锡林河流域羊草草原植物种群和功能群的长期变异性及其对群落稳定性的影响

 分析了内蒙古锡林河流域羊草(Leymus chinensis)草原群落植物种群、功能群和群落生物量的长期变异性,以及植物功能群间的补偿作用对群落稳定性的影响,结果表明：从种群水平到功能群和群落水平,地上生物量的年度间变异性逐渐降低,而稳定性则逐渐增加。植物功能群组成对群落稳定性具有更强烈的影响,在植物生活型功能群组成中多年生根茎禾草与多年生丛生禾草和多年生杂类草功能群,在生物量的年度变化上具有补偿作用,在生态类群组成中,旱生植物与中旱生植物也具有补偿作用。植物种群多度的长期变异性可能依赖于物种对环境波动的敏感性和种间相互作用对环境波动的放大效应,生物多样性使物种对环境波动响应的多样性增加,并通过不同响应类型(功能群)间的补偿作用使群落稳定性增加。     

Restoration of Botshol (The Netherlands) by reduction of external nutrient load: Recovery of the Characean community

The formerly rich characean community in Botshol with six species of which the rareNitellopsis obtusa andChara hispida dominated at many sites, decreased to only two species,Chara globularis andC. connivens, in the period 1980–1988. The macrophyteNajas marina also remained at some sites, and the aquatic mossFontinalis antipyretica and the filamentous algaVaucheria dichotoma predominated at many sites. These phenomena may have been due to eutrophication by the inlet of polluted water. This process of eutrophication was stopped by restoration measures in 1989, resulting in a lower phosphorus concentration (ca. 0.024 mg l^–1) and a higher water transparency. Immediately after these measures the Characeae community increased strongly in abundance and number of species. During the summer of 1990, and especially of 1991, a spectacular growth occurred ofChara connivens. Chara connivens was often accompanied byChara hispida. Other species with scattered occurrence wereChara aculeolata, C. aspera, C. contraria andC. Globularis. The reasons for the shift in dominance fromNitellopsis obtusa toChara connivens are discussed. One of the reasons may be the recent higher chloride content which is one of the consequences of the restoration measures.     

Differential roles of species richness versus species asynchrony in regulating community stability along a precipitation gradient

Plant community may provide products and services to humans. However, patterns and drivers of community stability along a precipitation gradient remain unclear. A regional‐scale transect survey was conducted over a 3‐year period from 2013 to 2015, along a precipitation gradient from 275 to 555 mm and spanning 440 km in length from west to east in a temperate semiarid grassland of northern China, a central part of the Eurasian steppe. Our study provided regional‐scale evidence that the community stability increased with increasing precipitation in the semiarid ecosystem. The patterns of community stability along a precipitation gradient were ascribed to community composition and community dynamics, such as species richness and species asynchrony, rather than the abiotic effect of precipitation. Species richness regulated the temporal mean (μ) of aboveground net primary productivity (ANPP), while species asynchrony regulated the temporal standard deviation (σ) of ANPP, which in turn contributed to community stability. Our findings highlight the crucial role of community composition and community dynamics in regulating community stability under climate change.     

Long-term changes in the benthic communities of the Pomeranian Bay (Southern Baltic Sea)

Long-term changes in the macrofauna of the Pomeranian Bay were studied by comparing survey data from the 1950s, 1980s, and 1990s. The study area has undergone significant eutrophication during the period of investigation. Biomass of filter-feeding bivalves increased significantly. Spatial distribution patterns of several species have changed. Strong decreases in species richness were caused by oxygen depletion at stations deeper than 15 m.Saduria entomon, Monoporeia affinis, andPontoporeia femorata vanished entirely between 1981 and 1993. Although a causal relationship between simultaneous increases of nutrient levels and macrobenthic biomass cannot be verified, eutrophication is proposed to be the major process affecing changes in macrofauna assemblages. In addition, changes in hydrography and climate increased frequency and severity of oxygen depletion events in the Pomeranian Bay since the mid 1980s.     

Species richness, environmental fluctuations, and temporal change in total community biomass

Theory and empirical results suggest that high biodiversity should often cause lower temporal variability in aggregate community properties such as total community biomass. We assembled microbial communities containing 2 to 8 species of competitors in aquatic microcosms and found that the temporal change in total community biomass was positively but insignificantly associated with diversity in a constant temperature environment. There was no evidence of any trend in variable temperature environments. Three non-exclusive mechanisms might explain the lack of a net stabilising effect of species richness on temporal change. (1) A direct destabilising effect of diversity on population level variances caused some populations to vary more when embedded in more diverse communities. (2) Similar responses of the different species to environmental variability might have limited any insurance effect of increased species richness. (3) Large differences in the population level variability of different species (i.e., unevenness) could weaken the relation between species richness and community level stability. These three mechanisms may outweigh the stabilising effects of increases in total community biomass with diversity, statistical averaging, and slightly more negative covariance in more diverse communities. Our experiment and analyses advocate for further experimental investigations of diversity-variability relations.     

Restoration of Botshol (The Netherlands) by reduction of external nutrient load: recovery of a characean community,dominated by Chara connivens

Till about 1965 a rich characean community occurred in the shallow peat lake Botshol with six species of which the rare Nitellopsis obtusa and Chara major dominated at many sites. In the period 1980–1988 characean biomass strongly decreased and only two species, Chara globularis and C. connivens, remained in small populations at a few localities. Of the macrophyte Najas marina also some small populations remained, while the aquatic moss Fontinalis antipyretica and the filamentous alga Vaucheria dichotoma predominated at many sites. These phenomena may have been due to eutrophication by the input of polluted water. This process of impoverishment was stopped by restoration measures in 1989, resulting in a lower phosphorus concentration (ca 25 µg l^-1) and a higher water transparency. Immediately after these measures the Characeae community increased in abundance and number of species. During the summer of 1990, and especially 1991, a spectacular growth occurred of Chara connivens. C. connivens was often accompanied by C. major. Other species with scattered occurrence were C. aculeolata, C. aspera, C. contraria and C. globularis. The reasons for the shift in dominance from Nitellopsis obtusa to Chara connivens are discussed. From growth experiments evidence was obtained that neither the recent higher chloride level, nor the lowered phosphate concentration were the main factors for the domination of Chara connivens.     

Fish community structure response to major habitat changes within the littoral zone of an estuarine coastal lake

Synopsis The littoral environment and fish fauna of Swartvlei, an estuarine lake, was monitored for four years during which major habitat changes occurred. Initially (1979) the zone was dominated by the submerged macrophytes Potamogeton pectinatus, Chara globularis and Lamprothamnium papulosum. This plant community was replaced by filamentous algal mats during 1980 and with the disappearance of these mats in 1981 the littoral zone was transformed into a sandy habitat. There was a highly significant decline in the numbers of fishes in the littoral zone between the macrophyte and sand phases but no significant decrease in fish biomass between the two phases. Analysis of gill net catches revealed an increase in the CPUE of the family Mugilidae between the macrophyte and sand phases but a decline in the CPUE of vegetation associated species such as Monodactylus falciformis and Rhabdosargus holubi over the same period. The increase in mullet stocks during the sand phase was attributed to epipsammic micro-algal production and the input of allochthonous detritus during the 1981 floods. The three fish species diversity indices used in this study showed minor fluctuations between the habitat phases and these variations were related to changes in the equitability of distribution between the individual species within each habitat type. The numbers of fish species recorded during the macrophyte, algal mat and sand phases varied by less than 20%. The resilience of estuarine fishes to major alterations in their environment was illustrated by the fact that all fish species recorded at the beginning of 1979 were present at the end of 1982, despite major habitat and food resource changes.     

Large-Scale Temporal Changes in Spatial Pattern During Declines of Abundance and Occupancy in a Common Moth

We examined the changes in spatial pattern that accompanied the population decline of the garden tiger moth, Arctia caja (L.) in Britain between 1968 and 1999 using Spatial Analysis by Distance Indices (SADIE) techniques. A principal co-ordinate analysis of all pair-wise spatial associations between years indicated three groupings of years: 1969–1978,1979–1990,1991–1999, which revealed three phases during the population decline: an early period with highly structured spatial pattern; a middle period with nearly random distribution overall; and a recent period with highly structured spatial pattern but small abundance overall. The change in spatial structure in the early 1980’s accompanied rapid changes in abundance but preceded a sharp decline in occupancy and confirms that the sharp decline in abundance included decreases from widespread high-density sites. Perhaps unusually, A. caja varied from spatially aggregated to randomly distributed and back to spatially aggregated, all while its abundance declined sharply. Present distribution pattern may reflect past abundance changes poorly in this species. Areas showing the greatest variation in abundance displayed the greatest range in spatial structure, but also the greatest stability of spatial pattern, indicating changes between extremes of spatial pattern occurred slowly. SADIE techniques are a powerful method to quantify temporal changes in spatial pattern and relate them to temporal changes in abundance.     

Long-term studies of macrozoobenthos in intertidal and shallow subtidal habitats near the island of Norderney (East Frisian coast,Germany)

Near the East Frisian island of Norderney two sites are investigated permanently in order to study long-term fluctuations of macrozoobenthos: one transect (since 1977) at the northern side in shallow subtidal waters and another one (since 1976) at the sheltered southern side in the intertidal area of the Wadden Sea. Since 1980 the investigations have been continued in the frame of COST-47, sedimentary intertidal programme (including the shallow subtidal habitats colonized by the Macoma balthica community).The results up to 1984, respectively to 1985, are presented and the changes of abundance of the dominant species are discussed. Discussed are also the influences of water temperatures and sediment disturbances caused by wave action. There is evidence that the intertidal variety of the Macoma balthica community shows a greater stability than the subtidal variety.     

The Flora and Invertebrate Fauna of a Relocated Grassland at Thrislington Plantation, County Durham, England

In order to extend quarrying near Thrislington Plantation, County Durham, England, 8.5 ha of magnesian limestone grassland was relocated over a period of eight years from October 1982. The effects of this on the flora and invertebrate fauna were examined within the Festuca-Helianthemum community at five plots relocated at different times. Plants were sampled with a point-quadrat, and invertebrates by pitfall trapping. Comparisons were made between age of the relocation, numbers of species and individuals, and diversity of flora and invertebrates. The plots were examined using the percentage similarity measure. The plots showed an initial change in some aspects of community structure for flora and invertebrate fauna, followed by a “recovery” period. This was particularly evident in the numbers of species and species diversity of plants and in the numbers of individuals and species diversity of invertebrates. Bare ground, left by the relocation process, was still evident between relocated turfs in the early plots, but it was successfully colonized by resident species in later plots. These results have implications for the future management of this and similar sites, particularly with respect to the emphasis placed on subsequent monitoring and the need to consider invertebrate faunas when implementing management strategies.     

The impact of environmental variability and species composition on the stability of experimental microbial populations and communities

Understanding how environmental fluctuations affect the stability of populations and communities is complex, for example, because direct effects of environmental variability on populations may be modified and propagated across communities by species interactions. One way to explore and further understand these complexities is via a factorial manipulation of community composition and environmental conditions. Using laboratory based aquatic microcosms we manipulated environmental fluctuation by creating two environments; one with variable light and one with constant light. Within these environments, community composition was manipulated by constructing communities from all possible combinations of three species that vary in their reliance on light for growth (an autotroph: a diatom completely reliant on light, a heterotroph: a Paramecium species not reliant on light, and a mixotroph: a Paramecium species somewhat reliant on light). Community composition was predicted to affect populations and communities by introducing and altering competitive interactions between species and affecting the degree of niche differentiation between species. We found that population stability was predominantly influenced by an interaction between community composition and environmental variability, whereby the effect of environmental variability synergistically combined with effects of community composition to reduce population stability. Covariance of populations was determined by an interaction between community composition and environmental variability, though this did not result from the effect of niche differentiation between species. Species interactions drove correlations between population biomass and the environment which otherwise did not exist. Our results demonstrate the complex and interrelated effects of abiotic and biotic factors on population and community stability, and suggest the need to consider aspects of community composition when predicting the impact of environmental fluctuations.     

Estuarine nematodes as indicators of organic pollution; An example from the Ems estuary (The Netherlands)

A comparison is made of the structure and abundance of the nematode community of an intertidal, brackish-water mudflat in the Ems estuary under conditions of high (1980) and reduced (1987) organic waste input. Three stations, at different distances from the waste water inlet, were sampled monthly; nematodes were identified and counted in the upper 1 cm of the sediment. In 1987, numerical density of nematodes was lower, and species diversity was higher than in 1980. Diatom eating nematode species dominated in 1980, to decrease by 1987.Eudiplogaster pararmatus, an indicator of organic enrichment, also decreased strongly. The response of the nematode community to reduced organic waste input could be adequately described with the BONGERS' Maturity Index.     

Competition and specialization in an African forest carnivore community

Globally, human activities have led to the impoverishment of species assemblages and the disruption of ecosystem function. Determining whether this poses a threat to future ecosystem stability necessitates a thorough understanding of mechanisms underpinning community assembly and niche selection. Here, we tested for niche segregation within an African small carnivore community in Kibale National Park, Uganda. We used occupancy modeling based on systematic camera trap surveys and fine‐scale habitat measures, to identify opposing preferences between closely related species (cats, genets, and mongooses). We modeled diel activity patterns using kernel density functions and calculated the overlap of activity periods between related species. We also used co‐occupancy modeling and activity overlap analyses to test whether African golden cats Caracal aurata influenced the smaller carnivores along the spatial and/or temporal axes. There was some evidence that related species segregated habitat and activity patterns. Specialization was particularly strong among forest species. The cats and genets partitioned habitat, while the mongooses partitioned both habitat and activity period. We found little evidence for interference competition between African golden cats and other small carnivores, although weak interference competition was suggested by lower detection probabilities of some species at stations where African golden cats were present. This suggests that community assembly and coexistence in this ecosystem are primarily driven by more complex processes. The studied carnivore community contains several forest specialists, which are typically more prone to localized extinction. Preserving the observed community assemblage will therefore require the maintenance of a large variety of habitats, with a particular focus on those required by the more specialized carnivores.     

Euhydrophyte communities of the River Nile and its impoundments in Egyptian Nubia

The River Nile and its two impoundments, the Aswan Reservoir and Lake Nasser, are important habitats for submerged and floating-leaved freshwater macrophytes (euhydrophytes) in the desert region of Egyptian Nubia. Ordination and classification analysis of survey data collected during the period 1980–1986 suggested that the Aswan High Dam forms a man-made vegetational boundary, delineating two basic macrophyte community types. In Lake Nasser a community dominated by Najas spp. is present. In the Aswan Reservoir and the R. Nile downstream of the old Aswan Dam the euhydrophyte community is dominated by a Potamogeton crispus — Ceratophyllum demersum association. Differences between the two community types appear to be related to differences in physical factors (e.g. water level fluctuation and flow regime), and water chemistry, to phenological factors, and to the differing successional ages of the macrophyte communities of the Nile system upstream and downstream of the Aswan High Dam. There is some evidence for depth zonation of the submerged macrophyte community in both lake and river habitats. Strategy analysis of the euhydrophyte communities present upstream and downstream of the High Dam, over the period 1963–89, indicated that successful established-phase strategy types were similar on both sides of the dam. In the long term there seems little to prevent euhydrophyte species at present confined to below the High Dam from crossing this boundary to colonise Lake Nasser.     

Introgressive hybridization between two species of waterstriders (Hemiptera: Gerridae: Limnoporus): geographical structure and temporal change of a hybrid zone

Where the distribution ranges of the waterstriders Limnoporus notabilis and L. dissortis meet in western Canada, extensive hybridization and introgression occurs. Multivariate ordination analyses of genetic and morphometric data by principal component analysis revealed that a single axis separating the two parent species could account for nearly all the variation in both data sets. Maps of principal component scores for both data sets revealed geographical patterns of variation reflecting specific topographic features in the region. Comparisons of morphometric data from some of the samples collected in the 1980s and from the same sites revisited in the 1990s revealed substantial changes. An ‘island’ of dissortis‐like populations inside the range of L. notabilis in interior British Columbia expanded, and a marked local protrusion of notabilis‐like phenotypes into the range of L. dissortis on the east slope of the Rocky Mountains diminished during the decade between collections. We conclude that introgressive hybridization between these two species of waterstriders is a spatially complex and highly dynamic process.     

EVIDENCE FOR COMPETITIVE RELEASE IN SIMPLIFIED SAXICOLOUS LICHEN COMMUNITIES

Saxicolous cryptogam communities were sampled quantitatively on two Potomac River island habitats in June of 1980. As a result of air pollution stress, the community on one island was found to be much simpler than that found on the other island. Two relatively pollution-tolerant foliose lichen species, Xanthoparmelia conspersa and Pseudoparmelia baltimorensis, were found to dominate the communities on both islands. An examination of niche breadth and position along a light intensity gradient demonstrated that P. baltimorensis was most frequent at low light intensities and X. conspersa was most frequent at high light intensities. However, X. conspersa exhibited a niche shift toward intermediate light intensities in the species-poor community, likely the result of reduced competitor diversity in this community since the intermediate light intensities supported the greatest number of species in the species-rich community. Niche overlap between the two species was found to occur at lower light intensities in the species-poor community, suggesting that X. conspersa is more likely to appropriate intermediate light intensities in this community. The significance of competition as a regulatory factor in lichen communities has not been fully appreciated. Since lichens and other cryptogams are frequently used as indicators of environmental quality, competitive processes in naturally occurring lichen communities must be thoroughly understood before changes in species distribution that apparently result from disturbance can be properly interpreted.     

The fish community of Loch Lomond,Scotland: its history and rapidly changing status

The fish community of Loch Lomond is of national importance. Its diversity of species and rare populations of powan (Coregonus lavaretus) and freshwater feeding river lampreys (Lampetra fluviatilis) warrant high conservation status. It is also of value for its sport fisheries for sea-trout (Salmo trutta), salmon (Salmo salar) and pike (Esox lucius). Historical records demonstrate that the species composition of the fish community has remained stable over a very long period until recently when a series of introductions of fish species new to the catchment has resulted in successful colonisation by a number of species. These have resulted in fundamental changes in the ecosystem. Here using historical records the long-term stability of the fish community is examined, recent rapid changes in the fish community are documented and some of the resultant effects of changes in the fish community are demonstrated.     

Ectoparasite fitness in auxiliary hosts: phylogenetic distance from a principal host matters

We studied reproductive performance in two flea species (Parapulex chephrenis and Xenopsylla ramesis) exploiting either a principal or one of eight auxiliary host species. We predicted that fleas would produce more eggs and adult offspring when exploiting (i) a principal host than an auxiliary host and (ii) an auxiliary host phylogenetically close to a principal host than an auxiliary host phylogenetically distant from a principal host. In both flea species, egg production per female after one feeding and production of new imago after a timed period of an uninterrupted stay on a host differed significantly between host species. In general, egg and/or new imago production in fleas feeding on an auxiliary host was lower than in fleas feeding on the principal host, except for the auxiliary host that was the closest relative of the principal host. When all auxiliary host species were considered, we did not find any significant relationship between either egg or new imago production in fleas exploiting an auxiliary host and phylogenetic distance between this host and the principal host. However, when the analyses were restricted to auxiliary hosts belonging to the same family as the principal host (Muridae), new imago production (for P. chephrenis) or both egg and new imago production (for X. ramesis) in an auxiliary host decreased significantly with an increase in phylogenetic distance between the auxiliary and principal host. Our results demonstrated that a parasite achieves higher fitness in auxiliary hosts that are either the most closely related to or the most distant from its principal host. This may affect host associations of a parasite invading new areas.     

Anthropogenic Pressure on a Molluscan–Trematode Community over a Long-term Period in the Basingstoke Canal, UK, and Its Implications for Ecosystem Health

A long-term study of a molluscan–trematode community in the Basingstoke Canal, UK, was undertaken over the period 1970–2003 which coincided with a significant restoration program involving substantial anthropogenic changes to the canal’s ecosystem. The aim of this study was to correlate these changes with alterations in the molluscan–trematode community, focusing on fluctuations in the prevalence and species richness of the trematode population as a good indicator, in terms of biodiversity, of ecosystem health. Molluscs were sampled at four time periods (1970, 1982, 1983, 2003) and examined for trematode parasites. The molluscan population over the sampling period demonstrated a limited stability with few species being present during all time periods. During 1982 and 1983, when restoration of the sampling site was being undertaken, Lymnaea stagnalis dominated the molluscan fauna, possibly because it was best able to take advantage of the disturbed conditions, while other species such as Bithynia tentaculata were absent. In the trematode population, the prevalence and diversity of both cercarial and metacercarial infections was high in 1970 prior to the period of restoration work. However, during 1982 and 1983, the trematode community was significantly reduced with cercarial prevalence declining to less than 1%. By 2003, more than 12 years after restoration had been completed, the trematode population had shown only a modest recovery. Trematodes use a wide range of different host species for completing their life-cycles and may be used as bioindicators of ecosystem diversity and health. An interpretation of the structure of the molluscan–trematode community over the sampling period suggests that the restoration project had an initial negative effect on ecosystem health, in terms of biodiversity, but this has subsequently only shown modest signs of recovery suggesting continuing problems in ecological functioning and stability.     

功能多样性和功能冗余对高寒草甸群落稳定性的影响

功能多样性和功能冗余是影响群落稳定性的重要因素,但它们对稳定性影响的相对强弱尚有争论。通过在青藏高原高寒矮嵩草(Kobresia humilis)草甸为期6a的刈割(不刈割、留茬3cm、留茬1cm)和施肥(施肥、不施肥)控制实验对此进行了探讨。研究结果显示,群落稳定性随着功能多样性和功能冗余的增大而单调增加,但由于功能多样性的变异性大于功能冗余的变异性,功能多样性与物种多样性间的相关性强于功能冗余与物种多样性间的相关性,功能多样性与群落稳定性间的相关性也强于功能冗余与群落稳定性间的相关性,因此,尽管功能冗余产生的保险效应对维持群落稳定性具有促进作用,但功能多样性的互补效应对维持群落稳定性的作用更大。结果表明,功能多样性和功能冗余对群落稳定性的相对影响与其变化程度正相关,功能多样性与群落稳定性的变化具有更紧密的联系,能更好地预测生态系统稳定性的变化。研究为草原生态系统的可持续管理提供了重要启示。