2014 Southeastern Naturalist Notes Vol. 13, No. 3
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A.E. Rosenblatt, S. Zona, M.R. Heithaus, and F.J. Mazzotti
Are Seeds Consumed by Crocodilians Viable? A Test of the
Crocodilian Saurochory Hypothesis
Adam E. Rosenblatt1,3,*, Scott Zona1, Michael R. Heithaus1, and Frank J. Mazzotti2
Abstract - Many animal species are important dispersers of seeds; however, relatively little attention
has been paid to the seed-dispersal capabilities of reptiles, and almost nothing is known about
the seed-dispersal capabilities of crocodilians. This lack of information is surprising given that seeds
have been found in the stomach contents of a majority of crocodilian species. Here we present the
first experimental investigation of the seed-dispersal potential of a crocodilian. Using a comparative
germination experiment, we tested the viability of Annona glabra (Pond-apple Tree) seeds recovered
from the stomach of an Alligator mississippiensis (American Alligator [Alligator]) captured in the
Florida Coastal Everglades. We found that seeds from the Alligator’s stomach were nonviable under
ideal germination conditions and that fresh, non-digested Pond-apple seeds exposed to the same
germination conditions were highly viable. The seeds recovered from the Alligator’s stomach were
nonviable because they were likely destroyed by stomach acids. Thus, Alligators are likely not dispersers
of Pond-apple seeds and may instead act as seed predators. Further research is needed to test
the potential of crocodilians as dispersers of other types of seeds from different plant families.
Seeds are dispersed by a wide variety of mammals, birds, and insects, leading to changes
in plant demography and distribution and, in some cases, evolution of animal–plant mutualisms
(Howe and Smallwood 1982). However, seed dispersal by reptiles, or saurochory, has
typically received much less attention than seed dispersal by other vertebrates (Traveset
1998). Yet reptiles can be important dispersers of seeds. For example, many terrestrial and
aquatic chelonians disperse seeds across terrestrial and riparian landscapes (reviewed in
Moll and Jansen 1995), and 280 species of lizards (Squamata) are known to consume fleshy
fruits, with 25% of the species tested showing enhanced germination of seeds that pass
through their digestive systems (reviewed in Valido and Olesen 2007).
One omission from the seed-dispersal literature is the order Crocodylia. Indeed, we
know of no studies that have experimentally examined seed consumption, excretion, or
dispersal by any crocodilians even though a recent comprehensive review of frugivory in
crocodilians found that more than 70% of species for which diet data exist regularly had
seeds in their stomach contents or have been directly observed consuming fruit (Platt et al.
2013). Crocodilians clearly have potential to act as seed dispersers, but evaluation of this
potential requires experimentation, especially concerning viability of seeds ingested by
crocodilians (Platt et al. 2013).
Using stomach contents collected from wild Alligator mississippiensis Daudin (American
Alligator, hereafter Alligator) we conducted a simple comparative germination experiment
to test viability of seeds ingested by crocodilians. We collected stomach-contents
samples from 54 adult Alligators inhabiting the Shark River Estuary in the Florida Coastal
Everglades (25°25'N, 81°00'W; for full description of the study site see Rosenblatt and
Heithaus 2011) from 2009–2011 using the hose-Heimlich technique (Fitzgerald 1989,
Nifong et al. 2012, Rice et al. 2005). Twelve (22%) of the individuals had seeds in their
1Department of Biological Sciences, Florida International University, Miami, FL. 2Fort Lauderdale
Research and Education Center, University of Florida, Davie, FL. 3Present address - School of Forestry
and Environmental Studies, Yale University, New Haven, CT. *Corresponding author - arose007@
fiu.edu.
Manuscript Editor: Scott Markwith
Notes of the Southeastern Naturalist, Issue 13/3, 2014
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2014 Southeastern Naturalist Notes Vol. 13, No. 3
A.E. Rosenblatt, S. Zona, M.R. Heithaus, and F.J. Mazzotti
stomachs. The seeds came from three plants: Rhizophora mangle L. (Red Mangrove),
Chrysobalanus icaco L. (Coco Plum), and Annona glabra L. (Pond-apple). Consumption
of Pond-apple fruits by crocodilians was documented almost 100 years ago (Guppy 1917,
Standley 1922). Pond-apple seeds were by far the most abundant seeds consumed, with one
individual’s stomach containing 1286 seeds. We chose to test viability of Pond-apple seeds
recovered from Alligator-stomach contents because this species provided us with a relatively
large sample size of seeds and because other vertebrate species are known to consume
and disperse viable Pond-apple seeds (Setter and Patane 2011, Setter et al. 2002, Westcott
et al. 2008). Typically, seed dispersal in Pond-apple is diplochorous: if not consumed when
ripe (leading to endozoochory), Pond-apple fruits quickly disintegrate and release their
large seeds, which disperse by floatation (hydrochory; Setter and P atane 2011).
An adult male Alligator (tag number: FWC 52611; 232 cm total length) that contained
Pond-apple seeds in its stomach was captured on 19 November 2010. We placed 20 of the
seeds in a plastic bag filled with approximately 100 mL of water, because Pond-apple seeds
normally disperse by hydrochory, and transported the seeds to the Florida International University
(FIU) greenhouse. On 2 December 2010, we planted all 20 seeds (evenly spaced) in
a 15-cm tall by 15-cm diameter pot that contained a commercial potting medium (Fafard 4;
Conrad Fafard Inc., Agawam, MA) consisting of sphagnum peat-moss, processed pine bark,
and vermiculite. The seeds were irrigated 3–5 times per week because Pond-apple seeds
require moist soil for germination (Swarbrick 1993). Despite the ideal growing conditions
we provided, none of the seeds germinated and we terminated the experiment on 29 September
2011 (302 days after planting). We dug up the seeds at the end of the experiment and
found that they were rotten and quickly disintegrated upon handling. This finding suggests
that the Pond-apple seeds were not lying dormant, as has been reported for seeds that have
passed through the guts of other reptiles, such as Terrapene carolina bauri Taylor (Florida
Box Turtle; Liu et al. 2004).
As a post hoc control, on 29 September 2011, we planted 40 fresh Pond-apple seeds (collected
directly from 1 ripe fruit taken from a Pond-apple tree in the Shark River Estuary)
in the FIU greenhouse in two 15-cm tall by 15-cm diameter pots (20 seeds per pot, evenly
spaced) containing the Fafard 4 potting medium. The control seeds were irrigated following
the same protocol used for the seeds ingested by the Alligator, and by 21 November 2011
(54 days after planting) more than 75% of the seeds had germinated and we terminated the
experiment. The difference in germination rates between the control and Alligator-ingested
seeds was likely not caused by the fact that the 2 seed batches were planted at different times
of the year because Pond-apple seeds are able to germinate year-round in Florida (S. Zona,
pers. observ.).
The results from this simple experiment show that fresh Pond-apple seeds are highly
viable and readily germinate, as has been shown in other studies (Setter et al. 2004, 2008),
whereas Pond-apple seeds that have been ingested by Alligators are likely rendered nonviable.
Thus, Alligators may act as predators, not dispersers, of Pond-apple seeds and likely
do not play a role in Pond-apple demography or distribution.
We hypothesize that the Pond-apples’ porous seedcoat (Guppy 1917) combined with
the highly acidic conditions in the Alligator’s stomach (pH = less than 2; Coulson and Hernandez
1964) likely rendered the experimental seeds nonviable. Also, Alligators can retain hard
or indigestible food items in their stomachs for weeks or even hundreds of days (Garnett
1985, Nifong et al. 2012), thereby allowing the seeds to potentially be exposed to the acidic
conditions for long time periods. In contrast, other species that consume Pond-apple seeds
and excrete them in a viable form, like Casuarius casuarius L. (Southern Cassowary),
2014 Southeastern Naturalist Notes Vol. 13, No. 3
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A.E. Rosenblatt, S. Zona, M.R. Heithaus, and F.J. Mazzotti
have gentle digestive systems that do not significantly impact seeds either chemically or
mechanically (Setter et al. 2002, Stocker and Irvine 1983).
The results of our study suggested that Alligators are likely not dispersers of Pond-apple
seeds and may instead act as seed predators. However, much more research is necessary
because our sample size was small and we focused on only one type of seed in one species
of crocodilian. Crocodilians are known to consume seeds from 46 genera of plants representing
33 families (Platt et al. 2013). If any of the other seed types possess hard seed coats
or exhibit short gut-retention times, then crocodilians could still play a role in their seed
dispersal.
Acknowledgments. This material is based upon work supported by the National Science
Foundation through the Florida Coastal Everglades Long-Term Ecological Research
program under Grant No. DBI-0620409. Additional funding was provided by Florida International
University (FIU). We thank Everglades National Park (ENP), P. Matich, D. Burkholder,
R. Sarabia, K. Gastrich, and A. Fritz for assistance with field work. All procedures
were carried out under permits from ENP (permit EVER-00093) and FIU’s Institutional
Animal Care and Use Committee (permit 09-013).
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