Patterns in species composition of rocky shore communities in sub-arctic fjords of eastern Iceland

Quantitative data on plants and animals from 20 transects of the eulittoral zone in 8 fjords of sub-arctic east Iceland were analysed by a number of classification and ordination techniques. Field work was carried out during two periods of spring tides in June and July 1987. The study was restricted to gently sloping stable bedrock, but transects were otherwise randomly chosen. Species composition was strongly influenced by the relative position of the transects along the length of the fjords. Species richness increased from heads towards mouths. Increased temperature fluctuations towards inner parts of fjords are suggested as an explanation for these patterns, while salinity is unlikely to be a critical factor. The analyses also indicate that degree of exposure, as measured both by a physically derived index and by a simple biological index, is an important factor in structuring these eulittoral communities, although affecting species richness only slightly, if at all. Classification of transects results in a number of community types which, however, are not well defined. A classification based on the presence/absence of three canopy-forming fucoids yields groups of transects differing in species composition and in degree of exposure. The rocky eulittoral communities of the fjords of eastern Iceland resemble those of northern Norway, but differ in that several key species of the latter communities are missing, probably largely due to the isolation of Iceland.     

Desperado siblings: uncontrollably aggressive junior chicks

According to the desperado sibling hypothesis, chicks of obligately siblicidal species kill their junior broodmates as early as possible because junior broodmates face dire ecological prospects and are consequently predisposed to aggressively overthrow elder broodmates by all-out aggression. The agonistic behavior of junior chicks is virtually unknown because they die so young. We investigated the agonistic behavior of hypothetical desperados by fostering junior brown boobies (Sula leucogaster, an obligately siblicidal species) into nests of the blue-footed booby (S. nebouxii, a facultatively siblicidal species) containing an older singleton blue-foot chick. Controls were junior blue-footed boobies fostered into the same situation. Junior brown boobies were 7 times more aggressive than controls and most of them dominated their elder and larger nestmates. Four of nine brown booby juniors showed relentless aggression, delivering up to 711 pecks, bites and pushes (including "expulsion pushes") per hour, thereby overwhelming nestmates 90% heavier and permanently expelling one of them from the nest. Similarly, in natural broods of two surviving brown booby chicks, the losing chick was 13 times as aggressive as blue-foot subordinates, up to at least age 7 weeks. Contrast of the two species of booby suggests the evolution of agonistic roles within broods may be partly driven by selection on potential victims to express a level and type of aggressiveness appropriate to their status-related ecological prospects.     

Influence of industry on the geochemical urban environment of Mieres (Spain) and associated health risk

This study is concerned with the elemental composition of soils and street dust collected in an historical industrial city of approximately 27 000 inhabitants, where old Hg mining and metallurgical activities strongly affected the load of heavy metals in the urban environment. For the purpose of the study, representative samples of soils and street dust were collected at different locations in the whole urban area (3 km²). Elevated mean concentrations of As in soils and street dust (69 and 135 g g^–1, respectively), and Hg (3.07 and 4.24 g g^–1, respectively), compared to background levels and to those found in other cities, reflect the anomalous geochemical nature of these materials and the strong influence exerted by the old mining sites.     

Roles of male residence and relative size in the social behavior of Iberian rock lizards, Lacerta monticola

Many studies on contest competition used residency asymmetry as a discrete variable. However, the probability of winning an interaction may change as a continuous function of the value of the location where the encounter occurs. We performed a field study to examine the importance of location within a home range and relative body size to the outcomes of agonistic interactions between male lizards, Lacerta monticola. The distances to activity centers (the most used locations based on a density function of sightings) and relative size play important roles in agonistic interactions and had interacting effects in natural conditions. On the other hand, previous studies with lizards suggested that inferior competitors are able to avoid agonistic interactions in the field. Thus, we staged encounters in the laboratory to examine the behavioral responses of smaller individuals. The responses of each focal smaller male were measured in its own home cage (resident), in the cage of a larger male (intruder) and in a cage in which no male was previously present (control). The predominant behavioral tactics of smaller males were avoidance when they are the intruders and displaying when they are the residents. Submissive displays by smaller males may help reduce the costs of agonistic encounters.     

Client preferences by Caribbean cleaning gobies: food,safety or something else?

Predation risk is amongst the most pervasive selective pressures influencing behaviour and animals have been repeatedly shown to trade-off foraging success for safety. We examined the nature of this trade-off in cleaning symbioses amongst Caribbean coral reef fishes. We predicted that cleaning gobies (Elacatinus evelynae and Elacatinus prochilos) should prefer fish clients that pose a low risk of predation (e.g. herbivores) over clients that may have more ectoparasites but pose a higher risk (e.g. piscivores). Our field observations revealed that cleaners did clean preferentially client species with more parasites but predatory and non-predatory clients had similar ectoparasite loads. Despite the lack of a foraging advantage for inspecting predators, cleaners did not avoid risky clients. On the contrary, a larger proportion of visiting predators than non-predators was inspected, gobies initiated more interactions with predatory clients, and predators were attended to immediately upon arrival at cleaning stations. This preferential treatment of dangerous clients may allow the rapid identification of cleaners as non-prey item or may be due to the effect of predators on the rest of the cleaners’ clientele, which avoided cleaning stations whilst predators were present. Dealing with potentially risky clients may allow gobies to regain access to their main food source: non-predatory clients.     

Valuation of climate-change effects on Mediterranean shrublands.

In general, the socioeconomic analysis of natural systems does not enter into the realms of natural science. This paper, however, estimates the human-welfare effects of possible physicochemical and biological impacts of climate change on Mediterranean shrublands over the coming 50 years. The contingent choice method was applied to elicit the trade-offs in perceived values for three climate-sensitive attributes of shrubland (plant cover, fire risk, and soil erosion) and for the costs of programs designed to mitigate changes. Soil erosion was found to be the attribute of shrubland that most concerned the population, followed by fire risk and then plant cover. An increase of 1% in the shrubland area affected by erosion was estimated to cost each person on average 2.9 euros per year in terms of lost welfare, a figure that is equivalent in terms of perceptions of social welfare to an increase of 0.24% in the shrub area burned annually and a decrease of 3.19% in the area of plant cover. These trade-off values may help ecologists, policy makers, and land managers to take social preferences into account.     

Loss of mating opportunities influences refuge use in the Iberian rock lizard,<Emphasis Type="Italic"> Lacerta monticola</Emphasis>

Because time spent in refuge may be costly if prey lose opportunities to forage, fight, or mate, prey allow predators to approach closer before beginning to flee when opportunity costs are high. Because the same opportunity costs may apply to refuge use as to escape, prey should make similar trade-offs between risk of emerging and cost of remaining in refuge. In the Iberian rock lizard, Lacerta monticola, we studied the effects of sex, reproductive season, speed of predator approach, and potential loss of mating opportunities on time spent in refuge following simulated predatory attacks. Lizards of both sexes adjusted refuge use to the level of risk by spending more time in refuge when approached rapidly than slowly. Females remained in refuge for equal times in the mating and postreproductive seasons, but males emerged sooner during the mating season, suggesting adjustment to a cost of lost opportunity to search for mates during the mating season. When a tethered female was nearby, males emerged from refuge earlier than if no female was present, indicating a trade-off between risk and mating opportunity. Approach speed affected emergence time when females were absent, but not when a female was present. Approach speed did not affect the probability that, after emerging, a male would return to court the female. For males that courted females intensely (bit them) before entering refuge, approach speed did not affect latency to emerge, but males that courted less intensely emerged sooner if approached slowly than rapidly. These findings show that males adjust the length of time spent in refuge to both risk of predation and reproductive cost of refuge use.Communicated by A. Mathis     

Symmetry, male dominance and female mate preferences in the Iberian rock lizard, Lacerta monticola

Female preference for dominant males is widespread and it is generally assumed that success in male-male competition reflects high quality. However, male dominance is not always attractive to females. Alternatively, relatively symmetric individuals may experience fitness advantages, but it remains to be determined whether males with more symmetrical secondary sexual traits experience advantages in both intra- and intersexual selection. We analysed the factors that determine dominance status in males of the lizard Lacerta monticola, and their relationship to female mate preference, estimated by the attractiveness of males' scents to females. Sexually dimorphic traits of this lizard (head size and femoral pores) appear to be advanced by different selection pressures. Males with relatively higher heads, which give them advantage in intrasexual contests, were more dominant. However, head size was unimportant to females, which preferred to be in areas marked by relatively heavier males, but also by males more symmetric in their counts of left and right femoral pores. Chemicals arising from the femoral pores and other glands might honestly indicate quality (i.e. related to the symmetry levels) of a male to females and may result from intersexual selection. Females may use this information because the only benefit of mate choice to female lizards may be genetic quality. Chemical signals may be more reliable and have a greater importance in sexual selection processes of lizards than has previously been considered.     

Mitochondrial DNA variation in king mackerel (Scomberomorus cavalla) from the western Atlantic Ocean and Gulf of Mexico

King mackerel (Scomberomorus cavalla Cuvier) collected in 1992 and 1993 from 13 localities along the Atlantic coast of the southeastern USA and in the northern Gulf of Mexico were surveyed for variation in mitochondrial (mt)DNA and a nuclear-encoded dipeptidase locus (PEPA-2). Both polymorphic and fixed mtDNA restriction sites were identified and mapped using conventional and polymerase chain-reaction (PCR)-based methods. Heterogeneity in mtDNA haplotype frequencies was found only in comparisons of pooled haplotypes from Atlantic localities versus pooled haplotypes from Gulf localities. This finding indicates weak genetic divergence between king mackerel from the Atlantic and those from the Gulf. Frequencies of two PEPA-2 alleles essentially paralleled previous findings: one allele (PEPA-2a) was common among samples from western Gulf localities, whereas the other allele (PEPA-2b) was common among samples from Atlantic and eastern Gulf localities. There was considerable variation in PEPA-2 allele frequencies within broadly-defined regions. Variation in mtDNA haplotypes and PEPA-2 genotypes was independent, as was variation in mtDNA haplotypes with sex or age of individuals. Variation in PEPA-2 genotypes was not independent of sex or age of individuals. The latter result suggests that frequencies of PEPA-2 alleles in samples of king mackerel may stem, in part, from sex and age distributions of individuals within samples, and indicates that caution should be exercised in using allelic variation at PEPA-2 as a measure of population (stock) structure in king mackerel. The discordance in spatial patterning of mtDNA haplotypes versus PEPA-2 alleles across the Gulf (i.e. homogeneity in mtDNA haplotype frequencies versus heterogeneity in PEPA-2 allele frequencies) may be due to either female excess at several localities, sex-biased migration, or both. Observed patterns of genetic variation also are consistent with the hypothesis that king mackerel in the western Atlantic may have been subdivided during Pleistocene glaciation, and that the current distribution of PEPA-2 alleles may be a historical artefact. Received: 17 December 1996 / Accepted: 2 April 1997     

Precipitation of aragonite by calcitic bivalves in Mg-enriched marine waters

To understand the relative importance of biological versus physicochemical control over biomineralization, we have tested if the chemical composition of the medium (i.e., the Mg/Ca ratio) can change the mineralogy of mollusk shells. The shells of mollusks are made of calcite and/or aragonite, which are by far the most common CaCO₃ polymorphs. Several species of bivalves with predominantly calcitic shells have been cultivated in artificial seawater with a Mg/Ca molar ratio within the range of 8.3–9.2, well above the present value for seawater (5.2). Four out of six species used (the scallop Chlamys varia, the oyster Ostrea edulis, the saddle oyster Anomia ephippium and the mussel Mytilus edulis) survived long enough to secrete significant amounts of calcium carbonate. The deposits (sometimes extensive) formed on the interior shell surfaces were predominantly aragonitic. Three individuals of C. varia also increased their length by adding new shell at the margin. Contrary to the internal shell deposits, these margins were high-Mg calcite. This implies that the marginal mantle is able to exert a more strict control on the secreted mineral phase than the mantle facing the internal shell surface. This is the first report on an in vivo experimentally forced switch in bivalve shell mineralogy, from calcite to aragonite due to a change in water chemistry.