Citation
Effects of the exotic plants melaleuca quinquenervia and casuarina equisetifolia on small mammal populations in the Eastern Florida Everglades

Material Information

Title:
Effects of the exotic plants melaleuca quinquenervia and casuarina equisetifolia on small mammal populations in the Eastern Florida Everglades
Series Title:
Florida Scientist, Quarterly Journal of the Florida Academy of Sciences, 44 (2) : 1981
Creator:
Mazzotti, Frank J.
Ostrenko, Witold
Smith, Andrew T.
Publisher:
Florida Scientist, Quarterly Journal of the Florida Academy of Sciences
Publication Date:
Language:
English

Subjects

Subjects / Keywords:
University of Florida. ( LCSH )
Biotic communities -- Florida ( LCSH )
Natural history -- Florida ( LCSH )
City of Miami ( local )
The Everglades ( local )
Mice ( jstor )
Hammocks ( jstor )
Everglades ( jstor )
Spatial Coverage:
North America -- United States of America -- Florida

Notes

Funding:
This collection includes items related to Florida’s environments, ecosystems, and species. It includes the subcollections of Florida Cooperative Fish and Wildlife Research Unit project documents, the Sea Grant technical series, the Florida Geological Survey series, the Coastal Engineering Department series, the Howard T. Odum Center for Wetland technical reports, and other entities devoted to the study and preservation of Florida's natural resources.

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Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
All rights reserved, Board of Trustees of the University of Florida

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Florida Scientist
QUARTERLY JOURNAL OF THE FLORIDA ACADEMY OF SCIENCES

WALTER K. TAYLOR, Editor HENRY 0. WHITTIER, Editor

Volume 44 Spring, 1981 Number 2


Biological Sciences

EFFECTS OF THE EXOTIC PLANTS
MELALEUCA QUINQUENERVIA AND CASUARINA
EQUISETIFOLIA ON SMALL MAMMAL POPULATIONS
IN THE EASTERN FLORIDA EVERGLADES


(1) FRANK J. MAZZOTTI, (2) WITOLD OSTRENKO, AND (3) ANDREW T. SMITH

(1) South Florida Research Center, Everglades National Park, Homestead, Florida 33030;
(2) Historical Museum of Southern Fla., 3280 So. Miami Avenue, Miami, Florida 33129;
(3) Department of Zoology, Arizona State University, Tempe, Arizona 85281.

ABSTrAcr: The exotic plants Casuarina equisetifolia and Melaleuca quinquenervia have
become established in South Florida. The effect of these plants on the local fauna is not known.
We studied the effects of Melaleuca and Casuarina on the 3 sympatric rodents (Peromyscus
gossypinus, Sigmodon hispidus and Oryzomys palustris) found in the Everglades. Three study
areas with different types of habitats were established. The habitats trapped included Casuarina
heads, cocoplum heads, combination Casuarina and cocoplum heads, Melaleuca heads and
mixed Melaleuca-graminoid heads. Sherman live traps baited with oats were set in 2 successive
nights during each rotation. Casuarina habitats supported fewer rodents than either cocoplum or
Melaleuca habitats. Rodents captured on the combination Casuarina-cocoplum head showed a
clear preference for the cocoplum half. Peromyscus were found primarily in the interior of the
mature Melaleuca head, while Oryzomys occurred primarily and Sigmodon exclusively in mixed
Melaleuca-graminoid habitat. Frequency of recaptures of Peromyscus and Sigmodon indicated
that each was resident in its preferred habitat.

ExoTIC plants are invading southern Florida at a rapid rate. These plants
were originally introduced for a variety of purposes: for food, to dry out in-
terior wetlands, to provide wind-breaks for farmland, to consolidate canal
banks, and as ornamentals. Most of these plants have not become established
and pose no threat to natural plant communities in South Florida. A few of
these plants, however, have escaped cultivation and are spreading into
native plant communities (Lahart, 1977; Austin, 1978).
Australian pine (Casuarina equisetifolia) and paperbark tree (Melaleuca
quinquenervia) are 2 exotic trees that are established in South Florida. They
are displacing native plants resulting in a decrease in plant species richness in
the habitats they are invading (Austin, 1978). The effects of these plants on










Florida Scientist
QUARTERLY JOURNAL OF THE FLORIDA ACADEMY OF SCIENCES

WALTER K. TAYLOR, Editor HENRY 0. WHITTIER, Editor

Volume 44 Spring, 1981 Number 2


Biological Sciences

EFFECTS OF THE EXOTIC PLANTS
MELALEUCA QUINQUENERVIA AND CASUARINA
EQUISETIFOLIA ON SMALL MAMMAL POPULATIONS
IN THE EASTERN FLORIDA EVERGLADES


(1) FRANK J. MAZZOTTI, (2) WITOLD OSTRENKO, AND (3) ANDREW T. SMITH

(1) South Florida Research Center, Everglades National Park, Homestead, Florida 33030;
(2) Historical Museum of Southern Fla., 3280 So. Miami Avenue, Miami, Florida 33129;
(3) Department of Zoology, Arizona State University, Tempe, Arizona 85281.

ABSTrAcr: The exotic plants Casuarina equisetifolia and Melaleuca quinquenervia have
become established in South Florida. The effect of these plants on the local fauna is not known.
We studied the effects of Melaleuca and Casuarina on the 3 sympatric rodents (Peromyscus
gossypinus, Sigmodon hispidus and Oryzomys palustris) found in the Everglades. Three study
areas with different types of habitats were established. The habitats trapped included Casuarina
heads, cocoplum heads, combination Casuarina and cocoplum heads, Melaleuca heads and
mixed Melaleuca-graminoid heads. Sherman live traps baited with oats were set in 2 successive
nights during each rotation. Casuarina habitats supported fewer rodents than either cocoplum or
Melaleuca habitats. Rodents captured on the combination Casuarina-cocoplum head showed a
clear preference for the cocoplum half. Peromyscus were found primarily in the interior of the
mature Melaleuca head, while Oryzomys occurred primarily and Sigmodon exclusively in mixed
Melaleuca-graminoid habitat. Frequency of recaptures of Peromyscus and Sigmodon indicated
that each was resident in its preferred habitat.

ExoTIC plants are invading southern Florida at a rapid rate. These plants
were originally introduced for a variety of purposes: for food, to dry out in-
terior wetlands, to provide wind-breaks for farmland, to consolidate canal
banks, and as ornamentals. Most of these plants have not become established
and pose no threat to natural plant communities in South Florida. A few of
these plants, however, have escaped cultivation and are spreading into
native plant communities (Lahart, 1977; Austin, 1978).
Australian pine (Casuarina equisetifolia) and paperbark tree (Melaleuca
quinquenervia) are 2 exotic trees that are established in South Florida. They
are displacing native plants resulting in a decrease in plant species richness in
the habitats they are invading (Austin, 1978). The effects of these plants on









66 FLORIDA SCIENTIST [VQ.L 44
the local fauna is unknown, but it is generally felt that few animals are
associated with these exotic plant communities (Lahart, 1977; Austin, 1978).
Small mammals are an important link in the food chain between plants
and other animals, especially raptorial birds, snakes, and medium-size
mammals. If native animals are being displaced, this could have a serious ef-
fect on Jocal food webs. We investigated the effects of Melaleuca and
Casuarina on the 3 sympatric rodents (Peromyscus gossypinus, Sigmodon
hispidus and Oryzomys palustris) found in the Everglades.
We asked the following questions to determine the effects of Melaleuca
and Casuarina on small mammals in the Everglades: 1) What small mam-
mals live in these habitats? 2) What are the relative densities of rodents and
are they permanent residents or transients? and 3) Does recruitment
(breeding) occur in these habitats?
DESCRIPTION OF STUDY A EAs-We set up 3 study areas during this in-
vestigation (Fig. 1). The Chekika study area is at the south-eastern edge of
the Davis Everglades region (Davis, :. i: -; The study area is dominated by
well-defined, elevated, roughly circular tree islands separated by a sawgrass
(Cladium jamaicense)-mixed graminoid prairie. During the wet season
(June-October) the prairie is flooded and the tree islands provide the only
dry ground. During the dry season ("'.. ... ) .: y) the prairie becomes dry
and dusty.
Three types of tree islands are found at the Chekika study area. Most
abundant are tropical hardwood hammocks. These hammocks are
characterized by high plant species richness and complex habitat structure
(Smith and Vrieze, 1979). At least some portion of the hammock remains dry
during the wet season allowing for the colonization of tropical hardwood
trees. Low ground along the perimeter of the hammocks is dominated by
cocoplum (Chrysobalanus icaco). Smaller tree islands which become at least
partially flooded during the wet season consist almost exclusively of
cocoplum. They are termed cocoplum heads. The third type of tree island in
this area is termed Casuarina head. These may or may not become partially
flooded. Casuarina heads have virtually no understory vegetation.
The Tamiami ',:: -. area is located 27 km west of Miami and south of the
Tamiami Trail (U.S. 41). This area shows all phases of Melaleuca invasion
into wet prairies. There is a 2 ha, Melaleuca head estimated to be 30 yr old,
which contains tall mature trees in its center. There is almost no understory.
The periphery of this head is a dense ring of saplings approximately 6-7 yr
old. Surrounding this head is a partially drained sawgrass-mixed graminoid
prairie dotted with clumps of Melaleuca. These areas are dry from January
to June. The large head floods faster and takes longer to dry down (by 2-3
wk) than the surrounding area.
The South study area is close to and southeast of the intersection of U.S. 1
and the Card South Road (State Highway 905). Here, there is an extensive
expanse of mature Casuarina. Like the smaller Casuarina heads at the
Chekika site, there is no understory. Within 200 m south of this Casuarina










MAZZOTTI ET AL. -EXOTIC PLANTS


Lake
Okeechobee


Tamiami 0 i Miami


Chekika

South a




FIG. 1. Location of study areas Eastern Everglades, Florida.

forest are hammock tree islands with high species richness of trees each
skirted by single species fringes of cocoplum, The hydrology of this area is
similar to that of the other 2 study areas.
MATERIALS AND METHODs-Sherman Live Traps baited with oats were
set on 2 successive nights during each trapping rotation. Traps were set at
dusk and picked up at dawn. Inter-trap distance at all sites was between 3-4
m. Each animal caught was weighed, sexed, classified as adult or juvenile,
identified by toe clipping, and examined for reproductive condition. Traps,
with 2 exceptions, were set in grids. The grids were either rectangular or
conformed to the shape of the tree island. One exception was the large
Melaleuca head. Here 2 trap lines were set perpendicular to each other. The
other exception was a trap line set in the prairie near the Casuarina head.
These general techniques have proven effective in sampling Everglades
rodents (Smith and Vrieze, 1979).


NQ. 2, 1981]









FLORIDA SCIENTIST


Chekika study area: Three tree islands were trapped at the Chekika site.
They were 0.06 ha Casuarina head, a 0.03 ha cocoplum head, and a 0.14 ha
tree island that was half Casuarina and half cocoplum (termed combination
head). These grids conformed to the shape of the island. The cocoplum head
was trapped in an attempt to separate the effects of exotic plants from that of
a monoculture. These data can be compared with those of Smith and Vrieze
(1979) who trapped species-rich hammock islands in the same area. The
combination head was trapped to determine habitat preference within a
limited spatial dimension. Seventy traps were set each night on the
Casuarina head, 40 were set on the cocoplum head, and 80 on the combina-
tion head. The Casuarina and cocoplum heads were trapped for 10 rotations
between April 1976 and April 1977. The combination head was trapped for
6 rotations between September 1976 and April 1977.
Tamiami study area: We trapped 2 heads at the Tamiami study area: a 2
ha mature Melaleuca head and a 0.03 ha mixed Melaeuca-graminoid head.
A grid of 40 traps was set in the mixed habitat. Because of the large area of
the mature head, trap lines were used to census this habitat. Two lines of 40
traps perpendicular to each other were established. The Tamiami site was
trapped for 7 rotations from May 1976 to April 1977.
South study area: Two grids of 40 traps were set at the South study area
in December 1976 and April 1977. One grid was in a solid forest of
Casuarina, the other in a plant species-rich hammock with a high proportion
of cocoplum.
RESULTS-In all habitats sampled, the occupancy patterns of Everglades
rodents were nonrandom. At the Chekika study area Casuarina habitats
were essentially depauperate compared to cocoplum habitats (Tables 1 and
2). On the Casuarina head low relative densities of Peromyscus were found
only in April and May 1976, while on the nearby cocoplum head, high
relative densities were found in the dry season of each year (Table 1). No

TABLE 1. Number of animals caught per trap night on the Casuarina head and cocoplum
head from April 1976 to April 1977. No Sigmodon or Oryzomys were caught in Casuarina.

Casuarina Cocoplum
Peromyscus Peromyscus Sigmodon Oryzomys

April 0.2 0 0 0
Early May 0.15 0.9 0 0
Late May 0.05 1.4 0 0.1
June 0 0 0 0.1
July 0 0 0 0.6
August 0 0 0 0
October 0 0 0 0
December 0 0 0 0.5
January 0 0.6 0.1 0
April 0 0.7 0.1 0.1


[Vol.-44










MAZZOTTI ET AL. EXOTIC PLANTS


TABLE 2. Number of animals caught per trap night on the 2 halves of the combination head
S.: 1976-April, 1977).

Habitat Species Sept Oct Nov Dec Feb Apr

... 0.12 0.18 0.22 0.26 0.30 0.33
Cocoplum
Sigmodon 0.08 0.16 0.08 0.18 0,02 0
Peromyscus 0 0 0 0 0 0.01
Casuarina
.. .. .. 0 0.02 0 0.02 0 0



Peromyscus were caught on the cocoplum head in the wet season when it
was almost completely flooded. No Sigmodon or Oryzomys were trapped on
the Casuarina head, while they were found sporadically on the cocoplum
head. In January and April 1977, traps set in the prairie near the Casuarina
head yielded Peromyscus and Oryzomys, but no animals were trapped on
the Casuarina head.
On the combination head both Peromyscus and Sigmodon were trapped
almost exclusively in the cocoplum half of the island compared to the
Casuarina half (Table 2). Further, when animals were released in the
cocoplum half, they immediately sought cover there. Animals released in the
Casuarina half did not seek cover until they had wandered into the
cocoplum half.
The same pattern of habitat occupancy emerges from trapping at the
South study area (Table 3). Here, despite the fact that the Casuarina forest
was only 200 m from the hammock island, almost all captures of Peromyscus
and all captures of Sigmodon were on the hammock.
Not only were few individuals of each species of rodent captured in these
Casuarina habitats, but periods of residency was also significantly shorter
than in the natural habitats. Of all captures in Casuarina, only I individual
(a Peromyscus in April-May 1976) was ever recaptured there. By com-
parison, many individuals of each species on natural habitat trapping grids
appeared to be permanent residents (Smith and Vrieze, 1979).

TABLE 3. Number of animals caught per trap night on the South study site. Total captures in 2
nights divided by 80 traps.

Hammock Island Casuarina
Dec 1976 Apr 1977 Dec 1976 Apr 1977

0.19 0.34 0 0.04
Sigmodon 0.11 0 0 0


No. 2, 1981]











TAaLE 4. Number of animals caught per trap night on the Melaleuca head and the Melaleuca
mixed head (May, 1976-April, 1977). No .... were caught in Melaleuca head.

(Early) (Late)
Habitat May May July Aug Nov Jun Apr

Melaleuca Peromyscus 0.05 0.07 0.06 0.01 0.06 0.03 0.11
head Oryzomys 0.01 0.01 0 0 0 0 0
Melaleuca 0 0 0 0.01 0.01 0.01 0
mixed head Sigmodon 0.03 0.09 0.10 0.03 0.08 0 0.05
Oryzomys 0.01 0 0 0.01 0.06 0.04 0.01



In contrast to the depauperate fauna in Casuarina habitats, each rodent
species was common in Melaleuca habitats (Table 4). Peromyscus were
found primarily in the interior mature stands of Melaleuca where they were
at highest density throughout the dry season. Oryzomys occurred primarily
and Sigmodon exclusively in mixed Melaleuca-graminoid habitat. Fre-
quency of recaptures of Peromyscus and Sigmodon indicated that each
species was resident in its preferred habitat. Oryzomys appeared to be tran-
sients on the study area.
Data on reproduction and recruitment are too few to present a quan-
titative analysis of their phenology. One trend, however, was clear: no
reproductive animals were ever caught in Casuarina habitat. Reproductive
animals and juveniles occurred in native and Melaleuca habitats.
DIscUssION-The importance and role of rodent populations in the
Everglades ecosystem has recently been stressed by Smith and Vrieze (1979).
Working on a constellation of 6 native hardwood hammocks in the Chekika
study area, they determined that densities of Peromyscus gossypinus,
Sigmodon hispidus and Oryzomys palustris were significantly higher than
those reported for other populations of each species throughout its respective
geographic range. Because rodents are a source of food to species in all
vertebrate classes, these high densities should not be overlooked. The present
study expands upon the work of Smith and Vrieze to include cocoplum
heads, a hammock island in a different drainage system, and most impor-
tantly, the exotic habitats of Casuarina and Melaleuca.
Iterating the data on relative density, reproduction and permanency
within habitats, it is clear there are distinct differences in occupancy among
habitat types by Everglades rodents. Using all criteria, Casuarina may be
considered a poor habitat for rodents. In contrast, Melaleuca may contain
each of the co-dominant Everglades rodents. The distinction between
Casuarina and Melaleuca is important because it points out that not all ex-
otic habitats are equal. Each habitat must be evaluated separately for its
suitability for animal populations.
The cues used by rodents to assess habitats were not critically tested in
this study, but appears that low species richness of plants per se does not


[Vol. 44


FLORIDA SCIENTIST











MAZZOTTI ET AL. EXOTIC PLANTS


determine rodent distribution and abundance. Three of the habitats trapped
were monocultures (cocoplum, Casuarina and Melaleuca), yet there were
distinct *.:. ,. :.- among habitat types in their usage by rodents. Further,
it does not appear that f. 1 :. structure is a proximate cue; despite their dif-
ferences in rodent occupancy patterns, Casuarina and Melaleuca are more
similar structurally than they are to cocoplum or hammock habitats.
Exotic plant communities can no longer be intuitively classified as
biological deserts. There are differences in their ability to support native
wildlife. However, this should not be interpreted to mean that Melaleuca is
a good habitat for wildlife. Low numbers of rodents were caught in the
Melaleuca head throughout the duration of the study (e.g., only 17
Peromyscus) compared with an average of over 100 per ha of Peromyscus
found by Smith and Vrieze (1979) in native hammock communities.
There are no data relating to the use of Melaleuca as a direct food source
by rodents. Further, it is unknown if this habitat is accessible to higher
members of the food web that would normally utilize Everglades rodents.
These aspects of the dynamics of Melaleuca-rodent interactions should be
determined to assess the ability of Melaleuca to support native wildlife.

ACNowLEDCMcaErs-We thank the many colleagues who assisted with the trapping in this
study. Further we appreciate the comments of Daniel Austin, Steve Woodall, and James Kushlan
who reviewed the manuscript. The study was funded in part by an NIH Institutional Grant
: ..... of Miami) to A. T. Smith, a contract on endangered species awarded by Florida
Power and Light through ( ... :: Metcalf, and Eddy to A. T. Smith, and a U.S. Forest Service
Contract on small mammals in Melaleuca awarded to W. Ostrenko.



LITERATURE CITED

AuSTIN, D. F. 1978. Exotic plants and their effects in Southeastern Florida. Environmental Con-
serv. 1:25-34.
DAvis, J. H. 1943. The natural features of Southern Florida. Geological Bull. No. 25. Florida
Geological Soc. Tallahassee, Florida.
LAHarT, D. 1977. Invaders of the T ..-1. Florida Wildlife. 31:33-36.
SMITH, A. T., AND J. M. VRIEZE. 1979. Population structure of Everglades rodents: responses to a
patchy environment. J. of Mammalogy. 60:778-794.

Florida Sci. :. ... -71. 1981.


No. 2, 1981]