Food Aversion Plus Odor Cue Protects Crop From Wild Mammals

Abstract: Wild mammals cause foraging damage to crops worldwide and nonlethal methods are required for controlling such damage. Many wildlife management situations demand protection of untreated foods. We tested learned food aversion plus an odor cue as a paradigm for protecting untreated model crop items from European badgers (Meles meles). Following conditioning with a combination of ziram and clove oil, badgers avoided untreated maize cobs in presence of a clove odor cue. A clove oil control did not condition badgers. This work has been an important step before proceeding to full-scale field trials for protecting growing crops on a wider scale. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):785–791; 2008)     

Rabbit populations and game management: the situation after 15 years of rabbit haemorrhagic disease in central-southern Spain

Over recent decades wild rabbit populations have undergone a sharp decline in Spain with consequent negative impact both on a game-based economy, and on the conservation of threatened species that depend on rabbits. We investigated the relationships between rabbit population change and habitat and game management in central-southern Spain. To determine recent rabbit population changes we revisited 60 localities during summer 2002 to repeat surveys previously carried out in 1993. Each survey consisted of 4-km walked transects to record indices of rabbit abundance. The percentage of vegetation cover and of different soil types were also estimated during these transects. In the same areas, the type and intensity of game management practices were obtained by interviewing hunting managers, hunters or gamekeepers. Rabbit populations were stable or increasing only in 26.6% of the studied populations, more commonly in areas with soft soils where warren building is easier for rabbits and where rabbits were an important game species and managed to increase their numbers. Although we could not establish causality, habitat management and predator removal were the main management practices related to rabbit population change. Rabbit scarcity in Spain constitutes a serious problem for conservation, so hunters, researchers and policy makers need to reach a consensus to establish a long-term program to monitor rabbit population trends and share results obtained, especially when intense manage programs are being carried out to improve rabbit abundance.     

Predator-induced changes in morphology of a prey fish: the effects of food level and temporal frequency of predation risk

In a series of experiments, we investigated the effects of food availability and risk frequency on the dynamics of predator-induced changes in growth and morphology of prey fish using goldfish (Carassius auratus) as our test species. In experiment 1, we fed goldfish high or low food rations and exposed them to either alarm cues from conspecifics, cues from swordtails or a water control. After 60 days, goldfish in the alarm cue treatment significantly increased their body depth and body weight but had smaller body length than goldfish exposed to swordtails cues or water, likely reducing their vulnerability to gape-limited predators. Importantly, food level had an impact on the amplitude of the morphological changes. In experiment 2, goldfish were exposed to two different frequencies of predation cues or a water control for 50 days. The cues were either continued or discontinued from day 51 to 100, and all cues were resumed from day 101 to 150. We found that goldfish exposed to predation cues increased their depth and weight at a faster rate than did the goldfish exposed to water, and of particular significance was the fact that frequency of risk had an effect on the amplitude of the change. When the cues were interrupted, the increase in growth rate parameters was reduced to the level of the goldfish exposed to water. However, when the cues were resumed, the rate increased to match the growth rate of the goldfish that were continuously exposed to the cues. Finally, we staged encounters between goldfish of differing morphologies and yellow perch (Perca flavescens) and found that deep-bodied goldfish had better survival than the shallow-bodied ones. These experiments illustrate the dynamic nature of inducible morphological defences.     

Reduced byssal thread production and movement by the intertidal mussel<Emphasis Type="Italic"> Hormomya mutabilis</Emphasis> in response to effluent from predators

Laboratory experiments were carried out to investigate byssal thread production by the intertidal mytilid mussel Hormomya mutabilis in response to effluent from the predatory crab Eriphia smithii and the starfish Coscinasterias acutispina. During the early period of the experiment, large H. mutabilis exposed to crab effluent produced a significantly smaller number of functional byssal threads than mussels in crab-free water. No significant difference in the diameter of threads produced in the two treatments was detected. The number of functional byssal threads produced by small H. mutabilis exposed to crab effluent did not differ significantly from that of mussels in crab-free water. However, small H. mutabilis exposed to crab effluent tended to discard fewer byssal bundles, that is, they shifted their attaching sites less frequently than similar mussels in crab-free water. In the presence of waterborne cues from the crab, H. mutabilis tended to reduce both the secretion of byssal threads and movement across the substratum. No significant differences in behaviour were observed between large mussels exposed to effluent from the starfish and those unexposed. The adaptive significance of the responses shown by H. mutabilis is discussed in terms of protection against predators differing in foraging behaviour. Electronic Publication     

Difference in response by two cyprinid species to predatory threat from the nocturnal catfish Silurus asotus

Response to predators may not be identical between different prey species with different life histories and body sizes, particularly when the threat of predation is not great. To clarify this hypothesis, we introduced two prey species (10 Japanese dace, Tribolodon hakonensis, and 10 pale chub, Zacco platypus) into each experimental pond (in total, 8 ponds×4 trials) in which benthic algae had been allowed to grow. The presence or absence of Far Eastern catfish, Silurus asotus, and a refuge for prey fish was used to produce four treatments. The presence of catfish and/or a refuge did not affect either the feeding behavior or growth rate of Japanese dace. In contrast, when catfish were present and no refuge was available, the incidence of bottom feeding for pale chub greatly decreased. Pale chub growth rate was low when catfish were present and a refuge was available, indicating that pale chub spent more of their time in the refuge and lost opportunities of acquiring food. Japanese dace can reach a threshold size at which the prey are safe from predation, but pale chub cannot, and this may explain the differences in response to predators of the two species.     

Ventilatory frequency indicates visual recognition of an allopatric predator in nai;ve Nile tilapia

Perceiving a possible predator may promote physiological changes to support prey ‘fight or flight’. In this case, an increase in ventilatory frequency (VF) may be expected, because this is a way to improve oxygen uptake for escape tasks. Therefore, changes in VF may be used as a behavioral tool to evaluate visual recognition of a predator threat. Thus, we tested the effects of predator visual exposure on VF in the fish Nile tilapia, Oreochromis niloticus. For this, we measured tilapia VF before and after the presentation of three stimuli: an aquarium with a harmless fish or a predator or water (control). Nile tilapia VF increased significantly in the group visually exposed to a predator compared with the other two, which were similar to each other. Hence, we conclude that Nile tilapia may recognize an allopatric predator; consequently VF is an effective tool to indicate visual recognition of predator threat in fish.     

No influence of scopolamine hydrobromide on odor detection performance of rats

Despite speculation that the muscarinic cholinergic antagonist, scopolamine, may influence the olfactory sensitivity of rats, there have been no definitive studies on this point to date. In this study, we examined the influence of a range of doses of scopolamine hydrobromine (namely, 0.10, 0.125, 0.15 and 0.20 mg/kg i.p.) on the odor detection performance of 15 adult male Long-Evans rats to ethyl acetate. Air-dilution olfactometry and a go/no-go operant signal detection task were employed. The drug conditions and a saline control were administered to each animal in an order counterbalanced by Latin squares, with 2 day intervals interspersed between tests. Scopolamine had no significant influence on odor detection performance per se, as measured by percent correct S+ and S- responses and a non-parametric signal detection measure of sensitivity. This is in contrast to the relatively large effects previously observed in the same test paradigm for such drugs as the D-1 agonist SKF 38393 and the D-2 agonist quinpirole. These data suggest that scopolamine has no meaningful influence on a well-practiced odor detection task.     

The prevalence of androstenone anosmia

It has been estimated that approximately 30% of the population is unable to detect the odor of androstenone. These estimates, however, were made using tests and criteria optimized for identifying detection. Such criteria favor Type II over Type I errors--that is, they are excellent at identifying true detectors at the cost of erroneously labeling some detectors as non-detectors. Because these criteria were used to identify non-detectors, it is possible that the rate of non-detection may have been overestimated. To test this we screened 55 subjects for non-detection employing previously used methods. This screen yielded nine putative non-detectors, a 16.3% putative non-detection rate. We then retested these putative non-detectors using a forced choice (yes-no) paradigm to obtain a precise measure of their sensitivity. We found that this group of putative non-detectors was significantly above chance at detecting androstenone (P < 0.001), despite very low self-confidence in their performance. Based on the results of the signal detection analysis in this sample, we estimate the rate of actual androstenone non-detection in young healthy adults is between 1.8 and 5.96%, which is significantly lower than previously estimated. This finding is significant considering the implications of specific anosmias on the understanding of odor discrimination.     

A study of prey-predator relations for mammals

In this paper, we present a prey-predator nonlinear model for mammals, consisting of large- and small-size prey species with group defence, in a partially protected habitat. If the prey size is small, then it is more prone to the predator at higher densities. Conversely, large prey size at higher densities tend to develop group defence. Therefore, the predator will be attracted towards that area where prey are less in number. A new physical constant has been introduced into the radiation-type condition on that part of the boundary where interaction between prey and predator takes place. This constant allows us to efficiently model group defence capabilities of the herds and its numerical values have to be determined for different pairs of prey-predator species from field observations. A way of measuring the constants involved in the model is suggested. Numerical results are provided and thoroughly discussed for a habitat of circular shape. The obtained results show that in the region away from the protected area, the density of large-size prey species is higher than that of small-size prey species, a fact that is in accordance with observations.     

The evolutionary importance of mechanoreception in three erpobdellid leech species

Summary The ability of an erpobdellid leech, Erpobdella montezuma, to discriminate between two congeneric amphipod prey (Hyalella montezuma and Hyalella azteca) through mechanoreception was examined. Both E. montezuma and H. montezuma, a pelagic filter feeder, are endemic to the near thermally constant environment of Montezuma Well, Arizona, and form a highly specialized predator-prey relationship. In contrast, H. azteca, a benthic detritivore, is widely distributed throughout North America. Erpobdella montezuma was highly responsive to the prey signals of the endemic H. montezuma and showed only a limited response to H. azteca. An inverse relationship occurred between the frequency of attack and size of the leech. The abilities of Erpobdella punctata and Nephelopsis obscura, neither found in Montezuma Well, to detect the signals of both amphipod prey were also examined. These species with non-specialized diets showed a low response to the signals of both prey species. This study demonstrates that very close predator-prey relationships can develop over evolutionary time in isolated aquatic systems through the use of mechanoreception.