Predation and priority effects in experimental zooplankton communities

During colonization of new habitats, the sequence of arrival among species is in many cases determined by chance. Priority effects imply that differences in arrival time may lead to long-lasting differences in species dominance. To evaluate the importance of priority effects, we performed a community assembly experiment, manipulating the inoculation order of three large cladoceran zooplankton species. The inoculation treatments were crossed with a predation treatment to test whether the presence of a predator (larvae of the phantom midge Chaoborus ) results in changes in the strength of species sorting and priority effects. Our results clearly demonstrate priority effects, but also that the presence of a predator impacts both community assembly and the strength of priority effects. In the predation-free treatments, communities were dominated by either Daphnia magna or Daphnia obtusa , depending on the species arrival sequence. Whenever D. obtusa was inoculated after D. magna , the species displayed negative growth. In the presence of Chaoborus predation, the communities were generally dominated by the third species, Simocephalus vetulus . Here, the growth of D. magna was negative when the species was inoculated as second or third. Overall, our results underscore the importance of both priority effects and species sorting during community assembly.     

Predation risk and the structure of freshwater zooplankton communities

Summary Many predators inflict substantial mortality on their prey. The prey respond to these selective pressures with changes in their spatial and temporal overlap with the predator (density risk responses), or with changes in their vulnerability to the predator (prey vulnerability responses). Here we develop a simple predation model that permits quantification of the basic response types of the prey in nature. We then test the hypothesis that prey response will be proportional to the intensity of the predation mortality relative to all other sources of mortality and decreased natality acting on the prey. A significant regression relationship is obtained for the prey vulnerability response but not for any of the density risk responses. The individual response values and regression statistics are used to interpret the relative importance of the different response types and to assess the predator's influence on prey community structure.Supported by Lehigh University Environmental Studies Center     

Water: its importance to life

Textbooks increasingly include material concerning the importance of water but this topic is often treated over-simplistically with insufficient attention being given to the central position of water in life processes. In this article, modern views of the fundamental role that water plays in biochemical function and process are summarized. The importance of water in the structures of nucleic acids and proteins is explained.     

Predation by a water mite (Piona exigua) on enclosed populations of zooplankton

Short term, replicated experimental alteration of densities of a predatory water mite Piona exigua Viets, inside 0.45–0.475 m³ litre enclosures, revealed little evidence of the effects of predation on the number and relative abundance of the enclosed zooplankton species. Predation rates more closely approximated those estimated from single prey functional response experiments in the second experimental period (December) than in the first (March). In December Daphnia was the only susceptible taxon present in large numbers, whereas in March, Ceriodaphnia and Chydorus were also present. This result is consistent with laboratory findings that predation rates are lowered in the presence of more than one prey type.The difficulty of obtaining evidence for significant effects of these planktonic predators is in part due to changes in the preferred prey species in the diet of Piona depending on stage and sex of the mite and to aspects of experimental design. The wide variability between replicate enclosures at each predator density reduced the power of the statistical analyses used to test the null hypothesis. Enclosures with no predators are necessary to investigate the effects of enclosure on the zooplankton prey, since these effects may outweigh those due to predator consumption.     

Estimating predation risk in zooplankton communities: the importance of vertical overlap

In order to estimate predation risk in nature, two basic components of predation need to be quantified: prey vulnerability, and density risk. Prey vulnerability can be estimated from clearance rates obtained from enclosure experiments with and without predators. Density risk is a function of predator density, and the spatial and temporal overlap of the predator and prey populations. In the current study we examine the importance of the vertical component of overlap in making accurate estimates of predation risk from the invertebrate predator Mesocyclops edax on rotifer versus crustacean prey. The results indicate that assumptions of uniform predator and prey densities cause a significant underestimation of predation risk for many crustacean prey due to the coincident vertical migration of these prey with the predator. The assumption of uniformity is more reasonable for estimating predation risk for most rotifer prey.     

Role of Pore Size Location in Determining Bacterial Activity during Predation by Protozoa in Soil

The predation of a luminescence-marked strain of Pseudomonas fluorescens by the soil ciliate Colpoda steinii was studied in soil microcosms. Bacterial cells were introduced in either small (neck diameter, <6 (mu)m) or intermediate-sized (neck diameter, 6 to 30 (mu)m) pores in the soil by inoculation at appropriate matric potentials, and ciliates were introduced into large pores (neck diameter, 30 to 60 (mu)m). Viable cell concentrations of bacteria introduced into intermediate-sized pores decreased at a greater rate than those in small pores, with reductions in bacterial populations being accompanied by an increase in viable cell numbers of the ciliate. The data indicate that the location of bacteria in small pores provides significant protection from predation. In the absence of C. steinii, the level of metabolic activity of the bacterial population, measured by luminometry, decreased at a greater rate than cell number, and the level of luminescence cell(sup-1) consequently decreased. The decrease in levels of luminescence indicates a loss of activity due to starvation. During predation by C. steinii, the level of the activity of cells introduced into small pores fell in a similar manner. The level of cell activity was, however, significantly greater for cells introduced into intermediate-sized pores, despite their greater susceptibility to predation. The data suggest that increased activity arises from a release of nutrients by the predator and the greater accessibility of bacteria to nutrients in larger pores. Nutrient amendment of microcosms resulted in increases in bacterial populations to sustained, higher levels, while levels of luminescence increased transiently. The predation of cells introduced into intermediate-sized pores was greater, and there was also evidence that the level of activity of surviving bacteria was greater for bacteria in intermediate-sized but not small pores.     

Predation by Buenoa macrotibialis (Insecta, Hemiptera) on zooplankton: effect of light on selection and consumption of prey

In this study we test the hypothesis that the notonectid Buenoamacrotibialis shows a strong periodicity in foraging on smallzooplankton because it relies on sight to detect the smalleritems of its diet. In contrast, B. macrotibialis may be ableto detect larger prey organisms by mechanoreceptors and thereforeconsume them independently of light availability. We conductedlaboratory and field experiments with light and dark treatmentsto analyze the effect of light on the efficacy of B. macrotibialis(1.2–7mm) in preying on the rotifer Brachionus calyciflorus (~0.25mm body length), the cyclopoid copepod Tropocyclops extensus(~0.5 mm) and the cladoceran Daphnia pulex (~1.8 mm). We studiedthe feeding of B. macrotibialis on Tropocyclops extensus duringthe daytime and night-time in light and dark treatments in thelaboratory, and in natural daylight and full moonlight in thefield. Our results show that B. macrotibialis depends on sightto capture small (<0.5 mm) prey, probably because these preyproduce little disturbance in the water, but that it appearsto rely almost exclusively on mechanoreception to capture largerprey (>1 mm). Buenoa macrotibialis consumed Daphnia pulex,the largest prey offered, independently of light availability,while the consumption of T. extensus and Brachionus calycifloruswas recorded only in lit treatments. Furthermore, Buenoa macrotibialispresented a strong periodicity in feeding on small prey, controlledexclusively by light. The inability of B. macrotibialis to feedon small organisms during the night was found to be due to inadequatelight for prey detection, rather than to an endogenously controlleddecrease in feeding activity during the night. Under naturallight conditions, B. macrotibialis preyed voraciously on T.extensus in daylight but not in the full-moon treatment or inthe dark treatments, regardless of the time of day, suggestingthat there is a threshold of light intensity below which smallprey cannot be detected by the backswimmer.     

Phytoplankton and zooplankton seasonal dynamics in a subtropical estuary: importance of cyanobacteria

A seasonal study of phytoplankton and zooplankton was conductedfrom 1999 to 2001 in Pensacola Bay, Florida, USA, to furtherthe understanding of pelagic food webs in sub-tropical estuaries.Monthly measurements included size-fractionated chlorophyll(whole water, <5 µm, <20 µm), net- and picophytoplanktoncomposition analyzed using microscopy, flow cytometry, and HPLCpigment analysis. Additionally, zooplankton abundance and dryweight were determined from net tows. The results show a phytoplanktoncommunity dominated by the small size fraction (<5 µm),especially during the warm periods. The <5 µm chlorophyllfraction was strongly correlated with cyanobacterial abundanceand zeaxanthin. Cyanobacteria (cf. Synechococcus) abundancepeaked during summer in the upper estuary, typically exceeding3 x 10⁹ L^-1, and was strongly correlated with temperature. Cyanobacteriaabundance at the freshwater end of the Bay (in the EscambiaRiver) was very low, suggesting that cyanobacteria were notdelivered via freshwater. Two pigmentation types of cyanobacteriawere observed. Phycoerythrin-containing cells (PE-rich) weremore abundant at the marine end, while phycocyanin-containingcells (PC-rich) were more abundant in the upper estuary. Thelarger algae (>5–10 µm) were predominantly composedof diatoms, followed by chlorophytes, cryptophytes and dinoflagellates.The three most abundant genera of diatoms were Thalassiosira,Pennales and Cyclotella. Zooplankton biomass averaged 12.2 µgC L^-1, with peak biomass occurring during May (     

DNA条形码及其在海洋浮游动物生态学研究中的应用

浮游动物的准确鉴定是浮游动物生态学研究的基础.传统的基于形态特征的鉴定不仅费时费力,而且部分类群特别是浮游幼体由于形态差异细微,鉴定存在困难,导致物种多样性被低估.DNA条形码(DNA barcodes)技术为浮游动物物种鉴定提供了一个有力工具,已迅速应用于海洋浮游动物生态学研究.本文介绍了DNA条形码的基本概念、优势及局限性,总结了该技术(主要是基于线粒体细胞色素C氧化酶第一亚基(mtCOI)基因序列片段的DNA条形码)在海洋浮游动物物种快速鉴定、隐种发现、营养关系研究、生物入侵种监测、群落历史演变反演、种群遗传学以及生物地理学中的成功应用.随着DNA条形码数据库信息量覆盖率的不断提高和新一代测序技术的快速发展,DNA条形码将提供除了种类鉴定外更加丰富的信息,从而帮助人们更好地理解海洋浮游动物的多样性及其在生态系统中的功能,推动海洋浮游动物生态学的发展.     

Laminarinase induction in marine zooplankton and its variability in zooplankton samples

Laminarinase, or ß-l, 3-glucanohydrolase, is a stableand highly active catalyst of the breakdown of ß-l,3 linked polysaccharides into glucose subunits. The enzyme isapparently unique to herbivores among marine planktonic zooplankton,and its specific substrate, chrysolaminarin-a ß-1,3 linked storage product-is unique to phytoplankton. Evidenceis presented to show that the enzyme is substrate inducibleand that enzyme activities rise and fall in proportion to theamount of ß-1, 3-glucan in the diet. Our data from SanClemente and Santa Barbara Basins (California) showed a negativecorrelation between laminarinase activity and zooplankton biomassdensity when samples were taken at closely spaced intervalsover a three day period. This result suggests that the negativecorrelation between phytoplankton and zooplankton which is oftenobserved may at least in part be due to grazing activity. Implicationsfor phytoplankton-zooplankton relationships are discussed.     

捕食风险及其对动物觅食行为的影响

对捕食风险的涵义及其对猎物动物觅食行为的影响、猎物动物面对捕食风险时的反应进行了论述。捕食风险可以简单地理解为一定时间内猎物动物被杀死的概率。当捕食风险存在时 ,动物会选择相对安全但觅食效益较低的地点觅食 ;由于死亡率和消化方面的限制 ,一般都会产生食谱收缩 ;觅食活动方式的时间格局也会因捕食风险而发生改变 ,如水生动物的昼夜垂直迁移、某些陆生动物昼行性与夜行性活动的转换、月光回避等。在与捕食者发生遭遇时 ,猎物动物的主要反应是 :①发出某些信号以阻止捕食者的追捕 ;②靠近并注视捕食者 ;③逃逸 ;④在一定的时间恢复觅食活动。在以往的研究中 ,对捕食者种类已经有了较多的了解 ,而对猎物如何判断捕食者丰富度信息、估计风险程度等方面则知之甚少 ;同时 ,对捕食风险水平的调控、对多种因素的综合分析也较少涉及。在今后的研究中 ,还应该考虑研究的尺度问题 ,因为在不同尺度的环境条件下 ,猎物动物对于捕食风险的反应可能大相径庭。     

The importance of Protozoa in controlling the abundance of planktonic algae in lakes

Apart from ciliates, there are other protozoans which can form an important element in the herbivorous zooplankton of lakes.
The protozoans discussed in this paper feed on colonial algae. They can greatly reduce the numbers of certain Chlorophyta in Windermere, Esthwaite Water and Blelham Tarn, lakes in the English Lake District.
A very short period, often 7–14 days, can suffice for the destruction of more than 99% of an algal population.
Experiments with a species of Pseudospora showed that it would only ingest one out of six green algal species, although, in nature, Pseudosporae which are morphologically similar to this species have been observed in all these algae.
The importance of such protozoans, and of parasitic fungi, has been underrated or neglected in studies of the quantitative relationships between primary and secondary production in the plankton.     

Three Avenues to Ecologic Research on Parasitic Protozoa

Our knowledge of parasitic protozoa can be greatly enhanced by increased use of the following 3 ecological approaches to the study of parasitism. A) Studies of energy flow between parasite and host. B) Systems analysis. C) Studies of nutrition through an analysis of the parasite's environment. Most of the energy in cysts and spores is never returned to the parasite-host system. The more integrated the system the more difficult an analysis of the role of parasites in the host energy budget. A parasite-host system can be understood only through a careful study of each part, and the relationships among these parts. A measure of the nutrient status of a body fluid should take into consideration the nutrient status of any population of parasites that may be residing in that fluid. The above considerations were applied to problems of parasitism in deepsea fishes. Small, delicate midwater fishes do not have much energy for pursuing prey. We need to know details of the effects of great pressures and low temperatures on parasites. Energy flow between parasites and deep marine fishes has never been investigated. It is possible that parasites in these fishes are more efficient in energy transformation than are their hosts. These kinds of studies may be labeled “integrative parasitology.”     

Short-term temporal variation in coastal zooplankton communities: the relative importance of physical and biological mechanisms

Drogues were deployed off the coast of Northumberland (north-eastEngland), as they were tracked zooplankton were collected, byfour vertical hauls of a UNESCO WP-2 net (200 µm), adjacentto the drogue at hourly intervals Sampling covered a full tidalcycle, at least once each month from February to April, andin July and August 1993. Short-term changes in the communitystructure (in terms of species composition and abundance) wereinvestigated with respect to the local wind field and tidaladvection. It was observed, from a cluster analysis that duringhorizontal transport, the zooplankton maintained the same communitystructure for at least three consecutive hours on each samplingoccasion [Pearson correlation (r) 0.70; P0.01] even during periodsof high turbulent mixing, driven by wind stress Multiple regressionmodels including parameters of the wind field and the rate ofhorizontal transport only accounted for a maximum of 52% ofthe temporal variation in zooplankton community structure. Theunaccounted for variation provides the basis for the considerationof the zooplankton as ‘active drifters’ rather than‘passive particles’, this is discussed.     

Nature of Predation Risk Cues in Container Systems: Mosquito Responses to Solid Residues From Predation

In aquatic systems, prey animals associate predation risk with cues that originate either from the predator or from injured conspecifics. Sources and benefits of these cues have received considerable attention in river, lake, and pond ecosystems but are less well understood in small container ecosystems that can hold less than a liter of water. Mosquitoes Aedes triseriatus (Say) and Aedes albopictus (Skuse) encounter predatory Corethrella appendiculata (Grabham) and Toxorhynchites rutilus (Coquillett) in small containers and show antipredatory behavioral responses. We investigated the sources of the predation cues to which these prey larvae respond. We tested whether Ae. albopictus larvae show behavioral responses to cues emanating from the predator or from damage to prey caused by the act of predation. We also tested whether Ae. triseriatus respond to cues present in fluid or solid residues from predator activity. Ae. albopictus showed behavioral modifications only in response to waterborne cues from a feeding predator and not to cues from a starving predator, indicating that Ae. albopictus respond to cues created by the act of predation, which could include substances derived from damaged prey or substances in predator feces. Ae. triseriatus showed behavioral responses to solid residues from predation but not to fluid without those solids, indicating that the cues to which they respond originate in predator feces or uneaten prey body parts. Our results suggest that cues in this system may be primarily chemicals that are detected upon contact with solid residues that are products of the feeding processes of these predators.     

Predation on prokaryotes in the water column and its ecological implications

The oxic realms of freshwater and marine environments are zones of high prokaryotic mortality. Lysis by viruses and predation by ciliated and flagellated protists result in the consumption of microbial biomass at approximately the same rate as it is produced. Protist predation can favour or suppress particular bacterial species, and the successful microbial groups in the water column are those that survive this selective grazing pressure. In turn, aquatic bacteria have developed various antipredator strategies that range from simply 'outrunning' protists to the production of highly effective cytotoxins. This ancient predator-prey system can be regarded as an evolutionary precursor of many other interactions between prokaryotic and eukaryotic organisms.     

The importance of zooplankton to the daily metabolic carbon requirements of healthy and bleached corals at two depths

Bleached and non-bleached fragments of three species of Hawaiian corals were exposed to enhanced and ambient concentrations of zooplankton at 1 and 6 m depth to determine the contribution of zooplankton to the coral's daily carbon budget. The size and taxonomic grouping were recorded for every zooplankton captured and the relative input of zooplankton of different size classes was determined. The contribution of heterotrophy to animal respiration (CHAR) was calculated using an improved method that included the proportionate contribution of zooplankton from all size classes. Results show that the proportionate effects of species, depth and bleaching treatments on coral feeding rates were not significantly different between ambient and enhanced zooplankton concentrations. Corals captured the same size and assemblage of zooplankton under all evaluated conditions, and preferentially captured plankters smaller than 400 µm. Feeding rates of Porites lobata increased with depth regardless of bleaching status. Feeding rates of Porites compressa increased with depth in non-bleached corals, but not in bleached corals. Within depth, feeding rates of bleached Montipora capitata increased, P. compressa decreased and P. lobata remained unchanged relative to non-bleached fragments. Therefore, the feeding response of corals to the same disturbance may vary considerably. Calculated CHAR values show that heterotrophic carbon from zooplankton plays a much larger role in the daily carbon budget of corals than previously estimated, accounting for 46% of some coral species' daily metabolic carbon requirements when healthy and 147% when bleached. Thus, heterotrophically acquired carbon made an important contribution to the daily carbon budget of corals under all experimental conditions. These results suggest that the relative importance of autotrophic and heterotrophic carbon to a coral's energetic needs is mediated by a coral's bleaching status and environment, and should be considered on a continuum, from 100% photoautotrophy to 100% heterotrophy.