Habitat-predator association and avoidance in rainbowfish (Melanotaenia spp.)

The ability to recall the location of a predator and later avoid it was tested in nine populations of rainbowfish (Melanotaenia spp.), representing three species from a variety of environments. Following the introduction of a model predator into a particular microhabitat, the model was removed, the arena rotated and the distribution of the fish recorded again. In this manner it could be determined what cues the fish relied on in order to recall the previous location of the predator model. Fish from all populations but one (Dirran Creek) were capable of avoiding the predator by remembering either the location and/or the microhabitat in which the predator was recently observed. Reliance on different types of visual cues appears to vary between populations but the reason for this variation remains elusive. Of the ecological variables tested (flow variability, predator density and habitat complexity), only the level of predation appeared to be correlated with the orientation technique employed by each population. There was no effect of species identity, which suggests that the habitat that each population occupies plays a strong role in the development of both predator avoidance responses and the cues used to track predators in the wild.

Microhabitat use by the rainbowfish Melanotaenia duboulayi in a subtropical Australian stream

Microhabitat use and feeding behavior of the rainbowfish Melanotaenia duboulayi (Castelnau) were investigated in a slow-flowing stream adjacent to riparian forest in south-eastern Queensland, Australia. Fish were more abundant in vegetated areas, but did not enter dense Vallisneria beds, where predators were observed. In sunny conditions shoals of juveniles occurred near the water surface feeding floating material on the surface, but larger fish tended to occur at the bottom near submerged vegetation, often utilizing the overhanging aquatic plant community as a refuge and food source. In the middle of the day, juveniles and small fish seemed to show behavioral thermoregulation at the surface in the warmest site. Under cloudy conditions, however, fish of all sizes preferred deeper water. The present study suggests that in still and sunny pools thermal change caused by sunlight influences the microhabitat choice of small fish. A field experiment using a kingfisher model implies that fish swimming at the surface could escape from aerial predators in sunlit conditions by responding to moving shadows, but could not do so under cloudy conditions.

Infrasound initiates directional fast-start escape responses in juvenile roach Rutilus rutilus

Acoustic stimuli within the sonic range are effective triggers of C-type escape behaviours in fish. We have previously shown that fish have an acute sensitivity to infrasound also, with acceleration thresholds in the range of 10(-5) m s(-2). In addition, infrasound at high intensities around 10(-2) m s(-2) elicits strong and sustained avoidance responses in several fish species. In the present study, the possible triggering of C-escapes by infrasonic single-cycle vibrations was examined in juvenile roach Rutilus rutilus. The fish were accelerated in a controlled and quantifiable manner using a swing system. The applied stimuli simulated essential components of the accelerations that a small fish would encounter in the hydrodynamic flow field produced by a predatory fish. Typical C- and S-type escape responses were induced by accelerations within the infrasonic range with a threshold of 0.023 m s(-2) for an initial acceleration at 6.7 Hz. Response trajectories were on average in the same direction as the initial acceleration. Unexpectedly, startle behaviours mainly occurred in the trailing half of the test chamber, in which the fish were subjected to linear acceleration in combination with compression, i.e. the expected stimuli produced by an approaching predator. Very few responses were observed in the leading half of the test chamber, where the fish were subjected to acceleration and rarefaction, i.e. the stimuli expected from a suction type of predator. We conclude that particle acceleration is essential for the directionality of the startle response to infrasound, and that the response is triggered by the synergistic effects of acceleration and compression.

Freshwater to seawater acclimation of juvenile bull sharks ( Carcharhinus leucas): plasma osmolytes and Na +/K +-ATPase activity in gill, rectal gland, kidney and intestine

This study examined the osmoregulatory status of the euryhaline elasmobranch Carcharhinus leucas acclimated to freshwater (FW) and seawater ( SW). Juvenile C. leucas captured in FW ( 3 mOsm l(-1) kg(-1)) were acclimated to SW ( 980 - 1,000 mOsm l(-1) kg(-1)) over 16 days. A FW group was maintained in captivity over a similar time period. In FW, bull sharks were hyper-osmotic regulators, having a plasma osmolarity of 595 mOsm l(-1) kg(-1). In SW, bull sharks had significantly higher plasma osmolarities ( 940 mOsm l(-1) kg(-1)) than FW-acclimated animals and were slightly hypoosmotic to the environment. Plasma Na+, Cl-, K+, Mg2+, Ca2+, urea and trimethylamine oxide (TMAO) concentrations were all significantly higher in bull sharks acclimated to SW, with urea and TMAO showing the greatest increase. Gill, rectal gland, kidney and intestinal tissue were taken from animals acclimated to FW and SW and analysed for maximal Na+/ K+-ATPase activity. Na+/ K+-ATPase activity in the gills and intestine was less than 1 mmol Pi mg(-1) protein h(-1) and there was no difference in activity between FW- and SW-acclimated animals. In contrast Na+/ K+-ATPase activity in the rectal gland and kidney were significantly higher than gill and intestine and showed significant differences between the FW- and SW-acclimated groups. In FW and SW, rectal gland Na+/ K+-ATPase activity was 5.6 +/- 0.8 and 9.2 +/- 0.6 mmol Pi mg(-1) protein h(-1), respectively. Na+/ K+-ATPase activity in the kidney of FW and SW acclimated animals was 8.4 +/- 1.1 and 3.3 +/- 1.1 Pi mg(-1) protein h(-1), respectively. Thus juvenile bull sharks have the osmoregulatory plasticity to acclimate to SW; their preference for the upper reaches of rivers where salinity is low is therefore likely to be for predator avoidance and/or increased food abundance rather than because of a physiological constraint.

The effects of predator odors in mammalian prey species: A review of field and laboratory studies

wPrey species show specific adaptations that allow recognition, avoidance and defense against predators. For many mammalian species this includes sensitivity towards predator-derived odors. The typical sources of such odors include predator skin and fur, urine, feces and anal gland secretions. Avoidance of predator odors has been observed in many mammalian prey species including rats, mice, voles, deer, rabbits, gophers, hedgehogs, possums and sheep. Field and laboratory studies show that predator odors have distinctive behavioral effects which include (1) inhibition of activity, (2) suppression of non-defensive behaviors such as foraging, feeding and grooming, and (3) shifts to habitats or secure locations where such odors are not present. The repellent effect of predator odors in the field may sometimes be of practical use in the protection of crops and natural resources, although not all attempts at this have been successful. The failure of some studies to obtain repellent effects with predator odors may relate to (1) mismatches between the predator odors and prey species employed, (2) strain and individual differences in sensitivity to predator odors, and (3) the use of predator odors that have low efficacy. In this regard, a small number of recent studies have suggested that skin and fur-derived predator odors may have a more profound lasting effect on prey species than those derived from urine or feces. Predator odors can have powerful effects on the endocrine system including a suppression of testosterone and increased levels of stress hormones such as corticosterone and ACTH. Inhibitory effects of predator odors on reproductive behavior have been demonstrated, and these are particularly prevalent in female rodent species. Pregnant female rodents exposed to predator odors may give birth to smaller litters while exposure to predator odors during early life can hinder normal development. Recent research is starting to uncover the neural circuitry activated by predator odors, leading to hypotheses about how such activation leads to observable effects on reproduction, foraging and feeding. (c) 2005 Elsevier Ltd. All rights reserved.

Effect of density on spatial distribution, pit formation and pit diameter of Myrmeleon acer Walker, (Neuroptera : Myrmeleontidae): patterns and processes

The effect of increasing population density on the formation of pits, their size and spatial distribution, and on levels of mortality was examined in the antlion Myrmeleon acer Walker. Antlions were kept at densities ranging from 0.4 to 12.8 individuals per 100 cm(2). The distribution of pits was regular or uniform across all densities, but antlions constructed proportionally fewer and smaller pits as density increased. Mortality through cannibalism was very low and only occurred at densities greater than five individuals per 100 cm(2). Antlions in artificially crowded situations frequently relocated their pits and when more space became available, individuals became more dispersed with time. Redistribution of this species results from active avoidance of other antlions and sand throwing associated with pit construction and maintenance, rather than any attempt to optimise prey capture per se.

The response of native Australian rodents to predator odours varies seasonally: a by-product of life history variation?

Small mammals are subject to predation from mammalian, avian and reptilian predators. There is an obvious advantage for prey species to detect the presence of predators in their environment, enabling them to make decisions about movement and foraging behaviour based on perceived risk of predation. We examined the effect of faecal odours from marsupial and eutherian predators, and a native reptilian predator, on the behaviour of three endemic Australian rodent species (the fawn-footed melomys, Melomys cervinipes, the bush rat, Rattus fuscipes, and the giant white-tailed rat, Uromys caudimaculatus) in rainforest remnants on the Atherton Tableland, North Queensland, Australia. Infrared camera traps were used to assess visit rates of rodents to odour stations containing faecal and control odours. Rodents avoided odour stations containing predator faeces, but did not avoid herbivore or control odours. The responses of the three prey species differed: in the late wet season U. caudimaculatus avoided predator odours, whereas R. fuscipes and M. cervinipes did not. In contrast, in the late dry season all three species avoided odour stations containing predator odours. We speculate that these different responses may result from variation in life history traits between the species. (c) 2006 The Association for the Study of Animal Behaviour Published by Elsevier Ltd. All rights reserved.

Australia, the United States and a 'China growing strong': managing conflict avoidance

How to deal with a rising China constitutes one of the most seminal challenges facing the ANZUS alliance since its inception a half a century ago. Australia must reconcile its geography and economic interests in Asia with its post-war strategic and historic cultural orientation towards the United States. It must succeed in this policy task without alienating either Beijing or Washington in the process. The extent to which this is achieved will shape Australia's national security posture for decades to come. Three specific components of the 'Sino-American-Australian' triangle are assessed here: the future of Taiwan, the American development of a National Missile Defence (NMD), and the interplay between Sino-American power balancing and multilateral security politics. The policy stakes for Australia and for the continued viability of ANZUS are high in all three policy areas as a new US Administration takes office in early 2001. The article concludes that Australia's best interest is served by applying deliberate modes of decisionmaking in its own relations with both China and the US and by facilitating consistent and systematic dialogue and consultations with both of those great powers on key strategic issues.

Divorce, dispersal and incest avoidance in the cooperatively breeding superb fairy-wren Malurus cyaneus

1. Between 1988 and 2001, we studied social relationships in the superb fairy-wren Malurus cyaneus (Latham), a cooperative breeder with male helpers in which extra-group fertilizations are more common than within-pair fertilizations. 2. Unlike other fairy-wren species, females never bred on their natal territory. First-year females dispersed either directly from their natal territory to a breeding vacancy or to a foreign 'staging-post' territory where they spent their first winter as a subordinate. Females dispersing to a foreign territory settled in larger groups. Females on foreign territories inherited the territory if the dominant female died, and were sometimes able to split the territory into two by pairing with a helper male. However, most dispersed again to obtain a vacancy. 3. Females dispersing from a staging post usually gained a neighbouring vacancy, but females gaining a vacancy directly from their natal territory travelled further, perhaps to avoid pairing or mating with related males. 4. Females frequently divorced their partner, although the majority of relationships were terminated by the death of one of the pair. If death did not intervene, one-third of pairings were terminated by female-initiated divorce within 1000 days. 5. Three divorce syndromes were recognized. First, females that failed to obtain a preferred territory moved to territories with more helpers. Secondly, females that became paired to their sons when their partner died usually divorced away from them. Thirdly, females that have been in a long relationship divorce once a son has gained the senior helper position. 6. Dispersal to avoid pairing with sons is consistent with incest avoidance. However, there may be two additional benefits. Mothers do not mate with their sons, so dispersal by the mother liberates her sons to compete for within-group matings. Further, divorcing once their son has become a breeder or a senior helper allows the female to start sons in a queue for dominance on another territory. Females that do not take this option face constraints on their ability to recruit more sons into the local neighbourhood.