrease
.25 < p< .5 Not significant
.01<p<.025 Significant
increase
Significant
increase
Not significant
Table 2. Encounter rates for Anolis carolinensis for 2005 and 2006 at six surveyed
locations.
Encounter rates for A. carolinensis
2005
2006
UM Campus
.09
.025
Barracoa St.
.23
.05
Ancona St.
.10
.05
Larry & Penny Thompson
.01
.06
Location
Park
Barnes Park
Tropical Park
.01
.08
.125
.05
Table 3. The results of a 2-way ANOVA examining the differences in Anolis counts
between sunny and overcast days in native and artificial habitats. Only native habitats
were compared to native and artificial to artificial.
Source of
Variation
Habitat
Weather
Habitat x
Weather
Residual
Total
DF
SS
MS
F
P
1
1
1
115.783
363.055
2216.469
115.783
363.055
2216.469
0.178
0.559
3.411
0.677
0.462
0.078
23
26
14944.978
17834.296
649.782
685.934
UM Physics
10%
0%
7%
Memorial
0%
10%
7%
Tropical Park Natural
Austrailian Pine
7%
9%
Matthiesen Hammocks
Barnes Park
Larry and Penny Thompson
Park
Barracoa Street
22%
28%
Ancoa Street
Urbino Street
A. carolinensis found
Total Anoles Found
UM Physics:
Memorial:
10%
5% 0%
Tropical Park Natural
7%
7%
5%
Austrailian Pine
5%
Matthiesen Hammocks Park
10%
Barnes Park
Lenny and Penny Thompson
Park
20%
Barracoa Street
31%
Ancona Street
Urbino Street
Figure 1. Geographic distribution of A. carolinensis found and total anoles found.
Native Habitats
200
180
160
Count
140
p < 0.005
120
100
80
60
40
20
0
A. carolinensis
A. sagrei
Species
Artifical Habitats
300
250
Count
200
150
100
p < 0.005
50
0
A. carolinensis
A. sagrei
Species
Figure 2. Comparison of A. carolinensis counts vs. A. sagrei in both native and artificial
habitats.
Acknowledgements
We would like to thank the many dedicated and hard working people that helped to make
this program a success. First of all, we would like to give a special thanks to Dr. Michael Gaines
for organizing and overseeing the program. We also appreciate the wonderful guest lectures that
he set up so that we could gain further enrichment into the field of Ecology. Second, we would
like to thank Dr. Dana Krempels for her innovative lessons, leadership, and patience. Third, we
would like to thank Dr. DeAngelis and Mr. Danté Fenolio for working with us to make us better
researchers and for not going absolutely crazy when we lost our data. Their guidance and
tenacity has greatly improved the way we think about science. Fourth, we would like thank Ms.
Suzy Papas and Ms. Daneesha Wilson for bravely teaching Statistics and Computers to hyper 11
and 12 year olds in the summer. Fifth, we would like thank Miss Jessica Snug and Mr. Vevek
Parikh for offering us help when we needed it and keeping us on a track towards success in this
program and in the rest of our lives. Finally, we would like to show appreciation to University of
Miami for letting us study and learn on campus and for providing us with transportation to see
the many sights off campus that we may have never had the opportunity to see before.
Literature Cited
Ashton , R.E. and P.S Ashton. 1985. Handbook of Reptiles and Amphibians of Florida. Part
Two: lizards, turtles, and Crocodilians. Windward Publishing Inc. 191pp.
Florida Fish and Wildlife Conservation Commission (FFWCC). 2006.
http://www.myfwc.com/critters/exotics
Gerber, G.P. and A.C. Echternacht. 2000. Evidence for a symmetrical intrigued predation
between native and introduced Anoles lizards. Oncologia 124 (4): 599-607.
Honorat , R., T. Joseph , A .Reyes, A. Clarke , F. Irizarry, and J . Smith. 2005. A survey of
native and introduced Anolis lizards in southern Florida . The Howard Hughes Medical
Institute , and The University of Miami , Department of Biology.
OTA. 1993. Harmful Non-Indigenous Species in the United States. Washington, DC: Office of
Technology Assessment, United States Congress.
Pimentel, D. 2003. Economic and ecological costs associated with aquatic invasive species.
Cornell University: http://sgnis.org/publicat/proceed/aide/pime2003.htm.
Roughgarden, J. 1995. Anolis lizards of the Caribbean Oxford University Press 200pp
Salzburg, M.A. 1984 . Anolis sagrei and Anolis cristatellus in southern Florida: a case study in
interspecific competition. Ecology 65:14-19.
Simberloff, D. 1996. Impact of Introduced species in the United States. Consequences 2(1). US
global change office
Wilson, D.W. and L. Porras. 1983. The Ecological Impact of man on the South Florida
Herpetofauna. University of Kansas Museum of natural History: Special Publication No.
9. 89 pp.