Short- and Long-term Changes in Elk Use and Forage Production in Sagebrush Communities Following Prescribed Burning

Burning shrub and grassland communities often leads to increases in plant production and nutritional quality that benefit herbivores, resulting in increased herbivore use of burned areas. Increased use has been ascribed more specifically to changes in plant community structure, community composition and diversity, nutritional quality, and seasonal availability. These hypotheses can be evaluated more precisely if changes in plant communities following burning are monitored concurrently with changes in herbivore use, especially in longer-term studies. From 1988 to 1999, we examined responses of elk (Cervus elaphus) following prescribed burning of areas burned in 1984 and 1988 that had been formerly dominated by mountain big sagebrush (Artemisia tridentata ssp. vaseyana) in south-central Montana (USA), with concurrent monitoring of changes in plant production, nutritional quality, and community composition. Elk made increased use of burned sites up to 15 years after burning. Burning transformed big sagebrush-dominated communities into native herbaceous communities that persisted for 15 years without sagebrush reinvasion. Forage biomass and protein content remained higher on burned sites for 15 years, although differences were not significant in every year and declined as time elapsed after burning. Forage production, forage protein, and elk use were temporally correlated, suggesting the possibility that grazing by elk might have contributed to persistence of elevated plant production and protein levels on burned sites.     

Soil-Borne Bacterial Structure and Diversity Does Not Reflect Community Activity in Pampa Biome

The Pampa biome is considered one of the main hotspots of the world’s biodiversity and it is estimated that half of its original vegetation was removed and converted to agricultural land and tree plantations. Although an increasing amount of knowledge is being assembled regarding the response of soil bacterial communities to land use change, to the associated plant community and to soil properties, our understanding about how these interactions affect the microbial community from the Brazilian Pampa is still poor and incomplete. In this study, we hypothesized that the same soil type from the same geographic region but under distinct land use present dissimilar soil bacterial communities. To test this hypothesis, we assessed the soil bacterial communities from four land-uses within the same soil type by 454-pyrosequencing of 16S rRNA gene and by soil microbial activity analyzes. We found that the same soil type under different land uses harbor similar (but not equal) bacterial communities and the differences were controlled by many microbial taxa. No differences regarding diversity and richness between natural areas and areas under anthropogenic disturbance were detected. However, the measures of microbial activity did not converge with the 16S rRNA data supporting the idea that the coupling between functioning and composition of bacterial communities is not necessarily correlated.     

桂西北喀斯特地区不同退化程度植被群落物种组成及多样性特征

世界范围内,很多自然生态系统均在不同程度上受到了损害,喀斯特脆弱生态系统的退化是一个复合过程,喀斯特地区不同退化程度植被群落特征有何差异有待研究。该文采用样方法进行全面的调查,研究了桂西北喀斯特地区5个退化程度植被群落的物种组成、群落结构特征和物种多样性。结果表明:(1)不同退化程度群落物种组成和生活型组成有较大差异,潜在退化群落科属种丰富度最高,沿着退化程度递增的梯度,群落乔木树种逐渐减少至消失,灌木比例呈先增后减的趋势,草本比例逐渐增加。(2)调查到维管束植物218种,隶属于86科168属;以大戟科、楝科、蔷薇科、马鞭草科、禾本科和肾蕨科植物为主;退化过程中,优势种的重要值逐渐降低,其在群落内的支配地位逐渐减弱,伴生种重要值逐渐升高。(3)退化过程中,群落结构趋于简单化,群落木本植物密度、高度和盖度逐渐减少。(4)不同退化程度植被群落乔灌草层物种多样性存在显著性差异,随着退化程度的增加,群落总植被物种丰富度指数、Shannon-Wiener多样性指数、Simpson优势度指数整体呈下降趋势。     

Urbanization increases floral specialization of pollinators

Understanding how urbanization alters functional interactions among pollinators and plants is critically important given increasing anthropogenic land use and declines in pollinator populations. Pollinators often exhibit short‐term specialization and visit plants of the same species during one foraging trip. This facilitates plant receipt of conspecific pollen—pollen on a pollinator that is the same species as the plant on which the pollinator was foraging. Conspecific pollen receipt facilitates plant reproductive success and is thus important to plant and pollinator persistence. We investigated how urbanization affects short‐term specialization of insect pollinators by examining pollen loads on insects’ bodies and identifying the number and species of pollen grains on insects caught in urban habitat fragments and natural areas. We assessed possible drivers of differences between urban and natural areas, including frequency dependence in foraging, species richness and diversity of the plant and pollinator communities, floral abundance, and the presence of invasive plant species. Pollinators were more specialized in urban fragments than in natural areas, despite no differences in the species richness of plant communities across site types. These differences were likely driven by higher specialization of common pollinators, which were more abundant in urban sites. In addition, pollinators preferred to forage on invasive plants at urban sites and native plants at natural sites. Our findings reveal indirect effects of urbanization on pollinator fidelity to individual plant species and have implications for the maintenance of plant species diversity in small habitat fragments. Higher preference of pollinators for invasive plants at urban sites suggests that native species may receive fewer visits by pollinators. Therefore, native plant species diversity may decline in urban sites without continued augmentation of urban flora or removal of invasive species.     

Anthropogenic disturbance and rainfall variation threaten the stability of plant–ant interactions in the Brazilian Caatinga

Climate change is projected to exacerbate the effects of anthropogenic disturbance, with negative impacts on ecosystem stability and functioning. We evaluate the additive and combined effects of chronic anthropogenic disturbance (CAD) and rainfall variation on the temporal stability of mutualistic EFN‐bearing plant–ant networks in a Caatinga dry forest. We evaluated whether changes in the stability of these interactions are driven by changes in the stability of the communities of partners involved and/or in ant behavior. We sampled EFN‐bearing plant–ant networks in sixteen 20 × 20 m plots distributed across CAD and rainfall gradients. The stability of EFN‐bearing plant and attendant–ant communities were measured as the inverse of temporal differences in their community structure and composition. We also computed the stability of EFN‐bearing plant–ant networks by measuring the inverse of temporal differences in network specialization metrics. We found that, in general, the structure and composition of plant and ant interacting communities were similarly stable along both environmental gradients. Only CAD and its interaction with rainfall affected the temporal stability of EFN‐bearing plant diversity, which declined as CAD increased, with a more pronounced relationship in wetter areas. However, variation in levels of CAD and, to a lesser extent, rainfall greatly modulated the stability of EFN‐bearing plant–ant network specialization. CAD reduced the stability of network generality (specialization at the ant level), an effect that was much stronger in wetter areas. Meanwhile, the stability in network vulnerability (specialization at the plant level) decreased with the increase of CAD and the decrease of rainfall levels. Finally, there was a trend of decreasing stability in specialization of the overall network with increasing CAD. Our results suggest that changes in the structure of interaction networks are mainly driven by a switch in ant behavior rather than by changes in the structure and composition of plant and ant communities between years.     

Regional adaptation improves the performance of grassland plant communities

Many plant species are adapted locally or regionally. Whether such individual species performance translates into effects at community and ecosystem levels has rarely been tested. Such tests are crucial, however, to predict ecosystem consequences of sowing seed mixtures for grassland restoration or hay production. We compared the performance of replicated sown plant communities of regional origin with the performance of four foreign communities consisting of the same grassland species but originating from distances up to 890 km from our experimental site. The regional communities performed better than foreign communities in plant cover and diversity but not in aboveground biomass production. Additionally, in communities based on regional seeds fewer unsown species occurred and less bare ground was left open for erosion. Variation in community performance among source regions was related to climatic differences rather than to geographic distance to source regions. Individual species performance only partly explained community patterns, highlighting the importance of community level experiments. Our results suggest that the use of regional seeds represents an important approach to improve sown managed grasslands.     

Response of Elk to Changes in Plant Production and Nutrition Following Prescribed Burning

Abstract: Researchers have ascribed use of areas by grazers after burning to changes in plant community structure, community composition, nutritional quality, and seasonal availability. Researchers can better evaluate these alternatives if they monitor changes in plant communities following burning concurrently with changes in animal use. We examined responses of elk (Cervus elaphus) to prescribed burning of areas dominated by sagebrush (Artemisia spp.) in south-central Montana, USA, within which we monitored changes in plant production, nutritional quality, and community composition and diversity from 1989 to 1999. Elk increased use of burned sites 1–2 years after burning, then reduced use to levels associated with preburn conditions over the next 3–10 years. Burning transformed low-diversity, sagebrush-dominated communities into relatively high-diversity, grass- and forb-dominated communities that persisted for 10 years, but forage biomass and protein content declined on burned sites after initial short-term increases. Changes in elk use closely tracked changes in production and nutritional quality of plants. Therefore, we concluded that increases in quantity and quality of forage were the primary cause for increased use of burned sites by elk. Managers may observe only short-term responses from elk following burning but can expect longer-term increases in plant diversity and persistence of grass—forb communities on burned sites for >10 years that may be important to elk or other grazing ungulates.     

The impact of recreational use and access on biotic and abiotic disturbances on areas protected by local communities and a state conservation agency

Local communities often conserve nearby natural areas to support recreational activities and other benefits these areas provide. Areas protected by local communities could contribute to wider efforts to achieve large-scale conservation goals, such as biodiversity protection, provided the ecological conditions on-site are compatible with achieving these goals. To explore the potential contribution of locally established protected areas, we focus on areas protected by local communities in California, USA, using ballot initiatives, a form of direct democracy. We compare the ecological condition of wooded habitat on protected areas funded by local communities through the ballot box to that of similar habitats on protected areas funded by a state conservation agency. As an indicator of ecological condition, we focus on coverage by exotic plant species. We examine whether protected area characteristics or aspects of human-mediated onsite disturbance related to recreational use explain exotic plant cover found on each type of protected area. Exotic plant cover did not differ between areas protected by local communities and those protected by our larger scale conservation actor. Instead, elevation was the best predictor of exotic plant cover. Our results suggest protected areas established by local communities may be in no worse a condition than those established by a state public agency and warrant inclusion when tracking progress towards large-scale conservation goals for protected areas.     

Biotic homogenization and changes in species diversity across human-modified ecosystems

Changing land use and the spread of 'winning' native or exotic plants are expected to lead to biotic homogenization (BH), in which previously distinct plant communities become progressively more similar. In parallel, many ecosystems have recently seen increases in local species (alpha-) diversity, yet gamma-diversity has continued to decline at larger scales. Using national ecological surveillance data for Great Britain, we quantify relationships between change in alpha-diversity and between-habitat homogenizations at two levels of organization: species composition and plant functional traits. Across Britain both increases and decreases in alpha-diversity were observed in small random sampling plots (10-200m2) located within a national random sample of 1km square regions. As alpha-diversity declined (spatially in 1978 or temporally between 1978 and 1998), plant communities became functionally more similar, but species-compositional similarity declined. Thus, different communities converged on a narrower range of winning trait syndromes, but species identities remained historically contingent, differentiating a mosaic of residual species-poor habitat patches within each 1km square. The reverse trends in beta-diversity occurred where alpha-diversity increased. When impacted by the same type and intensity of environmental change, directions of change in alpha-diversity are likely to depend upon differences in starting productivity and disturbance. This is one reason why local diversity change and BH across habitats are not likely to be consistently coupled.     

Formation and succession of alvar communities in the Baltic land uplift area

Calciphilous plant communities, soil and geomorphology along the gradient of elevation in land uplift area in the coast of western Estonia were described. In grazed areas, species rich alvar grassland is a final stage in successional sere. The differences in site history in various points of the transect were reflected by the variability of underlying deposits. When soils with different ages but having similar parent material were compared, some successional trends (decrease of the content of Ca, increase of the content of P and humus supply) became evident. Species composition of plant communities was determined mainly by local ecological conditions (moisture level, soil pH, also grazing) at any particular site. Differences between communities of the same association but with different successional age were negligible.     

盐城滨海滩涂湿地典型植物群落土壤微生物组成与结构特征

土壤微生物是生态系统维持正常结构与功能的重要组成部分,为探究盐城滩涂典型湿地土壤微生物群落结构特征,以江苏盐城滩涂互花米草、藨草、盐地碱蓬、芦苇及淤泥质光滩5种典型群落为对象,采用16S rRNA高通量测序技术分析0—10 cm(表层)、10—30 cm(中层)、30—60 cm(深层)土壤微生物多样性及群落结构。结果表明：(1)几种植物群落间,土壤微生物群落结构差异较大,主要体现在细菌群落结构的差异性,古菌群落结构差异相对较小。光滩与植物群落间,在土壤细菌种类及相对丰度上差异相对较大,互花米草群落与本土植物群落间,在微生物群落的细菌种类组成上存在较大差异;藨草群落土壤表层微生物群落结构与互花米草群落相似,深层与盐地碱蓬、芦苇群落相似。(2)同一群落不同层次土壤微生物群落结构相似,差异小于不同群落间土壤微生物群落的结构差异性;不同群落对应层次间,表深层土壤中五种群落土壤微生物多样性存在显著差异,中层土壤中五种群落微生物多样性差异不显著。总体上,植物群落类型对土壤微生物群落结构的影响大于土壤深度;与本土植物群落相比,互花米草群落土壤主要优势门微生物种类差异较小,但部分优势门微生物相对丰度...     

Shifts in rhizoplane communities of aquatic plants after cadmium exposure

In this study we present the comparative molecular analysis of bacterial communities of the aquatic plant Lemna minor from a contaminated site (RCP) and from a laboratory culture (EPA), as well as each of these with the addition of cadmium. Plants were identified as L. minor by analysis of the rpl16 chloroplast region. Comparative bacterial community studies were based on the analyses of 16S rRNA clone libraries, each containing about 100 clones from the root surfaces of plants. Bacterial communities were compared at three phylogenetic levels of resolution. At the level of bacterial divisions, differences in diversity index scores between treatments, with and without cadmium within the same plant type (EPA or RCP), were small, indicating that cadmium had little effect. When we compared genera within the most dominant group, the beta-proteobacteria, differences between unamended and cadmium-amended libraries were much larger. Bacterial diversity increased upon cadmium addition for both EPA and RCP libraries. Analyses of diversity at the phylotype level showed parallel shifts to more even communities upon cadmium addition; that is, percentage changes in diversity indices due to cadmium addition were the same for either plant type, indicating that contamination history might be independent of disturbance-induced diversity shifts. At finer phylogenetic levels of resolution, the effects of cadmium addition on bacterial communities were very noticeable. This study is a first step in understanding the role of aquatic plant-associated microbial communities in phytoremediation of heavy metals.     

Edge effects: impact of anthropogenic activities on vegetation structure and diversity in western Umfurudzi Park,Zimbabwe

Understanding the patterns and intensity of anthropogenic impacts on habitats is important in the conservation of tropical ecosystems. The aim of the study was to establish the associated edge effects of anthropogenic disturbances on vegetation in western Umfurudzi Park, Zimbabwe. Three study strata were established using distance from the boundary into the park. Vegetation attributes and anthropogenic disturbance levels data were collected in 2012. Significant differences (P < 0.05) were noted on tree and shrub density, woody plant height, woody plant diversity, grass height and grass sward width across the three strata. Land clearing, livestock grazing and firewood collection were the most frequent and pronounced disturbances occurring along the park boundary. These disturbances decreased in intensity as distance from the boundary increased. We recommend the following: (i) the need to revisit the buffer zone concept and policy measures associated with ecosystem services and goods provision for communities surrounding protected areas, (ii) engaging neighbouring communities on sustainable ways of deriving ecosystem goods and services from buffer zones and protected areas and (iii) further studies on the regeneration and recovery of cleared patches along the boundary and their use by wildlife species in the park.     

Shifts in Rhizoplane Communities of Aquatic Plants after Cadmium Exposure

In this study we present the comparative molecular analysis of bacterial communities of the aquatic plant Lemna minor from a contaminated site (RCP) and from a laboratory culture (EPA), as well as each of these with the addition of cadmium. Plants were identified as L. minor by analysis of the rpl16 chloroplast region. Comparative bacterial community studies were based on the analyses of 16S rRNA clone libraries, each containing about 100 clones from the root surfaces of plants. Bacterial communities were compared at three phylogenetic levels of resolution. At the level of bacterial divisions, differences in diversity index scores between treatments, with and without cadmium within the same plant type (EPA or RCP), were small, indicating that cadmium had little effect. When we compared genera within the most dominant group, the β-proteobacteria, differences between unamended and cadmium-amended libraries were much larger. Bacterial diversity increased upon cadmium addition for both EPA and RCP libraries. Analyses of diversity at the phylotype level showed parallel shifts to more even communities upon cadmium addition; that is, percentage changes in diversity indices due to cadmium addition were the same for either plant type, indicating that contamination history might be independent of disturbance-induced diversity shifts. At finer phylogenetic levels of resolution, the effects of cadmium addition on bacterial communities were very noticeable. This study is a first step in understanding the role of aquatic plant-associated microbial communities in phytoremediation of heavy metals.     

Regional effects on competition–productivity relationship: a set of field experiments in two distant regions

We studied the effect of productivity on competition intensity and the relationship between competition intensity and community species richness, using a removal experiment with the perennial plant Solidago virgaurea . The experiment was conducted in 16 different communities from two geographically distant areas (western Estonia and northern Norway). The results were compared with the results of previous experiments with Anthoxanthum odoratum from the same areas. Removal of neighbors had a positive effect on the biomass of both Solidago and Anthoxanthum , and this response was stronger in communities with higher productivity. Thus, the corrected index of relative competition intensity, CRCI, increased with increasing community productivity. Species richness was negatively correlated with CRCI in Estonia but not in Norway and not in the case of the pooled material. The results suggest that competitive exclusion operates at least in these communities which species pool is large.
Our results indicate that the relationship between competition intensity and productivity is non-linear. In our data, competition prevails in communities where living plant biomass exceeds 200 g m⁻², whereas in less productive communities, competition remains undetected and direct plant–plant relationships might at times be even mutualistic. Moreover, we found that the relationship between competition intensity and productivity is strongly dependent on regional differences and is intimately connected to a concordant variation in the intensity of grazing. The least productive communities both in Estonia and in Norway are characterized by intensive grazing, which reduces importance of competition. Hence, the contrasting results corroborates the predictions of the hypothesis of exploitation ecosystems, predicting that trophic dynamics account for the relationship between competition intensity and primary productivity.     

A survey of the physiochemical characteristics and the zooplankton communities in an ephemeral karst lake

Chaney Lake State Nature Preserve is a 68 ha ephemeral karst lake in southern Warren County, Kentucky (USA). Chaney typically fills with water in the winter as groundwater levels rise and then slowly dries via evaporation and drainage back into the subsurface over the summer months. The lake contains several habitat types, identifiable by the dominant plant communities, which may have different physiochemical characteristics. Since these differences may result in an increase in habitat heterogeneity and niches available for colonization by resident zooplankton, a suite of physiochemical and nutrient parameters was monitored in these habitats from January 1997–August 1998. Zooplankton densities and community structure were assessed from January 1997 through May 1998. There were few significant differences among the habitats but there were significantly higher concentrations of NO_x and higher specific conductivities associated with some of the groundwater inlet areas in the lake. Zooplankton were abundant, but there were no differences in zooplankton densities among the areas sampled. These results suggest that the physiochemical properties in the lake are heavily influenced by the groundwater inputs and that land use patterns around Chaney Lake may be having an impact on the preserve.     

Intraspecific variation in species interactions promotes the feasibility of mutualistic assemblages

Patterns of resource use observed at the species level emerge from the way individuals exploit the range of available resources. Hence, accounting for interindividual differences in resource use, such as pollinator use by plants, is essential to advance our understanding of community assembly and persistence. By using finely resolved data on plant–pollinator interactions, we evaluated how interindividual plant variation in pollinator use scales up to affect community structure and dynamics. All co-occurring plant species comprised specialists interacting with proper subsets of pollinators that visited generalists, and differences in interaction patterns were driven by among-individual trait variation. Furthermore, the nested structure and feasibility of plant–pollinator communities were maximised at higher levels of interindividual plant variation in traits and pollinator use. Our study sheds light on how pervasive properties of community structure arise from individual-level processes and contributes to elucidate the importance of preserving intraspecific variation in traits and resource use within populations.     

Two Invasive Plants Alter Soil Microbial Community Composition in Serpentine Grasslands

Plant invasions pose a serious threat to native ecosystem structure and function. However, little is known about the potential role that rhizosphere soil microbial communities play in facilitating or resisting the spread of invasive species into native plant communities. The objective of this study was to compare the microbial communities of invasive and native plant rhizospheres in serpentine soils. We compared rhizosphere microbial communities, of two invasive species, Centaurea solstitialis (yellow starthistle) and Aegilops triuncialis (barb goatgrass), with those of five native species that may be competitively affected by these invasive species in the field (Lotus wrangelianus, Hemizonia congesta, Holocarpha virgata, Plantago erecta, and Lasthenia californica). Phospholipid fatty acid analysis (PLFA) was used to compare the rhizosphere microbial communities of invasive and native plants. Correspondence analyses (CA) of PLFA data indicated that despite yearly variation, both starthistle and goatgrass appear to change microbial communities in areas they invade, and that invaded and native microbial communities significantly differ. Additionally, rhizosphere microbial communities in newly invaded areas are more similar to the original native soil communities than are microbial communities in areas that have been invaded for several years. Compared to native plant rhizospheres, starthistle and goatgrass rhizospheres have higher levels of PLFA biomarkers for sulfate reducing bacteria, and goatgrass rhizospheres have higher fatty acid diversity and higher levels of biomarkers for sulfur-oxidizing bacteria, and arbuscular mycorrhizal fungi. Changes in soil microbial community composition induced by plant invasion may affect native plant fitness and/or ecosystem function.     

Segregation in space and time explains the coexistence of two sympatric sub‐Antarctic petrels

Biological communities are shaped by competition between and within species. Competition is often reduced by inter‐ and intraspecific specialization on resources, such as differencet foraging areas or time, allowing similar species to coexist and potentially contributing to reproductive isolation. Here, we examine the simultaneous role of temporal and spatial foraging segregation within and between two sympatric sister species of seabirds, Northern Macronectes halli and Southern Macronectes giganteus Giant Petrels. These species show marked sexual size dimorphism and allochrony (with earlier breeding by Northern Giant Petrels) but this is the first study to test for differences in foraging behaviours and areas across the entire breeding season both between the two species and between the sexes. We tracked males and females of both species in all breeding stages at Bird Island, South Georgia, to test how foraging distribution, behaviour and habitat use vary between and within species in biological time (incubation, brood‐guard or post‐brood stages) and in absolute time (calendar date). Within each breeding stage, both species took trips of comparable duration to similar areas, but due to breeding allochrony they segregated temporally. Northern Giant Petrels had a somewhat smaller foraging range than Southern Giant Petrels, reflecting their greater exploitation of local carrion and probably contributing to their recent higher population growth. Within species, segregation was spatial, with females generally taking longer, more pelagic trips than males, although both sexes of both species showed unexpectedly plastic foraging behaviour. There was little evidence of interspecific differences in habitat use. Thus, in giant petrels, temporal segregation reduces interspecific competition and sexual segregation reduces intraspecific competition. These results demonstrate how both specialization and dynamic changes in foraging strategies at different scales underpin resource division within a community.     

Effects of Habitat Quality and Isolation on the Colonization of Restored Heathlands by Butterflies

In areas with intensive land use, such as the Netherlands, habitat fragmentation and loss of habitat quality due to eutrophication and drainage are major threats to the preservation of species‐rich communities of heathland and acid grassland. Restoration of such nutrient‐poor habitats may be carried out by removing the topsoil from ex‐arable land, in order to lower the nutrient levels. However, the establishment of target plant communities is known to be fragmentary. The current study shows that this also applies to butterflies. Ten years after topsoil removal in eight study areas, on average, only 3.5 of 10 characteristic heathland species were recorded on the sites. Species that did colonize had a significantly lower density than in the source populations. Our study indicates that although isolation effects were limiting colonization, poor habitat quality was the main limiting factor, mainly due to lack of host plants, hydrological conditions, and, to a lesser extent, lack of nectar plants and excessive residual nutrient levels. An experiment with the introduction of cut heather in one study area showed a significantly higher abundance of both target and nontarget butterflies in manipulated sites than in control sites. It can be concluded that habitat restoration by topsoil removal can be successful for butterflies of especially wet heathland habitats, provided that source populations are at close range and care is taken that complete plant communities are restored.