Biotic and abiotic effects on cohort size distributions in fish

Intraspecific variation in body size is common in animals and plants. Body size affects trophic interactions like foraging ability and vulnerability to predation, which in turn affect individual fitness as well as population stability and extinction risk. Experimental and theoretical work has shown that the size distribution of individuals within cohorts is strongly influenced by intraspecific competition for resources, often leading to skewed frequency distributions. However, little is known about the effects of environmental factors such as climate and eutrophication on the cohort size‐structure of natural populations. We use a long‐term time series of scientific monitoring of a freshwater fish (European perch Perca fluviatilis) to investigate the effects of density dependence, predation, nutrient availability, climate and the timing of spawning on the cohort size distributions. We find that the mean length of the fish is best predicted by the extrinsic factors phosphorus concentration and summer temperature, and the densities of the different age‐classes, whereas the skewness of the length distribution is best predicted by phosphorus concentration, summer temperature, abundance of small fish, and the timing of spawning. Higher nutrient levels, temperatures and densities of small fish increase food availability and thus reduce competition, which is reflected in increased mean length and decreased skewness. The timing of spawning affects skewness presumably through changes in the initial size variation of the cohort and the length of the first growth season. Our results indicate that higher temperatures increase the mean length and decrease skewness due to the concurrent eutrophication of the lake. The study thereby highlights the potential impact of human‐induced environmental change on the size structure of fish populations. More studies are needed to understand better the complex mechanisms through which these factors alter the intensity of intraspecific competition in fish communities.     

Biotic and abiotic effects on endoparasites infecting Dipodomys and Perognathus species

Between 1989 and 1998, 3,504 rodents of the genera Dipodomys and Perognathus were collected from 4 permanent collecting sites on the University of New Mexico's Long Term Ecological Research station, located on the Sevilleta National Wildlife Refuge (SNWR), Socorro County. New Mexico. All animals were killed and examined for endoparasites (acanthocephalans, cestodes, coccidia, and nematodes). The present report focuses on 3 endoparasite groups, cestodes, coccidia, and nematodes. Specific analyses address how prevalence changes were related to abiotic factors such as habitat, season, or precipitation, and how prevalence of each parasite species in each host species differed in relation to host age, host sex, host reproductive status, host body mass, host density, parasite-parasite interactions, and host specificity. A logistic regression was used to determine which host characters and which abiotic factors are correlated with a parasite infection. Significant variables for at least half of the parasites include season, site, and winter precipitation. However, no parasite prevalences were correlated, and significant variables were not identical between parasites, indicating that each parasite species varied independently and that no generalizations can be drawn. The parasite prevalences in these rodents on the SNWR vary in independent and complex ways.     

Biotic and abiotic consequences of differences in leaf structure

Both within and between species, leaves of plants display wide ranges in structural features. These features include: gross investments of carbon and nitrogen substrates (e.g. leaf mass per unit area); stomatal density, distribution between adaxial and abaxial surfaces, and aperture; internal and external optical scattering structures; defensive structures, such as trichomes and spines; and defensive compounds, including UV screens, antifeedants, toxins, and silica abrasives. I offer a synthesis of selected publications, including some of my own. A unifying theme is the adaptive value of expressing certain structural features, posed as metabolic costs and benefits, for (1) competitive acquisition and use of abiotic resources (such as water, light and nitrogen) and (2) regulation of biotic interactions, particularly fungal attack and herbivory. Both acclimatory responses in one plant and adaptations over evolutionary time scales are covered where possible. The ubiquity of trade-offs in function is a recurrent theme; this helps to explain diversity in solutions to the same environmental challenges but poses problems for investigators to uncover numerous important trade-offs. I offer some suggestions for research, such as on the need for models that integrate biotic and abiotic effects (these must be highly focused), and some speculations, such as on the intensity of selection pressures for these structures.     

Biotic and abiotic immobilization of ammonium, nitrite, and nitrate in soils developed under different tree species in the Catskill Mountains, New York, USA

Nitrogen retention in soil organic matter (SOM) is a key process influencing the accumulation and loss of N in forest ecosystems, but the rates and mechanisms of inorganic N retention in soils are not well understood. The primary objectives of this study were to compare ammonium (NH₄⁺), nitrite (NO₂^?), and nitrate (NO₃^?) immobilization among soils developed under different tree species in the Catskill Mountains of New York State, and to determine the relative roles of biotic or abiotic processes in soil N retention. A laboratory experiment was performed, where ¹⁵N was added as NH₄⁺, NO₂^?, or NO₃^? to live and mercury‐treated O horizon soils from three tree species (American beech, northern red oak, sugar maple), and ¹⁵N recoveries were determined in the SOM pool. Mercuric chloride was used to treat soils as this chemical inhibits microbial metabolism without significantly altering the chemistry of SOM. The recovery of ¹⁵N in SOM was almost always greater for NH₄⁺ (mean 20%) and NO₂^? (47%) than for NO₃^? (10%). Ammonium immobilization occurred primarily by biotic processes, with mean recoveries in live soils increasing from 9% at 15 min to 53% after 28 days of incubation. The incorporation of NO₂^? into SOM occurred rapidly (<15 min) via abiotic processes. Abiotic immobilization of NO₂^? (mean recovery 58%) was significantly greater than abiotic immobilization of NH₄⁺ (7%) or NO₃^? (7%). The incorporation of NO₂^? into SOM did not vary significantly among tree species, so this mechanism likely does not contribute to differences in soil NO₃^? dynamics among species. As over 30% of the ¹⁵NO₂^? label was recovered in SOM within 15 min in live soils, and the products of NO₂^? incorporation into SOM remained relatively stable throughout the 28‐day incubation, our results suggest that NO₂^? incorporation into SOM may be an important mechanism of N retention in forest soils. The importance of NO₂^? immobilization for N retention in field soils, however, will depend on the competition between incorporation into SOM and nitrification for transiently available NO₂^?. Further research is required to determine the importance of this process in field environments.     

Biotic–abiotic hybrids for bioanalytics and biocatalysis

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Germination responses to abiotic stress shape species distributions on coastal dunes

Plant species occupy distinct zones on coastal dunes, but the mechanisms limiting their distributions have not been fully explained. We combined field surveys of plant distributions and abiotic conditions with controlled germination experiments to assess the contribution of germination requirements to plant zonation. Species presence and abiotic conditions were measured in ten transects across the barrier dune at Waquoit Bay, Massachusetts. Germinating seeds of six species were exposed to four fully crossed treatments: pre-treatment (soaked in fresh water, soaked in salt water, or not soaked), temperature (low, moderate, or high), soil salinity (none, moderate, or high), and light (full light, shade, dark). Species distributions in the field were affected by both distance from the shore and presence of dominant shrubs. Germination tolerance of soil salinity reflected species zonation: species found on the front slope of the dune tolerated salinity, while germination of other species was limited by salinity alone or by salinity in combination with high temperature. Shrubs reduced soil surface temperature and decreased light, but these conditions had limited effects on germination. These results indicate that limitations to germination can contribute to explaining species distributions on coastal dunes.     

Influence of species and abiotic factors on extreme tree ring modulation:

 The influence of biotic (tree species) and abiotic factors (regional climate, altitude and stand aspect) on extreme tree-ring widths is dendroecologically investigated. Negative pointer years are observed when abrupt radial growth reductions (exceeding 40%) occurred synchronously in a given tree population. Pointer year intensity is expected to follow several theoretical models when trees are sampled along ecological gradients in various site conditions. Hypotheses are made about expected patterns of pointer year spatial distribution. They are compared with observed results obtained with Norway spruce [Picea abies (L.) Karst.] and silver fir (Abies alba Mill.) sampled in two French Alpine valleys (Tarentaise and Maurienne) with different regional climates, on two aspects and three altitude levels. Results reveal that extreme years follow expected patterns well. Thus, clear site modulations are observed in 1956 and 1986 (only trees located in Maurienne reacted). Moreover, species differences are observed, with typical cases of single species sensitivity (for spruce, occurring in 1962 and 1992). Abiotic factors such as altitude and aspect also involve clear pointer year patterns, such as narrow rings in 1976 due to summer drought that occurred especially at lower altitudes. However, some observed extreme years sometimes appear to be a combination of two (or three) of these one-factor theoretical models (e.g. 1921 with both lower altitude level and only observed in Tarentaise; 1948 involving both higher altitude and northern slopes). These results demonstrate the consistency of various tree-ring and climate relationships along ecological gradients.     

Biotic and abiotic initiators for rishitin formation and accumulation in tomato

γ-Ray irradiation of pre-sowing seeds of tomato did not trigger the formation of the phytoalexin “rishitin” in either leaves or fruits of tomato plants through different growth seasons. Application of copper sulfate initiated rishitin formation in both leaves and fruits. Increasing of γ-ray dose was accompanied by decreasing rishitin accumulation in the presence of copper sulfate. Rishitin of tomato leaves was found to be reduced significantly, concomitant with increasing the disease incidence for late and early blight, andFusarium wilt disease, after applying γ-irradiation, in the case of biotic initiatorsPhytophthora infestans, Alternaria solani orFusarium oxysporum alone or together with the abiotic inducer copper sulfate. Shelf-extending γ-ray doses of 1.0, 1.5 and 2.0 kGy decreased rishitin amounts in tomato fruits treated with copper sulfate alone or infected withPhytophthora infestans. Also, the amount of formed rishitin was reduced by extending the storage period.     

Factors determining distributions of tree species and plant functional types

Plant functional types have been identified by the International Geosphere Biosphere Program as functionally similar basic plant types, especially trees, as needed for global ecological modeling. Based to some extent on an earlier set of pheno-physiognomically defined plant types, a Global Biome Model was produced but has not satisfied all the desired functional criteria posed by IGBP physiologists and modelers. This paper asks two questions: what are the main environmental factors which limit terrestrial plant types, especially tree types; and how many types of potential vegetation are needed to cover the world's terrestrial vegetation patterns? Based on the main environmental factors recognized, a model of world potential dominant vegetation types was produced and used to estimate the minimal number of vegetation types needed. The resulting set of 40 potential dominant vegetation types may serve as an initial basis for a structural-functionally based set of world plant functional types.     

Biotic and abiotic interactions between surface and interstitial systems in rivers

Water chemistry and community assemblages of surface and interstitial invertebrates were studied at seven sues on the French Rivers Rhône and Am at surface and at 50 cm depth into the bed sediments Chemical factors allowed differentiation of surface water from groundwater and detection of water exchanges defining clear downwelling and upwelling zones At some sites, interstitial water showed both surface and phreatic conditions, characterizing the underflows of the Rhone or of the Am In the interstitial area, most taxa showed no significant correlations with water chemistry Some epigean and hypogean fauna showed correlations with certain factors Clear relationships appeared between the water exchanges and the distribution of surface and interstitial faunas In interstitial samples, epigean and some hypogean species characterized the downwelling zones while others seemed to be strictly linked to the upwelling zones In surface samples, the presence of hypogean species was associated with regions of groundwater upwelling     

Differential response to abiotic stress controls species distributions at biogeographic transition zones

Understanding range limits is critical to predicting species responses to climate change. Subtropical environments, where many species overlap at their range margins, are cooler, more light‐limited and variable than tropical environments. It is thus likely that species respond variably to these multi‐stressor regimes and that factors other than mean climatic conditions drive biodiversity patterns. Here, we tested these hypotheses for scleractinian corals at their high‐latitude range limits in eastern Australia and investigated the role of mean climatic conditions and of parameters linked to abiotic stress in explaining the distribution and abundance of different groups of species. We found that environmental drivers varied among taxa and were predominantly linked to abiotic stress. The distribution and abundance of tropical species and gradients in species richness (alpha diversity) and turnover (beta diversity) were best explained by light limitation, whereas minimum temperatures and temperature fluctuations best explained gradients in subtropical species, species nestedness and functional diversity. Variation in community structure (considering species composition and abundance) was most closely linked to the combined thermal and light regime. Our study demonstrates the role of abiotic stress in controlling the distribution of species towards their high‐latitude range limits and suggests that, at biogeographic transition zones, robust predictions of the impacts of climate change require approaches that account for various aspects of physiological stress and for species abundances and characteristics. These findings support the hypothesis that abiotic stress controls high‐latitude range limits and caution that projections solely based on mean temperature could underestimate species’ vulnerabilities to climate change.     

Biotic and abiotic methane releases from Lake Biwa sediment slurry

To determine the rate and mechanism of CH₄ production in Lake Biwa sediment, slurry was prepared and incubated. Surface sediment (sed) slurry (1.5–6cm) showed a CH₄ release rate (4.9–9.5nmolg-dry-sed^–1 day^–1) higher than that observed in the 5- to 10-cm sediment slurry (0.2–2nmolg-dry-sed^–1 day^–1). Methane release from the surface (1.5–6cm) sediment slurry was biotic and was inhibited by addition of 2-bromoethanesulfonate (BES, an inhibitor of CH₄ production), whereas that from 5- to 10-cm sediment slurry was abiotic. The addition of BES, HNO₃, and O₂ showed no effect on the CH₄ release rate from the 5- to 10-cm sediment slurry. In addition, tracers (NaH¹³CO₃, ¹³CH₃COONa) were not incorporated into the released CH₄. However, ¹³C of CH₄ released from the 5- to 10-cm sediment slurry (–74.0 ± 0.6) indicated that this CH₄ was produced by bacterial metabolism in the past, stored by adsorption on the surface of clay minerals in the sediment, and then released abiotically by desorption from the sediment slurry as a result of a decrease in hydraulic pressure and CH₄ concentration in the pore water. This CH₄ stored by adsorption could be extracted by autoclaving. In the sediment below 5cm, bacterial activity for CH₄ production ceased, possibly because of the limitated availability of H₂. To clarify the mechanism of CH₄ production in the sediment, biotic CH₄ production and the abiotic CH₄ release found here should be estimated separately.     

Biotic and abiotic preferences of the cladoceran invader Limnosida frontosa

During the late 1980s and early 1990s, the cladoceran Limnosida frontosa invaded several lakes within its natural range in southeastern Norway. In this project, we wanted to study the types of lakes preferred by Limnosida. We also wanted to evaluate the potential competitive effects on other zooplankton species. In a survey of 65 Norwegian lakes, Limnosida showed preference for lakes of low Ca concentrations and low productivity. This is probably due to decreased competition from species with higher Ca requirements and a lower fish predation on zooplankton in these lakes compared to more productive lakes. Particle size preferences of Limnosida were studied and compared with those of the microfiltrator Daphnia magna, as there was no published information on the food preference of Limnosida.When fed monodisperse fluorescent latex beads (0.5, 1.0, 6.0 m), Limnosida strongly selected the largest beads, while D. magna had a more nonselective feeding behaviour. Mesh sizes of Limnosida's filtering appendages were 0.4–1.2 m depending on the animal size, and the particle selection was correlated with the filter mesh sizes. Limnosida should thus be considered a low efficiency grazer on bacteria and -algae. Hence, this species probably does not interfere significantly with microfiltrators like Diaphanosoma brachyurumand most daphnids. This was supported by community analysis of lakes with and without Limnosida. In general, Limnosida commonly co-occurred with a number of filter-feeding cladocerans, and we found no sign of competitive exclusion in lakes where the species has become established.     

Geological substrates shape tree species and trait distributions in african moist forests

Background

Understanding the factors that shape the distribution of tropical tree species at large scales is a central issue in ecology, conservation and forest management. The aims of this study were to (i) assess the importance of environmental factors relative to historical factors for tree species distributions in the semi-evergreen forests of the northern Congo basin; and to (ii) identify potential mechanisms explaining distribution patterns through a trait-based approach.

Methodology/Principal Findings

We analyzed the distribution patterns of 31 common tree species in an area of more than 700,000 km² spanning the borders of Cameroon, the Central African Republic, and the Republic of Congo using forest inventory data from 56,445 0.5-ha plots. Spatial variation of environmental (climate, topography and geology) and historical factors (human disturbance) were quantified from maps and satellite records. Four key functional traits (leaf phenology, shade tolerance, wood density, and maximum growth rate) were extracted from the literature. The geological substrate was of major importance for the distribution of the focal species, while climate and past human disturbances had a significant but lesser impact. Species distribution patterns were significantly related to functional traits. Species associated with sandy soils typical of sandstone and alluvium were characterized by slow growth rates, shade tolerance, evergreen leaves, and high wood density, traits allowing persistence on resource-poor soils. In contrast, fast-growing pioneer species rarely occurred on sandy soils, except for Lophira alata.

Conclusions/Significance

The results indicate strong environmental filtering due to differential soil resource availability across geological substrates. Additionally, long-term human disturbances in resource-rich areas may have accentuated the observed patterns of species and trait distributions. Trait differences across geological substrates imply pronounced differences in population and ecosystem processes, and call for different conservation and management strategies.     

Biotic and abiotic factors determining the distribution of two prawn species: Palaemon adspersus and P. squilla

Summary The reasons behind the absence of the prawn Palaemon adspersus and the presence of P. squilla in rockpools and on bare sand bottoms were studied. Some maximal abundances in different habitats are given. Introduction experiments into natural and artificial rockpools and measurements of tolerance towards low oxygen levels showed that nocturnal hypoxia excluded P. adspersus which was significantly more sensitive to oxygen depletion. Respiration rates measured by the closed-bottle method showed no interspecific difference.On bare sand bottoms P. aspersus was probably excluded by predators, since predator exclusion experiments in cages and predator inclusion experiments in containers showed that P. adaspersus was more vulnerable to predation than P. squilla.The costs for being able to cope with a wide array of habitat in P. squilla are probably balanced by the benefits of access to habitats such as intertidal rockpools, very shallow bottoms and deeper sand bottoms. Tolerance towards abiotic factors extends its habitat range upwards into shallower waters, and tolerance towards biotic factors, i.e. predation, extends it downwards.     

Biotic and abiotic factors driving the diversification dynamics of Crocodylia

Species diversity patterns are governed by complex interactions among biotic and abiotic factors over time and space, but are essentially the result of the diversification dynamics (differential speciation and extinction rates) over the long-term evolutionary history of a clade. Previous studies have suggested that temporal variation in global temperature drove long-term diversity changes in Crocodylia, a monophyletic group of large ectothermic organisms. We use a large database of crocodylian fossil occurrences (192 spp.) and body mass estimations, under a taxic approach, to characterize the global diversification dynamics of crocodylians since the Cretaceous, and their correlation with multiple biotic and abiotic factors in a Bayesian framework. The diversification dynamic of crocodylians, which appears to have originated in the Turonian (c. 92.5 Ma), is characterized by several phases with high extinction and speciation rates within a predominantly low long-term mean rate. Our results reveal long-term diversification dynamics of Crocodylia to be a highly complex process driven by a combination of biotic and abiotic factors which influenced the speciation and extinction rates in dissimilar ways. Higher crocodylian extinction rates are related to low body mass disparity, indicating selective extinctions of taxa at both ends of the body mass spectrum. Speciation rate slowdowns are noted when the diversity of the clade is high and the warm temperate climatic belt is reduced. Our finding supports the idea that temporal variations of body mass disparity, self-diversity, and the warm climate belt size provided more direct mechanistic explanations for crocodylian diversification than do proxies of global temperature.     

Spatial distributions of tree species in a subtropical forest of China

The spatial dispersion of individuals in a species is an important pattern that is controlled by many mechanisms. In this study we analyzed spatial distributions of tree species in a large-scale (20 ha) stem-mapping plot in a species-rich subtropical forest of China. O-ring statistic was used to measure spatial patterns of species with abundance >10. Ω_0–10, the mean conspecific density within 10 m of a tree, was used as a measure of the intensity of aggregation of a species. Our results showed: (1) aggregated distribution was the dominant pattern in the plot. The percentage of aggregated species decreased with increased spatial scale. (2) The percentages of significantly aggregated species decreased from abundant to intermediate and to rare species. Rare species was more strongly aggregated than common species. Aggregation was weaker in larger diameter classes. (3) Seed traits determined the spatial patterns of trees. Seed dispersal mode can influence spatial patterns of species, with species dispersed by both modes being less clumped than species dispersed by animal or wind, respectively. Considering these results, we concluded that seed dispersal limitation, self-thinning and habitat heterogeneity primarily contributed to spatial patterns and species coexistence in the forest.