Predation (Biology)

The tropical fire ant, Solenopsis geminata is a New World species with a wide native
range including South America as well as several Caribbean islands. The red imported
fire ant, Solenopsis invicta is native to parts of South America. Both species are known
for preying on sea turtles’ eggs and hatchlings. The objectives of this thesis research
were to conduct follow-up and baseline ant species distribution surveys on four sea turtle
nesting beaches in St. Croix, U. S. Virgin Islands. Tuna baits were set out at beaches;
specimens were collected, frozen, preserved then identified. Results show that there was
a significant change in the fire ants’ distribution at Sandy Point National Wildlife Refuge
(SPNWR) while none were found at Jack Bay. Fire ants were also present on the other
two baseline surveyed nesting beaches. The displacement of S. geminata by S. invicta
was observed at SPNWR, which also was presumed by previous surveys.

Dietary resource use for diamondback terrapins (Malaclemys terrapins) in
subtropical mangrove habitats in south Florida creeks and islands was examined to
elucidate long-term individual foraging strategies. Fecal analysis revealed seven
categories of food items with gastropods, crabs, and bivalves being the most dominant
food items respectively. Non-metric multidimensional scaling revealed differences in
habitat, but not terrapin size class. Stable isotope analysis confirmed the findings,
identifying habitat and site differences in δ13C and δ15N values for both terrapins and
their prey. Bi-plots of terrapin and potential prey δ 13C and δ 15N values revealed potential
dietary sources previously undetermined by fecal analysis. Comparisons of scute and
blood isotope data revealed significant differences in δ13C indicating potential shifts in
either food resources and/or habitat use through the time period recorded in the scute
tissue. These tissue comparisons represent a powerful tool for estimating long term
foraging strategies for a key estuarine species.

The first of five chapters describe the study area and study species, including a short description
about the impetus for this research. The second chapter describes a unique hydrologic model for application
in tidal ecosystems. The second chapter represents new information on the effects of various abiotic and
biotic factors on foraging wading birds in this highly dynamic environment. The third chapter identifies
important factors affecting the abundance of foraging wading birds in intertidal environments. The fourth
chapter presents a study of the foraging habitat preferences of two wading bird species in intertidal
environments. The fifth chapter describes a conceptual model of wading bird foraging ecology and a
predictive model of foraging habitat in intertidal zones. The conceptual model captures the major drivers
and linkages between the abiotic and biotic variables thought to affect wading bird foraging abundance in
intertidal habitats. The conceptual model also identifies major knowledge gaps in our understanding of
foraging ecology of wading birds in coastal intertidal areas. The predictive model of foraging habitat is
meant to be used by resource managers, but its framework may be useful for ecological studies in general.
The final and sixth chapter provides a summary of all the major findings. Each chapter has been written so
as to be independent of the other chapters. As such, a full background, along with a discussion of the
relevance of the chapter's findings is provided for each chapter.

The red imported fire ant, Solenopsis invicta, is a South American native
introduced in Alabama in the early 20th century. This predatory species has rapidly
spread throughout the southeastern US and parts of the West Indies, inflicting great
ecological and economic damage. For example, Solenopsis invicta is known to attack the
eggs and hatchlings of ground nesting birds and reptiles. The ants swarm into the nests
attacking hatchlings and diminishing their chance for survival. My thesis research aimed
to survey the distribution of ants on sea turtle nesting beaches in South Florida and St.
Croix, USVI, and to evaluate the possible threat of Solenopsis invicta and other predatory
ants to sea turtle hatchlings.

Masking or decorator crabs, conceal themselves partially through camouflage, by
selecting or indiscriminately attaching materials from their environment to their
exoskeleton. Functional aspects of decorating behavior and morphology in this group
have not been documented. Using Microphrys bicornutus as a model species, this
dissertation demonstrates clearly that decorating is an advantageous phenotype that has
evolved to serve several functions. Decorating is a complex behavior that begins when a crab approaches an algal substrate and results in the attachment of algae to hooked setae on the exoskeleton. Once decorated, crabs remain motionless on the substrate until disturbed or until another behavior is initiated. This was confirmed for M. bicornutus, as crabs spent a significant
amount of time feeding, remaining motionless, picking, and walking when compared to
decorating. Crabs displayed agonistic behaviors during encounters with conspecifics conspecifics. These included both active aggressive behavior and display behavior.
Crabs showed a decrease in motility during these encounters, helping maintain dispersed
distributions, thereby decreasing intrsapecific encounters in the field. Trials were done to determine the effect of conspecifics, predators and feeding preferences on algal utilization. M. bicornutus showed a significant decrease in the amount of algae used for decoration in the highest density trials (i.e., 4 and 8 crabs). Agonistic displays and aggressive behavior between these crabs likely affected the time available for decorating. Decorated crabs isolated from an algal substrate were more likely to survive in the presence of either of two sympatric fish predators. Thus, being protected by the algal decoration on their exoskeletons. Trials also showed a parallel between algal consumption and algal materials used for decoration. In addition to its protective function, algae used by M. bicornutus for decoration simultaneously serve as
short term food supplies for the crabs. Eleven morphologically complex structures were identified and mapped on the exoskeleton. Hooked setae were the primary structures used to attach algae to the crab’s body. Ten additional setal structures were present, including two novel types of setae. On the basis of location and morphological variation exhibited among these latter structures, a primary sensory function may be inferred.

The younger life history stages of marine turtles (eggs, hatchlings) often fail to survive. To compensate, sea turtles nest several times/season and produce large clutches of eggs. The hawksbill produces the largest clutches (150 eggs) and the smallest hatchlings of any marine turtle. My study, done at Jumby Bay in Antigua, West Indies, was designed to determine whether they did so to compensate for loss in the nest, hatchling loss in the water, or both factors. I
found that most of the eggs (79 %) survived to become hatchlings that left the nest and entered the sea. However, 88 % of the hatchlings swimming offshore were taken by predators within minutes after they began their migration. These results suggest that at Jumby Bay, large clutch size is favored in hawksbills because of predation pressures on the hatchlings.

The role of acetylcholine in feline predatory attack was examined by
pharmacological manipulations. Attack behavior was partitioned into
components of app roach (visualorientation, approach, extension of the
head, trapping, seizing in the jaws, biting) and withdrawal (whole
body withdrawal, retraction of the head and upper torso, swiping ) in
an attempt to selectively affect specific components of the attack
pattern. Carbachol, a cholinomimetic, produced an increase in the
percentage of head and upper torso retractions, as well as a slight
inhibition of prey seizing. Atropine methyl nitrate, an anticholinergic,
was found to decrease the percentage of head and upper torso
retractions, as well as the rate of swiping. The primary effect of
atropine, however, was a slight, non-specific inhibition of all
behaviors, as evidenced by longer latencies to kill the prey, as
well as by long periods of pausing and dry mouth symptoms. Leakage
of the drug into the periphery may have contributed to these effects.

Grazing on bioluminescent and nonluminescent prey by the copepod Acartia tonsa was examined to determine the effect dinoflagellate bioluminescence has on copepod feeding preferences and rates. The percentage of cells ml-1 remaining after 30 minutes of copepod grazing on the dinoflagellates Lingulodinium polyedrum and Pyrodinium bahamense in their bioluminescent and nonbioluminescent phases was used to compare results for concentrations of 10, 1,000, and 3,000 cells ml-1. The nonluminescent diatom Thalassiosira eccentrica was later offered along with each of the dinoflagellates. When diatoms were offered with P. bahamense, the copepods consumed them in equal amounts regardless of bioluminescence at the lower concentration, while the higher concentration showed decreased grazing with bioluminescence. Nonbioluminescent L. polyedrum was consumed at a high rate for all concentrations, but grazing decreased once they were bioluminescent. Copepods switched to T. eccentrica once the dinoflagellates became bioluminescent, except at 3,000 cells ml-1, at which all grazing was reduced. These results indicate there may be a threshold concentration separating two functions of dinoflagellate bioluminescence.

Few studies document mortality rates for hatchling sea turtles during their migration away from the nesting beach. This study quantifies and compares nearshore predation rates on loggerhead hatchlings (Caretta caretta) at several locations in southern Florida. Hatchlings were followed by observers in kayaks during the first 15 min of the migration away from the beach. The overall observed predation rate (4.6%) is similar to a previous estimate (5%) from a natural high density Florida nesting beach, and lower than at a hatchery site. Predation rates were higher on Florida's southeast coast than the southwest coast. Predation increased towards the end of the hatching season. Results suggest that currently, hatchling mortality rates are relative low in Florida's shallow nearshore waters. Given the lack of growth by loggerhead populations, the cumulative mortality must be high after hatchlings depart shallow coastal waters.

Predator-prey relationships were studied between the shrimps Latreutes fucorum and Leander tenuicornis and the predatory fishes Stephanolepis hispidus and Histrio histrio, all found within pelagic Sargassum communities. Average survival times of shrimps were compared in species, size/density, and habitat selection studies. The results showed that S. hispidus had a preference for prey species while H. histrio did not. 30 mm shrimp survived longer than the 10 mm shrimp for both S. hispidus and H. histrio. Density was a factor in the survival times of the 20 mm shrimps with S. hispidus only. L. tenuicornis survived longer in artificial Sargassum habitats with H. histrio. The larger shrimps survived longer in the artificial habitats than the smaller shrimps with S. hispidus. Both fish predators employ optimal foraging strategies with similarities and differences, the latter of which are likely related to behavioral differences in the these predator and prey.