ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1993.tb02667.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

This paper tests the predictions of parental investment theory and other hypotheses relating to variation in brood defence by examining aggression displayed by great skuasCatharacta skuatowards intruders within their territories. Aggression serves the function of nest defence; hatching success of adults breeding in Shetland increased with aggression displayed during incubation, and the correlation between aggression and hatching success was apparent in three separate age classes. Adults displayed higher levels of aggression and greater parental investment in reproduction in years of poor food supply. This was not due to an increase in adults' expectations of future benefits of brood defence with increased investment. since hatching success was unaffected by food supply, and breeding success was lower in years of poor food supply. The observed increase in aggression therefore supports parental investment theory. Aggression increased with body condition index (in terms of mass corrected for body size) for females, but decreased with increasing body condition index for males. This probably reflects size‐specific differences in the relative benefits of weight and manoeuvrability as means of promoting effective brood defence and reducing the risk of injury to parents. Aggression may also reflect adult quality, with body condition reflecting quality in opposite ways in males and females, as a result of their different roles during the breeding seaso

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1993.tb02668.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

In general, populations ofAnolislizards on West Indian islands face few predators, are at high density and are thought to be limited by food. This paper describes how the foraging ecology ofAnolis oculatus, a solitary species confined to the island of Dominica, Lesser Antilles, varies with habitat and season in relation to the quantity and quality of available food.Availability of invertebrate food (determined using pitfall traps and sticky traps) was greater in a dry scrub woodland site, Cabrits National Park (CNP), compared with a montane rainforest site, Palmiste Ridge. In the former, there were general increases in abundance, volumes of softbodied prey and sizes of invertebrates from dry season to wet season. Concomitant dietary changes, as determined principally by stomach flushing, included an increase (by volume) in the proportion of soft‐bodied prey. Dietary analyses confirmed the importance of ants (Formicidae) in the diet ofA. oculatus, although for large individuals (mainly adult males) at the rainforest site, soft‐bodied prey such as Oligochaeta and Orthoptera were, in volumetric terms, more important. Prey capture observations showed that largeA. oculatusfed mainly above ground.Anolis oculatusat the montane rainforest site used higher perch heights than those in dry scrub woodland, although in both habitats, small individuals (mainly juveniles) fed mainly at ground level on ants. In the dry season in CNP, the diet (in volumetric terms) of smallerAnoliswas dominated by hardbodied prey such as ants, springtails (Collembola), barklice (Psocoptera) and beetles (Coleoptera). largeAnolisused springtails and barklice to a lesser extent, resulting in relatively low food niche overlap values between size classes and a reduced potential for intraspecific competition compared with the wet sea

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1993.tb02669.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The pattern and characteristics of diving in two female macaroni penguinsEudyptes chrysolophuswas studied, during the brooding period, using continuous‐recording time‐depth recorders, for a total of I8 days (15 consecutive days) during which the depth, duration and timing of 4876 dives were recorded. Diving in the first 11 days was exclusively diurnal, averaging 244 dives on trips lasting 12 hours. Near the end of the brooding period trips were longer and included diving at night. About half of all trips (except those involving continuous night‐time diving) was spent in diving and dive rate averaged 14–25 dives per hour (42 per hour at night). The duration of day time dives varied between trips, and averaged 1.4–1.7 min, with a subsequent surface interval of 0.5–0.9 min. Dive duration was significantly directly related to depth, the latter accounting for 53% of the variation. The average depths of daytime dives were 20–35 m (maximum depth 11 5 m). Dives at night were shorter (average duration 0.9 min) and much shallower (maximum 11 m); depth accounted for only 6% of the variation in duration. Estimates of potential prey capture rates (3–5 krill per dive; one krill every 17–20 s) are made. Daily weight changes in chicks were directly related to number of dives, but not to foraging trip duration nor time spent diving. Of the other species at the same site which live by diving to catch krill, gentoo penguins forage exclusively diurnally, making longer. deeper dives; Antarctic fur seals, which dive to similar depths as macaroni penguins, do s

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1993.tb02670.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The ultrastructure of the aesthetes ofLeptochiton asellusis described. Comparisons are made with the ultrastructure of the aesthetes of other chiton species and a number of unusual features are highlighted. In particular the perforated structure of the subsidiary caps and the extensive areas of banded molecular strands are discussed.

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1993.tb02671.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The gut of the pterobranch hemichordateCephalodiscus nigrescenscontains plankton of sizes from less than 1 μm to over 100 μm in diameter. Some of the smaller plankton are clumped together in spherical bolus that is mucus‐bound. Most plankton types known from the habitat are respresnted amongst the gut conte

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1993.tb02672.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Anatomical evidence suggests that the dormourse is a specialist feeder. Radio‐tracking and direct observation confirm this, highly selective, arboreal feeding behaviour. Dormice choose flowers and fruits from a series of trees and shrubs as each becomes seasonally available. Deferred breeding and a high incidence of diurnal torper suggest that dormice experience food shortage in spring. In early summer, when flowering has ended, but fruits are not yet ripe, dormice may again suffer food shortage. At this time they appear to supplement their diet by taking insects, another high‐quality food with cyclic availability. Although some tree species are particularly valuable to dormice, they may not be essential if alternatives exist. A spectrum of species which will ensure a continuum of differeing food supplies, within a small area, is essential. This im;plies a need for heterogeneous woodland structure. The implications for conversation management are discus

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1993.tb02673.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The land snailsChondrina clientaandBaleaperversacompete most probably for a limited food resource (calcicolous lichens) on rock‐faces on the Baltic Island of Öland (Sweden). Two laboratory and three field experiments were conducted to determine whether food availability and intra‐ and interspecific interactions affect the dispersal tendency inC. clienta. Under laboratory conditions, individuals ofC. clientashowed a higher tendency to disperse from previously grazed than from ungrazed pieces of limestone (their natural substratum), whereas conspecific density or presence ofB. perversahad no effect. However, when snails had been kept on the pieces of limestone for 40 days prior to testing, dispersal tended to increase with increasing density of conspecifics. In the field, marked individuals ofC. clientawere released at different densities on vertical rock walls. Density of conspecifics at the release points did not influence the distances travelled. Similarly, intraspecific density did not affect dispersal when the snails' food resource (lichens) had been experimentally reduced on the quarry walls. Neither was the dispersal tendency influenced by different crowding conditions experienced for 40 days prior to release. The discrepancy between the results of laboratory and field experiments suggest that additional factors acting on dispersal are of importance in natural populations ofC. cli

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1993.tb02674.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The relationship between number of ventral scales, correlating with number of body vertebrae, and body size of adders,Vipera berus, was investigated using captive‐born young and wild‐caught adults (snout‐vent length>400 mm) from six populations in eastern Sweden. Females had significantly more ventral scales, and were larger, than males in all populations. Among adult individuals, snout‐vent length was highly positively correlated with the number of ventral scales when differences due to sex and locality were controlled for. The same pattern was true for newborn individuals when differences due to litter and sex were controlled for. The influence of number of ventral scales on survival and growth rate as possible causes of this positive correlation was examined. Mean number of ventral scales was lower in new‐born snakes than in adults, indicating selection against individuals with a low scale count. Since this selection appears to take place in the early juvenile phase, it is inadequate to explain the relationship between adult body size and number of ventral scales. However, individuals with many ventral scales had significantly higher growth rates than individuals with few ventrals. This suggests that individuals with many ventral scales enjoy a higher growth rate and therefore are able to reach a larger size than their conspecifics of the same age with few ventral scales. This would explain the positive relationship between body size and ventral scale number observed in new‐born and a

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1993.tb02675.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Arvicanthis, the unstriped grass‐rat, is a widespread genus occurring in many regions of Africa and is major pest in agricultural farmland. Despite its economic importance for developing countries, the taxonomy of the genus is stillin a chaotic state. We used univariate and multivariate morphometrics to investigate two species,A. abyssinicusandA. dembeensis, occurring in Ethiopia. Results show that these taxa are well separated, this contradicting authors who lump allArvicanthisasA. niloticus. There is a longitudinal cline in the morphology ofA. dembeensisfrom eastern regions along the Rift Valley. Differences between the species in morphlogy seem to reflect adaptation to different ecological niches at high (A. abyssinicus) and low (A. dembeensis) altitude

ISSN:0952-8369    

DOI:10.1111/j.1469-7998.1993.tb02676.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY