Small stonefly predators affect microbenthic and meiobenthic communities in stream leaf packs

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Numbers of mononchid nematodes in soils sown to cereals and grasses

The distribution of mononchid nematodes Mylonchulus sigmaturus, Mylonchulus brachyuris, Clarkus papillatus, Prionchulus punctatus and Anatonchus tridentatus found in grassland and arable soils in England were studied. Mononchid nematode populations in excess of 5% of the total soil nematode population and in biomass more than 2% of the total soil nematode population were rare. No relationship was found between numbers of mononchids and those of other soil nematodes. In soils sown to spring barley there was no difference in the total numbers of female M. sigmaturus, C. papillatus or A. tridentatus found throughout the year. Juveniles of C. papillatus were most common while those of M. sigmaturus were least common. In grass leys and arable soil P. punctatus numbers were extremely low. Neither phorate nor oxamyl applied at 1.12 kg a.i./ha in March affected mononchid numbers. Although oxamyl at 11.2 kg a.i./ha did not affect the adult female numbers, the numbers of juvenile mononchids were reduced by 38% and 50% in June and November respectively.     

Effects of weed harrowing frequency on beneficial arthropods,plants and crop yield

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Toxic Microcystis (cyanobacteria) inhibit recruitment of the bloom‐enhancing invasive bivalve Limnoperna fortunei

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Nematode–citrus plant interactions: host preference,damage rate and molecular characterization of Citrus root nematode Tylenchulus semipenetrans

• Citrus plants are host to several plant parasitic nematodes (PPNs), which are microscopic organisms. Among PPNs, the citrus root nematode, T. semipenetrans (Cobb 1913) (Tylenchida: Tylenchulidae), causes significant damage to citrus plantations worldwide. Understanding citrus nematode populations, precise identification, host preference among citrus species, and damage threshold are crucial to control T. semipenetrans. The minutiae of citrus plant–nematode interactions, nematode density and molecular nematode identification are not well understood. In this study, nematode species and density in citrus orchards, host specialization, molecular and morphological characteristics of nematodes were assessed.
• Molecular and morphological methods, host–nematode interactions, host (citrus species) preference, damage economic threshold (ET), and economic injury level (EIL) were determined using laboratory methods and field sampling. Citrus plantations in different provinces in the Mediterranean region of Turkey were investigated.
• Nematode species were identified molecularly and morphologically. ITS sequences revealed that samples were infected by citrus root nematode T. semipenetrans. The lowest nematode density was in C. reticulata in Mersin (53 2nd stage juveniles (J2s) 100 g⁻¹ soil), while the highest density was from Hatay in C. sinensis (12173 J2s 100 g⁻¹ soil). Highest citrus nematode population density was on roots of C. reticulata, followed by C. sinensis, C. limon, and C. paradisi.
• The citrus nematode is more common than was thought and population fluctuations change according to specific citrus species. Environmental conditions, host and ecological factors, such as temperature, soil pH, and soil nutrients, might influence nematode populations in citrus orchards. Investigating nematode density in diverse soil ecologies and the responses of different resistant/tolerant citrus species and cultivars to nematode populations is essential in future studies.

     

Cyanobacterial bloom termination: the disappearance of Planktothrix rubescens from Lake Bourget (France) after restoration

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Estimating the density and biomass of moray eels (Muraenidae) using a modified visual census method for hole-dwelling reef fauna

Synopsis We developed a modified visual census technique suitable for fairly sedentary, hole-dwelling species and used it to determine the diversity, density, biomass, and habitat use of morays at four sites including fringing, patch, and bank reefs in Barbados, West Indies. The method involved a careful search during two passages over transects by day and by night, noting size and position of morays seen, and using the number of new observations on the second passage to estimate the proportion of morays not seen. First passage counts were generally higher than numbers of morays recorded in previous visual censuses. These estimates were raised when we used the time period (day or night) with the highest average density visible for each species, added different individuals from the two passages, and corrected for individuals not seen. We saw more goldentail morays (Gymnothorax miliaris) during the day but more spotted (G. moringa), viper (Enchelycore nigricans), and chestnut (E. carychroa) morays at night. Counts of chain morays (Echidna catenata) did not differ significantly between night and day. Relative abundance and size of moray species varied among sites and to a lesser extent among habitat types within sites, but spotted morays were generally the most important in numbers and biomass. Mean estimated moray density and biomass were much higher than in most previous visual censuses, but similar to rotenone samples on other reefs and comparable to those of other families of predatory fishes. Our findings confirm that morays are abundant and potentially important predators that should be the focus of more attention in ecological studies of coral reefs.     

The density and stability of birds in shrubland and drainage line woodland in the southern Karoo,South Africa

Comparative surveys of bird species richness and abundance showed that a total of 69 bird species was recorded on 1 km transects (n = 996) through shrubland, with a total estimated density of birds of 32.7 ± 32.8 (S.D.) birds/km², of which resident birds made up 24.4 ± 21.0 birds/km², nomads made up 1.9 ± 11.7 birds/km² and local nomads made up 6.3 ± 20.1 birds/km². There was no correlation in general between total bird numbers or total bird biomass and rain, but numbers and biomass of nomads showed the strongest correlations with rainfall two months previously. A total of 86 species was recorded on 276 surveys along a 1 km stretch of drainage line woodland. Species richness varied from an average of about nine species to 24 species each month, and only showed a marked change during the 'dry' period of 1990 to early 1991. Density of birds in this woodland was 59.2 ± 20.8 birds/km. Biomass of birds was relatively constant throughout the study period, with marked increases in certain months when large species were present.     

Productivity modifications to flour beetles (Coleoptera: Tenebrionidae) by gamma radiation (60Co) of one or both sexes and by the addition of radiated males or females to population

The effects on productivity by the addition of various numbers of radiated adult males or females to populations of two densities were determined for two species of flour beetles. Modifications in productivity after exposure to gamma radiation from⁶⁰Co included:

1. females of T. confusum were sterilized by an exposure between 2620 to 5230 R.
2. females of T. castaneum were not sterilized by 10, 200 R.
3. males were not sterilized by 10, 200 R.
4. sterile females may serve as depositories for normal sperm thereby reducing the productivity. Addition of such females to populations of flour beetles did not reduce the numbers of progeny.
5. since sterile females did not suppress population development, and since they destroy grain and cereal products, they should be eliminated from control programs featuring the sterile insect release technique.
6. population density decreased the numbers of progeny.

The use of the sterile insect release technique to control insects of stored grain products does not seem likely with present day sanitary standards since large numbers of insects need be added to effect control.     

Chlorophyll‐a concentrations and macroinvertebrate declines coincide with the collapse of overwintering diving duck populations in a large eutrophic lake

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Feeding behaviour,predatory functional responses and trophic interactions of the invasive Chinese mitten crab (Eriocheir sinensis) and signal crayfish (Pacifastacus leniusculus)

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Depth distribution of the native freshwater mussel (Echyridella menziesii) in warm monomictic lakes: Towards a general model for mussels in lakes

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Studies on Chironomidae in experimental recirculating stream systems. II. The growth, development and production of a spring generation of Orthocladius (Euorthodadius) calvus Pinder

SUMMARY.

• 1 Orthodadius (Euorthodadius) calvus Pinder. similar to Orthocladius (Euorthodadius) thienemanni Kieffer. colonized a new gravel substratum in two recirculating stream channels. A maximum population density of 68.621 m^-2 was attained after only 16 days. This had fallen to a negligible density by the thirty-third day.
• 2 Some recruitment occurred over most of the study period (April-May 1981) and no single sharply defined cohort was evident. There was a large range of body lengths within each instar. and considerable overlap between instars. The population density estimates for instars I and II were low compared with instars III and IV.
• 3 The relationship between instantaneous growth rate (g) and geometric mean length indicated that growth was best described by a Gompertz curve. Growth rate decreased with increasing length from a value of about 40% length day^-1 at 2 mm body length to about 5% length day^-1 at 9 mm.
• 4 Growth rates for individual larvae, kept in culture, were very variable with maximum rates close to the values determined from the field data. Mean duration of larval life was 16 days.
• 5 Estimates of production for the study period ranged from 13.5 g dry wt m^-2 (Channel III, size-frequency method) to 34.2 g dry wt m^-2 (Channel II, Allen's graphical method, values corrected for non-linear growth).
• 6 Gut contents were estimated to represent about 55% of the total weight therefore production values should be reduced by this amount.

     

Climate-driven changes in shoot density and shoot biomass in Leymus chinensis (Poaceae) on the North-east China Transect (NECT)

Aim Climate‐driven changes affecting ecosystem primary production have been well documented for many vegetation types, while the effects of climate on plant populations remains unclear. Herein, we address the relationships between climatic variables and shoot density, reproductive allocation and shoot biomass in Leymus chinensis on a large‐scale climatic gradient in 2000. Location Nine sites experiencing similar light regimes, but differing in longitude, precipitation and altitude were selected on the North‐east China Transect (NECT) from 115° to 124°E, around a latitude of 43.5°N. Methods Densities of total, vegetative and reproductive shoots and of shoot biomass were measured twice over the growing season in each site. Climatic data were taken from the climate database of the Laboratory of Quantitative Vegetation Ecology, Institute of Botany, Chinese Academy of Sciences and from the local weather stations throughout the NECT. Results Densities of total, vegetative and reproductive shoots increased significantly from the west to the east and from dry to moist along the NECT, and were strongly correlated with annual precipitation (r² = 0.934, 0.943 and 0.863, respectively) and an aridity index (r² = 0.809, 0.816 and 0.744, respectively). The average total shoot density at the east end (470/m²) was about three times that at the west (160/m²). Reproductive allocation and shoot biomass for both vegetative and reproductive shoots increased with precipitation and declined with the aridity index along the NECT. There were positive correlations between shoot biomass and annual precipitation for vegetative shoots (P < 0.05, R² = 0.604) and March precipitation for reproductive shoots (P < 0.05, R² = 0.533), respectively. Main conclusions These findings suggest that L. chinensis adjusts to decreasing precipitation/increasing aridity by alterations in shoot density, reproductive allocation and shoot biomass along the drought gradient of the NECT.     

Influence of fishes on macroinvertebrate communities and insect emergence production in intermittent stream refuges

1. Drying intermittent stream networks often have permanent water refuges that are important for recolonisation. These habitats may be hotspots for interactions between fishes and invertebrates as they become isolated, but densities and diversity of fishes in these refuges can be highly variable across time and space.
2. Insect emergence from streams provides energy and nutrient subsidies to riparian habitats. The magnitude of such subsidies may be influenced by in-stream predators such as fishes.
3. We examined whether benthic macroinvertebrate communities, emerging adult insects, and algal biomass in permanent grassland stream pools differed among sites with naturally varying densities of fishes. We also manipulated fish densities in a mesocosm experiment to address how fishes might affect colonisation during recovery from hydrologic disturbance.
4. Fish biomass had a negative impact on invertebrate abundance, but not biomass or taxa richness, in natural pools. Total fish biomass was not correlated with total insect emergence in natural pools, but orangethroat darter (Etheostoma spectabile) biomass was inversely correlated with emerging Chironomidae biomass and individual midge body size. The interaction in our models between predatory fish biomass and date suggested that fishes may also delay insect emergence from natural pools, altering the timing of aquatic–terrestrial subsidies.
5. There was an increase over time in algal biomass (chlorophyll-a) in mesocosms, but this did not differ among fish density treatments. Regardless, fish presence in mesocosms reduced the abundance of colonising insects and total invertebrate biomass. Mesocosm invertebrate communities in treatments without fishes were characterised by more Chironomidae, Culicidae, and Corduliidae.
6. Results suggest that fishes influence invertebrates in habitats that represent important refuges during hydrologic disturbance, hot spots for subsidy exports to riparian food webs, and source areas for colonists during recovery from hydrologic disturbance. Fish effects in these systems include decreasing invertebrate abundance, shifting community structure, and altering patterns of invertebrate emergence and colonisation.

     

Numbers and distribution of the Great Cormorant in Iceland: Limitation at the regional and metapopulation level

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Effect of the presence of predatory cues and hunger on cannibalistic behaviour of ladybird beetle,Menochilus sexmaculatus Fabricius (Coleoptera: Coccinellidae)

1. Cannibalism and its role in population dynamics, along with various factors influencing the rate of cannibalism, have been widely studied across taxa.
2. The effects of predatory cue concentrations and starvation on cannibalistic tendencies and other life-history traits in cannibalistic and non-cannibalistic adults of Menochilus sexmaculatus were investigated.
3. Egg cannibalism increased with increasing predatory cue concentration and was maximum in high predatory cue treatment; increased with starvation irrespective of their diet history.
4. Latency to cannibalise eggs was shorter for cannibalistic adults as compared to non-cannibalistic adults irrespective of their hunger status and concentration of conspecific cues.
5. Non-cannibalistic females have higher fecundity than cannibalistic females.
6. In conclusion, both cannibalistic and non-cannibalistic individuals respond differently to intrinsic (hunger) and extrinsic cues (predatory cue concentrations). Cannibalistic individuals cannibalise more than non-cannibalistic ones at low levels of starvation and predatory cues.
7. Our finding suggests that cannibalistic individuals are better at assessing the risk and removing future competitors, which might favour these individuals over non-cannibalistic ones in adverse conditions and increased competition.

     

Horizontal migration of zooplankton in a littoral zone of the lowland Sulejow Reservoir (Central Poland)

Horizontal migrations of zooplankton between macrophyte patches and open areas were investigated in the sparsely vegetated littoral zone of the Sulejow Reservoir in June-July 2000 and 2001, using one-litre plastic traps. Large-bodied zooplankton: daphnids and copepods generally swam towards the open water at dusk and towards submerged macrophytes at dawn. Small-bodied zooplankton (Bosmina sp., Chydorus sp.) did not show any pattern of horizontal movement. At the time of the research the phytoplankton community was dominated by eatable diatoms (Cyclotella sp.), whose biomass reached 14 mg l⁻¹. Thus, bottom-up forces (food scarcity) are not likely to be responsible for the observed zooplankton migrations. Analyses of fish stomach contents showed high contribution of large zooplankters to the food of juvenile roach (Rutilus rutilus) and perch (Perca fluviatilis) which densely inhabited the littoral zone of reservoir. High fish pressure in the littoral zone along with high density of the predatory cladoceran, Leptodora kindtii in the open water, suggest that top-down forces (predatory pressure) were responsible for the migration of large zooplankton. At dusk predatory pressure of fish fry exceeded that of L. kindtii, forcing endangered zooplankton to escape from macrophytes towards open water. The opposite situation occurred at dawn. The consequences of the relationships for both zooplankton and fish fry communities dynamics are discussed.

     

Impacts of defoliation by tussock moths (Orgyia vetusta) on the growth and reproduction of bush lupine (Lupinus arboreus)

Abstract.

• 1 Outbreaks of tussock moths (Orygia verusta Bdv.) on bush lupines (Lupinus arboreus Sims) may be very intense, although spatially localized, and may last >10 years. To understand better how such outbreaks may persist, we defoliated lupine bushes using variable realistic numbers of tussock moth larvae, and measured the immediate and delayed impacts of defoliation on the growth and seed production of lupine bushes.
• 2 Immediate effects of defoliation included the production of new leaves that were significantly smaller in diameter and biomass, and lower in water content, than the new leaves of undamaged bushes. Also, seed output was reduced by up to 80% on heavily damaged bushes.
• 3 In the longer term, surviving bushes recovered remarkably well, despite having received the full range of possible (survivable) insect densities. After 1 or 2 years’rapid growth, surviving bushes were not affected in terms of height, basal stem diameter or volume by their previous defoliation. However, there was a significant tendency for juvenile bushes to produce more seeds the more heavily they had been attacked the previous year.
• 4 The ability of the host plant to recover, in terms of its biomass, helps to explain the sustained nature of the insect outbreak.