Mean Number Of Species Research Articles

Germinable soil seed‐bank of former grassland converted to coniferous plantation

The influence of afforestation with cedars on field layer vegetation and on the germinable soil seed‐bank were investigated along a 60‐m transect merging from open grassland to sparse and dense canopy cover. A total of 132 species were found, 76 in the seed‐bank and 109 in the vegetation, with 53 species in common. Conifer cover was not found to be associated with a decrease in total number of species in the vegetation or seed‐bank, but the mean number of species in the vegetation, total cover in field layer vegetation and mean number of individuals in the seed‐bank decreased significantly from grassland to forest stands. The grassland seed‐bank was dominated by Saxifraga tridactylites and Veronica agrestis; the seed‐bank of plots of scattered cedars was dominated by Trifolium incarnatum ssp. molinerii; and that of dense cedar plantations was dominated by Campanula rapunculus. The number and cover of grassland species of field layer vegetation decreased in the forest, with respect to open grassland, and the same trend was found for density of individuals in the seed‐bank. It is concluded that grassland restoration by cutting cedars cannot rely on the presence of grassland species in the soil seed‐bank.

Effects of Intertidal Elevation on the Rockpool Ichthyofaunas of Temperate Australia

A quantitative assessment of the effects of intertidal elevation on rockpool ichthyofaunas was investigated at four locations in southeastern New South Wales, Australia. Rockpools supported high diversity and abundance of fishes mainly comprising the families Clinidae, Blennidae, Tripterygiidae, Gobiidae, Gobiesocidae and Girellidae, which are mostly permanent residents. Mean numbers of species and individuals did not differ among low, medium and high rockpools. In contrast, species composition differed among intertidal rockpool heights with pools mainly being dominated by transient and opportunist species in lower intertidal, opportunists and permanent residents in the mid intertidal, and mainly permanent residents in the high intertidal. Distribution patterns appeared to be related to the morphological and/or physiological adaptations of species to the increasingly harsh and variable environmental conditions with increasing intertidal elevation. Residential status of each species may be used as a proxy for intertidal vertical distribution although some exceptions exist, namely Girella elevata, which may posses behavioural adaptations to cope with harsh environmental conditions.

The power of time: spatiotemporal scaling of species diversity

AbstractThe species–area relationship (SAR) provides the foundation for much of theoretical ecology and conservation practice. However, by ignoring time the SAR offers an incomplete model for biodiversity dynamics. We used long‐term data from permanent plots in Kansas grasslands, USA, to show that the increase in the number of species found with increasing periods of observation takes the same power‐law form as the SAR. A statistical model including time, area, and their interaction explains 98% of variation in mean species number and demonstrates that while the effect of time depends on area, and vice versa, time has strong effects on species number even at relatively broad spatial scales. Our results suggest equivalence of underlying processes in space and time and raise questions about the diversity estimates currently used by basic researchers and conservation practitioners.

Weed species diversity and community composition in organic and conventional cropping of spring cereals

Interest in organic farming is growing rapidly in Europe. The resulting expansion of the organic farming area has been expected to enhance the biodiversity of agricultural habitats. Organic cropping practices can be hypothesized to support a higher number of weed species than conventional cropping and also to favor herbicide-susceptible and less-nitrophilous species. The diversity and species composition of weed communities were compared in spring cereal fields cultivated by organic, conventional cereal and conventional dairy cropping methods in southern Finland between 1997 and 1999. Samples were taken before (May–June) and after (July–August) the treatment of conventional fields with herbicides. The number of species was used as a measure of species diversity. The total and mean numbers of species between cropping practices were compared by applying rarefaction and ANCOVA, respectively. In organically cultivated, fields the adjusted mean number of species per field exceeded that in conventionally cultivated fields by about two species in both May–June and July–August. The total number of species was higher in organically cultivated fields only in July–August. The species composition of organically cultivated fields was closer to that of conventional dairy than to that of conventional cereal fields. Species susceptible to herbicides (e.g. Chenopodium album) were abundant in organically cultivated fields in both sampling periods whereas the relative abundance of some of them declined in conventional fields from May–June to July–August. In conventional fields, the relative abundances of Viola arvensis, Stellaria media and Elymus repens increased from May–June to July–August. Only weak support was found for the hypothesis that organic cropping favors less-nitrophilous weed species. It is concluded that organic cropping promotes weed species diversity at an early phase of cropping history but that a change in species composition would require a longer period of organic cropping.

Microbial flora of hands of homemakers

Objectives and methods: Because of increasing concern about antimicrobial resistance in the community, aerobic flora of hands of 224 healthy homemakers in northern Manhattan, New York, were examined. Results: Mean log colony-forming unit counts before and after handwashing were 5.72 and 5.69, respectively, P =.60; mean number of species identified/sample was 3.6 before washing and 3.3 after (P =.02). After handwashing gram-negative bacteria were isolated from 75.1% of subjects; yeast from 32.9%; and Staphylococcus aureus from 18.5%, 1 of which (2.4%) was oxacillin-resistant. Generally, these community isolates were more sensitive than isolates from inpatients in the local hospital, although community isolates of Pseudomonas aeruginosa were significantly more resistant than inpatient isolates for 4/10 agents tested. Conclusions: Hands of healthy persons in the community were usually colonized with gram-negative bacteria, a single handwash had little impact on microbial counts, and hands of healthy adults may increasingly become one reservoir for antimicrobial resistance. (Am J Infect Control 2002;31:72-9.)

Diversity of soil oribatid mites (Acari: Oribatida) from High Katanga (Democratic Republic of Congo): a multiscale and multifactor approach

Although the soil is a major reservoir of biodiversity, our knowledge ofits mesofauna remains scanty, especially in the tropics. The diversity oforibatids (149 adult oribatid mite species) is analyzed for the first time in anAfrican soil and studied in three ecosystems of a regressive sere: forest,woodland and savanna. Savanna is the richest ecosystem overall, with 105collected species, whereas the mean number of species per releve (αdiversity) is highest in forest. In barren soils, the number of species observedalong the sere drops regularly from the typical forest to the savanna. However,this pattern is complicated by other factors acting at different scales. Theincrease of oribatid richness parallels that of habitat complexity, from barrensoil to termitaria colonized by grasses and trees. On a finer scale, soilproperties also influence species richness, either indirectly through density(water content) or directly (total nitrogen, C/N ratio, organic matter), buttheir importance varies in relation to seasons. Most exclusive species (nearly90%) are housed in the two extreme types of vegetation, forest and savanna. On afiner scale, two habitats, the typical forest and the termitaria in the savanna,are remarkable by the number of exclusive species and are worth protectingthrough effective conservation measures.

Succession of Diptera on dead beech wood: A 10-year study

Summary This study describes the decomposition of dead beech wood and the succession of xylobiont Diptera. Branch wood (∅=4.3–11.5cm) was sampled from two beech trees felled by wind in autumn 1984. In each spring (1987–1995) 6 to 8logs were selected and placed individually in closed emergence traps to collect adult Diptera. Decay state of the logs was described by measuring relative density, water content, bark cover, moss cover, litter cover, carbon and nitrogen contents, C:N ratio, and residual weight. Overall, the environmental factors decreased or increased with log age as expected but variation within cohorts was considerable. For some common dipteran species clear temporal patterns of occurrence were identified, and it was also possible to relate abundances of some species to individual environmental factors. On the community level, mean number of individuals per log tended to increase with log age, suggesting that dead wood becomes a more rewarding food resource in the course of decomposition. Diversity of Diptera measured as the mean number of species per log increased with log age, indicating that resource heterogeneity increased with log age. Diversity of Diptera also increased with water content and moss cover but was negatively correlated with bark cover, C:N ratio, and relative density.

A comparison of the vegetation in semi‐natural grasslands under different agricultural practices in Finnish and Russian Karelia

The vegetation of semi‐natural grasslands under modern, cereal/forage cropping in Finnish Karelia (n = 11) and old fashioned animal husbandry in adjacent Russian Karelia (n = 11) was compared in terms of their species composition. Each grassland site was paired with one in the other country which was as similar as possible in respect to its natural conditions. The species composition indicated differences in management between the two countries. The mean number of species was 4S.S in the Finnish sites and 52.6 in the Russian sites. A total of 12 species exhibited a statistical difference in their indicator values between the two countries. Traditional grassland species (e.g. Leontodon hispidus, Dianthus deltoides), indicating grazing, hay making and old settlement, occurred more oñen in Russian sites, while species related to nutrient enrichment and cultivation (e.g. Urtica dioica, Elymus repens) were more characteristic of Finnish sites.

Dynamics or constancy inSphagnumdominated mire ecosystems? A 40‐year study

Traditionally mire ecosystems (especially bogs) have been viewed as stable systems with slow changes in the vegetation over time. In this study the mire Åkhultmyren, south‐central Sweden was re‐investigated in 1997 after 40 yr of continued natural development. The results show a high degree of dynamics in aSphagnumdominated bog and fen. Altogether 97 vascular plant and bryophyte species were recorded in the two inventories of the bog and poor fen vegetation. pH and electrical conductivity in the mire water were also surveyed. In 1997 we found 10 new species and that 8 species had disappeared since 1954 but the over‐all mean number of species per plot (size 400 m2) had hardly changed. However, 21% of the species increased and 21% decreased significantly in frequency. Most of the species that decreased in frequency were low‐grown vascular plants, most common in wet microhabitats. Vascular plant species that increased in frequency included trees (defined as >1.3 m in height) and were generally taller than the unchanged or decreasing species. The frequency of dwarf shrubs and hummock bryophytes increased too. Areas with an initial pH of 4.5–5.0 showed the strongest decrease in pH, coinciding with an enlarged distribution of someSphagnumspecies. The species diversity increased on the bog, but decreased in the wettest parts of the fen, where the pH also decreased. Species with unchanged or increasing frequency often showed high capacity to colonise new plots. On average the sum of gains and losses of species in the plots in 1997 was ca 50% of the species number in 1954. The vegetation changes indicate a drier mire surface and an increased availability of nitrogen. The increased tree cover may have triggered further changes in the plant cover.

Effects of increased habitat complexity on fish assemblages associated with large artificial reef units (French Mediterranean coast)

Large artificial reef units (LARUs; 158 m 3 ) comprise 38% of 40 000 m 3 of artificial reefs deployed in France since 1985. Habitat complexity of one LARU was increased in situ in 1991 when 37 m 3 of small-sized building materials was placed randomly inside the empty chambers. The fish fauna, before and after added complexity, was compared with the fauna of an unmodified control LARU through 1987–1989 and 1997–1998, respectively, by visual censuses. The experimental LARU showed higher values of all community metrics investigated after treatment: total species richness had become twice as high, mean number of species per census 3 times higher, density 10 times, and biomass 40 times higher. Exceptionally large increases were observed among commercially important species such as sparids. In contrast, few changes were observed at the control unit: species richness had not changed significantly, while density and biomass showed moderate increases by a factor of 2–3, which might be explained by reef maturation. The results confirm the prominent role of habitat complexity in relation to artificial reef design on diversity and abundance of fish assemblages.

Factors influencing the characteristics of fish assemblages in a large subtropical marine embayment

Mean number of species and density of fishes in nearshore shallow waters of Shark Bay, a large subtropical embayment, were c. seven and 19.5 times greater in seagrass than over bare sand, where protection from predators and the abundance of potential invertebrate prey were less. The number of fish species and density of fishes over bare sand were lower in nearshore than offshore waters, where there was a greater amount of organic material and thus presumably a greater density of benthic macroinvertebrate prey. Species composition in vegetated and unvegetated habitats differed markedly, with species such as Monacanthus chinensis, Apogon rueppellii and Pelates quadrilineatus being largely confined to seagrass, whereas others such as Pseudorhombus jenynsii, Torquigener whitleyi and Engyprosopon grandisquama were found predominantly or exclusively over bare sand. The ichthyofauna in beds of Posidonia australis, in which the canopy is uniformly dense, differed in composition and comprised a greater number of species and density of fishes than that in Amphibolis antarctica, in which an open space is present beneath the terminal clusters of relatively short leaves. Species composition in the beds of both of these seagrass species underwent well defined cyclical changes, caused by out‐of‐phase sequential changes in the densities of certain species. Such changes were less common over bare sand, where the ichthyofaunal composition was more variable. The number of species and density of fishes over bare sand were greater at night than during the day, reflecting, in part, a tendency for species such as A. rueppellii to move into unvegetated areas to feed at night, when the likelihood of predation by visual predators would be reduced. Within Shark Bay, ichthyofaunal composition is influenced most by habitat type (vegetated v. unvegetated), followed in general by water depth and then region in the bay and time of year.

Correspondence between regional delineations and spatial patterns in macroinvertebrate assemblages of boreal headwater streams

Geographical stratification may provide a useful framework for stream management programs, yet most studies testing the utility of such stratifications have been conducted in temperate regions. We studied the correspondence between regional delineations (5 ecoregions, 11 subecoregions), environmental characteristics, and benthic macroinvertebrate assemblages in 156 boreal headwater streams in Finland, using a combination of principal components analysis, nonmetric multidimensional scaling, and discriminant function analysis (DFA). Both stream characteristics and macroinvertebrate assemblage structure showed a closer correspondence to ecoregions than to subecoregions, a pattern partly attributable to the smaller number of classes at the ecoregion level. Based on environmental variables, DFA classified correctly 84.0% of the streams by ecoregion and 74.4% by subecoregion. For macroinvertebrate assemblages, 64.7% of the streams were correctly classified at the ecoregion, and 51.9% at the subecoregion level. Arctic-alpine and north boreal ecoregions supported the most distinct benthic assemblages. There were significant differences among ecoregions in mean species number, with lowest species richness in the middle boreal and highest in the south boreal streams. However, no clear latitudinal gradients in local species richness were detected. Relative abundances of functional-feeding groups also exhibited regional differences. Shredders dominated the middle boreal brown-water streams, whereas scrapers attained their highest abundances in the arctic-alpine and north boreal clear-water streams. Despite some congruence among ecoregions and macroinvertebrate assemblages, regional delineations alone do not provide a suitable background for stream biomonitoring programs. A combination of regional delineations and local characteristics probably provides a better framework for the classification of boreal headwater streams, and for the prediction of their benthic fauna.

Food and density limitations of the Seychelles Magpie Robin, Copsychus sechellarum, on Cousine Island

The critically endangered Seychelles Magpie Robin, Copsychus sechellarum, is one of the rarest birds in the world. At the end of December 1999, there were 88 individuals distributed on four small granite islands: Fregate, Aride, Cousin and Cousine. Little is known of Magpie Robin ecology in its natural habitat. Studies carried out on Aride, Cousin and Cousine are therefore valuable as each island is dominated by native woodland. The composition of Magpie Robin diet was compared between Fregate and Cousine. An exotic species of cockroach, Pycnoscelus indicus, and dropped fish were found to be considerably more important prey items on Cousine. Observations of chick food provisioning indicated habitat quality differences between the territories. Invertebrate and vertebrate food resources available to the Magpie Robin were sampled on Cousine between 1997 and 1998. Fourteen sites were sampled for invertebrates and fifty-two species from fifteen taxa were identified. There were significant differences between the mean number of species recorded per site and the mean number of animals found at each site. Skink density was estimated at between 1219-1516/ha and 354-538/ha for Mabuya sechellensis and Mabuya wrightii respectively. Invertebrate diversity and abundance was greatest in areas dominated by closed-canopy woodland on or near the coastal plain. These results explained the current distribution of Magpie Robin territories. The invertebrate abundance data were used to estimate the carrying capacity of the island for the Magpie Robin. Cousine could theoretically support up to six breeding pairs but it is questionable that a population of this size could be self-sustaining in the long-term.

Breeding birds in short-rotation coppices on farmland in central Sweden—the importance of Salix height and adjacent habitats

Plantations of short-rotation coppice (SRC) have a potential for being a useful measure to stop the ongoing impoverishment of farmland biodiversity by increasing structural diversity, and decreasing cultivation intensity and use of pesticides in intensively managed farmland landscapes. The aim of this study was to investigate the relative importance of the structure of the plantation and composition of adjacent habitats for breeding birds in 41 SRCs ( mean size ± S. E.=9.4±1.6 ha). Mean number of species per ha in the SRCs was 2.8±0.3 species and there were more farmland birds (32 species, 808 territories) than forest birds (22 species, 400 territories). A major result of the present study was the strong influence of adjacent habitats on bird community composition (18 of 22 analysed species affected). There were large differences in bird communities between forest-bordered and open-bordered sites, but occurrence of residual habitats (i.e. other habitats than forest, pastures, shrub areas and arable fields) was also associated with occurrence of several species. The second factor of major importance for the bird fauna was the height of the plantations. Most species (14) were associated with tall plantations (>2 m), seven species were associated with plantations of intermediate (1–2 m) height, and six species were associated with plantations of low height (<1 m). A comparison of ecological traits between species classified as preferring SRC and species classified as avoiding SRC suggests that nest height was the only ecological character associated with a preference for Salix habitats, i.e. species with nests on the ground or in shrubs were more abundant in Salix habitats than in farmland landscapes in general. However, a broad spectrum of species was found in the SRCs and many of these seemed to be dependent on habitat features outside the plantations. Planting of Salix in intensively managed farmland plains will have positive effects on bird diversity by increasing the structural diversity of the landscape. In contrast, plantations on infields in forest-dominated landscapes will have negative effects, since the mosaic structure (i.e. mixture of open and forested habitats) positive for most farmland birds will disappear, and Salix plantations favour relatively few forest species. Additionally, Salix could be planted along sharp edges between coniferous plantations and open farmland in order to increase the complexity of the ecotone in intensively managed forest-farmland landscapes.

Dung beetles in a Central Amazonian rainforest and their ecological role as secondary seed dispersers

Abstract1. The role of several factors that affect the composition of the dung beetle assemblages in an Amazonian rainforest was quantified, together with the effect of these factors on the role that dung beetles play as secondary seed dispersers.2. A total of 61 dung beetle species was captured during 3360 h of trapping. During nocturnal trapping periods, more dung beetles, of larger mean size, and more species were captured per trap than during diurnal trapping periods.3. During the rainy season, more dung beetle species were captured per trap than during the dry season, but the number of individuals and their mean size did not vary between seasons.4. Bait size had a significant effect on the mean number of beetles and mean number of species but not on mean beetle size. As bait size increased from 5, 10, 25, to 50 g, more beetles and more species were captured per trap.5. Between 6 and 73% of plastic beads, used as seed mimics, were buried by dung beetles at depths that ranged from 0.5 to 7 cm. Both the proportion of beads buried and burial depth decreased with increasing bead size, and increased with increasing amounts of dung surrounding each bead (5, 10, and 25 g).6. The proportion of buried seeds for three species varying in size between 5 and 27 mm, increased with increasing dung beetle size, using beetles of seven sizes, varying between 10 and 25 mm.7. Seeds surrounded by dung were buried more often and more deeply when placed on the forest floor during the late afternoon than when placed during the early morning. Seeds were also buried more often when placed on the forest floor during the rainy season than when placed during the dry season, but season had no effect on burial depth.8. Forests in Central Amazonia hold a rich dung beetle community that plays an active role in secondary seed dispersal, and consequently in plant regeneration. The interaction between seeds and beetles is complex because it is affected by many factors.

Plant invasion and management in turf‐dominated waste landfills in South Korea

AbstractA floristic survey was conducted in turf‐dominated fields on some waste landfills in South Korea, to quantify the degree of plant invasion in those degraded lands. The dominant species, except turf (Zoysia japonica), were Conyza canadensis, Setaria viridis, Digitaria sanguinalis and Aster tripolium. Mean species number declined linearly with distance from the edge of the turf stands. Biomass of each species ranged between 0.1 g and 122.6 g, decreasing linearly with distance from the edge of the stand and declining exponentially with turf coverage. Mean soil moisture storage and organic matter content were 12.59 per cent and 5.81 per cent, respectively. Sum of relative cover, frequency and biomass of all species with environmental variables (distance from the stand edge, turf cover, soil moisture storage, soil organic matter content and the ratio of species number of exotic plants to that of native plants) were ordinated by DCA (detrended correspondence analysis). The first axis of the DCA was positively correlated with distance from the stand edge and turf cover and the second axis of the DCA was negatively correlated with soil organic matter content. Highly and lowly invasive species were indicated from DCA results. From analysis of dispersal type, barochore and anemochore were the most widespread of other dispersal types but it was suggested that anthropochore played an important role in plant invasion in these degraded wastelands. Establishment of an edge transition zone, enhancement of turf cover and reduction in traffic is recommended as management options for turf fields. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Restoration of wooded meadows ‐ a comparative analysis along a chronosequence on Öland (Sweden)

Abstract. Wooded meadows on the Baltic Island of Öland result from traditional agricultural management over centuries which has led to a species‐rich vegetation with high species diversity. Today, nearly all of these meadows have been abandoned and became rapidly overgrown by deciduous shrub and tree species forming a closed canopy which resulted in a rapid and strong decrease in species numbers of the herb layer. Recent efforts aim to restore overgrown wooded meadows by cutting single shrubs and trees to open the canopy. However, the effects of abandonment as well as of any restoration management in wooded meadows have rarely been documented until now. Mechanisms driving succession after restoration such as the dispersal potential of the respective species over time and space have not been analysed yet. Therefore, a chronosequence was studied which included a traditionally managed wooded meadow, an overgrown meadow which has been abandoned for more than 100 yr and a meadow which was restored 36 yr ago by cutting and is now grazed. We analysed the soil seed bank of the 3 meadows in comparison with the established vegetation and endozoochorous seed dispersal by cattle and sheep. After abandonment 87% of the typical grassland species vanished from the established vegetation and were replaced by species characteristic of woodland and disturbed grassland communities. The mean number of species decreased from 52 species per plot (4 m2) to 18 species. Mean species number and number of seeds in the seed bank declined significantly from the traditionally managed to the overgrown meadow. Most of the grassland species were assigned to a transient seed bank type while only 1/3 could be classified as having a short‐term persistent seed bank. Thus, restoration of wooded meadows cannot rely on the soil seed bank. Endozoochorous seed dispersal by cattle and sheep was shown for 15% of the species with seed densities per 100 g air dried dung of 737 and 767, respectively. Movement of animals between ancient and restored wooded meadows is recommended since many of the species only occurred in low densities and therefore, will probably not be found in the dung samples.

Species Diversity of Edible Plants Grown in Homegardens of Chibchan Amerindians From Costa Rica

We studied edible crop species diversity at homegardens of two Chibchan Amerindian Reserves in Costa Rica: Talamanca and Coto Brus. We visited six settlements at Talamanca and five at Coto Brus. We recorded the number of edible crop species growing homegardens; we found 46 edible plant species at Talamanca and 27 at Coto Brus. The mean number of species per homegarden ranged between 3.80 and 6.80 at Coto Brus and 4.50 and 8.63 at Talamanca. We identified species that were common, i.e., found in most households and all settlements, and species that were rare. We estimated diversity indexes for each settlement and each Reserve. Also, we compared crop species composition between both Reserves and among settlements within each Reserve, using the Jaccard coefficient of community similarity. Settlements from the same Reserve were grouped together, with the exception of Villa Palacios from the Coto Brus Reserve.

Short-term impacts of logging on understorey vegetation in a jarrah forest

Summary In 1985, new silvicultural treatments were implemented in jarrah (Eucalyptus marginata) forests available for wood production. As part of a scientific investigation into the ecological impacts of two of these treatments, gap cutting and shelterwood cutting, a survey was conducted 4 years after logging to examine the effects of these treatments on understorey vegetation species richness and abundance. Sampling scale was found to be an important factor affecting the results and subsequent interpretation of impacts. At the coupe scale, native plant species richness in unlogged coupe buffers was similar to that in adjacent logged patches. However, the mean number of species per 1 m2 was 20%-30% higher in the unlogged buffers than the logged patches. At all sampling scales, the abundance (number of individual plants) of native plants was 20%-35% higher in the buffers, but the abundance of introduced (weed) species was significantly higher in the logged patches. The abundance of weeds, which are mostly annual grasses and short-lived herbs, is likely to diminish with time. The time to recovery of native species abundance and the ecological significance of this is uncertain. Given the reported low seedling regeneration rate and limited dispersal capacity of many woody shrubs and perennial herbs, they are unlikely to return to pre-logging levels in the medium term. We attribute the reduction in the abundance of native plants mainly to mechanical soil disturbance, which ranged from 60% to 80% of the area of logged coupes, physical damage to the vegetation associated with logging and to intense heating of the topsoil during the post-logging silvicultural burn. Recommendations are made for reducing the negative impacts of logging operations on the understorey.

Long-term dynamics of winter and summer annual communities in the Chihuahuan Desert

Winter and summer annuals in the Chihuahuan Desert have been intensively studied in recent years but little is known about the similarities and differences in the dynamics between these two communities. Using 15 yr of census data from permanent quadrats, this paper compared the character- istics and temporal dynamics of these two distinct, spatially co-existent but temporally segregated communities. Although the total number of summer annual species recorded during our 15 yr of observation was higher than winter annuals, the mean number of species observed each year was higher in the winter community. The winter community exhibited lower temporal variation in total plant abundance and populations of individual species, lower species turnover rate and higher evenness than the summer community. The rank abundances of species in winter were significantly positively correlated for a period of up to 7 yr while in summer significant positive correlations in rank abundance disappeared after 2 to 3 yr. The higher seasonal species diversity (i.e. number of species ob- served in each season) in winter rather than the overall special pool (over 15 yr) may be responsible for the greater community stability of winter annuals. The difference in long-term commu- nity dynamics between the two communities of annual plants are likely due to the differences in total species pool, life history traits (e.g. seed size), and seasonal climatic regimes.