Functional importance vs keystoneness: Reformulating some questions in theoretical biocenology

Abstract Two concepts relating to the influence of individual species on the biocenoses in which they occur are reviewed. The first, the general functional importance of a species, is denned as the sum, over all species, of the changes (sign ignored) in productivity which would occur on removal of the particular species from the biocenosis. General functional importance is calculated as: where P_j is the productivity of the jth species before (t= 0) and after (t= 1) removal of the particular (ith) species being evaluated. Though I_i values cannot be determined empirically, this concept raises provocative questions for theoretical biocenology. The second concept reviewed is that of the keystone species. Never having been precisely or operationally defined,‘keystone’ has come to mean little more than ‘important for something.’ Moreover, there is no empirical or theoretical foundation for the idea that there exists in any biocenosis a natural dichotomy corresponding to the verbal one of keystone and non-keystone species. Some investigators have implied that such a dichotomy is suggested by the frequency distributions of experimentally determined values of interaction strength. The patterns they refer to are, however, artifacts resulting from small sample sizes and the plotting of frequency distributions on arithmetic rather than logarithmic scales. As a casual metaphor ‘keystone species’ was appealing and harmless; but the pretence that it is a well-defined concept or phenomenon has had a stultifying effect on ecological thought and argument.     

The Impact of Oxygen Tension on Cell Density and Metabolic Diversity of Microbial Communities in Alkane Degrading Continuous-Flow Cultures

Abstract The impact of the dissolved O₂ tension (DOT) and the dilution rate on the metabolic diversity of an autochthonous hexadecane-degrading community in continuous-flow cultures containing hexadecane-coated intertidal sediment was determined in a set of experiments. The DOT was kept constant within each culture at values of 80% (168 μmol O₂L⁻¹) or 0.4% (0.84 μmol O₂ L⁻¹). The dilution rate was increased from D= 0.012 h⁻¹ to D= 0.06 h⁻¹. To determine the culture activity, we analyzed the hexadecane degradation rate, the protein production rate, and the oxygen consumption rate. The cell concentration of different metabolic groups was determined by colony forming units (CFU), and by most probable number (MPN). The metabolic diversity was determined by the substrate utilization spectrum in Biolog GN microtiter plates. The substrate utilization pattern of the cultures decreased considerably as D increased. This effect was more pronounced at 0.4% of DOT than at 80% of DOT. The MPN and CFU revealed that as D increased, only minor changes occurred in the community structure. The hexadecane degradation rate, the protein production rate, and the oxygen consumption rate increased parallel to D independently of the DOT. This means that the biocenosis at 0.4% of DOT was different from the biocenosis at 80% of DOT, although the metabolic activity of the cultures was unaffected by a 200-factor difference in the oxygen tension and revealed a considerable buffer capacity with respect to changes in DOT. Received: 23 May 1998; Accepted: 24 August 1998     

Biocenoses of Anadyr Estuary (Bering Sea) and conditions of their existence

Some bottom biocenoses in the river mouth area of Anadyr Estuary are studied. Seasonal biocenosis of filamentous algae Acrosiphonia spp. occurs in the intertidal zone, biocenosis of the bivalve Macoma balthica is common at a depth of 4–8 m. Species diversity increases with depth. The distribution of biocenoses and population structure depend on the hydrological regime and substrate type in the surveyed area.     

A simulation model of sulfur transformations in forested Spodosols

Transformations of organic and inorganic S in two forested Spodosols from the Hubbard Brook Experimental Forest, New Hampshire and the Huntington Forest in the Adirondack Mts. of New York were investigated using laboratory³⁵SO₄ ^2- incorporation experiments. Sulfur transformations were modeled as a set of three reversible, first-order reactions in which soluble SO ₄ ^2- is converted to adsorbed SO ₄ ^2- , ester sulfate and carbon-bonded S. Reaction rate contants for³⁵SO ₄ ^2- adsorption/desorption and immobilization reactions involving ester sulfate and carbon-bonded S were determined using a fifth order Runge-Kutta-Fehlberg integration routine combined with least squares fitting. Model simulations were able to account for over 93% of the variation in the distribution of³⁵S in S fractions. A hypothetical application of immobilization rate constants to field situations at the Hubbard Brook Experimental Forest suggests that large quantities of S cycle through organic forms in Northern Hardwood Forest Ecosystems.     

Subtidal Underwater Rock Communities of the White Sea: Structure and Interaction with Bottom Flow

The taxonomic composition and quantitative characteristics of typical subtidal rock communities of the White Sea (biocenosis of Laminaria and biocenosis of Lithothamnion and the sponges Polymastia arctica) were studied. The hydrodynamic activity of the near-bottom water layer within and beyond the communities was estimated using the plaster structures technique. A comparative analysis of our results and the literature data revealed three main types of interactions between the benthic community and the water flow: turbulation of the water flow (mussel banks), smoothing of turbulent pulsations (Laminaria community), and an insignificant effect on the water flow (community of Lithothamnion and sponges).     

不同污染程度下毛白杨叶表面PM2.5颗粒的数量及性质和叶片气孔形态的比较研究

选择了北京市环境PM_(2.5)浓度不同的两个采样点的毛白杨(Populus tomentosa Carr.)作为研究对象,利用环境扫描电镜及X-射线能谱仪对杨树叶片表面滞留的PM_(2.5)颗粒进行了观察、统计和成分分析,并研究了叶片气孔对环境颗粒物污染的适应性变化。结果表明:夏秋两季西直门叶片样品上下表面的PM_(2.5)数量均多于森林公园样品这说明环境PM_(2.5)浓度是影响叶片表面滞留颗粒物数量的主要原因;其中叶片上表面是滞留PM_(2.5)颗粒的主要区域。森林公园样品中PM_(2.5)颗粒性质比较单一,硅铝酸盐颗粒和石英颗粒占很大比例,二者的主要来源均为天然源,如土壤扬尘、矿物颗粒等;而西直门采样点叶片样品滞留的PM_(2.5)颗粒的元素组成更为复杂,其中50%以上的硅铝酸盐颗粒检测出了明显的铜、钾、氯、钠等元素的谱峰其来源主要是工业排放;西直门样品PM_(2.5)的含硫量高于森林公园样品,且夏季明显高于秋季。研究还发现有少数PM_(2.5)颗粒进入了毛白杨叶片的气孔而且不同污染程度下气孔的形态特征存在差异。与森林公园毛白杨叶片的气孔相比,西直门处的毛白杨叶片气孔的长度、宽度、面积和气孔密度均较小,说明较高的PM_(2.5)污染程度对毛白杨叶片的形态发育有一定影响。研究结果可以为揭示植物叶片阻滞、吸收大气颗粒污染物的机制、合理选择和优化城市绿化树种从而改善空气质量提供一定的科学理论依据。     

Uprooted trees,their distribution and influence in the primeval forest biotope

Summary The paper reports results of a long-term (1964–1974) investigation on permanent study sites in natural forest ecosystems of the Tilio-Carpinetum and the Pino-Quercetum in the Bialowieza Forest. The influence of decaying logs and root craters was investigated. It was found that the main causes of uprooting were the spring and autumn winds. Wind direction and the position of logs lying on the ground are correlated. Picea is most susceptible to uprooting by winds. Almost one half of the trees of this species are alive at the moment of uprooting.By mapping changes in the distribution of uprooted trees on a permanent area in time, a balance of the change over in a 10-year period was determined. It appeared that the decomposition is slower than accumulation. From this, it was concluded that the stand is in a phase of natural thinning. In the study site, compartments were disinguished with various degrees of change in the number of uprooted trees, and the consequences of differentiation and constant transformation of the biotope and biocenosis by the occurrence of uprooted trees and by their decay are described.Nomenclature of species follows Flora Europaea.Contribution to the Symposium of the Working Group for Succession Research on Permanent Plots, held at Yerseke, the Netherlands, October 1975.     

Integrated ecological research of catchment-lake ecosystems in the Bohemian Forest (Central Europe): A preface

The Bohemian Forest (?umava, Böhmerwald) is situated in Central Europe and is among the most acidified lake districts in the world. Deposition of S and N compounds in the area rapidly increased between 1950 and 1980, and reached a maximum in the 1980s. During the 1990s, acid deposition decreased substantially, and current levels are comparable to the early 20^th century for SO ₄ ^2? and NH ₄ ⁺ , and to the mid 1960s for NO ₃ ^? . These changes in acid deposition have led to a partial recovery of the Bohemian Forest lakes. This paper provides an overview of previous research, and details on the organization and aims of current research on the Bohemian Forest lakes. Available historical data and regular monitoring (since 1984) provide a valuable background for long-term ecological research of the catchment-lake ecosystems that currently focuses on (i) chemical reversal and biological recovery of the lakes, (ii) acidification impacts on in-lake nutrient cycling, (iii) climatic effects on water chemistry, and (iv) catchment processes, including soil biogeochemistry and acidification impacts on vegetation.     

Effective stomatal and boundary-layer resistances of heterogeneous surfaces

In nature surfaces are rarely uniform, so terms such as ‘surface’, ‘stomatal’ or ‘canopy’ resistance usually indicate some kind of average over a population of sub-areas, each with its own separate resistance. Questions then arise as to how gross measurements of these resistances should be interpreted in terms of the components, or how components should be aggregated into representative single values. Aggregation schemes have been published by Raupach (1991, Vegetatio 91, 105–120) and Lhomme (1992, Agriculture and Forest Meteorology 61, 11–21), but these are different for reasons that were not explained. This paper develops the idea that averaging schemes should be designed to serve particular purposes, and that they can be varied to suit these purposes. It is shown that the ‘effective’ resistances defined by Raupach and Lhomme preserve different quantities. A further averaging scheme is developed which preserves both correct transpiration rate and CO₂ flux when used in the Penman-Monteith equation and an equation describing assimilation. All of these schemes are fairly complex, so the work provides a warning against naive use of effective variables.     

New location of fungus species registered in the red data book of the Tver region

Rare fungus species: Hericium coralloides, Cortinarius violàñås, and Leccanium percandidu were detected for the first time in the Zubtsov area of the Tver region. We note that, in the search for rare species of fungus, attention should be paid to the type of biocenosis.     

Feeding of the Snailfish Careproctus roseofuscus in Pacific Waters of the Northern Kuril Islands and Southeastern Kamchatka

The paper describes the feeding of two phenotypically different forms of the snailfish Careproctus roseofuscus (Scorpaeniformes, Liparidae) from the Pacific waters of the northern Kuril Islands and southeastern Kamchatka. The diet in the first form is comprised of actiniae. The second form mostly feeds on fish eggs and the amphipod Metopa majuscula Gurjanova. The second form is supposed to be confined to the biocenosis of Ophiopholis aculeata + Spongia.     

A mathematical model for zoonotic transmission of malaria in the Atlantic Forest: Exploring the effects of variations in vector abundance and acrodendrophily

Transmission foci of autochthonous malaria caused by Plasmodium vivax-like parasites have frequently been reported in the Atlantic Forest in Southeastern and Southern Brazil. Evidence suggests that malaria is a zoonosis in these areas as human infections by simian Plasmodium species have been detected, and the main vector of malaria in the Atlantic Forest, Anopheles (Kerteszia) cruzii, can blood feed on human and simian hosts. In view of the lack of models that seek to predict the dynamics of zoonotic transmission in this part of the Atlantic Forest, the present study proposes a new deterministic mathematical model that includes a transmission compartment for non-human primates and parameters that take into account vector displacement between the upper and lower forest strata. The effects of variations in the abundance and acrodendrophily of An. cruzii on the prevalence of infected humans in the study area and the basic reproduction number (R₀) for malaria were analyzed. The model parameters are based on the literature and fitting of the empirical data. Simulations performed with the model indicate that (1) an increase in the abundance of the vector in relation to the total number of blood-seeking mosquitoes leads to an asymptotic increase in both the proportion of infected individuals at steady state and R₀; (2) the proportion of infected humans at steady state is higher when displacement of the vector mosquito between the forest strata increases; and (3) in most scenarios, Plasmodium transmission cannot be sustained only between mosquitoes and humans, which implies that non-human primates play an important role in maintaining the transmission cycle. The proposed model contributes to a better understanding of the dynamics of malaria transmission in the Atlantic Forest.     

Effects of the Hemlock Woolly Adelgid on Nitrogen Losses from Urban and Rural Northern Forest Ecosystems

The objectives of this study were to quantify rates of nitrogen inputs to the forest floor, determine rates of nitrogen losses via leaching and to partition the sources of NO₃ ⁻ from healthy, declining, and salvage or preemptively cut eastern hemlock (Tsuga canadensis) stands in both an urban forest at the Arnold Arboretum in Boston, MA and a rural forest at Harvard Forest in Petersham, MA. Rates of nitrogen inputs (NH₄ ⁺ and NO₃ ⁻) to the forest floor were 4–5 times greater, and rates of nitrogen losses via leachate were more than ten times greater, at the Arnold Arboretum compared to Harvard Forest. Nitrate that was lost via leachate at Harvard Forest came predominantly from atmospheric deposition inputs, whereas NO₃ ⁻ losses at the Arnold Arboretum came predominantly from nitrification. Although our study was limited to one urban and one rural site, our results suggest that current management regimes used to control the hemlock woolly adelgid (Adelges tsugae), such as salvage cutting, may be reducing nitrogen losses in urban areas due to rapid regrowth of vegetation and uptake of nitrogen by those plants. In contrast, preemptive cutting of trees in rural areas may be leading to proportionately greater losses of nitrogen in those sites, though the total magnitude of nitrogen lost is still smaller than in urban sites. Results of our study suggest that the combination of the hemlock woolly adelgid, nitrogen inputs, and management practices lead to changes in the movement and source of NO₃ ⁻ losses from eastern hemlock forest ecosystems.     

Short-term effects of rain on soil respiration in two New England forests

To gain new insights into the underlying mechanisms responsible for wetting-induced soil respiration, rain simulation field experiments were carried out in two temperate mixed-hardwood forests in New England (Great Mountain Forest and Harvard Forest). The rain-induced CO₂ pulses were observed in both xeric and mesic soils. The pulse intensity was negatively correlated with the site moisture level and the pre-rain soil CO₂ flux. At both forests, plots without O horizon responded to wetting with limited or even negative enhancement, confirming previous finding that the rain pulse was likely due to enhanced microbial consumption on substrates mainly of microbial origin. Our results show that the flux rain pulse was a reproducible phenomenon not limited to dry soils.     

Influence of experimental extreme water pulses on greenhouse gas emissions from soils

Climate models predict increased frequency and intensity of storm events, but it is unclear how extreme precipitation events influence the dynamics of soil fluxes for multiple greenhouse gases (GHGs). Intact soil mesocosms (0–10 cm depth) from a temperate forested watershed in the piedmont region of Maryland [two upland forest soils, and two hydric soils (i.e., wetland, creek bank)] were exposed to experimental water pulses with periods of drying, forcing soils towards extreme wet conditions under controlled temperature. Automated measurements (hourly resolution) of soil CO₂, CH₄, and N₂O fluxes were coupled with porewater chemistry analyses (i.e., pH, Eh, Fe, S, NO₃ ^?), and polymerase chain reaction–denaturing gradient gel electrophoresis to characterize changes in microbial community structure. Automated measurements quantified unexpected increases in emissions up to 245% for CO₂ (Wetland), >23,000% for CH₄ (Creek), and >110,000% for N₂O (Forest Soils) following pulse events. The Creek soil produced the highest soil CO₂ emissions, the Wetland soil produced the highest CH₄ emissions, and the Forest soils produced the highest N₂O emissions during the experiment. Using carbon dioxide equivalencies of the three GHGs, we determined the Creek soil contributed the most to a 20-year global warming potential (GWP; 30.3%). Forest soils contributed the most to the 100-year GWP (up to 53.7%) as a result of large N₂O emissions. These results provide insights on the influence of extreme wet conditions on porewater chemistry and factors controlling soil GHGs fluxes. Finally, this study addresses the need to test biogeochemical thresholds and responses of ecosystem functions to climate extremes.     

Features of the Biology of the False Zokor (<Emphasis Type="Italic">Myospalax aspalax</Emphasis>, Rodentia,Spalacidae) from Eastern Transbaikalia

The features, population characteristics of reproduction, nutrition, and lifestyle of an extremely poorly studied narrow-range species of underground rodents—the false zokor (Myospalax aspalax)—have been described on the basis of original field materials. The data were obtained within the Russian part of the species range in Zabaikal’skii krai. The false zokor is characterized by a pronounced sexual dimorphism in body size (males are larger) and a predominance of females in the population. Mating takes place in April; at other times of the year, zokors lead a solitary lifestyle. The size of the brood is small: 3.7 embryos per breeding female. Their preferred food is bulbs and rhizomes of Allium, Thermopsis, Phragmites, and Leymus. In Eastern Transbaikalia, they are active in winter.     

On the selection of thresholds for predicting species occurrence with presence‐only data

Presence‐only data present challenges for selecting thresholds to transform species distribution modeling results into binary outputs. In this article, we compare two recently published threshold selection methods (maxSSS and maxF_pb) and examine the effectiveness of the threshold‐based prevalence estimation approach. Six virtual species with varying prevalence were simulated within a real landscape in southeastern Australia. Presence‐only models were built with DOMAIN, generalized linear model, Maxent, and Random Forest. Thresholds were selected with two methods maxSSS and maxF_pb with four presence‐only datasets with different ratios of the number of known presences to the number of random points (KP–RP_ratio). Sensitivity, specificity, true skill statistic, and F measure were used to evaluate the performance of the results. Species prevalence was estimated as the ratio of the number of predicted presences to the total number of points in the evaluation dataset. Thresholds selected with maxF_pb varied as the KP–RP_ratio of the threshold selection datasets changed. Datasets with the KP–RP_ratio around 1 generally produced better results than scores distant from 1. Results produced by We conclude that maxF_pb had specificity too low for very common species using Random Forest and Maxent models. In contrast, maxSSS produced consistent results whichever dataset was used. The estimation of prevalence was almost always biased, and the bias was very large for DOMAIN and Random Forest predictions. We conclude that maxF_pb is affected by the KP–RP_ratio of the threshold selection datasets, but maxSSS is almost unaffected by this ratio. Unbiased estimations of prevalence are difficult to be determined using the threshold‐based approach.     

Annual wood production in a tropical rain forest in NE Costa Rica linked to climatic variation but not to increasing CO2

Increased atmospheric [CO₂] could theoretically lead to increased forest productivity (‘CO₂ fertilization’). This mechanism was hypothesized as a possible explanation for biomass increases reported from tropical forests in the last 30+ years. We used unique long‐term records of annually measured stands (eighteen 0.5 ha plots, 10 years) and focal tree species (six species, 24 years) to assess the effects of rainfall, temperature, and atmospheric [CO₂] on annual wood production in a neotropical rain forest. Our study area was a meso‐scale section (600 ha) of old‐growth Tropical Wet Forest in NE Costa Rica. Using the repeated remeasurements we directly assessed the relative effects of interannual climatic variation and increasing atmospheric [CO₂] on wood production. A remarkably simple two‐factor model explained 91% of the interannual variance in stand‐level tree growth; the statistically independent factors were total dry season rainfall (positive effect, r²=0.85) and night‐time temperature (negative effect, r²=0.42). Stand‐level tree mortality increased significantly with night‐time temperature. After accounting for dry season rainfall and night‐time temperature, there was no effect of annual [CO₂] on tree growth in either the stand or focal species data. Tree growth in this Tropical Wet Forest was surprisingly sensitive to the current range of dry season conditions and to variations in mean annual night‐time temperature of 1–2°. Our results suggest that wood production in the lowland rainforests of NE Costa Rica (and by extension in other tropical regions) may be severely reduced in future climates that are only slightly drier and/or warmer.     

Semliki Forest virus induced cell-cell fusion at neutral extracellular pH

Semliki Forest virus-induced cell-cell fusion from within was considered to exclusively occur at mildly acidic pH (<6.2). Data of this study show that such cell fusion can also be triggered by transient acidification of the cytoplasm of infected cells at an extracellular, neutral pH. Results were obtained by utilizing NH₄Cl pulses combined with covalent modification of cell surface proteins. The observation implies a revision of the current consensus regarding the mechanism of Semliki Forest virus induced cell-cell fusion. We propose a model in which at least two peptide segments of the viral spike protein E₁ may be involved in triggering the fusion event.     

Evidence for a nutritional disorder of Oxalis acetosella L. on acid forest soils; II. Diagnostic field experiments and nutrient solution studies

Different field experiments were performed to discover the main factor(s) responsible for the poor leaf growth, moderate propagation and leaf chlorosis of Oxalis acetosella in an old Norway spruce stand with acid soil (Höglwald Forest). A previous study had suggested, that Ca (or Mg) deficiency or Mn toxicity could be involved.In a Main Diagnostic Field Experiment with an intact population, Ca and Mg were either applied as sulphate or carbonate to distinguish between nutritional and pH effects. Mn and Si were also applied to aggravate or overcome possible effects of Mn toxicity. Enhancement experiments with different amounts of CaSO₄ were conducted to investigate the Ca dose-effect relationship under field conditions. Additional trials with SrCO₃, BaCO₃ and NaHCO₃ had the goal to raise the soil pH without supply of nutrients.Greenhouse experiments with Oxalis acetosella supplemented the field studies by investigating the Ca and Mn dose-effect relationships under controlled conditions. Growth, vitality and nutrition of Oxalis were studied in a nutrient solution culture at pH 4.0 over a range of concentrations of Ca (20 to 5000 mol L_-1) and Mn (5 to 1000 mol L_-1) respectively. Furthermore, the effects of two contrasting ammonium/nitrate ratios were tested. The nutritional composition of the basal nutrient solution and the microclimate in the greenhouse were as far as possible adjusted to the environmental conditions of the plant in the Höglwald Forest.All these studies led to the conclusion, that the moderate growth and vitality of Oxalis in the Höglwald Forest was mainly due to an insufficient Ca supply, rather than an effect of Mg deficiency, low soil pH or Mn toxicity. The application of CaSO₄ caused a similar stimulation of the growth as CaCO₃. A clearly positive, close CaSO₄ dose-effect relationship was detected in field experiments as well as in the nutrient solution study. The same type of leaf chloroses as in the field was reproduced through low Ca nutrient solutions. Predominant ammonium nutrition may significantly impair Ca uptake.Oxalis acetosella displayed a relatively high leaf tissue tolerance of excessive Mn. There was no indication for a Mn-induced Ca deficiency in the Höglwald Forest. Enhanced Si uptake led to a partial vitalization of Oxalis; the reason for that remained unclear.