Statistical Tests for Effects of Introduced Fishes on Native Fish Communities Inhabiting Wet
Prairie and Mangrove Habitats in South Florida
Joel C. Trexler,
Florida International University, Miami, FL
Jerome J. Lorenz
National Audubon Society, Tavernier, FL
William F. Loftus
U.S. Geological Survey, Miami, FL
Mayan cichlids
Ave. no. per net
All fishes
Ave. no. per net
In a recent paper, we noted that the abundance of non-native fish species was generally
low in freshwater marshes of the Everglades at sites distant from canals, but was relatively high
in some mangrove-dominated areas north of Florida Bay. Further, we reported a negative
correlation over a 10-year period between the numbers and biomass of native fish and the same
parameter for the non-native Mayan
90
16
cichlid, Cichlasoma uropthalmus (Fig.
total fish
14
Mayan cichlids
80
1, reprinted from Trexler et al. 2000).
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Here we report an update from our
70
ongoing sampling in both the freshwater
10
60
Everglades habitats and the mangroves
8
north of Florida Bay. Also, we describe
50
6
the results of an analysis of fish
40
4
community data testing for evidence of
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2
impacts by introduced taxa on native
0
ones in those habitats.
20
1988
1990
1992
1994
1996
1998
2000
2002
Year
The density and relative
abundance of non-native fish taxa have
remained much greater in mangrove
Fig. 1. Plot of catch per unit effort of all fish and Mayan
cichlids from 1990 to 2000 from drop traps placed in the
habitats compared to upstream
mangrove zone north of Florida Bay.
freshwater marshes in Taylor and Shark
River sloughs in Everglades National
Park since the completion of our past analyses. In addition, we can identify no statistical
evidence for effects from the non-native taxa on native fish communities in freshwater wetprairie habitats. While no effect from non-native taxa is possible, we cannot exclude several
factors that can be categorized as either technical limitations of the data (effects are weak or
absent relative to statistical power to detect them) or as inherent in the temporal variation in the
communities themselves. The abundance and standing stocks of non-native taxa, especially the
Mayan cichlid, are elevated in wet prairie habitats bordering the mangrove zone in Shark River
Slough.
The picture is clearly different in the mangrove zone on the northern fringe of Florida
Bay. Mayan cichlids continue to be abundant in collections there. We have extended the
correlation analysis reported in our earlier work to document the taxa of native species that
appear to be adversely affected by Mayans. The native species sheepshead minnow (Cyprinodon
variegatus) and marsh killifish (Fundulus confluentus) decline in abundance in periods when
Mayan cichlids are common, and increase in periods of cold weather when Mayans relatively
less abundant. Two other small, abundant native fishes, sailfin molly (Poecilia latipinna) and
rainwater killifish (Lucania parva), appear to be unaffected by the changing abundance of
Mayan cichlids.
Our work indicates that non-native fish have altered the community structure and
dynamics of native fishes in some habitats in southern Florida, but not others. There are
probably multiple reasons for this, but the interaction of salinity and temperature tolerance of the
introduced taxa currently present plays some role. Shafland has suggested that cold-temperature
sensitivity has precluded some cichlids from expanding far from canals, where a permanent
temperature refuge is provided by ground-water infusion. However, Mayan cichlids have no
such refuges in the mangrove zone (the creeks there are not deep enough and their numbers do
fluctuate with the severity of annual minimum temperature) and yet their abundance is much
higher there than wet prairies. Thus, factors other than temperature tolerance may be involved in
limiting their current expansion into wet prairies. The paucity of deep-water refuges during
droughts, perhaps leading to local extirpation or severe reductions in population size may be a
key factor in keeping cichlids out of the wet prairies.
This research was supported by the National Science Foundation under Cooperative Agreement
DEB-9910514 for the Florida Coastal Everglades Long-term Ecological Research project and
Cooperative Agreement 1443CA5280-01-014 from the Everglades National Park and the US
Army Corps of Engineers.
Trexler, J. C., W. F. Loftus, F. Jordan, J. Lorenz, J. Chick, and R. M. Kobza. 2000. Empirical
assessment of fish introductions in a subtropical wetland: an evaluation of contrasting views.
Biological Invasions 2:265-277
Joel Trexler,
Dept. of Biological Sciences,
Florida International University,
University Park,
Miami, FL 33199
Phone: 305-348-1966
trexlerj@fiu.edu