Annual Species Richness Research Articles

Species richness in relation to phosphorus and competition in a Mediterranean dwarf-shrub community

Changes in species richness and productivity in a Mediterranean dwarf-shrub community were documented during 5 years following treatments intended to improve soil fertility and reduce shrub cover. Five treatments, replicated five times, were tested: (a) shrub cover reduction by selective herbicide application; (b) application of medium levels of phosphorus; (c) application of high doses of phosphorus; (d) a combined herbicide and phosphorus application; (e) an untreated control. Species were classified into nine functional groups according to life cycle, growth form and taxonomy: trees, shrubs, climbers, geophytes, perennial and annual grasses, annual legumes, perennial and annual forbs. The perennial and annual grasses, climbers, perennial forbs and geophytes showed no significant response to any treatment. Phosphorus application significantly increased the productivity and the richness of annual legume species, while herbicide treatment significantly reduced the frequency and richness of shrubs and increased those of annual forbs. Greater biomass production did not lead to a decrease in species richness; on the contrary, it was positively related to greater species richness, especially of the legume component.

Understorey plant community structure in lower montane and subalpine forests, Grand Canyon National Park, USA

AbstractAim Our objectives were to compare understorey plant community structure among forest types, and to test hypotheses relating understorey community structure within lower montane and subalpine forests to fire history, forest structure, fuel loads and topography.Location Forests on the North Rim of Grand Canyon National Park, Arizona, USA.Methods We measured understorey (< 1.4 m) plant community structure in 0.1‐ha plots. We examined differences in univariate response variables among forest types, used permutational manova to assess compositional differences between forest types, and used indicator species analysis to identify species driving the differences between forest types. We then compiled sets of proposed models for predicting plant community structure, and used Akaike's information criterion (AICC) to determine the support for each model. Model averaging was used to make multi‐model inferences if no single model was supported.Results Within the lower montane zone, pine–oak forests had greater understorey plant cover, richness and diversity than pure stands of ponderosa pine (Pinus ponderosa P. & C. Lawson var. scopulorum Engelm.). Plant cover was negatively related to time since fire and to ponderosa pine basal area, and was highest on northern slopes and where Gambel oak (Quercus gambelii Nutt.) was present. Species richness was negatively related to time since fire and to ponderosa pine basal area, and was highest on southern slopes and where Gambel oak was present. Annual forb species richness was negatively related to time since fire. Community composition was related to time since fire, pine and oak basal area, and topography. Within subalpine forests, plant cover was negatively related to subalpine fir basal area and amounts of coarse woody debris (CWD), and positively related to Engelmann spruce basal area. Species richness was negatively related to subalpine fir basal area and amounts of CWD, was positively related to Engelmann spruce basal area, and was highest on southern slopes. Community composition was related to spruce, fir and aspen basal areas, amounts of CWD, and topography.Main conclusions In montane forests, low‐intensity surface fire is an important ecological process that maintains understorey communities within the range of natural variability and appears to promote landscape heterogeneity. The presence of Gambel oak was positively associated with high floristic diversity. Therefore management that encourages lightning‐initiated wildfires and Gambel oak production may promote floristic diversity. In subalpine forests, warm southern slopes and areas with low amounts of subalpine fir and CWD were positively associated with high floristic diversity. Therefore the reduction of CWD and forest densities through managed wildfire may promote floristic diversity, although fire use in subalpine forests is inherently more difficult due to intense fire behaviour in dense spruce–fir forests.

Life-history Habitat Matching in Invading Non-native Plant Species

We briefly reviewed the literature on habitat matching in invading non-native plant species. Then we hypothesized that the richness and cover of native annual and perennial plant species integrate complex local information of vegetation and soils that would help to predict invasion success by similarly adapted non-native plant species. We tested these ‘life-history habitat matching’ relationships in 603 0.1-ha plots, including 294 plots in Colorado, which were relatively high for the cover of native perennial plant species, and for 309 0.1-ha plots in southern Utah, which were relatively high in the cover of native annual plant species. We found strong positive relationships between the richness and foliar cover for both native and non-native species, whether they were annual or perennial species (0.34 > r 2 < 0.53; P < 0.0001). We also found significant positive relationships between the cover of native annual species at a site and the richness (r 2 = 0.13; P < 0.0001) and the foliar cover (r 2 = 0.06; P < 0.0001) of non-native annual species. The proportion of non-native annual species in the flora of a plot also increased significantly with the foliar cover of native annual species. Conversely, the richness and cover of non-native annual species were significantly negatively associated with the foliar cover of native perennial species (r 2 = 0.05 and 0.06, respectively; P < 0.0001). The cover of non-native annual or perennial species was not significantly correlated with soil texture variables, %N, or %C. We conclude that there may be a high degree of life-history habitat matching by non-native annual species in these study sites. Information on native annual and perennial species richness and cover may help characterize the complex soils, climate, and disturbance environment in which similarly adapted non-native plant species establish and gain foliar cover.

Nectar resource diversity organises flower‐visitor community structure

AbstractCommunities of nectar‐producing plants show high spatio‐temporal variation in the patterns of volume and concentration presentation. We illustrate a novel approach for quantifying nectar reward structures in complex communities, demonstrating that nectar resource diversity (defined as the variety of nectar volume–concentration combinations available) may be a fundamental factor organising nectarivore communities. In a series of diverse bee and entomophilous flower communities in Israel, our measure of nectar resource diversity alone explains the majority of variation in bee species richness, while other nectar variables (volume, concentration, energy value, and water content) have little predictive value per se. The new measure of nectar resource diversity is highly correlated with floral species richness and particularly with the species richness of annuals, yet it is additive in its effect on bee diversity. We conclude that relying solely upon measurements of mean nectar volume and mean nectar concentration overlooks a key characteristic of community‐level reward structure, nectar resource diversity, so that previous studies may have failed to identify an important determinant of flower‐visitor community structure.

Cattle Grazing Impacts on Annual Forbs and Vegetation Composition of Mesic Grasslands in California

Abstract: Livestock grazing represents a major human alteration of natural disturbance regimes in grasslands throughout the world, and its impacts on plant communities have been highly debated. We investigated the impact of cattle grazing on the California coastal prairie plant community with a focus on native annual forbs, a number of which are of conservation concern. In spring 2000 and 2001, we surveyed the vegetation community composition, vegetation structure, and soil chemical parameters at 25 paired grazed and ungrazed sites over a 670‐km range of the ecosystem. Native annual forb species richness and cover were higher in grazed sites, and this effect was concomitant with decreased vegetation height and litter depth. Soil properties explained less of the variation. Exotic annual grass and forb cover were higher in grazed sites. Native grass cover and species richness did not differ in grazed and ungrazed sites, but cover and species richness of native perennial forbs were higher in ungrazed sites. Our results suggest that cattle grazing may be a valuable management tool with which to conserve native annual forbs in the ecosystem we studied but that grazing differentially affects the various life‐history guilds. Therefore, land managers must focus on creating a matrix of disturbance regimes to maintain the suite of species native to these mesic grasslands. The results of this and other studies highlight the importance of considering the adaptation of vegetation communities to disturbance in making recommendations for grazing management.

Distinguishing between signal and noise in faunal responses to environmental change

ABSTRACTAim We tested whether variation in snapshots of butterfly species composition and species richness taken from one to six years apart could be interpreted as an ecologically meaningful trend or whether they might merely reflect stochasticity.Location Field research was conducted in the Toquima Range and Shoshone Mountains, Lander and Nye counties, Nevada, USA.Methods We obtained data for 49 sites in the Toquima Range from 1996 to 2002 and 39 sites in the Shoshone Mountains from 2000 to 2002. Sites spanned the gradient of local topographic and climatic conditions in those mountain ranges. Data on species composition and species richness were based on comprehensive field inventories. We calculated similarity of species composition using the Jaccard index. We conducted one‐factor repeated‐measures analyses of variance to test whether the distribution of similarity of species composition and the distribution of mean species richness depended on the number of years between inventories.Results In both mountain ranges, much less of the difference in species composition was attributable to turnover of species composition within sites over time than to spatial differences among sites. Annual species richness in the Toquima Range was more variable than in the Shoshone Mountains, but again far less of the variation in species richness was attributable to year than to differences among sites.Main conclusions Despite the fact that desert ecosystems are not expected to be highly resilient to global environmental change, there may be a time lag between deterministic environmental changes and a detectable faunal response, even in taxonomic groups that are known to be sensitive to changes in climate and vegetation. Although information on species richness and similarity of species composition are among the most practical data to collect in managed landscapes, these measures may not be highly sensitive to environmental changes over the short to moderate term.

Species richness, diversity and biomass production of desert annuals in an ungrazed Rhanterium epapposum community over three growth seasons in Kuwait

Two blocks, each consisting of twelve 0.25 m2permanent plots, were established in a community dominated by desert annuals inan area of Kuwait protected from grazing, and community attributes wereinvestigated over three growth seasons. A linear relationship was found betweenestimated desert annual cover and biomass production. Species frequency wasassessed by the number of 100 cm2 subplots occupied byaspecies in a block (“block incidence”). Over the three seasons,vegetation features varied considerably. The first season (spring 1997) wascharacterised by very sparse vegetation cover, low vegetation block incidence(sum of individual block incidences of each species present in a block) and lowspecies richness. The second season (spring 1998) had high vegetation cover,relatively low vegetation block incidence, but high species richness. In thethird season (spring 2000), vegetation cover was very sparse (as in 1997), butboth blocks had the highest vegetation block incidence of the three years andspecies richness was moderately high, although individual plants were verysmall. The growth period was much shorter in the very productive andspecies-rich 1998 season than in 2000. Fluctuations in biomass and speciesincidence coincided with pronounced variation in key meteorological variables,in particular the onset of the first rains, the amount of rainfall during thegrowing season and its temporal distribution. Species composition, however,appears mainly to be determined by the amount and possibly the timing of thefirst rainfalls of the season to trigger germination. There was little evidenceto suggest that particularly favourable or unfavourable microsites existed inplots for more than one vegetation period, either for individual species or fordiversity in general. Despite substantial between-season fluctuations inincidence, the relative abundances of the more frequent species to each otherremained broadly similar over the three seasons, with Plantagoboissieri being the predominant species and accounting for thelargest proportion of biomass.

Grazing effect on diversity of annual plant communities in a semi‐arid rangeland: interactions with small‐scale spatial and temporal variation in primary productivity

Summary The interactive effect of grazing and small‐scale variation in primary productivity on the diversity of an annual plant community was studied in a semiarid Mediterranean rangeland in Israel over 4 years. The response of the community to protection from sheep grazing by fenced exclosures was compared in four neighbouring topographic sites (south‐ and north‐facing slopes, hilltop and wadi (dry stream) shoulders), differing in vegetation, physical characteristics and soil resources. The herbaceous annual vegetation was highly diverse, including 128 species. Average small‐scale species richness of annuals ranged between 5 and 16 species within a 20 × 20 cm quadrat, and was strongly affected by year and site. Above‐ground potential productivity at peak season (i.e. in fenced subplots) was typical of semiarid ecosystems (10–200 g m−2), except on wadi shoulders (up to 700 g m−2), where it reached the range of subhumid grassland ecosystems. Grazing increased richness in the high productivity site (i.e. wadi), but did not affect, or reduced, it in the low productivity sites (south‐ and north‐facing slopes, hilltop). Under grazing, species richness was positively and linearly related to potential productivity along the whole range of productivity. Without grazing, this relationship was observed only at low productivity (&lt; 200 g m−2). The effect of grazing along the productivity gradient on different components of richness was analysed. At low productivity, number of abundant, common and rare species all tended to increase with productivity, both with and without grazing. Rare species increased three times compared with common and abundant species. At high productivity, only rare species continued to increase with productivity under grazing, while in the absence of grazing species number in the different abundance groups was not related to productivity. In this semiarid Mediterranean rangeland, diversity of the annual plant community is determined by the interaction between grazing and small‐scale spatial and temporal variation in primary productivity, operating mainly on the less abundant species in the community.

Trends in abundance of benthic and demersal fish populations of the lower Forth Estuary, East Scotland, from 1982–2001

The benthic and demersal fishes of the lower Forth Estuary, east Scotland, were sampled by Agassiz trawling from January 1982–December 2001. Three stations of varying distance from the mouth of the estuary were trawled at high and low water in 5 months of each year, a total of 30 trawls per annum using the same ship and net design throughout. Of 30 species collected over this period, whiting Merlangius merlangus was the most abundant, followed by eelpout Zoarces viviparus, pogge Agonus cataphractus, flounder Platichthys flesus and plaice Pleuronectes platessa. The 10 most abundant species accounted for 97·8% of the total benthic‐demersal fish abundance. There was no trend in total annual species richness sampled, though total annual abundance of fishes captured decreased significantly from 1982–2001. This was largely caused by significant declines in abundance of whiting and eelpout. Fatherlasher Myoxocephalus scorpius showed a significant linear increase. None of the seven remaining most abundant species exhibited significant trends in abundance. Decline of eelpout may be attributable to increases in water temperature adversely affecting reproductive success. This is suggested by a significant negative correlation of mean annual abundance with January bottom temperature in the previous year.

Effect of experimental trampling and off-road motorcycle traffic on soil and vegetation of stabilized coastal dunes, Israel

Coastal sand dunes are considered to be amongst the most fragile natural systems, however they may be subject to high-intensity recreational stresses. The aim of this study was to assess the response of soil and annual plants of stabilized Mediterranean coastal dunes in Israel to various short-duration pedestrian and motorcycle traffic intensities. A standard experimental procedure was used comprising of 0, 50, 100, 300 and 500 pedestrian passes, and 0, 20, 50, 100, 200 straight and 150 turn motorcycle passes. The response of annual plants was assessed by determining ground cover, height, species richness and diversity, and soil penetrable depth, organic matter and moisture content. The pedestrian traffic did not affect the cover of annual plants, however; mean annual height, species richness and species diversity were significantly but temporarily affected by 500 passes. Conversely, motorcycle passage had an immediate significant impact on annual plants at all traffic intensities. The maximum effect on plants was observed in the wheel tracks and in the turn lanes. The mean annual ground cover and height were less sensitive measures than species richness and diversity for determining the overall impact of motorcycles on the area. Impact of pedestrian and motorcycle traffic on soil was detected only as an increase in penetrable depth, which was significant at 300 and 500 pedestrian passes, and at 100, 200 straight and 150 turn motorcycle passes. The soil and herbaceous vegetation of Mediterranean stabilized coastal dunes is relatively resistant and shows recovery potential to recreational impacts.

Vegetation response to possible scenarios of rainfall variations along a Mediterranean–extreme arid climatic transect

The vegetation response to variation in rainfall totals along a climatic transect extending from a Mediterranean region to an extreme arid region was studied. A curvilinear relationship was suggested between annual rainfall, species richness, species diversity and dominance. The maximum number of species was calculated to be in the range of 900–950 mm, the maximum diversity between 750 and 800 mm, and the minimum dominance in the range of 600–700 mm. Annual species decrease logarithmically from the extreme desert to the Mediterranean region with a parallel increase of perennial herbaceous and woody plants. Wet and dry scenarios are considered as a framework to evaluate future vegetation responses to possible climate change.

The role of water depth and soil temperature in determining initial composition of prairie wetland coenoclines

In this study, we examined the effects of water depth and temperature on seedling recruitment from a prairie wetland seed bank. We collected seed-bank samples from natural and restored prairie pothole wetlands in northwestern Iowa and combined them into a single sample. We examined seedling recruitment from this seed-bank sample in an experimental study using a factorial design of 4 temperature treatments (5 night and 15 day to 20 night and 30 day) and 3 water-depth treatments (0, 2, and 7 cm). Principal Components Analysis showed that both water depth and temperature had significant effects on the composition of the seedling community as measured by changes in relative stem density and biomass. Water depth had its strongest effects on stem density while temperature had its strongest effects on biomass. For the 22 most common species, stem density varied with water depth for 95% of the species and with temperature for 50% of the species. Most species with water depth responses had lower stem counts as water depth increased, and for the majority of species with temperature responses stem density increased with temperature. Total, annual, and perennial species richness was negatively correlated with water depth. Total and annual species richness was positively correlated to temperature, while perennial species richness was unresponsive to temperature. In addition, species found at low elevations as adults emerged at higher rates in the deep water treatments while species that occurred at higher elevations as adults had their highest emergence rates in the low water treatments. Our results suggest that differences in environmental conditions along coenoclines can affect the initial distribution of species emerging from the soil seed bank. Water depth sorted seedlings according to their adult water-depth tolerances, and temperature determined the proportion of annuals in the seedling community.

Manipulation of vegetation communities on the Abu Dhabi rangelands. II. The effects of topsoiling and drip irrigation

The effect of topsoiling on the vegetation communities of Abu Dhabi coastal desart rangelands with sand taken from an inland area of rangeland supporting a different vegetation community, was investigated. The study was carried out on ghanada Island, an inshore desert island which had been extensively topsoiled in the previous 5 years. Parts of the island also had been drip irrigated. Perennial vegetation communities on Ghanada were markedly different on topsoiled areas compared to non-topsoiled areas. However not all the species common in the topsoil source area were subsequently found to be common on the topsoiled areas. Zygophyllum hamiense, thought to be a colonizer of disturbed soil in the source areas, was common on the topsoiled areas. Annual plant species richness was greater on topsoiled areas compared to untreated native soil indicating (i) that the source areas had a greater annual species richness than Ghanada, and (ii) annual species propagules successfully survived the processes of topsoiling. Annual and perennial species richness was not significantly different between irrigated and non-irrigated areas. The perennial percentage cover was greatest on drip irrigated areas and the perennial which benefited the most was Heliotropium kotschyi, probably due to its rhizomous growth habit.

Manipulation of vegetation communities on the Abu Dhabi rangelands. I. The effects of irrigation and release from longterm grazing

The effect on vegetation communities of release from grazing by camels and goats has been investigated in the Baynunah region of Abu Dhabi emirate, in The United Arab Emirates, by the study of an exclosure established 11 years previously. Also the effect of sprinkle irrigation (in the absence of grazing) on the rangeland vegetation was investigated. Perennial species richness was significantly lower outside the exclosure compared with inside on both sand and gravel substrata. Annual species richness however was not significantly different. Perrenial percentage covers were lower outside the exclosure compared with inside, especially on sand substrata. The perennial grass Stipagrostis plumosa (L) showed the greatest difference in percentage cover in this respect. The species richness of annuals and perennials was not significantly different between irrigated and non-irrigated areas within the exclosure. The perennial percentage cover was much greater on sprinkle irrigated sand and gravel substrata. The perennial which benefited the most was Zygophyllum hamiense, Scweinf. Annual percentage cover was lower in irrigated quadrats. Suggestions are made about the effect of intensive grazing on the vegetation communities at Baynunah and on the effectiveness of irrigation as a tool for increasing the quality of the rangeland for livestock and wildlife.

Limnological Factors Influencing Bird Abundance and Species Richness on Florida Lakes

ABSTRACT Forty-six bird species were observed on 33 Florida lakes with some species occurring on only one lake and others on as many as 26 lakes. Average annual bird abundance ranged from seven to 750 bird/km2 and total species richness ranged from two to 30 species per lake. Regression analyses were used to examine the effects of lake trophic status, aquatic macrophyte abundance, and lake morphology on average annual bird abundance and total species richness. All trophic state parameters (total phosphorus, total chlorophyll a, etc.) accounted for significant portions of the variance in average annual bird abundance, but total chlorophyll a concentrations (μg/L) accounted for the highest percentage (47 percent) of the variance. The best fit regression equation was: Log Bird Abundance = 1.35 + 0.56 Log Total Chlorophyll a . Lake area, shoreline length, and all trophic state parameters accounted for significant portions of the variance in total species richness. Multiple regression analyses indicated that l...