MESOAMERICANA - Sociedad Mesoamericana para la Biología y la ...

Mesoamericana 13 (1) Agosto de 2009
McComb, 1981) and wigeongrass is more frequently used
as nursery areas (Congdon and McComb, 1981). With
regards this issue, Darnell (1958) found out that just one
species consumes significant amount of this plant in
Luoisiana state; and Carr and Adams (1973) found low
rates of consumption among 10 foraging groups of fish
in Florida, out of three just developed an herbivory stage.
In our study area, there are just two species of genera
Opsanus and Archosargus, but considered as local residents
(F. P. Amargós, pers. comm.), just migrating towards coral
reefs during breeding seasons.
In the particular case of bird-mediated
endozoochory, the broad spatial overlap between the
angiosperm geographic distribution in Northamerica and
the Atlantic Coast Migratory Route must be taken into
account. Such a fact could have favoured the accessibility
of this important food resource to various waterfowl
species for refuelling in critical stopovers during fall
migrations movements. In fact, there is a trend for
migratory ducks in the northern hemisphere to feed more
on seeds with high carbohydrate levels during fall and
winter (Baldassarre and Bolen, 1994). Endozoochory
experienced by these ducks is based on the fact that this
group of birds is widely recognized as important
dispersers of various aquatic organisms due to their
abundance, wide distribution ranges and long-distance
migrations along the wetlands of the world. Besides, the
importance of the R. maritima drupelets in dabbling ducks
diet has been broadly pointed out by an extensive
literature compiled for over 70 yr (McAtee, 1915;
Mabbott, 1920; Campbell, 1946; Smith, 1951;
Chamberlain, 1959; Stewart, 1962; Tamisier, 1971;
Johnsgard, 1975; Krapu and Swanson, 1978; Prevost et al.,
1978; Saunders and Saunders, 1981; Swiderek, 1982;
Euliss, 1989).
Once the plausibility of waterfowl feeding on the R.
maritima seeds while migrating southward is considered,
another key phase involved in a possible internal transport
is the retention time of drupelets in the gut. Such a factor
determines the distance range these seeds can travel
(Proctor, 1968). Therefore, the farthermost distance the
seeds can be transported will be limited by their duration
in the gut and how far the disperser can fly during this
time. For instance, if the flight speed of Anas sp. ranges
between 60 to 78 km/h (Welham, 1994), and the pattern
of retrieved seeds from the disperser indicates that
dispersion will take place some hours after ingestion, then
endozoochory could be a feasible event between southern
regions of the U.S.A. and Cayo Coco during fall
32
migrations. Such a statement is supported by the fact that
the highest probabilities of dispersion can occur about 4 h
after ingestion, comprising distances ranging from 80 to
320 km, even though periods of time exceeding 8 h could
be also attainable (Charalambidou et al., 2003), but at lower
probabilities.
In addition, the proportion of seeds capable of
germination once excreted must be also considered as key
factor involved in the occurrence of any dispersion event.
Despite the fact the proportion of seeds successfully
germinating after being released by any given duck is low,
ranging from 0.4 to 1.3% (Charalambidou et al., 2003), in
wetlands where hundreds and thousands of individuals
are passing through during fall migration, coinciding with
the peak of consumption of R. maritma seeds (Cramp and
Simmons, 1977), the overall figures become significantly
higher. Besides, as the number of individuals carrying the
propagule increases, the probability of one of them
dispersing the seeds over a long distance to a suitable
habitat will be favoured, according to Green et al. (2002).
According to the criteria of abundance and
permanence during winter season in the salty and brackish
wetlands of Cayo Coco, the species Anas discors, A.
americana and A. clypeata, are thought to be possible
dispersers in the study site. On the contrary, species such
as A. strepera (Gadwall), A. bahamensis (White-cheeked
Teal), A. acuta (Northern Pintail), Aythya affinis (Lesser
Scaup) and A. collaris (Ring-necked Duck) considered as
rare and vagrants, are represented by only small
populations in this insular territory. Particularly, A. clypeata
should be an interesting candidate based on the fact this
species showed the highest probability of germinating
seeds per digested seeds recorded in SE Spain (Figuerola et
al., 2002, 2003), and because of its lamellar density,
particularly high among the northern hemisphere ducks
(Nudds et al., 1994). In this regard, the range sizes of
Ruppia drupelets (0.5-4 mm) can be easily ingested as the
high lamellar densities enable ducks to filter smaller
particles (Crome, 1985) by reducing the costs of filtering
small items, leading to negative correlations between
lamellar densities and seed size (Nummi, 1993; Tamisier
and Dehorter, 1999).
Other species presented in the study area, have also
been reported as possible dispersers of R. maritima, such
as shorebirds (Scolopacidae) (Sperry, 1940; Bourn and
Cottam, 1950; Martin et al., 1951), and gallinules (Rallidae)
(Quay and Critcher, 1962; Gaevskaya, 1966). Nonetheless,
more updated researches approaching the feeding ecology
of Himantopus mexicanus (Black-necked Stilt) (Hamilton,