Temperature- and Light-Dependent Performance of the Cyanobacterium <Emphasis Type="Italic">Leptolyngbya Foveolarum</Emphasis> and the Diatom <Emphasis Type="Italic">Nitzschia Perminuta</Emphasis> in Mixed Biofilms

This paper investigates the role of species interactions as a mechanism determining the changing seasonal abundance of microphytobenthic species. Different kinds of interactions can occur between microphytobenthic species, e.g., interference competition (a species directly hindering the growth of another) or resource competition. If such interactions are strong, the capacity of species to exploit parts of the seasonal spectrum of temperature and light conditions could be greatly affected. A model system of two freshwater benthic phototrophs, the cyanobacterium Leptolyngbya foveolarum (Rabenhorst ex Gomont) Anagnostidis et Komárek and the diatom Nitzschia perminuta (Grunow) M. Pergallo, was used to study the capacity of each species to grow in ranges of temperature (7, 15 and 25 °C) and light (5, 40 and 200 μmol m⁻² s⁻¹) conditions in single-species and two-species cultures. Growth was followed for 14–17 days by measuring chlorophyll a and maximum photosynthetic capacity using spectrophotometry and pulse amplitude modulated (PAM) fluorimetry. A PHYTO-PAM fluorimeter facilitated simultaneous observations in mixed cultures on the two species. In mixed cultures, the diatom appeared to be a ‘cool season species’ (low temperature and low light intensity) and the cyanobacterium a ‘summer or autumn species’ (higher temperature and light intensities). This is different than predicted by monoculture experiments, where a wide range of optimal growth conditions was found. Two-species biofilm tests indicated inhibitory effects of the cyanobacterium on the diatom species, especially under conditions favorable to the cyanobacterium. High or low light intensities, increase of local pH caused by depletion of inorganic carbon, and limitation of other inorganic nutrients (resource competition) were examined as factors contributing to diatom inhibition, but none provided an acceptable explanation for observed growth patterns. Our results pointed towards interference competition.     

Control of microbial communities by the macrofauna: a sensitive interaction in the context of extreme summer temperatures?

Climate models predict an increasing frequency of extremely hot summer events in the northern hemisphere for the near future. We hypothesised that microbial grazing by the metazoan macrofauna is an interaction that becomes unbalanced at high temperatures due to the different development of the grazing rates of the metazoans and the growth rates of the microbial community with increasing temperature. In order to test this hypothesis, we performed grazing experiments in which we measured the impact of increasing temperatures on the development of the grazing rates of riverine mussels in relation to the growth rates of a unicellular prey community (a natural heterotrophic flagellate community from a large river). In a first experimental series using Corbicula fluminea as a grazer and under the addition of a carbon source (yeast extract), the increase of the prey’s growth rates was considerably stronger than that of the predator’s grazing rates when temperatures were increased from 19 to over 25°C. This was also the outcome when the mussels had been acclimatized to warm temperatures. Hereafter, specific experiments with natural river water at temperatures of 25 and 30°C were performed. Again, a strong decrease of the mussels’ grazing rates in relation to the flagellate growth rates with increasing temperature occurred for two mussel species (C. fluminea and Dreissena polymorpha). When performing the same experiment using a benthic microbial predator community (biofilms dominated by ciliates) instead of the benthic mussels, an increase of the grazing rates relative to the growth rates with temperature could be observed. Our data suggest that predator–prey interactions (between metazoans and microbes) that are balanced at moderate temperatures could become unbalanced at high temperatures. This could have significant effects on the structure and function of microbial communities in light of the predicted increasing frequency of summer heat waves. Priority programme of the German Research Foundation—contribution 7.     

Local environment,not local adaptation,drives leaf‐out phenology in common gardens along an elevational gradient in Acadia National Park,Maine

Premise of the Study

Climate‐driven changes in phenology are substantially affecting ecological relationships and ecosystem processes. The role of variation among species has received particular attention; for example, variation among species’ phenological responses to climate can disrupt trophic interactions and can influence plant performance. Variation within species in phenological responses to climate, however, has received much less attention, despite its potential role in ecological interactions and local adaptation to climate change.

Methods

We constructed three common gardens across an elevation gradient on Cadillac Mountain in Acadia National Park, Maine, to test population‐level responses in leaf‐out phenology in a reciprocal transplant experiment. The experiment included three native species: low bush blueberry (Vaccinium angustifolium), sheep's laurel (Kalmia angustifolia), and three‐toothed cinquefoil (Sibbaldiopsis tridentata).

Key Results

Evidence for local adaptation of phenological response to temperature varied among the species, but was weak for all three. Rather, variation in phenological response to temperature appeared to be driven by local microclimate at each garden site and year‐to‐year variation in temperature.

Conclusions

Population‐level adaptations in leaf‐out phenology appear to be relatively unimportant for these species in Acadia National Park, perhaps a reflection of strong genetic mixing across elevations, or weak differences in selection on phenological response to spring temperatures at different elevations. These results concur with other observational data in Acadia and highlight the utility of experimental approaches to understand the importance of annual and local site variation in affecting phenology both among and within plant species.     

Including species interactions in risk assessments for global change

Most ecological risk assessments for global change are restricted to the effects of trends in climate or atmospheric carbon dioxide. In order to move beyond investigation of the effects of climate alone, the climex ^™ model was extended to investigate the effects of species interactions, in the same or different trophic levels, along environmental gradients on a geographical scale. Specific needs that were revealed during the investigations include: better treatment of the effects of temporal and spatial climatic variation; elucidation of the nature of boundaries of species ranges; data to quantify the role of species traits in interspecies interactions; integrated observational, experimental, and modelling studies on mechanisms of species interactions along environmental gradients; and high‐resolution global environmental datasets. Greater acknowledgement of the shared limitations of simplified models and experimental studies is also needed. Above all, use of the scientific method to understand representative species ranges is essential. This requires the use of mechanistic approaches capable of progressive enhancement.     

Mediation of benthic–pelagic coupling by microphytobenthos: an energy- and material-based model for initiation of blooms of Aureococcus anophagefferens

We present a conceptual model for initiation of blooms of the estuarine brown-tide pelagophyte Aureococcus anophagefferens. The model is based on the observation that in addition to its well-documented stimulation by organic nutrients, Aureococcus is pre-adapted to low light levels. Its relatively low maximum (light-saturated) growth rate makes it a poor competitor with other estuarine species at high light under acclimated conditions. Its large photosynthetic antenna and relatively low quota of photoprotective pigments make it more susceptible to photoinhibition than other species to which it is compared. These same characteristics give it a competitive advantage at low light levels. In its shallow habitat, both the light level and the rate of nutrient supply from groundwater and benthic porewater are determined by the degree of benthic coupling. Experimental manipulations in a microcosm and a survey of the literature demonstrate the ability of the sediment-associated microphytobenthos (MPB) to regulate both the light- and nutrient-environment in the overlying water column. The model predicts that the growth dynamics of the MPB are such that the benthic/water column interactions tend towards one of two stable states. In one, a well-developed population of MPB restricts resuspension of particulate material and efflux of dissolved nutrients, resulting in clear and nutrient-poor overlying waters. This condition does not favor growth of Aureococcus. In the alternative state, erosion of the MPB results in turbid, nutrient-rich waters that do favor bloom initiation. Alternation between the states is caused by external physical forcing, through wind-driven mixing of the water column. Field data from Quantuck Bay, New York (USA), failed to document the transition from non-bloom to bloom conditions. Even so, they are consistent with the model’s predictions.     

Characterization and comparisons of five N2-fixing Azolla-Anabaena associations,I. Optimization of growth conditions for biomass increase and N content in a controlled environment*

Abstract Biomass increase, C and N content, C₂H₂ reduction, percentage dry weight and chlorophyll a/b ratios were determined for clones of Azolla caroliniana Willd., A. filiculoides Lam., A. mexicana Presl., and A. pinnata R. Br. as a function of nutrient solution, pH, temperature, photoperiod, and light intensity in controlled environment studies. These studies were supplemented by a glasshouse study. Under a 16 h, 26°C day at a light intensity of 200 μmol m^?2 s^?1 and an 8 h, 19° C dark period, there was no significant difference in the growth rates of the individual species on the five nutrient solutions employed. Growth was comparable from pH 5 to pH 8, but decreased at pH 9. Using the same photoperiod and light intensity but constant growth temperatures of 15–40°C, at 5°C intervals, the individual species exhibited maximum growth, nitro-genase (N²ase) activity and N content at either 25° or 30°C. There was no difference in the temperature optima at pH 6 and pH 8. The tolerance of the individual species to elevated temperature was indicated to be A. mexicana> A. pinnata> A. caroliniana> A.filiculoides. At the optimum temperature, growth rates increased with increasing photoperiod at both pH 6 and pH 8 but N₂ase activity was usually highest at a 16 h light period. At photon flux densities of 100, 200, 400 and 600 μmol m^?2 s^?1, during a 16 h light period and optimum growth temperature of the individual species, N₂ase activity was saturated at less than 200 μmol m^?2 s^?1 and growth at 400 μmol m^?2 s^?1.No interacting effects of light and pH were noted for any species, nor were light intensities up to 1700 μmol m^?2 s^?1 detrimental to the growth rate or N content of any species in a 5 week glasshouse study with a natural 14.5 h light period and a constant temperature of 27.5°C. Using the optimum growth temperature, a 16 h light period, and a photon flux density of at least 400 μmol m^?2 s^?1, the Azolla species all doubled their biomass in 2 days or less and contained 5–6% N on a dry weight basis.     

The response of three chydorid species to temperature, pH and food

The responses of three chydorid species, Chydorus sphaericus(O.F. Müller), Alona affinis (Leydig) and Alonopsis elongata (Sars) to temperature, pH and food type were examined. Egg development time of all species decreased with increasing temperature, although the degree of change was different for each species. C. sphaericus had the fastest development time at all temperatures, and A. elongata the slowest. pH also affected the egg development time of each species differently. A. elongata failed to reproduce at low and medium pH, the egg development time of C. sphaericus was fastest at high pH while that of A. affinis was fastest at low pH. Food type was found to have significant effects on the population growth of individual species. C. sphaericus populations grew equally well in all three food types provided, and grew more than the other two species when fed on an algae culture, and filtered pond water. A. affinisand A. elongata populations grew best when fed on a detritus food source. The responses of each species to the different variables tested are discussed in relation to field observations of their distribution and abundance.     

Newly dominant benthic invertebrates reshape competitive networks on contemporary Caribbean reefs

Competition is a fundamental process structuring ecological communities. On coral reefs, space is a highly contested resource and the outcomes of spatial competition can dictate community composition. In the Caribbean, reefs are increasingly dominated by non-scleractinian species like sponges, gorgonians, and zoanthids, yet there is a paucity of data on interactions between these increasingly common organisms and historically dominant corals. Here, we investigated interactions among these groups of sessile benthic invertebrates to better understand the role of spatial competition in shaping benthic communities on Caribbean reefs. We coupled surveys of competitive interactions on the reef with a common garden competition experiment to determine the frequency and outcome of interference competition among eight focal species. We found that competitive interactions were pervasive on Florida reefs, with 60% of sessile benthic invertebrates interacting with at least one other invertebrate. Increasingly common non-scleractinian species were some of the most abundant taxa and consistently outcompeted the contemporarily common scleractinian species Porites porites and Siderastrea siderea. The encrusting gorgonian, Erythropodium caribaeorum, was the most aggressive species, reducing the live area of its competitors on average 42% ± 7.04 (SE) over the course of 5 months. Surprisingly, the most aggressive species declined in size when competing, while some less aggressive species were able to increase or maintain area, suggesting a trade-off between aggressiveness and growth. Our findings suggest that competition among sessile invertebrates is likely to remain an important process in structuring coral reefs, but that the optimal strategies for maintaining space on the benthos may change. Importantly, many non-scleractinian species that now dominate reefs appear to be superior competitors, potentially increasing the stress on corals on contemporary reefs.

     

DENSITY-DEPENDENT GROWTH,ECOLOGICAL STRATEGIES,AND EFFECTS OF NUTRIENTS AND SHADING ON BENTHIC DIATOM SUCCESSION IN STREAMS1

The importance of immigration, growth, and competition for nutrients and light in benthic diatom succession was studied in experimental channels in a low-nutrient stream. Diatom accumulation was greater in channels enriched with nitrate and phosphate (NP) than in control channels, reaching about 5 × 10⁶ and 2 × 10⁶ cells-cm^?2, respectively, after 30 d. Shading during late stages of community development reduced algal standing crop. Synedra ulna (Nitz.) Ehr. and Achnanthes minutissima Kütz. were codominant during early stages of community development in both habitats, but succession to an A. minutissima-dominated community was much faster in NP-enriched than in control conditions. Species dominating early stages tended to immigrate quickly, whereas species that increased in relative abundance during community development had either fast growth rates or fast immigration and average growth rates. Decreases in growth rates indicated resource supply became limiting during community development in control and enriched channels. Density-dependent competition was indicated because nutrient concentrations in the water column and light did not decrease during the 30-d study. Species autecologies were defined by effects of nutrient enrichment, shading, and community development on species growth rates. Differing autecologies of early and late succession species indicated that competition for nutrients was more important than competition for light. Species autecologies also indicated ecological strategies. The species most stimulated by nutrient enrichment were least able to maintain growth rates as algal abundances on substrata increased. In addition, these species that best sustained their growth rates during succession tended to have the highest immigration rates, indicating that drift and immigration may have been an important mechanism of persistence for some populations when resources become limiting within thick benthic mats.     

The response of stream fish to local and reach‐scale variation in the occurrence of a benthic aquatic macrophyte

1. The aquatic macrophyte Podostemum ceratophyllum has been shown to increase stream productivity, abundance and biomass of benthic invertebrates, and local occurrences of some stream fishes. However, experimental evidence that fishes preferentially associate with Podostemum is lacking, and the value of Podostemum as a predictor of stream fish assemblage composition has not been studied. 2. We conducted two short‐term (2 week), small‐scale (36 m²) experimental manipulations of Podostemum cover in the Conasauga River (Georgia and Tennessee, U.S.), and found higher abundances of benthic insectivorous fishes in patches with augmented (>80%) compared to reduced (7%) Podostemum cover. In an observational study, we quantified associations among percent cover of Podostemum, fish species richness, land cover, shoal length and base‐flow turbidity at 20 randomly selected shoals from a 39‐km reach that spanned a gradient of decreasing forest land cover. 3. Richness of all fish species and of lotic fishes peaked in the centre of the study reach, and richness was weakly correlated with predictor variables. Occupancy models for individual species also indicated that longitudinal position was a strong covariate for 13 of 19 species examined, with little support that Podostemum cover influenced occupancy. 4. Local associations may reflect choices by benthic fishes to utilise Podostemum, whereas downstream decline in fish species richness and Podostemum cover may reflect altered capacity of the system to support native species.     

Grazing intensity influences the strength of an associational refuge on temperate reefs

Recent studies have emphasized the role of positive interactions in ecological communities, but few have addressed how positive interactions are mediated by abiotic stress and biotic interactions. Here, I investigate the effect of a facilitator species on the abundance of macroalgae over a gradient of herbivory. Grazing by sea urchins can be intense on temperate reefs along the California coast, with benthic macroalgae growing exclusively in physical refuges and interspersed within colonies of the strawberry anemone, Corynactis californica. Field experiments indicated that the net effect of C. californica on turf algae was strongly nonlinear over a gradient in density of sea urchins. At low intensities of urchin grazing, the anemone and macroalgae competed for space, with algae capable of overgrowing C. californica. At intermediate grazing intensities, C. californica provided a refuge for turf algae but not for juvenile kelp. Neither turf algae nor kelp benefited from the presence of C. californica at the highest levels of grazing intensity, as sea urchins consumed nearly all macroalgae. The hump-shaped effect observed for C. californica contrasts with the prevailing view in ecological theory that positive interactions are more common in harsh environmental conditions. The results reported here qualify this view and underscore the need to evaluate positive interactions over a range of abiotic stress and consumer pressure.     

Radiation and soil temperature interactions on the growth and physiology of eastern white pine ( Pinus strobus L.) seedlings

A greenhouse experiment was set up during one growing season to test the hypothesis that soil temperature controls a significant part of the light response of eastern white pine (Pinus strobus L.) seedlings that is observed in the field. The experimental design was a three by three factorial split-plot design, with three levels of light availability: 10%, 40% and 80% of full light; and three levels of soil temperature: 16 °C, 21 °C, and 26 °C in the soil at midday. The results show significant interactions between light and soil temperature factors on several variables (gas exchange, root growth, leaf-mass ratio and leaf–mass per unit area), but not on shoot dry mass. These interactions indicate that, in the field, a significant proportion of the light response of young eastern white pine could result from changes in soil temperature, especially under conditions of limiting water availability. Our results suggest that soil temperature must be taken explicitly into account as a driving variable when relating the growth of young eastern white pine to photosynthetic radiation.     

Impact of two specialist insect herbivores on reproduction of horse nettle,Solanum carolinense

The frequency of coevolution as a process of strong mutual interaction between a single plant and herbivore species has been questioned in light of more commonly observed, complex relationships between a plant and a suite of herbivore species. Despite recognition of the possibility of diffuse coevolution, relatively few studies have examined ecological responses of plants to herbivores in complex associations. We studied the impact of two specialist herbivores, the horse nettle beetle, Leptinotarsa juncta, and the eggplant flea beetle, Epitrix fuscula, on reproduction of their host, Solanum carolinense. Our study involved field and controlled-environment experimental tests of the impact on sexual and potential asexual reproduction of attack by individuals of the two herbivore species, individually and in combination. Field tests demonstrated that under normal levels of phytophagous insect attack, horse nettle plants experienced a reduction in fruit production of more than 75% compared with plants from which insects were excluded. In controlled-environment experiments using enclosure-exclosure cages, the horse nettle's two principal herbivores, the flea beetle and the horse nettle beetle, caused decreases in sexual reproduction similar to those observed in the field, and a reduction in potential asexual reproduction, represented by root biomass. Attack by each herbivore reduced the numbers of fruits produced, and root growth, when feeding in isolation. When both species were feeding together, fruit production, but not root growth, was lower than when either beetle species fed alone. Ecological interactions between horse nettle and its two primary herbivores necessary for diffuse coevolution to occur were evident from an overall analysis of the statistical interactions between the two herbivores for combined assessment of fruit and vegetative traits. For either of these traits alone, the interactions necessary to promote diffuse coevolution apparently were lacking.     

Regional and local drivers of macroinvertebrate assemblages in boreal springs

Aim To identify the most important environmental drivers of benthic macroinvertebrate assemblages in boreal springs at different spatial scales, and to assess how well benthic assemblages correspond to terrestrially derived ecoregions. Location Finland. Methods Benthic invertebrates were sampled from 153 springs across four boreal ecoregions of Finland, and these data were used to analyse patterns in assemblage variation in relation to environmental factors. Species data were classified using hierarchical divisive clustering (twinspan ) and ordinated using non‐metric multidimensional scaling. The prediction success of the species and environmental data into a priori (ecoregions) and a posteriori (twinspan ) groups was compared using discriminant function analysis. Indicator species analysis was used to identify indicator taxa for both a priori and a posteriori assemblage types. Results The main patterns in assemblage clusters were related to large‐scale geographical variation in temperature. A secondary gradient in species data reflected variation in local habitat structure, particularly abundance of minerogenic spring brooks. Water chemistry variables were only weakly related to assemblage variation. Several indicator species representing southern faunistic elements in boreal springs were identified. Discriminant function analysis showed poorer success in classifying sites into ecoregions based on environmental than on species data. Similarly, when classifying springs into the twinspan groups, classification based on species data vastly outperformed that based on environmental data. Main conclusions A latitudinal zonation pattern of spring assemblages driven by regional thermal conditions is documented, closely paralleling corresponding latitudinal patterns in both terrestrial and freshwater assemblages in Fennoscandia. The importance of local‐scale environmental variables increased with decreasing spatial extent. Ecoregions provide an initial stratification scheme for the bioassessment of benthic macroinvertebrates of North European springs. Our results imply that climate warming, landscape disturbance and degradation of spring habitat pose serious threats to spring biodiversity in northern Europe, especially to its already threatened southern faunistic elements.     

Environmental correlates of the abundance and distribution of <Emphasis Type="Italic">Belonesox belizanus</Emphasis> in a novel environment

Environmental factors, such as temperature, dissolved oxygen, salinity, and pH may influence the population dynamics of an introduced species by imposing limits to its distribution and abundance. In 1957, the non-indigenous pike killifish, Belonesox belizanus Kner, was released into a Miami-Dade County, Florida, canal, from which it has since spread across most of south Florida. The main goal of this study was to characterize patterns of covariation between B. belizanus density and temporal, spatial, and physicochemical variables, and attempt to identify which physicochemical variables may explain variation in densities of this species. Results of AIC_c model selection indicated that patterns of physicochemical variables such as pH, salinity, and temperature correlated with annual change in B. belizanus density, and that these physicochemical-density patterns were mesohabitat specific. For the southern most sites, the interaction between temperature and salinity provide the best model to explain B. belizanus density, whereas variability in pH provides the best model at northern sites. These patterns of covariance between density and specific physicochemical variables suggests that specific mesohabitat characteristics may play a role in mediating the physiological, behavioral, and/or ecological performance of this introduced species in Florida and elsewhere. Future studies will test hypotheses on the direct and indirect effects of these physicochemical variables within the context of specific mesohabitats on the behavior and physiology of B. belizanus in its novel environment in South Florida.     

Effects of temperature and pH on growth and photosynthesis of the thermophilic cyanobacterium Synechococcus lividus as measured by pulse-amplitude modulated fluorometry

In this study, the effects of five different temperatures and pH conditions on growth and photosynthetic performance of Synechococcus lividus Copeland from Taiwan were monitored in the field and the laboratory by using an underwater pulse‐amplitude modulated (Diving‐PAM) fluorometer. In the field, the optimal growth temperature of S. lividus was found to be 57°C. Such a finding was congruent with the growth rate in the laboratory culture, in which the optimal growth temperatures ranged from 45 to 60°C. In photosynthetic performance, the light‐saturated maximum relative electron transport rate (ETR_max) and the light‐limited slope (α^ETR) exhibited highest values at 50°C. At five different pH conditions, higher ETR_max and α^ETR were observed from pH 7 to 9. In addition, regression analysis demonstrated a significant positive relationship between the growth rate and the ETR_max values (R² = 0.9527), indicating that the growth of S. lividus was largely restricted to its photosynthetic performance. In conclusion, the photosynthetic performance and growth of the thermophilic cyanobacterium S. lividus were sensitive to fluctuations in temperature but not in pH. The present investigation offers a better understanding of the photosynthetic physiology.     

Ecological synopsis for Chironomus flaviplumus (Diptera: Chironomidae) in the Jung-rang stream

In this study, we conducted field sampling to assess the relative influences of water and substrate quality on benthic macroinvertebrate communities living in the Jung‐rang stream, Korea. We collected macroinvertebrates and assessed physicochemical variables from three sites in the stream between May 2001 and January 2002. Sites were located approximately within 20 km from the headwater. The structure of the benthic macroinvertebrate communities may be strongly affected by the physical conditions inherent to the environment in which they live. In this stream, we detected profound differences in water temperature (18 ～ 19.75°C), the concentrations of suspended solids (3.935 ～ 7.87 mg/L), and demand for chemical oxygen (10.575 ～ 14.425 mg/L). Nonylphenol concentrations ranging from 0.375 to 0.55 ng/mL were found in the water, and the sediments were measured to contain between 2.45 and 3.425 ng/mL. We identified a total of 20 macroinvertebrate species, including seven species of Chironomidae, the most abundant of which was Chironomus flaviplumus. At none of the sites did we find any significant differences in the structure of the communities. Using canonical correspondence analysis for the relation of species and environmental variables, chemical oxygen demand and suspended sediment gradients (SS) had significant preferences for site 1 with SS. The results of our study suggest that physico‐chemical variables exerted complex effects on the structure of the benthic community in the Jung‐rang stream. This study supports the contention that physico‐chemical analyses as well as community analysis are valuable tools to assess the effect of pollution on the ecological condition of a stream. Chironomids, in particular, showed a high degree of tolerance against contaminants.     

Modeling in vitro cholesterol reduction in relation to growth of probiotic Lactobacillus casei

Lactobacillus casei LA‐1 isolated from a nondairy fermented source was evaluated for its in vitro ability to reduce cholesterol. The bacterium tested positive for bile salt deconjugation in relation to cholesterol removal. Tested growth‐associated physiological variables such as pH, temperature and inoculum size were all found to have significant effects on in vitro cholesterol reduction and biomass production (both P < 0.005). Furthermore, a central composite design was used to evaluate the effects of significant variables and their interactions. A linear regression model was developed for in vitro cholesterol reduction as a function of growth‐associated variables. Maximum cholesterol reduction achieved was 45% whereas maximum biomass yield of 2.34 optical density was observed at the central point. Our study possibly indicates that the growth of L. casei LA‐1 depends on its cholesterol removing ability.     

Regeneration Patterns of European Oak Species (Quercus petraea (Matt.) Liebl., Quercus robur L.) in Dependence of Environment and Neighborhood

Quercus robur L. (pedunculate oak) and Quercus petraea (Matt.) Liebl. (sessile oak) are two European oak species of great economic and ecological importance. Even though both oaks have wide ecological amplitudes of suitable growing conditions, forests dominated by oaks often fail to regenerate naturally. The regeneration performance of both oak species is assumed to be subject to a variety of variables that interact with one another in complex ways. The novel approach of this research was to study the effect of many ecological variables on the regeneration performance of both oak species together and identify key variables and interactions for different development stages of the oak regeneration on a large scale in the field. For this purpose, overstory and regeneration inventories were conducted in oak dominated forests throughout southern Germany and paired with data on browsing, soil, and light availability. The study was able to verify the assumption that the occurrence of oak regeneration depends on a set of variables and their interactions. Specifically, combinations of site and stand specific variables such as light availability, soil pH and iron content on the one hand, and basal area and species composition of the overstory on the other hand. Also browsing pressure was related to oak abundance. The results also show that the importance of variables and their combinations differs among the development stages of the regeneration. Light availability becomes more important during later development stages, whereas the number of oaks in the overstory is important during early development stages. We conclude that successful natural oak regeneration is more likely to be achieved on sites with lower fertility and requires constantly controlling overstory density. Initially sufficient mature oaks in the overstory should be ensured. In later stages, overstory density should be reduced continuously to meet the increasing light demand of oak seedlings and saplings.     

Species‐specific mediation of temperature and community interactions by multiple foundation species

Foundation species can provide habitat that modify abiotic and biotic processes that contribute to ecosystem function. While many studies have focused on the processes and consequences of a focal foundation species, understanding the ecological equivalence of co‐occurring foundation species is important to identify key species responsible for ecosystem function. Here, we investigated the relative contributions of co‐occurring foundation species on abiotic (temperature) and biotic responses of invertebrate species (recruitment, persistence, growth and survival). In a series of experimental field studies, we manipulated foundation species to measure invertebrate recruitment, persistence, and predation. A laboratory experiment measured foundation species effects on herbivore growth. Results demonstrated that macroalgal (Fucus vesiculosus ecad and Ascophyllum nodosum ecad scorpioides) intermediate foundation species provide habitat, food, and alleviate abiotic stress for dominant littorinid herbivores that surpass that provided by the primary species (Spartina alterniflora). These foundation effects were species‐specific with F. vesiculosus ecad important for early life‐history stages (enhanced recruitment and early growth of littorinid snails) and A. nodosum ecad important later on as a refuge from predators (Carcinus meanas) and stressful temperature. Understanding of the different effects of co‐occurring foundation species on population and community processes is necessary for predicting community response to natural disturbance, species invasion, and ecosystem‐based management actions.