Changes In Community Similarity Research Articles

滇西北退化高寒草甸植物群落结构对刈割的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 滇西北退化高寒草甸植物群落结构对刈割的响应 DOI: 10.5846/stxb202108112210 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 第二次青藏高原综合科学考察研究项目（2019QZKK0307）；国家自然科学基金项目资助（31901394，31860620） Responses of plant community structure to mowing in the degraded alpine meadows, Northwestern Yunnan Province Author: Affiliation: Fund Project: 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:为探究滇西北不同退化级别高寒草甸植物群落结构对外界干扰的响应敏感性，以香格里拉市的典型高寒草甸为研究对象，于2018-2020年在三个退化梯度上（严重退化，S1；中度退化，S2；轻度退化，S3）开展控制刈割实验，进而分析草甸植物物种丰富度、群落组成相似性、群落复杂度和关键种的变化规律。结果表明：（1）刈割后，S1的物种丰富度显著增加（P<0.05），S2和S3的物种丰富度未发生显著变化（P>0.05）；（2）相较于S2和S3，S1梯度的植物群落组成变化最大；（3） S1、S2和S3的植物群落复杂度在刈割后均呈先下降后增加的趋势，但S1的植物群落复杂度变化幅度高于S2和S3；（4）刈割导致各退化草甸植物群落的关键种发生了变化，2018、2019和2020年S1梯度的关键种在豆科（Leguminsae）和蔷薇科（Rosaceae）之间变化，S2梯度的关键种在禾本科（Gramineae）和菊科（Compositae）之间变化，S3梯度的关键种在蔷薇科（Rosaceae）、菊科（Compositae）和禾本科（Gramineae）之间转变。研究表明，滇西北高寒草甸植物物种丰富度、群落组成和群落复杂度对外界干扰响应的敏感性可能随退化加剧而上升，但群落关键种的响应过程较复杂。 Abstract:To explore the sensibility of the response of plant community structure to external disturbances under different degradation conditions in the Northwestern Yunnan Province (NWYP), we conducted a mowing experiment at three degradation gradients (i.e., S1:severe degradation; S2:moderate degradation; S3:slight degradation) in an alpine meadow in Shangri-La from 2018 to 2020. The effects of mowing on community structure indicators, including species richness, community similarity, community complexity and keystone species were analyzed. The results showed that (1) after mowing, the species richness of S1 increased significantly (P<0.05), while the species richness of S2 and S3 did not change significantly (P>0.05). (2) Mowing caused a greater change in community similarity in S1 than in S2 and S3. (3) The network connectivity of plant community decreased firstly and then increased after mowing in all degradation levels. Moreover, the change range of community complexity in S1 was higher than in S2 and S3. (4) The keystone species of plant communities changed in 2018, 2019 and 2020. In S1, the keystone species varied between Leguminsae and Rosaceae. In S2, the keystone species varied between Gramineae and Compositae. In S3, the keystone species varied among Rosaceae, Compositae and Gramineae. The study suggests that the sensitivity of the response of species richness, community composition and complexity of plant community to external disturbance might increase with meadow degradation levels, while the shifting of the keystone species would be complex in NWYP. 参考文献 相似文献 引证文献

Analysing the distance decay of community similarity in river networks using Bayesian methods

The distance decay of community similarity (DDCS) is a pattern that is widely observed in terrestrial and aquatic environments. Niche-based theories argue that species are sorted in space according to their ability to adapt to new environmental conditions. The ecological neutral theory argues that community similarity decays due to ecological drift. The continuum hypothesis provides an intermediate perspective between niche-based theories and the neutral theory, arguing that niche and neutral factors are at the opposite ends of a continuum that ranges from competitive to stochastic exclusion. We assessed the association between niche-based and neutral factors and changes in community similarity measured by Sorensen’s index in riparian plant communities. We assessed the importance of neutral processes using network distances and flow connection and of niche-based processes using Strahler order differences and precipitation differences. We used a hierarchical Bayesian approach to determine which perspective is best supported by the results. We used dataset composed of 338 vegetation censuses from eleven river basins in continental Portugal. We observed that changes in Sorensen indices were associated with network distance, flow connection, Strahler order difference and precipitation difference but to different degrees. The results suggest that community similarity changes are associated with environmental and neutral factors, supporting the continuum hypothesis.

A comprehensive formula for decomposing change in community similarity into introduction and extinction events

Biological invasion, climate change and urbanization are presently altering species compositions worldwide (McKinney and Lockwood 1999, McKinney 2006, Qian and Ricklefs 2006, Magurran et al. 2015, Gossner et al. 2016, Newbold et al. 2018), while changes in community composition are generally associated with higher community similarities and losses of community distinctiveness (McKinney and Lockwood 1999, Olden et al. 2004). The underlying processes of homogenization are still unclear and especially lack theoretical underpinnings (Olden and Poff 2003, Rosenblad and Sax 2017). It was theoretically and empirically proposed that similarity changes are determined by different events (Olden and Poff 2003, Villéger and Brosse 2012, Rosenblad and Sax 2017). For example, the introduction of the same species to two sites would result in an increase in similarity, while the extinction of same native species from two sites would lead to a decrease in similarity. In complement to earlier works on the mathematical description of homogenization (Olden and Poff 2003, Villéger and Brosse 2012). Rosenblad and Sax (2017) provided a concise framework of six types of introduction and extinction events with formula derivations to qualify the relative importance of these events on changes in community similarity. They found that the effects of these events vary according to event type and initial similarity. However, their conclusions mainly derive from simplified assumptions of species richness and number of events, which prevent us from understanding the precise relationships among initial similarity, different event types and total number of species. Through mathematical derivation and simulations (Fig. 1), we thus aim to: 1) combine previously identified determinants of change in similarity into a single comprehensive formula; 2) illustrate how these determinants interact with each other; and 3) highlight the important role of gradient in species richness in affecting the magnitude of similarity changes.

Culvert Replacement Enhances Connectivity of Stream Fish Communities in a Michigan Drainage Network

AbstractCulverts installed at road–stream intersections are pervasive in many watersheds and can function as dispersal barriers for aquatic organisms, thereby fragmenting watersheds. We hypothesized that the replacement of culverts with bridges would restore ecosystem connectivity via remediation of dispersal barriers. Our study objectives were to (1) characterize fish assemblages in three Michigan streams before and after culvert replacement by bridges, and (2) determine the effect of fish sample size on our ability to quantify fish assemblage similarity. To address the first objective, we surveyed the fish assemblages of the three study streams (upstream and downstream of the culvert) prior to, 1 year after, and 3 years after culvert removal via standardized electrofishing. The similarity of upstream and downstream fish assemblages increased by 9–25% following culvert removal. Relative fish abundance decreased but biomass of fishes remained constant, indicating a shift in size structure toward larger individuals. To address the second objective, we conducted a bootstrap analysis for all samples. Large sample sizes of fishes (150–350 individuals) were necessary to accurately and precisely measure community similarity. However, changes in community similarity could be detected with relatively small samples (50–100 individuals). Our study illustrates the ecological potential of culvert removal for restoring stream connectivity.

Pattern and process of biotic homogenization in the New Pangaea

Human activities have reorganized the earth's biota resulting in spatially disparate locales becoming more or less similar in species composition over time through the processes of biotic homogenization and biotic differentiation, respectively. Despite mounting evidence suggesting that this process may be widespread in both aquatic and terrestrial systems, past studies have predominantly focused on single taxonomic groups at a single spatial scale. Furthermore, change in pairwise similarity is itself dependent on two distinct processes, spatial turnover in species composition and changes in gradients of species richness. Most past research has failed to disentangle the effect of these two mechanisms on homogenization patterns. Here, we use recent statistical advances and collate a global database of homogenization studies (20 studies, 50 datasets) to provide the first global investigation of the homogenization process across major faunal and floral groups and elucidate the relative role of changes in species richness and turnover. We found evidence of homogenization (change in similarity ranging from -0.02 to 0.09) across nearly all taxonomic groups, spatial extent and grain sizes. Partitioning of change in pairwise similarity shows that overall change in community similarity is driven by changes in species richness. Our results show that biotic homogenization is truly a global phenomenon and put into question many of the ecological mechanisms invoked in previous studies to explain patterns of homogenization.

Dendritic network structure constrains metacommunity properties in riverine ecosystems

1. Increasingly, ecologists conceptualize local communities as connected to a regional species pool rather than as isolated entities. By this paradigm, community structure is determined through the relative strengths of dispersal-driven regional effects and local environmental factors. However, despite explicit incorporation of dispersal, metacommunity models and frameworks often fail to capture the realities of natural systems by not accounting for the configuration of space within which organisms disperse. This shortcoming may be of particular consequence in riverine networks which consist of linearly -arranged, hierarchical, branching habitat elements. Our goal was to understand how constraints of network connectivity in riverine systems change the relative importance of local vs. regional factors in structuring communities. 2. We hypothesized that communities in more isolated headwaters of riverine networks would be structured by local forces, while mainstem sections would be structured by both local and regional processes. We examined these hypotheses using a spatially explicit regional analysis of riverine macroinvertebrate communities, focusing on change in community similarity with distance between local communities [i.e., distance-decay relationships; (DDRs)], and the change in environmental similarity with distance. Strong DDRs frequently indicate dispersal-driven dynamics. 3. There was no evidence of a DDR in headwater communities, supporting our hypothesis that dispersal is a weak structuring force. Furthermore, a positive relationship between community similarity and environmental similarity supported dynamics driven by local environmental factors (i.e., species sorting). In mainstem habitats, significant DDRs and community x environment similarity relationships suggested both dispersal-driven and environmental constraints on local community structure (i.e., mass effects). 4. We used species traits to compare communities characterized by low vs. high dispersal taxa. In headwaters, neither strength nor mode (in-network vs. out of network) of dispersal changed our results. However, outcomes in mainstems changed substantially with both dispersal mode and strength, further supporting the hypothesis that regional forces drive community dynamics in mainstems. 5. Our findings demonstrate that the balance of local and regional effects changes depending on location within riverine network with local (environmental) factors dictating community structure in headwaters, and regional (dispersal driven) forces dominating in mainstems.

Avifauna response to hurricanes: regional changes in community similarity

AbstractGlobal climate models predict increases in the frequency and intensity of extreme climatic events such as hurricanes, which may abruptly alter ecological processes in forests and thus affect avian diversity. Developing appropriate conservation measures necessitates identifying patterns of avifauna response to hurricanes. We sought to answer two questions: (1) does avian diversity, measured as community similarity, abundance, and species richness, change in areas affected by hurricane compared with unaffected areas, and (2) what factors are associated with the change(s) in avian diversity? We used North American Breeding Bird Survey data, hurricane track information, and a time series of Landsat images in a repeated measures framework to answer these questions. Our results show a decrease in community similarity in the first posthurricane breeding season for all species as a group, and for species that nest in the midstory and canopy. We also found significant effects of hurricanes on abundance for species that breed in urban and woodland habitats, but not on the richness of any guild. In total, hurricanes produced regional changes in community similarity largely without significant loss of richness or overall avian abundance. We identified several potential mechanisms for these changes in avian diversity, including hurricane‐induced changes in forest habitat and the use of refugia by birds displaced from hurricane‐damaged forests. The prospect of increasing frequency and intensity of hurricanes is not likely to invoke a conservation crisis for birds provided we maintain sufficient forest habitat so that avifauna can respond to hurricanes by shifting to areas of suitable habitat.

The varying role of population abundance in structuring indices of biotic homogenization

AbstractAim An important component of human‐induced global change is the decrease or increase in community distinctiveness (taxonomic homogenization or differentiation, respectively) that follows the loss of native species and gain of non‐native species. We use simulation approaches to assess the extent to which conclusions about the outcome of the homogenization process depend on whether or not abundance data are incorporated.Location Data were produced through computer simulation.Methods The frequency with which occurrence‐based similarity indices and abundance‐based similarity indices give different views of changes in community similarity, and the conditions under which such differences occurred were assessed using both deterministic and stochastic modelling approaches to simulate species assemblage states.Results Occurrence‐based and abundance‐based indices were positively correlated across the set of simulations for both the deterministic and stochastic models. However, in both situations approximately one quarter (25%) of models resulted in contrasting outcomes for the two approaches of calculating changes in compositional similarity; that is, one data type showed a positive value (homogenization), whereas the other showed a negative value (differentiation).Main conclusions In the majority of cases, species abundances will not change drastically enough after perturbation to produce large differences between homogenization scores measured using occurrence versus abundance information. However, in cases where these changes are large, it is important to recognize that the choice of metric to analyse homogenization trends will influence the qualitative and quantitative conclusions drawn. Studies of real assemblages are therefore necessary to evaluate the role of species abundance in defining the magnitude and direction of changes in community composition across space, and the implications of these changes for native biodiversity.

Null model of biotic homogenization: a test with the European freshwater fish fauna

ABSTRACTIn recent years, there has been growing concern about how species invasions and extinctions could change the distinctiveness of formerly disparate fauna and flora, a process called biotic homogenization. In the present study, a null model of biotic of homogenization was developed and applied to the European freshwater fish fauna. We found that non‐native fish species led to the greatest homogenization in south‐western Europe and greatest differentiation in north‐eastern Europe. Comparing these observed patterns to those expected by our null model empirically demonstrated that biotic homogenization is a non‐random ecological pattern, providing evidence for previous assumptions. The place of origin of non‐native species was also considered by distinguishing between exotic (originating from outside Europe) and translocated species (originating from within Europe). We showed that exotic and translocated species generated distinct geographical patterns of biotic homogenization across Europe because of their contrasting effects on the changes in community similarity among river basins. Translocated species promoted homogenization among basins, whereas exotic species tended to decrease their compositional similarity. Quantifying the individual effect of exotic and translocated species is therefore an absolute prerequisite to accurately assess the spatial dynamics of biotic homogenization.

Forecasting faunal and floral homogenization associated with human population geography in North America

Human population and urbanization is unprecedented in its rate of growth and geographic scope. With the help of humans, exotic species have piggybacked their way to distant lands, which in combination with the loss of endemic native species, has led to the convergence of biological communities toward common and ubiquitous forms. However, the extent to which this “biotic homogenization” varies along gradients of human population size and urbanization remains mostly unexplored, especially at broad spatial scales. The present paper combines a recent conceptual model of homogenization with estimates of species invasions and extinctions to provide the first estimates of homogenization for five major taxonomic groups – land birds, freshwater fish, terrestrial mammals, plants, and freshwater reptiles and amphibians – at the continental-scale of North America (exclusive of Mexico). On average, the greatest levels of biotic homogenization were predicted for plants (22%) and fishes (14%), followed by reptiles/amphibians (12%), mammals (9%) and birds (8%). Substantial spatial variation in predictions of community similarity exists and emphasize that the outcome of species invasions and extinctions may not only increase community similarity, but may also decrease it (i.e., differentiation). Homogenization is predicted to be greatest for fish in southwestern and northeastern US, highest in eastern North America for plants, greatest for birds and mammals along the west coast of North America, and peak in southern US for reptiles and amphibians. We show that predicted change in community similarity for all taxonomic groups is positively related to human population size and urbanization, thus providing the first quantitative linkage between human population geography and homogenization for a number of major taxonomic groups at the continental-scale of North America. Our study helps identify regional hotspots of biotic homogenization across North America, thus setting the stage for future studies where more directed investigations of biotic homogenization along urban gradients can be conducted.

Toward a mechanistic understanding and prediction of biotic homogenization.

The widespread replacement of native species with cosmopolitan, nonnative species is homogenizing the global fauna and flora. While the empirical study of biotic homogenization is substantial and growing, theoretical aspects have yet to be explored. Consequently, the breadth of possible ecological mechanisms that can shape current and future patterns and rates of homogenization remain largely unknown. Here, we develop a conceptual model that describes 14 potential scenarios by which species invasions and/or extinctions can lead to various trajectories of biotic homogenization (increased community similarity) or differentiation (decreased community similarity); we then use a simulation approach to explore the model's predictions. We found changes in community similarity to vary with the type and number of nonnative and native species, the historical degree of similarity among the communities, and, to a lesser degree, the richness of the recipient communities. Homogenization is greatest when similar species invade communities, causing either no extinction or differential extinction of native species. The model predictions are consistent with current empirical data for fish, bird, and plant communities and therefore may represent the dominant mechanisms of contemporary homogenization. We present a unifying model illustrating how the balance between invading and extinct species dictates the outcome of biotic homogenization. We conclude by discussing a number of critical but largely unrecognized issues that bear on the empirical study of biotic homogenization, including the importance of spatial scale, temporal scale, and data resolution. We argue that the study of biotic homogenization needs to be placed in a more mechanistic and predictive framework in order for studies to provide adequate guidance in conservation efforts to maintain regional distinctness of the global biota.