Trophic polymorphism amongst Arctic charr from Loch Rannoch, Scotland

This paper describes the results of a multivariate and univariate morphometric analysis of three groups of Arctic charr Salvelinus alpinus from Loch Rannoch, Perthshire, Scotland, distinguished a priori on the basis of coloration (bright v. cryptic) and site of capture (from two locations 12 km apart). The analysis produced a clear and highly significant distinction, not only between brightly and cryptically coloured charr, but also between the two cryptically coloured groups, one of which was more robust in terms of several size-independent head measurements. Stomach analysis showed that the brightly coloured charr fed entirely on zooplankton, the less robust, cryptically coloured fish, fed on benthic macroinvertebrates, whereas a significant proportion of the diet of the more robust cryptically-coloured form consisted of other fish. Differences in length at age also distinguished the three forms, with the robust, piscivorous charr, which live longer and potentially reach a larger final size, attaining smaller sizes at a given age. These data clearly confirm the previous identification of a distinct planktivorous morph of Arctic charr in Loch Rannoch and extend the morph analysis by distinguishing two additional morphs, a benthivorous morph and a piscivorous morph that are morphologically and ecologically distinct. The results are discussed in the context of other systems in which sympatric morphs of Arctic charr have been described.     

Rotifer occurrence in relation to age,depth and trophic state of quarry lakes

An effect of age of quarry lakes on rotifer abundance and species composition has been evaluated. Rotifers occurred in all lakes under study. They were even found in the youngest (2 years of age) one, Rogonica 4, but both rotifer density and species richness were low there. Rotifer communities of much higher density and species diversity were noted in lakes only 4–6 years older. Lakes of over 30 years of age were strongly differentiated in rotifer numbers and species structure. In general, age of quarry lakes has an impact on rotifer communities only at the very beginning of the process of colonization. Several years later other factors become more important, e.g., depth or trophic state of the lakes.     

Phototrophic Picoplankton in Temperate Lakes: Seasonal Abundance and Importance along a Trophic Gradient

The seasonal development of autotrophic picoplankton was investigated in seven Danish lakes representing a eutrophication gradient. Highest cell abundance between 1.5 to 6 × 10⁵ cells ml⁻¹ were found in mid-summer. Minor peaks were observed in spring. In winter, densities were below 10³ ml⁻¹. The highest relative picoplankton contribution to total autotrophic biomass also occurred in mid-summer. In the eutrophic lakes and one humic lake the average seasonal contribution of picoplankton to total chlorophyll was below 1% increasing to 5-8% in the meso- and oligotrophic clear water lakes. During short periods the proportion of picoplankton did reach 25%. The higher relative importance of picoplankton in less productive lakes was not due to higher actual chlorophyll concentrations, but due to a much more pronounced response by larger algae at higher nutrient loading. Both cyanobacteria and eukaryote organisms were present as picoplankton. Only eukaryotes were found in one eutrophic lake and an acidic, humic lake. In the eutrophic lakes eukaryote picoplankton was dominant; both with respect to cell densities and biovolume, whereas cyanobacteria dominated the two meso-oligotrophic lakes. Autotrophic picoplankton were present in all lake types, however their importance seemed to be less in most eutrophic lakes than in less productive, meso-oligotrophic lakes.     

Distribution of rotifers in North Island,New Zealand,and their potential use as bioindicators of lake trophic state

The distribution and ecology of planktonic rotifers was investigated in 33 lakes in the North Island, New Zealand, between 1997 and 1999. A total of 79 species of monogonont rotifer were identified, with an average of 21 species per lake, a diversity which is high in comparison with many previous New Zealand studies. Most species recorded were cosmopolitan taxa, and were widespread in their distribution over the North Island. Multivariate analyses (Multi-Dimensional Scaling and Canonical Correspondence Analysis) did not distinguish distinct lake groupings based on rotifer communities, but rather gradients in assemblages, which were most highly associated with lake trophic state. Based on these responses, the development of potential rotifer bioindicator schemes for lake trophic state is described and discussed.     

Chemical and Microbial Composition of Sediments in Reservoirs with Different Trophic State

For the assessment of the metabolic potential of a sediment, the upper 5 cm layer should preferentially be regarded, since this is the horizon with the highest biochemical activity in the entire reservoir. Sediment cores from four different reservoirs were examined. These represent a broad range of trophic conditions (Neunzehnhain – oligotrophic; Muldenberg – oligotrophic, acidic, dystrophic; Saidenbach – mesotrophic; Quitzdorf – highly eutrophic). The vertical concentration gradients in the interstitial water of the examined sediments showed the tendencies characteristic of the trophic state of the reservoirs. The gradients increased with the trophic state, which affected the release of dissolved substances. The internal P load was substantial in all cases, in Quitzdorf it even exceeded the external P load. The total cell numbers of the bacteria in the sediment were only slightly influenced by the trophic state, all being in the same order of magnitude. The reservoir Quitzdorf displayed very high P release rates from the sediment and mass growths of Microcystis with a high content of intracellular polyphosphate granules in the summer months.     

Seasonal changes in phytoplankton community structure in relation to physico-chemical factors in Loch Lomond,Scotland

Surface waters, sediments and the polychaete Nereis diversicolor were sampled in the ScheldtEstuary between 1990 and 1994. In surface watersparticulate Hg (Hg_P) concentrations ranged from350–1610 ng g^-1. They are essentiallycontrolled by physical mixing of polluted fluvialparticulates with relatively unpolluted marineparticulates, but unaffected by seasonal changes.Dissolved Hg species, on the other hand, show largeseasonal variations essentially controlled by theredox conditions in the estuary, as well as bybacterial and phytoplankton activity. Total dissolvedHg (Hg_TD) concentrations ranged from 0.5 to 3.0 ngl^-1 with 10 to 90% as reactive Hg. Highconcentrations of Hg_TD are found in the upperestuary in the winter and decrease rapidly withincreasing salinity. In summer Hg_TDconcentrations are low in the anoxic upper estuary andincrease as oxygen is restored in the estuary.Significant variations were observed in dissolvedMonomethyl Hg (MMHg) concentrations withconcentrations ranging from 0.01 to 0.120 ng l^-1 in the winter and 0.08 to 0.6 ng l^-1 in summerand autumn. Particulate MMHg ranged from 2 to 6 ngg^-1 in winter and from 4 to 10 ng g^-1 insummer and accounted for 20 to 80% of the total MMHg.Hg° concentrations ranged from 0.02 to 0.130 ngl^-1 and are higher in summer than in winter. Inthe lower estuary a positive correlation betweenHg° and phytoplankton pigments was observed. Sediments and the polychaete N. diversicolorwere sampled on the intertidal flat GrootBuitenschoor. Hg_{_T} concentrations in surfacesediments ranged from 144 to 1890 ng g^-1 and MMHgfrom 0.8 to 6 ng g^-1 accounting for 0.4 to 0.8%of the total mercury present. Both total Hg (Hg_T)and MMHg concentrations increased with increasedorganic matter content and anoxic conditions. On theother hand, accumulation of Hg_T and MMHg washigher in N. diversicolor living in coarse grainsandy sediments than in muddy sediments. MMHgconcentrations in N. diversicolor ranged from2.2 to 20.9 ng g^-1 accounting for an average of18% of the Hg_T. Seasonal variationssignificantly affected Hg speciation in sediments andN. diversicolor. Higher Hg_T concentrationswere found in the sediments in autumn and winter,whereas MMHg concentrations increased in spring andsummer. Likewise, higher MMHg concentrations were alsoobserved in N. diversicolor in spring andsummer. This revised version was published online in July 2006 with corrections to the Cover Date.     

The fish community of Loch Lomond,Scotland: its history and rapidly changing status

The fish community of Loch Lomond is of national importance. Its diversity of species and rare populations of powan (Coregonus lavaretus) and freshwater feeding river lampreys (Lampetra fluviatilis) warrant high conservation status. It is also of value for its sport fisheries for sea-trout (Salmo trutta), salmon (Salmo salar) and pike (Esox lucius). Historical records demonstrate that the species composition of the fish community has remained stable over a very long period until recently when a series of introductions of fish species new to the catchment has resulted in successful colonisation by a number of species. These have resulted in fundamental changes in the ecosystem. Here using historical records the long-term stability of the fish community is examined, recent rapid changes in the fish community are documented and some of the resultant effects of changes in the fish community are demonstrated.     

Inherited differences in head allometry in polymorphic Arctic charr from Loch Rannoch, Scotland

Planktivorous and benthivorous morphs of wild Arctic charr Salelinus alpinus from Loch Rannoch, Perthshire, Scotland, reared in the laboratory from artificially fertilized eggs under identical conditions, were morphologically distinct (based on a series of head measurements) from an early age. For some morphometric characters, these differences became more marked with increasing body size, reflecting differences in the allometric growth patterns of the two forms. These data show that the observed phenotypic differences between these two trophic variants were, to some extent at least, inherited. Thus it is concluded that the mechanisms regulating expression of phenotype in the sympatric morphs of Loch Rannoch are significantly different from the environmentally determined body size polymorphisms reported from Norway but are closer to the more completely divergent forms from Thingvalavatn, Iceland.     

Species Composition, Abundance, and Distribution of Seabirds along the Northeastern Coast of Sakhalin

Seabirds were counted in September 1998 from the research vessel Professor Khromovand a motorboat in Pil'tun and Lunskii bays and in the contiguous areas of the eastern Sakhalin shelf. Data on the species composition, abundance, and distribution of seabirds are presented. A fairly high species diversity and significantly high density of seabirds were recorded in Pil'tun and Lunskii bays, which are the main areas where they concentrate during the summer months.     

Changes in Species Richness,Abundance, and Composition of Arboreal Twig‐nesting Ants Along an Elevational Gradient in Coffee Landscapes

The distribution, diversity, and assembly of tropical insects have long intrigued ecologists, and for tropical ants, can be affected by competitive interactions, microhabitat requirements, dispersal, and availability and diversity of nesting sites. Arboreal twig‐nesting ants are limited by the number of hollow twigs available, especially in intensive agricultural systems. Ant diversity and abundance may shift along elevation gradients, but no studies have examined if the proportion of occupied twigs or richness of arboreal twig‐nesting ants vary with elevation. In coffee agroecosystems, there are over 40 species of arboreal twig‐nesting ants. We examined communities of twig‐nesting ants in coffee plants along an elevational gradient to answer the following questions: (1) Do species richness and colony abundance decline with elevation or show a mid‐elevation peak? (2) Does community composition change with elevation? (3) Is elevation an important predictor of change in ant abundance, richness, and relative abundance of common species? We surveyed 42 10 × 10 m plots in 2013 from 450 to1550 m elevation across a coffee landscape in Chiapas, Mexico. We sampled a total of 2211 hollow coffee twigs, 77.1 percent of which were occupied by one of 28 species of ants. Pseudomyrmex simplex was more abundant in lower elevations, whereas Pseudomyrmex ejectus dominated in high elevations. Species richness and the percent of occupied hollow twigs both peaked at mid‐elevations (800–1050 m). In sum, we found that species richness, abundance, and composition of arboreal twig‐nesting ants shift with elevation. These findings may provide important insights for understanding ant communities in coffee agroecosystems.     

Bryophyte Species Richness and Composition along an Altitudinal Gradient in Gongga Mountain,China

An investigation of terrestrial bryophyte species diversity and community structure along an altitudinal gradient from 2,001 to 4,221 m a.s.l. in Gongga Mountain in Sichuan, China was carried out in June 2010. Factors which might affect bryophyte species composition and diversity, including climate, elevation, slope, depth of litter, vegetation type, soil pH and soil Eh, were examined to understand the altitudinal feature of bryophyte distribution. A total of 14 representative elevations were chosen along an altitudinal gradient, with study sites at each elevation chosen according to habitat type (forests, grasslands) and accessibility. At each elevation, three 100 m × 2 m transects that are 50 m apart were set along the contour line, and three 50 cm × 50 cm quadrats were set along each transect at an interval of 30 m. Species diversity, cover, biomass, and thickness of terrestrial bryophytes were examined. A total of 165 species, including 42 liverworts and 123 mosses, are recorded in Gongga mountain. Ground bryophyte species richness does not show any clear elevation trend. The terrestrial bryophyte cover increases with elevation. The terrestrial bryophyte biomass and thickness display a clear humped relationship with the elevation, with the maximum around 3,758 m. At this altitude, biomass is 700.3 g m⁻² and the maximum thickness is 8 cm. Bryophyte distribution is primarily associated with the depth of litter, the air temperature and the precipitation. Further studies are necessary to include other epiphytes types and vascular vegetation in a larger altitudinal range.     

Zooplankton in Loch Lomond: perspectives,predation and powan

Published and unpublished accounts of the zooplankton community of Loch Lomond are reviewed. Loch Lomond's zooplankton community is unique amongst those of Scotland's other large lochs. Holopedium gibberum appeared in Loch Lomond in the years between the studies of Slack & Hamilton in the 1950s and zooplankton surveys in the late 1970s.The annual cycles of Eudiaptomus gracilis, Cyclops strenuus abyssorum and Mesocyclops leuckarti are described for the mid basin of Loch Lomond. E. gracilis overwinter mainly as adult with variable egg production during their lifespan of 5–8 months. The cyclopoid copepods have variable life history characteristics. C. str. abyssorum produce a single generation per year, overwinter by means of resting eggs and a small population of planktonic adults, while M. leuckarti is present in the plankton throughout the year, but in low numbers during winter.Zooplankton populations in Loch Lomond are predated by the diverse fish community which includes a facultative planktivore in the powan, Coregonus lavaretus. Powan feed heavily on zooplankton from late spring until late autumn. Powan display selectivity in the prey species taken, in the size distribution and morph types taken within prey species. Zooplankton species, morphs and forms in Loch Lomond tend to reflect this predation.Zoology Department, University of St. AndrewsZoology Department, University of St. Andrews     

Trophic state and water turn-over time in six choked coastal lagoons in Brazil

Comparison of total phosphorus and chlorophyll-a concentration, nutrient loading, and water turn-over time in six shallow choked lagoons along the coast of the state of Rio de Janeiro, Brazil, established that water turn-over time is related to the trophic state of the lagoons with additional anthropogenic nutrient loading affecting this relationship. Turnover time was calculated as a flushing half-life from rainfall, evaporation, runoff, and tidal exchange data, and trophic state was calculated from the quantity and quality of dissolved inorganic nutrients, total phosphorus, and chlorophyll-a standing stock. Flushing half-life of the lagoons ranged between 1 and 27 days, annual phosphorus areal loading from 3 to 18 mg m^–2d^–1, and chlorophyll-a standing stock from 6 to 160 mg M^–2     

A comparative assessment of temporal variation in diet of powan, Coregonus lavaretus (L.), from Loch Lomond and Loch Eck, Scotland, U.K.

Stomach contents of powan caught throughout the year from Loch Lomond and Loch Eck were examined. Adult powan in Loch Lomond fed mainly on planktonic Cladocera, switching to benthic food during December-April. Bosmina coregoni was the principal planktonic food with Daphnia hyalina an important late summer and autumn prey. Loch Eck powan fed throughout the year on chironomid larvae and Pisidium spp. from the benthos and ingested large amounts of non-food material. Mean dry weights of food in stomachs were correlated with water temperature in Loch Lomond but not in Loch Eck and were higher in powan from Loch Eck over most of the year.     

Coyote Abundance,Sheep Predation,and Wild Prey Correlates Illuminate Mediterranean Trophic Dynamics

ABSTRACT Sheep predation by coyotes (Canis latrans) is a major problem for sheep producers in North America. Solutions are facilitated by a basic understanding of the trophic dynamic context of this problem, one that likely varies geographically in important qualitative ways. Little is known about vertebrate trophic dynamics in Mediterranean ecosystems, where prey are diverse and their biomass is strongly influenced multi-annually by variable rainfall. We used long-term data sets from north-coastal California, USA, to investigate whether wild prey fluctuations caused immediate negative effects on sheep predation via a reduction in the coyote functional response or delayed positive effects on sheep predation via a numerical response by coyote predators. Because we could not measure prey biomass directly, we used variables associated with lower trophic levels (e.g., annual plant productivity, vole abundance, rainfall) as proxies for wild prey biomass. Coyote population growth rate was positively correlated with lower-trophic-level variables of the previous year, suggesting a numerical response, and sheep (ad F + lambs) predation was positively correlated with coyote abundance in the current year. Sheep predation also was negatively correlated with lower-trophic-level variables of the current year, suggesting an immediate buffering effect of wild prey on sheep predation. Together, coyote abundance and lower-trophic-level variables explained 47% of the multi-annual variation in sheep kills. The negative pathway between lower-trophic-level variables and sheep predation was stronger than the positive pathway, possibly due to the erratic nature of multi-annual fluctuations in lower-trophic-level variables, which could prevent the numerical response from reaching its full potential. Monthly analyses revealed a type III functional response of coyotes to lambs, which is expected to enhance buffering effects of wild prey on sheep predation. Our findings suggest the dominant effect of wild prey biomass on sheep predation by coyotes in this Mediterranean-type community is as a buffer.     

黄河三角洲自然保护区典型植物群落物种组成及多样性梯度变化

以黄河三角洲自然保护区典型湿地群落为研究对象,探讨其物种组成及物种多样性的梯度变化规律。结果表明,从芦苇－香蒲群落到翅碱蓬群落梯度上：（1）群落物种丰富度呈波动性变化,旱柳－芦苇－白茅群落的物种丰富度最高,其次是芦苇－柽柳－翅碱蓬群落、芦苇－香蒲群落、柽柳－翅碱蓬群落,翅碱蓬群落的物种丰富最低;（2）群落的α多样性的变化格局与丰富度的变化格局不太一致,其中Shannon-Winner多样性指数与Pelou均匀度指数表现为波动性的下降趋势,而Simpson优势度指数则表现为波动性的上升趋势;（3）群落的β多样性变化格局也不完全相同,其中相异性系数呈波动性降低趋势,Copy指数则表现为先升高再降低的变化趋势。黄河三角洲典型湿地植物群落组成和物种多样性的梯度变化主要与生境变化有关。     

A multivariate morphometric and meristic description of a population of freshwater-feeding river lampreys, Lampetra fluviatilis (L.), from Loch Lomond, Scotland

Adults of a freshwater-feeding population of Lampetra fluviatilis (L.) in Loch Lomond, Scotland, were trapped on their upstream (spawning) migration in the main inflow to the loch, the Endrick Water. These animals could be distinguished from the more typical anadromous upstream migrant L. fluviatilis , from the Endrick Water and the nearby catchment of the River Forth, principally by their smaller total length, greater disc, snout and eye size and much darker pigmentation. These, and other morphometric and meristic characteristics have been compared for populations of L. fluviatilis and Lampetra planeri (Bloch) from the Lomond and Forth catchments using univariate and multivariate statistics. The Endrick Water 'dwarf' L. fluviatilis was found to differ significantly from the other Lampetra studied, in a number of body proportions in addition to those traits mentioned above, and also in mean numbers of trunk myomeres and teeth. These differences are likely to be due to a combination of the effects of genetic isolation, and the short (freshwater) feeding phase of the 'dwarf' L. fluviatilis , which may, therefore, represent the intermediate stage between parasitic and non-parasitic forms in the L. fluviatilis/L. planeri species pair.     

Picoplankton in Six New Zealand Lakes: Abundance in Relation to Season and Trophic State

The abundance of picoplankton (0.2-2 μm) was measured seasonally in the surface waters of six New Zealand lakes that represent a range of trophic states. The lakes were: Wakatipu, Te Anau, Manapouri, Hayes, Mahinerangi and Ross Creek Reservoir. Among the lakes, picoplankton abundance was associated positively with temperature; picoplankton were most abundant in summer and autumn when they attained densities of 108,000-270,000 cells/ml in the oligotrophic lakes. In these lakes, prokaryotic picoplankton was generally an order of magnitude more abundant than eukaryotic picoplankton. Consistent with the hypothesis that picoplankton are more important in oligotrophic than eutrophic ecosystems, there was a weak negative correlation between the density of prokaryotic picoplankton in the lakes and the level of chlorophyll a. The presence of large numbers of chroococcoid cyanobacteria in the guts of Ceriodaphnia dubia and Bosmina meridionalis implies that prokaryotic picoplankton are collected, but not digested, by these species.     

Environmental factors determining the structure of rotifer communities in a river-shed reservoir

This study was designed to find out which environmental factors (temperature, oxygen concentration and food resources) are more important in steering the rotifers vertical distribution and community structure in an oligo-changing to-mesotrophic reservoir. It was observed that, despite the influence of temperature and oxygen content of the water, biotic factors especially the food availability and changes in trophic state were crucial in shaping the vertical distribution and species composition of rotifers in Meimoa Reservoir, located in Tagus River in Portugal.