Zoogeography of Chiropotes albinasus (Platyrrhini,Atelidae) in Southwestern Amazonia

White-nosed bearded sakis (Chiropotes albinasus) are endemic to the Madeira–Xingú interfluvium in southern Amazonia, though recent fieldwork has produced conflicting data on the southwestern limits of the species's geographic range. We reevaluated the distribution of bearded sakis on the basis of surveys from 34 sites throughout the Brazilian state of Rondônia. Chiropotes albinasus occurred at seven sites in the eastern part of the state, including two west of the Jiparaná–Pimenta Bueno river system in the extreme south, but there is no record of their presence further north and west in the Jiparaná–Guaporé interfluvium and they were absent from the Jiparaná–Mamoré interfluvium. The data suggest that ecological, rather than geographic barriers restrict the distribution of Chiropotes albinasus in southern Rondônia, but are contradictory with regard to the possible determining factors. Chiropotes albinasus appears able to thrive in transitional, savanna-like ecosystems in southern Rondônia, but is unexpectedly absent from adjacent areas of terra firme forest. Syntopy with the only other pitheciine found in the state (Pithecia irrorata) appears to have a negative effect on the abundance of Chiropotes albinasus which implies that interspecific competition may reinforce a complex of limiting factors, such as the availability of key plant species. Despite showing that Chiropotes albinasus is widespread in southern Rondônia, we also confirm its absence from the western two thirds of the state, a significant reduction in the known range of the species.     

Biology of Platycephala planifrons (Diptera: Chloropidae) and its potential effectiveness as biological control agent for invasive Phragmites australis in North America

Phragmites australis is a cosmopolitan clonal grass valued for its support of diversity-rich communities in its native range and feared for its devastating effects on native diversity where the species is introduced. Lack of successful control in North America resulted in the initiation of a biological control program. We used a combination of field surveys and common garden experiments in Europe to study life history and ecology of a chloropid fly, Platycephala planifrons, to assess its potential as a biological control agent. The fly is widely distributed (in non-flooded sites) throughout Eurasia but attack rates are generally low (mean 5–10%; max. 29%). Adults emerge in late June and may live for several months. Females lay eggs at the base of Ph. australis shoots. First instar larvae of this stem-feeding fly overwinter in dormant below-ground shoots of Ph. australis and rapidly complete development in early spring. Larval feeding destroys the growing meristem of the shoot causing premature wilting and 60–70% reductions in shoot biomass production. Early season attack and considerable impact suggest that Pl. planifrons could be a potent biocontrol agent, if it can escape suppression by natural enemies in the introduced range. However, the generally low attack rates in its native range and its dependence on dry sites appear to make the species a “second-choice” candidate for potential release in North America.     

Population dynamics of Tenagomysis tasmaniae Fenton,Anisomysis mixta australis (Zimmer) and Paramesopodopsis rufa Fenton from south-eastern Tasmania (Crustacea:Mysidacea)

The population dynamics of a coastal mysid community was examined at One Tree Point in southern Tasmania over a 12-month period, including three 24-hour sampling sessions. Fourteen mysid species were recorded. Zonation patterns, life-history and diel activity of the three most abundant species, Tenagomysis tasmaniae, Anisomysis mixta australis and Paramesopodopsis rufa were examined. These three species were found in large numbers throughout the year associated with the macroalgal fringe on either side of the bay. Habitat partitioning within this zone of occurrence was evident. T. tasmaniae was the most abundant species (annual mean density 32.4 m^–3), followed by A. mixta australis (annual mean density 20.5 m^–3 ) and P. rufa (annual mean density 11.3 m^–3). The major peaks of abundance of these three species were temporally separate. Breeding was intensive for the three species from spring till late autumn. A cessation of breeding in winter was evident for A. mixta australis and to a lesser extent for P. rufa but T. tasmaniae bred throughout the year although at a reduced rate during winter. Examination of the diel behaviour identified peaks of abundance at sunrise and sunset for T. tasmaniae; P. rufa was caught in greater numbers at night, but no consistent pattern was observed for A. mixta australis.     

The combined use of acoustic tracking and echosounding to investigate the movement and distribution of common bream (Abramis brama) in the River Trent,England

Spatial behaviour and distribution of fishes along a 7.6-km lowland reach of the River Trent, England, were examined using two complementary telemetry techniques: acoustic tracking to assess the movement and activity of common bream Abramis brama (L.) and quantitative echosounding for measuring the density and distribution of fish shoals. Nine adult bream (39.3–53.2 cm) were tracked by means of intraperitoneally implanted acoustic transmitters from 19 July to 12 September 2000. Home range size varied between 0.35 and 5.40 km of river length over this period. Bream were relatively inactive during daylight hours, began moving near dusk, and tended to move throughout the night. A distinct daytime residence area was occupied by most tagged fish on most occasions, while river use at night was more variable between individuals. Mobile echosounding surveys, with the transducer beaming horizontally across the river, conducted at night between July and September 2000, showed a highly contagious fish distribution within the study reach. For 200-m sections of river, there was a negative correlation between the relative frequency of acoustic tracking fixes at night and mean fish densities, as measured by echosounding for targets larger than –50 dB (c. 5-cm long). However, there was a highly significant positive rank correlation between the relative frequency of acoustic tracking fixes and acoustic targets larger than –30 dB (c. 22-cm long), most of which in this river are bream. This suggests that telemetry and echosounding can, in this part of the River Trent, be combined to provide valuable spatial information at individual and population scales for bream.     

Phylogenetic Relationships within GenusLeuciscus(Pisces, Cyprinidae) in Portuguese Fresh Waters, Based on Mitochondrial DNA CytochromebSequences

To investigate phylogenetic relationships amongLeuciscusspecies occurring in Portuguese inland waters, the cytochromebgene was sequenced from representatives of the main rivers. This study supports the recognition of the species level forL. pyrenaicus,including populations from the southern Portuguese drainages (Tejo, Sado, and Guadiana drainages), and forL. carolitertii,including populations from the northern Portuguese drainages. The existence of two new species occurring in the extreme southwestern drainages of Mira and Arade is also suggested. The present results support the monophyly of the Mira and the Arade populations, as well as an early divergence of these two lineages. The present-day distribution ofLeuciscusspecies is seen as a consequence of Pliocene and Pleistocene events, such as river disjunctions and posterior confluence in epicontinental seas and river captures. A mixture of haplotypes was observed in the Mondego and the Tejo drainages, which could be a consequence of ancient river captures, with a possible mitochondrial DNA introgression in the Tejo drainage and a recent introduction by man in the Mondego drainage. The pattern of differentiation among mtDNA haplotypes and their geographic distribution is discussed in terms of evolutionary aspects.     

Conservation and management implications of fine-scale genetic structure of Gulf sturgeon in the Pascagoula River, Mississippi

The anadromous Gulf sturgeon occurs along the north central coast of the Gulf of Mexico and is federally listed as threatened. We analyzed fine‐scale patterns of Gulf sturgeon population structure, focusing on the Pascagoula River drainage of Mississippi, in reference to movement patterns as determined via telemetry and capture data. We genotyped 361 Gulf sturgeon using eight microsatellite loci including samples from the Pascagoula, Pearl, Escambia, Yellow, Choctawhatchee, and Apalachicola river drainages. Pairwise F_ST estimates indicated that genetic structure occurs at least at the drainage level. The Pascagoula and Pearl rivers form a western group, demonstrating 100% bootstrap support for a division with drainages to the east. Assignment tests detected non‐natal genotypes occurring in all drainages. According to assignment tests, the Pascagoula supports an admixture of individuals, containing minimal influence from drainages to the east (2%) and substantial interaction with the Pearl River (14.1%). The occurrence of Pascagoula River fish in the Pearl was non‐reciprocal, observed at 1.1%. After accounting for non‐natal genetic diversity within the Pascagoula, there remained a disparity between a pooled Pascagoula group and the only documented spawning site within the drainage located in the Bouie River. We interpret this as an indication of a second genetic stock within the Pascagoula River drainage. Radio telemetry data suggest that spawning likely occurs in the Chickasawhay River, in areas isolated from the Bouie River spawning site by about 350 river kilometers. We emphasize the utility of integrating field and molecular approaches when delineating fine‐scale patterns of population structure in anadromous fishes.     

Geographic Distribution of Red Howlers (Alouatta seniculus) in Southwestern Brazilian Amazonia, with Notes on Alouatta caraya

We surveyed howler (Alouatta) populations at 36 sites throughout the Brazilian state of Rondônia, in southwestern Amazonia, using quantitative (line transect surveys) and qualitative (interviews) methods. We recorded the red howler (Alouatta seniculus) at only one- third of the sites, and the species was relatively rare at most of them, especially in comparison with sympatric atelids (Ateles chamek and Lagothrix cana). In addition to local discontinuities, Alouatta was absent from a wide area (possibly as much as 100,000 km²) of northern Rondônia, south of the upper Madeira river. This lacuna apparently contradicts the typical association of the species with flooded forest ecosystems, but the ecological factors that may underlie it remain unclear. Competition with sympatric atelids does not appear to be a significant factor anywhere within the study area. Also, there is no evidence to suggest that the distribution patterns are related to recent human colonization of the state. We collected indirect evidence of the presence of a second howler species – Alouatta caraya – at two sites in southern Rondônia, where they are associated with highland savanna habitats and gallery forests in the Guaporé grasslands.     

Spatial and temporal dynamics of phytoplankton communities along a regulated river system, the Nakdong River, Korea

The longitudinal distribution and seasonal fluctuation of phytoplankton communities was studied along the middle to lower part of a regulated river system (Nakdong River, Korea). Phytoplankton biomass decreased sharply in the middle part of the river (182 km upward the estuary dam), and then increased downstream reaching a maximum at the last sampling station (27 km upward the estuary dam). In contrast, there was little downstream fluctuation in species composition, irrespective of pronounced differences in nutrient concentrations (TN, TP, NO₃, NH₄, PO₄) as well as in algal biomass. In the main river channel, small centric diatoms (Stephanodiscus hantzschii, Cyclotella meneghiniana) and pennate diatoms (Synedra, Fragilaria, Nitzschia) were dominant from winter to early spring (November–April). A mixed community of cryptomonads, centric and pennate diatoms, and coenobial greens (Pediastrum, Scenedesmus) was dominant in late spring (May–June). Blue-green algae (Anabaena, Microcystis, Oscillatoria) were dominant in the summer (July–September). A mid-summer Microcystis bloom occurred at all study sites during the dry season, when discharge was low, though the nutrient concentration varied in each study site. Nutrients appeared everywhere to be in excess of algal requirement and apparently did not influence markedly the downstream and seasonal phytoplankton compositional differences in this river.     

Relative contributions of sexual and asexual regeneration strategies in Populus nigra and Salix alba during the first years of establishment on a braided gravel bed river

Populus nigra L. var betulifolia and Salix alba L. var alba are early successional riparian tree species threatened throughout Continental Europe by significant changes to the natural physical processes governing their natural habitat – geomorphologically active floodplains. River management activities have dramatically altered natural patterns of river flow and rates of sediment delivery along rivers, with possible consequences for the balance between sexual and asexual regeneration strategies in these species. Conservation strategies will benefit from a greater understanding of the ways in which dynamic physical processes on the floodplain influence sexual and asexual recruitment. This paper describes a field survey investigating the relative abundance and spatial distributions of P. nigra and S. alba sexual and asexual recruits during the first years of establishment along a braided gravel bed river. Sexual and asexual recruits were identified by excavation along transects in a wet and a dry field season and distributional differences were described in terms of elevation on the floodplain, local sediment type and exposure to floodwaters. Regeneration was overwhelmingly from seed in the first 2–3 years following recruitment, but poor survival rates among sexual recruits saw a shift in the relative abundance of regeneration strategies over time. In relating hydrological data to recruitment, unseasonal flood disturbances had a negative effect on recruitment from seed and a positive effect on vegetative regeneration. Seedlings were associated with fine sediment deposits and were restricted primarily to low elevations on the flood plain, while asexual recruits had a wider spatial distribution. Certain microsite types were unique to either regeneration strategy.     

Amidohydrolase activity,soil N status,and the invasive crucifer Lepidium latifolium

Wetlands and riparian habitats in the western United States are being invaded by the exotic crucifer Lepidium latifolium (perennial pepperweed, tall whitetop). It was hypothesized that L. latifolium was an effective competitor due to its ability to make available and take up more nitrogen than vegetation it is replacing. The hypothesis was tested by comparing amidohydrolase activities, available soil N, 30 day aerobic N-mineralization rates, and plant uptake of N in paired L. latifolium invaded and non-invaded plots occupied by Elytrigia elongata (tall wheatgrass). Attributes were measured by date (June 1998, September 1998, April 1999, and May 2000) and by soil depth (0–15, 15–30, 30–50, and 50–86 cm). Lepidium latifolium invaded sites had significantly (p 0.05) greater urease, amidase, glutaminase, and asparaginase activities than sites occupied by E. elongata for most dates and soil depths. In addition, despite far greater uptake of N per unit area, L. latifolium sites still had significantly greater available N and N-mineralization potentials than E. elongata for most dates and depths. In general, enzyme activities significantly correlated with available soil N, with a stronger relationship for sites invaded by L. latifolium. There were few significant linear correlations of enzyme activities with net N mineralization potentials for L. latifolium sites, but many for sites occupied by E. elongata. These data support the working hypothesis.     

The longitudinal distribution and community dynamics of zooplankton in a regulated large river: a case study of the Nakdong River (Korea)

The longitudinal distribution and seasonal dynamics of zooplankton were examined along a 200-km section of the middle to lower Nakdong River, Korea. Zooplankton was sampled twice a month from January 1995 to December 1997 at five sites in the main river channel. There was considerable longitudinal variation in total zooplankton abundance (ANOVA, p < 0.001). All major zooplankton groups (rotifers, cladocerans, copepodids and nauplii) increased significantly with distance downstream along the river. There also were statistically significant seasonal differences in zooplankton abundance at the sampling sites (ANOVA, p < 0.01). Zooplankton abundance was high in spring and fall and low in summer and winter. The seasonal pattern of rotifers was similar to that of total zooplankton. This reflected the fact that rotifers (Brachionus calyciflorus, B. rubens, Keratella cochlearis and Polyarthra spp.) strongly dominated the zooplankton community at all locations. Among the macrozooplankton, small-bodied cladocerans (e.g. Bosmina spp.) dominated; the abundance of large-bodied cladocerans (e.g. Daphnia) was negligible (0–5 ind. l^–1). Among the environmental variables considered, partial residence time seemed to play the most important role in determining characteristics of the river zooplankton community.     

Densities,Distributions, and Seasonal Movements of Gorillas and Chimpanzees in Swamp Forest in Northern Congo

The conservation of gorillas (Gorilla spp.) and chimpanzees (Pan troglodytes) depends upon knowledge of their densities and distribution throughout their ranges. However, information about ape populations in swamp forests is scarce. Here we build on current knowledge of ape populations by conducting line transect surveys of nests throughout a reserve dominated by swamp forest: the Lac Télé Community Reserve in northern Congo. We estimated gorilla and chimpanzee densities, distributions across habitats, and seasonal changes in abundance. Gorilla density was 2.9 gorillas km^–2, but densities varied by habitat (0.3–5.4 gorillas km^–2) with highest densities in swamp forest and terra firma mixed forest. Average chimpanzee density is 0.7 chimpanzees km^–2 (0.1–1.3 chimpanzees km^–2), with highest densities in swamp forest. Habitat was the best predictor of ape nest abundance, as neither the number of human indices nor the distance from the nearest village predicted nest abundance. We recorded significantly greater numbers of apes in terra firma forest during the high-water season than the low-water season, indicating that many gorillas and chimpanzees are at times concentrated in terra firma forest amid a matrix of swamp forest. Seasonally high numbers of apes on terra firma forest islands easily accessible to local people may expose them to substantial hunting pressure. Conversely, the nearly impenetrable nature of swamp forests and their low value for logging makes them promising sites for the conservation of apes.     

Soil seed banks of woodland, heathland, grassland, mire and montane communities, Cairngorm Mountains, Scotland

The size and species composition of soil seed banks were assessed at 111 altitudinally diverse sites in the Cairngorm Mountains. Mean densities of germinable seeds varied from 83 000 m^–2 in Scots pine (Pinus sylvestris L.) woodland at 230–490 m to 200 m^–2 in moss (Racomitrium lanuginosum (Hedw.) Brid.) heath at 1000–1120 m. Seed banks were dominated by Calluna vulgaris (L.) Hull, not only wherever it was prominent in the vegetation, but also at some sites with less than 5% cover of parent plants in the ground vegetation. Many species conspicuous in the vegetation were under-represented in or absent from the seed bank and surface vegetation generally was more species rich than was the underlying seed bank, especially in high montane communities. Multiple regression was used to examine the relationship between the density of buried Calluna seeds and the abundance of parent plants in the vegetation, site altitude and the organic matter content of the soil. The model fitted to woodland communities accounted for 95% of the variation in seed density. The heathland model was less predictive but still explained 52% of the variation in seed bank size. In mire communities there was no relationship, collective or individual, between buried seed density and the measured environmental variables, possibly due to variations in the duration and frequency of waterlogging at these sites. The potential role of seed banks for initiating the recolonisation of disturbed ground is discussed. Densities of buried seeds at most Calluna-dominant sites were probably sufficient to generate successful recolonisation but the prospects for recovery were poor at other sites, particularly in graminaceous communities at 800 m or higher.     

再生水补水河道芦苇碳氮化学计量特征及其对环境的响应

在再生水补水河道内,芦苇（Phragmites australis）受高氮再生水的长期影响,具有独特的碳（C）、氮（N）化学计量特征。为查明芦苇C、N化学计量特征及其对高氮环境的响应,在芦苇生长季节（5、7、9月份）,分析了再生水补水的潮白河顺义段内河水、土壤及芦苇各器官（根、茎和叶）中C、N含量及碳氮比（C/N）。结果表明：河水中C、N含量和C/N比分别在22.20-37.25 mg/L、2.24-11.20 mg/L和3.33-9.92之间。土壤中C、N含量和C/N比的范围为5.69-35.17、0.28-2.63、8.77-25.39。在整个生长季节的所有采样点内,芦苇根、茎和叶中C含量的平均值分别为（170.84±63.56）、（369.02±39.12）、（431.80±96.70） mg/g;N含量的平均值分别为（8.20±3.96）、（14.11±6.22）和（30.73±8.66） mg/g;C/N比的平均值分别为23.89±12.84、32.65±18.48、15.21±5.60。方差分析表明,芦苇各器官中C、N计量特征具有显著的季节性差异（P<0.05）,这主要与芦苇在生长过程中的生理作用有关。环境中C、N计量特征具有显著的空间差异（P<0.05）,受环境变量的影响,芦苇叶中N含量和C/N比从上游到下游显著降低（P<0.05）。逐步回归分析的结果显示,土壤和河水中的C、N含量能够解释芦苇叶中71.0%的变量（P<0.05）;土壤中C、N含量和河水中N含量能够解释芦苇叶C/N比82.6%的变量（P<0.05）。相关分析指出,河水中N含量与土壤中N含量显著正相关（P<0.05）,说明土壤受到高氮再生水的影响而具有较强的供N能力。高氮环境下,芦苇叶中N含量较高;相较于芦苇茎和叶,根中C含量较小。研究证明在再生水补水河道中,芦苇对环境中的N有良好的吸收能力,其C、N计量特征对高氮环境表现出明显的响应。     

Spatial and temporal variation of benthic Cladocera (Crustacea) studied with activity traps in Lake Myvatn, Iceland

Benthic Cladocera were studied with a modified type of an activity trap in Lake Myvatn in 1990–1992. After feasibility experiments, the operation time and the distance of the traps from the benthic substrate were adjusted in order to minimize the effects of diurnal variation and the trapping of planktonic organisms. The trap catches of Eurycercus lamellatus were positively correlated with their abundance at the bottom as estimated by grab sampling (r = 0.910, P < 0.001). The usefulness of the activity trap was demonstrated by: (1) a lake-wide survey of the benthic Cladocera; (2) a study of the seasonal variation in the size distribution, abundance and sex ratio of E. lamellatus; and (3) a study of the seasonal succession of Chydorus sphaericus and Alona affinis. The variation of benthic Cladocera among 21 trap sites distributed on a 1–2-km scale across the lake exceeded the within-site variation. The sampling sites could be divided into five main groups based on cluster analysis. Eurycercus lamellatus was the most common species in the mat of filamentous green algae (Cladophorales). Alonella nana dominated the area of spring water inflow in the north basin and Macrothrix hirsuticornis the area of spring water inflow in the southeastern part of the lake. In other parts of the lake either Chydorus sphaericus or Alona quadrangularis tended to dominate. The size distribution and sex ratio of E. lamellatus was followed at two sites through one summer. In early summer most individuals were females less than 1.45 mm long. Around mid-summer they had grown to 0.69–3.1 mm. By the end of August the size distribution had become bimodal, with a large number of small males and a smaller number of much larger females. The seasonal succession in the abundance of E. lamellatus, A. affinis and C. sphaericus was followed at four sites over two seasons. With some exceptions the abundance of a species followed a similar seasonal trajectory on the different stations in any one year. There was, however, a marked difference between the two years (1991 and 1992), probably related to different temperatures.     

Population dynamics of alien gammarid species in the River Odra estuary

During the period of 1988–2000, three alien gammarid species, i.e. Gammarus tigrinus Sexton, 1939, Pontogammarus robustoides G. O. Sars, 1894, and Dikerogammarus haemobaphes (Eichwald, 1841) were recorded in the Odra estuary. This study, the first record of G. tigrinus and P. robustoides in Poland, focuses on the distribution, abundance, and biomass as well as on population structure of the three new species found in the coastal zone of the estuary. G. tigrinus and P. robustoides were first sampled in the Szczecin Lagoon (mid-part of the estuary) in 1988. The densities of both species were high from the time they were first recorded and exceeded 10 000 ind. m^–2, while the biomass was 25 and 140 g m^–2, respectively. G.tigrinus occurred at higher densities in northern and eastern parts of the Lagoon, while P. robustoides was particularly abundant in the south-eastern part, most heavily affected by River Odra discharge. In 1999, the third gammarid, D. haemobaphes, was recorded in the southern part of the estuary. Both in 1999 and 2000, the species was found in qualitative samples (dredge collections of Dreissena polymorpha) taken from the western branch of the river. As estimated from quantitative samples, densities and biomass in the eastern branch were rather low and did not exceed 150 ind. m^–2 and 2.7 g m^–2, respectively. The Szczecin Lagoon population of G. tigrinus produces at least two generations within a year: a summer one and an overwintering one. The latter is dominated by older and larger specimens. The species may reproduce in the Lagoon from April until November.     

Recolonization and possible recovery of Burrowing Mayflies (Ephemeroptera: Ephemeridae: Hexagenia spp.) in Lake Erie of the Laurentian Great Lakes

Burrowing mayflies of the genus Hexagenia spp. were widely distributed (ca. 80% of sites) and abundant (ca. 160 nymphs/m²) in the western basin of Lake Erie of the Laurentian Great Lakes in 1929–1930, prior to a period of anoxia in the mid 1950s. Nymphs were absent or rare in the basin between 1961 and 1973–1975. In 1979–1991, nymphs were infrequently found (13–46% of sites) in low abundance (3–40 nymphs/m²) near shore (<7.5 km from shore), but were absent or rare offshore (0–7% of sites at 0–1 nymphs/m²). Increased abundance occurred offshore between 1991 (0% of sites) and 1993 (52% of sites at 7/m²). Annual sampling, beginning in 1995, indicates that nymphs increased in both nearshore and offshore waters. By 1997, nymphs were found throughout the lake (88% of sites) at a mean density 40-fold greater (392/m²) than that observed in 1993 (11/m²). In 1998, the distribution of nymphs remained the same as 1997 (88% of sites) but density declined 3-fold (392 to 134/m²). These data indicate that mayflies have recolonized sediments of western Lake Erie and that their abundance may be similar to levels observed before their disappearance in the mid 1950s. However, prior to the mid 1950s, densities were greater in offshore than nearshore waters, but between 1979 and 1998 greater densities occurred near shore than offshore. In addition, there were two areas in the 1990s where low densities consistently occurred. Therefore, recovery of nymphs in western Lake Erie may not have been complete in 1998. At present we do not know the cause for the sudden recolonization of nymphs in large portions of western Lake Erie. Undoubtedly, pollution-abatement programs contributed to improved conditions that would have ultimately led to mayfly recovery in the future. However, the explosive growth of the exotic zebra mussel, Dreissena polymorpha, undoubtedly diverted plankton foods to bottom substrates which could have increased the speed at which Hexagenia spp. nymphs recolonized sediments in western Lake Erie in the 1990s.     

Establishment,distribution and abundance of <Emphasis Type="Italic">Mimosa pigra</Emphasis> biological control agents in northern Australia: implications for biological control

Mimosa pigra L. is one of the most troublesome weeds in northern Australia, and is the target of a large biological control program, with 14 agents released to date. This paper describes surveys conducted between 1997 and 2004, for eight of these biological control agents. Surveys assessed the establishment of key agents. Both distribution and abundance of the most damaging agent, the stem-borer Carmenta mimosa Eichlin and Passoa (Lep.: Sesiidae), increased during the eight year period and the moth is now present in all catchments with major M. pigra infestations. The tip-borer, Neurostrota gunniella Busck (Lep.: Gracillariidae) is present in all M. pigra infestations, attacking 94% of tips. The leaf and flower-feeder, Coelocephalapion pigrae Kissinger (Col., Curculionidae) is widespread and its abundance is stable. Neither Acanthoscelides puniceus Johnson (Col., Bruchidae) nor Chlamisus mimosae Karren (Col., Chrysomelidae) were widespread or abundant when surveys commenced and populations declined during the survey period. The nocturnal beetle Malacorhinus irregularis Jacoby (Col., Chrysomelidae) was not found during these surveys, but later searches using different methods found it at three sites. Six other agents appeared not to have established, or are present at densities too low to be detected. How the results of these surveys affect management of M. pigra, and projections for future impacts against this weed are discussed. Using survey results and published literature we concluded that (1) seed and flower feeders must be capable of surviving periods of low food availability; (2) some climate matching may be beneficial before fungal biocontrol agents are released and (3) even in well studied systems such as M. pigra, the failure of an agent to establish cannot always be explained.     

Influence of hydrological seasonality on bacterioplankton in two neotropical floodplain lakes

Seasonal fluctuation in river stage strongly affects the ecological functioning of tropical floodplain lakes. This study was conducted to assess the influence of hydrological seasonality on bacterial production and abundance in two floodplain lakes of the Autana River, a blackwater river in the Middle Orinoco basin, Venezuela. Water samples for nutrient chemistry, chlorophyll a, and microbiological determinations were collected in two floodplain lakes and in the mainstem of the river during 1997–98. DOC and chlorophyll a concentrations were similar between mainstem and lake sites during high water when river and lakes were well connected but became different during the period of low water when the interaction was minimal. Higher values of bacterial production were observed in the floodplain lakes (0.62–1.03 g C l^–1 h^–1) compared to the mainstem sites (0.17–0.19 g C l^–1 h^–1) during the period of low water, while during the period of high water river and lake sites showed similar levels (0.04 g C l^–1 h^–1). Bacterial numbers followed bacterial production in the floodplain lakes, reaching higher numbers during the period of low water (1.41–2.40 × 10⁶ cells ml^–1). Availability of substrate and inorganic nutrients, pH, and inputs and losses of bacterial cells could be determining the observed seasonal patterns in bacterial production and abundance. The Autana lakes exhibited a strong seasonal pattern in the chemical and biological conditions, showing higher productivity during the lentic phase that lasted between 5 and 6 months.     

Long-term decline and recent recovery of Fucus populations along the rocky shores of southeast Sweden, Baltic Sea

The Fucus populations on rocky shores along 300 km of the coastal waters of southeast Sweden in the Baltic proper have been studied since 1984 at a number of fixed sites as part of monitoring programmes. This paper describes changes in distribution and abundance of F. vesiculosus and F. serratus during the period 1984–2001. Sheltered sites showed a consistent temporal and spatial pattern of Fucus spp. distribution over a coastline of 300 kilometres. The depth penetration and abundance of Fucus spp. increased during the 1980s. Around 1990 the development reversed as a consequence of grazing and in 1997 many sites were almost devoid of Fucus spp. Since 1998 both abundance and depth penetration have increased again, possibly as a result of local measures against eutrophication. Exposed sites, on the other hand, lost their Fucus populations at the beginning of the 1990s, and they have not recovered. Extended field studies lead us to deduce that the fixed sites referred to above were representative of the Fucus populations in the area investigated. Major declines, both at sheltered and exposed sites, are attributed to grazing by the isopod Idotea baltica. The populations of I. baltica may have been favoured by the continuing eutrophication of the Baltic, a series of mild winters in the 1990s, and a contemporary decline in some potential predators.