Effects of Cuban Treefrog (Osteopilus Septentrionalis) Removal

EFFECTS OF CUBAN TREEFROG (OSTEOPILUS SEPTENTRIONALIS) REMOVAL

ON NATIVE FLORIDA HYLA POPULATIONS

Miranda Cunningham

A Thesis Submitted to the Faculty of

The Charles E. Schmidt College of Science

In Partial Fulfillment of the Requirements for the Degree of

Master of Science

Florida Atlantic University

Boca Raton, FL

May 2015

ACKNOWLEDGEMENTS

The author wishes to express sincere gratitude to her committee members for all of their guidance and support. The author is grateful to the Florida Park Service and

Jonathan Dickinson State Park for allowing research to be conducted on state land. Last but not least, the author wishes to thank all of the park staff and volunteers that helped collect the field information, especially Ernie Cowan and Jeff Bach.

iv ABSTRACT

Author: Miranda Cunningham

Title: Effects of Cuban Treefrog (Osteopilus Septentrionalis) Removal on Native Florida Hyla Populations

Institution: Florida Atlantic University

Thesis Advisor: Dr. Jon Moore

Degree: Master of Science

Year: 2015

Invasive species are one of the major threats to biodiversity and understanding the effects any one invasive species has on members of its new ecosystem can help land managers decide how to best use their limited resources. This study attempted to show the effect Cuban Treefrogs (Osteopilus Septentrionalis) were having on native Florida hylids. For a year, Cuban Treefrogs were removed from three cypress domes and monitored in three other cypress domes, a change in the native population in the experimental domes was the eventual desired effect. Due to weather issues and low native hylid numbers no effect was shown, however due to environmental constraints an effect could not be ruled out either.

v DEDICATION

This manuscript is dedicated to my family, especially my husband, Rob, who has encouraged and helped beyond what one could ever hope for, and to my daughter,

Sophie, whose life has brought meaning to mine. I also dedicate this work to the late

Hank Smith, whose belief in me both professionally and academically made much of this work possible. EFFECTS OF CUBAN TREEFROG (OSTEOPILUS SEPTENTRIONALIS) REMOVAL

ON NATIVE FLORIDA HYLA POPULATIONS

List of Tables ...... ix

List of Figures ...... x

Introduction ...... 1

The Impacts of Invasive Species ...... 2

Control of Invasive Species ...... 3

Cuban Treefrog Life History ...... 3

Florida Native Treefrogs Life Histories ...... 5

Background and Rationale ...... 7

Study Site ...... 8

Study Objectives ...... 10

Hypothesis ...... 11

Methods...... 12

The Cypress Domes ...... 12

PVC Pipe Refugia ...... 13

Statistical Analyses ...... 16

Results ...... 17

Discussion ...... 37

Appendix ...... 46

vii References ...... 51

viii LIST OF TABLES

Table 1. Date of Surveys ...... 15

Table 2. Average Number of Cuban Treefrogs and Native Hylids Caught by Dome. .... 19

Table 3. Average Number of Native Species Caught by Dome ...... 21

Table 4. Study P-values and F ratios...... 23

ix LIST OF FIGURES

Figure 1. Locations in Jonathan Dickinson State Park of Six Cypress Domes...... 9

Figure 2. Initial Numbers of Native Hylids in All Six Domes ...... 18

Figure 3. Initial Numbers of Cuban Treefrogs (Os) in All Six Domes...... 18

Figure 4. Average Number of Native Hylids and O. septentrionalis Caught Over All

17 Surveys ...... 19

Figure 5. Total Number of Hylids Caught Across All Domes and Surveys...... 20

Figure 6. Total Number of O. septentrionalis Versus Native Hylids Average by

Dome...... 20

Figure 7. Average Number of Native Hylids Caught in Surveys by Dome...... 21

Figure 8. Total number of frogs by species in each dome for all surveys...... 22

Figure 9. Osteopilus septentrionalis in Control Versus Removal Domes...... 24

Figure 10. Number of Cuban Treefrogs (O. septentrionalis) Control Versus

Removal Domes Prior to Removal...... 25

Figure 11. Total Number of O. septentrionalis Captured in Control and Removal

Domes by Survey ...... 25

Figure 12. Combined Numbers of All Four Native Hylid Species in Control Versus

Removal Domes ...... 26

Figure 13. Treatment by Survey for All Four Native Hylid Species Combined...... 26

Figure 14. Hyla femoralis in Control Versus Removal Domes ...... 27 x Figure 15. Treatment by Survey for H. femoralis ...... 27

Figure 16. Hyla gratiosa in Control Versus Removal Domes ...... 28

Figure 17. Treatment by Survey for H. gratiosa...... 28

Figure 18. Hyla squirella in Control Versus Removal Domes ...... 29

Figure 19. Treatment by Survey for H. squirella...... 29

Figure 20. Hyla cinerea in Control Versus Removal Domes...... 30

Figure 21. Treatment by Survey for H. cinerea...... 30

Figure 22. Average SVL of O. septentrionalis Difference Between Control and

Experimental Treatment...... 31

Figure 23. Average SVL of O. septentrionalis Treatment by Survey ...... 31

Figure 24. Total number of O. septentrionalis in Control Versus Experimental

Treatment ...... 32

Figure 25. Osteopilus septentrionalis Treatment by Survey Excluding Pre-and Post-

Removal Data...... 32

Figure 26. Ratio of O. septentrionalis in Control Domes Versus Removal Domes in

Pre- and Post-Treatment Surveys...... 33

Figure 27. Number of O. septentrionalis for the 17 Surveys ...... 34

Figure 28. Average Number of Treefrogs Per Survey for Control Domes, Grouped

by Months Since a Freeze Event ...... 35

Figure 29. Only Surveys Were Domes Differed in Moisture Levels, in All Other

Surveys Domes Were Either All Wet or All Dry ...... 36

Figure 30. Number of O. septentrionalis Caught in Control Domes Only, Wet

Versus When They Were Dry ...... 36

xi Figure 31. Average Annual Rain Fall by Month in West Palm Beach, Florida, From

1981-2010...... 39

xii INTRODUCTION

Invasive plants and animals pose several of threats to indigenous species,

ecosystems, human activities, and are hard to control (Simberloff et al., 1997). The

economic impacts invasive species have in control costs, in native species losses, and agricultural damages are over 126 billion dollars a year in the United States alone

(Pimentel et al., 2005). In Florida, plants like Lygodium microphyllum (Cavanilles,

1810) cover cypress strands causing headaches for prescribed burners. Feral hogs (Sus

scrofa; Reichenbach, 1846) cause major ecological ground disturbances (Engeman et al.,

2004a). Cuban Treefrogs (Osteopilus septentrionalis; Duméril and Bibron, 1841), the

focus of this study, not only compete with, but also prey on, native hylids (Meshaka,

2001 and 2011). Florida is one of the leading states for invasive species and South

Florida is the top region in the country for exotic animals (Ferriter et al., 2005). Many

consider invasive species to be one of the top threats to biodiversity, second only to

habitat destruction and fragmentation (Vitousek et al., 1996). Not all non-indigenous

species become established, nor do all that do survive become invasive causing problems

ecologically (Simberloff et al., 1997). Many are innocuous or their threat is at least to

this point unknown. However, for those species that do become invasive and cause

problems within an ecosystem, management action is needed. Removal is often a just a

stop gap of maintaining a population at an acceptable low level, though eradication is

usually not an option for a well-established invasive species (Simberloff et al., 2005).

1 The impacts an invasive species has on native species can be divided into two basic categories, direct and indirect effects (Simberloff et al., 1997). A direct effect is when one species impacts another through predation, parasitism, or competition for the same food source or reproductive habitat (Groom et al., 2006; Moon et al., 2012). In contrast an indirect effect is when one species impacts another through the use of a third party (Moon et al., 2012). Observing the direct effects of an invasive species is often a much easier task than that of indirect effects. One example of a direct effect is that of the invasive Cane Toads (Rhinella marina; Linnaeus, 1758) in tropical Australia, they have caused the major decline of several predatory monitors who eat the toads and then die of the toxic poisons released by the toads (Doody et al., 2012). In many places the toads have caused a direct decrease in the predators by as much as 97% (Doody et al., 2012).

Some indirect effects include apparent competition and trophic cascades (Groom et al.,

2006, Moon et al., 2012) that are much more difficult to show because they require a greater understanding of community and ecosystem (Doody et al., 2012) rather than the simpler two species interaction. An indirect effect of Cane Toad invasion occurred with the Common Tree Snake (Dendrelaphis punctulatus; Gray, 1826), which is a prey species for monitors. As the monitor population was significantly decreased by the arrival of the

Cane Toad, the Common Tree Snake saw an increase in its population, most likely from the release of predation by the monitors (Doody et al., 2012). Many invasive species cause both direct and indirect effects though understanding the complete picture is often beyond the scope of one study. This project is an investigation to better understand the relationships, direct or indirect, between the Cuban Treefrog (O. septentrionalis) population and the native hylid treefrog populations.

2 Control for invasive species has three main parts; prevention, eradication, and maintenance at a low level (Simberloff et al., 2005). Common problems to all three include: 1) multiple agencies and stakeholders, which can produce jurisdictional

conflicts, 2) funding and adequate resources, and 3) disagreement of the threat

assessment of any one invasive species (Simberloff et al., 2005). The first part of control

is preventing an invasive species gaining entry into a foreign land and has little to do with

property managers. Prevention has more to do with state and federal policies and regulations along with the private industry self regulating (Simberloff et al., 2005).

When these policies and regulations fail, it leaves property managers to pick up the pieces in the next two phases. Eradication is most likely to be successful when infestations are caught early, but efforts are often stymied by lack of sufficient resources

(Simberloff et al., 2005). Finally, maintenance at a low level is where many invasive species programs find themselves. Common maintenance control methods include

mechanical, chemical and biological (The National Invasive Species Council, 2005).

Both mechanical and chemical control can be labor intensive and expensive, but are more traditional methods with less controversy than biological controls. Biocontrols can be effective if they work (Simberloff et al., 2005). The problem with biocontrols is that, more often than not, they do not work, are expensive to develop, and in some cases the biocontrols can do more harm than good and can eliminate native species instead of invasive (Cowie, 2001). For this study, the control method used to remove Cuban

Treefrogs is mechanical.

The Cuban Treefrog, the focus of this study, was first discovered in Key West in

1931 (Barbour, 1931) and was found in mainland South Florida in the 1940’s in Dade

3 County (Meshaka, 2001). In 1994 the Cuban Treefrog was captured at Jonathan

Dickinson State Park (JDSP) in Martin County; however, it was thought to only exist in ruderal areas particularly around buildings and not much of a threat to invade the natural habitats (Timmerman et al., 1994). However, a recent study showed that Cuban

Treefrogs were found in cypress domes, far from any developed areas (Rossmanith and

Cunningham, unpublished data).

Originally a native of Cuba, the Cayman Islands, the Bahamas and the Isle of

Pines, the Cuban Treefrog is a large hylid of the West Indian genus Osteopilus (Meshaka,

2001). There are seven other species in this genus and all eight share the distinct characteristic of having the skin fused to the skull, making them easily distinguishable from other hylids (Faivovich et al., 2005). The Cuban Treefrog also has large toe pads in comparison to other Florida hylids and in size dwarfs the native Florida tree frog species, with an average size range of 2.5 to 10 cm and some females can reach 15 cm (Johnson,

2010). The largest native, Barking Treefrog (Hyla gratiosa; LeConte, 1857), is at most

6.9 cm (Wright and Wright, 1942). Female Cuban Treefrogs are a third to twice as large as males (McGarrity and Johnson, 2009). They are an aggressive predators, shown to be a frog eater and cannibal (Meshaka, 2001; Wyatt and Forys, 2004). Their diet also includes many different invertebrates, small snakes and lizards (Johnson, 2010). Studies imply that when Cuban Treefrogs establish in an ecosystem, the native tree frog population goes down (Meshaka, 2001; Rice et al., 2011). Homeowners in Florida have claimed for years, that Cuban Treefrogs have replaced the native frogs they used to see around their homes (Johnson, 2010). The goal of this study is to experimentally test the effect of Cuban Treefrogs on native tree frog species.

4 The four native tree frog species of Jonathan Dickinson State Park, Green

Treefrog (H. cinerea; Schneider, 1799), Pine Woods Treefrog (H. femoralis; Bosc, 1800),

Barking Treefrog (H. gratiosa) and Squirrel Treefrog (H. squirella; Bosc, 1800), are similar to each other. All have a diet which consists of insects. All breed in the spring and summer, ranging from March to September (Wright and Wright, 1942). Tadpoles generally metamorphose around the same length of 50-75 days (Wright and Wright,

1942). The Barking Treefrog has the shortest time to metamorphosis with the low end of its range at 40 days and Pine Woods Treefrog the longest having a range up to 75 days

(Wright and Wright, 1942). Frog size and egg production are the biggest differences among the native hylids. Pine Woods Treefrog and Squirrel Treefrog are the smallest in size with a range of 2.5 – 3.8 cm and 2.2 – 4.1 cm, respectively. Green Treefrog is a medium to large frog at 3.2 – 6.4 cm and Barking Treefrog is the largest at 5.1 – 6.9 cm

(Wright and Wright, 1942). Egg production can be singular (Barking Treefrog and

Squirrel Treefrog) or in small films (Green Treefrog and Pine Woods Treefrog) (Wright and Wright, 1942). Native hylids can all be found in moist areas in trees, swamps or wetlands, with Barking Treefrog and Pine Woods Treefrog also being in trees in drier systems like pine flatwoods.

The Cuban Treefrog has characteristics predisposing it to invading novel ecosystems. Cuban Treefrog has a high fecundity laying up to 16,000 eggs for a large female in a year (Meshaka, 2001), short generation times (Meshaka, 2001) a broad diet

(Meshaka, 2001), and is very adaptable to many habitats including urban areas and natural ecosystems (Meshaka, 2001). Their ability to coexist with humans and human activity has helped to expand their range to peninsular Florida, much of the Caribbean,

5 and Hawaii (Salinas, 2006). Cuban Treefrogs are stowaways in cars, on shipments of nursery plants, and even on boat trailers (Johnson, 2010). Cuban Treefrog are also a part of the pet trade, which is believed to be the route of introduction into Hawaii (Meshaka,

2001). The Cuban Treefrog invasion north of peninsular Florida is limited by climate, but breeding populations have been established from a line south of Jacksonville to

Gainesville to Cedar Key (Johnson, 2010) and though successive freezes in 2010 and

2011 may have had an impact on northern populations, rebound is almost certain

(Johnson, 2010). One fear with Cuban Treefrogs and other tropical invaders is that with climate change their range, which is currently limited by temperature, will begin to increase northward (Rödder and Weinsheimer, 2009; Johnson, 2010).

Aspects of this invasive species’ behavior can be exploited in studies of its population biology. The Cuban Treefrog is active mostly at night and seeks refuge during the day in tight spaces (Meshaka, 2001). They can breed year-round with an emphasis on the late spring and summer months, coinciding with the Florida wet season

(Meshaka, 2001). Cuban Treefrogs can live in a wide variety of habitats from suburbia and agricultural sites, to natural environments like cypress domes, pinelands and hammocks (McGarrity and Johnson, 2009). Although study of Cuban Treefrog behavior requires nighttime observations, measurement of abundance and presence of Cuban

Treefrogs only needs daytime checks of refugia or artificial refugia established for this purpose. Boughton et al. (2000) developed the polyvinyl chloride (PVC) pipe refugia for tree frog species surveys done during the daytime

6 BACKGROUND AND RATIONALE

Simberloff et al. (2005) suggests that there are three stages to preventing

invasion: 1. Prevention 2. Eradicate shortly after arrival or before establishment and 3.

Manage at low levels. The Cuban Treefrog invasion in peninsular Florida is in stage 3

but is not to this point really being managed at any level in most places. Much of this is

due to a lack of concrete evidence on the impact that Cuban Treefrogs are having on the native tree frog populations or on ecosystems as a whole. They are not much more than a nuisance to the public and to this point have no known agricultural impact, so economically there are no major costs associated with Cuban Treefrogs (Johnson, 2010).

Land management agencies have a limited number of resources to spend on exotic species. Typically those resources are spent in areas where known positive gains will come or known negative impacts will occur if nothing is done. For Cuban Treefrogs neither of these scenarios is known with any great confidence so agencies largely ignore

Cuban Treefrogs and spend resources on more high profile and understood species like feral hogs or Burmese Pythons (Python molurus bivittatus; Kuhl, 1820). It has been

shown that removal of Cuban Treefrogs does have a positive impact on some native tree

frog abundance (Rice et al., 2011) but not necessarily survival. More studies are needed

to determine the effects of Cuban Treefrog invasion, so the priority for control can be properly determined.

7 STUDY SITE

The study area was contained entirely within Jonathan Dickinson State Park

(JDSP), which is managed by the Florida Park Service (FPS) under the Florida

Department of Environmental Protection (FDEP). JDSP is a 4,036 ha park in southern

Martin County in southeast Florida (Florida Park Service, 2012). JDSP was originally used as a top-secret military base during World War II. After the base was closed, it was turned over to the state in 1947 and opened as a state park in 1950. JDSP is known for its large intact sand pine scrub on the eastern edge of the park and the National Wild and

Scenic Loxahatchee River in the western portion of the park. Beside these two rare ecosystems, one can find 11 other natural communities including pine flatwoods, cypress domes and strands, wet prairies and depression marshes (Florida Park Service, 2012).

The park is home to over 40 designated plants and over 35 designated animals but, at the same time, at least 150 non-native plants and 18 non-native animals including Cuban

8 Treefrog are found in the park (Florida Park Service, 2012).

Figure 1. Locations in Jonathan Dickinson State Park of six cypress domes used in this study. Odd numbers represent control domes, even numbers represent removal domes.

9 STUDY OBJECTIVES

A recent study in the park tested a more efficient and safer technique for capturing

Cuban Treefrogs, since it was to be done during the day versus at night, and laid some

ground-work for this study. For Cuban Treefrogs, the park has no real removal method

employed and these frogs are now believed to be found throughout the park. Recent

studies have estimated population densities for specific locations (Campbell et al, 2010;

Rice et al., 2011); however no such study has been done at JDSP. A preliminary study

conducted at JDSP to test removal techniques and to find natural areas colonized by the

Cuban Treefrog (Rossmanith and Cunningham, unpublished data) formed the foundation for this thesis project. The two capture techniques used were the traditional visual

encounter survey done at night and PVC pipes checked during the day (Moulton et al.

1996; Boughton et al., 2000; Campbell et al., 2010). It was found that the PVC pipes

were overwhelmingly the most effective technique for catching Cuban Treefrogs

(Rossmanith and Cunningham, in review). Not only were more frogs captured, but it was safer and more efficient (Rossmanith and Cunningham, unpublished data), therefore this

present study used only the PVC pipes as the trapping technique. The natural areas tested

were cypress domes since an entire dome could be surveyed relatively easily. Cypress

domes will also be the natural area of choice for this project. The preliminary study answered the questions; where are Cuban Treefrogs and how do we catch them? In this work, I will address the following hypotheses:

10 Ho: Removal of Cuban Treefrogs has no effect on population size of native hylid treefrogs.

Ha: Removal of Cuban Treefrogs is followed by an increase in population sizes of native hylid treefrogs.

11 METHODS

The project included six cypress domes located in the park. The cypress domes

were chosen as the test community because it is known habitat for both native treefrogs

and Cuban Treefrogs (Rossmanith and Cunningham, unpublished data) and each dome

could be sampled completely. Six cypress domes were used, three control and three removal sites (Fig. 1). The domes had three different pairs of sizes; small (1 and 2), medium (3 and 4), and large (5 and 6) with one of each pair being either a control or a removal dome. The control domes were, one (0.09 ha), three (0.14 ha), five (0.15 ha) and the removal domes were two (0.08 ha), four (0.13 ha), and six (0.18 ha). JDSP is over

11,000 acres and the domes were chosen based on access, size, and distance apart from each other so that there would be no movement of Cuban Treefrogs between domes.

Vegetation in the domes is similar with a canopy of Cypress Trees (Taxodium ascendens;

Brongniart, 1833) and an under story dominated by Sawgrass (Cladium jamaicense;

Crantz, 1766), Pond Apple (Annona glabra; Linnaeus, 1753), Swamp Rosemallow

(Hibiscus grandiflorus; Michaux, 1803) and greenbrier (Smilax sp.). There was a vegetative density difference, with two domes having a much less dense under story but both had a highly dense island in the middle of the dome. Water level was recorded for each survey as being either wet or dry. Wet surveys had standing water across the majority of the dome. Densities of the Cuban Treefrog varied based on the size of the domes with larger domes having the largest population of Cuban Treefrogs. The domes were then blindly assigned to control or to removal based on size with one of each size 12 being in either control or removal. In the control sites Cuban Treefrogs were marked

with a unique toe clip (Donnelly et al., 1994) and released and native hylids were weighed and measured and released. In the removal domes Cuban Treefrogs were euthanized and native hylids were again weighed and measured and released. Native

hylids were not marked because of a previous study (Rossmanith and Cunningham,

unpublished data) finding marks not effective for the smaller native hylids, based on the

size of toe pads and frequency of capture. Weight using a ± 0.1 g Pesola scale and the

snout-vent length (SVL) using ± 0.1 mm calipers were also taken for all frogs. The frogs were shaken from the pipes and into plastic bags where the measurements took place.

Released frogs were let go onto the nearest natural feature, not released back into the pipe. The pipe was rinsed if water was available, filled if water was available, and hung back into place. If no water was available, all pipes were emptied and hung back dry.

Frogs were captured in PVC pipe refugia that were placed vertically in the domes.

All pipes were all 0.61 m in length. Three diameters were equally represented: 2.54 cm,

3.81 cm and 5.08 cm. The different pipe diameters were a holdover from a previous pilot study conducted by the Florida Park Service and was meant to account for the possible

different body sizes of frogs (Zacharow et al, 2003; Rossmanith and Cunningham,

unpublished data). The pipes were capped at the bottom and two holes were drilled 10.2

cm up from the bottom and hung using inverted peg board hooks. The caps provide a moist environment and the holes prevent the entire pipe from filling up (Boughton et al.,

2000). The pipes were set out at a density of 1096 total pipes per ha (Rossmanith and

Cunningham, unpublished data) and the typical dome was around 0.15 ha. The pipes

were open for a total of two years and 11 months (5/2008 – 4/2011). Table 1 lists the

13 dates of survey and whether or not the domes were wet at the time. Any one survey typically ranged over a few days, with the exception of survey 3 which was done in the aftermath of Tropical Storm Fay.

After the initial set up of the pipes, they sat open for an entire month before being checked to allow the frogs to find and begin using them. After the first month they were checked once a month for four months to establish a baseline estimated population. After the initial four months, the removal study began for the next year, with each dome being checked once a month. Then the pipes remained open and unchecked for another year to see what the recovery of the Cuban Treefrogs would be in the removal sites. This allowed for a real life management scenario of removal and then a break in management.

After one year of recovery, the pipes were checked for another four months for the final population estimation.

Table 1. Date of Surveys Survey # Year Month / Date Dome 1 Dome 2 Dome 3 Dome 4 Dome 5 Dome 6 1 2008 5/7 to 5/8 Dry Dry NS Dry NS Dry 2 2008 6/3 to 6/6 Wet Wet Wet Wet Wet Dry 3 2008 8/21 to 9/4 Wet Wet Wet Wet Wet Wet 4 2008 10/7 to 10/15 Wet Wet Wet Wet Wet Wet 5 2009 3/3 to 3/5 Dry Dry Dry Dry Dry Dry 6 2009 4/6 to 4/8 Dry Dry Dry Dry Dry Dry 7 2009 5/5 to 5/7 Dry Dry Dry Dry Dry Dry 8 2009 6/18 to 6/22 Dry Wet Wet Wet Wet Wet 9 2009 7/22 to 7/23 Wet Wet Wet Wet Wet Wet 10 2009 8/31 to 9/2 Wet Wet Wet Wet Wet Wet 15 Dry Wet Wet Wet Dry Dry

11 2009 10/17 to 10/24 12 2009 12/7 to12/9 Wet Wet Dry Wet Wet Dry 13 2010 1/24 to 1/27 Wet Wet Wet Wet Wet Dry 14 2011 1/24 to 1/25 Dry Dry Dry Dry Dry Dry 15 2011 2/23 to 2/25 Dry Dry Dry Dry Dry Dry 16 2011 3/22 to 3/23 Dry Dry Dry Dry Dry Dry 17 2011 4/20 to 4/21 Dry Dry Dry Dry Dry Dry List if dates for surveys and whether the domes were wet or dry at time of survey. NS – No survey

STATISTICAL ANALYSES

Analysis of variance (ANOVA), as implemented by JMP software (student

Edition 8), was used to analyze the experimental results for this project. Repeated measures two-way ANOVA was used to analyze treatment by survey, dome by survey and treatment by dome. Due to low degrees of freedom no three-way combination of treatment by survey by dome was done. The two-way combination of treatment by survey was the best way to see the effect of the treatment. Other ANOVAs included the ratios between control and removal of Cuban Treefrogs and Pine Woods Treefrog in the pre-surveys and post-surveys. Due to lack of frogs this could not be done with the other native hylids. In addition to ANOVA analyses, least squares regression was used to examine the relationship between frog numbers and months since a freeze event, independent of treatment; for this analysis, the raw count data for each dome was adjusted to a unit dome size, and all variables were normalized to a standard score.

RESULTS

Basic informational results which did not have any analysis done include pre removal numbers for native hylids (Figure 2) and for Cuban Treefrogs (Figure 3). The numbers exclude the first survey since it was not done at all six domes. The average number of Cuban Treefrogs and native hylids caught in all six domes are shown in Figure

4 and Table 2; this includes all surveys done in each dome. Since it was an average the first survey was not excluded for domes one, two, four and six; those domes were divided by 17 and domes three and five were divided by 16. The total number of Cuban

Treefrogs caught across all domes and the overall number of native hylids caught across all domes are shown in Figure 5, and in Figure 6 the total number of Cuban Treefrogs and native hylids caught in each dome are shown. The average number of native hylids by species per dome over the entire study is shown in Table 3 and Figure 7. Finally, in

Figure 8 shows the breakdown of frogs by species caught in each dome for each survey.

Figure 2. Initial numbers of native hylids in all six domes. Number of captures from surveys 2-4. Control domes - 1, 3, and 5. Removal domes - 2, 4, and 6.

Figure 3. Initial numbers of Cuban Treefrogs (Os) in all six domes. Number of captures from surveys 2-4. Control domes – 1, 3, and 5. Removal domes – 2, 4, and 6.

Figure 4. Average number of native hylids and O. septentrionalis caught over all 17 surveys except in domes three and five was over 16 surveys. Control domes – 1, 3, and 5. Removal domes – 2, 4, and 6.

Table 2. Average number of captures of O. septentrionalis by dome and average number of combined totals for native hylids (±SE). Avg. # Avg. # Os Domes Natives Captures Captures 1 8.00 ± 1.80 3.41 ± 0.62 2 2.70 ± 0.65 2.76 ± 0.57 3 19.87 ± 4.06 3.50 ± 1.14 4 5.35 ± 1.55 4.64 ± 1.30 5 18.75 ± 2.77 9.68 ± 2.94 6 20.88 ± 4.28 2.41 ± 0.92 Os – Osteopilus septentrionalis, Control domes – 1, 3, and 5. Removal domes – 2, 4, and 6.

Figure 5. Total number of hylids caught across all domes and surveys. P value – 0.002, F ratio – 4.317.

Figure 6. Total number of O. septentrionalis versus native hylids average by dome. Control domes – 1, 3, and 5. Removal domes – 2, 4, and 6. Os – Osteopilus septentrionalis, Hf – Hyla femoralis, Hg – Hyla gratiosa, Hs – Hyla squirella, Hc – Hyla cinerea.

Table 3. By dome the average number of native species (±SE) Avg. # Hf Avg. # Hg Avg. # Hs Avg. # Hc Domes captured captured captured captured 1 3.35 ± 0.64 0.05 ± 0.06 0 0 2 2.58 ± 0.53 0.18 ± 0.09 0 0 3 1.58 ± 0.56 0.29 ± 0.22 0.18 ± 0.10 1.24 ± 0.58 4 4.05 ± 1.34 0.47 ± 0.15 0.12 ± 0.08 0 5 1.41 ± 0.56 0.12 ± 0.09 5.53 ± 2.24 2.06 ± 0.67 6 2.12 ± 0.94 0 0.18 ± 0.18 0.12 ± 0.12 Hf – Hyla femoralis, Hg – Hyla gratiosa, Hs – Hyla squirella, Hc – Hyla cinerea. Control domes – 1, 3, and 5. Removal domes – 2, 4, and 6.

Figure 7. Average number of native hylids caught over all 17 surveys by dome. Control domes – 1, 3, and 5. Removal domes – 2, 4, and 6. Hf – Hyla femoralis, Hg – Hyla gratiosa, Hs – Hyla squirella, Hc – Hyla cinerea.

Figure 8. Total number of frogs by species in each dome for all surveys. Red lines indicate freeze events. Surveys 5-13 represent the removal phase. There is a one year break between surveys 13 and 14. Os – Osteopilus septentrionalis, Hf – Hyla femoralis, Hg – Hyla gratiosa, Hs – Hyla squirella, Hc – Hyla cinerea

Analyses were done on a set of data that included 17 surveys in six different cypress domes over almost three years. The data set includes three phases; phase 1 were

surveys 1-4 and represent the initial four months meant to establish a population estimate

for each dome, phase two was the removal phase as surveys 5-13 and phase three was the

second census study meant to establish the post-recovery population estimates. Table 4 provides a list of significant p values for these data

Table 4. Study P-values and F ratios. Treatment and Variables Natural Set of Data Recovery Treatment P value F ratio P value F ratio P value F ratio Avg. Os SVL TxS 0.1137 1.5329 0.3281 4.2833 0.025* 2.5697 Avg. Os SVL T 0.3899 0.7489 0.0478* 4.1085 0.0072* 8.1262 Os TxS 0.8125 0.6703 0.6214 0.8281 0.5962 0.8126 Os T 0.0232* 5.3970 0.0020* 10.6311 0.0087* 7.7112 Natives TxS 0.4856 0.9822 0.5679 0.8841 0.9507 0.3257 Natives T 0.0542 3.8377 0.0284* 5.0812 0.3854 0.7721 Hs TxS 0.6452 0.8327 0.6861 0.7611 0.3209 1.2101 Hs T 0.0305* 4.8840 0.0331* 4.7922 0.1006 2.8406 Hc TxS 0.0095* 2.2914 0.0371* 2.0565 0.4117 1.0602 Hc T 0.0001* 17.2544 0.0002* 16.7202 0.0139* 6.6852 Hf TxS 0.9905 0.3401 0.9730 0.3556 0.9251 0.3785 Hf T 0.1821 1.1817 0.2897 1.1489 0.7011 0.1497 Hg TxS 0.9940 0.3401 0.9878 0.2937 1 0 Hg T 0.5246 0.4091 0.6643 0.1905 1 0 SVL – Snout Vent Length, Os – Osteopilus septentrionalis, Hs – Hyla squirella, Hc – Hyla cinerea, Hf – Hyla femoralis, Hg – Hyla gratiosa. TxS – treatment by survey, T – treatment. * - significant P values. Natural Set of Data includes all surveys, Treatment and recovery includes surveys 5-17, and treatment includes surveys 5-13.

Three major findings were evident. First, there were fewer Cuban Treefrogs in the treatment domes versus the control dome during the removal and recovery period (Figure

9). In other words, Cuban Treefrogs were found less commonly in areas where they were removed. Prior to removal there was no statistical difference between the numbers of

Cuban Treefrogs found in the control domes versus the removal domes (205 and 206 frogs respectively) (Figure 10). However, two-way ANOVA with a cross of treatment and survey showed no statistically significant difference (Figure 11). So over time,

which is represented by the individual surveys, there was no significant difference between the number of Cuban Treefrogs found in the control domes versus the removal domes.

Figure 9. Osteopilus septentrionalis in control versus removal domes. Number includes totals for three control domes and three removal domes during removal and recovery phase. P value – 0.002, F ratio – 10.631.

Figure 10. Number of Cuban Treefrogs (O. septentrionalis) control versus removal domes prior to removal.

Figure 11. Total Number of O. septentrionalis captured in control and removal domes by survey, not the statistical model. Shaded box indicates the removal phase of the study (P value – 0.812, F ratio – 0.670, these values are from the ANOVA model run). Red lines represent freeze events.

Second, there were more native frogs in the control domes versus the removal domes during the removal and recovery phase (Figure 12 and Figure 13). This is the opposite of what was expected; over time the treatment of removal of Cuban Treefrogs had no effect on the total native population (Table 4 and Figure 13). There was actually a

significant in increase in Green Treefrogs over time in the control domes, but not in the

treatment domes (Table 4 and Figure 21)

Figure 12. Combined numbers of all four native hylid species in control versus removal domes. Number includes totals for three control domes and three removal domes during removal and recovery phase. P value – 0.028, F ratio – 5.081.

Figure 13. Treatment by survey for all four native hylid species combined. P value – 0.486, F ratio – 0.982.

Third, when looking at individual species, Pine Woods Treefrog and Barking

Treefrog were more commonly encountered in treatment domes than in control domes, but not significantly (Figures 14 and 16 respectively), therefore removal of Cuban

Treefrog in those domes did not greatly affect their numbers (Figures 15 and 17).

Squirrel Treefrog and Green Treefrog were significantly more prevalent in control domes

versus treatment domes (Figures 18 and 20 respectively). Green Treefrog also had

significant difference between the two-way analysis of treatment and survey (Table 4 and

Figure 21) but not the Squirrel Treefrog (Table 4 and Figure 19).

Figure 14. Hyla femoralis in control versus removal domes. Number includes totals for three control domes and three removal domes. P value – 0.289, F ratio – 1.149.

Figure 15. Treatment by survey for H. femoralis. P value – 0.991, F ratio – 0.340.

Figure 16. Hyla gratiosa in control versus removal domes. Number includes totals for three control domes and three removal domes during removal and recovery phase. P value – 0.664, F ratio – 0.191

Figure 17. Treatment by survey for H. gratiosa. P value – 0.994, F ratio – 0.313.

Figure 18. Hyla squirella in control versus removal domes. Number includes totals for three control domes and three removal domes during removal and recovery phase. P value – 0.033, F ratio – 4.792.

Figure 19. Treatment by survey for H. squirella. P value – 0.645, F ratio – 0.833.

Figure 20. Hyla cinerea in control versus removal domes. Number includes totals for three control domes and three removal domes during removal and recovery phase. P value – 0.0002, F ratio 16.720.

Figure 21. Treatment by survey for H. cinerea. P value – 0.010, F ratio – 2.291.

Other analyses were run on data that focused just on the experimental surveys.

The recovery data was the data collected one year after removal of frogs ended and was

intended to see the population recovery of Cuban Treefrog. By excluding the recovery

data and the pre-removal date, it was found that there were smaller, on average, Cuban

Treefrogs in the treatment domes (Figures 22 and 23), but not fewer Cuban Treefrogs

when looked at through the two way repeated measures ANOVA of treatment by survey

(Figures 24 and 25).

Figure 22. Average SVL of O. septentrionalis difference between control and experimental treatment, excluding the pre-removal and recovery data. P value – 0.007, F ratio – 8.126.

Figure 23. Average SVL of O. septentrionalis treatment by survey, excluding the pre-removal and recovery data. P value – 0.025, F ratio – 2.569.

Figure 24. Total number of O. septentrionalis in control versus experimental treatment, excluding pre-removal and post-removal data. P value – 0.009, F ratio – 7.711.

Figure 25. Osteopilus septentrionalis treatment by survey excluding pre-removal and post-removal data. P value – 0.596, F ratio –0.813.

Finally the Jolly-Seber Stochastic Method for predicting populations was not

possible due to the inconsistent number of recaptures. Instead, to see a change in the

beginning populations versus recovery populations of the control and removal domes the

ratio of Cuban Treefrogs between control and removal domes was calculated for pre-

treatment and post-treatment surveys (Figure 26) and an ANOVA was used to compare the ratios in paired pre- and post-treatment surveys. The first pair of surveys in each phase were excluded, since data was not collected for domes in the first pre-treatment survey. By a factor of almost seven to one, more Cuban Treefrogs were found in the

control domes versus the removal domes during the post-treatment phase (P value –

0.001, F ratio – 72.009).

Figure 26. Ratio of O. septentrionalis in control domes versus removal domes in pre- and post- treatment surveys.

During the three years in which this study took place, several natural events

occurred which directly impacted the hylids in this study. First, there were three major

freeze events in the middle of this study, which caused a significant die off of Cuban

Treefrogs (Figure 27). Between surveys 4 and 5, 12 and 13 and before 14 were when these freezes occurred and they were important because of when in the study it took place. Survey 5 marks the beginning of Cuban Treefrogs removal. Survey 13 was the last survey where Cuban Treefrogs were removed. Survey 14 was the start of the

recovery data (after a 1-year interval). The impact of the freezes on the experimental results could not be controlled for statistically, but will be examined further in the discussion.

To determine the relationship between freeze events and frog numbers independent of any removal effect, survey data from control domes was examined relative to the number of months since a freeze event (Figure 28). Least squares regression analysis of control dome surveys grouped by months since a freeze showed a highly significant, but opposite, relationship between frog numbers and freeze events for

Cuban Treefrogs and Pine Woods Treefrogs; standardized regression coefficients were

0.642 (P value - <0.0001) and -0.426 (P value -0.0023), respectively. No statistically significant relationship between months since freeze and frog numbers was found for any native frogs other than Pine Woods Treefrog.

Figure 27. Number of O. septentrionalis for the 17 surveys. Each survey includes the total number of Os for all six domes combined. Red lines indicate freeze events.

Figure 28. Average number of treefrogs per survey for control domes, grouped by months since a freeze event. Os – O. septentrionalis, Hf – H. femoralis, Hs – H. squirella, Hc – H. cinerea. H. gratiosa not shown due to multiple zero values.

Water readings were also recorded during each survey and analyzed for each

dome as either wet or dry. The domes were either all wet or all dry, except in surveys

two, eight, eleven, twelve and thirteen (Figure 29). Only 4 surveys occurred when all six domes were wet, and 7 surveys occurred when all six domes were dry. Dome 6 was the driest dome, having 11 surveys that were dry and domes 2 and 4 were the wettest with 9 surveys that were wet. There were overall more Cuban Treefrogs captured across all surveys and control domes when it was wet versus when it was dry but it was not significant (P value – 0.077, F ratio – 3.229) (Figure 30). Water level data was not used for statistical analyses because the experimental design for this study used control domes to account for factors other than removal, including water levels that were expected to affect frog populations.

Figure 29. Only surveys were domes differed in moisture levels, in all other surveys domes were either all wet or all dry. Domes that are wet or dry by survey, dry =1 and wet = 2. Control domes – 1, 3, and 5. Removal domes – 2, 4, and 6.

Figure 30. Number of O. septentrionalis caught in control domes only, wet versus when they were dry. (P value – 0.077, F ratio – 3.229)

DISCUSSION

This study did not find that Cuban Treefrogs were having an impact on native tree

frogs. However, as is often the case in experimental ecology it was not possible to

control for environmental factors that could confound treatment effects; although this

study failed to confirm an impact it does not rule out possible impacts.

This study attempted to experimentally demonstrate the impact of the Cuban

Treefrog on native hylid species. The null hypothesis was that the Cuban Treefrogs have

no significant effect on native hylids. The results in this study agree with that hypothesis;

more native species were found in the control domes than in the removal domes (Figure

12). Though a previous study found evidence that the invasive Cuban Treefrog had a negative effect on native hylids (Rice et. al. 2011), the present study did not reveal any significant effect. However, the experimental results may have been confounded by environmental disturbances, or conditions that vary annually and seasonally, but could not be controlled for statistically given the relatively short time-frame of the study.

Another consideration is the timing of the removals; they were done about once a month over a year, whereas another study (Rice et al., 2011) removed twice a month for year and did show a positive response by natives. Removing twice a month so that frogs are removed quicker, could mimic a more natural event like a freeze, where a massive die off of Cuban Treefrogs occurs in a very short period of time versus a slow steady removal, which allows for some recovery.

The three freeze events during the course of this study appeared to have had a

major impact on data collection. The timing of the freeze events occurred at points in the

study which did not allow for an accurate account of the dead frogs, many of which were

so decomposed that the species of frog could not be determined. In addition, the freeze events derailed the mark and recapture portion of the study, which could have provided another statistic for comparison between the control and treatment domes.

The freeze events could help shape management efforts in controlling Cuban

Treefrogs. If mimicking a freeze event allows managers to do multiple removals in a

month and have a better result than one removal a month multiple times over a year, it

could make scheduling removal times easier for management. This could mean land

managers can devote time and man hours at a key point or two in the year rather than dedicating time throughout the entire year. Based on this study, that time might be in

fall, both the 4th and the 11th survey (Figure 26) took place in October and they yielded

the two highest numbers of Cuban Treefrogs. October marks the end of breeding season

for Cuban Treefrogs (Meshaka, 2001) even though it is capable of breeding year round.

October is also when wet season rainfall totals begin to drop heading into the dry season

(Figure 31). Future studies of mass removals during different seasons, may yield the

best use of time for land managers in removal efforts for Cuban Treefrogs.

Figure 31. Average annual rain fall in West Palm Beach, Florida, from 1981-2010. Provided by the Florida Climate Center.

Removals may only be part of the solution and are not the best long term solution.

Focusing on a more overall ecosystem management may help to control or contain Cuban

Treefrogs. An improved and sustained fire management program could help to reduce

immigration into domes from the surrounding pine flatwoods. A sustained fire program

could help to reduce tree cover and snags which would reduce day time refugia for Cuban

Treefrogs. With less day time refugia, there could be less Cuban Treefrogs in habitats

surrounding cypress domes and thus reducing immigration. With less immigration

removal efforts could be more successful. The most important management could be

hydrological restoration, which could mean that some of the domes are wetter longer

allowing for more predatory fish. Predatory fish and their presence is one of the control

theories for Cuban Treefrogs (Meshaka, 2001). The nice thing about other management efforts, besides specific removal, is that many will be done or planned to be done regardless of Cuban Treefrog presence or not since they are an overall ecosystem benefit.

Another issue for the study could also be pipe bias. Rossmanith and Cunningham

(unpublished data) show that Cuban Treefrogs were more commonly encountered in pipes than in the visual encounter survey, but the native hylids were not. Therefore, a change in the population of the native hylids may not have been accurately captured by the pipes. Similar to the pipe bias is the overall starting population of native hylids within each dome (Figure 2). Some domes had small native populations to begin with

(domes 3, 5 and 6) or at least few found by the pipes suggesting that there was just not much of a native population left to rebound. The use of frog loggers, which can automatically record frog calls, in future studies could overcome some pipe bias of native hylids and help establish a population in a dome or help in confirming its absence. The length of time for the study may have also been an issue, in that it just did allow enough time for an impacted and barely hanging on native population to recover. Increasing the timeline of removal may have a positive impact on the native populations.

One major finding in this study was not the impact that the removal of Cuban

Treefrogs was or was not having on native hyla, but what impact it was having on the

Cuban Treefrog population in those removal domes. The average SVL in the removal domes during the time of the experiment was smaller than that of the control dome. This suggests that slowly the Cuban Treefrog population may have been on the decline and had the removal process continued then that may have been seen in the two-way ANOVA in the number of Cuban Treefrogs in the treatment domes. Immigration is going to play a factor in the decline, the domes were nowhere near a closed system and overcoming the immigration could take longer than the length of this study. This could explain why a year was not long enough to make an impact on the population as a whole.

The biggest question as to whether Cuban Treefrogs have a negative impact on

native hylids is raised by the control dome on the edge of Eaglesview recreation area

(Dome 5). This dome has the closest proximity to structures and to people and yet had the highest number of native hylids on average over the entire course of the study, by more than two-fold (Figure 4). It also had the third highest average number of Cuban

Treefrogs (Table 2). This dome also had high diversity, with all four native hylids being found in the dome at some point in the study. This dome does raise a lot of questions on

Cuban Treefrogs’ possible effects on natives. One question that should be asked is what the carrying capacity of a particular dome is? If that dome has enough resources to handle both Cuban Treefrogs and a healthy population of native hylids then maybe the

direct effect of Cuban Treefrogs on native hylids is not that great. Perhaps, the effect of

Cuban Treefrogs on native hylids are more pronounced in degraded systems or systems

that have a lower carrying capacity where predation and competition can have a larger

impact. A study of plant diversity and density and an invertebrate study could determine a carrying capacity for a particular dome or system. This could lead land managers to

focus on areas where natives might have a harder time surviving.

One basic fact cannot be ignored and that is Cuban Treefrogs were by far the most

dominant tree frog in the domes (Figure 5) by almost 3 to 1. With a ratio of Cuban

Treefrogs to native hylids that was highly significant (P value – 0.002, F ratio – 4.317).

Cuban Treefrogs were, on average, the most common frog in the control domes and in

one removal dome (Figure 4). The ratio of Cuban Treefrogs in the control domes versus

the removal domes in the pre versus post treatment surveys was also significant (P value

– 0.001, F ratio – 72.009). Caution needs to be taken though when looking at the

numbers here, since the surveys were done at different times of the year, 2-4 were in the summer and fall and surveys 15-17 were in the winter and spring. A freeze also occurred just two months prior to survey 15. It is interesting to note that, although a lot of environmental factors could be contributing to this significant ratio, almost seven to one

Cuban Treefrogs occurred in the control versus removal domes. The removal domes by far did not recover as quickly as the control domes when it came to major freeze events leaving, perhaps, a legacy of removal. In the pretreatment surveys the ratio was nearly one to one (Figure 26) and in post treatment it is between five and seven to one, and it

would be tempting to conclude that it was due to removal but that just is not the case.

Domes 2 and 4 had few frogs overall, and the Cuban Treefrogs were believed to have

been decimated by the first freeze event of this study. The population of Cuban

Treefrogs in those two domes did not recover, but it cannot be determined if that was due solely to the freeze or a combination of freeze and removal efforts.

The Cuban Treefrogs that were removed from the domes during this study were donated to a biology lab at Florida Atlantic University where they had their stomach contents analyzed. Of the 135 frogs examined only 94 (70%) were listed as having stomach contents and of those only 58 (62%) had identifiable parts. Of those 58 frogs only one had a known frog part in its stomach a Pine Woods Treefrog. Invertebrates made up most of the stomach contents. This could be due to low native hylid populations in the domes so there just were not many natives left to be eaten. It could also suggest that Cuban Treefrog impact on native hylids has to do more with direct competition and only occasionally predation. If competition is a major effect on native hylids, Cuban

Treefrog may have a greater impact on Green Treefrogs and Barking Treefrogs which are

closer in size to Cuban Treefrogs. This could be why Rice et al. (2011) showed that

Green Treefrogs went up in abundance once Cuban Treefrog removals began. If direct

competition were the major impact of Cuban Treefrog on native hylids it could explain

why on average there were more Pine Woods Treefrog in all the domes than any other

native tree frog species (except for dome 5 where Squirrel Treefrog was the highest, a

frog comparable in size to Pine Woods Treefrog) (Table 3 and Figure 7). Rice et al.

(2011) also showed that Squirrel Treefrog went up in abundance as well once Cuban

Treefrog was removed, but for both frogs this occurred only in one site. This suggests

that the relationship between native hylids and Cuban Treefrog is a complex one that

might be more site specific. Competition, predation, breeding and sometimes a

combination of all of the above have been anecdotal reasons as to why Cuban Treefrog is

having an impact on native hylids (Babbitt and Meshaka 2000; Salinas, 2006).

It is often difficult to quantify the impacts an invasive, especially an amphibian,

can have on an ecosystem or even on an individual species. A deeper understanding of

an invasive species’ impact may take a better understanding of the life histories of an

invasive but perhaps more importantly its native competitors. The American Bullfrog

(Rana catesbeiana; Shaw, 1802) is one of the most harmful invaders to freshwater

systems worldwide (Abbey-Lambertz et al., 2014). In Oregon it was found to affect one

native species, the Oregon Spotted Frog (R. pretiosa; Baird and Girard 1853), extirpating

it from 70% of its native range, but had smaller effect on another, The Red-legged Frog

(R. aurora aurora; Baird and Girard, 1852; Pearl et al., 2004). The difference in effects was based on a greater common use of similar habitats by the Oregon Spotted Frog with the American Bullfrog.

Overlapping with juvenile habitats may explain the decline of some native conspecific. In the case of the Green Anole (Anolis carolinensis; Voigt, 1832) and the

Brown Anole (A. sagrei; Duméril and Bibron, 1837) it is suggested that in disturbed areas the juvenile Green Anole is preyed upon by the adult invasive Brown Anole, as they share the same habitat (Echternacht, 1999). Once an adult, Green Anole occupies a different though still overlapping niche of Brown Anole, recruitment of Green Anole is

significantly reduced and it eventually leads to the collapse of the population in disturbed

sites (Echternacht, 1999).

Predation has been invoked as a major way invasive species lead to extirpation

and extinction. While competition has not been directly linked to the cause of extinction

of a native species, it has caused population declines (Davis, 2003). One reason as to

why competition does not get the lions’ share of the blame is that it perhaps takes longer

to cause an extinction than the quicker direct cause by predation or habitat loss (Davis,

2003). If this is the case, and it is the competition between Cuban Treefrogs and native

hylids that is having a greater impact than it would seem, long term studies would be

needed in order to show that interaction. The design of this study was more likely to

detect a predation interaction than competition.

Billions of dollars are spent each year on managing invasive species and being

able to show a negative impact on native species or systems helps to focus some of that

money. Removal of Feral Hogs (Sus scrofa) was in part justified by placing a monetary

value on the wetlands that the hogs damaged (Engeman et al. 2004b). It is also easy to justify removal of high profile invasive species like the Burmese Python (Python molurus bivittatus) not because of their ecological impacts but as a public safety issue to motor

vehicles and human safety (Harvey et al. 2013). Old World Climbing Fern is a plant that can cover the ground and reaches to the top of the canopy in cypress domes and sloughs, tree islands in the Everglades, and open wetlands (Langland and Hutchinson, 2013). The impact can be devastating for the system by killing trees and creating thick mats that cover and shade out plants including rare and endemic species (Langland and

Hutchinson, 2013). Old World Climbing Fern also creates an issue for fire managers by carrying fire into systems that might not naturally burn and by compromising fire control by carrying fire across fire lines (Langland and Hutchinson, 2013). Based on these multilayered negative effects is an easy choice for land managers to try to control Old

World Climbing Fern and its spread. With Feral Hogs, Burmese Pythons and Old World

Climbing Fern the damage is often easy to see, making the choice obvious to spend money on their management. For other species the impacts are not so clear cut. Cuban

Treefrogs are one of those species, which is why continued studies are needed to better establish their effects on native species and support the argument for a larger slice of the management pie.

APPENDIX

Raw data, number of frogs caught per survey by dome.

Treatment Dome Year Month Survey # OS HF HG HS HC 1 1 2008 5 1 4 6 0 0 0 1 1 2008 6 2 17 0 0 0 0 1 1 2008 8 3 11 0 0 0 0 1 1 2008 10 4 15 2 0 0 0 1 1 2009 3 5 7 3 1 0 0 1 1 2009 4 6 7 4 0 0 0 1 1 2009 5 7 4 2 0 0 0 1 1 2009 6 8 8 4 0 0 0 1 1 2009 7 9 7 1 0 0 0 1 1 2009 9 10 14 3 0 0 0 1 1 2009 10 11 28 3 0 0 0 1 1 2009 12 12 13 1 0 0 0

47 1 1 2010 1 13 1 4 0 0 0

1 1 2011 1 14 0 11 0 0 0 1 1 2011 2 15 0 6 0 0 0 1 1 2011 3 16 0 4 0 0 0 1 1 2011 4 17 0 3 0 0 0 2 2 2008 5 1 2 2 0 0 0 2 2 2008 6 2 5 1 0 0 0 2 2 2008 8 3 10 0 0 0 0 2 2 2008 10 4 5 1 0 0 0 2 2 2009 3 5 2 5 0 0 0 2 2 2009 4 6 1 5 0 0 0 2 2 2009 5 7 0 0 0 0 0 2 2 2009 6 8 1 2 0 0 0 2 2 2009 7 9 1 0 0 0 0 2 2 2009 9 10 3 1 0 0 0 2 2 2009 10 11 5 3 0 0 0 2 2 2009 12 12 7 3 0 0 0

Treatment Dome Year Month Survey # OS HF HG HS HC 2 2 2010 1 13 0 2 0 0 0 2 2 2011 1 14 1 8 1 0 0 2 2 2011 2 15 1 3 1 0 0 2 2 2011 3 16 1 5 1 0 0 2 2 2011 4 17 1 3 0 0 0 1 3 2008 5 1 0 0 0 0 0 1 3 2008 6 2 23 0 0 0 0 1 3 2008 9 3 43 0 0 0 0 1 3 2008 10 4 35 0 0 0 0 1 3 2009 3 5 28 2 0 1 1 1 3 2009 4 6 25 2 0 0 0 1 3 2009 5 7 16 0 0 0 0 1 3 2009 6 8 20 1 0 0 0 1 3 2009 7 9 6 0 0 0 0

48 1 3 2009 8 10 5 7 0 1 0

1 3 2009 10 11 48 0 0 0 3 1 3 2009 12 12 48 0 0 0 0 1 3 2010 1 13 7 5 0 0 1 1 3 2011 1 14 3 5 3 1 9 1 3 2011 2 15 3 3 2 0 3 1 3 2011 3 16 4 2 0 0 2 1 3 2011 4 17 4 0 0 0 2 2 4 2008 5 1 3 13 0 0 0 2 4 2008 6 2 22 1 0 0 0 2 4 2008 8 3 10 2 0 0 0 2 4 2008 10 4 20 0 1 1 0 2 4 2009 3 5 6 5 1 0 0 2 4 2009 4 6 4 4 0 1 0 2 4 2009 5 7 2 2 0 0 0 2 4 2009 6 8 8 0 0 0 0 2 4 2009 7 9 3 1 0 0 0

Treatment Dome Year Month Survey # OS HF HG HS HC 2 4 2009 9 10 3 1 0 0 0 2 4 2009 10 11 7 8 1 0 0 2 4 2009 12 12 2 0 0 0 0 2 4 2010 1 13 0 21 0 0 0 2 4 2011 1 14 0 6 2 0 0 2 4 2011 2 15 0 2 1 0 0 2 4 2011 3 16 0 1 1 0 0 2 4 2011 4 17 1 2 1 0 0 1 5 2008 5 1 0 0 0 0 0 1 5 2008 6 2 17 0 0 2 0 1 5 2008 9 3 20 0 0 0 0 1 5 2008 10 4 24 0 0 0 1 1 5 2009 3 5 28 3 0 6 3 1 5 2009 4 6 23 3 0 0 0

4 1 5 2009 5 7 21 0 0 0 0 9

1 5 2009 6 8 13 0 0 2 0 1 5 2009 7 9 11 0 0 0 0 1 5 2009 8 10 15 0 0 0 1 1 5 2009 10 11 38 3 1 1 4 1 5 2009 12 12 44 0 0 4 4 1 5 2010 1 13 5 8 0 3 4 1 5 2011 1 14 7 4 1 32 10 1 5 2011 2 15 11 1 0 16 4 1 5 2011 3 16 11 1 0 11 3 1 5 2011 4 17 12 1 0 17 1 2 6 2008 5 1 15 0 0 0 0 2 6 2008 6 2 30 0 0 0 0 2 6 2008 9 3 44 0 0 0 0 2 6 2008 10 4 60 0 0 0 0 2 6 2009 3 5 28 0 0 0 0 2 6 2009 4 6 21 0 0 3 0

Treatment Dome Year Month Survey # OS HF HG HS HC 2 6 2009 5 7 9 0 0 0 0 2 6 2009 6 8 19 0 0 0 0 2 6 2009 7 9 24 2 0 0 0 2 6 2009 9 10 30 0 0 0 0 2 6 2009 10 11 43 0 0 0 0 2 6 2009 12 12 27 0 0 0 0 2 6 2010 1 13 2 3 0 0 2 2 6 2011 1 14 0 13 0 0 0 2 6 2011 2 15 1 10 0 0 0 2 6 2011 3 16 1 3 0 0 0 2 6 2011 4 17 1 5 0 0 0

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