Notes on the feeding of Ectemnorrhinus similis waterhouse (Curculionidae) adults on Marion Island

Summary Little is known regarding the role of arthropods as herbivores on subantarctic islands. In grassland and drainage line communities on Marion Island maximum densities (up to 220/m²) of Ectemnorrhinus similis adults occur in March to April, representing a maximum biomass of ca. 1 g m^-2. Captured beetles ingest approximately 14% of body weight per day of Acaena magellanica leaf material and 37% of body weight per day of Brachythecium rutabulum fronds. No significant feeding on Poa cookii leaves was observed. It is proposed that E. similis be regarded as a significant primary consumer on the island.     

Fungal biomass and decomposition in Spartina maritima leaves in the Mondego salt marsh (Portugal)

Spartina maritima (Curtis) Fernald is a dominant species in the Mondego salt marsh on the western coast of Portugal, and it plays a significant role in estuarine productivity. In this work, leaf litter production dynamics and fungal importance for leaf decomposition processes in Spartina maritima were studied. Leaf fall was highly seasonal, being significantly higher during dry months. It ranged from 42 g m^-2 in June to less than 6 g m^-2 during the winter. Fungal biomass, measured as ergosterol content, did not differ significantly between standing-decaying leaves and naturally detached leaves. Fungal biomass increased in wet months, with a maximum of 614 g g^-1 of ergosterol in January in standing-decaying leaves, and 1077 g g^-1 in December, in naturally detached leaves, decreasing greatly in summer. Seasonal pattern of fungal colonization was similar in leaves placed in litterbags on the marsh-sediment surface. However, ergosterol concentrations associated with standing-decaying and naturally detached leaves were always much higher than in litterbagged leaves, suggesting that fungal activity was more important before leaf fall. Dry mass of litterbagged leaves declined rapidly after 1 month (about 50%), mostly due to leaching of soluble organic compounds. After 13 months, Spartina leaves had lost 88% of their original dry weight. The decomposition rate constant (k) for Spartina maritima leaves was 0.151 month^-1.     

The ecology of Lake Nakuru

Summary The major pathways of energy flow in Lake Nakuru (East Africa) are presented. The trophic structure of this equatorial alkaline-saline lake shows no predictable long term continuity. During the five years of this study it had a bloom of Spirulina platensis that persisted at least two years, it had periods with low algal densities and in addition it had various transitional phases with dramatic fluctuations of species composition and density.The Spirulina platensis bloom is characterized by a rich and almost unialgal bloom of the cyanophyte Spirulina platensis minor, with a mean biomass of 3,500 kJ m^-3 (20 kJ 1 g dry weight). Net photosynthetic rates were very high at depths with optimal light conditions (230 kJ m^-3 h^-1), but algal self-shading made integrated rates modest (45 kJ m^-3 24 h^-1) relative to the high biomass. Of the eight primary consumers only five species contributed significantly to the consumer biomass of 220 kJ m^-3: the flamingo Phoeniconaias minor, the cichlid fish Sarotherodon alcalicus grahami, the copepod Lovenula africana, the dipteran larva Leptochironomus deribae, and the rotifer Brachionus dimidiatus. Consumption rates were 50% of net photosynthetic rates, production rates 10%. Secondary consumers (90% being the pelican Pelecanus onocrotalus and the Greater Flamingo Phoenicopterus ruber) had a biomass of about 6.8 kJ m^-3. Pelicans consumed almost the whole fish production (7.5 metric tons wet weight/day).At low algal densities the lake had a more diverse algal population but a reduced mean biomass of 1,500 kJ m^-3 and mean net photosynthetic rates of 12 kJ m^-3 24 h^-1. Primary consumer species diversity and biomass were also reduced. Consumption rates sometimes exceeded primary production rates. Rotifers probably contributed 50% to total consumption and 75% to total secondary production but the estimates of their role is speculative as the relative contributions of algae, bacteria and detritus to rotifer consumption are not known. Transitional phases are characterized by rapidly changing abiotic and biotic conditions with algal breakdowns and sudden population peaks at all levels. Rotifers dominated secondary consumers, they contributed 25% to the total biomass of 380 kJ m^-3, 90% to the total consumption rate of 290 kJ m^-3d^-1 and 95% to the total production of 41 kJ m^-3d^-1.The discussion focusses on problems of measuring primary production in alkaline-saline lakes, and the control of producer and consumer densities. The difficulty in assessing the importance of bacteria and rotifers is emphasized. Also questions of ecological stability and efficiency are addressed. Finally, some recommendations for conservational policy are included.     

Growth and physiological responses of cotton (Gossypium hirsutum L.) to elevated carbon dioxide and ultraviolet-B radiation under controlled environmental conditions

Better understanding of crop responses to projected changes in climate is an important requirement. An experiment was conducted in sunlit, controlled environment chambers known as soil–plant–atmosphere–research units to determine the interactive effects of atmospheric carbon dioxide concentration [CO₂] and ultraviolet‐B (UV‐B) radiation on cotton (Gossypium hirsutum L.) growth, development and leaf photosynthetic characteristics. Six treatments were used, comprising two levels of [CO₂] (360 and 720 µmol mol^?1) and three levels of 0 (control), 7.7 and 15.1 kJ m^?2 d^?1 biologically effective UV‐B radiations within each CO₂ level. Treatments were imposed for 66 d from emergence until 3 weeks after the first flower stage. Plants grown in elevated [CO₂] had greater leaf area and higher leaf photosynthesis, non‐structural carbohydrates, and total biomass than plants in ambient [CO₂]. Neither dry matter partitioning among plant organs nor pigment concentrations was affected by elevated [CO₂]. On the other hand, high UV‐B (15.1 kJ m^?2 d^?1) radiation treatment altered growth resulting in shorter stem and branch lengths and smaller leaf area. Shorter plants at high UV‐B radiation were related to internode lengths rather than the number of mainstem nodes. Fruit dry matter accumulation was most sensitive to UV‐B radiation due to fruit abscission. Even under 7.7 kJ m^?2 d^?1 of UV‐B radiation, fruit dry weight was significantly lower than the control although total biomass and leaf photosynthesis did not differ from the control. The UV‐B radiation of 15.1 kJ m^?2 d^?1 reduced both total (43%) and fruit (88%) dry weights due to smaller leaf area and lower leaf net photosynthesis. Elevated [CO₂] did not ameliorate the adverse effects of UV‐B radiation on cotton growth and physiology, particularly the boll retention under UV‐B stress.     

Leaf litter processing and energy flow through macroinvertebrates in a woodland pond (Switzerland)

Energy generated by leaf litter processing and its flow through the associated macroinvertebrate community was quantified in a pond near Geneva (Switzerland). Annual density, biomass, and production on oak (Quercus robur) leaf litter were assessed for all macroinvertebrate taxa with emphasis on predators. Empirical energetic relations provided an energy budget for the macroinvertebrate community. On 1 m² of pond bottom, the processing of 5641 kJ of oak leaf litter resulted in 8.5% of leachate (6 days), and after 1 year 32% of material remained; the other 59.5% was biologically (animal or microbial) converted, including 11.2% processed by shredders. The mean annual density of associated macroinvertebrates was 51374 individuals, mean biomass was 3.53 g (dry mass) and production was about 1451 kJ (or 65 g). Predator production was 170 kJ/m², non-chironomid primary consumer production was 101 kJ/m² (including 57 kJ from shredders) and chironomid primary consumer production was estimated at 1180 kJ/m². Predators contributed to a high proportion of total biomass (39%) but to a smaller amount of production (12%) or density (6%). In this two-stepped food-chain mainly based on detritus, the transfer coefficient between first level (detritus + primary producers) and third level (secondary consumers) was high (2–2.5%) and indicated efficient conversion of energy. This high efficiency was partly related to the reutilization of fine particulate organic matter by the collectors. The production estimate measured on leaf litter was compared with two other predominant substrates (Typha latifolia stems and Chara sp.), and exhibited the highest value. This study shows how leaf litter can constitute a direct source for high secondary production and be an efficient energy source in freshwater ecosystems. It is also demonstrated that a woodland pond can support a high macroinvertebrate production as compared with other freshwater ecosystems.     

Earthworm numbers,biomass and respiratory metabolism in a beech woodland-Wytham Woods,Oxford

Summary The mean annual population density of earthworms was found to be 164.6 m^-2 during a period of detailed study between October 1971 and September 1972. In a year of less detailed study between November 1972 and October 1973 the population density was 117.5 m^-2 (139.8 m^-2 when the type of extraction method was allowed for). Mean biomass densities in the two years of investigation were 41.0 g preserved wet wt m^-2 (1971–1972) and 38.6 (possibly 39.2) g preserved wet wt m^-2 (1972–1973).Comparison of the Brogden's Belt population and biomass densities with those reported from other woodlands indicates that soil type is more important than leaf litter type in determining the numerical abundance of earthworms. Population densities are lower in beechwoods on mor soils, mor soils also support significantly fewer species. As with numbers, mean biomass density in beechwoods on mor soils was significantly lower than that occurring in beechwoods on mull soils; the latter, in turn, being lower than those found in mixed deciduous woods on mull soils. Unlike population density biomass density is influenced by both soil and litter type, this is discussed by reference to mean body weights and food quality as reflected by tannin, nitrogen and carbohydrate content.The annual respiratory metabolism of the Brogden's Belt earthworms was calculated to be between 10.7 and 13.41 O₂ m^-2 a^-1, which is equivalent to between 4.1 and 5.1% of the total soil metabolism. A production/biomass ratio of 0.49–0.58 was estimated, as was a net population efficiency of 22%.     

Population dynamics and production of the tropical freshwater shrimp Caridina nilotica (Decapoda: Atyidae) in the littoral of Lake Sibaya

SUMMARY. Seasonal changes in population structure, standing stock levels and production of Caridina nilotica were studied at three sites in the littoral margins of subtropical Lake Sibaya between January 1975 and March 1976. Average population density at these sites declined from a maximum of c. 1400 to a minimum of c. 350 individuals per m² (3.4–0.4 g m^?2 dry wt) during the study, possibly as a result of emigration into peripheral vegetation inundated by rising lake levels. Shrimps bred perennially and, although egg stocks and instantaneous birth rates (b) were highest during summer, no corresponding increases in populaton density were observed, suggesting that the seasonally higher birth rates were offset by higher mortality rates. Population size structure and size-specific sex ratios did not change seasonally to any marked extent. Relative abundance declined with size and females grew larger than males. Clutch size increased linearly as a function of female carapace length. Estimates of overall mean annual somatic production (g m^?2 year^?1 dry wt) for the three sites between January 1975 and January 1976 ranged between c. 132 (egg-ratio method), 37.5 (summation of growth increments) and 24 (Hynes-Hamilton method) at an annual mean standing stock level of 2.7 g m^?2 dry wt (calorific value, 20.34 kJ g^?1 dry wt). Production at sites 1, 2 and 3 decreased in line with declining annual mean standing stocks (5.32, 3.67 and 0.23 g m^?2, respectively). The growth increment method gave an overall mean annual P/B value of 13.9. Egg production amounted to a further 5.6, 3.6 and 0.1 g m^?2 year^?1 dry wt (calorific value, 28.01 kJ g^?1) at sites 1, 2 and 3, or 2.7 g m^?2 year^?1 on average.     

PRODUCTIVITY AND COMPOSITION OF A BALDCYPRESS-WATER TUPELO SITE AND A BOTTOMLAND HARDWOOD SITE IN A LOUISIANA SWAMP

The productivity and composition of two study sites in a southern Louisiana freshwater swamp were studied from October 1973 to November 1974. Net productivity was determined from measurements of litter-fall, stem growth of woody species, and harvest samples of annual herbaceous understory. Annual stem growth was calculated from biomass estimates on two different dates. The annual increase in stem biomass was 800 g dry wt/m² for a bottomland hardwood site (BLH) and 500 g dry wt/m² for a baldcypress-water tupelo site (CT). Litter-fall was 574 g dry wt/m²/yr for BLH and 620 g dry wt/m²/yr for CT. Harvest samples within the two plots yielded 200 g dry wt/m² and 20 g dry wt/m² for BLH and CT, respectively. Minimum net primary production was calculated as the sum of the three: 1574 g dry wt/m²/ yr for BLH and 1140 g dry wt/m²/yr for CT. Maximum estimates of herbaceous production and insect consumption were made by using values from the literature. Estimated total net primary productivity was 1733 g dry wt/m²/yr for BLH and 1516 g dry wt/m²/yr for CT. Tree composition was determined by the point-centered quarter method. Relative frequency, relative density, absolute density, relative dominance, and importance value (IV) were calculated for the tree species along each transect. In the bottomland hardwood area many woody species exist with Acer rubrum var. drummondii (IV = 23.9) and Nyssa aquatica (IV = 18.4) the most dominant. In the baldcypress-water tupelo area, fewer woody species exist and Taxodium distichum (IV = 39.2) and N. aquatica (IV = 37.6) dominated. Comparison of productivity data from several southeastern swamps indicate that flowing water regimes tend to result in the highest swamp forest productivity.     

Seaweed succession on artificial reefs on different bottom substrata

Artificial rest reefs were set on sandy and rocky bottoms at 5–10 m depth along the coast of southern Japan. Mature thalli ofSargassum, Gelidium and other seaweds were transported from other coastal areas, packed in mesh bags and attached to the reefs to start the beds. After one year, the seaweed flora on the reef on a sandy bottom consisted of more than 20 species, includingSargassum spp. andGelidium amansii, which are important animal food species. Coralline algae were the dominants on the rocky bottom reefs. The lower biomass on reefs on the rocky bottom was due to grazing by urchins. The same number of species was present in the first and second years on reefs on sandy bottoms, but there were moreSargassum thalli the second year.Maximum algal biomass of the artificial reef in May of the second year was 9998 g wet wt m^–2 in sandy areas, 441 g wet wt m^–2 in boulder areas and 228 g wet wt m^–2 in rocky areas. Reefs on rocky bottoms continued to be covered by coralline algae and several species ofCodium andDictyota.     

Numbers and biomass of centipedes (Lithobiomorpha: Chilopoda) in a Betula-Alnus woodland in N.E. England

Summary Over a period of 1 year the mean monthly population densities of L. forficatus varied between 7.58 m^-2 (February) and 24.07 m^-2 (October). The equivalent values for L. crassipes were 17.05 m^-2 (February) and 64.17 m^-2 (October). The annual mean population density of the two species was estimated at 51 m^-2 with a biomass of 0.585 g live wt m^-2. Less than 4% of the total lithobiid population was found in decaying logs and tree stumps, most of the population inhabited the soil/litter layers.Seasonal fluctuation in numbers was shown to be unimodal in L. forficatus and bimodal in L. crassipes. A similar pattern was noted in the status of the ovaries, L. forficatus appears to have a single peak breeding period (September) while L. crassipes has two (June and September).In terms of biomass, the relative importance of centipedes among other woodland invertebrate predators is high.     

内蒙古温带草原大针茅叶片光合生理特性对氮添加的响应

大气氮沉降增加生态系统氮有效性,优势种植物对不同水平氮输入的响应影响草原生态系统结构和功能。研究设置4个氮添加水平,分析内蒙古温带草原优势种大针茅（Stipa grandis）光合生理特性对不同梯度氮添加的响应。结果表明：低氮（0-2 g m^-2 a^-1）处理时,大针茅叶片氮含量较低,叶绿素含量和1,5-二磷酸核酮糖羧化/加氧酶的活性不高,光能利用效率低,导致光系统II出现过剩激发能,光合器官受到抑制,净光合速率相对较低。适量氮添加（5-10 g m^-2 a^-1）提高了大针茅叶片羧化系统和电子传递系统的氮分配,进而提高了1,5-二磷酸核酮糖羧化/加氧酶的活性以及电子传递速率,净光合速率增大。高氮（25 g m^-2 a^-1）处理时,叶片氮含量较高,但光合氮分配比例下降,降低了光合氮利用效率。大针茅光抑制程度增大,叶绿素含量、1,5-二磷酸核酮糖羧化/加氧酶的活性下降,不利于生物量积累。研究结果有助于进一步了解全球变化背景下草原生态系统优势种的生理响应机制,并为草原的可持续发展提供一定的理论依据。     

The soil fauna of a beech forest on limestone: trophic structure and energy budget

Summary The soil fauna of a mull beech forest on lime-stone in southern Lower Saxony (West Germany) was sampled quantitatively. Biomass estimates, trophic characteristics, and measurement and calculation of the energetic parameters of the constituent animal populations were used to construct an energy budget of the total heterotrophic subsystem of the forest. Mean annual zoomass amounted to about 15 g d wt m^–2; earthworms (about 10 g d wt m^–2) and other groups of the macrofauna were dominant. Protozoa constituted about 1.5 g d wt m^–2. Relative distribution of zoomass among the trophic categories was 50% macrosaprophages, 30% microsaprophages, 12% microphytophages, and 4% zoophages. Total annual consumption rate of the saprophagous and microphytophagous soil fauna (6328 and 4096 kJ m^–2 yr^–1, respectively) was of the same order of magnitude as annual litter fall (canopy leaves 6124 kJ m^–2 yr^–1, flowers and fruits 944 kJ m^–2 yr^–1, herbs 1839 kJ m^–2 yr^–1, fine woody material 870 kJ m^–2 yr^–1, tree roots 3404 kJ m^–2 yr^–1, without coarse woody litter). Primary decomposers (macrosaprophages) were the key group for litter comminution and translocation onto and into the soil, thus contributing to the high decomposition rate (k=0.8) for leaf litter. Consumption rates of the other trophic groups were (values as kJ m^–2 yr^–1): bacteriophages 2954, micromycophages 416, zoophages 153. Grazing pressure of macrophytophages (including rhizophages) was low. Faeces input from the canopy layer was not significant. Grazing pressure on soil microflora almost equalled microbial biomass; hence, a large fraction of microbial production is channelled into the animal component. Predator pressure on soil animals is high, as a comparison between consumption rates by zoophages and production by potential prey — mainly microsaprophages, microphytophages and zoophages — demonstrated. Soil animals contributed only about 11% to heterotrophic respiration. However, there is evidence that animals are important driving variables for matter and energy transfer: key processes are the transformation of dead organic material and grazing on the microflora. It is hypothesized that the soil macrosaprophages are donor-limited.     

典型草原建群种羊草对氮磷添加的生理生态响应

由于人类活动和气候变化的共同作用, 大气氮(N)沉降日益加剧, 使得陆地生态系统中的可利用性N显著增加, 生态系统更易受其他元素如磷(P)的限制。然而, 目前关于N、P养分添加对草原生态系统不同组织水平的影响研究较少, 相关机制尚不清楚。该文以内蒙古典型羊草(Leymus chinensis)草原为研究对象, 通过连续两年(2011-2012年)的N和P养分添加实验, 研究建群种羊草的生理生态性状、种群生物量和群落初级生产力对N、P添加的响应及其适应机制。结果表明: 羊草草原不同组织水平对N、P添加的响应不同。群落水平上, 地上净初级生产力在不同降水年份均受N和P元素的共同限制, N、P共同添加显著提高了地上净初级生产力; 物种水平上, N、P添加对羊草种群生物量和密度, 以及相对生物量均没有显著影响, 表明羊草能够维持种群的相对稳定; 个体水平上, 在正常降水年份(2011年), 羊草生长主要受N素限制, 而在湿润年份(2012年), 降水增加使得羊草生长没有受到明显的养分限制。羊草通过增加比叶面积、叶片大小和叶片N含量, 提高整体光合能力, 以促进个体生长。总之, 内蒙古典型草原群落净初级生产力受N、P元素共同限制, 作为建群种的羊草, 其对N、P添加的响应因组织水平而异, 也受年际间降水变化的影响。     

Carry-over of enhanced ultraviolet-B exposure effects to successive generations of a desert annual: interaction with atmospheric CO2 and nutrient supply

The performance of fifth generation offspring of a desert annual (Dimorphotheca sinuata DC.) were compared in the absence of UV-B, under variable atmospheric CO₂ and nutrient supply, after four consecutive generations of concurrent exposure of their progenitors to UV-B at ambient (seasonal range: 2.55–8.85 kJ m^–2 d^–1) and enhanced (seasonal range: 4.70–11.41 kJ m^–2 d^–1) levels. Offspring of progenitors grown under elevated UV-B exhibited a diminished photosynthetic rate, a consequence of a reduced leaf density, and diminished foliar levels of carotenoids, polyphenolics and anthocyanins. Conversely, nonstructural carbohydrate and chlorophyll b levels were increased. Altered physiology was accompanied by reduced apical dominance and earlier flowering, features generally considered under photomorphogenic control, increased branching and inflorescence production and greater partitioning of biomass to reproductive structures, but diminished seed production. Many of these changes were magnified under nutrient limitation and intensified under atmospheric CO₂ enriched conditions. The latter disagrees with current opinion that elevated CO₂ may reduce detrimental UV-B effects, at least over the long-term. Observed correlations between seed production and polyphenolic, especially anthocyanin, levels in offspring, and indications of diminished lignification (thinner leaves, less robust stems and fewer lignified seeds set) all pointed to the involvement of the phenylpropanoid pathway in seed formation and plant structural development and its disruption during long-term UV-B exposure. Comparisons with earlier generations revealed trends with cumulative generations of enhanced UV-B exposure of increasing chlorophyll b and nonstructural carbohydrates, decreasing polyphenolics and biomass allocation to vegetative structures, and diminishing seed production despite increasing biomass allocation to reproductive structures. Notwithstanding some physiological compensation (increased chlorophyll b), the accumulation and persistence of these ostensibly inherited changes in physiological and reproductive performance suggest a greater impact of elevated UV-B on vegetation, primary production and regeneration over the long-term than presently envisaged.     

Life history, growth and production of Mysis relicta in the large, fiord-type Lake Mjøsa, Norway

SUMMARY.

• 1 Biomass, production and life history of Mysis relicta were studied in the large Lake Mjøsa during the years 1976–80. Biomass fluctuations were large, but biomass averaged about 1 g wet wt m^?2 or 200 ind. m^?2. Cumulative net production during summer ranged from 1.6 to 2.1 g wet wt m^?2. Mean population P/B-ratio was close to 2.
• 2 Neither production or biomass of Mysis were correlated with the biomass of phytoplankton or the main Zooplankton prey species (Daphnia and Bosmina), suggesting a predominant ‘top down’ control of Mysis in this lake.
• 3 The life cycle was well synchronized with development of food items, but predation pressure also affected life-history patterns. The proportion of juveniles apparently increased in years with strong fish predation pressure, producing a predominantly 1-year life-cycle pattern the following year.
• 4 Mysis had a predominant 2-year life history, but a traction of the population may reproduce after 1 or 3 years. Reproduction occurred exclusively during winter. Even in such a large and stable system, where Mysis has coexisted with its main food items and predators for 8–10 000 years, a flexible life history is maintained and is probably an important buffer against year-to-year fluctuations in food and predator abundance.

     

Snail numbers,biomass and respiratory metabolism in a beech woodland — Wytham Woods,Oxford

Summary Two methods of extraction were used in the estimation of snail population densities in woodland litter. The time-consuming-Vágvölgyi technique proved to be 6.25 times more efficient than infra-red heat extraction but it was shown that the results obtained by the latter method could be easily corrected to conform with those of the former.Snail density varied with season (Winter, 1,000–1,250 m^-2, Summer, 50–600 m^-2), the annual mean density being 645 m^-2. The annual mean ash-free dry weight biomass was 176 mg m^-2 while annual population metabolism equalled 0.8941 O₂ (=17.84 kJ m^-2 yr^-1).Two independent estimates of the energy equivalent of food consumption gave rise to values of 25.37 and 57.98 kJ m^-2 yr^-1, these respectively account for 0.54 and 1.23% of the known ground litter disappearance of 4,716.58 kJ (=235 g dry wt. m^-2 yr^-1).     

Seasonal variation in standing crop,density and leaf growth rate of the seagrass, Heterozostera tasmanica, in western Port and Port Phillip Bay,Victoria, Australia

Standing crop, density and leaf growth rate of Heterozostera tasmanica (Martens ex Aschers.) den Hartog along with light, temperature, nutrient and sediment characteristics were determined monthly for fifteen months at three study sites in Western Port and one site in Port Phillip Bay, Victoria, Australia. Erect vegetative stems of H. tasmanica were frequently branched, were present throughout the year and accounted for 25–60% of the above-sediment biomass, with the stem proportion higher during winter than summer. At three of the four sites there was a unimodal seasonal pattern in which minimum leaf standing crop (27–61 g dry wt. m^?2), density (600–2000 leaf cluster m^?2) and leaf productivity (0.34–0.77 g dry wt. m^?2 day^?1) generally occurred during winter (June–August) and maximum leaf standing crop (105–173 g dry wt. m^?2), density (2700–5000 leaf cluster m^?2) and leaf productivity (2.6–4.2 g dry wt. m^?2 day^?1) occurred during summer (December–February). A bimodal seasonal pattern with minimum standing crop and density during midsummer occurred at one site. This anomalous seasonal pattern may be due to exposure and desiccation stress during spring low tides. At the site receiving the lowest irradiance, standing crop, density and annual leaf production also were lowest, but length and width of leaves, shoot height and leaf growth rate per leaf cluster were the highest of the four study sites. On average, each leaf cluster at any one of the study sites produced 30–31 leaves per year with mean leaf turnover rates of 1.3–1.7% day^?1. Annual leaf production of H. tasmanica ranged from 410 to 640 g dry wt.m^?2 at the four sites.     

Sexual differences in the diet of king cormorants at Macquarie Island

Sexual differences in the diet of king cormorants,Phalacrocorax albiventer, were investigated during the 1993/1994 austral summer at Macquarie Island. The major food items, identified by otoliths in regurgitations, were demersal fish; fish mass consumed could be estimated using a wet mass-otolith length relationship. Two fish species,Paranotothenia magellanica andHarpagifer georgianus, constituted 98% of the wet mass (male and female cormorants combined). Estimated individual fish mass ofParanotothenia magellanica (19.6±11.6 g) was greater than that ofH. georgianus (2.8±1.3 g). Total wet mass of food and number of fish in regurgitations did not differ statistically between the sexes of cormorants. However, males tended to feed on larger fish than did females.     

Enchytraeid numbers,biomass and respiratory metabolism in a beech woodland - Wytham Woods,Oxford

Summary The mean annual population density of enchytraeids in the litter and upper 6 cm of soil was found to be 14,590 m^-2. Mean individual weights approximated 116, 158 and 151 g wet wt. in the litter, 0–3 cm and 3–6 cm strata respectively. The mean biomass was estimated to be 1.908 g wet wt m^-2. Vertical migration was shown to occur, the upward migration in late Autumn was a response to temperatures in the litter being temporarily higher than those of the 0–3 cm stratum. As a result of upward vertical migration and possibly recruitment, numbers reached a maximum in the litter during Winter. On an annual basis the litter, 0–3 and 3–6 cm strata contained 41.43, 46.44 and 12.12% respectively of the extracted enchytraeids. The equivalent biomass values were 33.18, 52.46 and 14.36%. Total numbers and biomass revealed a general picture of high values in late Autumn to Winter which gradually decreased through Spring and Summer except for a minor peak in May–June. The annual oxygen consumption of the enchytraeids approximated 4.285 l O₂ m^-2 yr^-1 (20.461 kcal85.610 kJ) and accounted for 1.63% of the total soil metabolism. A production/biomass (P/B) ratio of 4.93 was estimated as was a net population efficiency of 32%. For this site the contribution by enchytraeids to total soil respiration is about one-third that of the earthworms and an order of magnitude greater than that of the nematodes.     

Estimation of the primary productivity of Spartina alterniflora using a canopy model

A comprehensive canopy productivity model was built to study the productivity of a primary salt marsh grass, Spartina alterniflora. in Georgia, USA The canopy model was unique in employing plant demographic data to reconstruct canopy profiles and dynamics, which showed many growth processes that are otherwise difficult to discern in the field By linking canopy dynamics and leaf photosynthesis, the net total primary productivity of S alterniflora m a Georgia salt marsh was estimated to be 1421, 749, and 1441 g C m^-2 yr^-1 for the tall, short, and N-fertilized short populations respectively These estimates are reasonable in terms of the physiological capacity of S alterniflora and well below the range of 3000–4200 g C m^-2 yr^-1 as reported by some recent harvest studies Our detailed analysis suggested the net total productivity of S alterniflora might be greatly overestimated in the past This is mainly because of 1) failure to consider the translocation of photosynthate between aboveground and belowground parts, and 2) possible overestimates of belowground production We estimated the net belowground production to be 872, 397, and 762 g C m^-2 yr^-1 for the tall, short, and N-fertilized populations respectively After receiving nitrogen fertilizer, the net leaf carbon fixation in the short population increased from 1489 to 2487 g C m^-2 yr^-1, and our simulation showed the contribution of elevated leaf N to this increase was small, 21%, compared with that of increased leaf area, 79% Both tall and short populations allocated ca 48-49% of their annual gross leaf carbon fixation to belowground structures Nitrogen enrichment caused more allocation to aboveground parts in the short population, mainly for increasing leaf area The canopy model assumed that there was no leaf photosynthesis under tidal submergence, but if this assumption was relaxed, then leaf carbon fixation might increase 7–13% for different S alterniflora populations Although this research focused only on a salt marsh species, our general approaches, especially the coupling of leaf physiology with the reconstructed canopies, should be applicable to the study of production processes of many other plant populations