Predator-Prey Interactions

Ecosystem restoration with teeth: what role for predators?

by Euan Ritchie

Recent advances highlight the potential for predators to restore ecosystems and confer resilience against globally... more Recent advances highlight the potential for predators to restore ecosystems and confer resilience against globally threatening processes, including climate change and biological invasions. However, releasing the ecological benefits of predators entails significant challenges. Here, we discuss the economic, environmental and social considerations affecting predator-driven ecological restoration programmes, and suggest approaches for reducing the undesirable impacts of predators. Because the roles of predators are context dependent, we argue for increased emphasis on predator functionality in ecosystems and less on the identities and origins of species and genotypes. We emphasise that insufficient attention is currently given to the importance of variation in the social structures and behaviours of predators in influencing the dynamics of trophic interactions. Lastly, we outline experiments specifically designed to clarify the ecological roles of predators and their potential utility in ecosystem restoration.

Modelling evolutionarily stable strategies in oviposition site selection, with varying risks of predation and intraspecific competition

by Arik Kershenbaum

Many ovipositing mosquitoes, as well as other species, can detect biotic factors that affect fitness. However, a... more Many ovipositing mosquitoes, as well as other species, can detect biotic factors that affect fitness. However, a female mosquito seeking a high quality oviposition site (e.g. one with low risk of predation and competition to her progeny) must often balance the competing risk of increasing probability of mortality to herself while she continues to search, against increased probability of finding a high quality site. Such oviposition site selection may affect adult population size. We examined a female mosquito’s expected strategy of oviposition site selection under conditions of varying predator prevalence and adult mortality risk, by combining a detailed structured population model with a Markov chain implementation of the adult behavioural process. We used parameter values from the specific mosquito-predator system, Culiseta longiareolata-Notonecta maculata, although the overall results can be generalised to many mosquito species. Our model finds the evolutionarily stable strategy of oviposition site selection for different parameter combinations. Our model predicts that oviposition strategy does not vary smoothly with varying environmental risk of adult mortality, but that certain oviposition strategies become unstable at some parameter values. Mosquitoes will distribute their reproductive effort between breeding sites of varying predation risk only when adult mortality is low or larval competition high. Our model predicts that females will continue searching for predator-free pools, rather than oviposit in the first site encountered, regardless of the risk of mortality to the adult. The ecological basis for a reproductive strategy with alternative behaviours is important for understanding the effect of biotic factors on the population dynamics of mosquitoes, and for the development of biological control strategies, such as the dissemination of predator-cue chemicals.

High rate of prey consumption in a small predatory fish on coral reefs

by William Feeney

Feeney, W. E., Lönnstedt, O., Bosiger, Y., Martin, J., Jones, G., Rowe, R. & McCormick, M.

Small piscivores are regarded as important regulators of the composition of coral reef fish communities, but few... more Small piscivores are regarded as important regulators of the composition of coral reef fish communities, but few studies have investigated their predatory ecology or impact on assemblages of juvenile fishes. This study investigated the foraging ecology of a common coral reef predator, the dottyback Pseudochromis fuscus, using underwater focal animal observations. Observations were conducted at two times of year: the summer, when recruit fishes were an available food item and winter, when remaining juveniles had outgrown vulnerability to P. fuscus. During the summer, P. fuscus directed 76% of its strikes at invertebrates and 24% at recruiting juvenile fishes. When striking at fishes, P. fuscus exhibited two distinct feeding modes: an ambush (26% successful) and a pursuit mode (5% successful). Predator activity in the field peaked at midday, averaging 2.5 captures h−1 of juvenile fishes. Monitoring of activity and foraging in the laboratory over 24-h periods found that P. fuscus was a diurnal predator and was active for 13 h d−1 during the summer. The number of hours during which foraging was recorded differed greatly among individuals (n = 10), ranging from 4 to 13 h. The number of predatory strikes did not increase with standard length, but the success rate and consumption rate of juvenile fishes did increase with size. Estimated hourly mortality on juvenile fish ranged from 0.49 fish h−1 in small P. fuscus individuals (30–39 mm standard length, SL; equating to 6.3 per 13 h day) to 2.4 fish h−1 in large P. fuscus individuals (55–65 mm SL; 30.6 per 13 h day). During the winter, P. fuscus struck at invertebrates with a similar rate to the summer period. These observations of the predatory ecology of P. fuscus support the hypothesis that in coral reef systems, small piscivores, because of their high metabolism and activity, are probably important regulators of coral reef fish community composition.

Barking Owl Diet in the Pilliga Forests of Northern NSW

by Matthew Stanton

Master of Science Thesis (UNE 2011)

The Barking Owl Ninox connivens population in the Pilliga forests of northern New South Wales is the largest known in... more The Barking Owl Ninox connivens population in the Pilliga forests of northern New South Wales is the largest known in southern Australia. Breeding pairs in this population occupy large home-ranges across less than half of the forest. In this thesis, I quantify the diet of Barking Owls in the Pilliga. I consider a number of hypotheses that could explain the species’ large home ranges and restricted distribution, particularly those that are related to prey availability.
This is the first diet study of a Barking Owl population to incorporate data from many territories over several years and all seasons of the year. Radio-tracking of nine owls provided the opportunity to begin a substantial collection of prey remains (regurgitated pellets, food debris and faecal material). Ultimately, the collection period spanned 2003 – 2009, with prey remains from 19 territories in the Pilliga and one territory in a small forest to the south near Dubbo. In total, 1546 regurgitated pellets and 315 faecal samples were collected and examined. Foraging observations improved the understanding of the results.
Barking Owls in the Pilliga forests preyed on most species of diurnal and nocturnal birds, as well as Sugar Gliders, bats and insects, with a few items being taken from the ground. Prey size ranged from 0.3 gram insects to ~800 gram cockatoos and mammals, a similar size to the owls. Most prey were native animals in contrast to some other studies.
The proportions of consumed prey, as determined by pellet analysis, were compared with available prey, as determined by bird counts, spotlight surveys, small mammal trapping, bat surveys and insect netting. Prey items from all prey groups were available from all sampled areas of the Pilliga. Barking Owls distribution was positively associated with prey availability: significantly with the biomass of birds and with flying insect numbers. Mammal groups were not significantly different but showed the same positive trend.
Spatial availability of total prey biomass offered a good explanation for the distribution of Barking Owls within the Pilliga forests. Crucial food resources, particularly available biomass of diurnal birds and nocturnally active prey, may limit the population density and distribution of owls in what appears to be marginal rather than prime habitat. Land cleared for agriculture, because of its higher productivity, may have previously supported higher densities of Barking Owls when wooded.

The confusion effect in predatory neural networks

by Andrew Jackson

A simple artificial neural network model of image reconstruction in sensory maps is presented to explain the... more A simple artificial neural network model of image reconstruction in sensory maps is presented to explain the difficulty predators experience in targeting prey in large groups (the confusion effect). Networks are trained to reconstruct multiple randomly conformed “retinal” images of prey groups in an internal spatial map of their immediate environment. They are then used to simulate prey targeting by predators on groups of specific conformation. Networks trained with the biologically plausible associative reward‐penalty method produce a more realistic model of the confusion effect than those trained with the popular but biologically implausible backpropagation method. The associative reward‐penalty model makes the novel prediction that the accuracy–group size relationship is U shaped, and this prediction is confirmed by empirical data gathered from interactive computer simulation experiments with humans as “predators.” The model further predicts all factors known from previous empirical work (and most factors suspected) to alleviate the confusion effect: increased relative intensity of the target object, heterogeneity of group composition, and isolation of the target. Interestingly, group compaction per se is not predicted to worsen predator confusion. This study indicates that the relatively simple, nonattentional mechanism of information degradation in the sensory mapping process is potentially important in generating the confusion effect.

The effects of group size, shape and composition on ease of detection

by Andrew Jackson

The role of aggregation in prey defence has been the subject of much debate. For example, the commonly cited... more The role of aggregation in prey defence has been the subject of much debate. For example, the commonly cited assumption of encounter-dilution effects requires that attack rates increase asymptotically with increasing group size. One key parameter that is still poorly understood is how ease of detection of cryptic prey aggregations is affected by group size, shape, density and composition. We have developed a computer based visual test to elucidate these effects using human subjects. We show that ease of detection of cryptic prey increases asymptotically and quickly saturates with group size: this is in accordance with a previously reported laboratory test of birds. We also discovered that horizontally-orientated groups were more easily detected than either circular or vertically arranged ones. No effect of the degree of spatial clustering of prey occurring in groups was found, and nor did heterogeneity or homogeneity in the visual appearance of group members affect ease of detection — although future work on these aspects is warranted.

On predator deterrence by pronounced shell ornament in epifaunal bivalves

by Hywel Stone

Early Evolutionary Trends In Ammonoid Embryonic Development

by Kenneth De Baets

De Baets, K., Klug, C., Korn, D. & Landman, N. H. (2012). Evolution. doi: 10.1111/j.1558-5646.2011.01567.x

During the Devonian Nekton Revolution, ammonoids show a progressive coiling of their shell just like many other... more During the Devonian Nekton Revolution, ammonoids show a progressive coiling of their shell just like many other pelagic mollusk groups. These now extinct, externally shelled cephalopods derived from bactritoid cephalopods with a straight shell in the Early Devonian. During the Devonian, evolutionary trends toward tighter coiling and a size reduction occurred in ammonoid embryonic shells. In at least three lineages, descendants with a closed umbilicus evolved convergently from forms with an opening in the first whorl (umbilical window). Other lineages having representatives with open umbilici became extinct around important Devonian events while only those with more tightly coiled embryonic shells survived. This change was accompanied by an evolutionary trend in shape of the initial chamber, but no clear trend in its size. The fact that several ammonoid lineages independently reduced and closed the umbilical window more or less synchronously indicates that common driving factors were involved. A trend in size decrease of the embryos as well as the concurrent increase in adult size in some lineages likely reflects a fundamental change in reproductive strategies toward a higher fecundity early in the evolutionary history of ammonoids. This must have played an important role in their subsequent success as well as in their demise.

Excess digestive capacity in predators reflects a life of feast and famine

by Jonathan Armstrong

Predatory trading and risk minimisation: how to (b)eat the competition

by Anita Mehta

Predatory Diversity of Finfish Species Inhabiting the Same Ecological Niche: Dissertation Submitted in Partial Fulfillment of Degree of Master of Science in …

by Deepak Pazhayamadom

Persistent predator–prey dynamics revealed by mass extinction

by Lauren Sallan

COMPLEX BEHAVIOR IN DYNAMICAL SYSTEMS

by Edmund Brekke

Secondary metabolites help biocontrol strain Pseudomonas fluorescens CHA0 to escape protozoan grazing

by Alexandre Jousset

Predators promote defence of rhizosphere bacterial populations by selective feeding on non-toxic cheaters

by Alexandre Jousset

Predator-prey chemical warfare determines the expression of biocontrol genes by rhizosphere-associated Pseudomonas fluorescens

by Alexandre Jousset

Secondary Metabolites of Pseudomonas fluorescens CHA0 Drive Complex Non-Trophic Interactions with Bacterivorous Nematodes

by Alexandre Jousset

The model predator Acanthamoeba castellanii induces the production of 2, 4, DAPG by the biocontrol strain Pseudomonas fluorescens Q2-87

by Alexandre Jousset

Ecological and evolutive implications of bacterial defences against predators

by Alexandre Jousset

Secondary metabolite production facilitates establishment of rhizobacteria by reducing both protozoan predation and the competitive effects of indigenous bacteria

by Alexandre Jousset