Effects of digenean trematodes and heterotrophic bacteria on mortality and burying capability of the common cockle Cerastoderma edule (L.)

Population dynamics of marine invertebrates is controlled by a variety of abiotic and biotic factors. Among these, some have received lesser attention from marine ecologists because of their ‘discrete’ nature. This is the case of parasitism and bacterial load. In the present study, we focused on the role that both digenean trematodes and heterotrophic aerobic bacteria might play in the mortality and burying behaviour of cockles, Cerastoderma edule.The bivalves were sampled monthly during 1 year from two sites in Arcachon Bay (French Atlantic coast). Mortality rates were assessed after transferring in the laboratory normally buried and unburied (i.e. found lying at the sediment surface at low tide) cockles. Their digenean and bacterial loads were determined for both positions (normally buried and unburied). Mortality rate was significantly higher for cockles found out of the sediment at low tide, suggesting that this abnormal position was a prelude to cockles' death. Comparison of digenean load of cockles showed no significant difference between buried and unburied bivalves. In contrast, bacterial load was significantly higher in unburied cockles than in normally buried animals. The effect of high concentration of a marine bacterial strain (Pseudomonas fluorescens) on cockles' burying behaviour and mortality was tested in the laboratory. Results showed that these bacteria could trigger the emergence of animals from the sediment but did not cause cockles' death. These field observations and laboratory experiments suggest that bacteria, rather than digenean trematodes, could play a role in the emergence of cockles and, hence, affect their survival in the wild.     

Arginine metabolism of the Antarctic Bivalve <Emphasis Type="Italic">Laternula elliptica</Emphasis> (King &; Broderip, 1831): an ecophysiological approach

The potential aerobic ATP-generating pathway and the argininolytic capacity of the Antarctic bivalve Laternula elliptica in its main tissues were measured by the specific activity of the enzymes malate dehydrogenase (MDH), citrate synthase (CS) and arginase. The kidney showed the major potential for aerobic ATP-generating pathway and argininolytic capacity. High levels of CS and MDH activities indicated that renal tissue can be involved in activities that require a lot of energy such as excretion of metabolic end products, amino acids catabolism or even gluconeogenic activities related to inter-tissue metabolism. The fact that kidneys are the main site for arginase activity is very unusual for mollusks and could be related to the living habits of L. elliptica. Genetic expression of the L. elliptica renal arginase could be controlling the levels of l-arginine and forming urea in the excretory organ, which may not have its physiological functions directly affected by the seasonal retraction of its siphons. Compared to the bivalve Dreissena polymorpha, renal arginase of L. elliptica is more resistant to inhibition by copper and cadmium. This could be related to naturally high levels of these metals in the Antarctic marine environment and its bioaccumulation in the renal tissue of L. elliptica, as a probable advantage to its environmental adaptation. Different from other Antarctic animals that feed on Krill, the arginase of L. elliptica is much more sensitive to fluoride inhibition. However, diet composition of L. elliptica would be expected to be variable site to site and its high sensitivity to fluoride inhibition may be a matter of concern in areas near ornithogenic soils subjected to ice-melting processes.     

Iceberg Scour and Shell Damage in the Antarctic Bivalve Laternula elliptica

We document differences in shell damage and shell thickness in a bivalve mollusc (Laternula elliptica) from seven sites around Antarctica with differing exposures to ice movement. These range from 60% of the sea bed impacted by ice per year (Hangar Cove, Antarctic Peninsula) to those protected by virtually permanent sea ice cover (McMurdo Sound). Patterns of shell damage consistent with blunt force trauma were observed in populations where ice scour frequently occurs; damage repair frequencies and the thickness of shells correlated positively with the frequency of iceberg scour at the different sites with the highest repair rates and thicker shells at Hangar Cove (74.2% of animals damaged) compared to the other less impacted sites (less than 10% at McMurdo Sound). Genetic analysis of population structure using Amplified Fragment Length Polymorphisms (AFLPs) revealed no genetic differences between the two sites showing the greatest difference in shell morphology and repair rates. Taken together, our results suggest that L. elliptica exhibits considerable phenotypic plasticity in response to geographic variation in physical disturbance.     

Predation by blue crabs, Callinectes sapidus, on rapa whelks, Rapana venosa: possible natural controls for an invasive species?

Blue crabs Callinectes sapidus are voracious predators in Chesapeake Bay and other estuarine habitats. The rapa whelk Rapana venosa is native to Asian waters but was discovered in Chesapeake Bay in 1998. This predatory gastropod grows to large terminal sizes (in excess of 150 mm shell length (SL)) and has a thick shell that may contribute to an ontogenetic predation refuge. However, juvenile rapa whelks in Chesapeake Bay may be vulnerable to predation by the blue crab given probable habitat overlap, relative lack of whelk shell architectural defenses, and the relatively large size of potential crab predators. Feeding experiments using three size classes of blue crab predators in relation to a size range of rapa whelks of two different ages (Age 1 and Age 2) were conducted. Blue crabs of all sizes tested consumed Age 1 rapa whelks; 58% of all Age 1 whelks offered were eaten. Age 2 rapa whelks were consumed by medium (67% of whelks offered were eaten) and large (70% of whelks offered were eaten) blue crabs but not by small crabs. The attack methods of medium and large crabs changed with whelk age and related shell weight. Age 1 whelks were typically crushed by blue crabs while Age 2 whelk shells were chipped or left intact by predators removing prey. Rapa whelks less than approximately 35 mm SL are vulnerable to predation by all sizes of blue crabs tested. Rapa whelk critical size may be greater than 55 mm SL in the presence of large blue crabs indicating that a size refugia from crab predation may not be achieved by rapa whelks in Chesapeake Bay until at least Age 2 or Age 3. Predation by blue crabs on young rapa whelks may offer a natural control strategy for rapa whelks in Chesapeake Bay and other estuarine habitats along the North American Atlantic coast.     

Ignorant seed predators and factors affecting the seed survival of a tropical palm

In addition to acting as seed predators, some terrestrial mammals bury seeds via scatter hoarding. This study system used two permanent plots in examining the interaction between small rodents and the seeds of the palm Astrocaryum mexicanum. We tested how experimental burial, and fruiting status of the parent, distance to the parent, seed size, and microsite characteristics affect the survival of these seeds. Up to 34% of the buried seeds that were exposed only to ignorant rodent foragers (individuals not responsible for burial) survived. In comparison, less than 1% of seeds buried by scatter hoarding rodents survived in previous studies, a percentage that is comparable to the low survival of unburied seeds in this study (<2%). Although unburied seeds had very low survival, increasing distance and/or seed density positively affected survival of unburied seeds. Distance to parent had no effect on buried seed survival.
Buried seed survival was most strongly and significantly determined by the fruiting status of the trees under which they occurred. Seeds experienced significantly greater predation if buried under “parent” trees that fruited during the experiment. Buried seed survival was also negatively affected by germination, as germination may signal the presence of a seed to foraging rodents. There was some indication of a positive effect of tree density on seed survival between the two plots, whereas differences in rodent abundance appear to have no effect on seed survival. Seed size and microsite characteristics had no significant effect on buried seed survival, likely due to the greater proportional effects of other factors and the longevity of A. mexicanum seeds. The results of this study were used to generate a hypothetical causal network showing how comparatively low recovery of buried seeds by ignorant foragers – combined with processes determining the removal of scatter hoarding foragers from their scattered seed caches – may affect seedling recruitment in A. mexicanum.     

Survival of A-group and B-group Leptosphaeria maculans (phoma stem canker) ascospores in air and mycelium on oilseed rape stem debris

Mycelium of Leptosphaeria maculans survived on oilseed rape stem base debris buried in sand for 2,4, 6, 8,10 or 12 months and produced pseudothecia after subsequent exposure on the surface of the ground under natural conditions for 2–4 months, but did not survive on upper stem debris buried for 2 months. Only A‐group L. maculans ascospores were produced on the stem base debris which had been buried; no B‐group ascospores were produced. Mycelium of L. maculans survived on both stem base and upper stem debris exposed on the sand surface for 2, 4, 6, 8, 10 or 12 months and pseudothecia with viable ascospores were observed at the time of sampling. Both A‐group L. maculans (predominant on stem bases) and B‐group L. maculans (predominant on upper stems) ascospores were produced on unburied stem base and upper stem debris. Thus B‐group L. maculans survived longer on unburied debris than on buried debris. A‐group ascospores which were exposed in dry air in darkness at 5–20°C survived longer than B‐group ascospores; 10–37% of A‐group ascospores, compared with 2–31% of B‐group ascospores, survived after 35 days.     

Shell utilization,predation pressure,and thermal stress in panamanian hermit crabs: An interoceanic comparison

Shell preference patterns of two common hermit crabs from hard bottom reef flats on the Caribbean coast of Panama are examined in relation to the predation pressures and physical stresses of their habitat. Clibanarius antillensis Stimpson lives in the high intertidal habitat and minimizes exposure to predators by seeking refuge during high tides. It prefers high-spired shells which maximize protection from thermal stress. Calcinus tibicen Herbst avoids tidal emersion and prefers low-spired shells which enhance resistance to the predators common on Caribbean reef flats.The results are compared with similar results from the tropical eastern Pacific Bay of Panama. Shell-crushing predation on Caribbean hermit crabs is suggested to differ quantitatively and qualitatively from predation on hermit crabs in the Bay of Panama. Predation on hermit crabs in the Bay of Panama is more intense and effects larger individuals than predation on Caribbean reef flat hermit crabs. In addition, shell-crushing predation on hermit crabs in the Bay of Panama is primarily from teleost fish predators (Diodon spp.), while predation on Caribbean hermit crabs is primarily by bottom-dwelling crustaceans.Differences in predation pressures and tidal regimes between the Caribbean and Pacific coasts of Panama are reflected in the shell preferences and behavior of hermit crabs from the two areas.     

Predation on exotic zebra mussels by native fishes: effects on predator and prey

SUMMARY 1. Exotic zebra mussels, Dreissena polymorpha, occur in southern U.S. waterways in high densities, but little is known about the interaction between native fish predators and zebra mussels. Previous studies have suggested that exotic zebra mussels are low profitability prey items and native vertebrate predators are unlikely to reduce zebra mussel densities. We tested these hypotheses by observing prey use of fishes, determining energy content of primary prey species of fishes, and conducting predator exclusion experiments in Lake Dardanelle, Arkansas. 2. Zebra mussels were the primary prey eaten by 52.9% of blue catfish, Ictalurus furcatus; 48.2% of freshwater drum, Aplodinotus grunniens; and 100% of adult redear sunfish, Lepomis microlophus. Blue catfish showed distinct seasonal prey shifts, feeding on zebra mussels in summer and shad, Dorosoma spp., during winter. Energy content (joules g⁻¹) of blue catfish prey (threadfin shad, Dorosoma petenense; gizzard shad, D. cepedianum; zebra mussels; and asiatic clams, Corbicula fluminea) showed a significant species by season interaction, but shad were always significantly greater in energy content than bivalves examined as either ash-free dry mass or whole organism dry mass. Fish predators significantly reduced densities of large zebra mussels (>5 mm length) colonising clay tiles in the summers of 1997 and 1998, but predation effects on small zebra mussels (≤5 mm length) were less clear. 3. Freshwater drum and redear sunfish process bivalve prey by crushing shells and obtain low amounts of higher-energy food (only the flesh), whereas blue catfish lack a shell-crushing apparatus and ingest large amounts of low-energy food per unit time (bivalves with their shells). Blue catfish appeared to select the abundant zebra mussel over the more energetically rich shad during summer, then shifted to shad during winter when shad experienced temperature-dependent stress and mortality. Native fish predators can suppress adult zebra mussel colonisation, but are ultimately unlikely to limit population density because of zebra mussel reproductive potential.     

Ocean acidification at high latitudes: potential effects on functioning of the Antarctic bivalve Laternula elliptica

Ocean acidification is a well recognised threat to marine ecosystems. High latitude regions are predicted to be particularly affected due to cold waters and naturally low carbonate saturation levels. This is of concern for organisms utilising calcium carbonate (CaCO₃) to generate shells or skeletons. Studies of potential effects of future levels of pCO₂ on high latitude calcifiers are at present limited, and there is little understanding of their potential to acclimate to these changes. We describe a laboratory experiment to compare physiological and metabolic responses of a key benthic bivalve, Laternula elliptica, at pCO₂ levels of their natural environment (430 µatm, pH 7.99; based on field measurements) with those predicted for 2100 (735 µatm, pH 7.78) and glacial levels (187 µatm, pH 8.32). Adult L. elliptica basal metabolism (oxygen consumption rates) and heat shock protein HSP70 gene expression levels increased in response both to lowering and elevation of pH. Expression of chitin synthase (CHS), a key enzyme involved in synthesis of bivalve shells, was significantly up-regulated in individuals at pH 7.78, indicating L. elliptica were working harder to calcify in seawater undersaturated in aragonite (Ω_Ar = 0.71), the CaCO₃ polymorph of which their shells are comprised. The different response variables were influenced by pH in differing ways, highlighting the importance of assessing a variety of factors to determine the likely impact of pH change. In combination, the results indicate a negative effect of ocean acidification on whole-organism functioning of L. elliptica over relatively short terms (weeks-months) that may be energetically difficult to maintain over longer time periods. Importantly, however, the observed changes in L. elliptica CHS gene expression provides evidence for biological control over the shell formation process, which may enable some degree of adaptation or acclimation to future ocean acidification scenarios.     

Lipid radical generation in polar (Laternula elliptica) and temperate (Mya arenaria) bivalves

Lipid peroxidation in Laternula elliptica was assessed by detecting lipid radicals by electronic paramagnetic resonance. The values were compared with data from the temperate mud clam Mya arenaria. Lipid radical content was higher in the Antarctic bivalve than in the temperate mud clam, even within the range of its habitat temperature. The rate of generation of lipid radicals was affected by the iron content in the samples. The iron content in individual samples of digestive glands in L. elliptica ranged from 3 to 6 nmol g⁻¹ fresh weight (fwt) and in M. arenaria from 0.6 to 2.7 nmol g⁻¹ fwt. Arrhenius plots, developed from the rates obtained in the presence of 25 μM iron, showed no significant differences between the activation energy calculated for digestive glands of L. elliptica and M. arenaria. The Fe³⁺ reduction rate in L. elliptica was higher than in M. arenaria (4.7±0.9 vs. 1.8±0.4 nmol mg⁻¹ protein min⁻¹, respectively). L. elliptica had a higher content of α-tocopherol and β-carotene than M. arenaria. Our data suggest that increased lipid radical content in the membranes of cold-adapted organisms could be related to iron content.     

Significant fish predation on zebra mussels Dreissena polymorpha in Lake Champlain,U.S.A.

The objectives of this study were to: (1) determine which fishes were consistently eating zebra mussels Dreissena polymorpha in Lake Champlain and document their feeding behaviour and (2) quantify the diet composition of the fish predators that were found to consume zebra mussels. From 2002 to 2005, freshwater drum Aplodinotus grunniens, pumpkinseed Lepomis gibbosus, yellow perch Perca flavescens and rock bass Ambloplites rupestris all consumed zebra mussels at varying frequencies and amounts. Aplodinotusgrunniens and L. gibbosus chewed clumps of zebra mussels, expelling shells, whereas P. flavescens and A. rupestris swallowed small individuals whole. Lepomis gibbosus consumed zebra mussels at the highest frequency (65–89% of prey consumed) and zebra mussels comprised a large part of this fish’s diet (up to 40% by dry mass). Zebra mussels were also an important component of the diet of A. grunniens (up to 59% of the diet by dry mass, 40–63% frequency of consumption). The percentage of the diet comprising zebra mussels in P. flavescens and A. rupestris varied significantly from year to year but never exceeded 10%. Because A. grunniens and L. gibbosus crushed zebra mussels, the nutritional return from consuming zebra mussels would be similar to other prey; for P. flavescens and A. rupestris zebra mussels were only partially digested and the nutritional return would probably be low. As predation on zebra mussels is widespread and significant, it is possible that fish predators could contribute to regulating the population of zebra mussels in Lake Champlain.     

Characteristics of shell microstructure and growth analysis of the Antarctic bivalve <Emphasis Type="Italic">Laternula elliptica</Emphasis> from Lützow-Holm Bay,Antarctica

Growth performance of the Antarctic bivalve Laternula elliptica was examined both by shell microstructural observation and by applying a fluorescent substance, tetracycline, as a shell growth marker. The shell was composed of two calcareous layers: the thick outer layer was homogeneous or granular in structure and the thin inner layer was nacreous. The architecture of Antarctic L. elliptica was different from that of temperate L. marilina, and the ratio of thickness between the outer and inner layers appeared to be different. The growth rate of the nacreous layer was analyzed to be very low. High correlations were found between the major axis of chondrophore and both shell length and shell dry weight, respectively. It is suggested that the chondrophore is an appropriate growth indicator, and combining the information of growth increments with the fluorescent method may be useful in estimating the bivalve growth performance in the Antarctic sea.     

Byssal hairs in the invasive Asian freshwater bivalve Limnoperna fortunei (Mytilidae) in the Paraná River system with comments on this species in South America

We recorded, for the first time, byssal hairs in the Asian freshwater bivalve Limnoperna fortunei from the Paraná River system. We analysed the presence of hairs and their distribution on the shell in relation to habitat and shell size in 12 sites. Hairs were present in lentic habitats associated with macrophytes or organic matter, but were absent in lotic environments. The proportion of mussels with hairs was negatively correlated with current velocity. Hairs were more frequent and abundant in larger mussels. In general, the hairs are a similar length over the bivalve and almost entirely cover the shells in≥60% in lentic habitats. The projections allow L. fortunei to be camouflaged among the roots of macrophytes or coarse organic matter, assisting in avoiding visual predators. The clear-cut separation of L. fortunei populations into two different groups could be associated with phenotypic plasticity in this species.     

Seed Dispersal by Monkeys and the Fate of Dispersed Seeds in a Peruvian Rain Forest1

Primary seed dispersal by two species of monkeys and the effects of rodents and dung beetles on the fate of dispersed seeds are described for a rain forest in southeastern Perú. During the six-month study period (June–November 1992) spider monkeys (Ateles paniscus) dispersed the seeds of 71 plant species, whereas howler monkeys (Alouatta seniculus) dispersed seeds of 14 species. Spider and howler monkeys also differed greatly in their ranging behavior and defecation patterns, and as a consequence, produced different seed rain patterns. Monkey defecations were visited by 27 species of dung beetles (Scarabaeidae). Dung beetles buried 41 percent of the seeds in the dung, but the number of seeds buried varied greatly, according to seed size. Removal rates of unburied seeds by rodents varied between 63–97 percent after 30 d for 8 plant species. The presence of fecal material increased the percentage of seeds removed by seed predators, but this effect became insignificant with time. Although seed predators found some seeds buried in dung balls (mimicking burial by dung beetles), depth of burial significantly affected the fate of these seeds. Less than 35 percent of Brosimum lactescens seeds buried inside dung balls at a depth of 1 cm remained undiscovered by rodents, whereas at least 75 percent of the seeds escaped rodent detection at a depth of 3 cm and 96 percent escaped at 5 cm. Both dung beetles and rodents greatly affected the fate of seeds dispersed by monkeys. It is thus important to consider postdispersal factors affecting the fate of seeds when assessing the effectiveness of frugivores as seed dispersers.     

Does diet in Celtic Sea fishes reflect prey availability?

Feeding preferences of Celtic Sea fishes were investigated using a database of stomach content records, collected between 1977 and 1994. The diet of cod Gadus morhua, hake Merluccius merluccius, megrim Lepidorhombus whiffiagonis, whiting Merlangius merlangus and saithe Pollachius virens changed markedly as the animals grew larger, and although large predators generally chose larger bodied prey, the variability of prey sizes consumed also increased. Large predators continued to select small, low value, benthic prey (e.g. Callionymus spp. and Trisopterus spp.) which were easier to catch, rather than larger, more energy lucrative pelagic prey (e.g. mackerel Scomber scombrus), even though these pelagic prey‐fishes were nearly always available and were often very abundant. Stock estimates of the International Council for the Exploration of the Sea and U.K. groundfish survey catches were used as indices of prey abundance. Blue‐whiting Micromesistius poutassou and other small pelagic fishes (Argentina spp. and clupeoids) were identified as being particularly important, and were consumed by some predators more often than would be expected given the abundance of these prey in the environment. There was no evidence for density‐dependent feeding by predators on mackerel and only hake exhibited density‐dependent feeding on horse‐mackerel. Hake, cod and megrim consumed more blue‐whiting when this prey was at higher abundance in the environment. In choosing what prey to consume, predators must balance costs and benefits, considering the quality of prey and the energy expended during search, capture and handling.     

Lipid content and composition of the Antarctic lamellibranch, Laternula elliptica (King & Broderip) (Anomalodesmata: Laternulidae), in King George Island during an austral summer

Total lipid content, lipid classes and fatty acid composition were studied in various tissues of the Antarctic clam Laternula elliptica in an early austral summer. A histological examination of the gonads revealed that most of the clams examined were spawning or ready to spawn. Lipid content was highest in gills (14.9% of tissue dry weight), followed by gonads (10.9%) and digestive glands (9.9%), and averaged 8.2% for the soft tissues. The overall lipid contents were relatively low compared to temperate bivalves at a similar reproductive stage. Lipid class composition in the total lipid of L. elliptica was quite similar to those of most marine bivalves at lower latitudes, being dominated by triacylglycerols (19.3–41.4% of total lipids) and phospholipids (18.9–28.3%) in most of the organs. Large amounts of triacylglycerol deposits in non-reproductive tissues, particularly in siphon and gill, indicate a potential role of lipid as maintenance energy reserve, although the low lipid contents suggest that lipid may not serve as an energy reserve for any food-limited periods. Fatty acid composition in L. elliptica was also typical of marine bivalves with predominance of 16:0 (26%) and 20:5n-3 (18%) acids. Total fatty acids from the soft tissues showed a moderate level of unsaturation (50.6%), and about 35% of the total fatty acids were polyunsaturated. These values were not significantly different from, or even lower than those of marine bivalves in warmer waters. However, the content of 20:5n-3 (18.2% of total fatty acids), which dominated n-3 polyunsaturated fatty acids, was similar to those reported for other marine bivalve species in temperate waters. The fatty acid composition of L. elliptica reflected dietary input of some microalgal species. The nanoflagellates Cryptomonas spp., which were reportedly rich in 16:0, 18:3n-3 and 20:5n-3, predominated in the water column during the present investigation. Accepted: 19 June 1999     

Vertical structure and predator refuge mediate oyster reef development and community dynamics

In addition to their economic value, oysters supply a number of critical ecosystem services such as controlling eutrophication, recycling nutrients, and providing habitat for many invertebrates and fishes. Thus, the maintenance and restoration of oyster reefs is vital for properly functioning estuarine ecosystems. We hypothesized that spatially heterogeneous and refuge-rich reefs are superior habitats for oysters and associated invertebrates and fishes. If this is shown to be the case, then vertical structure and refuge should be included in the design of newly constructed oyster reefs and conserved in existing reefs. To test our hypothesis, models were built as concrete blocks into which shells were placed horizontally, vertically, and widely spaced, and vertically and closely spaced. Respectively, the units represent horizontal orientation with no refuge (HNR), vertical orientation with no refuge (VNR), and vertical orientation with refuge (VWR). Flume studies of velocity distributions over each model type showed distinctive differences that may contribute to differential settlement on the models in the absence of predators or sediment. A subsequent settlement study in the same flume showed significantly higher settlement densities to horizontal shells than to vertical shells regardless of refuge (HNR>VNR=VWR). This result indicates the primary importance of settlement surface orientation (horizontal vs. vertical) over predation refuge when predators are absent. In contrast, two field recruitment studies indicated that the importance of orientation relative to predation refuge might depend on sedimentation rates. When sedimentation was low, the number of oysters and barnacles (live, dead, and total) was significantly higher on no-refuge models than on refuge models (HNR=VNR>VWR). However, percent mortality was lower on the refuge models than on the no refuge models (HNR=VNR>VWR). This leads to a conclusion that although fewer oysters may settle on refuge shells, those that do have a higher rate of survival. In a year when sedimentation was high, recruitment and survival of oysters, barnacles, and bryozoans was higher on vertical models regardless of refuge. In aggregate, our results indicate that both vertical orientation and predation refuge are critical to the early development of the oyster reef community and should be included in restoration designs.     

Evidence of predation in Early Cretaceous unionoid bivalves from freshwater sediments in the Cameros Basin,Spain

Here, we present evidence of possible vertebrate predation on freshwater bivalves from the Lower Cretaceous strata of the Cameros Basin (Spain). The described collection contains the largest number of vertebrate‐inflicted shell injuries in freshwater bivalve shells yet reported in the Mesozoic continental record. Several types of shell damage on fossil shells of Protopleurobema numantina (Bivalvia: Unionoida) are described and their respective modes of formation interpreted in the context of morphological attributes of the shell injuries and the inferred tooth morphology of predators that could have inflicted such injuries. Detailed study of these bite marks shows similarities with the well‐documented injuries in the shells of marine molluscs, namely ammonoids, that have likewise been attributed to reptilian predators. The most parsimonious interpretation suggests crocodiles as the vertebrates interacting with the bivalves in the Cameros Basin. □Barremian–Aptian; bite marks; freshwater bivalves; predation; reptile; Unionoida.     

The Effect of Refuge on Dermestes ater (Coleoptera: Dermestidae) Predation on Musca domestica (Diptera: Muscidae): Refuge for Prey or the Predator?

It is believed that habitat heterogeneity can change the extent of predator-prey interactions. Therefore, in this study we examined the effect of habitat heterogeneity (characterized here as an addition of refuge) on D. ater predation on M. domestica. Predation of D. ater on M. domestica larvae was carried out in experimental habitats with and without refuge, and examined at different prey densities. The number of prey eaten by beetles over 24 h of predator-prey interaction was recorded, and we investigated the strength of interaction between prey and predator in both experimental habitats by determining predator functional response. The mean number of prey eaten by beetles in the presence of refuge was significantly higher than in the absence of refuge. Females had greater weight gains than males. Logistic regression analyses revealed the type II functional response for both experimental habitats, even though data did not fit well into the random predator model. Results suggest that the addition of refuge in fact enhanced predation, as prey consumption increased in the presence of refuge. Predators kept in the presence of refuge also consumed more prey at high prey densities. Thus, we concluded that the addition of refuge was an important component mediating D. ater-M. domestica population interactions. Refuge actually acted as a refuge for predators from prey, since prey behaviors detrimental to predators were reduced in this case.     

沙埋对无芒雀麦种子萌发和幼苗生长的影响

研究了沙埋对浑善达克沙地植物群落中多年生禾草无芒雀麦种子萌发、出苗和幼苗生长的影响.结果表明:无芒雀麦种子能在深度≤12cm的沙埋中萌发,≤8cm的沙埋中出苗.在此范围内,随着沙埋深度的增加,无芒雀麦种子的萌发率和出苗率逐渐降低.沙埋深度在植株高度的33%时,无芒雀麦1周龄和2周龄幼苗均全部存活,且总生物量≥对照(未沙埋幼苗);当沙埋深度增至植株高度的66%时,1周龄和2周龄幼苗的存活率分别降至70%和25%,生长也受到抑制;而遭受全部沙埋时,1周龄和2周龄幼苗均不能存活.遭受沙埋后,无芒雀麦幼苗分配较多的生物量用于地上部分的生长,其生物量分配模式改变可能是无芒雀麦幼苗对沙埋环境的重要适应对策.