Single and dual annual growing seasons in the tellinid bivalve Macoma balthica (L.)

Seasonal patterns of changes in length and weight during their second year of life were studied in two intertidal populations of the tellinid bivalve Macoma balthica (L.), viz. in The Netherlands (Wadden Sea) and in France (Seine estuary). The Wadden Sea population showed a single and short annual period of growth in spring (March through June), followed by a long annual period of nearly stagnant length growth and loss of weight of the soft parts. The Seine population started to grow earlier in the year (February), likewise retarded growth in summer, but restarted in autumn, thus showing a dual annual growing season with periods of rapid gain of length and weight both during spring and in October.The timing and the presence and absence of a second annual growing season are discussed in relation to temperature and feeding conditions in the various habitats.     

Demography of Carex brevicuspis (Cyperaceae) rhizome populations: a wetland sedge that produces both elongated and shortened rhizomes

The wetland sedge Carex brevicuspis reproduces vegetatively by producing short rhizomes to form clumping ramets phalanx) and long rhizomes to form spreading ramets (guerrilla), resulting in a combined growth form. As an initial step towards understanding the adaptation of Carex growth strategies to seasonal fluctuations in wetland habitats, we investigated the density and composition of C. brevicuspis rhizome populations immediately after flooding (November), in winter (January), in spring (March), and before flooding (May) in the Dongting Lake wetlands, China. The total rhizome density peaked in winter and was lowest before flooding. A large rhizome population in winter may enable C. brevicuspis to survive the seasonal cold weather and recruit a shoot population in the spring. A small rhizome population before flooding may optimize reproductive allocations and be a strategy for enduring the long flooding season. Regardless of date, short rhizomes comprised the majority of the rhizome population (73.0% in March to 98.2% in May). This indicates that C. brevicuspis primarily uses a phalanx growth strategy to utilize locally abundant resources in wetlands. The percentage of long rhizomes in the rhizome population varies significantly between seasons (1.8% in May to 27.0% in March), indicating that growth form also changes with seasonal fluctuation of wetland habitats. The results show that C. brevicuspis may adapt to seasonal changes in wetland habitats through changes in demography of rhizome populations.     

The influence of floodplain habitat on the quantity and quality of riverine phytoplankton carbon produced during the flood season in San Francisco Estuary

Primary productivity, community respiration, chlorophyll a concentration, phytoplankton species composition, and environmental factors were compared in the Yolo Bypass floodplain and adjacent Sacramento River in order to determine if passage of Sacramento River through floodplain habitat enhanced the quantity and quality of phytoplankton carbon available to the aquatic food web and how primary productivity and phytoplankton species composition in these habitats were affected by environmental conditions during the flood season. Greater net primary productivity of Sacramento River water in the floodplain than the main river channel was associated with more frequent autotrophy and a higher P:R ratio, chlorophyll a concentration, and phytoplankton growth efficiency (α^B). Total irradiance and water temperature in the euphotic zone were positively correlated with net primary productivity in winter and early spring but negatively correlated with net primary productivity in the late spring and early summer in the floodplain. In contrast, net primary productivity was correlated with chlorophyll a concentration and streamflow in the Sacramento River. The flood pulse cycle was important for floodplain production because it facilitated the accumulation of chlorophyll a and wide diameter diatom and green algal cells during the drain phase. High chlorophyll a concentration and diatom and green algal biomass enabled the floodplain to export 14–37% of the combined floodplain plus river load of total, diatom and green algal biomass and wide diameter cells to the estuary downstream, even though it had only 3% of the river streamflow. The study suggested the quantity and quality of riverine phytoplankton biomass available to the aquatic food web could be enhanced by passing river water through a floodplain during the flood season.     

Clinal life-history variation in the river-sculpin,Cottus hangiongensis: an example of phenotypic plasticity

An amphidromous sculpin,Cottus hangiongensis, distributed freely in a natural river system, exhibited clinal differences in population density, sex ratio, age composition and life-history. In a second river, in which the distribution was restricted to a narrow area in the lower reaches by a notched weir, the species was characterized by high population density and a similar population structure in two different habitats. Little life-history variation was evident. Field observations suggested that clinal life-history variations inC. hangiongensis were not genotypic, but environmentally-induced, phenotypic responses. Rearing experiments demonstrated that the maturity of one-year old males was delayed under low density conditions, and that no relationship existed between the timing of maturity and the sex ratio. This suggests that phenotypic life-history variation inC. hangiongensis is induced primarily in response to population density. Such phenotypic plasticity in life-histories of individualC. hangiongensis populations may be an adaptation for exploitation of broad and heterogenous river habitats.     

Source and sink dynamics of density-dependent otter (<Emphasis Type="Italic">Lutra lutra</Emphasis>) populations in rivers of central Finland

Long-term studies were carried out in central Finland between 1985 and 2003 to examine the temporal and spatial variation in the density of otter populations. Snow tracking was used to estimate the total population and the number of litters in the study area. In total 52 otters, including 16 cubs in 11 litters, lived in the study area (1,650 km²) in 2002–2003. The otter population clearly increased during the study period. The increase in density of the otter population was sigmoid, indicating that the population had reached the local carrying capacity. The density of the population was 0.12 individuals per river ha in 1985 and 0.29 individuals per river ha in 2002. The number of cubs per litter decreased when the density of the population increased. Density-dependent offspring production, together with the auto-correlation function of growth rate, indicates intraspecific competition in otter populations. Otters in a few river systems produced most of the cubs, creating several small source populations in the entire study area. Otters in secondary (sink) habitats had a low reproduction rate. Most otters lived in river systems with large lake surfaces. The number or area of lakes within the river system correlated positively with the total number of otters, litters and cubs in the river system. The six river systems (out of 16) with the largest water area of lakes produced 81.2% of all cubs born in the study area. However, the population growth rate per river hectare or per river kilometre was equal in all kinds of river systems. Thus, among local otter populations in central Finland, a source–sink system between different habitats seems to be prevalent.     

Life-history traits of the endangered river blenny Salaria fluviatilis (Asso) and their implications for conservation

The life-history characteristics of the river blenny Salaria fluviatilis in a Mediterranean stream in north-east Spain have been studied. The maximum age observed was 4+ years in both sexes, although only age groups 0+ and 1+ years were well represented. For both sexes, growth was rapid between April and June (before the summer drought) and in October. The instantaneous rate of monthly growth (April to October) was positively correlated with water depth. All fish attained sexual maturity during their first year of life. Females spawned multiple times. Spawning occurred mainly from June to August, although older females (2+ years old) began in May. The relationship between fecundity and total length recorded for older females in the spring was not significantly different from that obtained for 1 year-old females in the summer. The mean diameter of ripe oocytes, however, was greater in older females. Larger eggs that were laid during a period of good food supply (spring) might have a higher probability of survival. The results suggest that female fecundity is affected by environmental conditions. The species is characterized by fast growth, early maturity, multiple spawning and limited longevity. This may be a good life-history strategy for small fish species in unstable environments, where adult mortality is high, variable or unpredictable. Some life-history traits of the river blenny suggest that this species might be vulnerable to more severe drought conditions than those associated with the Mediterranean climate.     

Contribution of temperature and nutrient loading to growth rate variation of three cyprinid fishes in a lowland river

Scales collected during a maximum of seven fish population surveys over a 25-year period (1983–2008) in the River Wensum, a lowland river in Eastern England, enabled temporal analysis of the growth rates of roach Rutilus rutilus, dace Leuciscus leuciscus and chub Leuciscus cephalus. Across the study period, all species showed temporal variability in their growth patterns. Roach showed a significant temporal decrease in their growth, where rates recorded in surveys in 2005 and 2008 were significantly slower those recorded in surveys between 1983 and 1994. This change in growth rate was significantly associated with the implementation of phosphate stripping in the catchment’s sewage treatment works that reduced nutrient inputs (specifically orthophosphate). Prior to the implementation, temperature patterns explained most of the annual growth variability; following implementation and a consequent shift to the less eutrophic conditions, this relationship was lost, with changes in annual phosphate loadings now explaining most of the annual growth variation. This suggests that the changes in roach growth rates were related to shifts in river productivity resulting from water quality improvements.     

Phylogeography and Pleistocene demographic history of the endangered marsh deer (Blastocerus dichotomus) from the Río de la Plata Basin

The marsh deer is the largest neotropical cervid with morphological and ecological adaptations to wetlands and riparian habitats. Historically, this now endangered species occupied habitats along the major river basins in South America, ranging from southern Amazonia into northern Argentina to the Paraná river delta. This particularly close association with wetlands makes marsh deer an excellent species for studying the effects of Pleistocene climatic changes on their demographic and phylogeographic patterns. We examined mitochondrial DNA variation in 127 marsh deer from 4 areas distributed throughout the Río de la Plata basin. We found 17 haplotypes in marsh deer from Brazil, Bolivia and Argentina that differed by 1–8 substitutions in a 601 bp fragment of mitochondrial control region sequence, and 486 bp of cytochrome b revealed only 3 variable sites that defined 4 haplotypes. Phylogeny and distribution of control region haplotypes suggest that populations close to the Pantanal area in central Brazil underwent a rapid population expansion and that this occurred approximately 28,000–25,000 years BP. Paleoclimatic data from this period suggests that there was a dramatic increase for precipitation in the medium latitudes in South America and these conditions may have fostered marsh deer’s population growth.     

Variation in Condition Factor and Growth in Young-of-Year Fishes in Floodplain and Riverine Habitats of the Cosumnes River, California

Condition factors and growth rates of postlarval (young-of-year) fishes in a Central California river were compared in order to determine the relative importance of floodplain and riverine habitats for rearing. Sampling took place between April and June of 2001 and 2002 in the lower Cosumnes River and its floodplain. Sacramento splittail showed higher condition and length increment in floodplain habitats of than in riverine habitats. Sacramento suckers showed differences in condition between sites, but suckers from the floodplain had lower weight increments than those from the river. The weight increment in Sacramento splittail was not significantly different between habitats. In addition, two alien species, common carp and golden shiner, had similar condition factors and growth rates. This study shows the usefulness of condition factor and growth rate in evaluating the importance of different habitats for early life history stages of fishes.     

The effect of semi-natural habitats on aphids and their natural enemies across spatial and temporal scales

Semi-natural habitats in agricultural landscapes are generally assumed to enhance the biological control of insect pests based on native beneficial insects, by providing alternative prey and hosts, resources and refuges for overwintering. We hypothesized that natural enemies of winter wheat aphids should arrive sooner in fields near semi-natural habitats. We compared aphid, hoverfly (larvae and eggs) and parasitized aphid (mummies) abundances in 54 winter wheat fields located in southern France from 2003 to 2007. Six surveys were recorded each spring and were split into the early period (defined as the period before the peak of aphid growth) and the late period (after the peak). The wheat fields differed by their surrounding landscape composition measured as the proportion of semi-natural habitats (woods, hedges and grasslands), at three different spatial scales: 200 m, 500 m, and 1200 m. Despite great variability in abundance data between years, the abundance of hoverflies appeared more sensitive to landscape composition than aphid abundance was. Early abundance for both aphids and hoverflies was positively related to wood cover, but not late abundance in spring. The abundance of hoverflies was positively related to hedge and grassland cover at all spatial scales and both periods considered. Aphid parasitism was higher near hedges at the small spatial scale late in the spring. Our results confirmed that higher proportions of semi-natural habitats in agricultural landscapes enhance the biological control of pests, but this effect depends on the spatial scale, the time period in the spring and the natural enemies considered.     

Contrasting growth changes in two dominant species of a Mediterranean shrubland submitted to experimental drought and warming

BACKGROUND AND AIMS: Climate projections predict drier and warmer conditions in the Mediterranean basin in the next decades. The possibility of such climatic changes modifying the growth of two Mediterranean species, Erica multiflora and Globularia alypum, which are common components of Mediterranean shrublands, was assessed. METHODS: A field experiment was performed from March 1999 to March 2002 to prolong the drought period and to increase the night-time temperature in a Mediterranean shrubland, where E. multiflora and G. alypum are the dominant species. Annual growth in stem diameter and length of both species was measured and annual stem biomass production was estimated for 1999, 2000 and 2001. Plant seasonal growth was also assessed. KEY RESULTS: On average, drought treatment reduced soil moisture 22 %, and warming increased temperature by 0.7-1.6 degrees C. Erica multiflora plants in the drought treatment showed a 46 % lower annual stem elongation than controls. The decrease in water availability also reduced by 31 % the annual stem diameter increment and by 43 % the annual stem elongation of G. alypum plants. New shoot growth of G. alypum was also strongly reduced. Allometrically estimated biomass production was decreased by drought in both species. Warming treatment produced contrasting effects on the growth patterns of these species. Warmer conditions increased, on average, the stem basal diameter growth of E. multiflora plants by 35 %, raising also their estimated stem biomass production. On the contrary, plants of G. alypum in the warming treatment showed a 14 % lower annual stem growth in basal diameter and shorter new shoots in spring compared with controls. CONCLUSIONS: The results indicate changes in the annual productivity of these Mediterranean shrubs under near future drier and warmer conditions. They also point to alterations in their competitive abilities, which could lead to changes in the species composition of these ecosystems in the long term.     

An investigation into the growth of 0-group roach, (Rutilus rutilus L.) with special reference to temperature

The growth of 0-group roach in a chalk-fed river is traced over six seasons and the growth compared to that in a nearby gravel pit. The growth rate, the daily weight increase and the condition of the fish are all highest during the summer, falling to a minimum over the winter period and rising again in the spring. Considerable yearly variation in the growth of roach in the river was observed and correlated with water temperatures above 14° C. It is suggested that water temperature, acting through the food supply, is the dominant factor governing growth. The hot summer of 1976 appears to have resulted in excellent growth of roach in both habitats.     

Wood anatomy and tree growth covary in riparian ash forests along climatic and ecological gradients

Riparian ash forests subjected to seasonal drought are among the most endangered ecosystems in Europe. They are threatened by climate warming causing aridification and by land-use changes modifying river flow. To assess the impacts of these two stress factors on riparian forests, we studied radial growth and xylem anatomical traits in five narrow-leaved ash (Fraxinus angustifolia) stands across wide climatic and ecological gradients from northern Italy to southern Portugal. Radial growth rates and earlywood hydraulic diameter (Dh) were directly correlated, whilst earlywood vessel density and growth rates were inversely associated. Ash growth positively responded to precipitation. Higher and lower rates of growth increase in response to precipitation were found in dry (annual precipitation 357–750 mm, annual water balance −39 to −48 mm) and wet (annual precipitation 1030 mm, annual water balance 27 mm) sites, respectively. Wet conditions in autumn and winter of the year prior to tree-ring formation lead to larger Dh values, except in the wet site where warmer conditions from prior autumn to current spring were positively associated to wider vessels. Growth was also enhanced by a higher river flow, reflecting higher soil moisture due to elevated groundwater table levels. Peaks in river flow from late winter to early spring increased Dh in dry-continental sites. Growth and potential hydraulic conductivity in drought-prone riparian ash forests are differently impacted by climate variability and river flow depending on site and hydrological conditions. Nevertheless, covariation between radial growth and the earlywood vessel diameter was found, regardless of site specific differences. Wood production and hydraulic conductivity are coordinated through the production of large earlywood vessels which may allow reaching higher growth rates.     

Gene expression remodelling and immune response during adaptive divergence in an African cichlid fish

Variation in gene expression contributes to ecological speciation by facilitating population persistence in novel environments. Likewise, immune responses can be of relevance in speciation driven by adaptation to different environments. Previous studies examining gene expression differences between recently diverged ecotypes have often relied on only one pair of populations, targeted the expression of only a subset of genes or used wild‐caught individuals. Here, we investigated the contribution of habitat‐specific parasites and symbionts and the underlying immunological abilities of ecotype hosts to adaptive divergence in lake–river population pairs of the cichlid fish Astatotilapia burtoni. To shed light on the role of phenotypic plasticity in adaptive divergence, we compared parasite and microbiota communities, immune response, and gene expression patterns of fish from natural habitats and a lake‐like pond set‐up. In all investigated population pairs, lake fish were more heavily parasitized than river fish, in terms of both parasite taxon composition and infection abundance. The innate immune response in the wild was higher in lake than in river populations and was elevated in a river population exposed to lake parasites in the pond set‐up. Environmental differences between lake and river habitat and their distinct parasite communities have shaped differential gene expression, involving genes functioning in osmoregulation and immune response. Most changes in gene expression between lake and river samples in the wild and in the pond set‐up were based on a plastic response. Finally, gene expression and bacterial communities of wild‐caught individuals and individuals acclimatized to lake‐like pond conditions showed shifts underlying adaptive phenotypic plasticity.     

Occupancy and demographics of red river hog Potamochoerus porcus on Tiwai Island,Sierra Leone

The red river hog (Potamochoerus porcus, Linnaeus) is a species of Suidae with populations ranging from western to central Africa. Little is known about the population status of red river hog, and few studies have investigated habitat characteristics associated with their occupancy which is critical in determining possible reasons behind suspected population declines. We used camera traps and site occupancy models to examine the effects of habitat covariates on occupancy of red river hog on Tiwai Island and in surrounding forests of Sierra Leone during two field seasons, 2008–2011. We also estimated group size and composition and growth patterns of juveniles. In both sampling periods, understory vegetation strongly influenced red river hog occupancy with greatest association with riparian and swamp vegetation types. Red river hogs seemed to avoid habitats of high human impact such as farmbush and secondary growth forests. Average group size was 2.46 ± 0.28 (SE) hogs per group. Growth patterns of juveniles suggested the majority of piglets were born during the middle of dry season (January–February). Our research suggests landscape use by red river hog is influenced by presence of riparian habitats with dense vegetation.     

Seasonal variation of chromophore composition in the eye of the Japanese dace, <Emphasis Type="Italic">Tribolodon hakonensis</Emphasis>

The relationship between seasonal variation and the effect of several different environmental factors on chromophore composition was investigated in the eye of the Japanese dace, Tribolodon hakonensis which lives either in rivers or in the sea. Eyes obtained from river and sea populations had both retinal (A1) and 3,4-didehydroretinal (A2) all through the year but the ratio of these chromophores showed seasonal variation the relative amount of A2 was higher in winter and lower in summer. Besides seasonal variation, A2 showed marked differences depending on habitat: the highest proportion of A2 was 67% in January and the lowest 13% in July, in the river population, whereas in the sea population the highest and the lowest values were only 30 and 6%, respectively, during the same months. The seasonal variation in gonadosomatic index showed no correlation to variations in A2 proportion, and the maximum difference in water temperature between summer and winter was ca. 15°C for both habitats. Because spectral conditions at the locations of capture of both river and sea populations were similar, we conclude that Japanese dace eyes are affected by exogenous factors related to differences between freshwater and seawater environments.     

Intraspecific differences in thermal tolerance of Etheostoma spectabile (Agassiz) in constant versus fluctuating environments

The critical thermal maximum (CTM) of Etheostoma spectabile differed significantly among four populations whose habitats ranged from thermally constant to highly fluctuating conditions. Mean CTM of the population at the most fluctuating location was highest, populations in intermediate thermal environments were intermediate in thermal tolerance, and a population in a constant temperature spring run had thelowest CTM. The results support the view that thermal physiology can be evolutionarily labile within a species, and that changes respond to directional selection.     

Bacterial Community Composition in Central European Running Waters Examined by Temperature Gradient Gel Electrophoresis and Sequence Analysis of 16S rRNA Genes

The bacterial community composition in small streams and a river in central Germany was examined by temperature gradient gel electrophoresis (TGGE) with PCR products of 16S rRNA gene fragments and sequence analysis. Complex TGGE band patterns suggested high levels of diversity of bacterial species in all habitats of these environments. Cluster analyses demonstrated distinct differences among the communities in stream and spring water, sandy sediments, biofilms on stones, degrading leaves, and soil. The differences between stream water and sediment were more significant than those between sites within the same habitat along the stretch from the stream source to the mouth. TGGE data from an entire stream course suggest that, in the upper reach of the stream, a special suspended bacterial community is already established and changes only slightly downstream. The bacterial communities in water and sediment in an acidic headwater with a pH below 5 were highly similar to each other but deviated distinctly from the communities at the other sites. As ascertained by nucleotide sequence analysis, stream water communities were dominated by Betaproteobacteria (one-third of the total bacteria), whereas sediment communities were composed mainly of Betaproteobacteria and members of the Fibrobacteres/Acidobacteria group (each accounting for about 25% of bacteria). Sequences obtained from bacteria from water samples indicated the presence of typical cosmopolitan freshwater organisms. TGGE bands shared between stream and soil samples, as well as sequences found in bacteria from stream samples that were related to those of soil bacteria, demonstrated the occurrence of some species in both stream and soil habitats. Changes in bacterial community composition were correlated with geographic distance along a stream, but in comparisons of different streams and rivers, community composition was correlated only with environmental conditions.     

Ephemeral floodplain habitats provide best growth conditions for juvenile Chinook salmon in a California river

We reared juvenile Chinook salmon for two consecutive flood seasons within various habitats of the Cosumnes River and its floodplain to compare fish growth in river and floodplain habitats. Fish were placed in enclosures during times when wild salmon would naturally be rearing in floodplain habitats. We found significant differences in growth rates between salmon reared in floodplain and river enclosures. Salmon reared in seasonally inundated habitats with annual terrestrial vegetation experienced higher growth rates than those reared in a perennial pond on the floodplain. Growth of fish in the non-tidal river upstream of the floodplain varied with flow in the river. When flows were high, there was little growth and high mortality, but when the flows were low and clear, the fish grew rapidly. Fish displayed very poor growth in tidally influenced river habitat below the floodplain, a habitat type to which juveniles are commonly displaced during high flow events due to a lack of channel complexity in the main-stem river. Overall, ephemeral floodplain habitats supported higher growth rates for juvenile Chinook salmon than more permanent habitats in either the floodplain or river. Variable responses in both growth and mortality, however, indicate the importance of providing habitat complexity for juvenile salmon in floodplain reaches of streams, so fish can find optimal places for rearing under different flow conditions.