Increase In Species Evenness Research Articles

Longevity of centenarians is reflected by the gut microbiome with youth-associated signatures.

Centenarians are an excellent model to study the relationship between the gut microbiome and longevity. To characterize the gut microbiome signatures of aging, we conducted a cross-sectional investigation of 1,575 individuals (20-117 years) from Guangxi province of China, including 297 centenarians (n = 45 with longitudinal sampling). Compared to their old adult counterparts, centenarians displayed youth-associated features in the gut microbiome characterized by an over-representation of a Bacteroides-dominated enterotype, increase in species evenness, enrichment of potentially beneficial Bacteroidetes and depletion of potential pathobionts. Health status stratification in older individuals did not alter the directional trends for these signature comparisons but revealed more apparent associations in less healthy individuals. Importantly, longitudinal analysis of centenarians across a 1.5-year period indicated that the youth-associated gut microbial signatures were enhanced with regard to increased evenness, reduction in interindividual variation and stability of Bacteroides, and that centenarians with low microbial evenness were prone to large microbiome instability during aging. These results together highlight a youth-related aging pattern of the gut microbiome for long-lived individuals.

Synergistic Effect of Dwarf Bamboo Flowering and Wild Boar Rooting on Forest Regeneration

Sasa spp., monocarpic dwarf bamboos, are known to form recalcitrant understories, lower species diversity, and hinder forest development. Sasa borealis distributed throughout Korea showed a phenomenon of synchronized dieback after large-scale synchronized flowering nationwide around 2015. Therefore, we conducted this study to take advantage of the rare event and add prevailing activity of wild boars and culm removal to elucidate whether they promote the regeneration of a long-term suppressed forest. We set permanent plots in forests with different understory types, and tracked the vegetation change in 5 years with respect to species composition, tree regeneration, and S. borealis reestablishment. This study focused on comparison between plots established after mass flowering. In flowering stands, we found the species diversity increased significantly with increase in species evenness, but not with recruitment of new species. Furthermore, the seeds of mass-produced bamboo germinated, and the seedling abundance was found to increase considerably. In stands rooted by wild boar, species diversity increased through the recruitment of new species, including tree species. It increased the abundance of shrub and perennial herbs, while it suppressed the reestablishment of S. borealis. Although rooting effect was independently significant regardless of flowering, the synergistic effect of rooting and flowering on forest regeneration was outstanding. Wild boar seemed to function as a remover of dead culms and a breaker of remaining underground mats as well as a seed disperser. Consequently, the species composition became similar to the reference stands. However, culm cutting caused negative effects by facilitating S. borealis to re-occupy or resprout. Overall, as the wild boar population increases, the positive effect can be expected to enhance. At landscape scale, considering several factors such as flowering and non-flowering, and population size of wild boar, the long-term suppressed forests by S. borealis are projected to regenerate with mosaic forests.

Developing climate‐smart restoration: Can plant microbiomes be hardened against heat waves?

Heat waves are increasing in frequency and intensity, presenting a challenge for the already difficult practice of ecological restoration. We investigated whether pre-heating locally sourced rhizosphere soil (inoculum) could acclimatize plants to a field-imposed heat wave in a restoration setting. Soil heating in the laboratory caused a marked shift in rhizosphere bacterial community composition, accompanied by an increase in species evenness. Furthermore, pre-heated rhizosphere soil reduced plant height, number of leaves, and shoot mass of the C4 grass, blue grama (Bouteloua gracilis), and it reduced the shoot mass of the C3 grass, Arizona fescue (Festuca arizonica) in the glasshouse. Following transplantation and the application of a field heat wave, pre-heated inoculum did not influence heat wave survival for either plant species. However, there were strong species-level responses to the field heat wave. For instance, heat wave survivorship was over four times higher in blue grama (92%) than in Arizona fescue (22%). These results suggest that the use of C4 seeds may be preferable for sites exhibiting high heat wave risk. Further research is needed to understand whether inocula are more effective in highly degraded soil in comparison with partially degraded soils.

Habitat heterogeneity facilitates resilience of diurnal raptor communities to hurricane disturbance

The response of avian communities to hurricane disturbance may differ according to their specific requirements or functional groups, but little is known regarding the response of top-predator birds of prey to these disturbances. We aimed to evaluate the influence of the major Hurricane Patricia on the diversity of diurnal raptors in tropical dry forest, along the coast of Jalisco, Mexico. We conducted raptor surveys at 13 sites located within the eyewall radius of maximum hurricane winds along the path of the hurricane, and 16 sites located outside the hurricane eyewall. We compared the density and species richness of raptors among four habitats of tropical deciduous and semi-deciduous forest, mangroves, and agricultural fields, within the hurricane eyewall and outside the radius of maximum winds. Our results demonstrated a reduction in raptor density in tropical forests within the radius of maximum hurricane winds, where raptor density was significantly lower in deciduous forests within the hurricane eyewall compared to deciduous forests outside the eyewall. Species richness of diurnal raptors was similar among habitats and conditions with the exception that mangroves within the hurricane eyewall had significant higher raptor species richness compared to mangroves outside the eyewall. There was also a significant increase in species evenness, and decrease in similarity, of raptor communities in mangroves and deciduous forest sites within the hurricane eyewall compared to sites outside the eyewall. The reduced density of diurnal raptors in tropical forest sites within the path of the hurricane probably reflects the impact of hurricane winds on forest structure, whereas the increase in species richness and evenness of raptor communities in mangroves within the hurricane eyewall suggests that these habitats could provide a refuge for diurnal raptors following hurricane disturbance. Our results highlight the importance of maintaining landscape heterogeneity of native vegetation to provide alternate habitats for wildlife communities following major disturbance, and facilitate their resilience to extreme climatic events such as hurricanes.

Interactions between repeated fire, nutrients, and insect herbivores affect the recovery of diversity in the southern Amazon

Surface fires burn extensive areas of tropical forests each year, altering resource availability, biotic interactions, and, ultimately, plant diversity. In transitional forest between the Brazilian cerrado (savanna) and high stature Amazon forest, we took advantage of a long-term fire experiment to establish a factorial study of the interactions between fire, nutrient availability, and herbivory on early plant regeneration. Overall, five annual burns reduced the number and diversity of regenerating stems. Community composition changed substantially after repeated fires, and species common in the cerrado became more abundant. The number of recruits and their diversity were reduced in the burned area, but burned plots closed to herbivores with nitrogen additions had a 14 % increase in recruitment. Diversity of recruits also increased up to 50 % in burned plots when nitrogen was added. Phosphorus additions were related to an increase in species evenness in burned plots open to herbivores. Herbivory reduced seedling survival overall and increased diversity in burned plots when nutrients were added. This last result supports our hypothesis that positive relationships between herbivore presence and diversity would be strongest in treatments that favor herbivory--in this case herbivory was higher in burned plots which were initially lower in diversity. Regenerating seedlings in less diverse plots were likely more apparent to herbivores, enabling increased herbivory and a stronger signal of negative density dependence. In contrast, herbivores generally decreased diversity in more species rich unburned plots. Although this study documents complex interactions between repeated burns, nutrients, and herbivory, it is clear that fire initiates a shift in the factors that are most important in determining the diversity and number of recruits. This change may have long-lasting effects as the forest progresses through succession.

Life form and species diversity on abandoned croplands, Roggeveld, South Africa

The Roggeveld consists of an island of Mountain Renosterveld (Fynbos biome) surrounded by Succulent Karoo biome vegetation. Since management of abandoned croplands depends on a better understanding of their succession sequences, vegetation recovery on abandoned croplands in the Roggeveld was studied using species and life form diversity parameters. Abandoned croplands of different ages were compared with each other and to the natural vegetation. Therophytes and chamaephytes were the most abundant life forms. Chamaephytes made an overwhelming contribution to the relative cover. Species-area curves (exponential function) differed significantly between the abandoned croplands and natural vegetation. Species richness increased with time since abandonment but no similar increase in species evenness, Shannon or Simpson indices were found. A regression of species richness against age of abandoned cropland predicted that an abandoned cropland of approximately 33 years should be as species rich as the natural vegetation, but a principal cooordinate analysis of floristic data indicated that all the plots were floristically still extremely different from the natural vegetation. Across all nine survey plots only 15 species contributed to a high cover on the plots. Vegetation recovery on abandoned croplands in the Roggeveld occurs naturally, yet the rate of recovery varies among the life forms.

Plant diversity consequences of a herbivore‐driven biome switch from Grassland to Nama‐Karoo shrub steppe in South Africa

AbstractQuestionsHow does heavy grazing change plant community structure, composition and species richness and diversity in an ecotone between grassland and semi‐arid shrub steppe‐type vegetation? Does grazing favour plants with arid affinity over those with less arid affinity? Does the grazing‐induced transformation constitute a switch to the equivalent of a shrub‐dominated biome?LocationCentral South Africa.MethodsUsing systematic scanning of SPOT 5 imagery and ground‐truthing, a grazing treatment area was selected that met criteria of intensity of grazing, sampling requirements, and biogeographical position within a broad ecotonal zone. Differential vegetation responses to heavy grazing were tested for significant differences in plant traits, vegetation structure, and species diversity, richness and evenness. Gamma diversity was calculated for the whole study site, whereas, independent beta diversity was calculated across the treatments assuming the additive partitioning of diversity. In addition, the biogeographical association of grazing‐induced species shifts was determined using a range of available databases.ResultsCanopy cover and height of woody shrubs increased significantly with heavy grazing whereas that of graminoid plants declined. The resultant species turnover was modest, apparent extinctions of local species were minimal, species richness was maintained and species diversity was significantly enhanced. There was a significant increase in species evenness, through possible suppression of dominant species. Significant increases in species cover were those associated with mainly the Nama‐Karoo biome indicating that species from more arid areas are more resistant to grazing as would be expected by the convergence model of aridity and grazing resistance.ConclusionsThe significant increase in shrub cover in heavily grazed semi‐arid grassland followed general global expectations. The study confirmed that the supposed former large shift of grassland to shrubby Nama‐Karoo in the eastern upper Karoo can indeed be readily affected by heavy grazing. The negative connotations for biodiversity that have often been associated with intense grazing seem, in terms of the positive responses of plant species diversity in this study, to perhaps be exaggerated. The elevated species diversity with grazing of vegetation with a long evolutionary grazing history in a low resource area may require a reappraisal of the application of certain grazing hypotheses.

Changes in the planktonic copepod community in a landlocked bay in the subtropical coastal waters of Hong Kong during recovery from eutrophication

Tolo Harbour is a poorly flushed bay in the northeastern corner of Hong Kong. Eutrophication caused by discharge of untreated and secondarily treated sewage into the bay was first detected during the 1970s. Increased nutrient input led to a noticeable increase in algal biomass and algal bloom occurrences. Nutrient reduction measures, including the construction of a pipeline to export all sewage effluents from Tolo Harbour, were introduced during the late 1980s. Decline in nutrient levels and decrease in the number of algal blooms have been recorded since 1998 when all nutrient reduction measures became fully operational. Zooplankton samples collected during 2003–2004 revealed that Tolo Harbour still contained a higher density and lower diversity of planktonic copepods compared to Mirs Bay, a less-polluted sea area outside Tolo Harbour. A comparison between data collected in this study to those collected during 1988–1990, several years before nutrient reduction measures were to be fully implemented, showed a decrease in copepod densities and an increase in copepod diversity. Small copepods, notably species of Paracalanus and Oithona, dominated the copepod communities in both periods, but there was an increase in species evenness during 2003–2004, caused by an increase in the number of dominant species. These observations confirm that eutrophication may lead to increases in copepod densities accompanied by increased dominance of small species.

Sexual recruitment of trees in strip cuts in eastern Canada

I tested a sexual recruitment model that couples equations for seed production, dispersal, and juvenile survivorship using 10 sets of recent strip cuts in Quebec and New Brunswick. The model states that seed production is dependent on basal area and inversely proportional to seed mass, while juvenile survival is directly proportional to seed mass. In consequence, the seed mass effects should (roughly) cancel out, and fecundity should be primarily a function of basal area. Further, the model predicts that species evenness should be more or less the same following strip-cutting. As expected from the model, the single best predictor (r2 = 0.53) of recruitment density was the basal area density (area/area) of the source trees, and all cuts were well stocked. There was a stronger tendency toward a post-harvest increase in species evenness than was expected. Ninety percent of all stems were recruited by the fourth growing season.

Patterns of diversity and composition of Mediterranean ground ant communities tracking spatial and temporal variability in the thermal environment.

The present study analyzed ant community structure and the factors affecting it in the Spanish Mediterranean area. The aim of this study was to test whether temperature controls the composition and diversity of the ground ant fauna and the spatial and temporal distribution of dominance groups along adjacent communities. The main descriptors of community structure (except perharps species richness) were found to vary along the gradient of vegetation cover: increased vegetation cover resulted in an increase in the relative abundance of the most common species, which led to a significant decrease in species evenness, together with a reduction in total ant density on the ground. In open habitats, dominant and subordinate species were abundant during different periods of the day, and this led to an increase in species evenness. In areas with high vegetation cover, dominants benefited from the lower temperatures by lengthening their periods of activity. This resulted in a decrease in the abundance of subordinate species, and in lower evenness. Seasonal patterns in community structure tracked temperature fluctuations and varied between habitat types. Evenness was similar in the two habitat types in spring, but increased in grasslands and decreased in shrublands/forests in summer. Species richness did not vary between seasons or habitat types. The relative abundance of dominance groups in the two types of habitats showed a different pattern between seasons. In grasslands, subordinates increased and dominants decreased their relative abundance from spring to summer, while in shrublands/forests, the opposite pattern was found. The overall conclusion from this study is that ground ant communities in open areas are primarily regulated by temperature variations, while in shrublands and forests, dominant species are more abundant, and competitive interactions appear to be the major structuring force.

Sexual recruitment of trees in strip cuts in eastern Canada

I tested a sexual recruitment model that couples equations for seed production, dispersal, and juvenile survivorship using 10 sets of recent strip cuts in Quebec and New Brunswick. The model states that seed production is dependent on basal area and inversely proportional to seed mass, while juvenile survival is directly proportional to seed mass. In consequence, the seed mass effects should (roughly) cancel out, and fecundity should be primarily a function of basal area. Further, the model predicts that species evenness should be more or less the same following strip-cutting. As expected from the model, the single best predictor (r2 = 0.53) of recruitment density was the basal area density (area/area) of the source trees, and all cuts were well stocked. There was a stronger tendency toward a post-harvest increase in species evenness than was expected. Ninety percent of all stems were recruited by the fourth growing season.