Ecosystems Ecology

Large-scale structural patterns commonly occur in network models of complex systems including a skewed node degree distribution and small-world topology. These patterns suggest common organizational constraints and similar functional consequences. Here, we investigate a structural pattern termed pathway proliferation. Previous research enumerating pathways that link species determined that as pathway length increases, the number of pathways tends to increase without bound. We hypothesize that this pathway proliferation influences the flow of energy, matter, and information in ecosystems. In this paper, we clarify the pathway proliferation concept, introduce a measure of the node--node proliferation rate, describe factors influencing the rate, and characterize it in 17 large empirical food-webs. During this investigation, we uncovered a modular organization within these systems. Over half of the food-webs were composed of one or more subgroups that were strongly connected internally, but weakly connected to the rest of the system. Further, these modules had distinct proliferation rates. We conclude that pathway proliferation in ecological networks reveals subgroups of species that will be functionally integrated through cyclic indirect effects.

SUMMARY. — From 1905 to 1935, practitioners of pre-energetics ecology sought to clarify their field of study. One after another, basic units of ecology, such as plant formation, plant association, climax, biome, biotic community and the ecosystem, came to the fore and eclipsed other contenders. Between 1920 and 1930, the organicist philosophy of Alfred North Whitehead, along with the evolutionary perspective of Herbert Spencer and the emergentist theories of Samuel Alexander and Conwy L. Morgan laid a solid foundation for the epistemological debate over the basic units of ecology. Authors like Frederic E. Clements and John Phillips advanced a variety of forms of ecological organicism, while Henry A. Gleason viewed plant association as the result of a fortuitous juxtaposition of individual entities. Ultimately, and paradoxically, Arthur G. Tansley 's ecosystem, although originally part of the anti-organicist viewpoint, became the basic unit of research programmes that sought, or at least intended to develop, an emergentist perspective.

KEYWORDS. — Philosophical organicism; ecological organicism; climax; ecosystem; holism; emergentism.


RÉSUMÉ. — L'écologie préénergétique des années 1905-1935 est à la recherche de ses objets d'étude. Des unités fondamentales de la nature (telles que formation végétale, association végétale, climax, biome, communauté biotique, écosystème) se trouvent en compétition et se succèdent les unes aux autres. Autour des années 1920 et 1930, la philosophie organiciste d'Alfred N. Whitehead, ainsi que la perspective évolutionniste d'Herbert Spencer et les propositions émergentistes de Samuel Alexander et Conwy L. Morgan, deviennent des références sous-jacentes au débat épistémologique concernant les unités de base de l'écologie. Des auteurs comme Frederic E. Clements et John Phillips soutiendront plusieurs formes d'organicisme écologique, tandis que Henry A. Gleason interprétera l'association végétale comme le résultat d'une juxtaposition fortuite d'individus. Enfin, et paradoxalement, l'écosystème de Arthur G. Tansley, tout en faisant partie, à l'origine, d'une perspective anti-organiciste, deviendra l'unité fondamentale de programmes de recherche qui se voudront, au moins dans leurs intentions, émergentistes.

MOTS -CLÉS. — Organicisme philosophique; organicisme écologique; climax; écosystème; holisme; émergentisme.

Ecological and eco-social network models were constructed with different levels of complexity in order to represent and evaluate management strategies for controlling the alien species Pterois volitans in Chinchorro bank (Mexican Caribbean). Levins´s loop analysis was used as a methodological framework for assessing the local stability (considered as a component of sustainability) of the modeled management interventions represented by various scenarios. The results provided by models of different complexity (models 1 through 4) showed that a reduction of coral species cover would drive the system to unstable states. In the absence of the alien lionfish, the simultaneous fishing of large benthic epifaunal species, adult herbivorous fish and adult carnivorous fish could be sustainable only if the coral species present high levels of cover (models 2 and 3). Once the lionfish is added to the simulations (models 4 and 5), the analysis suggests that although the exploitation or removal of lionfish from shallow waters may be locally stable, it remains necessary to implement
additional and concurrent human interventions that increase the holistic sustainability of the control strategy. The supplementary interventions would require the implementation of programs for: (1) the restoration of corals for increasing their cover, (2) the exploitation or removal of lionfish from deeper waters (decreasing the chance of source/sink meta-population
dynamics) and (3) the implementation of bans and re-stocking programs for carnivorous fishes (such as grouper) that increase the predation and competition pressure on lionfish (i.e. biological control). An effective control management for the alien lionfish at Chinchorro bank should not be optimized for a single action plan: instead, we should investigate the concurrent implementation of multiple strategies.

It is difficult to determine if smaller urban landscapes such as foundation plantings around buildings are just ornamental or if they have crossed a threshold and become functional communities. We hypothesize that one measure of functionality is the emergence of symbiotic relationships and ecosystem engineers, in particular the appearance of mycorrhizae. The mycorrhizae themselves are difficult to detect but a good indicator of their presence would be the grazers of mycorrhizae and their predators, in particular the microarthropods (Oribatid, Mesostigmatid and Prostigmatid mites and Collembolans). We hypothesize that microarthropod diversity and abundance can indicate when the functional threshold has been crossed. In this study microarthropods in the top two cm of soil were compared among urban, mid-urban (transitional) and natural sites on the University of Victoria campus, British Columbia. We found significantly fewer total microarthropods in the urban sites compared with mid-urban and natural sites. When microarthropods were separated by trophic level, we found that low trophic level microarthropods (dominated by Oribatid mites and Collembolans), were significantly more abundant in natural sites, while predaceous microarthropods (Mesostigmatid mites and Pseudoscorpions) were significantly more abundant in the mid-urban sites. We conclude that soil microarthropod diversity and bundance can indicate when a community has become ecologically functional and is not just ornamental.

Kleptoparasitism involves the theft of resources such as food items from one individual by another. Such food-stealing behaviour can have important consequences for birds, in terms of individual fitness and population sizes. In order to understand avian host-kleptoparasite interactions, studies are needed which identify the factors which modulate the risk of kleptoparasitism. In temperate European intertidal areas, Eurasian oystercatchers (Haematopus ostralegus) feed primarily on bivalve molluscs, which may be stolen by kleptoparasitic species such as carrion crows (Corvus corone) and herring gulls (Larus argentatus). In this study we combined overwinter foraging observations of oystercatchers and their kleptoparasites on the Exe Estuary, UK, with statistical modelling to identify the factors that influence the likelihood of successful food stealing behaviour occurring. Across the winter, 16.4 % of oystercatcher foraging attempts ended in successful kleptoparasitism; the risk of theft was lowest in February (10.8 %) and highest in December (36.3 %). Using an information theoretic approach to compare multiple logistic regression models we present evidence that the outcome of host foraging attempts varied with the number of kleptoparasites per host within the foraging patch for two out of five individual months, and for all months grouped. Successful, kleptoparasitism was more likely to occur when the total number of all kleptoparasites per host was greater. Across the entire winter study period, oystercatcher foraging attempts that resulted in kleptoparasitism were associated with a mean number of kleptoparasites per host that was more than double that for foraging attempts that ended in the oystercatcher successfully consuming the mussel. Conversely, the stage of the tidal cycle within the estuary did not affect the outcome of oystercatcher foraging attempts. Our study provides evidence that bird numbers influence the risk of kleptoparasitism within avian assemblages.

""FOR CITATIONS:
Salem, H.S., 2013. Palestinian NGO Statement on the World Bank-Sponsored Red-Dead Sea Canal. Emergency Water Sanitation and Hygiene (EWASH) in the Occupied Palestinian Territory. 21 October, 2013

ABSTRACT:
"The undersigned Palestinian NGOs call on the Palestine Liberation Organization (PLO) and the Palestinian National Authority (PNA) to halt all forms of cooperation with the World Bank-sponsored Red Sea - Dead Sea Conveyance Project (RSDSCP) and to take an unequivocal public stance of rejection to the project. It has become clear beyond doubt that the project is an unacceptable attempt to force the Palestinian population to consent to their own dispossession and to compromise on their own rights. Any lack of a clear position by the Palestinian leadership on this outrageous project, any stand of ambiguity or positive criticism towards it, contributes to the impunity that for far too long has allowed Israel to appropriate Palestinian water and deny Palestinians their rights.""

Ecosystem climate manipulation experiments (ECMEs) are a key tool for predicting the effects of climate change on ecosystems. However, the strength of inferences drawn from these experiments depends on whether the manipulated conditions mimic future climate changes. While ECMEs have examined mean temperature and moisture conditions, ecosystem processes may respond more to microclimatic thresholds (e.g., freeze–thaw events). We reported the mean and microclimatic thresholds from a post-clearcut ECME in a temperate, mixed deciduous forest. Target treatments were ambient, warmed (+∼2 °C), wetted (+∼20 % precipitation), and warmed + wetted. Wetted treatments increased mean monthly precipitation by 23 %, but did not change the amount of time the soil water potential was below the permanent wilting point. Relative to ambient, warmed treatments increased the mean temperatures of the surface and soil by 1.8 and 2.5 °C, respectively. Warming decreased the number of soil freeze–thaw events and increased the number of growing degree days, frost-free days, and amount of time leaf surface temperatures were in the optimal photosynthetic range. Our results showed that, even when ECMEs mimic mean predicted climate conditions, their effect on microclimatic thresholds can be variable. We suggest that measuring these and other microclimatic thresholds will be essential for interpreting ECME results and assessing their value in predicting ecosystem responses to future climate change.

It is becoming more apparent that species richness alone many not be sufficient to fully understand ecosystem resilience but that functional diversity (diversity of species having similar effects on an ecosystem process) may be more relevant. In particular, response diversity (diversity of species that respond differently to disturbance) within functional groups (FG) is suggested to be critical for resilience. We assess for the first time the use of response diversity as a measure of resilience in an empirical study. Our experimental design consisted of sites with three disturbance intensities during a grazing exclosure period and the same sites, 1 year later, after grazing. Plant FGs were identified based on effect traits related to nutrient cycling and soil retention, and species richness within groups was assessed during exclosure and after grazing. To assess if response diversity could predict loss of species richness (resilience analysis), response diversity was calculated only during the exclosure period, based on traits related to grazing tolerance. We also assessed the contribution of richness to response diversity during exclosure (redundancy analysis). Response diversity was significantly and highly correlated with species richness within FGs during disturbance. That is, FGs with the lowest response diversity were the most affected, disappearing when disturbance appeared. Richness within FGs during exclosure was not significantly correlated with response diversity, showing that higher richness does not ensure resilience. We conclude that response diversity can be used to predict which FGs are more resilient, and hence, less vulnerable to future disturbance.

Éditorial
Pierre Charbonnier et Yaël Kreplak : Savoirs écologiques

Articles
Anthony Pecqueux : Pour une approche écologique des expériences urbaines

Natalia La Valle : Temporalités distribuées et partagées. Une approche écologique des activités familiales dans le foyer

Martín Tironi : Mettre l’écologie en mouvement. Les controverses aux origines du projet Vélib'

Baptiste Gille : De l’écologie symbolique à l’écologie politique. Anthropologie des controverses environnementales chez les Salish côtiers

Catherine Larrère : L’écoféminisme : féminisme écologique ou écologie féministe

Notes
Joffrey Becker : L’écologie prospective de la robotique

Lucile Garçon et Aurore Navarro : La Société des territorialistes ou la géographie italienne en mouvement

Pierre Charbonnier : De l’écologie à l’écologisme de Marx

Traductions
Tim Ingold : Culture, nature et environnement

Diana K. Davis : L’éco-gouvernance en Algérie française

Entretiens
Yaël Kreplak et Barbara Turquier : L’écologie en architecture et urbanisme : entre normes et pratiques. Entretien avec Nicolas Michelin

Émilie Hache et Valérie Pihet : « Getting back to the wrong nature ». Entretien avec Armin Linke

Above treeline at Goliath Peak, Colorado, Pinus aristata (bristlecone pine).and Picea engelmannii (Engelmann spruce) grow as krummholz tree forms. Due to the harsh alpine climate, these trees are dwarfed in sizeŽapproximately 0.5 to 3.0 m tall.and root along a horizontal stem. Soil nutrients, including carbon, nitrogen, and phosphorus fractions were examined to 10-cm depth beneath P. aristata krummholz and P. engelmannii krummholz, as well as from adjacent, undisturbed alpine soils. Plant available phosphorus was higher under P. engelmannii than P. aristata, suggesting that although these two species exist in the same environment, they have a different effect on the availability of labile soil phosphorus. Mineral soils under P. aristata were not significantly different than under P. engelmannii for total carbon, total nitrogen, and total phosphorus. Soil phosphorus differences are important in this ecosystem because of the proposed P limitation in some alpine ecosystems.

The carbon cycle modulates climate change, via the regulation of atmospheric CO2, and it represents one of the most important services provided by ecosystems. However, considerable uncertainties remain concerning potential feedback between the biota and the climate. In particular, it is unclear how global warming will affect the metabolic balance between the photosynthetic fixation and respiratory release of CO2 at the ecosystem scale. Here, we present a combination of experimental field data from freshwater mesocosms, and theoretical predictions derived from the metabolic theory of ecology to investigate whether warming will alter the capacity of ecosystems to absorb CO2. Our manipulative experiment simulated the temperature increases predicted for the end of the century and revealed that ecosystem respiration increased at a faster rate than primary production, reducing carbon sequestration by 13 per cent. These results confirmed our theoretical predictions based on the differential activation energies of these two processes. Using only the activation energies for whole ecosystem photosynthesis and respiration we provide a theoretical prediction that accurately quantified the precise magnitude of the reduction in carbon sequestration observed experimentally. We suggest the combination of whole-ecosystem manipulative experiments and ecological theory is one of the most promising and fruitful research areas to predict the impacts of climate change on key ecosystem services.

Ecosystem respiration is a primary component of the carbon cycle and understanding the mechanisms that determine its temperature dependence will be important for predicting how rates of carbon efflux might respond to global warming. We used a rare model system, comprising a network of geothermally heated streams ranging in temperature from 5 °C to 25 °C, to explore the nature of the relationship between respiration and temperature. Using this ‘natural experiment’, we tested whether the natal thermal regime of stream communities influenced the temperature dependence of respiration in the absence of other potentially confounding variables. An empirical survey of 13 streams across the thermal gradient revealed that the temperature dependence of whole-stream respiration was equivalent to the average activation energy of the respiratory complex (0.6–0.7 eV). This observation was also consistent for in-situ benthic respiration. Laboratory experiments, incubating biofilms from four streams across the thermal gradient at a range of temperatures, revealed that the activation energy and Q10 of respiration were remarkably consistent across streams, despite marked differences in their thermal history and significant turnover in species composition. Furthermore, absolute rates of respiration at standardised temperature were also unrelated to ambient stream temperature, but strongly reflected differences in biofilm biomass. Together, our results suggest that the core biochemistry,which drives the kinetics of oxidative respiratory metabolism, may be well conserved among diverse taxa and environments, and that the intrinsic sensitivity of respiration to temperature is not influenced by ambient environmental temperature.

In considerazione del successo di critica e di pubblico ottenuto con la prima edizione del volume “Etna. I vini del vulcano” di Salvo Foti edito nel 2005, abbiamo deciso di aggiornare i risultati della ricerca, arricchendola di nuovi contenuti, nella nuova edizione appena pubblicata. In particolare sono stati inseriti tre nuovi capitoli: “Alberello Etneo estetica ed eccellenza”, “La Maestranza de I vigneri”, “Il Parco dell’Etna”. Una pubblicazione in cui si configura quella che dovrebbe essere l’idea ed il programma di ogni azienda etnea: valorizzare un territorio ricco di storia e di tradizioni e da sempre vocato alla coltivazione della vite e alla produzione di vini originali e di alto livello qualitativo. L’autore ha saputo inserire in un contesto descrittivo preziose informazioni di tipo scientifico sull’applicazione delle nuove tecniche enologiche nella vinificazione dei vitigni Etnei; sul recupero di vigneti abbandonati e di antichi palmenti; su alcune varietà di Nerello Mascalese e di Carricante coltivate sull’Etna, dalle quali è possibile produrre vini con determinate caratteristiche organolettiche del tutto originali e inimitabili. Le varietà tipiche dell’Etna vengono presentate come componente essenziale della valorizzazione del territorio e vengono studiate dal punto di vista biochimico per capire come da esse si possano ottenere i risultati enologici migliori.

Il campo di ricerca che viene abbracciato dalla pubblicazione prende in considerazione la produzione oleolicola siciliana sin dalle sue prime tracce di attività. L'opera, dunque, offre un quadro storico che partendo dall'antichità arriva ai nostri giorni e comprende sezioni relative ai modi della produzione, ai frantoi, alle tradizioni popolari

SOMMARIO

Introduzione, Giovanni La Via

Olivo ed olio nella Sicilia antica
Sebastiano Barresi

Gli oli a Denominazione di Origine Protetta (D.O.P) della Sicilia: aspetti territoriali, varietali e qualitativi
Tiziano Caruso, Giuseppe Campisi

Sistemi e paesaggi
Giuseppe Barbera, Paolo Inglese

Le malattie dell’olivo: dalla collera degli dei ai postulati di Koch
Giovanni Enrico Agosteo, Santa Olga Cacciola, Gaetano Magnano di San Lio, Antonella Pane

Gli insetti dell’olivo
Santi Longo

L’estrazione dell’olio
Marco Poiana, Demetrio Antonio Zema, Santo Marcello Zimbone

La manifattura dell’olio d’oliva in Sicilia: dalla raccolta delle olive all’estrazione dell’olio
Giovanni Enrico Agosteo

I frantoi storici e tradizionali in Sicilia: aspetti funzionali e tecnico-costruttivi dei fabbricati
Salvatore Di Fazio

Olio di oliva e benessere
Annamaria Panico, Floriana Garufi

All’ombra dell’olivo. Canti, liti, suggestioni e un’identità controversa
Andrea Schembari

The reason I am speaking about death today is two-fold.  First, I have been somewhat preoccupied with the concept of death since entering a new decade of my life.  I no longer believe in the evangelical vision of heaven I learned about in my youth; but as an uncomfortable “un”-Christian, I also have no satisfactory vision to replace it.  Or rather, there are many visions I find appealing, but none that I “believe in,” as I had believed in heaven.  My family is getting older, my parents have been sick in the last few years, and I often feel that I have more to lose now than I used to.

My second reason for considering death today is that last Wednesday, Mimi, our family cat of 24 years—yes, 24—passed away.  After spending all nine of her lives living, Mimi could no longer eat and was suffering.  My mother had her put down after we all said goodbye; we held a funeral for her and buried her among the lilies in our yard, her home.

My sisters and myself were very, very saddened by Mimi’s passing; but my mother took it hardest of all.  Mimi had been her companion, her friend, her lap warmer, her snuggle buddy, her alarm clock and, we often joked, her favorite child for over two decades.  I wanted to comfort my mother; but my protest that it didn’t matter what the (her) Church said, Mimi was with the God/dess, was maybe, not very helpful.  It perhaps, only reminded her that in her view, I too am not going to heaven.

Rapid immobilization of inorganic nitrogen (N) in soil contributes to ecosystem N accumulation, even in old-growth and chronically-fertilized forests once thought to have poor N retention capacity. In old-growth conifer and hardwood stands in Pennsylvania, we tested the hypotheses that biotic and abiotic N immobilization are regulated by N form and forest type. We added 15NH4+, 15NO2-, and 15NO3- to sterile (gamma-irradiated) and live organic-horizon soil and define N immobilization as the mass of added 15N remaining in soil following extractions conducted 15 min, 24 h, and 21 days later. Immobilization of NO2- (19–25% of added N) occurred in sterile soils within 15 min and was little changed thereafter. Tracer NO3- immobilization was not observed, although soils had been pretreated (refrigerated) so as to quantify the lower limit of immobilization potential. Immobilization of NH4+ (27%) occurred in live conifer soils by 21 days but not in other treatments. In 21-day incubations, tracer N immobilization was greater in NO3-poor and humic-rich soils. Immobilization was greater in sterile than in live soil, perhaps owing to artifacts of sterilization. Conifer stands exhibited more massive O-horizons, so NO2- immobilization per unit area was greater in conifer (1.46 mg N m-2) than hardwood (0.43 mg N m-2) stands, possibly accounting for lower N leaching from conifer forests. Areal immobilization rates appear to be fast enough to retain all N transformed to NO2-, so NO2- production may be a limiting step in soil N retention in old-growth ecosystems.

Short-term experiments exposing calcifying organisms to acidification have revealed altered growth and strength of their exoskeletons. We tested the hypothesis that multi-generational exposure to sustained estuarine acidification from runoff from acid sulfate soils (ASS) would (1) reduce the shell strength of sessile or relatively immobile wild benthic invertebrates and (2) as a consequence render these invertebrates that rely on armour for anti-predator defence more susceptible to generalist benthic predators. First, we compared the force required to break the exoskeletons of Saccostrea glomerata, Bembicium auratum and Heloecius cordiformis between replicate south-east Australian mangrove forests close to (acidified) and away from (reference) major ASS outflow drains. Second, we assessed differences in the susceptibility of oysters from acidified and reference forests to predation by the generalist muricid gastropod, Morula marginalba. Mollusc shells were significantly weaker at ASS-affected than at reference sites but the strength of crab carapaces was not influenced by acidification. Oysters from acidified sites were consumed by M. marginalba at a faster rate than oysters from reference sites in choice and no-choice experiments because M. marginalba required less time to drill through weaker shells. Many other predators, such as crabs, are generalist feeders that consume prey at rates inversely proportional to their shell strength. Hence, in the absence of effects of acidification on the ability of these predators to consume prey, molluscs at acidified sites may also be more susceptible to other such predators. This study highlights how human stressors can rapidly alter predator-prey interactions that have evolved over many years.

Fixation of N by biological soil crusts and free-living heterotrophic soil microbes provides a significant proportion of ecosystem N in arid lands. To gain a better understanding of how elevated CO2 may affect N2-fixation in aridland ecosystems, we measured C2H2 reduction as a proxy for nitrogenase activity in biological soil crusts for 2 yr, and in soils either with or without dextrose-C additions for 1 yr, in an intact Mojave Desert ecosystem exposed to elevated CO2. We also measured crust and soil δ15N and total N to assess changes in N sources, and δ13C of crusts to determine a functional shift in crust species, with elevated CO2. The mean rate of C2H2 reduction by biological soil crusts was 76.9±5.6 μmol C2H4 m−2 h−1. There was no significant CO2 effect, but crusts from plant interspaces showed high variability in nitrogenase activity with elevated CO2. Additions of dextrose-C had a positive effect on rates of C2H2 reduction in soil. There was no elevated CO2 effect on soil nitrogenase activity. Plant cover affected soil response to C addition, with the largest response in plant interspaces. The mean rate of C2H2 reduction in soils either with or without C additions were 8.5±3.6 μmol C2H4 m−2 h−1 and 4.8±2.1 μmol m−2 h−1, respectively. Crust and soil δ15N and δ13C values were not affected by CO2 treatment, but did show an effect of cover type. Crust and soil samples in plant interspaces had the lowest values for both measurements. Analysis of soil and crust [N] and δ15N data with the Rayleigh distillation model suggests that any plant community changes with elevated CO2 and concomitant changes in litter composition likely will overwhelm any physiological changes in N2-fixation.

We transplanted Sphagnum ‘turfs’ containing abundant Drosera rotundifolia into an existing nitrogen deposition experiment at Whim Moss near to Edinburgh. These mesocosms received simulated N deposition in the form of either NH4+ or NO3-, to give total N deposition rates of approximately 8, 16 or 32, or 64 kg N ha-1 year-1. Simulated N deposition was added in a realistic way (i.e. with rainfall throughout the year). The δ15N of this added N was elevated relative to background N. We measured the tissue chemistry and δ15N of S. papillosum and D. rotundifolia over two years after transplant. Our aim was to determine uptake of the deposited N and the impact on S. papillosum tissue chemistry and D. rotundifolia tissue chemistry and ecology.

We found clear, significant impacts of N deposition on S. papillosum, with increased capitula N content and reduced C:N ratio. Increased δ15N indicated uptake of deposited N. The response of D. rotundifolia was less clear with impacts only at the highest rate of N deposition. There was no evidence of differential uptake of reduced or oxidised wet N deposition by either S. papillosum or D. rotundifolia.

Using the natural abundance stale isotope method we estimated the minimum contribution of prey N to the total N in D. rotundifolia to be 35%.

The results suggest that differences in the uptake of reduced or oxidised wet N deposition might not be ecologically significant when wet N deposition is added realistically. They also support the suggestion that a model of N dynamics in Sphagnum dominated ecosystems that includes the role of Sphagnum as a small scale ecosystem engineer, is required to predict accurately vascular plant responses to N deposition.

Contributors examine the current trends and state of biodiversity globally, the drivers of biodiversity loss including climate change and economic and population pressures, and the mechanisms and policies needed for conserving and restoring biodiversity in the future.

Strong emphasis is placed throughout on the fundamental importance of placing a realistic economic value on nature and the services that ecosystems provide if we are to manage our natural resources successfully; and also on the crucial role of international institutions and government policies achieving this goal.

This volume is an invaluable resource for conservationists, students and those in the private and public sectors concerned to redress the damage being done to the natural world.

Dryland ecosystems have long been considered to have a highly heterogeneous distribution of nutrients and soil biota, with greaterconcentrations of both in soils under plants relative to interspace soils. We examined the distribution of soil resources in two plantcommunities (dominated by either the shrub Coleogyne ramosissima or the grass Stipa hymenoides) at two locations. Interspace soils werecovered either by early successional biological soil crusts (BSCs) or by later successional BSCs (dominated by nitrogen (N)-fixingcyanobacteria and lichens). For each of the 8 plant typecrust type locations, we sampled the stem, dripline, and 3 interspacedistances around each of 3 plants. Soil analyses revealed that only available potassium (K ) and ammonium concentrations wereconsistently greater under plants (7 of 8 sites and 6 of 8 sites, respectively). Nitrate and iron (Fe) were greater under plants at 4 sites, whileall other nutrients were greater under plants at less than 50% of the sites. In contrast, calcium, copper, clay, phosphorus (P), and zincwere often greater in the interspace than under the plants. Soil microbial biomass was always greater under the plant compared to theinterspace. The community composition of N-fixing bacteria was highly variable, with no distinguishable patterns among microsites.Bacterivorous nematodes and rotifers were consistently more abundant under plants (8 and 7 sites, respectively), and fungivorous andomnivorous nematodes were greater under plants at 5 of the 8 sites. Abundance of other soil biota was greater under plants at less than50% of the sites, but highly correlated with the availability of N, P, K and Fe. Unlike other ecosystems, the soil biota was onlyinfrequently correlated with organic matter. Lack of plant-driven heterogeneity in soils of this ecosystem is likely due to (1) interspacesoils covered with BSCs, (2) little incorporation of above-ground plant litter into soils, and/or (3) root deployment patterns.