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Few studies have addressed whether terrestrial insects assess predation risk via chemical cues. We exposed predator-naïve fall field crickets ( Gryllus pennsylvanicus Burmeister, 1838) to filter paper containing the chemical cues of three wolf spiders ( Hogna helluo (Walckenaer, 1837), Rabidosa rabida (Walckenaer, 1837), Rabidosa punctulata (Hentz, 1844)), the house cricket ( Acheta domesticus L., 1758,) and blank filter paper. Crickets exhibited greater immobility and reduced speed of movement when exposed to chemical cues of all three spider species. Crickets exhibited reduced speed with increasing mass of R. punctulata, suggesting that larger spiders may pose a greater risk. Cricket response did not differ between cues of H. helluo fed conspecific crickets versus H. helluo fed house crickets, suggesting that crickets cannot distinguish between cues from H. helluo fed phylogenetically similar crickets. Our work nevertheless demonstrates that naïve field crickets respond to chemical cues of several species of wolf spiders.

The comment by Messier and Joly on a paper by Eberhardt (L.L. Eberhardt. 1997. Can. J. Zool. 75: 1940-1944) suggests that the data in the earlier paper do not demonstrate a regulatory effect of wolves (Canis lupus) on their ungulate prey. It appears that the disagreement results from the use of quite different models, with Messier's approach (F. Messier. 1994. Ecology, 75: 478-488) apparently depending on the assumption of an equilibrium between wolf abundance and prey abundance, while Eberhardt's model depicts non-equilibrium conditions. Some questions having to do with duplications in secondary data sources are further examined.

In this paper we explore the cyclic interactions of prey–predator systems by examining the relationship between cycle lengths of both species and the strength of their interaction. As a probe of interaction strength, we use the degree of counter-clockwise rotation in phase plots with the prey on the x axis and the predator on the y axis. We compare the results from a 25-year time series from the Hudson’s Bay Company data on American mink ( Neovison vison (Schreber, 1777)) and muskrat ( Ondatra zibethicus (L., 1766)) with results from three simulation models. We found that the strength of interaction (rotation range: –0.4 to 1.1 rad/year) was strongest when the two cycle lengths were similar and that it increased with the amplitude of the cycles (cycle range: 4–10 years). The time difference between prey and predator cycles that corresponded to the highest interaction strength was 2–3 years. Similar results were obtained with simulation models; the most complex Hanski model showing the overall best fit with observations. However, none of the models were able to reproduce long ranges of stable cycles by only changing one of their parameters at a time (ranges 2–4 years), whereas the observed range of stable cycles was 4–10 years.

Feeding by uloborid spiders is unusual in several respects: cheliceral venom glands are absent; prey wrapping is extensive (up to several hundred metres of silk line) and severely compresses the prey; the spider’s mouthparts usually never touch the prey; and the entire surface of the prey is covered with digestive fluid. This paper presents observations on Philoponella vicina O. Pickard-Cambridge, 1899, which provide possible causal links between these traits. The spider begins ingesting soon after it wets the prey, gaining access to the prey’s interior through a broken cuticle that was broken during wrapping and by digestion of the prey’s membranes. The more abundant of the two types of wrapping lines is also digested, but the remaining shroud of wrapping silk is dense and filters digested prey particles. Robust setae on the palpal tarsus and the spread position of the anterior legs during feeding probably protect the spider from contact with the digestive fluid. Spiders extracted about 65% of the wet contents of the prey, but feeding was slow and involved substantial water evaporation. We propose that selection in uloborid ancestors to recover wrapping silk led to increased wetting of the prey’s surface and that compressive wrapping facilitated this wetting. These traits could have led to loss of the now superfluous cheliceral poison glands. Instituto Smithsoniano de Investigaciones Tropicales (STRI) Universidad de Costa Rica Smithsonian Tropical Research Institute, Panama, USA UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biología

Prey often respond to predator presence by increasing refuge use. However, some types of refuges may expose prey to other types of predators. In addition, in selecting refuges ectothermic animals may have a conflict between safety and thermal suitability. In this paper we examined in the laboratory whether common wall lizards, Podarcis muralis (Laurenti, 1768), (i) prefer to use warm refuges to cold ones, (ii) prefer safe refuges to those with chemical cues of a saurophagous snake, and (iii) whether lizards face a trade-off between using a warm but snake-scented refuge or a cold but odorless one. Results did not show differences in refuge use in relation to refuge temperature, because common wall lizards only entered to investigate it, but they were not forced to hide. So, common wall lizards did not have to be at suboptimal temperatures for longer times. Common wall lizards avoided the use of predator-scented refuges, regardless of thermal conditions, and they also increased their movement rate, trying to escape from the terrarium. Because snakes are inconspicuous inside refuges, an avoidance response to their chemicals may enhance the survival possibilities of common wall lizards. We conclude that in common wall lizards, predation-risk costs are more important than thermal costs in determining refuge use.

Most tern species (Sternidae) are typically open-ground breeders; the Inca tern (Larosterna inca), however, breeds in crevices. This paper reports the first analysis of nest-site characteristics, predation rates, and breeding success in this species. We tested for evidence of natural selection on nest-site preferences in a colony subjected to high rates of predation by the peregrine falcon (Falco peregrinus). Characteristics of occupied sites differed from those of non-occupied sites. Terns selected sites with longer chambers, a greater number of cavities, and more overhead and lateral cover that were located close to the cliff edge. Predation was the main cause of breeding failure, and successful sites differed from unsuccessful sites, which is evidence for ongoing natural selection. Chicks at sites in larger crevices and more cavities remained at the site longer and were less likely to be depredated by peregrine falcons. Probably in response to the presence of predators, adults flew towards the colony in flocks, which "dissolved" at the cliff edge. Sites located far from the edge were more likely to be depredated and adults breeding there fed their chicks less frequently and, consequently, reared lighter chicks. The concordance between site preference and predation pressure on nest-site selection suggests that the use of non-preferred sites imposed a cost in the form of increased nest predation.

Assessment of food requirements is a key feature in the evaluation of the ecological status of the marine megafauna. However, this remains technically difficult because prey intake by marine top predators occurs mainly under water, out of sight. In this paper, we compare three independent methods currently available for use in quantitative dietary studies: (1) time-energy budget; (2) stomach-temperature measurements; and (3) automatic weighing. To this end, concurrent measurements were performed on Great Cormorants (Phalacrocorax carbo carbo) breeding in Normandy. According to the time-energy budget method, breeding males required 690 g of fish while incubating, 1050 g when rearing small chicks, and 1350 g when rearing large chicks; corresponding values for breeding females were 500, 760, and 970 g. These measurements are similar to estimates derived from automatic weighing data, which gave a mean food intake of 540 and 390 g for incubating males and females, 1150 and 830 g for those tending small chicks, and 1410 and 1010 g for those tending large ones, respectively. Stomach-temperature measurements, which can only be performed for birds raising small chicks, were lower (640 g fish in males and 450 g in females) than those obtained using the other two methods. We compare these results with former estimates obtained at the same study site and for other Great Cormorant subspecies and discuss the relative accuracies of the three techniques. Finally, we stress that better assessment of the ecological status of marine top predators requires further technical improvements and additional investigations outside of the reproductive phase.

Phaeacius malayensis (Salticidae: Spartaeinae) is an atypical jumping spider that routinely includes other jumping spiders in its diet. This paper presents the first detailed study of P. malayensis' prey preferences. Three basic types of tests of prey preference were used: different types of prey were provided on alternate days (alternate-day tests), two types of prey were provided simultaneously (simultaneous-presentation tests), and an alternative prey type was provided while the predator was already feeding (alternative-prey tests). In alternate-day and simultaneous- presentation testing, but not in alternative-prey testing, ( i) P. malayensis preferred spiders (salticids and hunting spiders) to insects; (ii) P. malayensis preferred salticids to hunting spiders; ( iii) these preferences were not exhibited in some paired choices when the background was nonmatching, indicating that visual concealment is important with respect to some, but not all, prey; (iv) P. malayensis' prey preferences were not affected by a prior 14-day period without food; (v) after 21 days of fasting, P. malayensis took different types of prey indiscriminately. The adaptive significance of preferences for particular types of prey is discussed in the context of optimal-foraging theory. Resume : Phaeacius malayensis (Salticidae : Spartaecinae) est une araignee sauteuse atypique qui consomme couram- ment d'autres araignees sauteuses. Les preferences de P. malayensis pour certaines proies sont decrites ici en details. Trois types de tests ont servi a evaluer les preferences : differents types de proies presentes tous les 2 jours (tests des jours en alternance), deux types de proies presentes en meme temps (test des presentations simultanees), ou un type de proie presente alors que le predateur est deja en train de se nourrir (test de presentation d'une proie de rechange). Le test des jours en alternance et le test des presentations simultanees, mais pas le test de la proie de rechange, ont de- montre que (i) P. malayensis prefere les araignees (Salticides et araignees chasseuses) aux insectes; ( ii) que P. malayen- sis prefere les araignees sauteuses aux araignees chasseuses; (iii) que ces preferences ne s'expriment pas lorsque le substrat est contrastant, ce qui indique que le camouflage est important pour certaines proies, mais pas pour toutes; (iv) que les preferences de P. malayensis pour certaines proies ne sont pas affectees par un jeune prealable de 14 jours et (v) qu'apres 21 jours de jeune, P. malayensis consomme indifferemment n'importe quelle proie. L'importance evolu- tive des preferences pour des types particuliers de proies est examinee dans le contexte de la theorie de la quete opti - male. (Traduit par la Redaction) 2226

Bat–insect interactions should be a useful source of case studies for the "arms race" of predator and prey adaptations; currently, well-detailed examples are needed for the formulation of general hypotheses. In this paper I add to information on bat–mantis interactions, testing four predictions of the hypothesis that mantises with ears can detect and avoid bats: that mantises will fly by night, that they will be vulnerable to bats, that echolocating bats will be better at catching deafened than normal mantises, and that mantises which can hear bats' calls will take evasive action. I found that tagged Miomantis cf. natalica Beier flew substantially on dark nights; indoors, undeafened mantises were better at avoiding Rhinolophus clivosus (Rhinolophidae: Microchiroptera) than were deafened mantises (n = 20 pairs; Mann–Whitney test, z = 4.58, p

Populations of the guppy Poecilia reticulata in Trinidad vary markedly in their tendency to school. In many cases this variation in behaviour can be attributed to variation in the predation regime: guppies that co-occur with the pike cichlid, Crenicichla alta, spend more time schooling and form larger schools than their counterparts from low-risk habitats. However, the association between schooling tendency and predation risk is not ubiquitous. In this paper we document the behaviour of guppies from populations in two Trinidad drainages. Guppies from the (Lower) Aripo River (in the Caroni drainage) display well-coordinated schooling behaviour irrespective of whether they are observed in the wild or raised under standard conditions in the laboratory. By comparison, Oropuche River guppies (from the Oropuche drainage) show only a weak schooling tendency. The contrast between the two populations is apparent even in newborn guppies. As pike cichlids are abundant at both sites it seems unlikely that reduced predation risk can account for the weaker schooling of the Oropuche River fish. The behavioural differences in the two drainages are paralleled by considerable genetic divergence and we therefore consider the possibility of phylogenetic constraints on the evolution of schooling.

It is generally believed that predation pressure may drive the evolution of long spines, a robust pelvic girdle, and a deep body in sticklebacks (Pisces: Gasterosteidae). However, the lack of such traits in environments under intense predation pressure suggests that there may be a limit to which these apparently defensive structures benefit sticklebacks. In some environments, well-developed defensive structures may not increase stickleback survival, but may actually reduce fitness if there is a cost associated with them. This paper focuses on a trade-off between defensive morphology and escape-response performance in the brook stickleback (Culaea inconstans). Our study of four populations of brook stickleback reveals that the population with the largest pelvic girdles and deepest bodies has a poorly developed escape response (i.e., small displacement, low maximum velocity, and low acceleration), while the population with the smallest pelvic girdles and shallowest bodies has a highly developed escape response. The two populations with intermediate defensive structures are intermediate in escape-response performance. Consideration of predation regimes in different environments may help us understand selection pressures that favor heavily versus poorly armored stickleback morphs.

The exotic macrophyte Myriophyllum spicatum spread widely in Lake Opinicon, Ontario, after 1974, dominating the 2.0- to 3.5-m depth zone which had previously been largely open water. In the shallows it formed beds within the species-rich native Potamogeton–Vallisneria community. This paper compares fish and prey-invertebrate abundance and distribution (i) before and after the milfoil invasion for a series of depth zones (1972 relative to 1979–1980), and (ii) in communities of M. spicatum relative to native macrophytes in the littoral zone shallows in the summer of 1980. At a depth of 2.0–3.5 m (major M. spicatum zone), there were significantly fewer bluegill but more black crappie and golden shiner in 1979–1980 compared with 1972, and significantly fewer isopods, chironomid and trichopteran larvae, and ephemeropteran nymphs. Differences were greatest in late summer. Inshore and offshore from the M. spicatum zone, differences were minor, suggesting that the invader, not time, was responsible. At a 1.0- to 1.3-m depth in the summer of 1980, three to four times as many fish occurred during the daytime feeding period in the Potamogeton–Vallisneria community than in the M. spicatum area. In the benthos, beneath the native beds, five major taxa of prey invertebrates were three to seven times more abundant. The foliage of Potamogeton plus Vallisneria supported twice as many invertebrates per square metre in late summer than did M. spicatum. Insect emergences over the summer (May–September) were twice as high. Up to the present, the net impact of the habitat change on the fish populations of Lake Opinicon has not been great. If in the future M. spicatum were to replace the rich native macrophyte beds in the shallows, this would be cause for concern.

This paper compares the succession of gastropods in two environments that are adjacent in space but differ as to their eutrophic level. One is hypereutrophic (du Sud River), the other is mesotrophic (Richelieu River). Canonical correlation analysis brings out the main differences between these two stations, while principal component analysis is used to describe the succession of species within each community. These analyses indicate that the occurrence of gastropod species, as well as their development cycles, may be adapted to the particular synecological evolution of each environment. Thus, the species would not react directly to nutrient concentrations but indirectly, through the effects of these concentrations on oxygen content, plant cover, and predators. In these two environments, some benthic species seem to be good indicators of the eutrophic level of the ecosystem.

This paper contains a taxonomic survey of nematodes belonging to the predaceous family Mononchidae, collected by Dr. Fields Caveness in western Nigeria during 1959–61. Four genera, new to science, Crassibucca, Hadronchus, Polyonchulus, and Prionchulellus, and 16 new species, Crassibucca penicula, C. macrocauda, C. microdonta, Hadronchus bisexualis, H. monohystera, Iotonchus acuticaudus, I. clarki, I. nigeriensts. I. parabasidontus, I. tarjani, Miconchus pararapax, M. thornei, Mylonchulus curvicaudus, Polyonchulus cobbi, P. megadontus, and Prionchulellus cavenessi are described and illustrated.Several already described species are also included. Iotonchus piracicabae (Lordello) and Mononchus (I.) piracicaboides Carvalho are placed in synonymy of I. trichurus (Cobb). Miconchus dadayi (Micoletzky) in Schneider, 1953 is considered a synonym of Miconchus pararapax n. sp. Miconchus dadayi (Micoletzky, 1914), (=Mononchus macrostoma of Daday, 1910) is regarded as species inquirenda. Mylonchulus hawaiiensis (Cassidy) is removed from synonymy, and Iotonchus similis (Cobb) is designated incertae sedis. Mylonchulus montanus (Thorne) is considered a synonym of Mylonchulus lacustris (Cobb). An illustrated taxonomic key to the 14 genera in the family Mononchidae is presented. Keys to most of the world species in these genera are also included.The value of the tuberculate and non-tuberculate valve as a generic character is discussed.