Predation (Biology)

Octopus predation and species selection contribute to community structure in benthic habitats, where plastic pollution accumulates. This study investigated how the bioactive plastic additive oleamide alters trophic interactions and behaviors of the common octopus (Octopus vulgaris) and its prey. We quantified activity budgets and trophic interactions for octopuses and multiple prey types (hermit crabs, free-living crabs, bivalves, and gastropods) before and after exposure to oleamide. Our analysis suggested that some taxa (octopuses and hermit crabs) exhibit more active behaviors during oleamide exposure. Free living crabs responded primarily to the threat of octopus predation, while other taxa did not show clear behavioral responses. Exposure to oleamide increased trophic interactions and the probability of mobile prey taxa being observed on the same side of the aquarium as the octopus, thus increasing the opportunity for predation. Our results support previous research showing that plastic leachates can impair decision-making, making prey more susceptible to predation.

By regulating the abundance of prey populations, predators can directly and indirectly influence food web interactions in ways that influence ecosystem function. Predator functional responses quantify how predator foraging rate changes with prey abundance. Due to the large numbers of individuals needed for these experiments, most studies are conducted on small, abundant taxa. Consequently, we know relatively little about the functional responses of many marine taxa, especially those that are large and highly mobile. We present a novel method for studying predator foraging behaviors by integrating two innovative approaches: passive acoustics to document the occurrence of underwater predation events in concert with a recently developed statistical method that uses the times between predation events to estimate functional response parameters. We demonstrate and expand on the application of these methods by quantifying the shape of the predator functional responses for whitespotted eagle rays (Aetobatus narinari) preying on hard clams (Mercenaria mercenaria).

Few studies on marine turtles focus on the variation in reproductive performance of individual females. I use a long-term nesting data set (1986 – 2018) of individual loggerheads including information on 1,854 individuals, of which 853 were seen nesting multiple times. During this time, emergence success has declined while the number of females nesting, and the number of nests deposited has increased. Declining emergence success can be linked to an increase in predation in most recent years; however, this does not fully explain the decline in emergence success over all years. Females were found to vary in productivity. Successful females were larger and deposited more eggs in nests. This study shows that an increasing in nesting numbers does not mean that productivity is increasing proportionally and that recovery efforts are uniformly successful. This study is also a powerful tool for understanding the reproductive strategies of individual female loggerheads.

The hermit crab Clibanarius vittatus kills Melongena corona solely to
acquire a better fitting shell. This finding is contrary to previous studies, which
found that hermit crabs of other species cannot kill gastropods or, in most
instances, remove freshly dead gastropods from their shells. This interaction
cannot be classified as predation because Melongena tissue was never
consumed. Clibanarius killed Melongena only when by doing so they could trade
up to a better fitting shell. It cannot be classified as competition because there is
no opportunity for Melongena to gain from the interaction. Therefore the term
“lethal eviction” is hereby proposed for this interaction. The ability to kill a
gastropod to obtain a superior shell gives Clibanarius vittatus an evolutionary
advantage over other hermit crab species. It is not known if the outcome of this
interaction is widespread where both species occur or if it is confined to the
study area.

Worldwide, sea turtles are especially vulnerable immediately after emerging from
nests. Many monitoring programs measure hatchling production from nest inventories.
These inventories rarely account for mortality occurring post-emergence, leaving an
incomplete estimate of hatchling production. This study addresses the nest-to-surf data gap
for Florida’s east coast nesting assemblages of loggerhead sea turtles (Caretta caretta).
Five locations were surveyed during the 2016 nesting season by using infrared time-lapse
imagery, night vision optics, and track maps. Over all beaches, 7.6% of the observed
hatchlings did not survive to reach the water. Mortality sources varied by location.
Observed predators included: foxes, bobcats, yellow-crowned night herons, ghost crabs,
and gulls. Hatchling disorientation and misorientation occurred more frequently in urban
areas than natural areas. Factors including number of hatchlings emerging, nest-to-surf
distance, and urbanization may help managers estimate nest-to-surf mortality. This study
will improve life history models that serve as foundations of conservation management.

Migratory bird and insect populations show differences in orientation direction, timing,
and distances moved depending upon where they reside in relation to their migratory
goals. These differences presumably occur because of selection for behavioral responses
that promote the most efficient migratory strategies among members of each population.
The purpose of this study was to determine whether migratory behavior in loggerhead
hatchlings differs between populations that exit nesting beaches on the East and West
coast of Florida. When the turtles emerge from the nests, they initially show a swimming
"frenzy" that serves to distance individuals from shallow coastal waters, displacing them
toward oceanic currents that are used to transport the turtles to the North Atlantic Gyre.
On the East coast of Florida, turtles swim eastward toward the Florida Current (western
portion of the Gulf Stream) located relatively close to the shoreline (on average, 2 km
offshore at Miami to 33 km offshore at Melbourne Beach). On the West coast of Florida,
turtles swim westward toward the Loop Current in the Gulf of Mexico, which is located
farther offshore (150 km offshore at St. Petersburg to over 200 km offshore at the Everglades National Park). In a previous study, we demonstrated that for East coast
loggerheads, the frenzy consists of continuous swimming for - 24 h, followed over the
next 5 days by postfrenzy (diurnal, with little nocturnal) swimming activity. No
comparable data exist that characterize the frenzy period of loggerheads from the West
coast ofFlorida.
We used identical methods to quantify the migratory activity of hatchlings from the West
coast of Florida. Hatchlings were captured as they emerged from nests located between
Venice and Sarasota, Florida. They were then tethered in water-filled pools under
laboratory conditions, where temperature and photoperiod could be controlled to
duplicate conditions used when studying the East coast turtles. Activity was continuously
recorded over the next six days. The data were analyzed to determine the proportion of
time the turtles spent swimming every day, and the proportion of that swimming activity
that occurred during the light and dark period of each day. Turtl~s from each coast
showed no statistical difference in the proportion oftime spent swimming each day.
However, after day 1, West coast hatchlings showed statistically lower levels of
swimming activity during the day and statistically higher levels of swimming activity at
night than did turtles from the East coast. We hypothesize that these differences may
reflect a more diffuse period of active "searching" for appropriate oceanic currents by the
West coast turtles, under conditions where greater predation pressures might select for
more movement under conditions of darkness. Such a response may be appropriate when
migratory goals are located at greater distances, and when turtles must migrate farther
from the coast to reach deeper, and presumably less predator-rich, waters.

Wetlands are some of the most diverse and productive ecosystems on earth. Water-level fluctuations determine the ecological function of shallow lakes and wetlands. Currently, anthropogenic modification to water-level fluctuations is the leading source of ecological degradation in lake and wetland ecosystems worldwide. I used wading birds nesting in Lake Okeechobee, as a model system to address the challenges of environmental restoration within an ecosystem greatly impacted by anthropogenic activities. Specifically, I 1) identified environmental factors most important for predicting the number of wading bird nests, 2) tested the assumptions of both the match-mismatch and the threshold hypothesis by modeling the relationship between nesting success and prey density with foraging habitat availability, and 3) measured the stress response of Great (Ardea alba) and Snowy Egrets (Egretta thula) to hydrologically-mediated changes in food availability. Collectively, the results suggest that the number of nests was greatest when area of nesting substrate was high and water-levels were moderate (3.9 - 4.4 m). Nest numbers dropped when either nesting substrate or foraging habitat was limited. My investigation into the predictions of the match-mismatch and threshold hypotheses found that indeed, prey density can reduce or intensify the effects of a mismatch event. The interaction of prey density and foraging habitat availability was significant and positive in both models. Saturation thresholds existed for both fledging success (147 prey (m^2)^-1) and total productivity (189 prey (m^2)^-1), above which high concentrations of prey could sustain nesting when foraging habitat availability was low. Finally, my studies of the stress response support the hypothesis that hydrologic factors associated with prey availability play an important role in regulating nesting patterns, although the level of food limitation the birds experience at the lake was not as severe as expected. Model selection identified foraging habitat availability as most influential to the nestling Great Egret stress response, whereas foraging habitat availability and prey density both influenced nestling Snowy Egret stress response. Moreover, the Snowy Egret stress response was more sensitive to changes in prey availability than was the Great Egret stress response. Temperature and foraging conditions influenced yolk corticosterone concentrations for both egret species.

Theory predicts that when prey can reach a size refuge from predation, prey
vulnerability to predation is a function of hatchling size, growth rate, and the handling
limitations of its predator, which collectively influence the amount of time prey spend
vulnerable. I examined the mechanistic role of prey size for the predator-prey interaction
between predatory crayfish (Procambarus fallax) and apple snail prey (Pomacea
paludosa and P. maculata) and found that crayfish feeding rates decreased with snail
size, such that smaller hatchling P. maculata were more than twenty times more
vulnerable than hatchling P. paludosa. Experimental manipulations of productivity
increased apple snail growth rates, reducing the effects of predatory crayfish on P.
maculata survivorship, but not P. paludosa survivorship. My results indicate that when
prey can reach a size refuge from predation, increased system productivity decreases
predator limitation of that prey.

The ecosystem created by pelagic Sargassum is important in the life histories of a
number of economically and ecologically important associated organisms. Fishes play a
vital role in this food web and nutrient flow within these systems, but it is unknown how
they locate these floating habitats. This study examined the role of natural chemical cues
from Sargassum patches and the synthetic chemical Dimethylsulfonionpropionate
(DMSP) for an associated fish, the planehead filefish (Stephanolepis hispidus) and a
control fish species not associated with Sargassum, the masked goby (Coryphopterus
personatus). Choice trials with a Y-maze apparatus determined that S. hispidus
responded significantly to chemical cues from Sargassum while C. personatus did not.
DMSP cues did not result in any significant behavioral responses for either fish.
Demonstrating that S. hispidus can respond to chemical cues from Sargassum helps
further our understanding of this unique floating algal reef and how fishes may locate it.

Anthropogenic impacts, such as habitat destruction and spread of exotic species,
are contributing to the sixth major extinction event in Earth’s history. To develop
effective management and conservation plans, it is important to understand the ecological
drivers of at-risk populations, assess the ability of a population to adapt to environmental
change, and develop research methods for long-term ecosystem monitoring. I used
wading birds nesting in the Florida Everglades, USA as a model system to address the
challenges of managing and monitoring populations within an ecosystem greatly
impacted by anthropogenic activities. Specifically, my project investigated 1) the prey
selection of wading bird species, and the role of prey and foraging habitat availability on
annual nesting numbers, 2) the ability of using diet change to predict species adaptability
to a rapidly changing environment, and 3) the use of sensory data to provide low-cost,
long-term monitoring of dynamic wetlands. I found that tricolored herons, snowy egrets, and little blue herons consumed marsh fish larger than those generally available across
the landscape. Additionally, number of nests initiated by tricolored herons, snowy egrets,
and little blue herons was strongly correlated with the annual densities of large fish
available within the Everglades landscape. Conversely, number of nests initiated by
wood storks, great egrets, and white ibises was more correlated with the amount of
foraging habitat availability across the nesting season. Wood stork diets changed
considerably since the 1960’s, consisting of mainly sunfish and exotic fish as opposed to
marsh fishes dominant in historical diet studies. Storks also consumed more exotic fish
species than they did historically. This diet plasticity and the species’ ability to exploit
anthropogenic habitats may be conducive to maintaining population viability as storks
experience widespread human-induced changes to their habitat. Sensory-only data
models generated complementary results to models that used site-specific field data.
Additionally, sensory-only models were able to detect different responses between size
classes of fish to the processes that increase their concentrations in drying pools.
However, the degree to which sensory variables were able to fit species data was
dependent upon the ability of sensors to measure species-specific population drivers and
the scale at which sensors can measure environmental change.