Diversity In Natural Ecosystems Research Articles

Analyzing mechanisms regulating diversity in rangelands through comparative studies: a case in the southwestern Pyrennees

The preservation of the floristic diversity of natural ecosystems and the maintenance of extensive livestock grazing are two of the major priorities of European Union agricultural and environmental policies. Temperate natural and seminatural grasslands are among the most threatened ecosystems in Europe. In order to establish the most appropriate management practices that prevent degradation and maintain the richness of these ecosystems, detailed analyses of the mechanisms that regulate biodiversity of the communities are particularly necessary. In this study we make a comparative analysis of the species richness and the diversity of the main rangeland communities in a widespread, heterogeneous area located in the Western Spanish Pyrennees. The nature and the contribution of perennials and annuals to the diversity patterns encountered are studied and related to the mechanisms suggested to regulate diversity in each case. Higher diversity values were reported in more environmentally stressed, xeric and moist communities. High spatial and temporal heterogeneity and low rates of competitive displacement related to the scarcity of basic resources are among the factors suggested to regulate the diversity of these communities. In areas where environmental factors are more favorable, such as perennial-dominated mesic rangelands, the enhancement of the diversity seemed more dependent on biotic disturbances, such as herbivory, that decreased the cover of perennials and favored the recruitment of short-lived species. Dispersal processes related to traditional nomadic grazing allow a flow of species from one rangeland to another but also enhance the establishment of species coming from lowland habitats. Most of the annuals enhancing the diversity of the mesic community were ruderals. The consideration of ruderals as exotics or as species belonging to this grazing ecosystem poses an interesting, controversial topic related to the ecological quality of the diversity estimated for these communities.

Biogeochemistry of trace metals in the ocean

A variety of metallic elements, particularly Fe and Zn, are considered essential for biological processes in a variety of natural ecosystems, but are generally present only in trace amounts. Although their essential nature in terrestrial ecosystems has been known for many decades, it is only in recent years that scientific methodology has improved to the point that the biogeochemical behaviour of trace metals can be adequately studied in aquatic ecosystems such as the ocean. This paper reviews some of the recent scientific progress and demonstrates how conventional thinking about the biogeochemical role of trace metals in the ocean has been advanced by the findings of this research. In particular, it is now clear that the availability of several trace elements is a factor that controls phytoplankton growth in the ocean.

Mycorrhizal fungal diversity determines plant biodiversity, ecosystem variability and productivity

The functioning and stability of terrestrial ecosystems are determined by plant biodiversity and species composition1,2,3,4,5. However, the ecological mechanisms by which plant biodiversity and species composition are regulated and maintained are not well understood. These mechanisms need to be identified to ensure successful management for conservation and restoration of diverse natural ecosystems. Here we show, by using two independent, but complementary, ecological experiments, that below-ground diversity of arbuscular mycorrhizal fungi (AMF) is a major factor contributing to the maintenance of plant biodiversity and to ecosystem functioning. At low AMF diversity, the plant species composition and overall structure of microcosms that simulate European calcareous grassland fluctuate greatly when the AMF taxa that are present are changed. Plant biodiversity, nutrient capture and productivity in macrocosms that simulate North American old-fields increase significantly with increasing AMF-species richness. These results emphasize the need to protect AMF and to consider these fungi in future management practices in order to maintain diverse ecosystems. Our results also show that microbial interactions can drive ecosystem functions such as plant biodiversity, productivity and variability.

Biodiversity enhances ecosystem reliability

Biodiversity may represent a form of biological insurance against the loss or poor performance of selected species1. If this is the case, then communities with larger numbers of species should be more predictable with respect to properties such as local biomass2. That is, larger numbers of species should enhance ecosystem reliability, where reliability refers to the probability that a system will provide a consistent level of performance over a given unit of time3. The validity of this hypothesis has important ecological, management and economic implications given the large-scale substitution of diverse natural ecosystems with less diverse managed systems4. No experimental evidence, however, has supported this hypothesis5. To test this hypothesis we established replicated microbial microcosms with varying numbers of species per functional group. We found that as the number of species per functional group increased, replicate communities were more consistent in biomass and density measures. These results suggest that redundancy (in the sense of having multiple species per functional group6,7,8) is a valuable commodity, and that the provision of adequate redundancy may be one reason for preserving biodiversity.

Description of prokaryotic biodiversity along the salinity gradient of a multipond solar saltern by direct PCR amplification of 16S rDNA

New methods based on PCR amplification of 16S rRNA genes from DNA samples extracted directly from the environment allow the description of microbial diversity in natural ecosystems without the need for cultivation. We have applied this technique to an extreme environment presumed to have very low diversity: the crystallizer ponds of a marine saltern with salinity over NaCl saturation. The molecular methodology has shown that indeed very low diversity can be found here. Prokaryotes belonging to the Bacteria domain are a minor component and only members of a closely related cluster of sequences were found, all relatives of the α-Proteobacteria (ca. 83% to Rhodopseudomonas marina). Halophilic Archaea were as expected the largest component of biomass in this environment. All the clones sequenced corresponded again to a highly homologous cluster (probably members of the same genus). However, all the sequences diverged considerably from the ones of the described genera of halophilic Archaea, in fact the data are consistent with the idea that the 16S rRNA genes directly amplified from the saltern correspond to members of an undescribed genus. This is remarkable since many collection strains sequenced come specifically from this saltern. Furthermore, 16S rDNA obtained from archaeal cultures isolated from the same sample had no homology to the sequences obtained by PCR amplification, instead they appear to be members of the well known genus Haloarcula. However, this concurs with the findings of other authors who obtained different organisms by culture from those detected by the sequences retrieved directly by PCR. A possible explanation is that culturability, in standard media, is the exception rather than the rule. To study the biodiversity gradient present along the salinity gradient found in a multi-pond solar saltern we have also applied a novel molecular strategy. This method is based on the restriction digestion of a population of 16S rDNA sequences directly amplified from an environmental sample. Digested fragments separated by polyacrylamide gel electrophoresis generate characteristic profile data for estimation of diversity and overall similarities between the organisms of different environments. The methodology has been applied to a set of five ponds covering the salinity gradient from about twice that of seawater (6.4%) to NaCI precipitation (30.8%). Bacterial (eubacterial) diversity estimated from the complexity of the banding pattern obtained by restriction of the amplicons from the different ponds decreased with increasing salinity while for Archaea (archaebacteria) the reverse was true i.e. the higher the salinity the higher the number of bands. The similarities in taxonomic composition of the prokaryotic populations present in those ponds were evaluated from the number of restriction bands shared by the different samples. The relationships found among the different environments were independent of the enzyme used for digestion and were consistent with previous descriptions obtained by the study of isolates from the different environments. This technique appears to be promising as a rapid method for microbial biodiversity fingerprinting useful to compare several environments and detect major shifts in species composition of the microbial population.

Bacterial diversity in two coastal lagoons deduced from 16S rDNA PCR amplification and partial sequencing

Amplification and sequence analysis of the 16S rRNA genes from DNA samples extracted directly from the environment allows the study of microbial diversity in natural ecosystems without the need for cultivation. In this study this methodology has been applied to two coastal lagoons. Activity and numbers of heterotrophic bacteria have indicated that, as expected, Prevost lagoon (located on the French Mediterranean coast) is more eutrophic than that of the Arcachon Bay (French Atlantic coast). Analysis of partial 16S rRNA gene sequences revealed that, in both environments, a relatively large number of clones related to Cytophaga/Flexibacter/Bacteroides as well as to α-Proteobacteria were found. One hundred percent similarity with the sequences of the data bases were not found for any of the more than a hundred clones studied, in fact for most clones maximum similarity was below 95% for the approx. 200 bases sequenced. Similarity was not higher with any of the sequences found for the 14 isolates (pure cultures) obtained from the same samples. Redundancy, i.e. number of identical sequences, was higher in the samples from Arcachon. In addition, sequences related to representatives of ten major phylogenetic branches of Bacteria were obtained from Prevost lagoon; however only five branches were represented by the data from Arcachon. These findings indicated a higher bacterial phylogenetic diversity in the Prevost lagoon.

Bacterial diversity in two coastal lagoons deduced from 16S rDNA PCR amplification and partial sequencing

Amplification and sequence analysis of the 16S rRNA genes from DNA samples extracted directly from the environment allows the study of microbial diversity in natural ecosystems without the need for cultivation. In this study this methodology has been applied to two coastal lagoons. Activity and numbers of heterotrophic bacteria have indicated that, as expected, Prévost lagoon (located on the French Mediterranean coast) is more eutrophic than that of the Arcachon Bay (French Atlantic coast). Analysis of partial 16S rRNA gene sequences revealed that, in both environments, a relatively large number of clones related to Cytophaga/Flexibacter/Bacteroides as well as to α-Proteobacteria were found. One hundred percent similarity with the sequences of the data bases were not found for any of the more than a hundred clones studied, in fact for most clones maximum similarity was below 95% for the approx. 200 bases sequenced. Similarity was not higher with any of the sequences found for the 14 isolates (pure cultures) obtained from the same samples. Redundancy, i.e. number of identical sequences, was higher in the samples from Arcachon. In addition, sequences related to representatives of ten major phylogenetic branches of Bacteria were obtained from Prévost lagoon; however only five branches were represented by the data from Arcachon. These findings indicated a higher bacterial phylogenetic diversity in the Prévost lagoon.

Pollination Effectiveness and Pollination Efficiency of Insects Foraging Prosopis velutina in South-Eastern Arizona

The genus Prosopis consists of woody leguminous trees and shrubs of interest for fuelwood and agroforestry purposes in arid and semi-arid regions. Prosopis velutina is common to the south-western United States and northern Mexico. Its flowers are an important food source for several native insects, as well as Apis mellifera used in the honey industry. This paper examines plant-pollinator interactions, and provides the first quantification of pollination effectiveness and pollination efficiency of several groups of insects that forage on P. velutina in the Sonoran Desert near Tucson, Arizona. Pollination effectiveness is defined as a measure of an insect's potential as a pollen vector, as reflected by its ability to effect fruit production significantly. Pollination effectiveness of small insects, determined by covering inflorescences with mesh bags with 3 mm pore size, was equal to that on completely open-pollinated inflorescences. Pollination effectiveness of nocturnal insects, determined by exposing inflorescences to visitation only at night, was nonsignificant. However, actual activity of nocturnal insects was not monitored. Pollination efficiency is defined as the relative ability of an insect to pollinate flowers effectively, as measured by fruit production per some unit of measure (i.e. per visit). Three measures of pollination efficiency based on pod production per visit (Spears' PE), per minute on the inflorescence (PE t ), and per unit of distance traversed on the inflorescence (PE d ), were determined for A. mellifera, Chalicodoma spp., Colletidae, Perdita spp. and Volucella spp. Chalicodoma spp. were most efficient according to Spears' PE and PE t . Perdita spp. and Volucella spp. were equally as efficient as A. mellifera. Colletidae had the lowest values for all three measures of PE. The results are discussed in regard to interactions between floral development and insect behaviour. When considering the number of visits required by a particular insect to effect pod production equal to that of open-pollinated inflorescences, native Chalicodoma spp., Perdita spp. and Volucella spp. were more efficient than the introduced A. mellifera. Implications of the results with regard to conservation of biological diversity in natural ecosystems, and utilization of insects in pod or seed production orchards, are discussed.

Biodiversity and CO2: Global Change is Under Way

In this article our current understanding of CO2 effects on complex vegetation is outlined and first results of the CO2 enrichment experiments conducted as part of the Biodiversity Module of the Swiss Priority Programme Environment are discussed. It is known for two centuries that plants need CO2 for photosynthesis. Elevated concentrations of CO2 were found to stimulate growth, and thus CO2 fertilization became a standard tool in greenhouse horticulture. Meanwhile it became clear that this stimulating effect of CO2 on plant growth depends on the availability of other resources like water, nitrogen and phosphate, which are usually very abundant in agro-systems but limited in natural ecosystems. However, even when resources are short some plants (the “winners”) may become more efficient competitors for these resources than others (the “losers”), causing global CO2 enrichment to become a biodiversity issue. While 1 per cent of the global biomass is growing under fertile agricultural conditions, more than 95 per cent of the global vegetation produces biomass without any artificial addition of resources. Hence, understanding CO2 effects on biodiversity requires experiments conducted in diverse, low-fertility systems, a model for which are calcareous grasslands. First results indicate increased carbon uptake by plants during the day but no change in biomass. In addition, tissue quality changes and species-specific responses were observed which were not predicted by any current theory. These results indicate that predictions of the future development of complex plant assemblages can not be made from data obtained in simplified fertile systems but need to consider the multitude of interactions between organisms as they occur in the field. With more than 70 plant species per 100 m2 this precious grassland system can serve as a model for other highly diverse natural ecosystems.

Sequencing of Bacterial and Archaeal 16S rRNA Genes Directly Amplified from a Hypersaline Environment

The new methods based on PCR amplification and sequencing of 16S rRNA genes from DNA samples extracted directly from the environment allow the description of microbial diversity in natural ecosystems without the need for cultivation. We have applied this technique to an extreme environment presumed to have very low diversity: the crystallizer ponds of a marine saltern (salinity over NaCl saturation). The molecular methodology has shown that indeed very low diversity can be found here. Bacteria (formerly eubacteria) are largely minoritary, and only a cluster of closely related sequences was found, all distant relatives of the α-Proteohacteria (82% to Rhodopseudoinonas marina ). Halophilic Archaea were shown by hybridization to be, as expected, the largest component of biomass in this environment. All the archaeal clones sequenced again were highly similar to each other suggesting that they are probably members of the same genus. However, all the sequences diverged considerably from those of the described genera of halophilic Archaea . In fact the data are consistent with the idea that the 16S rDNA genes directly amplified from the saltern correspond to members of an undescribed genus which seems to be abundant in the sample. This is remarkable since many collection strains sequenced come specifically from this same saltern. Furthermore, 16S rDNA obtained from archaeal cultures isolated from the same sample had no homology to the sequences obtained by PCR amplification, instead they appear to be members of the well known genus Haloarcula . However, this is in agreement with the findings of other authors who by culture have obtained organisms different from those indicated by the sequences retrieved directly by PCR. Possible explanations are discussed.

Nature Tourism and Enterprise Development in Ecuador

Nature-based observation and adventure figure prominently in Ecuador’s tourism attractions. From the standpoints of geography and biology, Ecuador is a small but highly diverse nation divided into four distinct zones: the Sierra Highlands, the Amazon Basin, the Pacific Coast Lowlands, and the Galapagos Islands. Across these four zones is found a wide variety of natural ecosystems for both casual and dedicated naturalists. Nature tourism is oriented primarily to visiting a few private holdings plus the publicly-owned national parks and related reserves. However, the major tour operators and airlines have not yet adopted a formal approach to promoting tourism which is specifically nature-oriented. The number of international visitors engaging in na-ture-oriented activities on the mainland falls far short of visitation to the Galapagos Islands. Responsible opinion concurs that development of tourism in the Galapagos must be carefully controlled, but disagreements concern practical interpretation of that idea...

Increased Diversion at Chicago: Initial Assessment

The Corps of Engineers has proposed and analyzed the effects of diverting Lake Michigan waters down the Illinois River in times of above average lake levels. Effects would vary considerably depending upon the rate and timing of diversion. Major benefits on the river portion will be an improvement in water quality, increased benefits to commercial navigation and increased power generation. On the Great Lakes the major benefits would be reduction in shoreline erosion and flooding. Adverse effects would be significant. On the river major adverse effects are due to increased flooding over existing conditions and longer flooding duration in the lower reaches. Current trends of habitat destruction and loss of species diversity in natural ecosystems will be accelerated by the increased diversion, resulting in the deterioration of natural ecosystems. Managed ecosystems such as leveed farmlands and duck clubs will suffer higher drainage costs as a result of the increased flooding. Unleveed areas will experience substantial crop losses, especially in low water years, and diversion may ultimately preclude agriculture in such areas. On the lakes, major adverse effects would result from power loss, lowered ship capacity resulting from shallower draft at docking facilities, and loss of water-edge ecosystems.

The environment from a systems viewpoint

The scientific method has been the touchstone of success in man's efforts to improve his condition relative to his environment. Reductionism has been a powerful tool in technological development. But technological capacity to modify the environment far outstrips man's ability to predict the consequences of those modifications. Systems analysis is a technique of synthesis and as such can provide a powerful tool for preventing adverse environmental effects and for suggesting methods to restore degraded environments. Until enough information becomes available to effectively utilize systems analysis in planning activities affecting the environment, man should recognize his limitations and “tread softly.” In order to avoid continued and irreversible damage, development of large and diverse areas of unspoiled land should be prohibited in recognition of the fact that balanced and diverse natural ecosystems are a necessary and integral part of man's life support system and in recognition of our ignorance regarding the capacity of that system to withstand modification.