An approach to quantifying the exploitability of human ecosystems

Patterns of ecosystem resiliency and differential exploitability by man exist, but they have not yet been worked out in detail This article presents a systematic approach for quantifying the responses of different ecosystems to various levels of human exploitation. It presents a model of the operations of natural ecosystems and suggests a useful analogue between exploitation ecosystems and different stages in ecological succession. This analogue enables us to define a coefficient of exploitability which relates the intensity of ecosystem responses to the intensity of management. The coefficient should prove useful in elucidating a number of types of man-environment interactions. It can be calculated from empirical data. Since it is a function of independent ecosystem variables such as climate, we can also suggest its probable global distribution patterns. Sample values of are calculated from two different types of data. The range of values is greater than one order of magnitude, and their trends are entirely consistent with their predicted distribution.     

Stomatal patchiness in Mediterranean evergreen sclerophylls

Midday depression of net photosynthesis and transpiration in the Mediterranean sclerophylls Arbutus unedo L. and Quercus suber L. occurs with a depression of mesophyll photosynthetic activity as indicated by calculated carboxylation efficiency (CE) and constant diurnal calculated leaf intercellular partial pressure of CO₂ (C_i). This work examines the hypothesis that this midday depression can be explained by the distribution of patches of either wide-open or closed stomata on the leaf surface, independent of a coupling mechanism between stomata and mesophyll that results in a midday depression of photosynthetic activity of the mesophyll. Pressure infiltration of four liquids differing in their surface tension was used as a method to show the occurrence of stomatal patchiness and to determine the status of stomatal aperture within the patches. Liquids were selected such that the threshold leaf conductance necessary for infiltration through the stomatal pores covered the expected diurnal range of calculated leaf conductance (g) for these species. Infiltration experiments were carried out with leaves of potted plants under simulated Mediterranean summer conditions in a growth chamber. For all four liquids, leaves of both species were found to be fully infiltratable in the morning and in the late afternoon while during the periods leading up to and away from midday the leaves showed a pronounced patchy distribution of infiltratable and non-infiltratable areas. Similar linear relationships between the amount of liquid infiltrated and g (measured by porometry prior to detachment and infiltration) for all liquids clearly revealed the existence of pneumatically isolated patches containing only wide-open or closed stomata. The good correspondence between the midday depression of CE, calculated under the assumption of no stomatal patchiness, and the diurnal changes in non-infiltratable leaf area strongly indicates that the apparent reduction in mesophyll activity results from assuming no stomatal patchiness. It is suggested that simultaneous responses of stomata and mesophyll activity reported for other species may also be attributed to the occurrence of stomatal patchiness. In Quercus coccifera L., where the lack of constant diurnal calculated C_i and major depression of measured CE at noontime indicates different stomatal behavior, non-linear and dissimilar relationships between g and the infiltratable quantities of the four liquids were found. This indicates a wide distribution of stomatal aperture on the leaf surface rather than only wide-open or closed stomata.Dedicated to Professor Otto L. Lange on the occasion of his 65th birthday     

The Influence of Environmental Factors and Microhabitat Availability on the Distribution of an Aquatic Oligochaete Assemblage in a Mediterranean River Basin

Some aquatic oligochaete species, mainly certain naidids and tubificids, are often associated with polluted environments, with high levels of organic matter and oxygen deficit. However, in the stations sampled in the Guadaira river basin, which can be arranged on an axis of organic pollution, the main aquatic oligochaete species (Nais elinguis and Tubifex tubifex) inhabiting these environments do not show a distribution pattern significantly related to the water physico-chemical characteristics measured. Nor, have we registered any association between these species and any kind of microhabitat, defined here: water current, presence of different types of vegetation, substrate coarseness and presence of anoxic sediments. Paranais litoralis is the exception, being related to areas without water current, located at higher altitudes, with high levels of dissolved organic matter and an anoxic substrate made up of fine particles. These results can be explained by the highly fluctuating nature of Mediterranean ecosystems and by the marked generalist character and ubiquity of the oligochaete assemblage species, able to colonize any kind of environment.     

A Review on Effect-Dose-Sensitivity Models for Aquatic Ecosystems.

Effect-dose-sensitivity (EDS) models for entire ecosystems, like lakes and defined coastal areas, ought to play a paramount role for environmental sciences and management. The aim of EDS-models is to provide quantitative predictions relating operationally defined ecological effect parameters to compatible dose and sensitivity parameters. Empirically validated EDS-models provide a tool to simulate ecosystem effects of practically feasible remedial measures. The main objective of this paper is to give a compilation of existing EDS-models for aquatic ecosystems. The aim is not to repeat derivations and equations but to present some basic components of EDS-models, their presuppositions and applicability. Since, at present, there exist EDS-models for mercury, radiocesium and phosphorus in lakes and nutrients (N and P) in coastal areas, this compilation can be rather short. To the best of the authors knowledge, there exist no EDS-models (that meet the criteria given in this work) for other types of ecosystems (like forests, agricultural land, urban areas, etc.) or for other types of contaminants (like metals, acidifying substances, halogenated toxins, etc.). Another aim is to clarify the difference between traditional mass-balance models (i.e., dynamic models) and ecometric (i.e., statistical/empirical models) EDS-models, and to give examples of EDS-models based on both these modelling approaches, and techniques (dimensionless moderators) to link these two ways of modelling. The paper also gives examples of the practical use of EDS-models. A new ecometric EDS-model for nutrients in coastal areas, where the oxygen concentration of the bottom water is used as an effect parameter, is presented. The idea with this part is also to give the steps in the ecometric derivation of EDS-models.     

Seasonal and Spatial Distribution of Vitamin B12 in a Coastal Area of Eastern Mediterranean Sea

The seasonal and spatial distribution of vitamin B₁₂ was investigated in Eastern Mediterranean (Saronicos Gulf, Aegean Sea). Vitamin B₁₂ concentration had an annual range 0.12–7.93 ng. 1⁻¹ and an annual mean 1.88 ng. 1⁻¹. The statistical analysis of data indicated significant seasonal and regional variations of vitamin B₁₂ in this area and an inverse relationship of this vitamin with chl a. The results showed that the Eastern Mediterranean Sea contains less vitamin B₁₂ than the Western Mediterranean Sea.     

Genetic relationships of populations and the origins of new infestations of the Mediterranean fruit fly

A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) approach based on the variation in intron sequences of the glucose-6-phosphate dehydrogenase (Zw) gene was used to assess genetic variability in 26 populations and infestations of the Mediterranean fruit fly (medfly), Ceratitis capitata. Beginning with the exon-primed intron-crossing PCR (EPIC-PCR) method to amplify introns of this gene, five alleles were identified on the basis of DNA sequence variants. Several of these variants affect recognition sites for the restriction enzymes RsaI and TaqI. Using these enzymes in successive digestions of the EPIC-PCR products, each of these alleles can be identified directly from individuals. From this, surveys were conducted to document genotypes and allele frequencies in these samples. The relationships of existing populations and the invasion process represented by new infestations of the medfly were analysed using a principal coordinate analysis and the amova method to quantify the distribution of genetic diversity at different levels in a hierarchical manner. From these results, a framework of genetic relationships among the populations and infestations is presented. In addition, for at least some of the infestations, populations that are probably acting as sources of origin have been identified.     

Nitrogen as a Factor Affecting Algal Growth Potential of an Oligotrophic Coastal Environment of Eastern Mediterranean Sea

Potential nitrogen limitation to chl a production in surface waters of Saronicos Gulf, Aegean Sea was assayed using the alga Pavlova lutheri as the test organism. The oligotrophic and eutrophic water types of this area were compared by in situ and in vitro chl a production estimations. Additions of ammonium alone as well as in combination with complete nutrient enrichment were made to the oligotrophic waters and the algal growth yield was determined and compared with the corresponding yield in unenriched water cultures. The results from routine nutrient analysis and bioassay experimentation support the view that nitrogen has a priority among the factors limiting phytoplankton growth in the Eastern Mediterranean Sea.     

Dégradation d'acides aminés à l'interface eau-sédiment réconstitué d'une lagune méditerranéenne (Golfe du Lion)

Degradation of Amino Acids at a Simulated Water-sediment Interface of a Mediterranean Lagoon Environment, Golfe du Lion The degradation of two ¹⁴C and ³H labelled amino acids at the simulated water-sediment interface of a Mediterranean lagoon was studied. The four day experiments included the respiratory activity measurement and the study of incorporation processes of the radioactivity in specific organic fractions of the ¹⁴C arginine. After active mineralization occurred during the first day, the radioactivity in the acid-soluble fraction decreased and polycondensed products were progressively incorporated. The radioactivity of the ³H lysine was included mainly in the acid soluble fraction. The nature of the substrate, and the reducing conditions in the environment affect the radioactivity distribution in the organic fractions. The identification of amino acids in the acid-soluble and base soluble fractions shows that the labelled arginine and lysine and other amino acids in the acid soluble and base soluble fractions shows that the labelled arginine and lysine released from the initial compounds are important quantitatively.     

Le phytoplancton des étangs de Berre et Vaïne (Méditerranée Nord-occidentale)

Phytoplankton of the Etang de Berre and Etang de Vaïne (N.W. Mediterranean) The phytoplankton in the brackish Etang de Berre and Etang de Vaïne was studied regularly at 12 stations for two years. The recent diversion of the Durance River into the Etang de Berre has effected a fundamental change in this formerly marine environment, which has had a great impact on its plankton populations. A total of 182 taxa were identified, including 111 Bacillariophyceae, 44 Chlorophyceae, and 15 Cyanophyceae. The most abundant species are small freshwater algae, mainly Chlorophyceae, since the salinity is generally less than 3 0/00. However, during summer and fall, as well as in waters near the bottom, the salinity can reach 15 0/00 and marine diatoms are predominant. Because the nutrients in the environment are constantly replenished, phytoplankters are always numerous, ranging in abundance between several million to several hundred million per liter. There is a somewhat irregular seasonal cycle. The average density is about 10⁸ cells/1 in the Etang de Berre, and about double that amount in the Etang de Vaïne. Differences in phytoplankton abundance and composition at the various stations or at various depths are slight.     

Geological age, ecosystem development, and local resource constraints on arthropod community structure in the Hawaiian Islands

An ongoing debate in evolutionary ecology concerns the relative role of contemporary vs. historical processes in determining local species richness and community structure. At sites along a 4 Mya geological chronosequence on Hawai'i, Moloka'i and Kaua'i, numerous extrinsic factors can be held constant, but ecosystem fertility and nutrient availability are low, both very young and very old sites, peaking at intermediate geological age across islands. Thus, contemporary resource traits are similar among sites with different biogeographical legacies, and these opposing gradients allowed a test of their relative importance for arboreal arthropod community structure. Pyrethrum knockdown was used to sample arboreal arthropods from Metrosideros polymorpha (Myrtaceae), the dominant tree throughout the Hawaiian Islands. Arthropod abundances and sample-based species richness peaked at more productive, intermediate-aged sites, but did not correlate with geological age. The proportions of individuals and biomass in trophic groups and in different taxonomic orders differed widely across sites, but proportions of species in trophic groups were more regular than the chance expectation. Species richness in local communities did not accumulate or pack more tightly with increasing geological age to the oldest island. Intermediate-aged islands may be contemporary peaks of richness, mediated by ecosystem development and senescence. Although historical and evolutionary processes generate diversity at broad scales, local communities converged in trophic structure and composition, and ecosystem resource availability constrained arthropod numbers and richness at local scales.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 551–570.