Andrew R. Watkinson

Multi-functionality and biodiversity in arbuscular mycorrhizas.

Plant roots in natural ecosystems are typically colonized by a wide range of fungi. Some of these are pathogenic, others appear to be opportunistic and have no apparent impact, while mycorrhizal fungi are generally regarded as mutualistic. Of the various types of mycorrhizal fungi, the arbuscular mycorrhizal (AM) association is by far the most abundant and widespread. While the most widely accepted model of AM function depends upon plants benefiting from the facilitation of phosphorus uptake, recent data from field-based studies in temperate ecosystems indicate that only plant species with poorly branched root systems benefit from AM fungi in this way: species with highly branched root systems may benefit in other ways, such as by being protected against root pathogenic fungi. These two responses apparently represent extremes along a continuum of AM benefit determined by root system architecture.

Arbuscular Mycorrhiza Protect an Annual Grass from Root Pathogenic Fungi in the Field

1 Seedlings of the annual grass Vulpia ciliata ssp. ambigua were inoculated in the laboratory with a factorial combination of the cosmopolitan root pathogen Fusarium oxysporum and an arbuscular mycorrhizal (AM) fungus (a Glomus sp.) before being planted out into a natural population of V. ciliata at Mildenhall, UK, from which both fungi had been isolated. 2 At both 62 and 90 days after transplantation, inoculation with Glomus sp. had not increased plant P concentrations, but had protected the plants from the deleterious effects of F. oxysporum infection on shoot and root growth, apparently by suppressing pathogen development in roots. The effects of Glomus sp. on plant performance were negligible in the absence of F. oxysporum. 3 After transplantation, comparisons made of the root-infecting mycofloras of uninoculated plants and plants inoculated only with Glomus sp. showed that the latter developed fewer naturally occurring infections of F. oxysporum and Embellisia chlamydospora, two species of fungi which are correlated with reductions in fecundity in natural populations of V. ciliata. 4 These results confirm conclusions from previous experiments that the main benefit supplied by AM fungi to V. ciliata is in protection from pathogenic fungi, rather than improved P uptake, and indicate that AM colonization significantly alters the rootinfecting mycoflora of V. ciliata. We propose that AM fungi may confer similar benefits in other plant species, which may account for the difficulty in demonstrating a benefit of AM fungi to the P nutrition of host plant species under natural conditions.

A horizon scan of global conservation issues for 2014

Highlights • This is the fifth in our annual series of horizon scans published in TREE.• We identify 15 issues that we considered insufficiently known by the conservation community.• These cover a wide range of issues. Four relate to climate change, two to invasives and two to disease spread.• This exercise has been influential in the past.

Flattening of Caribbean coral reefs: region-wide declines in architectural complexity.

Coral reefs are rich in biodiversity, in large part because their highly complex architecture provides shelter and resources for a wide range of organisms. Recent rapid declines in hard coral cover have occurred across the Caribbean region, but the concomitant consequences for reef architecture have not been quantified on a large scale to date. We provide, to our knowledge, the first region-wide analysis of changes in reef architectural complexity, using nearly 500 surveys across 200 reefs, between 1969 and 2008. The architectural complexity of Caribbean reefs has declined nonlinearly with the near disappearance of the most complex reefs over the last 40 years. The flattening of Caribbean reefs was apparent by the early 1980s, followed by a period of stasis between 1985 and 1998 and then a resumption of the decline in complexity to the present. Rates of loss are similar on shallow (<6 m), mid-water (6–20 m) and deep (>20 m) reefs and are consistent across all five subregions. The temporal pattern of declining architecture coincides with key events in recent Caribbean ecological history: the loss of structurally complex Acropora corals, the mass mortality of the grazing urchin Diadema antillarum and the 1998 El Nino Southern Oscillation-induced worldwide coral bleaching event. The consistently low estimates of current architectural complexity suggest regional-scale degradation and homogenization of reef structure. The widespread loss of architectural complexity is likely to have serious consequences for reef biodiversity, ecosystem functioning and associated environmental services.

One Hundred Questions of Importance to the Conservation of Global Biological Diversity

We identified 100 scientific questions that, if answered, would have the greatest impact on conservation practice and policy. Representatives from 21 international organizations, regional sections and working groups of the Society for Conservation Biology, and 12 academics, from all continents except Antarctica, compiled 2291 questions of relevance to conservation of biological diversity worldwide. The questions were gathered from 761 individuals through workshops, email requests, and discussions. Voting by email to short-list questions, followed by a 2-day workshop, was used to derive the final list of 100 questions. Most of the final questions were derived through a process of modification and combination as the workshop progressed. The questions are divided into 12 sections: ecosystem functions and services, climate change, technological change, protected areas, ecosystem management and restoration, terrestrial ecosystems, marine ecosystems, freshwater ecosystems, species management, organizational systems and processes, societal context and change, and impacts of conservation interventions. We anticipate that these questions will help identify new directions for researchers and assist funders in directing funds.

On the analysis of competition within two-species mixtures of plants

Based on the investigation data of 133 samples from 30 grid stations in the Fujian-Guangdong coastal upwelling region (21.6 degrees - 24.3 degrees N,115.7 degrees -118.7 degrees E) in 11-16 June 2009, this paper studied the phytoplankton species composition and cell abundance in the region in three dimensions (vertical, horizontal, and sectional), and approached their relations with major environmental factors. A total of 159 taxa belonging to 85 genera of 4 phyla were identified, among which, diatom was predominant, followed by dinoflagellate. Cyanophyceae mainly composed of Trichodesmium also occupied a greater proportion, but Chrysophyceae was only checked out in the upper 10 m water layer at coastal stations. The dominant species were Rhizosolenia alata f. gracillma, Thalassionema nitzschioides, Pseudonitzschia pungens, Skeletonema costatum, Thalassionema frauenfeldii, Paralia sulcata, Guinadia striata, Trichodesmium thiebautii, Ceratium fusus, and Gyrodinium spirale. Most of the phytoplankton taxa were cosmopolitan species, followed by warm-water species, while tropic high-salinity or oceanic eurythermal species were lesser. The cell abundance of the phytoplankton was average of 67.59 x10(2) ind x L(-1). In vertical profile, the cell abundance of the phytoplankton was the highest in surface water, and decreased with water depth. In horizontal and sectional profiles, the cell abundance had no definite patterns, but the high abundance region was in Nanao Island water area, being anastomosed with the center of upwelling region, which indicated that the weak and small intensity of deep-sea water upwelling caused lesser phytoplankton cell abundance and superposition. The comparatively high phytoplankton cell abundance in the four sections (B, C, D, E) along Nanao-Zhangpu was resulted from the upwelling from Taiwan Bank. The phytoplankton cell abundance had a significant positive correlation with the PO4(3-) concentration in the upper 10 m water layer, but no correlation with the dissolved inorganic nitrogen (DIN) concentration. Thereby, to study the eco-physiological responses of phytoplankton species to nutrient stress would be helpful to reveal the formation mechanism of algal bloom in upwelling region.(1) Replacement series experiments have been used extensively in studies of interactions between two species. These are usually carried out at a single total density, and, as a result, the effects of intraspecific competition cannot be isolated from those of interspecific competition. These factors can only be separated if both freqency and total density are varied. (2) A model to describe competition in two-species mixtures is presented which can be used to estimate survival, mean yield per plant and yield per unit area for each species at any combination of frequency and density. This model is more succinct and easier to interpret than the replacement series analysis of de Wit (1960). (3) The model is used to analyse data from an experiment in which Agrostemma githago and Triticum aestivum were grown in monocultures and 1:1 mixtures at five total densities. Surviving Triticum plants responded to the average Agrostemma plant as if the latter were equivalent to 1.63 Triticum plants, whilst Triticum was equivalent to 0.41 Agrostemma plants. (4) Data previously published by Marshall & Jain (1969) are reanalysed to show that the competitive superiority of Avena fatua over A. barbata was underestimated by replacement series analysis. (5) It is argued that this model should be used in preference to replacement series analysis whenever both frequency and total density vary, for example in weed-crop systems and in intercropping situations.

A Method to Quantify the Effects of Human Disturbance on Animal Populations

1. The extent and consequences of human disturbance on populations of vertebrates are contentious issues in conservation. As recreational and industrial uses of the countryside continue to expand, it is becoming increasingly important that the effects of such disturbance on wildlife are quantified. 2. This study describes a method of quantifying the effect of disturbance, based on measuring the trade-off between resource use and risk of disturbance. This approach is based on one used by ethologists to study the effects of predation risk on patch use. 3. Pink-footed geese, Anser brachyrhynchus, feeding on arable fields, are highly responsive to disturbance from surrounding roads. The extent to which these fields are exploited declines linearly with increasing risk of disturbance. The reduction in use of these feeding grounds caused by disturbance can be quantified by translating the biomass of food not exploited into the number of birds that this food could have supported. 4. This approach allows both quantification of the impact of disturbance on a population, and exploration of the potential consequences of changes in disturbance on the size of populations.

Density-dependence in single-species populations of plants

Abstract The general form of yield-density relationships in plant populations is discussed with reference to reciprocal equations and the 3 2 power law, which describes the concomitant changes in plant weight and density during self-thinning. A model to describe the pattern of mortality in high density populations is also discussed with particular reference to the nature of intraspecific competition within plant populations. A reparameterized version of a reciprocal equation proposed by Bleasdale & Nelder is used to describe the relationship between individual plant weight and surviving plant density. The biological interpretation of the parameters is discussed in relation to the dry matter production of isolated plants, the density at which mutual interference between neighbours becomes appreciable, and the efficiency of resource utilization at high densities. The reparameterized equation is then used together with an equation which describes mortality during self-thinning as the basis for a new model to describe the relation between total plant yield and sowing density. The law of allometry is used in conjunction with the model to describe the relationship between the weight of a plant part and density, and this then forms the basis for a model of the population dynamics of annual plants with effectively discrete generations. Finally the dynamical behaviour of plant populations is discussed. It is concluded that most plant populations will show neighbourhood stability with exponential or perhaps oscillatory damping towards an equilibrium.

HURRICANES AND CARIBBEAN CORAL REEFS: IMPACTS, RECOVERY PATTERNS, AND ROLE IN LONG-TERM DECLINE

The decline of corals on tropical reefs is usually ascribed to a combination of natural and anthropogenic factors, but the relative importance of these causes remains unclear. In this paper, we attempt to quantify the contribution of hurricanes to Caribbean coral cover decline over the past two decades using meta-analyses. Our study included published and unpublished data from 286 coral reef sites monitored for variable lengths of time between 1980 and 2001. Of these, 177 sites had experienced hurricane impacts during their period of survey. Across the Caribbean, coral cover is reduced by ∼17%, on average, in the year following a hurricane impact. The magnitude of this immediate loss increases with hurricane intensity and with the time elapsed since the last impact. In the following year, no further loss is discernible, but the decline in cover then resumes on impacted sites at a rate similar to the regional background rate of decline for nonimpacted sites. There is no evidence of recovery to a pre-storm state for at least eight years after impact. Overall, coral cover at sites impacted by a hurricane has declined at a significantly faster rate (6% per annum) than nonimpacted sites (2% per annum), due almost exclusively to higher rates of loss in the year after impact in the 1980s. While hurricanes, through their immediate impacts, appear to have contributed to changing coral cover on many Caribbean reefs in the 1980s, the similar decline in coral cover at impacted and nonimpacted sites in the 1990s suggests that other stressors are now relatively more important in driving the overall pattern of change in coral cover in this region. The overall lack of post-hurricane recovery points to a general impairment of the regeneration potential of Caribbean coral reefs.

Recent Region-wide Declines in Caribbean Reef Fish Abundance

Profound ecological changes are occurring on coral reefs throughout the tropics, with marked coral cover losses and concomitant algal increases, particularly in the Caribbean region. Historical declines in the abundance of large Caribbean reef fishes likely reflect centuries of overexploitation. However, effects of drastic recent degradation of reef habitats on reef fish assemblages have yet to be established. By using meta-analysis, we analyzed time series of reef fish density obtained from 48 studies that include 318 reefs across the Caribbean and span the time period 1955-2007. Our analyses show that overall reef fish density has been declining significantly for more than a decade, at rates that are consistent across all subregions of the Caribbean basin (2.7% to 6.0% loss per year) and in three of six trophic groups. Changes in fish density over the past half-century are modest relative to concurrent changes in benthic cover on Caribbean reefs. However, the recent significant decline in overall fish abundance and its consistency across several trophic groups and among both fished and nonfished species indicate that Caribbean fishes have begun to respond negatively to habitat degradation.