Response of invertebrates to lotic disturbance: a test of the hyporheic refuge hypothesis

Summary Recovery following hydrological disturbances is usually rapid for lotic invertebrates. Stream ecologists have assumed that recovery is facilitated by behavioral migrations during floods down into the hyporheic zone (the interstitial spaces of a streambed) to seek temporary refuge from possible erosion (the hyporheic refuge hypothesis). We provide the first explicit test of this hypothesis by evaluating three predictions of the hypothesis. We coupled field observations of the response of meiofaunal invertebrates to floods with field and flume experiments. The study site was a sandy-bottom stream in northern Virginia. Prediction 1, that loss of fauna from a streambed during floods should be minimal as long as the depth of scour in the streambed is less than the depth of the hyporheic zone, was not supported for any taxon. For two floods which varied considerably in magnitude, 50–90% of the fauna was lost from the bed despite the fact that the depth of scour (10–30 cm) was significantly less than the total depth of the hyporheic zone (50 cm). Prediction 2, that fauna should move deeper into the bed at higher flows, was supported by field observations during only one of two floods and then only for rotifers. In flume experiments that tested for finer scale behavioral movements, significant vertical migrations were found for copepods and chironomids which moved 1.5–3.5 cm downward as mean velocity (3 cm off bottom) was increased from 5–23 cm/s. Movements down by rotifers were not found in the flume experiments. Prediction 3, that the hyporheic zone is the most important source of colonists to defaunated areas, was supported in part by field experiments. The hyporheic route was not the primary route for any taxon but it was as important for the rotifers and copepods as water column or streambed surface routes. We conclude that, even though smallscale (cm's) migrations into the streambed in response to increased flow may be observed for some taxa and the hyporheic zone may serve as a partial source of colonists following disturbances, movements down are not adequate in preventing significant losses of meiofauna during floods.     

Spatial refuge from intraguild predation: implications for prey suppression and trophic cascades

The ability of predators to elicit a trophic cascade with positive impacts on primary productivity may depend on the complexity of the habitat where the players interact. In structurally-simple habitats, trophic interactions among predators, such as intraguild predation, can diminish the cascading effects of a predator community on herbivore suppression and plant biomass. However, complex habitats may provide a spatial refuge for predators from intraguild predation, enhance the collective ability of multiple predator species to limit herbivore populations, and thus increase the overall strength of a trophic cascade on plant productivity. Using the community of terrestrial arthropods inhabiting Atlantic coastal salt marshes, this study examined the impact of predation by an assemblage of predators containing Pardosa wolf spiders, Grammonota web-building spiders, and Tytthus mirid bugs on herbivore populations (Prokelisia planthoppers) and on the biomass of Spartina cordgrass in simple (thatch-free) and complex (thatch-rich) vegetation. We found that complex-structured habitats enhanced planthopper suppression by the predator assemblage because habitats with thatch provided a refuge for predators from intraguild predation including cannibalism. The ultimate result of reduced antagonistic interactions among predator species and increased prey suppression was enhanced conductance of predator effects through the food web to positively impact primary producers. Behavioral observations in the laboratory confirmed that intraguild predation occurred in the simple, thatch-free habitat, and that the encounter and capture rates of intraguild prey by intraguild predators was diminished in the presence of thatch. On the other hand, there was no effect of thatch on the encounter and capture rates of herbivores by predators. The differential impact of thatch on the susceptibility of intraguild and herbivorous prey resulted in enhanced top-down effects in the thatch-rich habitat. Therefore, changes in habitat complexity can enhance trophic cascades by predator communities and positively impact productivity by moderating negative interactions among predators.     

Feeding and Refuge Use by Small Fish in the Presence of Cyanobacteria Blooms

We studied the effect of cyanobacteria on foraging and refuge use in small fish. We measured pike larval feeding in the presence of cyanobacteria by counting leftover prey. Our results showed that feeding by pike larvae on zooplankton prey decreased significantly in the presence of non-toxic cyanobacteria. The behaviour can be due to lowered vision caused by turbidity or clogging of the gills. Further, we tested whether the three-spined stickleback use toxic cyanobacteria as a refuge against predators in a choice experiment. The choice experiment was performed in a Y-maze fluviarum, where the fish could select between two different environments. Our results support the refuge use hypothesis because the three-spined stickleback clearly preferred toxic cyanobacteria to the chemical predator signal. To conclude, cyanobacteria decrease feeding rates in fish larvae, but may function as important refuge for e.g. sticklebacks, during predation pressure in pelagic algal blooms.     

Selection of food patches by sympatric herbivores in response to concealment and distance from a refuge

Small herbivores face risks of predation while foraging and are often forced to trade off food quality for safety. Life history, behaviour, and habitat of predator and prey can influence these trade‐offs. We compared how two sympatric rabbits (pygmy rabbit, Brachylagus idahoensis; mountain cottontail, Sylvilagus nuttallii) that differ in size, use of burrows, and habitat specialization in the sagebrush‐steppe of western North America respond to amount and orientation of concealment cover and proximity to burrow refuges when selecting food patches. We predicted that both rabbit species would prefer food patches that offered greater concealment and food patches that were closer to burrow refuges. However, because pygmy rabbits are small, obligate burrowers that are restricted to sagebrush habitats, we predicted that they would show stronger preferences for greater cover, orientation of concealment, and patches closer to burrow refuges. We offered two food patches to individuals of each species during three experiments that either varied in the amount of concealment cover, orientation of concealment cover, or distance from a burrow refuge. Both species preferred food patches that offered greater concealment, but pygmy rabbits generally preferred terrestrial and mountain cottontails preferred aerial concealment. Only pygmy rabbits preferred food patches closer to their burrow refuge. Different responses to concealment and proximity to burrow refuges by the two species likely reflect differences in perceived predation risks. Because terrestrial predators are able to dig for prey in burrows, animals like pygmy rabbits that rely on burrow refuges might select food patches based more on terrestrial concealment. In contrast, larger habitat generalists that do not rely on burrow refuges, like mountain cottontails, might trade off terrestrial concealment for visibility to detect approaching terrestrial predators. This study suggests that body size and evolutionary adaptations for using habitat, even in closely related species, might influence anti‐predator behaviors in prey species.     

Allele fixation in a dynamic metapopulation: Founder effects vs refuge effects

The fixation of mutant alleles has been studied with models assuming various spatial population structures. In these models, the structure of the metapopulation that we call the “landscape” (number, size and connectivity of subpopulations) is often static. However, natural populations are subject to repetitive population size variations, fragmentation and secondary contacts at different spatiotemporal scales due to geological, climatic and ecological processes. In this paper, we examine how such dynamic landscapes can alter mutant fixation probability and time to fixation. We consider three stochastic landscape dynamics: (i) the population is subject to repetitive bottlenecks, (ii) to the repeated alternation of fragmentation and fusion of demes with a constant population carrying capacity, (iii) idem with a variable carrying capacity. We show by deriving a variance, a coalescent and a harmonic mean population effective size, and with simulations that these landscape dynamics generate repetitive founder effects which counteract selection, thereby decreasing the fixation probability of an advantageous mutant but accelerate fixation when it occurs. For models (ii) and (iii), we also highlight an antagonistic “refuge effect” which can strongly delay mutant fixation. The predominance of either founder effects or refuge effects determines the time to fixation and mainly depends on the characteristic time scales of the landscape dynamics.     

Population size and structure of giant clams at Rose Atoll, an important refuge in the Samoan Archipelago

Rose Atoll is an important refuge for giant clams (Tridacna maxima) that have been heavily exploited elsewhere in Samoa. During an extensive survey of six islands in the archipelago (50.5?ha surveyed in 420 transects), 97% of a total of 2853 clams were recorded at the atoll (42% of area surveyed). Clam densities were highest in the atoll lagoon, especially around the bases of the pinnacles (mean density=8870?ha^-1). Estimated population size for the small atoll (615?ha) was approximately 27800 clams. Twenty four percent of the population consisted of mature clams (?12?cm), 70% of which occupied the pinnacles and shallow lagoon habitat. Estimated mortality was low (Z=0.3) and primarily due to natural mortality (M=0.3). Maximum recorded size (L _max ) and asymptotic mean size (L _∞) were 25.0?cm and 27.8?cm respectively.     

Host plant acceptance by the phytophagous mite Tetranychus kanzawai Kishida is affected by the availability of a refuge on the leaf surface

We used 11 wild plants to experimentally test the effects of leaf trichomes and leaf quality on host plant acceptance by a phytophagous spider mite, Tetranychus kanzawai, in the absence of predators. There was a positive correlation between leaf hair traits (height/density) and host plant acceptance. We used two model plants (Phaseolus vulgaris and Phaseolus lunatus; the former had higher and denser leaf hairs than the latter) to examine the effects of leaf hairs on the dispersal and fecundity of T. kanzawai in the presence of a predatory mite, Neoseiulus womersleyi. In the presence of N. womersleyi, significantly fewer T. kanzawai females dispersed from a P. vulgaris leaf than from a P. lunatus leaf. Moreover, in the presence of the predator the fecundity of T. kanzawai females on P. lunatus was significantly lower than on P. vulgaris, although in terms of host quality the two plants were equivalent. In the presence of N. womersleyi, T. kanzawai females on P. vulgaris spent more time on webs than those on P. lunatus. Moreover, webs seemed to be less accessible than leaf surfaces to the predator. These results suggest that leaf hairs provide a refuge for T. kanzawai adult females.     

山东小麦种质资源研究回顾与展望

本文简要回顾了自50年代以来山东省小麦种质资源引进、鉴定评价及创新利用概况,提出山东省小麦种质资源研究所存在的问题及解决途径.     

Biological control of aphids and coccids: a comparative analysis

A comparison of the biological control of aphids and coccids was carried out by analyzing success rates for the three major types of biological control, i.e., classical, augmentative, and conservational. Because of the higher intrinsic rates of increase for aphids versus coccids, the working hypothesis that biological control of aphids is less successful compared to coccids was adopted. However, this hypothesis was not supported by an analysis of classical biological control using the BIOCAT database. In this analysis, parasitoids were more successful than predators when used against either aphids or coccids, but the control of Icerya spp. with Rodolia spp. (predators) was highly successful. Some reasons for success of Rodolia spp. are adduced, but field studies on the long-term population dynamics of Icerya–Rodolia systems are needed for determining the mechanisms of regulation. Comparative analyses of augmentative and conservational biological control of aphids and coccids were inconclusive, due to lack of adequate databases; some possible factors involved in the success of these types of biological control are discussed. It is suggested that parasitoids could be better control agents than predators in augmentative biological control of aphids in production greenhouses. Conservational biological control of either aphids or coccids should be aimed at enhancing populations of indigenous natural enemies, especially mobile generalist predators that are capable of keeping pace with mobile pests.     

Prey preference in stoneflies: a comparative analysis of prey vulnerability

Summary Laboratory feeding trials were conducted with the predaceous stonefly Hesperoperla pacifica and a number of mayfly and dipteran prey species to investigate the effects of predator size, and prey size and morphology, on the predator's success. Observations under dim red light permitted estimation of encounter rate (E/min), attack propensity (A/E), capture success (C/A) and handling time (HT). For prey of a particular species and size, HT decreased log-linearly with increasing predator size. Across all prey categories, HT increased log-linearly with increasing values of the ratio prey dry wt/predator dry wt, and differences among species appeared to be small. Overall, capture success was low, but C/A was higher for dipterans than for mayflies, especially with large H. pacifica. Predator size affected C/A when prey fell within a certain size range, but was not a detectable influence with very small or very large prey. Values of A/E of near 10% typified many predatorprey combinations; however, ephemerellid mayflies suffered markedly fewer attacks, and values of A/E up to 30% were obtained with some species-size combinations. We estimated benefit to the predator first as prey wt ingested per unit time (dry wt/HT), and second by mutliplying the former term by capture success. Values increased with increasing size of the predator, and inclusion of the C/A term indicated that predators would obtain greater reward from small relative to large prey, and from dipterans relative to mayflies. Howerver, there was little evidence that attacks were biased toward more profitable prey. We compare the relative contributions of E/min, A/E and C/A to prey choice, and discuss their applicability to predation events in nature.     

Parasite-induced alteration of plastic response to predation threat: increased refuge use but lower food intake in Gammarus pulex infected with the acanothocephalan Pomphorhynchus laevis

Larvae of many trophically-transmitted parasites alter the behaviour of their intermediate host in ways that increase their probability of transmission to the next host in their life cycle. Before reaching a stage that is infective to the next host, parasite larvae may develop through several larval stages in the intermediate host that are not infective to the definitive host. Early predation at these stages results in parasite death, and it has recently been shown that non-infective larvae of some helminths decrease such risk by enhancing the anti-predator defences of the host, including decreased activity and increased sheltering. However, these behavioural changes may divert infected hosts from an optimal balance between survival and foraging (either seeking food or a mate). In this study, this hypothesis was tested using the intermediate host of the acanthocephalan parasite Pomphorhynchus laevis, the freshwater amphipod Gammarus pulex. We compared activity, refuge use, food foraging and food intake of hosts experimentally infected with the non-infective stage (acanthella), with that of uninfected gammarids. Behavioural assays were conducted in four situations varying in predation risk and in food accessibility. Acanthella-infected amphipods showed an increase in refuge use and a general reduction in activity and food intake. There was no effect of parasite intensity on these traits. Uninfected individuals showed plastic responses to water-borne cues from fish by adjusting refuge use, activity and food intake. They also foraged more when the food was placed outside the refuge. At the intra-individual level, refuge use and food intake were positively correlated in infected gammarids only. Overall, our findings suggest that uninfected gammarids exhibit risk-sensitive behaviour including increased food intake under predation risk, whereas gammarids infected with the non-infective larvae of P. laevis exhibit a lower motivation to feed, irrespective of predation risk and food accessibility.     

Marine mussels Brachidontes variabilis selected smaller places of refuge and enhanced byssus production upon exposure to conspecific and heterospecific cues

Refuge selection and byssus production as anti-predator responses were examined in mussels Brachidontes variabilis exposed to cues either released from damaged or intact conspecifics, from damaged or intact heterospecific mussels Perna viridis sympatric with B. variabilis or from shrimp meat as novel cues. Most of the mussels from all treatment groups would seek and stay in a refuge for the first few hours, with a significantly higher number of mussels from the damaged conspecific group seeking refuge. More mussels preferred a smaller refuge when they were exposed to conspecific or heterospecific cues; mussels from other treatments did not select particular sizes of refuge. Damaged conspecific and heterospecific cues elicited the greatest responses in byssus production with more byssal threads being produced, which were also longer and thicker. Novel cues elicited medium levels of response, suggesting that some common cues from injured or dead individuals from different taxa were released, which induced anti-predator responses in B. variabilis.     

Repeated cluster analysis of stomach contents data: method and application to diet of cod in NAFO division 3L

Synopsis Data matrices of fish stomach contents frequently contain many zeros, and nonzero values often do not follow usually encountered statistical distributions. Therefore, many common methods of statistical analysis are inappropriate for such data. A method of repeated k-means cluster analysis is proposed for exploratory analysis of data sets on fish stomach contents. Objective rules are proposed for setting the clustering parameters, so the arbitrariness and subjectivity common in interpreting hierarchical clustering methods is avoided. Because the clusters are nonhierarchical, the analysis method also requires much less computer time and memory. Application of the method is illustrated with a data set of 1771 stomachs of cod (Gadus morhua), feeding on 38 different prey types. The results of the clusterings reveal that nine types of prey may account for the systematic information about the diet of cod in this sample from the northern Grand Bank in Spring of 1979. The results are also used to test specific hypotheses about size selectivity of the predator, spatial variation of feeding, environmental influences on diet, and relative preferences among prey taxa.     

滇黄精资源的开发应用进展及前景分析

滇黄精为重要药食两用资源,誉有"血气双补之王"之称。其在云南蕴藏量大,是黄精品种中产量及市场份额最大的,为重要的"云药"品种。对黄精的药用记载、生长环境、资源状况,以及化学成分、药理作用和产品研发进展进行了综述;并对滇黄精的产品研发前景、产业发展潜力及研发可行性进行了分析。结果显示有必要进一步加大滇黄精的研发力度,充分发挥其药食两用的特点及优势,努力把滇黄精发展成为云药产业、乃至我国中药产业的一大支柱。     

Functional and aggregative response of North Sea whiting

The functional response of whiting (Merlangius merlangus L.) to clupeid and gadoid prey was determined from estimates of food intake and prey density at five locations in the North Sea. The intake of most prey types was well described by a type II (decelerating) response, although in some cases a type III (sigmoid) response provided a slightly better fit. Though a saturation level was reached for all types of fish prey, none of the levels corresponded to the maximum digestive capacity of the predator. This was not caused by ingestion of other prey as the amount of other food and fish prey ingested were not negatively correlated. An investigation of the occurrence of fresh fish in the stomachs revealed that fish was ingested almost exclusively during dawn and dusk and the lack of negative correlation between the intake of fish and other prey may thus be a result of the limited time in which fish prey was vulnerable to predation. No aggregative response of the predators was detected towards any of the prey and catches of prey and predators were slightly negatively correlated. There was evidence of an increase in mortality with density at low clupeid densities, but mortality decreased to virtually zero at high densities. Whiting seem therefore unlikely to impose a regulatory effect on their fish prey outside a narrow range of prey densities.     

Occupancy and detectability of Snowy Plovers in western Utah: an application to a low density population

Occupancy modeling can be used to identify habitat characteristics associated with species occurrence. Additionally, occupancy sampling can provide measures of detection probability, increasing confidence in monitoring efforts. Little is known about the distribution and habitat preferences of a small population of Snowy Plovers (Charadrius nivosus) in western Utah. We conducted a study to estimate occupancy and detection probability of Snowy Plovers in western Utah during 2011 and 2012. We made repeated visits to randomly selected survey plots during the breeding period, sampling 84 64‐ha plots in 2011 and 100 64‐ha plots in 2012 and recording the number of adults and habitat characteristics in each plot. We then modeled the relationship between detection, occupancy, and covariates that included distance to water, distance to roads, land cover types, and characteristics of the vegetation. We also included covariates for observer, Julian date, temperature, cloud cover, and wind speed when modeling detection probability. Detection probability was high (0.74, 95% CI = 0.57–0.86) and positively influenced by temperature. Occupancy of 64‐ha plots was low (0.27, 95% CI = 0.18–0.39) and did not vary by year. Occupancy of Snowy Plovers was negatively associated with distance to water (β = ?0.62 ± 0.31, 95% CI = ?1.23 to ?0.01) and percent shrub cover (β = ?0.28 ± 0.02, 95% CI = ?0.58 to ?0.01). Land cover types also influenced plot occupancy. Management actions that conserve shallow water and adjacent habitats or minimize disturbance in these areas are likely to have conservation benefits for Snowy Plovers where water is scarce. Because our detection probabilities were high, investigators involved in future monitoring efforts can achieve reasonable precision with limited revisits to sample plots.     

Quantitative immunochromatographic analysis: theory and application to theophylline immunoassay

The development of an immunochromatographic technique suitable for rapid analysis of biological fluids is described. Quasi-one-dimensional antibody lattices specific for theophylline were constructed by packing Sepharose beads conjugated with specific antibody into specially designed narrow capillary tubes. The design of these capillary columns was such that they would subtract a preset threshold quantity of antigen (label and analyte) from the total amount presented. Labeled antigen, which appeared in the flowthrough, could then be used to precisely quantitate the analyte present. The ideal format would permit very precise subtraction of 100% of the available antigen up to the threshold amount and none of the remainder. The microcolumn described here comes close to this ideal behavior through the attainment of very high ratios of bound/free antigen. The elevated bound/free ratio could be explained by theoretical analysis of the effect on equilibria of the high antibody concentration in this quasi-one-dimensional system. Lattices containing anti-theophylline antibodies were used to develop a competitive enzyme immunoassay for theophylline which demonstrated a dose-response that was closely similar to that predicted by theoretical treatment. The entire assay procedure was performed in less than 30 min and demonstrated a sensitivity limit of approximately 20 ng/ml. Preliminary studies on clinical serum samples suggest that this assay has potential for the routine analysis of biological fluids.