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1.
Investigation of the dynamics of an oligosporous actinomycete population in chernozem soil in the course of succession induced by soil wetting allowed us to reveal the time intervals and conditions optimal for the isolation of particular oligosporous actinomycetes. Saccharopolysporas and microbisporas proved to be best isolated in the early and late stages of succession, whereas actinomycetes of the subgroupActinomadura and saccharomonosporas could be best isolated in the early and intermediate stages of succession  相似文献   

2.
1992—2018年内蒙古自治区植被动态演替特征及驱动力   总被引:1,自引:0,他引:1  
人类的建设与破坏活动是植被动态变化的重要根源之一,利用遥感探究植被演替的量化监测过程及驱动力能够很好揭示人类活动对生态本底的影响。本研究利用欧洲航天局逐年土地覆被数据及地理学信息图谱方法,从植被型组、植被型尺度分析1992—2018年内蒙古自治区植被动态演替方向、演替速度及演替序列,明晰植被演替特征并量化其演替驱动力。结果表明: 研究期间,内蒙古自治区植被数量结构为“植增荒减”,具体年增长速率依次为耕地(353.10 km2)>草原(243.92 km2)>森林(-16.22 km2)>灌丛(-120.37 km2)>荒漠(-556.31 km2),并且空间相邻分布的草原、荒漠、灌丛三者的面积变化存在权衡关系。植被演替空间呈“绿进沙退”格局,演替热点集中于西辽河平原、内蒙古中部荒漠-草原交界处及黄河沿岸;植被演替序列结构复杂,进展、逆行演替相互交错,不同群落演替流量的截流率差距突出,其中,植被型组草原、灌丛与植被型草地、雨养农田群落在演替过程中截获最多演替流量。植被动态演替的核心驱动力为农牧业生产、经济发展水平、人口规模、生态工程、气候变化。作为“植物群落学-景观生态学”的实例研究,本研究结果可为植被格局优化、演替等级提升等生态措施实施空间的划定提供科学依据。  相似文献   

3.
Ksudach Volcano, southern Kamchatka Peninsula, erupted in 1907 and impacted over 2000 km2 of forests with air-fall pumice deposits. We identified three impact zones. In Zone I, deposits deeper than 100 cm destroyed all vegetation. Two early successional stages occur, a lichen-dominated desert and isolated patches of a pioneer herb stage. Zone II is defined by pumice deposits 30 to 100 cm deep. Deposits of 70 to 100 cm destroyed all vegetation, but left scattered snags. Here primary succession dominates recovery, but its rate varies. Isolated trees survived in deposits of 30 to 70 cm and primary and secondary successional stages form a complex mosaic termed an intermediate succession. In Zone II, the primary stages found in Zone I are joined by a dwarf shrub-herb stage and a secondary birch forest stage. Zone III occurs where thinner deposits permitted some vegetation to survive in all locations. Secondary succession dominates in deposits of 10 to 30 cm. Trees suffered damage, but survived deposits of 20 to 30 cm, while other vegetation layers were eliminated. Deposits of 10 to 20 cm eliminated mosses and lichens and but only reduced the number of dwarf shrubs and herbs. Deposits of less than 10 cm damaged herb, moss and lichen layers but did not eliminate any species. All sampled vegetation remains in a pre-climax state, having yet to recover fully from earlier eruptions. Reconstructed vegetation maps for before 1907 and for ca. 1925 are compared to the map of vegetation in 1994. Based on degree of soil formation, vegetation recovery and colonization rates at different pumice depths, and the current vegetation, we estimate that full recovery of the soil-vegetation system will take more than 2000 years.  相似文献   

4.
Genetic variation is often lower within island populations, however islands may also harbor divergent genetic variation. The likelihood that insular populations are genetically diverse or divergent should be influenced by island size and isolation. We tested this assumption by comparing patterns of genetic variation across all major island song sparrow populations along the Pacific North American coast. Allelic richness was moderately lowered even on islands which are close to large, potential sources. The most significant differences in allelic richness occurred on very small or highly remote islands. Gene diversity was significantly lower only on remote or very small islands. We found that island populations contribute to regional genetic variation through both the amount of genetic variation and the uniqueness of that variation. The partitioning of this contribution was associated with the size and isolation of the island populations.  相似文献   

5.
Edwards  P.J.  Kollmann  J.  Gurnell  A.M.  Petts  G.E.  Tockner  K.  Ward  J.V. 《Wetlands Ecology and Management》1999,7(3):141-153
The concepts of large river systems have been advanced with limited empirical knowledge of natural systems. In particular, virually all large Alpine European rivers were trained during the 19th century. Without first hand knowledge of natural systems we lack baseline data to assess human impacts and to address restoration and conservation strategies. An exception is the River Tagliamento which rises in the limestone Alps of northern Italy and flows for 172 km to the Adriatic Sea. Following a very high flood, we observed the first stages of succession within the river's active zone. This article presents a conceptual model of vegetation dynamics on gravel bars based upon those observations. Thousands of trees and other large woody debris (LWD) lay scattered across the active zone after the flood. The larger pieces of debris had a marked influence on the deposition of sediments and other debris, and were sites of colonization by pioneer plants. They represent the first stage in the development of vegetated islands that have the potential to increase in size during subsequent floods. Islands are also eroded, particularly by lateral channel erosion, and the materials may be reincorporated into new islands downstream. The island vegetation is dominated by five Salix species and Populus nigra. The dynamics of vegetated islands results from the interaction between the fluvial regime and the dominant woody species, the Salicaceae. These plants act as autogenic ecosystem engineers, because the plant structures themselves alter the environmental conditions through trapping sediment and organic debris. These processes may help to maintain an island-braided channel system that supports a high habitat diversity. Management of the river to regulate flow or to reduce the supply of LWD is likely to result in a loss of the habitat heterogeneity produced by island dynamics.  相似文献   

6.
流域径流泥沙对多尺度植被变化响应研究进展   总被引:16,自引:0,他引:16  
张志强  王盛萍  孙阁  谢宝元 《生态学报》2006,26(7):2356-2364
植被变化与流域水文过程构成一个反馈调节系统,是目前生态水文学研究的重点对象.由于植被自身的生长发育以及受自然因素和人为干扰的作用,植被变化具有多尺度性;由于受流域水文环境的异质性和水文通量的变化性的影响,流域水文过程也同样具有多尺度性.因此,只有通过对不同尺度生态水文过程分析,才能揭示流域径流泥沙对植被变化的响应机理.从不同时空尺度回顾了植被生长、植被演替、植被分布格局变化、造林以及森林经营措施等对流域径流泥沙影响的主要研究成果;概括了目前研究采用的3种主要方法,即植被变化对坡面水流动力学影响的实验室模拟、坡面尺度和流域尺度野外对比观测实验以及水文生态模型模拟方法;分析了植被变化与径流泥沙响应研究要考虑的尺度问题,从小区尺度上推至流域尺度或区域尺度时应考虑不同的生物物理控制过程.研究认为,要确切理解植被与径流泥沙在不同时空尺度的相互作用,必须以等级生态系统的观点为基础,有效结合生态水文与景观生态的理论,从地质-生态-水文构成的反馈调节入手,系统地理解植被变化与径流泥沙等水分养分之间的联系及反馈机制,建立尺度转换的基础.同时,作为有效的研究工具,今后水文模型的发展应更加注重耦合植被生理生态过程以及景观生态过程,从流域径流泥沙对多尺度植被变化水文响应的过程与机制入手,为植被恢复与重建、改善流域水资源状况和流域生态环境奠定基础.  相似文献   

7.
借助地表沉陷预测模型,预测了地表沉陷状况,依据地表沉陷对景观的破坏程度划分出重度影响区和轻度影响区;在遥感及地理信息系统技术的支持下,把植被景观现状与地表沉陷影响区叠加,通过沉陷前后景观格局的变化分析,对山西省晋城市东大煤矿的生态影响进行了探索性评价研究。结果表明:1) 重度影响区地表会出现盆型、马鞍型和波浪型等塌陷或裂缝,土壤侵蚀的作用将导致土壤养分空间格局发生明显变化。塌陷或裂缝周围生境恶化,成为养分流失源,植被恢复困难;养分汇处土壤水、肥条件优越,植被演替迅速,适当的人为干扰可以加快区域生态环境的恢复步伐。2) 地表沉陷后,植被景观破碎及隔离程度严重,原有的稳定态景观格局被打破,随着地形、土壤的空间变化,植被开始新一轮发展演替。由于原先占绝对优势的退化植被类型白羊草(Bothriochloa ischemum)-百里香(Thymus mongolicus)型优势度下降,同时,大部分次优势景观的内部生态功能受影响不大,这对景观整体的生物多样性以及次优势景观类型的演替是有益的,但是,重度影响区对斑块的隔离呈直线性,这对物种迁移的障碍是明显的。因此,重视井田区的封育与引种工作,科学规划、合理布局,在此基础上,引导植被演替沿着白羊草-百里香型—白羊草-黄背草(Themeda japonica)型—灌木丛—阔叶林的方向发展是可行的。  相似文献   

8.
1. We test MacArthur and Wilson's theory about the biogeography of communities on isolated habitat patches using bird breeding records from 16 small islands off the coasts of Britain and Ireland. 2. A traditional examination of patterns of species richness on these islands suggests that area and habitat diversity are important predictors, but that isolation and latitude have a negligible impact in this system. 3. Unlike traditional studies, we directly examine the fundamental processes of colonization and local extinction (cessation of breeding), rather than higher-order phenomena such as species richness. 4. We find that many of MacArthur and Wilson's predictions hold: colonization probability is lower on more isolated islands, and extinction probability is lower on larger islands and those with a greater diversity of habitats. 5. We also find an unexpected pattern: extinction probability is much lower on more isolated islands. This is the strongest relationship in these data, and isolation is the best single predictor of colonization and extinction. 6. Our results show that examination of species richness alone is misleading. Isolation has a strong effect on both of the dynamic processes that underlie richness, and in this system, the reductions in both colonization and extinction probability seen on more distant islands have opposing influences on species richness, and largely cancel each other out. 7. We suggest that an appropriate model for this system might be optimal foraging theory, which predicts that organisms will stay longer in a resource patch if the distance to a neighbouring patch is large. If nest sites and food are the resources in this system, then optimal foraging theory predicts the pattern we observe. 8. We advance the hypothesis that there is a class of spatial systems, defined by their scale and by the taxon under consideration, at which decision-making processes are a key driver of the spatiotemporal dynamics. The appropriate theory for such systems will be a hybrid of concepts from biogeography/metapopulation theory and behavioural ecology.  相似文献   

9.
Many rare arthropod species occupy open grasslands. Mowing or grazing is needed to preserve the habitat for these species. Alternatively the vegetation cover in parts of the managed area can be periodically destroyed by ploughing or rototilling. Such treatment results in a dynamic mosaic of habitat patches in different stages of succession. This mosaic may serve as a habitat for many species. However, the interplay between the frequency of rototilling, the spatial structure of the landscape and life history attributes of the animal species will determine the success of such cyclic management strategies. We used a spatially implicit individual-based metapopulation model to examine optimal spatio-temporal management strategies. The model explicitly incorporates succession, population dynamics and dispersal between habitat patches.Optimal management patterns strongly depend on the species’ properties. Our simulation experiments show that in general the more fertile species with strong intraspecific competition are most robust against the large fluctuations of habitat quality resulting from cyclic management. However, the best management strategies found in our experiments cover the requirements of up to 70% of the species tested. Frequent management of relatively small sub-areas minimizes local fluctiations of patch capacity. Though reducing effective patch capacity by more than 50% these strategies may support the survival of the majority of species.  相似文献   

10.
1. The landscapes of large floodplain rivers are characterised by heterogeneous environments related to the interplay of flood flows, sediment transport and vegetation dynamics.
2. The large rivers of Europe, and probably most rivers throughout the forest biomes, were characterised by islands but over the period of major human interference, many have become dominated by incision and narrowing so that they are now characterised by single-thread and relatively simple channel forms.
3. Vegetation plays an active role in developing heterogeneous channel forms through (a) biotic processes such as seed dispersal, vegetative regeneration and succession and (b) abiotic effects such as increasing flow resistance inducing sedimentation, and decreasing bank erodibility.
4. In particular, accumulations of living driftwood (cf. dead driftwood accumulations and dispersed seedlings) accelerate sedimentation and island development.
5. River reaches with vegetated islands have a high habitat diversity.
6. The natural influences of flood disturbance, wood accumulation, vegetation growth, island development and tree die-off, cause island-dominated reaches to undergo cycles of island growth and decay that are related to cycles of aquatic habitat diversification and simplification.  相似文献   

11.
Although flying foxes (fruit bats in the genus Pteropus ) in continental forests often fly between scattered resources, little is known about their ranging behavior among islands. The inhospitable water matrix that surrounds the food patches (islands) in archipelagos may prevent flying foxes from tracking resources as efficiently as their counterparts on larger landmasses do. Our aim in this study was to determine whether the abundance of foraging flying foxes ( Pteropus tonganus ) reflected food availability on islands in the Vava'u archipelago of Tonga, regardless of island size and isolation. Overall, food availability was the strongest determinant of flying fox abundance, and spatial aspects of the islands (land area within 10 km) had only a small influence. Food availability appears to regulate flying fox abundance only when food resources are low, but when food sources are plentiful, flying fox abundance may be high or low. These results provide indirect evidence that flying foxes are able to track food resources efficiently in an archipelago, and the water matrix that surrounds the food patches (islands) is not a strong deterrent for foraging animals.  相似文献   

12.
The nucleation hypothesis appears to explain widespread patterns of succession in tropical pastures, specifically the tendency for isolated trees to promote woody species recruitment. Still, the nucleation hypothesis has usually been tested explicitly for only short durations and in some cases isolated trees fail to promote woody recruitment. Moreover, at times, nucleation occurs in other key habitat patches. Thus, we propose an extension, the matrix discontinuity hypothesis: woody colonization will occur in focal patches that function to mitigate the herbaceous vegetation effects, thus providing safe sites or regeneration niches. We tested predictions of the classical nucleation hypothesis, the matrix discontinuity hypothesis, and a distance from forest edge hypothesis, in five abandoned pastures in Costa Rica, across the first 11 years of succession. Our findings confirmed the matrix discontinuity hypothesis: specifically, rotting logs and steep slopes significantly enhanced woody colonization. Surprisingly, isolated trees did not consistently significantly enhance recruitment; only larger trees did so. Finally, woody recruitment consistently decreased with distance from forest. Our results as well as results from others suggest that the nucleation hypothesis needs to be broadened beyond its historical focus on isolated trees or patches; the matrix discontinuity hypothesis focuses attention on a suite of key patch types or microsites that promote woody species recruitment. We argue that any habitat discontinuities that ameliorate the inhibition by dense graminoid layers will be foci for recruitment. Such patches could easily be manipulated to speed the transition of pastures to closed canopy forests.  相似文献   

13.
Due to their specialised habitat requirements, butterflies are particularly vulnerable to habitat loss and fragmentation. Understanding the drivers of local abundances of species is essential for their effective conservation in fragmented landscapes. We investigated factors affecting population densities of an endangered European butterfly, the Violet Copper (Lycaena helle), occurring in a small metapopulation near the city of Kraków, southern Poland. The environmental parameters tested as predictors of the local densities of the species included both the variables associated with spatial structure of habitats such as patch sizes, their isolation and fragmentation as well as those potentially reflecting habitat quality. Patch area and vegetation height turned out to be the only factors significantly influencing L. helle densities, both having a positive effect. The positive impact of patch area is a bit surprising, since its relationship with population densities is typically negative in butterflies. In our study system it is likely to derive from source-sink dynamics as the smaller habitat patches are apparently too small to sustain viable local populations. In turn, the positive influence of vegetation height implies that the ongoing succession does not deteriorate the quality of the recently abandoned meadows yet, whereas higher turf may provide better sheltering places. The loss of almost half of L. helle habitat patches in the study area in recent years is alarming. However, its inclusion into the Natura 2000 system should help to conserve the species as long as this act is followed by proper management of its habitats.  相似文献   

14.
Fragmentation of the forested landscape poses a threat to many aspects of biodiversity associated with old-growth forests Studies of the effects of forest fragmentation are often complicated by the variation in composition and age of patches and the matrix This study used a system of isolated stands where patch age and composition were similar and the matrix variability negligible The patches were composed of old-growth Picea abies stands of varying size and shape in a wetland matrix The study organisms were epiphytic crustose calicioid lichens (also known as Caliciales), many of which are very substrate-specific and restricted to old-growth stands The aim of the study was to measure the effect of patch size, patch isolation, habitat and substrate quality on the species riochness and composition of epiphytic calicioids Twenty-four patches ranging from 0 4 to 15 9 ha in size were studied All species of calicioid lichens were registered in 0 1 ha plots in each patch Isolation was measured as the percentage of available habitat within 400 m of a patch Twenty-two species were found with an average of 9 48 ± 0 26 (SE) species per patch and 292 ± 0 18 (SE) species per tree Species richness at patch level correlated with stand structure, primarily tree density, while number of species per tree (reflecting population size) was strongly correlated with island size and several stand variables There was no effect of isolation on species richness Species composition was influenced by both substrate variables and patch size The species composition on the islands showed a significant nestedness, i e species composition on species-poor islands constituted a non-random subset of the species composition on species-rich islands We propose that the explanation for the strong relationship between species richness at tree level and stand size is an edge effect which implies that unaffected interior areas only occur on large islands The different microclimate of the patch edge enables only the hardiest species to establish large populations there whilst shade and moisture demanding species are restricted to the interiors of larger islands  相似文献   

15.
Plant community dynamics in Mediterranean basin ecosystems are mainly driven by an alternation of episodes of human intervention and land abandonment. As a result, a mosaic of plant communities has evolved following different stages of degradation and regeneration. Some authors has relate secondary succession to abandoned culture lands and regeneration to natural systems with abandonment of livestock or forestry exploitation. In this paper, the dynamics of shrublands in mid-mountain areas in the South of Spain after disturbance and land abandonment has been studied. The plant cover and 13 environmental variables of 137 selected sites on the Grazalema mountains was analysed to determine the vegetation pattern in relation to environmental factors and the succession types, either regenerative or secondary succession. The results show that today the Grazalema mountains have a heterogeneous vegetation pattern. Besides physical factors such as altitude or soil , human disturbance has modulated current vegetation patterns and dynamics. Two main types of vegetation dynamics can be distinguished in the study area. In areas affected by cutting, regeneration results in rich and dense shrub land, with resprouters as dominant species. In areas affected by recurrent wildfires or agriculture, secondary succession became dominant, resulting in less diverse shrubland, due to the dominance of seeders and decrease in resprouter species richness and cover.  相似文献   

16.
The effects of isolation on primary succession are poorly documented. I monitored vegetation recovery on two Mount St. Helens lahars (mud flows) with different degrees of isolation using contiguous plots. Seventeen years after the eruption, species richness was stable, but cover continued to increase. That isolation affects community structure was confirmed in several ways. The dominance hierarchies of the lahars differed sharply. Detrended correspondence analysis on Lahar I showed a trend related to distance from an adjacent woodland, whereas vegetation on Lahar II was relatively homogeneous. Spectra of growth forms and dispersal types also differed. Lahar I was dominated by species with modest dispersal ability, while Lahar II was dominated by species with better dispersal. Variation between plots should decline through time, a prediction confirmed on Lahar II. Lahar I remained heterogeneous despite having developed significantly higher cover. Here, the increasing distance from the forest has prevented plots from becoming more homogeneous. At this stage of early primary succession, neither lahar is converging towards the species composition of adjacent vegetation. This study shows that isolation and differential dispersal ability combine to determine initial vegetation structure. Stochastic effects resulting from dispersal limitations may resist the more deterministic effects of competition that could lead to floristic convergence.  相似文献   

17.
In this paper, we describe spatial variation in the demography of the Song Sparrow Melospiza melodia. Long-term population studies of birds have generally considered only single sites in optimal habitat, but recent theory has shown the value of taking spatial variation in population dynamics into account. In this theory, collections of local populations in habitat patches connected by dispersal are denned as metapopulations. We review metapopulation models briefly and then use these ideas in a study of the Song Sparrow. Sparrows were studied on islands of varying size and degree of isolation from the North American continent. For analysis, these islands are grouped into three areas. Sparrows on the isolated Mandarte Island usually reproduced and survived well over 17 years but suffered from catastrophic mortality in some winters. After such events, the population recovered quickly without much immigration. Sparrows on smaller islets near Mandarte also survived and reproduced well during 4 years, and they did not experience severe mortality in a winter in which those on Mandarte declined by over 90%. These small islets frequently exchanged first year birds, but only one yearling bird moved between the small islets and the more isolated Mandarte. Sparrows at one of two sites on the larger Westham Island, near the continental mainland, survived less well than on the small offshore islands. Reproduction on Westham Island was poor because of frequent nest failure and high levels of brood parasitism by Brown-headed Cowbirds Molothrus ater. Despite this poor reproduction and survival, the Westham population remained stable as a result of immigration. We interpret the dynamics of these sparrow populations in terms of H. R. Pulliam's source-sink metapopulation model.  相似文献   

18.
In this paper, we describe spatial variation in the demography of the Song Sparrow Melospiza melodia. Long-term population studies of birds have generally considered only single sites in optimal habitat, but recent theory has shown the value of taking spatial variation in population dynamics into account. In this theory, collections of local populations in habitat patches connected by dispersal are denned as metapopulations. We review metapopulation models briefly and then use these ideas in a study of the Song Sparrow. Sparrows were studied on islands of varying size and degree of isolation from the North American continent. For analysis, these islands are grouped into three areas. Sparrows on the isolated Mandarte Island usually reproduced and survived well over 17 years but suffered from catastrophic mortality in some winters. After such events, the population recovered quickly without much immigration. Sparrows on smaller islets near Mandarte also survived and reproduced well during 4 years, and they did not experience severe mortality in a winter in which those on Mandarte declined by over 90%. These small islets frequently exchanged first year birds, but only one yearling bird moved between the small islets and the more isolated Mandarte. Sparrows at one of two sites on the larger Westham Island, near the continental mainland, survived less well than on the small offshore islands. Reproduction on Westham Island was poor because of frequent nest failure and high levels of brood parasitism by Brown-headed Cowbirds Molothrus ater. Despite this poor reproduction and survival, the Westham population remained stable as a result of immigration. We interpret the dynamics of these sparrow populations in terms of H. R. Pulliam's source-sink metapopulation model.  相似文献   

19.
Habitat quality and metapopulation effects are the main hypotheses that currently explain the disproportionate decline of insects in cultivated Holarctic landscapes. The former assumes a degradation in habitat quality for insects within surviving ecosystems, the latter that too few, small or isolated islands of ecosystem remain in landscapes for populations to persist. These hypotheses are often treated as alternatives, and this can lead to serious conflict in the interpretations of conservationists. We present the first empirical demonstration that habitat quality and site isolation are both important determinants of where populations persist in modern landscapes. We described the precise habitat requirements of Melitaea cinxia, Polyommatus bellargus and Thymelicus acteon, and quantified the variation in carrying capacity within each butterfly's niche. We then made detailed surveys to compare the distribution and density of every population of each species with the size, distance apart and quality of their specific habitats in all their potential habitat patches in three UK landscapes. In each case, within-site variation in habitat quality explained which patches supported a species' population two to three times better than site isolation. Site area and occupancy were not correlated in any species. Instead of representing alternative paradigms, habitat quality and spatial effects operate at different hierarchical levels within the same process: habitat quality is the missing third parameter in metapopulation dynamics, contributing more to species persistence, on the basis of these results, than site area or isolation. A reorientation in conservation priorities is recommended.  相似文献   

20.
In the Gulf of Mexico, barrier islands absorb the majority of wind and wave action from storms, which modifies their dune morphology and vegetation dynamics. Storm frequency is predicted to increase as a result of climate change, yet the effects of this change on coastal ecosystems remain poorly understood. Using estimates of plant growth in storm and nonstorm years from long‐term census data describing the dynamics of dune vegetation on St. George Island, FL, we built a first‐order model that predicts how dune communities will respond to a change in storm frequency. It predicts that an increasing frequency of storms will result in a change in the vegetation across the dunes. The fore‐ and interdune communities are predicted to become more similar to one another through the dominance of a small number of common storm‐resilient species. Alternatively, the backdune community is predicted to become more distinct through an increase in rare species that represent primary succession. Finally, the model predicts that many species will not respond to an increase in the number of storms per year in the same manner in which they respond to current storm frequency. This model is beneficial both for the development of more complex approaches to predicting effects of climate change and for informing preventative management techniques.  相似文献   

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