Rick-sensitive foraging in common shrews: an interruption model and the effects of mean and variance in reward rate

Summary A model of risk-sensitive foraging based on a continuously foraging but interruptable predator is developed and tested in a simple choice experiment using common shrews.Given a choice of two feeding stations, shrews behaved in accordance with the broad predictions of the model. Having been trained below their estimated food requirement, shrewss preferred the station y elding the higher mean reward rate, but prefereence for a constant (constant reward rate) or risky variable reward rate) station was influenced by experience of variance in reward rate at the risky station.Preference was influenced most clearly by experience of reward rate variance during tests rather than training.     

Genetic evidence for hybridisation between Haliotis rubra and H. laevigata

Seventeen abalone whose appearance was intermediate between the two commonly fished species in south-eastern Australia, blacklip (Haliotis rubra) and greenlip (H. laevigata), were collected between 1986 and 1989. Protein electrophoresis revealed that rare, morphologically intermediate abalone are predominantly F₁ hybrids; others are backcross individuals. There is also evidence of possible local introgression of H. rubra genes into H. laevigata and vice versa in sympatric populations. These two species exhibit marked morphological, behavioural and genetic differences, and yet hybridisation, although rare, occurs in at least several regions of sympatry. The commonly invoked explanations for the breakdown of species barriers, environmental disturbance and rarity of one of the parent species, do not appear applicable, unless microhabitat separation creates local rarity of one species. The frequency of hybridisation is discussed in relation to regional biogeography.     

Lipid composition of yellowtail flounder (<Emphasis Type="Italic">Limanda ferruginea</Emphasis>) in relation to dietary lipid intake

Condition indices (CI), hepatosomatic indices (HSI) and proximate, lipid and fatty acid composition of wild and laboratory-reared yellowtail flounder (Limanda ferruginea) (Storer, 1839) were compared from data taken throughout spring and summer 1996–1998. Cluster analysis was performed on the fatty acid signatures of these two groups along with a commercial diet and several invertebrate species to determine possible feeding patterns in Conception Bay, Newfoundland. HSI and levels of storage fat were significantly higher in the muscle and liver of laboratory-reared yellowtail flounder, indicating an efficient absorption of dietary lipid and an increase in fat deposition. Fatty acid analysis of the liver showed that wild fish contained significantly higher proportions of the essential fatty acids 20:46, 20:53 and 22:63; whereas proportions of 18:1 and 18:26 were significantly higher in all fractions of lipid examined from laboratory-reared fish than they were from wild fish. Polar fractions of lipid were more similar than the neutral fraction of lipid when comparing wild and laboratory-reared fish. Taken together, the differences in CI, HSI, proximate and fatty acid composition suggest that feeding commercial diets to L. ferruginea can cause changes in patterns of lipid deposition and metabolism. Cluster analysis of marine plankton, sedimenting particulate matter, wild invertebrates, the commercial diet and fish tissues showed that the fatty acid signatures of both wild and laboratory-reared yellowtail flounder closely resembled their respective food items. Fatty acid signatures from wild fish were more closely related to plankton and settling particulate matter, suggesting relatively few steps in the food web leading to yellowtail flounder. In addition to the resemblance between fatty acids in the commercial diet and the tissues of laboratory-reared yellowtail flounder, these fish had similar fatty acid signatures to those of wild invertebrates.Communicated by J.P. Grassle, New Brunswick     

Herbivory in the gammarid amphipod Aora typica: relationships between consumption rates, performance and abundance across ten seaweed species

This paper reveals a substantial capacity for herbivory of seaweeds in the gammarid amphipod Aora typica, adults eating seven of ten taxonomically and morphologically diverse seaweed species offered to them in a no-choice assay. The green algae Ulva spathulata and Enteromorpha intestinalis were consumed at the highest rates in both no-choice (2.3–2.5 mg blotted weight individual⁻¹ day⁻¹) and multiple-choice assays (0.5–1.3 mg blotted weight individual⁻¹ day⁻¹). Adult A. typica collected from two different species of brown seaweeds had very similar feeding preferences to each other. Juvenile A. typica grew to reproductive maturity on the green algae E. intestinalis and U. spathulata, and the brown algae Carpophyllum maschalocarpum and Ecklonia radiata. In common with previous studies on members of other amphipod families, survivorship of juvenile amphipods was positively correlated with feeding preferences of adults across seaweed species (r ²=0.43, P=0.04). However, densities of A. typica on seaweeds in the field (excluding the intertidal E. intestinalis and U. spathulata) were not significantly correlated with feeding preferences of adults (r ²=0.07, P=0.5) or survivorship of juveniles (r ²=0.17, P=0.31). This suggests that either host seaweeds are not a major dietary component of these amphipods in nature, or that the host’s value as a food source is overridden by other properties such as the degree of shelter it affords from larger consumers. This study provides the first demonstration that a member of the cosmopolitan amphipod family Aoridae is capable of consuming a diverse range of seaweeds.     

Group-living in cliff swallows as an advantage in avoiding predators

Summary Cliff swallows (Hirundo pyrrhonota) in SW Nebraska, USA, nest in colonies and associate in groups away from their colonies. The degree to which group-living in this species affords advantages in the avoiding of predators was examined. The distance from the colony at which a snake predator was detected increased with colony size. In flocks away from the colonies, group vigilance increased, but the time that each individual spent vigilant decreased, with flock size. As a result, birds in large flocks had more time for preening and mud-gathering. Cliff swallows did not effectively mob predators and thus were unable to deter predators regardless of group size. Nesting within each colony was highly synchronous, but when the effects of ectoparasites on nesting success were removed, individuals nesting during the peak breeding period were no more successful than those nesting before or after the peak. This suggests that swamping of predators is unlikely in cliff swallow colonies. Nests at the edges of colonies were more likely to be preyed upon than nests nearer the center, suggesting that colonial nesting conferred some selfish herd benefits. Overall reproductive success did not vary with colony size. While cliff swallows receive some anti-predator benefits by living in groups, the avoidance of predators is probably not a major selective force for the evolution of coloniality in this species.     

Individual and species recognition in centrarchid fishes: evidence and hypotheses

Summary We conducted laboratory experiments to determine if juveniles of three species of centrarchid fishes displayed abilities for species or individual recognition. In one experiment we reared rock bass (Ambloplites rupestris) in social isolation and in social groups. Both the isolated and group-reared fish spent significantly more time close to conspecifics than to heterospecifics. These results suggest that species recognition in rock bass is controlled by a closed genetic program and that social experience is not necessary. A second set of experiments was conducted to determine if year-old blue-gill (Lepomis macrochirus), pumpkinseed (L. gibbosus), and rock bass juveniles could discriminate between familiar and unfamiliar conspecifics. Bluegill spent significantly more time with familiar conspecifics than with unfamiliar conspecifics, while the other two species displayed no such trend. Bluegill spent significantly more time with familiar conspecifics than did either of the other two species. We postulate that these interspecific differences in recognition abilities may be related to differences in habitat and group parameters among the species.     

Effects of reproduction on the antipredator tactics of snakes (Tropidonophis mairii, Colubridae)

Does an animal’s reproductive state influence the distance at which it flees from an approaching predator? We predicted that reproduction would increase approach distances in pregnant females (because they are burdened with eggs and thus less able to escape rapidly), but reduce them in males (because of lower vigilance due to males focusing on mate-searching rather than predator detection). Field data on approach distances of keelback snakes (Tropidonophis mairii, Natricinae, Colubridae) supported both of these predictions. We walked the same 1.3-km transect along a dam wall in tropical Australia on 135 nights, and recorded the distances at which snakes fled from our approach. Locomotor speeds were measured for a subset of these animals. Variations in approach distance due to season, weather conditions, prior capture history and snake body size were minor, but reproduction strongly affected approach distances for snakes of both sexes. Gravid females were slower than non-gravid females, and fled at greater distances. Reproductive status did not affect locomotor speeds of males, but males that were reproductive (i.e., contained sperm) permitted closer approach than did non-reproductive adult males. Reproduction thus affected approach distances in snakes of both sexes, but in opposite directions and for different reasons.     

Predator recognition and anti-predator responses in the rainbowfish Melanotaenia eachamensis

Predator evasion behaviour patterns of three populations of rainbowfish (Melanotaenia eachamensis) were compared. The populations differed in the level of complexity of their natural habitats and the type and extent of predation. The predator recognition abilities of fish were assessed by exposing them to models differing in their degree of predator realism. The availability of vegetated cover and the location of the models with respect to cover were manipulated. Fish from Lake Tinaroo, a relatively open habitat containing numerous predators, showed strong changes in elective group size (EGS) in response to the different models but did not rely on cover as a place of refuge. In contrast, Dirran Creek fish originate from a small, fast-flowing, structurally complex stream lacking predatory fish species, and they showed little ability to distinguish between the different models and responded to threat by spending longer in vegetated areas. Members of the Lake Eacham captive stock increased their EGS in response to models representing low threat and with more threatening models increased the amount of time spent in vegetated regions of the arena. The contrasting reactions to predatory threat displayed by these populations highlights the need to use a number of different response indices when comparing the anti-predator responses of different fish populations. These data suggest that the level of habitat complexity as well as prior predator experience influence anti-predator responses of different fish popu-lations. Received: 2 October 1996 / Accepted after revision: 27 March 1997     

A Comparison of Direct and Environmental Domain Approaches to Planning Reservation of Forest Higher Plant Communities and Species in Tasmania

The planning of representative systems of nature conservation reserves can be based on a wide variety of criteria. The ready availability of data on the physical attributes of the environment, and the patchiness of biological data, have made reservation planning based on environmental classifications an attractive option for decision makers. We developed an environmental classification based on ecologically relevant variables and used it to plan a forest reserve system for Tasmania. We then used biological distributional data and the same targets and procedures to choose a forest reserve system. The analyses based on the environmental classification selected the same areas as equivalent analyses based on biological distributional data to a greater degree than could be expected by chance. Many rare species and communities missed selection by environmental classificatory units (environmental domains), however, and the proportions of ranges of selected taxa varied widely. Conversely, environmental domains were missed by a reservation strategy based only on biological data. These domains might reflect some gaps in the biological data. A reservation planning approach based on both biological data and domains may produce better results than either used in isolation.     

Reclamation of the Urad molybdenum mine,Empire, Colorado

The Urad Mine, located at an elevation of 10,400 feet near the Continental Divide in central Colorado, was operated from 1967–1974 by AMAX Inc. Mine related activities disturbed approximately 234 acres, of which two tailing deposition areas comprised 121 acres. Comprehensive reclamation was initiated prior to mine closure in 1974 and was completed in 1980.Conventional revegetation techniques were implemented on typical disturbances while the tailing areas were reclaimed with the aid of three waste products. Mine waste rock was used to cap the tailing areas, and sewage and wood wastes were used to convert the rock into a rudimentary soil. The rock was revegetated and the vegetation is now permanent and selfsustaining.