Can suspension feeding by bivalves regulate phytoplankton biomass in Lake Waccamaw, North Carolina?

Suspension feeding by bivalves has been hypothesized to control phytoplankton biomass in shallow aquatic ecosystems. Lake Waccamaw, North Carolina, USA is a shallow lake with a diverse bivalve assemblage and low to moderate phytoplankton biomass levels. Filtration and ingestion rates of two relatively abundant species in the lake, the endemic unionid, Elliptio waccamawensis, and an introduced species, Corbicula fluminea, were measured in experiments using natural phytoplankton for durations of 1 to 6 days. Measured filtration and ingestion rates averaged 1.78 and 1.121 ind.^–1 d^–1, much too low to control phytoplankton at the observed phytoplankton biomass levels and growth rates. Measured ingestion rates averaged 4.80 and 1.50 µg chlorophyll a ind.^–1 d^–1, too low to support individuals of either species. The abundance of benthic microalgae in Lake Waccamaw reaches 200 mg chlorophyll a m^–2 in the littoral zone and averages almost an order of magnitude higher than depth-integrated phytoplankton chlorophyll a. Total microalgal biomass in the lake is therefore not controlled by suspension feeding by bivalves.     

Can migrants escape from density dependence?

Migration is thought to maximize growth by enabling individuals to escape from density dependence, but this has rarely been tested at the individual level in natural populations. We employed linear mixed modeling of the spacing between consecutive scale growth rings to reconstruct individual growth profiles of a paradigmatic fish migrant, the sea trout (Salmo trutta) and related these to estimates of year class strength over a 13‐year period. Variation in scale growth was 1.3 times greater among individuals than within individuals in freshwater and 10 times greater at sea. Scale growth was inversely related to year class strength, both in freshwater (before migration) and at sea (after migration). Competition for patchily distributed resources is the most plausible explanation of the negative density‐dependent growth observed in freshwater and, to a lesser extent, in the marine environment. Our study provides some of the strongest evidence for a role of density dependence in determining partial migrations because although migrants can maximize growth by moving into the sea, they do not appear to become free from density dependence constraints completely. This has implications for conservation and suggests that sea trout and other anadromous fish displaying partial migrations may not be best managed on a river by river basis, but rather from a broader, coastal perspective.     

Behavioral correlates of supplementary feeding of wildlife: Can general conclusions be drawn?

Supplementary feeding is a common, but controversial, tool in wildlife management, because it can benefit both humans and wildlife (e.g., increased wildlife densities), but has certain downsides (e.g., increased disease transmission). For species that are often involved in human-wildlife conflicts, two opposing paradigms with respect to supplementary feeding exist, i.e., (i) that supplementary feeding is efficient to lure animals away from undesired places (i.e., diversionary feeding; hypothesis 1), and (ii) that supplementary feeding stimulates ‘nuisance’ behavior (i.e., increased tolerance for humans and selection for human facilities; hypothesis 2). We formulated an alternative hypothesis (hypothesis 3); i.e., that behavioral variation among individuals dilutes population-wide, general patterns with respect to supplementary feeding. Based on GPS relocation data and resource selection functions, we show that neither of the two opposing management paradigms (hypothesis 1 and 2) hold in a particularly ‘conflict rich’ species, the brown bear (Ursus arctos), because individual variation in selection behavior with respect to supplementary feeding diluted population-wide patterns (hypothesis 3), even under very different environmental contexts (Sweden vs. Slovenia; i.e., different human and bear population density, history and intensity of supplementary feeding, topography, etc.). Our results emphasize that individual variation is an important component of behavioral ecology and should be considered in wildlife management and conservation.     

Seston dynamics and bivalve feeding in the Bay of Marennes-Oléron (France)

Within the framework of an investigation into the carrying capacity of the Bay of Marennes-Oléron (France) for bivalve culture, thein situ uptake of suspended particulate material by oysters (Crassostrea gigas) and mussels (Mytilus edulis) was determined in experiments with benthic ecosystem tunnels. Very high fluctuations in seston quantity and quality were observed within and between tidal cycles. The percentage of organic carbon was inversely related to seston quantity at low concentrations. Organic carbon was diluted by resuspension of material rich in inorganic matter. At high seston concentrations a constant level of about 2% organic carbon was found. The C/N ratio was relatively constant throughout the seasons and fairly low (6.5 to 8.4). Owing to the presence of bivalves large fluxes of suspended particulate material were observed in thein situ measurements. Selective retention of organic carbon or nitrogen could not be demonstrated. Clearance rates based on chlorophyll uptake were within a normal range compared to other studies. A large contribution to the food of the bivalves seemed to be formed by resuspended microphytobenthos. Judged by the low C/N ratio, the food was of good quality. Although its quantity was variable by dilution, it may support largely the carrying capacity of the Bay of Marennes-Oléron for the cultivation of bivalves. Communication no. 687 of the Netherlands Institute of Ecology, Centre for Estuarine and Coastal Ecology, Yerseke, the Netherlands.     

Can morphological and behavioral traits predict the foraging and feeding dynamics of social arachnids?

Complex social insect species exhibit task specialization mediated by morphological and behavioral traits. However, evidence of such traits is scarce for other social arthropods. We investigated whether the social pseudoscorpion Paratemnoides nidificator exhibits morphologically and behaviorally specialized individuals in prey capture. We measured body and chela sizes of adult pseudoscorpions and analyzed predation processes. Larger individuals spent more time moving through the colony and foraging than smaller pseudoscorpions. Individuals that captured prey had increased body and absolute chelae sizes. Although larger individuals had relatively small chelae size, they showed a higher probability of prey capture. Larger individuals manipulated prey often, although they fed less than smaller pseudoscorpions. Individuals that initiated captures fed more frequently and for more time than the others. Natural selection might be favoring individuals specialized in foraging and colony protection, allowing smaller and less efficient adults to avoid contact with dangerous prey. To our knowledge, there is incipient information regarding specialized individuals in arachnids, and our results might indicate the emergence of a morphologically specialized group in this species.     

Can one unrestricted meal buffer the effects of previous pre-meal intervals on the feeding behaviour of sheep?

Varying the time since the last meal is one means of manipulating feeding motivation. In order to use this method effectively it is necessary to know whether and the extent to which effects of one pre-meal interval are carried over to affect the behaviour during the following meals. Pre-meal interval (PMI) is defined here for practical purposes, for short meals, as the time between the start of two successive meals. The possibility that one unrestricted meal might buffer the effects of an 8h as opposed to a 4h PMI on aspects of feeding behaviour was studied with eight Scottish Blackface sheep. They were fed on a regime in which they were given access to food until they finished their meal and lay down (this always occurred within 60min) at which time the remaining food was withdrawn. Feeding behaviour was recorded during the meal after these 4 and 8h intervals, as well as during the following meal 4h later.At a meal after a PMI of 8h, compared to 4h, sheep had a higher intake per meal (mean+/-S.T.D. for 8 and 4h PMI, respectively: 604.4+/-78.8 and 430.1+/-100.9g; P<0.001), a longer meal duration (27.1+/-7.5 and 21.8+/-8.1min; P<0.001), and a tendency for a higher intake rate (23.8+/-6.2 and 21.9+/-8.2g/min; P=0.11). During the following meal 4h later these differences were smaller, but intake per meal still tended to be higher (430.8+/-81.5 and 338.5+/-45.6g; P<0.06) for sheep who had previously had the 8h PMI. Meal duration (21.9+/-7.2 and 20.6+/-7.08min; P=0.28) and intake rate (21.2+/-6.1 and 18.7+/-7.2g/min; P=0.13) were no longer different.A single meal after the different PMIs reduced differences in all three aspects of feeding behaviour observed during the subsequent meal, 4h later, but differences in intake per meal were still apparent. It is suggested that an additional meal may overcome the carry-over effect.     

Can gene delivery close the door to HIV-1 entry after escape?

BACKGROUND: Research efforts to prevent viral entry by developing small molecule inhibitors against HIV-1 chemokine coreceptors have yielded promising clinical results. However, resistance to some chemokine receptor inhibitors has been recently documented, and therefore, alternative methods of HIV-1 coreceptor disruption are needed. CONCLUSION: We will describe current HIV-1 vector-delivered genetic disruption mechanisms that target HIV-1 chemokine coreceptors, such as RNA interference, ribozymes, zinc fingers, intrakines, and intrabodies, and frame the use of these gene delivery chemokine receptor disruption mechanisms in the context of current small molecule blocker/antagonists of CCR5 and CXCR4. In addition, we will discuss the importance of evaluating HIV-1 vector-delivered viral entry prevention mechanisms in the rhesus macaque SIV non-human primate model in regard to pathogenesis and therapeutic efficacy.     

Can filter‐feeding fishes improve water quality in lakes?

1.  In this paper we examine the potential of a cichlid fish species ( Sarotherodon galilaeus ) to both maintain positive growth rates through filter-feeding on phytoplankton and improve water quality in Lake Kinneret through suppression of dinoflagellate ( Peridinium gatunense ) blooms.
2.  Seasonal plankton consumption by S. galilaeus from Lake Kinneret was examined experimentally by monitoring changes in plankton assemblages during 24 h in 5-m³ mesocosms containing varying densities of fish. Taxon-specific grazing rates ranged from 0 to 17 mg g_fish day^–1, with mean total consumption of 1.6% fish body weight per day. During the spring bloom of P. gatunense , S. galilaeus consumed mostly (94%) netphytoplankton (≥20 μm). The remaining 6% consisted mostly of nanophytoplankton (<20 μm). During the summer and fall, net- and nanophytoplankton accounted for 54 and 42%, respectively, of the diet of S. galilaeus . Zooplankton and flagellated and ciliated protozoans made up the remaining 4%.
3.  Simulations using a fish bioenergetics model indicated that consumption rates ( C ) were near maximum in spring (90% C _max), while consumption was reduced in summer-fall (59% C _max). Sarotherodon galilaeus obtains sufficient energy through filter-feeding year-round, although most growth (≥60%) occurs during the spring P. gatunense bloom.
4.  Despite efficient feeding on P. gatunense and nanophytoplankton by S. galilaeus , estimates of instantaneous plankton mortality caused by ingestion were two orders of magnitude lower than maximum potential plankton growth rates. Thus the potential for the S. galilaeus population in Lake Kinneret to positively affect water quality through algal suppression is low.     

Can unique amino acid profiles guide adult salmon to natal streams? A comparison of streams sampled prior to and after the arrival of adult Pacific salmon

Hydrobiologia - Homing is an essential aspect of the evolutionary ecology of salmon, and the final stages are guided by odors learned prior to migration from natal sites. Amino acids (AAs) have...     

Can selection to escape nectar thieving force plants to portion nectar in many flowers?

There are several hypotheses which try to explain why particular plants produce just the number of flowers that they do. These hypotheses include: compromises between the attraction of pollinators and avoiding self-pollination by geitonogamy; optimal nectar production as a result of diminishing gains of nectar production; opportunity for selective abortion; or different bet-hedging strategies. In this paper, I present a hypothesis which interferes with the others concerning flower numbers in plants: nectar thieving can apply a selection force in plants which result in a portioning of nectar in many flowers. Energy saved by reducing the quantity of nectar in each flower can be directed into greater flower numbers.     

Pollen as a vehicle for the escape of engineered genes?

Recent studies of pollen exchange between neighboring populations of plants have shown that interpopulation gene flow can proceed over much greater distances and at higher rates than hitherto believed. This means that the escape of engineered genes from crop plants to their wild relatives is not only possible, but also likely. The development of containment strategies, such as extra modifications for increased self-fertilization and decreased pollen longevity in engineered crop plants, will be necessary to safeguard against such escape.     

What does feeding system morphology tell us about feeding?

Feeding is the set of behaviors whereby organisms acquire and process the energy required for survival and reproduction. Thus, feeding system morphology is presumably subject to selection to maintain or improve feeding performance. Relationships among feeding system morphology, feeding behavior, and diet not only explain the morphological diversity of extant primates, but can also be used to reconstruct feeding behavior and diet in fossil taxa. Dental morphology has long been known to reflect aspects of feeding behavior and diet but strong relationships of craniomandibular morphology to feeding behavior and diet have yet to be defined.     

Can nest predation and predator type explain variation in dispersal of adult birds during the breeding season ?

Many types of predators depredate bird nests and thus potentiallyinfluence the spatial distribution of their prey. We used asimulation model of a double-brooded songbird's nesting seasonto test three predictions about the selective advantage ofdispersing different distances after nest predation by predatorswith varying home range sizes. Our results supported the predictions that (1) dispersing birds had higher success than nondispersingbirds after predation of the first nest, (2) dispersing beyondthe home range of the nest predator increased the success ofthe second nest, and (3) birds whose first nests were depredatedearly in the nesting cycle did better by dispersing fartherthan birds whose nests were depredated later in the nestingcycle. Our results provide evidence that predation and predatorcharacteristics may cause variation in adult dispersal distancesduring the breeding season. However, we did not find an advantagefor long-distance dispersal when predators with small- or medium-sizedhome ranges were responsible for the predation event. The criticaldecisions of dispersal and dispersal distance made by adultbirds are complex, but our model demonstrates that predationevents can create a selective advantage to disperse.     

How neoteny shapes human society: Can we escape our formative years,and fight the wrong kind of populism?

This article describes aspects of our biological nature that have contributed to the dangerous current state of societal, ecological and climatological affairs. Next, it deals with stratagems to take these aspects into account, so as to allow us better choices. I will concentrate on the concepts of evolved group mechanisms and “neoteny” and explain why they direct our responses throughout our lives. The connection between our biological make-up and our vulnerability to the current rise of certain kinds of irrational, undemocratic, populism is also laid bare. I will end by listing some simple, but possibly controversial, proposals that might have value in combating these societal tendencies and help decision making in a reality-based, more scientific, manner.