Removal Of Dominant Species Research Articles

Removal of Dominant Species Impairs Nitrogen Utilization in Co-Existing Ledum palustre and Vaccinium uliginosum Communities Subjected to Five-Year Continuous Interruptions

Unguided exploitation has impaired the sustainability of natural resources of agronomic non-wood forest plants from understory boglands in boreal forests. The extreme consequences of plant–soil interplay on medicinal plant communities under continuous interruptions need to be understood to implement strategies which can cope with possible ecological degradation. In this study, co-existing Ledum palustre and Vaccinium uliginosum communities were investigated after a four-year interruption of continuous removal of dominant species in stands at Xing’an Mountain. Nitrogen (N) availability was assessed by above-ground biomass and N content in nondominant plants and the biophysiological properties of rhizosphere soil. The removal treatment promoted soil mineral and organic N contents, but also reduced abundances of the soil communities of Rozellomycota phylum (by 82.76%), ericoid mycorrhiza of Meliniomyces varia (by 81.60%) and Phialocephala fort (by 69.54%). Vaccinium uliginosum overcame L. palustre through higher N utilization (biomass/%N) although the latter had higher abundances of soil Odiodendron maius and P. fort. The microbial community attributes accounted for a large proportion of N availability following the removal of dominance. In conclusion, our study demonstrates that understory agronomic plants in northern boglands should no longer be under continuous exploitation. Strategies should be considered to improve the promotion of N uptake by managing local soil microbial communities.

Response of Soil Respiration and Its Components to Warming and Dominant Species Removal along an Elevation Gradient in Alpine Meadow of the Qinghai-Tibetan Plateau.

The Qinghai-Tibetan Plateau is experiencing unprecedented temperature rises and changes in plant community composition owing to global warming. Few studies focused on the combined effects of warming and changes in species composition on soil respiration (Rs). We conducted a 4-year experiment (2015-2018) to examine the influences of warming and dominant plant species removal on Rs and its autotrophic (Ra) and heterotrophic (Rh) components along an elevation gradient (3200, 3700, and 4000 m) for alpine meadow of the Qinghai-Tibetan Plateau. Results showed that warming positively affected Rs, and the stimulation of Rs gradually diminished at 3200 m but remained stable at 3700 and 4000 m as warming progressed. Warming did not influence Ra at all sites. Dominant species removal produced hysteretic behavior that decreased Ra (29%) at 3700 m but increased Ra (55%) at 4000 m in 2018. No significant effect of dominant species removal on Rh was observed. Significant interactive effects of warming and dominant species removal were detected only on Ra at 3700 and 4000 m. Accordingly, under future warming, soil organic matter decomposition at higher elevation will enhance positive feedback to atmospheric CO2 concentration more than that at lower elevation, thus accelerating soil organic carbon loss.

Six-year removal of co-dominant grasses alleviated competitive pressure on subdominant grasses but dominant shrub removal had neutral effects in a subalpine ecosystem

The ‘stress-gradient hypothesis’ predicts increasing facilitative interactions with increasing environmental stress, but it remains unclear if the prevailing type of interaction (i.e. facilitative or competitive) between dominant and subordinate plant species occurring in harsh environments is dependent on the plant functional type. In addition, most plant-species removal experiments in grasslands are short-term (1–2 years), which may imprecisely reflect transient effects arising from methodological limitations. We conducted a dominant species removal experiment in a subalpine ecosystem, containing a mosaic of grass-dominated and shrub-dominated community patches, both of which are common in the subalpine zone of the Qinghai-Tibetan Plateau. We examined the direction and magnitude of the effects of three co-dominant grass and a dominant shrub species on subordinate species richness and biomass over a 6-year period. Removal of the dominant grass species alleviated their competitive pressure on subdominant grasses, which resulted in similar total and grass biomass detected in the final year of the study. By contrast, shrub removal showed no effects on its subordinate species biomass. Furthermore, neither the removal of the dominant shrubs nor the grasses altered their respective subordinate species richness. Thus, in subalpine ecosystems that experience harsh environmental conditions, our results showed that the direction of interactive effects of dominant plant species on subordinate species may be dependent on the plant functional type and are not necessarily facilitative. Furthermore, we showed that longer-term plant-removal experiment observations may be required to better determine the effects of species removal for this subalpine and other montane ecosystem(s).

Responses of tundra plant community carbon flux to experimental warming, dominant species removal and elevation

Abstract Rising temperatures can influence ecosystem processes both directly and indirectly, through effects on plant species and communities. An improved understanding of direct versus indirect effects of warming on ecosystem processes is needed for robust predictions of the impacts of climate change on terrestrial ecosystem carbon (C) dynamics. To explore potential direct and indirect effects of warming on C dynamics in arctic tundra heath, we established a warming (open top chambers) and dominant plant species (Empetrum hermaphroditum Hagerup) removal experiment at a high and low elevation site. We measured the individual and interactive effects of warming, dominant species removal and elevation on plant species cover, the normalized difference vegetation index (NDVI), leaf area index (LAI), temperature, soil moisture and instantaneous net ecosystem CO2 exchange. We hypothesized that ecosystems would be stronger CO2 sinks at the low elevation site, and that warming and species removal would weaken the CO2 sink because warming should increase ecosystem respiration (ER) and species removal should reduce gross primary productivity (GPP). Furthermore, we hypothesized that warming and species removal would have the greatest impact on processes at the high elevation where site temperature should be most limiting and dominant species may buffer the overall community to environmental stress more compared to the low elevation site where plants are more likely to compete with the dominant species. The instantaneous CO2 flux, which reflected a weak CO2 sink, was similar at both elevations. Neither experimental warming nor dominant species removal significantly changed GPP or instantaneous net ecosystem CO2 exchange even though species removal significantly reduced ER, NDVI and LAI. Our results show that even the loss of dominant plant species may not result in significant landscape‐scale responses of net ecosystem CO2 exchange to warming. They also show that NDVI and LAI may be limited in their ability to predict changes in GPP in these tundra heaths systems. Our study highlights the need for more detailed vegetation analyses and ground‐truthed measurements in order to accurately predict direct and indirect impacts of climatic change on ecosystem C dynamics. A free Plain Language Summary can be found within the Supporting Information of this article.

Testing the effects of plant species loss on multiple ecosystem functions based on extinction scenarios

Ecosystem functions are threatened by continuing global loss of biodiversity. We simultaneously investigated three ecosystem functions and forage nutrient values following potential species extinction scenarios (dominant species removal, rare species removal, end-member species removal and random species removal) in a Mongolian grassland. ANPP, forage nutrient values, litter decomposition, and soil respiration were measured one and/or two years after plant removal. DNA samples of microorganisms extracted from the soil were subjected to metagenomics analysis. Finally, we calculated the multifunctionality, and examined the relationship of multifunctionality with plant and microorganism diversity. Among ecosystem functions, ANPP and litter decomposition rate decreased under random and rare species extinction scenarios, respectively, and forage quality increased when only dominant species had been removed. Diversity and species composition of soil microorganism were not affected by plant species richness or removal scenario. Only genus-level diversity of bacteria and ANPP were significantly and positively correlated with microbial diversity. Taken together, decreasing species richness of plants and soil organisms rarely impaired multifunctionality. Ecosystem functions were relatively robust to realistic disturbances and species extinction in natural grasslands. However, as each function responded differently to the different sets of species removed, the consequences of a realistic non-random extinction scenario for multiple ecosystem functions should be critical to the management of biodiversity loss caused by different disturbances.

Seasonality promotes grassland diversity: Interactions with mowing, fertilization and removal of dominant species

Abstract Current biodiversity declines in species‐rich grasslands are connected with the cessation of management, eutrophication and the expansion of dominant grass species. One of the theoretical mechanisms limiting biodiversity loss is the ability of subordinate species to avoid competitive exclusion by seasonal niche separation from dominant species. Here, we explore how seasonality underpins the maintenance of diversity in temperate meadows under different management regimes and competition intensities in relation to species functional traits. We studied eight different communities in a long‐term meadow experiment that manipulated mowing, fertilization and dominant species (Molinia caerulea) removal. In each community, species‐specific trait and biomass data were taken five times during the year to test whether seasonal variation in species composition and functional strategies enable species to coexist. Mown unfertilized meadows exhibited pronounced seasonal variations in community composition and structure, linked to differences in resource‐use strategies between mid‐summer dominants and the spring and autumn subordinates. Higher specific leaf area and foliar nitrogen concentration in the fast‐growing dominants, and increased water use (δ13C) and nutrient acquisition (δ15N) efficiency in resource‐retentive subordinates, best predicted their temporal niche separation. Seasonal segregation of species with contrasting strategies increased after mowing cessation, and the resulting summer dominance of Molinia. Conversely, the seasonal dynamics were markedly reduced by fertilization, promoting tall grasses over sedges and forbs throughout the entire year, thereby decreasing the overall taxonomic and functional diversity. When Molinia was removed the compositional changes during the season became less pronounced, being significant only in mown unfertilized plots. Synthesis. Seasonal shifts in community composition reduced the competitive interactions and promoted the coexistence of dominant and subordinate species. Seasonality reversed the negative mid‐summer diversity‐productivity relationship with a positive one during the spring and autumn, and seasonality only prevented diversity loss in unfertilized conditions possibly because competition is most intense in summer. In fertilized meadows, subordinate species are not able to escape competitive exclusion by shifting their phenological peaks to the spring or autumn periods because asymmetric competition is intense over the entire growing season. Studying seasonal dynamics is key to understanding the maintenance of grassland diversity under ongoing land use change.

优势种去除对崇明东滩盐沼湿地生态系统的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 优势种去除对崇明东滩盐沼湿地生态系统的影响 DOI: 10.5846/stxb201701030023 作者: 作者单位: 华东师范大学生命科学学院,华东师范大学生命科学学院,华东师范大学生命科学学院,华东师范大学生命科学学院,华东师范大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31100317）；上海市科委科技创新行动计划（14DZ1206003） Effects of dominant species removal on salt marsh ecosystem in Chongming Dongtan Author: Affiliation: School of Life Science,East China Normal University,School of Life Science,East China Normal University,School of Life Science,East China Normal University,School of Life Science,East China Normal University,School of Life Science,East China Normal University Fund Project: National Natural Science Foundation of China (NSFC);Innovation action plan of Science and Technology Commission of Shanghai Municipality 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:盐沼生态系统环境梯度明显，物种组成较简单，是研究生物多样性与生态系统功能关系的理想对象。本研究以崇明东滩盐沼湿地为研究区域，研究优势种去除对植物群落结构以及底栖动物群落的影响。结果表明：（1）去除处理仅对植物群落分株密度有极显著效应（P<0.01）。去除组和对照组物种组成差异随时间增加而减小，处理效应逐渐减弱。（2）去除组底栖动物密度均低于对照组，但差异不显著。（3）盐沼植物群落特征与底栖动物群落有密切关系，植物密度、冠层高度与底栖动物密度相关性极显著。去除优势种后，植物群落分株密度升高，群落内剩余物种占比有所上升，次优势种对群落的补偿效应具有较大贡献；而底栖动物群落密度下降，其生物量和多样性指数的变化趋势与密度并不一致。上述结果表明生物多样性变化影响了盐沼湿地生态系统植物群落和底栖动物群落结构，进而可能影响物质循环和能量流动过程。 Abstract:The salt marsh ecosystem is considered ideal for studying the biodiversity-ecosystem functioning relationship(BEF) because of its steep environmental gradients and relatively few plant species. The salt marsh ecosystem is one of the ecosystems most affected by anthropogenic activities, which has drawn our attention to the need to protect and restore it intensively. The current research studies on BEF are mostly focused on grasslands ecosystems rather than salt marshes. The understanding of how the removal of specific species or functional groups would influence the structure and functioning of salt marsh ecosystems is still lacking. Therefore, this study, which was performed at Chongming Dongtan in the Yangtze estuary, examined the effects of dominant species removal on plant community structure and macrobenthic invertebrate communities. We also analyzed the relationship between plant community attributes and macrobenthic invertebrate communities using linear regression. The aim of the study was to provide a scientific basis for wetland restoration. The major findings of this study are as follows (1) Community type, season and their interaction had significant effects on the ramet density and canopy height of manipulated plant communities(P<0.01), whereas the removal treatment had significant effects on the ramet density only(P<0.01). Ramet density in species removal treatment was higher than that in the control treatment was, but the effect was not significant. The differences in species composition among the different plant communities decreased with time, indicating that the effects of species removal treatment weakened gradually. The probable underlying mechanism was that the system recovered from the initial disturbance and became more similar to the intact communities. There were no significant differences in ramet density, canopy height and belowground biomass of all the different plant communities between the control and species removal treatments. This might be due to the species compensatory effects and the recovery ability of dominant species since only the aboveground parts of the dominant plants were removed. (2) Community type and the season significantly affected the density and Shannon-Weiner diversity index of the macrobenthic invertebrate communities(P<0.01). Community type and interaction between the season and community type had significant effects on the biomass of macrobenthic invertebrates(P<0.01). The density of macrobenthic invertebrates in the species removal treatment was lower than that in control treatment, but the effects were not significant. The highest density, biomass and Shannon-Weiner diversity index of the macrobenthic invertebrates were observed in the Spartina alterniflora-Scirpus mariqueter community. This was mainly caused by differences in environmental factors and plant species attributes of the inhabiting communities. (3) There was a close relationship between salt marsh vegetation and benthic community. The density of macrobenthic invertebrates was positively and negatively correlated with shoot density and canopy height of the inhabiting plant communities, respectively (all P<0.01). After removal of the dominant species, ramet density of the plant communities and proportion of remaining species increased, while the subdominant species contributed greatly to the compensatory effect. The density of macrobenthic invertebrates decreased, but the pattern of biomass and diversity index change differed from that of the density, probably because of the influence of other environment factors. The above results indicated that the biodiversity change could affect the structure of plant and macrobenthic invertebrate communities to different degrees, which may then alter the processes of the biogeochemical cycle and energy flow. During our study, the removal effects were relatively weak in the intertidal zone of Chongming Dongtan, and they diminished with time. Therefore, the simple removal of dominant species may not be sufficient to restore the ecosystem functions of salt marshes, and further management measures should be used to maintain the long-term effects of habitat modification. 参考文献 相似文献 引证文献

The importance of predation and predator size on the development and structure of a subtropical fouling community

Predation plays a fundamental role in shaping marine fouling communities. However, its consequences for species diversity and community organization depend on several intrinsic properties of predators and prey. To evaluate how predators of different sizes affect the organization of sessile communities during their development, we deployed an experiment in which PVC plates were assigned to one of four predation exclusion treatments: partial exclusion cage (2.4 cm mesh), total exclusion cage (0.5 cm mesh), and two respective controls. We evaluated community richness and structure after 30, 90, and 150 days. Regardless of size, predation did not affect total species richness. After 30 days, communities on plates protected against all predators had less free space than any other treatments, but their structure was similar to those protected to large predators only. Therefore, the addition of predators smaller than 2.4 cm to the pool of consumers may intensify predation effects rather than change species dominance and composition. After 90 days, intensified consumption by smaller predators had no longer measurable effects. Our data suggest that the removal of dominant species by predation does not increase species richness but modulates the interaction among species. The removal of ascidians seems to facilitate the dominance of predator-resistant bryozoans.

Subordinate plant species impact on soil microbial communities and ecosystem functioning in grasslands: Findings from a removal experiment

Despite their low relative abundance, subordinate plant species may have larger impacts on ecosystem functioning than expected, but their role in plant communities remains poorly understood. The aim of this study was to test how subordinate plant species influence the functioning of a species-rich semi-natural grasslands. A plant removal experiment was set-up in the mountain grasslands of the Jura Mountains (Switzerland) to test the impact of subordinate plant species on soil microbial communities and ecosystem functioning. The experiment included three treatments: removal of all subordinate species, partial biomass removal of dominant species, and a no biomass removal control. After 2 years of treatments, we determined soil microbial community (bacteria and mycorrhizal fungi) by T-RFLP analysis and measured litter decomposition, soil respiration, soil inorganic nitrogen (DIN) availability and throughout aboveground biomass production as measures of ecosystem function. The removal of subordinate plant species strongly affected bacterial and weakly influenced mycorrhizal fungi communities and decreased rates of plant litter decomposition, soil respiration and DIN availability with larger effects than the partial loss of dominant biomass. The removal of subordinate plant species did not modify plant community structure, but it did reduce total above-ground biomass production compared to the control plots. Collectively, our findings indicate that the loss of subordinate species can have significant consequences for soil microbial communities and ecosystem functions, suggesting that subordinate species are important drivers of ecosystem properties. (C) 2012 Elsevier GmbH. All rights reserved.

Niche overlap reveals the effects of competition, disturbance and contrasting assembly processes in experimental grassland communities

Summary 1. Understanding the processes by which species sort themselves into communities remains a central puzzle for attempts to maintain biodiversity. It remains unclear whether any single assembly process is generally dominant or whether the influence of contrasting processes varies in a predictable way relative to biotic and abiotic gradients. Abundance‐weighted niche overlap between species provides a powerful means of contrasting two major assembly processes – niche complementarity and environmental filtering. 2. We examined mean overlap for four vegetative functional traits, relative to that expected when abundances were randomly allocated to species co‐occurring in experimental plots in a wet meadow. This provided a test of whether any single assembly process prevailed for the meadow as a whole and across all traits. The effects of mowing, fertilization and dominant species removal, and associated gradients of Simpson’s dominance and biomass on the niche overlap of plots, were also examined. 3. Niche overlap was higher than expected at random for three of the four traits studied (height, leaf and stem dry matter content, leaf C:N ratio). However, niche overlap was lower than expected for specific leaf area. 4. Mowing was the treatment with the greatest effect on both niche overlap and biomass, with overlap significantly lower in the absence of mowing for three of the traits, while biomass was lower in mown plots. For three of the traits there was evidence of a significant decrease in overlap with increasing biomass, but not increasing dominance. None of the significant mowing effects on overlap remained when the effect of biomass had been removed. 5. Synthesis: These results suggest that the importance of niche differences between species in structuring grassland communities should increase with increasing biomass and decrease with disturbance in grassland communities. They also emphasize that contrasting community assembly processes may occur for different niche axes, even within a single community.

Differential effects of two dominant plant species on community structure and invasibility in an old-field ecosystem

Aims In this study, we examined the effects of Solidago altissima (hereafter Solidago) and two species in the genus Verbesina, Verbesina virginica and Verbesina occidentalis (hereafter Verbesina), on the structure of an old-field plant community and establishment by an invasive plant species, Lespedeza cuneata (hereafter Lespedeza). Materials and Methods We removed Solidago, Verbesina and both Solidago and Verbesina from 4-m 2 plots in an intact old-field community during two growing seasons. We then quantified the effects of these removals on richness, evenness, diversity and composition of the subdominant plant community. We also measured the total aboveground biomass and the aboveground biomass of the subdominant community. To assess how these removals affected establishment by Lespedeza ,w e planted 20 seeds in each plot and tracked seedling emergence and survival for one growing season. Important Findings Subdominant community evenness and Shannon diversity were higher in plots from which Solidago and Verbesina were removed relative to control plots. However, there were no effects of dominant species removal on species richness or composition of the subdominant community. Total aboveground biomass was not affected by dominant species removal, suggesting that the community of subdominant species exhibited compensation. In fact, subdominant community biomass was greater when Solidago, but not Verbesina, was removed. Light availability was also greater in plots where Solidago was removed relative to control plots throughout the growing season. In addition, removal of dominant species, in particular Solidago, indirectly reduced the emergence, but not survival, of Lespedeza seedlings by directly promoting subdominant community biomass. Taken together, our results suggest that dominant old-field plant species affect subdominant community structure and indirectly promote establishment by Lespedeza.

Plant population and community responses to removal of dominant species in the shortgrass steppe

AbstractQuestion: What are the plant population‐ and community‐level effects of removal of dominant plant species in the shortgrass steppe?Location: The Shortgrass Steppe Long‐Term Ecological Research site in northern Colorado, USA.Methods: We annually measured plant cover and density by species for 10 years after a one‐time aboveground removal of the dominant perennial grass, Bouteloua gracilis. Removal and control plots (3 m × 3 m) were within grazed and ungrazed locations to assess the influence of grazing on recovery dynamics. Our analyses examined plant species, functional type, and community responses to removal, paying special attention to the dynamics of subdominant and rare species.Results: Basal cover of B. gracilis increased by an average of 1% per year, but there was significantly less plant cover in treatment compared to control plots for 5 years following removal. In contrast to the lower cover in treatment plots, the plant density (number of plants m−2) of certain subdominant perennial grasses, herbaceous perennial and annual forbs, a dwarf shrub, and cactus increased after removal of the dominant species, with no major change in species richness (number of species per 1 m × 1 m) or diversity. Subdominant species were more similar between years than rare species, but dominant removal resulted in significantly lower similarity of the subdominant species in the short term and increased the similarity of rare species in the long term.Conclusions: Removal of B. gracilis, the dominant perennial grass in the shortgrass steppe, increased the absolute density of subdominant plants, but caused little compensation of plant cover by other plants in the community and changes in species diversity.

Competition and species diversity: removal of dominant species increases diversity in Costa Rican butterfly communities

Biological communities are usually dominated by a few species and show characteristically skewed species abundance distributions. Although niche apportionment and resource competition are sometimes implicated in such patterns, few experimental studies have shown direct links between resource limitation, competition with dominant species and their impacts on the overall diversity and composition of large natural communities. Here I report the results of an experiment in which I first studied species diversity and composition in two Costa Rican nectar‐feeding butterfly communities numerically dominated by two species of Anartia butterflies. Then I removed Anartia from these communities to study changes in resource availability, species abundance relationships, community diversity and composition as an outcome of the removal of the dominant competitors. In the face of competition with Anartia, nectar was scarce, species abundance distributions were highly skewed, and species diversity was low in both communities. Within two weeks after the removal of Anartia, there were parallel changes in both communities: competition for nectar reduced and the nectar quantity increased substantially, which facilitated increase in community diversity and resulted in significantly less skewed species abundance distributions. Higher nectar quantity also enabled the distribution of body size and proboscis length of constituent species in the communities to expand at both ends. This study thus experimentally showed that resource competition with the dominant species was excluding many species from the communities, lowering their diversity and skewing relative species abundance relationships. These findings are of fundamental importance for competition theory and community ecology because they indicate ways in which diverse communities may be affected by and recover from competition with dominant species.

Gradients of disturbance to an algal canopy and the modification of an intertidal community

Disturbances over a range of intensities are common in intertidal communities, often causing partial removal of dominant species. However, most studies testing effects of disturbance on community structure use treatments where the dominant species is either present or absent, and usually record responses of only a few community components. Here, we test responses of the entire local community of benthic algae and invertebrates across a gradient of distur- bance to a habitat dominant in southern New Zealand, the fucoid alga Hormosira banksii. Replicate 0.25 m 2 plots of 100% cover of H. banksii were manipulated and maintained at 0, 25, 50 and 75% cover at 2 sites for 13 mo. Throughout the experiment, communities in the complete removal and control plots were the most different from each other, but intermediate plots had varied responses and were usually not significantly different from each other. Generally, as cover of H. banksii decreased, community variability increased through time. Taxa richness declined with reduced H. banksii cover, with up to 77% of its variation explained by variation in canopy cover. Other fucoid algae declined across the gradient, with complete canopy removals having 92% less fucoid cover than control plots. Complete canopy removal had positive effects on ephemeral algae, especially at one site which exhibited large seasonal blooms. Bare space was greatest where canopies were completely removed and understory algae died. Diversity was greatest in plots with complete canopies rather than at intermedi- ate levels, and there was no replacement of the domi- nant H. banksii by other species. There was no consis- tent effect on taxa across the gradient; some species responded linearly while others responded at thresh- old levels of canopy cover. This study shows the impor- tance of disturbance gradients interacting with key species, which may have considerable bearing on reef community structure.

Community effects following the deletion of a habitat-forming alga from rocky marine shores

Habitat-forming species increase spatial complexity and alter local environmental conditions, often facilitating a diversified assemblage of plants and animals. Removal of dominant species, therefore, can potentially lead to pronounced changes in diversity and community structure through a series of negative and positive interactions involving several components of the community. Here we test community responses to the deletion of the dominant, canopy-forming alga Hormosira banksii from the mid-intertidal zone of wave-protected rocky shores in southern New Zealand. This species was removed in winter (July) from three 3x3-m areas at each of two platforms (Kaikoura and Moeraki) on the east coast of the South Island. Initially, 59 taxa occurred in stands, but there were only four algal species with greater than 5% cover and three mobile invertebrate species with more than five individuals per 0.25 m(2). By 6 months after Hormosira removal, most fucoid and coralline algae had burned off, and there were blooms of ephemeral algae in the removal plots, but almost no change within controls. After 2 years, diversity declined by 44% relative to controls at Kaikoura and 36% at Moeraki, and the amount of bare space had increased by tenfold at Kaikoura and twofold at Moeraki. Few sessile or mobile invertebrates were present. Recruitment of Hormosira occurred after 14 months in the removal plots. At this time, a "press" disturbance was initiated into one half of each removal plot to test the effects of continued removal of Hormosira on diversity. Similar "end-points" of the control and "press" removal plots were not reached after 2 years, and even after Hormosira recruitment into the original "pulse" experiment there was little recovery of the community. In this mid-intertidal system with considerable thermal stress, and perhaps in others with few perennial species, diversity and community structure can critically depend on positive associations with a single dominant species.

The response of arbuscular mycorrhizae to fertilization, mowing, and removal of dominant species in a diverse oligotrophic wet meadow

In a wet oligotrophic meadow located in the Czech Republic, a factorial experiment with treatments consisting of fertilization, mowing, and removal of the dominant species (Molinia caerulea) was established in 1994. In 1997 Holcus lanatus, Molinia caerulea, Potentilla erecta, Prunella vulgaris, and Ranunculus auricomus were examined for arbuscular mycorrhizal (AM) hyphae, arbuscles, and vesicles three times over the season. Time had a significant effect on AM in all five species. Except for Molinia arbuscles, a modal effect occurred, with the second sampling having a greater level of AM structures than the first and the third. Fertilization had the greatest effect on AM levels by decreasing the level of Holcus hyphae and vesicles, Potentilla vesicles, Prunella hyphae, and Ranunculus hyphae and vesicles. Mowing significantly increased the number of Potentilla vesicles, and the removal of dominant species had no significant effects. Interactions between time and treatments were common. Significant effects to the arbuscle:vesicle ratio were infrequent, and those that occurred were related to changes over the season. Seasonal effects appear to have a more powerful effect on AM structures and the arbuscle:vesicle ratio than do treatment effects. In a second experiment, Ranunculus auricomus, R. acris, and R. nemorosus, sampled four times over the season, showed significant changes in AM colonization. Overall, AM structures either declined over the season or increased from April to May and then declined. There was no AM colonization response to a spring fertilization in the three species. It is postulated that the patterns observed are due to phosphorus availability and seasonal changes in soil moisture and rates of root growth and turnover.

Nutrient status, disturbance and competition: an experimental test of relationships in a wet meadow

Abstract. In many species‐rich hay meadows in Central Europe, the traditional extensive (low input, low output) management is no longer economical and meadows are either fertilized or abandoned. Both these practices lead to changes in species composition and usually to a loss in species diversity. The response of a species‐rich meadow plant community to fertilization, mowing and removal of dominant species was studied in a manipulative factorial experiment over four years. Both species richness and seedling recruitment were positively influenced by mowing and to a lesser extent by removal of the dominant species, Molinia caerulea, and were negatively influenced by fertilization. Fertilization caused an immediate increase in community biomass. Response to removal of the dominant species was delayed by one season, continued over the whole period, and by the fourth year the biomass reached a similar value as in the plots with Molinia present. Changes in species composition were evaluated by RDA for repeated measurements. The best and only significant predictor of species response to fertilization was plant height. This shows that with increased nutrient availability, nutrient limitation weakens and competition for light becomes the decisive factor. Competition for light appears to be more asymmetric than competition for nutrients, and consequently, it is more likely to drive inferior species to extinction. This is, together with seedling recruitment limitations, the most important cause of a decrease in species richness under high nutrient levels.

Plant interactions in alpine tundra: 13 years of experimental removal of dominant species

Plant species responses to the removal of each of the five dominant species were studied in an alpine tundra of the Teberda reserve of northwestern Caucasus, Russia, for 13 years. While dominant plant species (Anemone speciosa Adam ex G.Pritz, Antennaria dioica [L.] Gaertn., Festuca ovina L., Trifolium polyphyllum C.A. May, Carex sempervirens Vill., C. umbrosa Host, C. caryophyllea Latourr.) on the average increased the number of their shoots relative to the control after the removal of their presumed competitors, most subordinate species in the community responded negatively to the removal of dominants. The latter group may therefore depend on the dominant plants for survival in the harsh alpine environment, and not be as much affected by competition. Most species showed consistently either negative or positive responses for the whole duration of the experiment. Experimental removal of only one species in each treatment produced a coordinated response from a number of species, which suggests presence of diffuse competition among alpine tundra plants.

Effects of grazing, competition, disturbance and fire on species composition and diversity in grassland communities

Abstract. The effects of grazing, physical disturbance, interspecific competition, and fire on populations of individual species and on the structure and diversity of grassland communities were investigated in short‐, mid‐, and tall‐grasslands in the Serengeti National Park, Tanzania. The treatments included deep and shallow artificial disturbances, early dry‐season burning, and removal of dominant grass species from 2m2 plots located inside and outside of large‐mammal‐proof exclosures. Species‐cover data were collected for five years and analyzed by analysis of variance and diversity indices.In all three communities, protection from grazing and physical disturbance had greater impacts on species cover and diversity than removal of dominant species or fire. More species were significantly affected (positively and negatively) by disturbance and protection from grazing (50 ‐ 100%) than by species removals and fire (&lt; 41%). In most cases, the cover of tall, perennial species increased following protection from grazing while the cover of annual and short, perennial species decreased. Over the five years of the study, vegetatively reproducing species benefited more than sexually reproducing species from protection from grazing, and tall rhizomatous species benefited more than tall stoloniferous species.Disturbance caused annual and short perennial species to increase and tall perennials to decrease in cover. Following species removals, tall species were either unaffected or they increased in cover while some short species increased and others decreased in cover. Species diversity in two of the three communities decreased when the communities were protected from grazing but increased when disturbed, when dominant species were removed, and when burned.

Disturbance and Recovery in Intertidal Pools: Maintenance of Mosaic Patterns

The species composition of pools in the intertidal zone on the coast of Washington State varies greatly from pool to pool and from time to time. While assemblages change somewhat predictably from the low— to the high—intertidal zone (presumably owing to different stress tolerances of the species), the variance among pools at a given tidal height cannot be ascribed to such physical factors. Some pools at each height are dominated by one species that monopolizes space on the rock or in the water column and modifies the pool environment. Each dominant species, once established, can spread rapidly through a pool (either by vegetative growth or by enhanced recruitment of its conspecifics) and is thus potentially self—perpetuating. When abundant, most dominants appear to prevent potential competitors from settling and surviving by monopolization of resources, abrasion of the substratum, and/or collection of sediment. Six such dominants were identified for Washington tidepools: from low to high pools, these are (1) the surfgrass Phyllospadix scouleri, (2) articulated coralline algae, (3) the mussel Mytilus californianus (exposed shores), (4) the cloning anemone Anthopleura elegantissima (more protected shores), (5) the red alga Rhodomela larix, and (6) the green alga Cladophora sp. Colonial diatoms also appear capable of dominating low pools in the absence of wave disturbance. However, each dominant monopolizes only 20—50% of the pools at any height. Disturbances, defined here as a loss of biomass exceeding 10% cover of a sessile species within 6 mo and caused by extrinsic forces, were observed frequently in regularly censused tidepools. Disturbance agents included waves, excessive heat, wave—driven logs or rocks, and unusual influxes of predators and herbivores. Severe disturbances (those affecting a large proportion of the organisms in a pool) tended to occur in high pools in the summer (due to heat stress) and low pools in the winter (due to wave damage). Overall, a disturbance occurred in every pool studied an average of every 1.6 yr. About half of the 231 observed disturbances affected one of the six dominant species. The frequencies of these disturbances ranged from one every 2—5 yr, and recovery of the species to its original level required 3 mo to &gt; 2 yr. Some species (e.g., Rhodomela) were disturbed frequently bu recovered quickly because of rapid vegetative growth. However if asexual propagation was not possible, such as when the entire population of a species was removed from a pool, the slowness and irregularity of recruitment of sexual propagules greatly impeded recovery. Experimental manipulations involving the total removal of dominant species from pools showed that such large disturbances often require &gt; 3 yr for recovery. The irregularity of planktonic recruitment can be compounded by the presence of herbivores, which can remove most settling organisms from the substratum, or by the absence of other organisms that are necessary for the settlement of a dominant (e.g., seed—attachment sites for Phyllospadix). The combination of high disturbance frequency and slow rates of recovery makes it impossible for any dominant to occupy all the pools in its tidal range at any one time. Disturbance is viewed in these habitats as the stochastic factor overlying other, more predictable, community—structuring factors such as tidal height, pool size, wave exposure, and levels of herbivory, predation, and competition. Thus combined deterministic processes and random events operate to produce a complex mosaic of species assemblages in pools in one region. None of the tidepool assemblages is "stable" over many generations; rather, they seem to exist in a dynamic state where disturbances are an integral structuring factor.