Seasonal variation in biomass and photosynthetic activity of epilithic algae on a rock at the upper littoral area in the north basin of Lake Biwa, Japan

Vertical distributions of biomass and the photosynthetic activity of epilithic algae were observed seasonally with regard to their physical and chemical parameters along a rocky shoreline of the upper littoral area in the north basin of Lake Biwa. Chlorophyll a amounts in epilithic algae showed a marked change with depth from spring to early summer. The algal biomass showed higher values on the lower part of a large rock in early spring, and gradually increased on the upper part as a result of the growth of Spirogyra sp., a filamentous Chlorophyceae. This growth seems to be associated with a rise in water temperature, with the biomass at the upper depths seeming to be affected by a hydraulic disturbance. The standing crop of epilithic algae showed a maximum value in June and declined to a minimum in August because of the corresponding proliferation or disappearance of Spirogyra as well as changes in the water level. The maximum value of the assimilation number calculated from the potential photosynthetic rate of epilithic algae was obtained at the lower depths in June when Spirogyra grew vigorously. Appreciably high assimilation numbers were also observed in summer and fall, although chlorophyll a amounts were low. The present study is the first in a series to clarify the contribution of epilithic algae on rocky areas to productivity throughout the entire littoral ecosystem.     

Fish species richness and incidence patterns in isolated and connected stream pools: effects of pool volume and spatial position

I tested the effects of pool size and spatial position (upstream or downstream) on fish assemblage attributes in isolated and connected pools in an upland Oklahoma stream, United States. I hypothesized that there would be fundamental differences between assemblages in these two pool types due to the presence or absence of colonization opportunities. Analyses were carried out at three ecological scales: (1) the species richness of pool assemblages, (2) the species composition of pool assemblages, and (3) the responses of individual species. There were significant species-volume relationships for isolated and connected pools. However, the relationship was weaker and there were fewer species, on average, in isolated pools. For both pool types, species incidences were significantly nested such that species-poor pools tended to be subsets of species-rich pools, a common pattern that ultimately results from species-specific differences in colonization ability and/or extinction susceptibility. To examine the potential importance of these two processes in nestedness patterns in both pool types, I made the following two assumptions: (1) probability of extinction should decline with increasing pool size, and (2) probability of immigration should decline in an upstream direction (increasing isolation). When ordered by pool volume, only isolated pools were significantly nested suggesting that these assemblages were extinction-driven. When ordered by spatial position, only connected pools were significantly nested (more species downstream) suggesting that differences in species-specific dispersal abilities were important in structuring these assemblages. At the individual-species level, volume was a significant predictor of occurrence for three species in isolated pools. In connected pools, two species showed significant position effects, one species showed a pool volume effect, and one species showed pool volume and position effects. These results demonstrate that pool size and position within a watershed are important determinants of fish species assemblage structure, but their importance varies with the colonization potential of the pools. Isolated pool assemblages are similar to the presumed relaxed faunas of montane forest fragments and land bridge islands, but at much smaller space and time scales. Received: 6 December 1996 / Accepted: 10 December 1996     

The effects of plant dispersion and prey density on parasitism rates in a naturally patchy habitat

Despite extensive research on parasitoid-prey interactions and especially the effects of heterogeneity in parasitism on stability, sources of heterogeneity other than prey density have been little investigated. This research examines parasitism rates by three parasitoid species in relationship to prey density and habitat spatial pattern. The herbivore Itame andersoni (Geometridae) inhabits a subdivided habitat created by patches of its host plant, Dryas drummondii, in the Wrangell Mountains of Alaska. Dryas colonizes glacial moraines and spreads clonally to form distinct patches. Habitat subdivision occurs both on the patch scale and on the larger spatial scale of sites due to patchy successional patterns. Itame is attacked by three parasitoids: an ichneumonid wasp (Campoletis sp.), a braconid wasp (Aleiodes n. sp.), and the tachinid fly (Phyrxe pecosensis). I performed a large survey study at five distinct sites and censused Itame density and parasitism rates in 206 plant patches for 1–3 years. Parasitism rates varied with both plant patch size and isolation and also between sites, and the highest rates of overall parasitism were in the smallest patches. However, the effects of both small- and large-scale heterogeneity on parasitism differed for the three parasitoid species. There was weak evidence that Itame density was positively correlated with parasitism for the braconid and tachinid at the patch scale, but density effects differed for different patch sizes, patch isolations, and sites. At the site scale, there was no evidence of positive, but some indication of negative density-dependent parasitism. These patterns do not appear to be driven by negative interactions between the three parasitoid species, but reflect, rather, individual differences in habitat use and response to prey density. Finally, there was no evidence that parasitism strongly impacted the population dynamics of Itame. These results demonstrate the importance of considering habitat pattern when examining spatial heterogeneity of parasitism and the impacts of parasitoids. Received: 3 June 1999 / Accepted: 4 October 1999     

Community organization in streams: the importance of species interactions,physical factors,and chance

Summary Experimental studies were used to examine the mechanisms governing the distribution and abundance of two major patch types in unshaded reaches of Augusta Creek, Michigan (USA). One patch type is dominated by Cladophora glomerata, a macroalga potentially able to monopolize space, whereas the other type is comprised of a low-growing, epilithic microalgal lawn inhabited by several species of sessile grazers (especially the caddisflies Leucotrichia pictipes and Psychomyia flavida). Cladophora patches are absent from mid-channel sites characterized by current velocities ca. 50 cm s^–1; caging experiments indicate that their absence is due to grazing by crayfish (Orconectes propinquus). Cladophora's presence in sites with velocities >50 cm s^–1 apparently results in part because crayfish foraging activity is impaired in high flow regimes. The presence of Cladophora strongly affects various other invertebrates due to its alteration of abiotic and biotic characteristics of the microhabitat. For example, the abundance of sessile grazers (e.g. Leucotrichia and Psychomyia) that inhabit microalgal patches is negatively correlated to the abundance of Cladophora, whereas the abundance of several other invertebrates (e.g. Stenonema mayflies and Taeniopteryx stoneflies) is positively correlated to Cladophora's abundance. Therefore, in some portions of this system, crayfish act as keystone predators because of their ability to regulate the abundance of Cladophora, which in turn has strong positive and negative effects on other components of the community. Cladophora does not always monopolize space at high velocities in the absence of crayfish, however. If sessile grazers arrive at such sites before Cladophora, they can prevent its establishment. Thus, where crayfish are absent, the likelihood that a site will be dominated by either Cladophora patches or sessile grazer — microalgal lawn patches depends on two sets of stochastic processes: (1) those that create bare space (e.g. disturbance and grazer emergence); and (2) those controlling the timing of recruitment by Cladophora or grazers at these bare sites. These priority effects (i.e. the ability of grazers and Cladophora to inhibit each other's establishment) contribute to the marked spatial heterogeneity of these two patch types. Collectively, these results demonstrate how interactions between competition, predation, and physical factors can generate a complex mixture of community patterns.     

Marine molluscs and fish as biomarkers of pollution stress in littoral regions of the Red Sea, Mediterranean Sea and North Sea

The intensive development of industry and urban structures along the seashores of the world, as well as the immense increase in marine transportation and other activities, has resulted in the deposition of thousands of new chemicals and organic compounds, endangering the existence of organisms and ecosystems. The conventional single biomarker methods used in ecological assessment studies cannot provide an adequate base for environmental health assessment, management and sustainability planning. The present study uses a set of novel biochemical, physiological, cytogenetic and morphological methods to characterize the state of health of selected molluscs and fish along the shores of the German North Sea, as well as the Israeli Mediterranean and Red Sea. The methods include measurement of activity of multixenobiotic resistance-mediated transporter (MXRtr) and the system of active transport of organic anions (SATOA) as indicators of antixenobiotic defence; glutathione S-transferase (GST) activity as an indicator of biotransformation of xenobiotics; DNA unwinding as a marker of genotoxicity; micronucleus test for clastogenicity; levels of phagocytosis for immunotoxicity; cholinesterase (ChE) activity and level of catecholamines as indicators of neurotoxicity; permeability of external epithelia to anionic hydrophilic probe, intralysosomal accumulation of cationic amphiphilic probe and activity of non-specific esterases as indicators of cell/tissue viability. Complete histopathological examination was used for diagnostics of environmental pathology. The obtained data show that the activity of the defensive pumps, MXRtr and SATOA in the studied organisms was significantly higher in the surface epithelia of molluscs from a polluted site than that of the same species from control, unpolluted stations, providing clear evidence of response to stress. Enhanced frequency of DNA lesions (alkaline and acidic DNA unwinding) and micronucleus-containing cells was significantly higher in samples from polluted sites in comparison to those from the clean sites that exhibited genotoxic and clastogenic activity of the pollutants. In all the studied molluscs a negative correlation was found between the MXRtr levels of activity and the frequency of micronucleus-containing hemocytes. The expression of this was in accordance with the level of pollution. The complete histopathological examination demonstrates significantly higher frequencies of pathological alterations in organs of animals from polluted sites. A strong negative correlation was found between the frequency of these alterations and MXRtr activity in the same specimens. In addition to these parameters, a decrease in the viability was noted in molluscs from the polluted sites, but ChE activities remained similar at most sites. The methods applied in our study unmasked numerous early cryptic responses and negative alterations of health in populations of marine biota sampled from the polluted sites. This demonstrates that genotoxic, clastogenic and pathogenic xenobiotics are present and act in the studied sites and this knowledge can provide a reliable base for consideration for sustainable development. Received: 2 March 1999 / Received in revised form: 2 August 1999 / Accepted: 3 August 1999     

Maternal and direct effects of elevated CO2 on seed provisioning, germination and seedling growth in Bromus erectus

Elevated CO₂ can affect plant fitness not only through its effects on seed production but also by altering the quality of seeds and therefore germination and seedling performance. We collected seeds from mother plants of Bromus erectus grown in field plots at ambient and elevated CO₂ (m-CO₂, maternal CO₂) and germinated them in the greenhouse in a reciprocal design under ambient and elevated CO₂ (o-CO₂, offspring CO₂). This design allowed us to examine both the direct effects of elevated CO₂ on germination and seedling growth and the indirect (maternal) effects via altered seed quality. Elevated m-CO₂ significantly increased seed mass and increased the C:N ratio of seeds from field-grown plants. Percentage and rate of germination were not affected by the m-CO₂ or o-CO₂ treatments. Similarly, elevated m-CO₂ had no significant effect on seedling size as estimated by the total leaf length. When differences in seed mass were adjusted by using seed mass as a covariate in ANOVA, a negative effect of m-CO₂ on seedling size appeared which increased with increasing seed mass (significant covariate×m-CO₂ interaction). This may indicate that the advantage of increased seed mass at elevated m-CO₂ was offset by the reduced concentration of nitrogen (and possibly other nutrients) in these seeds. In contrast to m-CO₂, elevated o-CO₂ greatly increased seedling size, and this stimulatory effect of elevated o-CO₂ was found to increase with increasing seed mass (significant covariate×o-CO₂ interaction). Taken together, these results suggest that in B. erectus transgenerational effects of elevated CO₂ are relatively small. However, other factors (genetic and environmental) that contribute to variation in seed provisioning can critically influence the responsiveness of seedlings to elevated CO₂. Received: 10 May 1999 / Accepted: 6 January 2000     

Spatial and temporal patterns in the activity of European moles

 Using ratio-tracking data obtained at three sites, we assessed the effects of season and of neighbour avoidance on the activity and patterns of home range use by European moles (Talpa europaea). The home ranges of non-breeding male and female moles did not differ significantly in size, and averaged 2324 m² (minimum convex polygon). Although overlap between ranges was small (an average of 12.8% of each range being shared with neighbours and an average of only 3.3% of 2×2 m grid cells were shared with an individual neighbour, ranges were not oriented to avoid neighbours. Non-breeding male/female neighbours tended to share more of their grid cells (3.9±5.7%) mean ±SD than did neighbours of the same sex (male:male 1.2±0.95%; female:female 1.1±1.3%), but there was no significant difference in overlap between any combination of sex pairings. On average, each mole spent only 0.9% of its time within 6 m of another mole, and only 3 out of 46 dyads showed evidence of being attracted to each other; there was no evidence from the simultaneous movement patterns of neighbouring moles that they avoided each other. Although moles tended to return to the same part of their range at the same time on successive days, there was also some indication of gradual changes in the spatial pattern of daily home range use. Moles had a triphasic pattern of activity, but this became tetraphasic under drought conditions. There were significant differences between sites, but not between sexes, in sleeping behaviour and activity patterns. These differences could be related to seasonal differences in soil moisture and thus probably to prey renewal rates. We conclude that in our sites, the activity patterns and movements of moles depend on the temporal and spatial dispersion of food, rather than on short-term interactions between the movements of neighbours. Received: 13 January 1996 / Accepted: 26 June 1996     

Microsatellites in Zea - variability,patterns of mutations,and use for evolutionary studies

To evaluate the performance of microsatellites or simple sequence repeats (SSRs) for evolutionary studies in Zea, 46 microsatellite loci originally derived from maize were applied to diverse arrays of populations that represent all the diploid species of Zea and 101 maize inbreds. Although null phenotypes and amplification of more than two alleles per plant were observed at modest rates, no practical obstacle was encountered for applying maize microsatellites to other Zea species. Sequencing of microsatellite alleles revealed complex patterns of mutation including frequent indels in the regions flanking microsatellite repeats. In one case, all variation at a microsatellite locus came from indels in the flanking region rather than in the repeat motif. Maize microsatellites show great variability within populations and provide a reliable means to measure intraspecific variation. Phylogeographic relationships of Zea populations were successfully reconstructed with good resolution using a genetic distance based on the infinite allele model, indicating that microsatellite loci are useful in evolutionary studies in Zea. Microsatellite loci show a principal division between tropical and temperate inbred lines, and group inbreds within these two broad germplasm groups in a manner that is largely consistent with their known pedigrees. Received: 10 February 2001 / Accepted: 21 May 2001     

Shifting ecological baselines and the demise of Acropora cervicornis in the western North Atlantic and Caribbean Province: a Pleistocene perspective

 In recent years, marine scientists have become increasingly alarmed over the decline of live coral cover throughout the Caribbean and tropical western Atlantic region. The Holocene and Pleistocene fossil record of coral reefs from this region potentially provides a wealth of long-term ecologic information with which to assess the historical record of changes in shallow water coral reef communities. Before fossil data can be applied to the modern reef system, critical problems involving fossil preservation must be addressed. Moreover, it must be demonstrated that the classic reef coral zonation patterns described in the early days of coral reef ecology, and upon which “healthy” versus “unhealthy” reefs are determined, are themselves representative of reefs that existed prior to any human influence. To address these issues, we have conducted systematic censuses of life and death assemblages on modern “healthy” patch reefs in the Florida reef tract that conform to the classic Caribbean model of reef coral zonation, and a patch reef in the Bahamas that is currently undergoing a transition in coral dominance that is part of a greater Caribbean-wide phenomenon. Results were compared to censuses of ancient reef assemblages preserved in Pleistocene limestones in close proximity to each modern reef. We have determined that the Pleistocene fossil record of coral reefs may be used to calibrate an ecological baseline with which to compare modern reef assemblages, and suggest that the current and rapid decline of Acropora cervicornis observed on a Bahamian patch reef may be a unique event that contrasts with the long-term persistence of this taxon during Pleistocene and Holocene time. Accepted: 19 May 1998     

Resource limitation,biodiversity, and competitive effects interact to determine the invasibility of rock pool microcosms

The success of species invasions depends on both the characteristics of the invaded habitat and the traits of the invasive species. At local scales biodiversity may act as a barrier to invasion; however, the mechanism by which biodiversity confers invasion resistance to a community has been the subject of considerable debate. The purpose of this study was to test the hypothesis that productivity and diversity affected the ability of a regionally available species to colonize communities from which it is absent. We hypothesized that the invasibility of rock pool invertebrate communities would increase with increasing nutrients and decrease with increasing diversity. We tested this possibility using naturally invaded outdoor aquatic microcosms. We demonstrated that the invasibility of an experimental multi-trophic aquatic community by a competitive native midge species (Ceratopogonidae: Dasyhelea sp.) was determined by an interaction between resource availability, diversity, and the densities of two competitive ostracods species. Nutrient enrichment increased invasion success; however, within nutrient-enriched microcosms, invasion success was highest in the low-diversity treatments. Our results suggest that resource availability may in fact be the principal mechanism determining invasibility at local scales in multi-trophic rock pool communities; however resource availability can be determined by both nutrient input as well as by the diversity of the biotic community.     

Steric effects, solvent effects, and turnover in hydrolytic cleavage of peptides promoted by palladium(II) aqua complexes

 Dipeptides and tripeptides AcMet-aaH containing N-acetyl methionine, in which the group aaH is GlyH, AlaH, ValH, or Gly-GlyH, undergo hydrolytic cleavage of the Met-aaH peptide bond in the presence of the following complexes of palladium(II): cis-[Pd(en)(H₂O)₂]²⁺, cis-[Pd(tn)(H₂O)₂]²⁺, cis-[Pd(en)(CH₃OH)₂]²⁺, cis-[Pd(S,N-MetH)(H₂O)₂]²⁺, cis-[Pd(S,N-Met-GlyH)(H₂O)₂]²⁺, and cis-[Pd(S,N-Met-AlaH)(H₂O)₂]²⁺. These mononuclear complexes are precursors of binuclear palladium(II) complexes containing the substrates AcMet-aaH as bridging thioether ligands. The rate constant for cleavage is higher when the bidentate ligand in the precursor complex is ethylenediamine (which is completely displaced) than S,N-methionine (of which only the amino group is displaced), because the number of aqua ligands available for cleavage is greater in the former than in the latter case. The demonstrated dependence of the rate constant on the steric bulk (volume) of the leaving group, aaH, points the way toward achieving a degree of sequence selectivity in cleavage of peptide bonds by palladium(II) aqua complexes. One equivalent of cis-[Pd(en)(H₂O)₂]²⁺ cleaves as many as ten equivalents of AcMet-GlyH, but the rate constant decreases as the molar excess of the dipeptide over the catalyst increases. This demonstration of catalytic turnover points the way to our ultimate goal – artificial metallopeptidases. Received: 13 June 1997 / Accepted: 24 September 1997     

Statistical modelling and prediction of pollutants in the urban atmosphere of Salamanca, Spain

 The primary aim of the present work is to describe and analyze the temporal trends of concurrent hourly observations and its daily averaged series of the pollutants CO, NO₂, NO and SO₂ in the urban area of the City of Salamanca (environmental survey station SA001) for the period between 1 December 1993 and 30 November 1994. Using daily series corresponding to different meteorological variables recorded at the same site for the same period (wind direction, relative humidity, pressure, radiation, temperature and wind speed), linear regression techniques are used to study the relationships of these variables with each of the polluntants on both an individual and multivariate basis. The results obtained explain 40% of the variance of the series for NO₂ and 66% in the case of SO₂. Finally, in the modelling phase it was observed that the series of polluntants themselves have sufficient ’’information’’ to enable, by means of autoregressive and integrated moving average techniques (A.R.I.M.A.), the determination of future pollution. Once predicted, these were contrasted with the measured or observed values to check the goodness of the model. Received: 9 December 1996 / Accepted: 24 January 1997     

Ontogenetic patterns of leaf CO2 exchange, morphology and chemistry in Betula pendula trees

In order to explore ontogenetic variation in leaf-level physiological traits of Betula pendula trees, we measured changes in mass- (A _mass) and area-based (A _area) net photosynthesis under light-saturated conditions, mass- (RS_mass) and area-based (RS_area) leaf respiration, relative growth rate, leaf mass per area (LMA), total nonstructural carbohydrates (TNC), and macro- and micronutrient concentrations. Expanding leaves maintained high rates of A _area, but due to high growth respiration rates, net CO₂ fixation occurred only at irradiances >200 μmol photons m^–2 s^–1. We found that full structural leaf development is not a necessary prerequisite for maintaining positive CO₂ balance in young birch leaves. Maximum rates of A _area were realized in late June and early July, whereas the highest values of A _mass occurred in May and steadily declined thereafter. The maintenance respiration rate averaged ≈8 nmol CO₂ g^–1 s^–1, whereas growth respiration varied between 0 and 65 nmol CO₂ g^–1 s^–1. After reaching its lowest point in mid-June, leaf respiration increased gradually until the end of the growing season. Mass and area-based dark respiration were significantly positively correlated with LMA at stages of leaf maturity, and senescence. Concentrations of P and K decreased during leaf development and stabilized or increased during maturity, and concentrations of immobile elements such as Ca, Mn and B increased throughout the growing season. Identification of interrelations between leaf development, CO₂ exchange, TNC and leaf nutrients allowed us to define factors related to ontogenetic variation in leaf-level physiological traits and can be helpful in establishing periods appropriate for sampling birch leaves for diagnostic purposes such as assessment of plant and site productivity or effects of biotic or abiotic factors. Received: 29 December 1998 / Accepted: 26 July 1999     

Inter-decadal patterns of population and dietary change in sea otters at Amchitka Island, Alaska

After having been hunted to near-extinction in the Pacific maritime fur trade, the sea otter population at Amchitka Island, Alaska increased from very low numbers in the early 1900s to near equilibrium density by the 1940s. The population persisted at or near equilibrium through the 1980s, but declined sharply in the 1990s in apparent response to increased killer whale predation. Sea otter diet and foraging behavior were studied at Amchitka from August 1992 to March 1994 and the data compared with similar information obtained during several earlier periods. In contrast with dietary patterns in the 1960s and 1970s, when the sea otter population was at or near equilibrium density and kelp-forest fishes were the dietary mainstay, these fishes were rarely eaten in the 1990s. Benthic invertebrates, particularly sea urchins, dominated the otter’s diet from early summer to mid-winter, then decreased in importance during late winter and spring when numerous Pacific smooth lumpsuckers (a large and easily captured oceanic fish) were eaten. The occurrence of spawning lumpsuckers in coastal waters apparently is episodic on a scale of years to decades. The otters’ recent dietary shift away from kelp-forest fishes is probably a response to the increased availability of lumpsuckers and sea urchins (both high-preference prey). Additionally, increased urchin densities have reduced kelp beds, thus further reducing the availability of kelp-forest fishes. Our findings suggest that dietary patterns reflect changes in population status and show how an ecosystem normally under top-down control and limited by coastal zone processes can be significantly perturbed by exogenous events. Received: 23 March 1999 / Accepted: 19 January 2000     

Coexistence and niche segregation by field populations of the parasitoids Cotesia glomerata and C. rubecula in the Netherlands: predicting field performance from laboratory data

Field experiments with foraging parasitoids are essential to validate the conclusions from laboratory studies and to interpret differences in searching and host selection behaviour of parasitoid species. Furthermore, field experiments can indicate whether the parameters measured in the laboratory are relevant to elucidation of the ecological processes under study, such as adaptation or species interactions. In previous extensive laboratory studies we studied plant- and host-searching behaviour, host acceptance, host suitability; host plant preference, and learning of two congeneric parasitoids of Pieris caterpillars: the generalist Cotesia glomerata, which has been reported to attack several Pieridae species, and C. rubecula, a specialist of the small cabbage white Pieris rapae. In the present field study our aim was to verify the importance of these previous laboratory findings for explaining the performance of these two species in the field. We investigated experimentally whether parasitism on three Pieris species varied with parasitoid species and with food plant of the caterpillars. We exposed different types of host plants, infested with different Pieris species, to parasitism by natural populations of Cotesia species, by setting the experimental plants out in Brussels sprouts cabbage fields. Furthermore we made direct observations of parasitoid foraging in the field. In general, the field results confirmed our predictions on the range of host plant and host species used in the field. The two Cotesia species appear to coexist through niche segregation, since C. glomerata was mainly recovered from P. brassicae and C. rubecula from P. rapae. Although C. glomerata is a generalist at the species level, it can be a specialist at the population level under certain ecological circumstances. Our study shows the importance of variation in host plant attraction and host species acceptance in restricting host plant and host diet in the field. Furthermore the results suggest that, at least in the Netherlands, specialisation of C. glomerata on P. brassicae may occur as a result of C. rubecula outcompeting C. glomerata in P. rapae larvae. Received: 8 July 1999 / Accepted: 31 January 2000     

The effects of tail loss on survival, growth, reproduction, and sex ratio of offspring in the lizard Uta stansburiana in the field

Tail autotomy is a defense against predators used by many lizard species but is associated with various costs, most of which have been measured only in the laboratory. We conducted a field experiment in which we induced tail autotomy to approximately half (58%) of a marked sample (n=326) of Uta stansburiana from western Texas in the fall, and left the other half with intact tails. The following spring we determined survival, measured growth, and brought females to the laboratory to allow them to oviposit their eggs, which we incubated until hatching. Based on past studies, we anticipated inferior survival, growth, and reproduction following tail autotomy. We also predicted that females with tail loss would be energetically compromised and would alter the sex ratio of their offspring toward more daughters (as predicted by the Trivers-Willard hypothesis). Tailless lizards experienced significantly reduced survivorship, but those that survived grew the same as their tailed counterparts. Tailed and tailless females produced clutches equivalent in number of eggs and total mass. Whereas tailed females showed a significant positive relationship between average egg mass and snout-vent length, tailless females did not. Contrary to our expectations, tailless females produced heavier hatchlings than tailed ones, and sex ratios of hatchlings were equivalent for tailed and tailless females. In this population, tail loss in subadults leads to an increased risk of death, but apparently does not impose an energetic handicap such that later growth and reproduction suffer. We suggest that because tailless females are faced with decreased reproductive value, they respond by growing as much and laying as many eggs of the same mass as tailed females, despite the fact that they are also regenerating the tail. In addition, they somehow produce larger hatchlings than tailed females. Nevertheless, tailless females probably end up with lower overall lifetime fitness than tailed females, and tail loss thus induces the conditional reproductive strategy ”make the best of a bad situation”. Because tailless females produce larger, not smaller, hatchlings, they do not produce more daughters as predicted; i.e., we found no evidence for the Trivers-Willard effect following tail autotomy. Received: 29 November 1998 / Accepted: 17 September 1999     

Song organisation and patterns of variation in the serin (Serinus serinus)

This article describes the organisation of song in the serin (Serinus serinus) and analyses its variation among individuals. Serins have a repertoire of about 50 complex syllables that are sung at a very fast rate and in a very stereotyped order, forming discrete songs. Songs are high pitched for the serin’s body size. Song organisation is circular, with a limited number of starting points. Songs can stop at any point in their cycling. Within songs there are trilled sections and fast, non-repeated sections that account for the greatest part of songs. These two modes of singing also differ in average inter-element intervals and probably in their respiratory kinematics. Bird repertoire size was measured and the difficulties of measuring it in this species are discussed. Repertoires are individually specific and have a variable amount of syllable sharing with other birds. We found evidence for geographical variation in the composition of repertoires. Considering our current knowledge of song in carduelines, the stereotyped and circular nature of serin song appear to be unique within this group of birds. Received: 30 May 2000 / Received in revised from: 14 August 2000 / Accepted: 12 September 2000     

The effects of two parasitoids on the life history and metapopulation structure of the intertidal snail Littoraria filosa in different-sized patches of mangrove forest

We describe differences in life history of the intertidal arboreal snail, Littoraria filosa, among patches of mangroves ranging in size from isolated trees to large stands several square kilometres in area. Recruitment of L. filosa occurred from mid spring (October) to early winter (June), recruits grew rapidly and copulating adults were found during the following September–April. Populations within large patches of forest were annuals; all or most individuals died between October–January (spring–midsummer). In contrast, those in smaller peripheral patches were more likely to survive over the summer but survival differed among patches and years. These differences in life history were caused by a parasitoid fly (genus Sarcophaga) that attacked L. filosa 10 mm and longer and was present in all large patches, but absent from, or rare, in smaller peripheral patches. Experimental introductions to isolated trees confirmed that the fly could kill L. filosa. Another sarcophagid parasitoid that attacked L. filosa from 4 to less than 10 mm long was also found in every patch. The combined effects of these parasitoids appear to determine the metapopulation structure of L. filosa. Most adults in large patches were killed by the larger fly during early summer. Summer recruits were often killed by the smaller fly within a month of settlement and when this happened effective recruitment of L. filosa was reduced to autumn. The planktotrophic larval stage of L. filosa lasts less than 1 month, so the source of autumn recruits to all patches must have been adults that survived the early summer, most of which were in small patches or on isolated trees. Consequently these ”peripheral sources” are likely to be important for persistence of the metapopulation of L. filosa. The results of this study demonstrate that metapopulation structure may be determined by complex interactions and that common models cannot be assumed to apply in all habitats. Received: 15 September 1999 / Accepted: 31 January 2000