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1.
This paper reports field observational evidence on the diversity-biomass production relationship from eastern Mediterranean
shrublands dominated by Cistus salviifolius. The main results are: (1) plant diversity and ecosystem primary production are positively correlated in the Cistus shrublands, which are multigrowth form systems; (2) the taxonomic and growth form diversity in Cistus shrublands suggests that there is strong differentiation along the structural niche axis, and thus functional redundancy
is weak; (3) the performance of the dominant Cistus in terms of biomass production did not affect the overall diversity-biomass production of the studied communities.
Received: 18 October 1999 / Accepted: 13 April 2000 相似文献
2.
Plant communities are often assumed to be stable on a year-to-year basis. We present evidence that species composition in permanent quadrats changes considerably between years at a range of Environmental Change Network sites across the UK. The extent of this variability varies with habitat type. Communities associated with low disturbance levels and low agricultural inputs, particularly moorland (upland grass and heath) and bog communities, are most stable.Inter-annual variability should, therefore, be considered in designing monitoring schemes to ensure that frequency of recording is sufficient to avoid short-term fluctuations obscuring long-term trends.More diverse communities were more stable, with less species turnover between years. However, diverse communities also tended to be dominated by slow-growing, slow-reproducing plants, adapted to low nutrient conditions, identified as ‘stress tolerators’ in the Grime CSR scheme and low Ellenberg N values. Species compositional stability was more strongly correlated with these indices of plant functional types than species richness. Nevertheless, a significant effect of species richness could be identified, even after other causes of variation were accounted for.More stable communities in our study are likely to be resilient to low levels of environmental change, although they may still change, and possibly change dramatically if critical ‘tipping points’ are reached. 相似文献
3.
The abundance and structure of Bacteroidetes populations at diverse temporal and spatial scales were investigated in the Northwestern Mediterranean Sea. At a temporal scale, their relative abundance exhibited a marked seasonality, since it was higher in spring and decreased in winter. Similarly, Bacteroidetes community structure encompassed three main groups (winter, spring and summer-fall), which mimicked global bacterioplankton seasonality. At the spatial scale, relative abundances were similar in all surface samples along an inshore–offshore transect, but they decreased with depth. Analysis of the community structure identified four markedly different groups mostly related to different depths. Interestingly, seasonal changes in abundance and community structure were not synchronized. Furthermore, richness was higher when Bacteroidetes were less abundant. The variability of Bacteroidetes contributions to community structure in the temporal and spatial scales was correlated with different environmental factors: day length was the most important factor at the temporal scale, and salinity at the spatial scale. The community composition in terms of phylotypes changed significantly over time and along the depth gradients, but season or depth-specific phylogenetic clusters were not identified. Delineation of coherent Bacteroidetes sub-clusters should help to uncover higher resolution patterns within Bacteroidetes, and explore associations with environmental and biological variables. 相似文献
4.
U. Sommer 《Oecologia》2000,122(2):284-287
This study presents model experiments on the effect of the spatial pattern of herbivory on primary producer diversity. Microalgal
biofilms (periphyton) were exposed to different mixtures of two benthic herbivores, the isopod Idothea chelipes and the gastropod Littorina littorea. The herbivores are similar in their feeding selectivity but differ strongly in the spatial pattern of grazing. Idothea did not increase the spatial heterogeneity of algal cell densities beyond the level of ungrazed controls (<1 order of magnitude
between local minima and maxima at the 1 mm2 scale). Littorina grazing, in contrast, created a pronounced spatial heterogeneity with maximum:minmum ratios of almost 3 orders of magnitude.
When algae were exposed to mixtures of both gazers, the spatial heterogeneity of microalgal cell densities increased with
an increasing proportion of Littorina in the herbivore mixture. Algal species richness, diversity and evenness also increased with increasing proportions of Littorina, and was highly significantly correlated with the spatial heterogeneity of cell densities.
Received: 25 May 1999 / Accepted: 14 September 1999 相似文献
5.
Mauricio Cifuentes Martin Thiel Mark Lenz 《Journal of experimental marine biology and ecology》2007,352(2):280-294
We investigated the effects of temporal variability in a disturbance regime on fouling communities at two study sites in a northern-central Chilean bay. Fouling assemblages grown on artificial settlement substrata were disturbed by mechanical removal of biomass at different time intervals. Using one single disturbance frequency (10 disturbance events over 5 months) we applied 7 different temporal disturbance treatments: a constant disturbance regime (identical intervals between disturbance events), and 6 variable treatments where both variableness and sequences of intervals between disturbance events were manipulated. Two levels of temporal variableness (low and high, i.e. disturbance events were either dispersed or highly clumped in time) in the disturbance regime were applied by modifying the time intervals between subsequent disturbance events. To investigate the temporal coupling between disturbance events and other ecological processes (e.g. larval supply and recruitment intensity), three different sequences of disturbance intervals were nested in each of the two levels of temporal variableness. Species richness, evenness, total abundance, and structure of communities that experienced the various disturbance regimes were compared at the end of the experiment (15 days after the last disturbance event). Disturbance strongly influenced the community structure and led to a decrease in evenness and total abundance but not species richness. In undisturbed reference communities, the dominant competitor Pyura chilensis (Tunicata) occupied most available space while this species was suppressed in all disturbed treatments. Surprisingly, neither temporal variableness in the disturbance regime nor the sequence of intervals between disturbance events had an effect on community structure. Temporal variability in high disturbance regimes may be of minor importance for fouling communities, because they are dominated by opportunistic species that are adapted to rapidly exploit available space. 相似文献
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8.
L. Tommasi G. Vallortigara M. Zanforlin 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(5):567-572
Young chickens were trained to find food by ground-scratching in the centre of a closed uniform arena and were then tested
in arenas of similar areas but of different shapes. Chickens showed localized searching behaviour in the square-shaped arena,
and maintained this behaviour when placed in a circular or triangular (both equilateral and isosceles) arena. With a rectangular-shaped
arena, obtained by doubling the original square-shaped one, chickens showed more dispersed searching along the major axis,
but searching tended to be concentrated around the centres of the composing squares and around the centre of the rectangle
itself. When trained in a square- or triangle-shaped arena and then tested in an arena of the same shape but a larger area,
chickens displayed searching behaviour at two different distances from the wall of the arena, one corresponding to the correct
distance (i.e. centre) in the smaller (training) arena, the other to the actual centre of the test arena. On the other hand,
in a circular arena, chickens searched mainly at a distance midway between the radius of the small (training) and of the large
(testing) circular arena. These results suggest that, during training, chickens encoded information on both the absolute and
the relative distance of the food from the walls of the arena, the latter information being more accurate when the arena displayed
identifiable features such as corners.
Accepted: 28 December 1996 相似文献
9.
Small-scale spatial variability in intertidal and subtidal turfing algal assemblages and the temporal generality of these patterns 总被引:1,自引:0,他引:1
M.A Coleman 《Journal of experimental marine biology and ecology》2002,267(1):53-74
Spatial and temporal variation in patterns of distribution and abundance of algal assemblages is large and often occurs at extremely small spatial and temporal scales. Despite this, few studies investigate interactions between these scales, that is, how patterns of spatial variation change through time. This study investigated a number of scales of spatial variation (from tens of centimetres to kilometres) in assemblages of intertidal and subtidal turfing algae. Significant differences were found in the composition and abundances of species in assemblages of turf at all spatial scales tested. Much of the variation among assemblages could, however, be explained at the scale of quadrats (tens of centimetres apart) (27±1.4 (SE)% of dissimilarity) with an additional 7±1.2% explained at the scale of sites (tens of metres apart) and 10±1.5% at the scale of locations (kilometres apart). Although the greatest dissimilarity in assemblages occurred at the scale of habitats, this accounted for a relatively small proportion of the overall variation in assemblages. These patterns were consistent through time, that is, at each sampling time the spatial scale explaining the greatest proportion of variation in assemblages was replicate quadrats separated by tens of centimetres. These patterns appear to be due to small-scale variation in patterns of distribution and abundances of the individual species that comprise turfing algal assemblages. The results of this experiment suggest that large scale processes have less effect on patterns of variability of algal assemblages than those occurring on relatively smaller spatial scales and that small-scale spatial variation should not be considered as simply “noise”. 相似文献
10.
The scale of analysis determines the spatial pattern of woody species diversity in the Mediterranean environment 总被引:1,自引:0,他引:1
Athanasios S. Kallimanis John M. Halley Despina Vokou Stefanos P. Sgardelis 《Plant Ecology》2008,196(1):143-151
We examine the spatial pattern of woody species diversity at different scales, in two sites of Mt. Holomontas in northern
Greece, which falls within the transitional zone between temperate forests and Mediterranean-type ecosystems. We investigate
how diversity is distributed in space and whether the perceived pattern changes with the scale of observation. We use two
different metrics of diversity: species richness and species turnover. Our main finding is that the spatial pattern of diversity
changes with the scale of observation or analysis. For a given scale, the pattern of species richness (alpha diversity) is
negatively correlated with the pattern of species turnover (beta diversity). Species-rich areas have more species in common
with their neighbors than species-poor areas. The between-scale disparity of the spatial pattern of diversity may be a general
feature of ecological systems. For this to be validated, studies with different groups of species in different biomes and
in different biogeographical areas are required; our study contributes to this direction providing evidence that this holds
true for woody species in Mediterranean communities. Finally, we discuss how these findings might affect important issues
in theoretical and applied ecology, such as identifying the environmental factors driving biodiversity. 相似文献
11.
Bettina Saier 《Helgoland Marine Research》2002,56(1):44-50
In 1997 and 1998, surveys were performed to compare species composition, abundance and diversity of non-attached epifauna
(>1 mm) in low intertidal and adjacent shallow subtidal zones of three mussel beds (Mytilus edulis L.) near the island of Sylt in the North Sea. The community structure was similar when compared within tidal zones: no significant
differences in species numbers and abundances were recorded between locations and between years. A comparison between tidal
zones, however, revealed higher diversity, species densities and total species numbers in the subtidal (per 1,000 cm2: H
′=2.0±0.16; 12 ±1 species density; 22 species) than the intertidal zone (per 1,000 cm2: H
′=0.7±0.27; 6±2 species density; 19 species). Abundances significantly dropped with increasing submergence from 2,052 (±468)
m–2 to 1,184 (±475) m–2. This was mainly due to significantly higher densities of both juvenile periwinkles, Littorina littorea, and crabs, Carcinus maenas, in intertidal mussel beds. However, many less dominant species were significantly more abundant in subtidal mussel beds.
This study revealed that in the non-attached epifaunal community of mussel beds the tidal level effect within metres was strong,
whilst the spatial variability in a much wider (kilometre) range but the same tidal level was negligible. The high epifaunal
diversity in the subtidal zone suggests that the protective measures for mussel beds against the effects of mussel fishery
should be extended from the intertidal to the subtidal zone, if the integrity of the mussel bed community in the Wadden Sea
National Park is to be maintained.
Electronic Publication 相似文献
12.
Early environments drive diversity and floristic composition in Mediterranean old fields: Insights from a long-term experiment 总被引:1,自引:0,他引:1
Luis Cayuela Jos María Rey Benayas Fernando T. Maestre Adrin Escudero 《Acta Oecologica》2008,34(3):311-321
While many studies have explored how previous and current environmental conditions affect the performance of individual organisms, their relative importance as drivers of current diversity and composition of communities is virtually unknown. We evaluated the response of herbaceous communities to previous (experienced during early establishment) and current environmental conditions by comparing their composition and diversity in an abandoned Mediterranean cropland planted with Quercus ilex subsp. ballota L. seedlings. These seedlings received different experimental treatments (summer irrigation and artificial shading) during the first three years after planting, and were interrupted from then on. We tested two complementary hypotheses: (i) the previous environments experienced by the herbaceous communities during their establishment have a long-term carry-over effect on diversity and composition of species assemblages and (ii) these communities are influenced by their current environment, particularly by the woody layer and the soil conditions. Overall, we observed an important contribution of initial environmental conditions in determining the current diversity and composition of herbaceous communities. Amelioration of environmental conditions, particularly water stress, during community establishment resulted in a decrease in alpha and beta diversity, possibly as a consequence of decreasing environmental heterogeneity. Previous environments accounted for 26.3% of the explained variance in current community composition. Annuals, legumes and forbs also responded significantly to previous environments, which explained 27.9%, 36.2% and 30.1%, respectively, of the variance in their composition. Our results suggest that those species present at a particular site early in succession pre-empt the site and influence vegetation dynamics on that site for a long time. This study provides important insights for understanding the mechanisms underlying the ecological effects of issues like cropland reforestation and woody vegetation encroachment. 相似文献
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14.
The role of competition by dominants and temperature in the foraging of subordinate species in Mediterranean ant communities 总被引:3,自引:0,他引:3
In this paper we test the influence of temperature and interference competition by dominant species on the foraging of subordinate
species in Mediterranean ant communities. We have analyzed the changes in resource use by subordinate species in plots with
different abundances of dominant ants, and in different periods of the day and the year, i.e., at different temperatures.
The expected effects of competition by dominant species on foraging of subordinates were only detected for two species in
the number of baits occupied per day, and for one species in the number of foragers at pitfall traps. In all three cases,
subordinate species were less represented at baits or in traps in plots with a high density of dominants than in plots with
a medium or low density of dominants. The number of workers per bait, and the foraging efficiency of subordinate species did
not differ in plots differing in dominant abundance. Daily activity rhythms and curves of temperature versus foraging activity
of subordinate species were also similar in plots with different abundance of dominant species, indicating no effect of dominants
on the foraging times of subordinates. Instead, temperature had a considerable effect on the foraging of subordinate species.
A significant relationship was found between maximum daily temperature and several variables related to foraging (the number
of foragers at pitfall traps, the number of baits occupied per day, and the number of workers per bait) of a number subordinate
species, both in summer and autumn. These results suggest that the foraging of subordinate ant species in open Mediterranean
habitats is influenced more by temperature than by competition of dominants, although an effect of dominants on subordinates
has been shown in a few cases. In ant communities living in these severe and variable environments, thermal tolerance reduces
the importance of competition, and the mutual exclusion usually found between dominant and subordinate species appears to
be the result of physiological specialization to different temperature ranges.
Received: 8 May 1998 / Accepted: 30 July 1998 相似文献
15.
K.-P. Wittich 《International journal of biometeorology》1997,41(2):58-64
Simple equations are given which describe the relationships between the land-surface emissivity, the normalized difference
vegetation index and the fractional vegetation cover. The empirical equations are validated using data taken from the literature.
Adequate agreement is found between the formulas used in this study and those proposed by other authors.
Received: 9 December 1996 / Revised: 23 May 1997 / Accepted: 4 July 1997 相似文献
16.
Temporal variability in the diversity and composition of stream bacterioplankton communities 总被引:1,自引:0,他引:1
Bacterioplankton in freshwater streams play a critical role in stream nutrient cycling. Despite their ecological importance, the temporal variability in the structure of stream bacterioplankton communities remains understudied. We investigated the composition and temporal variability of stream bacterial communities and the influence of physicochemical parameters on these communities. We used barcoded pyrosequencing to survey bacterial communities in 107 streamwater samples collected from four locations in the Colorado Rocky Mountains from September 2008 to November 2009. The four sampled locations harboured distinct communities yet, at each sampling location, there was pronounced temporal variability in both community composition and alpha diversity levels. These temporal shifts in bacterioplankton community structure were not seasonal; rather, their diversity and composition appeared to be driven by intermittent changes in various streamwater biogeochemical conditions. Bacterial communities varied independently of time, as indicated by the observation that communities in samples collected close together in time were no more similar than those collected months apart. The temporal turnover in community composition was higher than observed in most previously studied microbial, plant or animal communities, highlighting the importance of stochastic processes and disturbance events in structuring these communities over time. Detailed temporal sampling is important if the objective is to monitor microbial community dynamics in pulsed ecosystems like streams. 相似文献
17.
Levels of genetic diversity at different stages of the domestication cycle of interior spruce in British Columbia 总被引:3,自引:0,他引:3
M. U. Stoehr Y. A. El-Kassaby 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,94(1):83-90
Concerns over the reductionist nature of the domestication of forest-tree species focus on the possibility of potential genetic
erosion during this process. To address these concerns, genetic diversity assessments in a breeding zone the Province of British
Columbia “interior” spruce (Picea glauca×engelmanni) program was conducted using allozyme markers. Genetic-variation comparisons were made between natural and production (seed
orchard) populations as well as seed and seedling crops produced from the same breeding zone’s seed orchard. The natural population
sample consisted of a total of 360 trees representing three stands within each of three watersheds present in the Shuswap-Adams
low-elevation zone of interior British Columbia. Small amounts of genetic differentiation were observed among the nine natural
populations (4%) and this was attributable to extensive gene flow Consequently, the sum of these nine populations was considered as a baseline for the genetic variation present in the breeding
zone. The comparisons between the seed orchard and the breeding zone produced a similar percentage of polymorphic loci while the expected hetrozygosity (0.207 vs 0.210) and the average number of alleles per locus (2.7 vs 2.4) were slightly lower in the seed orchard. A total
of seven natural populations’ rare alleles were not present in the orchard population, while one allele was unique to the orchard. The %P increased to 70.6% in the seedlot, but dropped to the natural populations level (64.7%) in the plantation. The observed increase
in %P was a result of pollen contamination in the orchard. It is suspected that the reduction in the plantation was caused by an
unintentional selection in the nursery. Simulated roguing in the orchard did not drastically reduce even if up to 50% of the orchard’s clones were rogued. However, roguing was associated with a reduction in the average number
of alleles per locus (i.e., sampling effect).
Received: 2 January 1996 / Accepted: 24 May 1996 相似文献
18.
Molecular diversity at the major cluster of disease resistance genes in cultivated and wild Lactuca spp. 总被引:3,自引:0,他引:3
D. Sicard S.-S. Woo R. Arroyo-Garcia O. Ochoa D. Nguyen A. Korol E. Nevo R. Michelmore 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1999,99(3-4):405-418
Diversity was analyzed in wild and cultivated Lactuca germplasm using molecular markers derived from resistance genes of the NBS-LRR type. Three molecular markers, one microsatellite
marker and two SCAR markers that amplified LRR-encoding regions, were developed from sequences of resistance gene homologs
at the main resistance gene cluster in lettuce. Variation for these markers were assessed in germplasm including accessions
of cultivated lettuce, Lactuca sativa
L. and three wild Lactuca spp., L. serriola
L., L. saligna and L. virosa
L. Diversity was also studied within and between natural populations of L. serriola from Israel and California; the former is close to the center of diversity for Lactuca spp. while the latter is an area of more recent colonization. Large numbers of haplotypes were detected indicating the presence
of numerous resistance genes in wild species. The diversity in haplotypes provided evidence for gene duplication and unequal
crossing-over during the evolution of this cluster of resistance genes. However, there was no evidence for duplications and
deletions within the LRR-encoding regions studied. The three markers were highly correlated with resistance phenotypes in
L. sativa. They were able to discriminate between accessions that had previously been shown to be resistant to all known isolates of
Bremia lactucae. Therefore, these markers will be highly informative for the establishment of core collections and marker-aided selection.
A hierarchical analysis of the population structure of L. serriola showed that countries, as well as locations, were significantly differentiated. These differences may reflect local founder
effects and/or divergent selection.
Received: 7 March 1999 / Accepted: 25 March 1999 相似文献
19.
Combining genetic gain and diversity by considering average coancestry in clonal selection of Norway spruce 总被引:3,自引:0,他引:3
Y. Q. Zheng D. Lindgren O. Rosvall J. Westin 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,95(8):1312-1319
Genetic relationship within a population can be measured by average coancestry. This can also be expressed as an effective
number which represents the relative genetic diversity of the population. The goal of breeding can be formulated to maximise
genetic value minus average coancestry times a constant (the “penalty constant”). An iterative search algorithm can then be
used to find the best selections for meeting this goal. Two such algorithms, one for a fixed number of selections and the
other for a variable optimum number, were applied to select a mixture of field-tested Norway spruce clones with known parents.
The results were compared with those from the conventional method of restricting parental contributions to the selected population
as a means to control diversity. Coancestry-adjusted selection always yielded more gain than restricted selection at a given
effective population size (except under circumstances where the methods were equivalent). Expressed another way, at any given
level of gain, coancestry-adjusted selection maintained a larger effective population size than did restricted selection.
The relative superiority of coancestry-adjusted selection declined when the effective population size approached the lowest
value, that at which no penalty or restriction was applied. The method was extended by the second search algorithm to optimise
the selected number of clones. The optimal number of clones can be rather large when diversity is heavily valued, but the
reduction in genetic gain becomes large.
Received: 7 April 1997 / Accepted: 9 June 1997 相似文献