Temporal Limitations on Social Learning of Novel Predators by Indian Mynahs, Acridotheres tristis

Antipredator vocalizations of social companions are important for facilitating long-term changes in the responses of prey to novel predator stimuli. However, dynamic variation in the time course of acoustic communication has important implications for learning of predator cues associated with auditory signals. While animals often experience acoustic signals simultaneously with predator cues, they may also at times experience signals and predator stimuli in succession. The ability to learn about stimuli that are perceived not only together, but also after, acoustic signals has the potential to expand the range of opportunities for learning about novel events. Earlier work in Indian mynahs ( Acridotheres tristis ) has revealed that subjects acquire a visual exploratory response to a novel avian mount after they have experienced it together with conspecific distress vocalizations, a call produced in response to seizure by a predator. The present study explored to what extent such learning occurred if the avian mount was experienced after, rather than simultaneously with, distress calls, such as might happen if call production is interrupted by prey death. Results showed that mynahs that experienced a novel avian mount simultaneously with the sound of distress calls exhibited a sustained exploratory response to the mount after training relative to before that was not apparent in birds that received distress calls and mount in succession. This finding suggests that vocal antipredator signals may only trigger learning of environmental stimuli with which they share some temporal overlap. Recipients may need to access complementary non-vocal cues from the prey victim to learn about predator stimuli that are perceived after vocal behaviour.     

Predators induce egg retention in prey

To prevent predation on their eggs, prey often avoid patches occupied by predators. As a result, they need to delay oviposition until they reach predator-free patches. Because many species allocate energy to egg production in a continuous fashion, it is not clear what kind of mechanism prey use to delay oviposition. We used females of the phytoseiid mite Neoseiulus cucumeris to study these mechanisms. Females were placed in patches with pollen, a food source they use for egg production, and they were exposed to another phytoseiid mite, Iphiseius degenerans, which is an intraguild predator of N. cucumeris juveniles. We found that the oviposition of N. cucumeris females on patches with the predator was lower than on patches without the predator. Cues left by the intraguild predator were not sufficient to elicit such behaviour. Females of N. cucumeris reduced oviposition when exposed to the predator by retaining the egg inside their body, resulting in a lower developmental rate once these eggs were laid. Hence, females are capable of retaining eggs, but the development of these eggs continues inside the mother’s body. In this way, females gain some time to search for less risky oviposition sites.     

Antagonistic and Synergistic Interactions Among Predators

The structure and dynamics of food webs are largely dependent upon interactions among consumers and their resources. However, interspecific interactions such as intraguild predation and interference competition can also play a significant role in the stability of communities. The role of antagonistic/synergistic interactions among predators has been largely ignored in food web theory. These mechanisms influence predation rates, which is one of the key factors regulating food web structure and dynamics, thus ignoring them can potentially limit understanding of food webs. Using nonlinear models, it is shown that critical aspects of multiple predator food web dynamics are antagonistic/synergistic interactions among predators. The influence of antagonistic/synergistic interactions on coexistence of predators depended largely upon the parameter set used and the degree of feeding niche differentiation. In all cases when there was no effect of antagonism or synergism (a _ij =1.00), the predators coexisted. Using the stable parameter set, coexistence occurred across the range of antagonism/synergism used. However, using the chaotic parameter strong antagonism resulted in the extinction of one or both species, while strong synergism tended to coexistence. Whereas using the limit cycle parameter set, coexistence was strongly dependent on the degree of feeding niche overlap. Additionally increasing the degree of feeding specialization of the predators on the two prey species increased the amount of parameter space in which coexistence of the two predators occurred. Bifurcation analyses supported the general pattern of increased stability when the predator interaction was synergistic and decreased stability when it was antagonistic. Thus, synergistic interactions should be more common than antagonistic interactions in ecological systems.     

Chemical Detection of Microbial Prey by Bacterial Predators

A motile, predacious bacterium which degraded Pythium debaryanum was strongly attracted to substances released into the medium by the fungus. A nonpredacious bacterium was not attracted to these substances. The predator bacterium was specifically attracted to cellulose and its oligomers which are known to be components of the cell wall of Pythium. Ethanol inhibited chemotaxis of the bacterium without affecting either its motility or its ability to degrade cellulose. A second predacious bacterium was isolated for the alga, Skeletonema costatum. The role of chemoreception in the detection of microbial prey by bacterial predators in natural habitats is discussed.     

Predators favour mimicry in a tropical reef fish

Batesian mimicry evolves when the 'umbrella' of protection provided by resemblance to a conspicuous unpalatable model species is sufficient to overcome increased predation risk associated with greater conspicuousness. However, the shape and extent of this umbrella, that is, how the level of protection provided by mimicry changes with degree of resemblance between model and mimic, is poorly known. We investigated the response of wild predatory fishes to plastic replicas of a model-mimic species pair of tropical reef fishes, Canthigaster valentini (a toxic pufferfish, the model) and Paraluteres prionurus (the putative mimic), and additional replicas with progressively lower degrees of resemblance to the mimic species. Our results reveal a relatively broad region of protection, indicated by a reduced approach rate by piscivorous fishes, surrounding the colour pattern of the model species. Protection increased with increasing resemblance. By contrast, the response of non-piscivorous fishes was unrelated to degree of resemblance of replicas to the model. Our results suggest that piscivorous fishes on the reef are educated regarding the toxicity of C. valentini, and that avoidance of fish having the pufferfish colour pattern has generated selection favouring mimetic resemblance by the palatable P. prionurus. The relatively broad protective umbrella has probably facilitated the initial evolution of resemblance in the palatable prey species despite the potential hazards of greater conspicuousness.     

Predators Reduce Extinction Risk in Noisy Metapopulations

Background

Spatial structure across fragmented landscapes can enhance regional population persistence by promoting local “rescue effects.” In small, vulnerable populations, where chance or random events between individuals may have disproportionately large effects on species interactions, such local processes are particularly important. However, existing theory often only describes the dynamics of metapopulations at regional scales, neglecting the role of multispecies population dynamics within habitat patches.

Findings

By coupling analysis across spatial scales we quantified the interaction between local scale population regulation, regional dispersal and noise processes in the dynamics of experimental host-parasitoid metapopulations. We find that increasing community complexity increases negative correlation between local population dynamics. A potential mechanism underpinning this finding was explored using a simple population dynamic model.

Conclusions

Our results suggest a paradox: parasitism, whilst clearly damaging to hosts at the individual level, reduces extinction risk at the population level.     

Geminiviruses Associated with Diseased Tomatoes in Cuba

Tomato plants displaying symptoms of yellowing and leaf curling were analysed for the presence of geminiviruses. Two distinct geminiviruses were present in the plants studied. One had a genome size and coat protein gene sequence similar to the Israeli strain of tomato yellow leaf curl virus (TYLCV), while the other had a smaller genome size than TYLCV that could not be amplified using primers specific for Israeli TYLCV. The presence of the Israeli strain of TYLCV has been reported in other Caribbean islands, but not in Southern Florida (USA) which is close to those islands where TYLCV has been detected. This suggests that the introduction of the Israeli strain of TYLCV to the Caribbean area may have occurred within recent times.     

Imidacloprid Alters Foraging and Decreases Bee Avoidance of Predators

Concern is growing over the effects of neonicotinoid pesticides, which can impair honey bee cognition. We provide the first demonstration that sublethal concentrations of imidacloprid can harm honey bee decision-making about danger by significantly increasing the probability of a bee visiting a dangerous food source. Apis cerana is a native bee that is an important pollinator of agricultural crops and native plants in Asia. When foraging on nectar containing 40 µg/L (34 ppb) imidacloprid, honey bees (Apis cerana) showed no aversion to a feeder with a hornet predator, and 1.8 fold more bees chose the dangerous feeder as compared to control bees. Control bees exhibited significant predator avoidance. We also give the first evidence that foraging by A. cerana workers can be inhibited by sublethal concentrations of the pesticide, imidacloprid, which is widely used in Asia. Compared to bees collecting uncontaminated nectar, 23% fewer foragers returned to collect the nectar with 40 µg/L imidacloprid. Bees that did return respectively collected 46% and 63% less nectar containing 20 µg/L and 40 µg/L imidacloprid. These results suggest that the effects of neonicotinoids on honey bee decision-making and other advanced cognitive functions should be explored. Moreover, research should extend beyond the classic model, the European honey bee (A. mellifera), to other important bee species.