Explore the vast range of titles available.

Trie fluctuating resource hypothesis (FRH) proposes that fluctuations in resource supply can temporally reduce competitive pressure from resident species, thereby providing ephemeral opportunities for invading species. Although FRH has the potential to integrate many existing hypotheses regarding mechanisms of community invasibility, previous tests and evaluations of FRH were based on single trophic level, did not take the timing effect into account, and had difficulties in distinguishing the effects of resource pulses from other simultaneous processes. Here we test FRH in multi-trophic aquatic microcosms by creating resource pulses, by controlling resource quantity, propagule supply and pulse recurrence frequency, and by manipulating the timing of pulses relative to the timing of the arrival of new species (i. e. invaders) to local communities.The novelty of our work lies in that we directly manipulate resource pulse timing relative to invader introduction events and thus demonstrate the importance of this timing effect for community invasibility. Our study supports FRH in general: invasion success was positively related to resource pulses, and invaders had strong performance in treatments receiving coincident pulses, although not all invaders gained more benefit when resources were supplied at large-magnitude than supplied at continuous rates. Since many ecosystems worldwide are experiencing high rates of anthropogenic nutrient input and increasing rates of precipitation, these ecosystems are potentially more fragile and susceptible to invasion. More experiments across multiple ecosystem types are needed to help formulate a general theory of community invasibility.

Background: Spore discharge in the majority of the 30,000 described species of Basidiomycota is powered by the rapid motion of a fluid droplet, called Buller's drop, over the spore surface. In basidiomycete yeasts, and phytopathogenic rusts and smuts, spores are discharged directly into the airflow around the fungal colony. Maximum discharge distances of 1–2 mm have been reported for these fungi. In mushroom-forming species, however, spores are propelled over much shorter ranges. In gilled mushrooms, for example, discharge distances of <0.1 mm ensure that spores do not collide with opposing gill surfaces. The way in which the range of the mechanism is controlled has not been studied previously. Methodology/Principal Findings: In this study, we report high-speed video analysis of spore discharge in selected basidiomycetes ranging from yeasts to wood-decay fungi with poroid fruiting bodies. Analysis of these video data and mathematical modeling show that discharge distance is determined by both spore size and the size of the Buller's drop. Furthermore, because the size of Buller's drop is controlled by spore shape, these experiments suggest that seemingly minor changes in spore morphology exert major effects upon discharge distance. Conclusions/Significance: This biomechanical analysis of spore discharge mechanisms in mushroom-forming fungi and their relatives is the first of its kind and provides a novel view of the incredible variety of spore morphology that has been catalogued by traditional taxonomists for more than 200 years. Rather than representing non-selected variations in micromorphology, the new experiments show that changes in spore architecture have adaptive significance because they control the distance that the spores are shot through air. For this reason, evolutionary modifications to fruiting body architecture, including changes in gill separation and tube diameter in mushrooms, must be tightly linked to alterations in spore morphology.

Nutrient enrichment, ecosystem size, and richness each may directly affect the stability of both populations and communities. Alternatively, nutrient enrichment and ecosystem size each may directly affect richness, which in turn may affect stability. No previous studies, however, have tested empirically how these three factors interact and co-determine stability. We manipulated nutrient input and ecosystem size in replicate microcosms containing a diverse bacterial flora, and a range of green algae and heterotrophic protozoa, and used these manipulations and the resulting variation in species richness to measure their combined effects on temporal stability of both populations and communities. Results showed that nutrient enrichment and ecosystem size controlled protist richness, and their effects on stability could be mediated by richness. In addition, both community-level and population-level stability increased with protist richness. Furthermore, mean species evenness and mean species richness was negatively related. Effects of statistical averaging, overyielding, and component population stability were identified as possible mechanisms involved explaini ng the stabilizing effects of richness on community stability. Their relative strength in influencing stability, however, is likely to change as mean evenness decreased with increasing richness. This decrease in evenness would tend to weaken the strength of the statistic averaging effect, but increase the strength of the other two mechanisms due to relatively lower population variability (component population stability) and higher mean biovolumes of dominant protists (overyielding).

1. Ecologists seem poised to reap the benefits of recent work examining the effects of energy and resources on plant taxonomic richness in local communities. My goal here is to present a qualitative model to further our understanding about the driving forces of plant taxonomic richness across spatial scales. 2. The model attempts to predict local plant species richness based on previous work regarding (i) correlations between temperature, precipitation and richness, (ii) correlations between soil nutrient availability and richness derived from both descriptions and experimental manipulations, and (iii) empirical demonstrations of the importance of the species pool in regulating local species richness. 3. The model consists of a phenomenlogical submodel of the multiplicative effects of temperature, water and mineral nutrients on plant species richness, with a spatially implicit submodel of immigration and extinction of species in local communities. 4. The model makes the following five testable predictions. (i) Local richness increases linearly with immigration rate of new species and curvilinearly with local extinction rate. (ii) The effects of altered local immigration and extinction rates will be most apparent in local communities embedded in species-rich metacommunities. (iii) Local communities are not saturated, but rather increase in richness directly with increasing metacommunity richness. (iv) Unimodal or hump-shaped productivity-richness relations arise when low water or temperature limit diversity at low productivity and mineral nutrients limit diversity at high productivity. (v) An apparent scale-dependence of the effect productivity on richness should arise when there exists a matching scale-dependence of the underlying environmental drivers. These predictions do not contrast sharply with available data, but remain largely untested. 5. I suggest that continued attempts to synthesize the most predictive patterns emerging from the burgeoning global data bases of both taxonomic and genetic diversity will guide us toward mechanistic explanations of the determinants of species richness, suggest why special cases differ from general patterns, and provide additional novel predictions not currently apparent.

A number of authors have suggested that, within areas a few square meters to many square kilometers in size, species diversity appears to peak at moderate levels of productivity, and this pattern is currently unexplained. Among the best examples of this pattern have been descriptions of vegetation in which species richness declines as soil fertility increases. We tested two hypotheses that have been proposed to explain this pattern. The interspecific competitive exclusion hypothesis proposes that dominant species suppress the growth of competitively subordinate species and exclude subordinate species as fertility rises. In contrast, the assemblage-level thinning hypothesis proposes that individuals of all species tend to become larger as fertility rises, and individuals of all species tend to exclude subordinate individuals of each species. Because total density declines, samples of finite numbers of individuals will result in fewer species by chance alone. To test these hypotheses, we established an experimental productivity gradient in a first-year old field using four levels of slow-release NPK fertilizer (0, 8, 16, and 32 g N/m2)). At the end of the growing season, we sampled aboveground biomass and numbers of stems for each species in 72 20 × 20 cm subplots (18 reps × 4 levels), with an average sample size of 260 individual stems per plot. We observed an 80% decline in stem density with increasing fertility, and a 50% decline in species richness along this fertility gradient. A simulation of random thinning along a fertility gradient showed a nearly identical decline in species richness, supporting the assemblage-level thinning hypothesis. We also found that responses of individual species to the soil fertility gradient showed virtually no support for interspecific competitive exclusion. The overwhelming influence of density found in this study suggests that plant species richness along many productivity gradients may be strongly influenced by total stem density, and that differences in competitive ability among species, although generally important, are not necessary to create dramatic changes in species richness along fertility gradients.

• Premise of the study: A growing body of literature now documents how ancient human management of the landscape echoes through to extant environments in eastern North America. Plant domestication is a major theme in the study of human–nature interactions. Long-term ecological impacts of human selection may last for centuries after management ends, yet little work has focused on legacies in the evolution of historically used trees. Ecological data will be valuable in teasing apart myriad variables that confound questions of land-use legacies. We discuss the potential for legacies of ancient human selection and present a preliminary case study for the approach of integrating ecological and historical data for Diospyros virginiana, the American persimmon.• Methods: Herbarium samples of D. virginiana (28 male and 40 female) from across the species range provided specimen localities for edaphic analysis. Soil and environmental data were analyzed using nonparametric ordination, Wilcoxon summed rank test, and permutational MANOVA.• Key results: Edaphic data demonstrated substantial variation among sites, but revealed no significant differences between sexes. Permutational MANOVA showed no difference in environmental preferences for the tested variables between male and female trees (R2 < 0.01, P = 0.8).• Conclusions: Extending our understanding of landscape history to the long-term impacts of artificial selection at the species or population level would be valuable in both theoretical and applied botanical research. Multidisciplinary approaches integrating ecological data will be essential for investigation of the evolutionary implications of historical human selection in economic species and the potential for adaptive flexibility in reproductive systems of long-lived perennials.

Neighboring genes predictably share similar evolutionary histories to an extent delineated by recombination. This correlation should extend across multiple linked genes in a selfing species such as Arabidopsis thaliana due to its low effective recombination rate. To test this prediction, we performed a molecular population genetics analysis of nucleotide polymorphism and divergence in chromosomal regions surrounding four low-diversity loci. Three of these loci, At1g67140, At3g03700, and TERMINAL FLOWER1 (TFL1), have been previously implicated as targets of selection and we would predict stronger correlations in polymorphism between neighboring loci due to genetic hitchhiking around these loci. The remaining locus, At1g04300, was identified in a study of linkage disequilibrium surrounding the CRYPTOCHROME2 (CRY2) locus. Although we found broad valleys of reduced nucleotide variation around two of our focal genes, At1g67140 and At3g03700, all chromosomal regions exhibited extreme variation in the patterns of polymorphism and evolution between neighboring loci. Although three of our four regions contained potential targets of selection, application of the composite-likelihood-ratio test of selection in conjunction with a goodness-of-fit test supports the selection hypothesis only for the region containing At3g03700. The degree of discordance in evolutionary histories between linked loci within each region generally correlated with estimates of recombination and linkage disequilibrium for that region, with the exception of the region containing At1g04300. We discuss the implications of these data for future population genetics analyses and genomics studies in A. thaliana.

An increase in the quantity of available resources is known to affect temporal variability of aggregate community properties. However, it is unclear how might fluctuations in resource availability alter community-level temporal variability. Here we conduct a microcosm experiment with laboratory protist community subjected to manipulated resource pulses that vary in intensity, duration and time of supply, and examine the impact of fluctuating resource availability on temporal variability of the recipient community. The results showed that the temporal variation of total protist abundance increased with the magnitude of resource pulses, as protist community receiving infrequent resource pulses (i.e., high-magnitude nutrients per pulse) was relatively more unstable than community receiving multiple resource pulses (i.e., low-magnitude nutrients per pulse), although the same total amounts of nutrients were added to each community. Meanwhile, the timing effect of fluctuating resources did not significantly alter community temporal variability. Further analysis showed that fluctuating resource availability increased community temporal variability by increasing the degree of community-wide species synchrony and decreasing the stabilizing effects of dominant species. Hence, the importance of fluctuating resource availability in influencing community stability and the regulatory mechanisms merit more attention, especially when global ecosystems are experiencing high rates of anthropogenic nutrient inputs.

Conservation requires knowledge of the interaction between an organism and its environment. Thermal conditions have an important role in habitat selection, movement, and maintenance of physiological processes for ectotherms. We found that box turtles chose cooler temperatures than expected and allowed their body temperatures to match the environment, but that this had little effect on their movement.AbstractEnvironmental conditions may affect individual physiological processes that influence short-term performance and ultimately growth, survival and reproduction. As such, habitats selected by animals must provide suitable and adequate resources. Ectothermic species are highly dependent on climatic conditions and ambient temperatures that dictate body temperature regulation and in turn physiological processes. We investigated the thermoregulatory performance, habitat selection, and movements of an ectothermic vertebrate, the Eastern box turtle (Terrapene carolina carolina) to assess the importance of thermoregulatory physiology in habitat selection. We evaluated the relationship between habitat selection and thermoregulatory performance in Southwest Ohio over two active seasons from May until October. We found that T. carolina selected shaded habitats, including evergreen and deciduous forests, as well as herbaceous grasslands, conformed to the ambient temperatures throughout the active season, although these habitats had temperatures below those expected based on thermal optima of box turtles. Further, we found that movement was not correlated with internal body temperature. Our study shows that thermal conditions are not paramount in habitat selection of box turtles, but that cooler temperatures do not have an effect on the extent of their locomotion.