Local Extinction Of Species Research Articles

Disentangling the influence of plants and herbivores on the local diversity of parasitoids in the Brazilian Cerrado

Abstract This study investigated the extent to which host plants and their associated herbivores determine the local diversity of parasitoids, which depend, directly or indirectly, on these two groups as food resource or shelter for their development. The tritrophic system studied here is composed of Asteraceae, endophagous herbivores associated with their flower heads and parasitoid wasps. Samplings were undertaken in 18 remnants of the Brazilian Cerrado. Path analysis was used to unveil the direct and indirect effects of species richness, average taxonomic distinctness (AvTD), and sampling effort of plants and herbivores on parasitoid richness and AvTD. Plant species richness had only an indirect effect – mediated by herbivores – on parasitoid species richness. On the other hand, there were both direct and indirect effects of plant species richness on the AvTD of parasitoids. An implication of our findings is that the local extinction of plant species promotes not only the local loss of their herbivores but also the loss of parasitoid species and a decrease in the phylogenetic diversity of parasitoids, which can jeopardise their future evolutionary history.

Colonization credit of post-agricultural forest patches in NE Germany remains 130–230 years after reforestation

In many temperate regions worldwide, a large portion of deciduous forest grows on former agricultural land, while a smaller portion is ‘ancient’ forest on sites with no historical record of agricultural land use. The differences in species diversity between ancient and post-agricultural forests have been well documented. However, in regions where forest fragmentation occurred only a few centuries ago, it remains unclear whether these differences are due to an extinction debt in ancient forests (i.e., a delay in local species extinction), a colonization credit in post-agricultural forests (i.e., species are yet to colonize a patch), or both. Additionally, our knowledge on how soil conditions and landscape configuration interact with species’ traits to determine the colonization credit is limited. Here, we surveyed ancient and post-agricultural forest patches in NE Germany to quantify the magnitude of the colonization credit and identify its determinants. The colonization credit in an average forest patch amounted to 4.7 forest specialist species and ranged up to 9 species in highly isolated patches. In contrast, we found more species than predicted in patches better connected to ancient forests. The colonization credit was not smaller in older patches than it was in younger ones. Species with a low dispersal potential and a low seed output contributed most to the colonization credit. Our study demonstrates that in a landscape where the extinction debt has already been paid and only a small fraction of ancient forest is left, the recovery of forest specialist diversity in post-agricultural forests may take several centuries.

Sex differences in developmental plasticity and canalization shape population divergence in mate preferences.

Sexual selection of high-quality mates can conflict with species recognition if traits that govern intraspecific mate preferences also influence interspecific recognition. This conflict might be resolved by developmental plasticity and learned mate preferences, which could drive preference divergence in populations that differ in local species composition. We integrate field and laboratory experiments on two calopterygid damselfly species with population genetic data to investigate how sex differences in developmental plasticity affect population divergence in the face of gene flow. Whereas male species recognition is fixed at emergence, females instead learn to recognize heterospecifics. Females are therefore more plastic in their mate preferences than males. We suggest that this results from sex differences in the balance between sexual selection for high-quality mates and selection for species recognition. As a result of these sex differences, females develop more pronounced population divergence in their mate preferences compared with males. Local ecological community context and presence of heterospecifics in combination with sex differences in plasticity and canalization therefore shape population divergence in mate preferences. As ongoing environmental change and habitat fragmentation bring formerly allopatric species into secondary contact, developmental plasticity of mate preferences in either or both sexes might facilitate coexistence and prevent local species extinction.

Jaguar Panthera onca in its southernmost range: use of a corridor between Bolivia and Argentina

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 26:167-177 (2014) - DOI: https://doi.org/10.3354/esr00640 Jaguar Panthera onca in its southernmost range: use of a corridor between Bolivia and Argentina Griet An Erica Cuyckens1,2,*, Fernando Falke3, Lisanne Petracca4 1Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Av. Rivadavia 1917 (C1033AAJ), Buenos Aires, Argentina 2Centro de Estudios Territoriales Ambientales y Sociales (CETAS), Alberdi 47, 4600 San Salvador de Jujuy, Argentina 3Red Yaguareté, Los Toldos s/calle, 4531 Salta, Argentina 4Panthera, 8 West 40th Street, 18th Floor, New York, NY 10018, USA *Corresponding author: grietcuyckens@yahoo.com ABSTRACT: Corridors can prevent local extinction of particular species by connecting populations and are crucial for the long-term conservation of large animals and species with large home-ranges such as jaguars. To assess the functionality of the proposed Tariquía-Baritú corridor between Bolivia and Argentina, we used the jaguar as a focal species. We conducted 254 interviews with local residents in 103 of 117 sampling units (each 36 km2) from November 2009 to February 2012, regarding the presence of the jaguar Panthera onca and 6 prey species: the white-lipped peccary Tayassu pecari, collared peccary Pecari tajacu, red brocket deer Mazama americana, gray brocket deer Mazama gouazoubira, capybara Hydrochaeris hydrochaeris and agouti Dasyprocta punctata. We applied site occupancy modeling using environmental co-variables. Sampling units effective for jaguar and for the future of the corridor were selected based on having a minimum 65% likelihood that the jaguar and at least 4 of 6 prey species use habitat within that unit. The final corridor was 3168 km2 and encompassed 88 of the sampling units, suggesting that connectivity still exists between Tariquía Reserve and Baritú National Park and, therefore, that this corridor qualifies for long-term conservation. Changes in human land use, direct hunting and the presence of a route bisecting the study area are considered the main threats to the future of the corridor. Corridors are an effective conservation measure but must be accompanied by other conservation solutions. KEY WORDS: Connectivity · Conservation planning · Detection probability · Interviews · Occupancy · Prey Full text in pdf format PreviousNextCite this article as: Cuyckens GAE, Falke F, Petracca L (2014) Jaguar Panthera onca in its southernmost range: use of a corridor between Bolivia and Argentina. Endang Species Res 26:167-177. https://doi.org/10.3354/esr00640 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 26, No. 2. Online publication date: December 10, 2014 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2014 Inter-Research.

Are removal experiments effective tools for assessing plant community resistance and recovery from invasion?

AbstractRemoval experiments are useful tools for assessing two important aspects of plant community invasion: (1) resistance to invasion and (2) recovery after invasive species removal. We discuss the potential of such experiments based on a brief systematic review of the literature on community resistance, as measured by invasibility after removal of resident species (reduction of taxonomic/functional richness), and on community recovery, as measured by resident community response after invasive species removal. We found 62 research articles, most of them related to invasive species removal. Few studies used removals to test biotic resistance, despite the importance of resident removals for identifying community components that play key roles in the often‐controversial invasion resistance hypotheses. Furthermore, appropriate experimental controls were rarely used, which would allow separation of the effect of local species extinction from that of disturbance. We hope this review stimulates plant ecologists to adopt removal experiments for studying invasion processes.

Deer density and plant palatability predict shrub cover, richness, diversity and aboriginal food value in a North American archipelago

AbstractAimTrophic cascades are a common consequence of herbivore outbreak and in the absence of hunting can cause the local extinction of native plant species and communities. We compared plant communities at 66 island and mainland sites to test the hypothesis that deer (Cervidae) determine species cover, richness and diversity and that palatable species become rare at high deer density. We validate a region‐wide index of deer density and impact on plant communities in a region where culturally significant food plants maintained by aboriginal people prior to European contact helped to define baseline plant communities.LocationGulf and San Juan Island archipelagos and North American mainland.MethodsWe conducted surveys of 49 native, 10 exotic and 15 culturally significant plant species and deer sign at 66 sites on 35 islands and mainland to determine deer abundance and plant species cover, richness and diversity. We identified culturally significant food plants facilitated by aboriginal people using ethnobotanical knowledge, quantified plant palatability via cafeteria trials and characterized shrub architecture.ResultsNative and culturally significant shrub cover, richness and diversity were 52–85% lower at sites with abundant deer (0.9–2.8 ha−1) versus no deer. However, these values were also 38–82% lower at sites in the lowest deer density class (< 0.08 ha−1) versus sites with no deer present. Palatable cover was 92% lower where deer were abundant versus absent and 28% lower in low‐density versus deer‐free sites. Shrub architecture provided an easily applied index of native and culturally significant plant cover and deer density.Main conclusionsWe provide comparative examples of endangered plant communities to demonstrate that, contrary to the intermediate disturbance hypothesis, any positive effect of deer on plant diversity on islands in the Pacific north‐west of North America occurs at densities < 0.08 ha−1, if at all. This detailed example of trophic downgrading highlights the need and provides the methods to identify herbivore densities compatible with the persistence of all native species in conserved landscapes.

Earthquakes trigger the loss of groundwater biodiversity.

Earthquakes are among the most destructive natural events. The 6 April 2009, 6.3-Mw earthquake in L'Aquila (Italy) markedly altered the karstic Gran Sasso Aquifer (GSA) hydrogeology and geochemistry. The GSA groundwater invertebrate community is mainly comprised of small-bodied, colourless, blind microcrustaceans. We compared abiotic and biotic data from two pre-earthquake and one post-earthquake complete but non-contiguous hydrological years to investigate the effects of the 2009 earthquake on the dominant copepod component of the obligate groundwater fauna. Our results suggest that the massive earthquake-induced aquifer strain biotriggered a flushing of groundwater fauna, with a dramatic decrease in subterranean species abundance. Population turnover rates appeared to have crashed, no longer replenishing the long-standing communities from aquifer fractures, and the aquifer became almost totally deprived of animal life. Groundwater communities are notorious for their low resilience. Therefore, any major disturbance that negatively impacts survival or reproduction may lead to local extinction of species, most of them being the only survivors of phylogenetic lineages extinct at the Earth surface. Given the ecological key role played by the subterranean fauna as decomposers of organic matter and “ecosystem engineers”, we urge more detailed, long-term studies on the effect of major disturbances to groundwater ecosystems.

Post-Release Monitoring of Diet Profile and Diet Quality of Reintroduced African Buffalo (Syncerus Caffer) in Umfurudzi Park, Zimbabwe

Post-release monitoring of wildlife is essential to the success of ecological restoration initiatives. Translocation of wildlife to new ecosystems is associated with changes in diet profiles of individuals and ultimately animal performance, since productivity of rangelands varies in time and space. The population decline and local extinction of buffalo and other species in Umfurudzi Park, Zimbabwe, in the late 1980s led to temporary suspension of hunting activities. Recently, efforts have been made to resuscitate Umfurudzi Park through wildlife reintroductions and active ecosystem management. We assessed the diet profile and diet quality of the African buffalo ( Syncerus caffer) between 2011 and 2012. A total of 42 grass species constituted the diet spectrum of buffalo. Heteropogon contortus, Eragrostis racemosa, Steroechlaena tenuifolia and Themeda triandra contributed significantly to the buffalo diet during the four seasons of the study period. Although a wide spectrum of grass species was selected in the wet season, the diversity of grass species selected was not significantly different among the seasons. Grass species crude protein deteriorated from 4.5% in the wet season to 3.5% in the dry season. Crude protein and phosphorus levels in buffalo faecal samples were within the recommended nutrient scale for southern Africa large herbivores. We conclude that feed availability and quality may not be limiting the persistence of the reintroduced buffalo. There is a need to closely monitor grass availability, dietary shifts, and forage quality over time, as well as resource partitioning with other feeding guilds.

Water quality of urban water bodies – a threat for amphibians?

Most studies on the effects of water quality on amphibians concern experimental conditions. The main aim of our study was to determine whether the quality of water bodies in urban environment may be a factor leading to local extinction of some amphibian species. We investigated the current amphibian richness in Krakow water bodies and the water quality of these water bodies. We compared our results with available historical data on amphibian richness in Krakow and we determined the number of amphibian species local extinction for each water body. Then, we compared water bodies with low amphibian extinction rates to water bodies with high amphibian extinction rates in respect to ten water quality chemical indicators. We found that the values of most chemical indicators were higher in water bodies with high amphibian extinction rates. The values of magnesium and chloride ion concentration, as well as conductivity appeared to differ the most between these two types of water bodies which is connected mainly with spring run-off into the water bodies. The results of this study demonstrate that water pollution may lead to local extinction of amphibian species.

Modeling Soil and Woody Vegetation in the Senegalese Sahel in the Context of Environmental Change

Climatic stress and anthropogenic disturbances have caused significant environmental changes in the Sahel. In this context, the importance of soil is often underrepresented. Thus, we analyze and discuss the interdependency of soil and vegetation by classifying soil types and its woody cover for a region in the Senegalese Ferlo. Clustering of 28 soil parameters led to four soil types which correspond with local Wolof denotations: Dek, Bowel, Dior and Bardial. The soil types were confirmed by a Non-metric Multidimensional-Scaling (NMDS) ordination and extrapolated via a Random Forest classifier using six significant variables derived from Landsat imagery and a digital elevation model (out-of-bag error rate: 7.3%). In addition, canopy cover was modeled using Landsat and a Reduced-Major-Axis (RMA) regression (R2 = 0.81). A woody vegetation survey showed that every soil type has its own species composition. However, 29% of Bowel regions are deforested (i.e., degraded) and interviews revealed extensive environmental changes and a strong decline and local extinction of woody species. The differences between the soil types are significant, showing that vegetation changes (i.e., degradation and greening), resilience to climatic stress and human activities largely depend on soil properties. We highlight that spatial heterogeneity is an important aspect when dealing with environmental changes in the Sahel, and local knowledge can be well used to classify spatial units by means of public Earth observation data.

Further east: eutrophication as a major threat to the flora of Vladimir Oblast, Russia

Eutrophication remains a major threat to the flora of Western Europe despite measures to reduce nitrogen emissions. Although nutrient enrichment has been recorded for both inland waters and adjacent seas, there is almost no evidence from Russia for large-scale anthropogenic eutrophication of soils and its impact on terrestrial biota. I used the distribution grid data (337 grid squares, ca. 96 km(2)) on 1,384 vascular plants of Vladimir Oblast for two periods (1869-1999 vs. 2000-2012) to estimate the shifts in mean Ellenberg's indicator values for nitrogen and soil reaction. Decadal changes in the flora of acid sandy Meshchera Lowlands were observed directly during two grid surveys of 2002 and 2012 based on a coarser grid (50 squares, ca. 24 km(2)). Despite the spatial correlation of Ellenberg's indicator values for soil reaction and nitrogen, mean grid values for nitrogen are growing in areas with both acid and neutral soils. The changes in mean grid indicator values for nitrogen are caused by either local extinctions of species from nutrient-poor habitats or spread of nitrophilous plants. I found that oligotrophic habitats are declining rapidly within the eutrophic loamy landscapes. In contrast, changes in landscapes with acid sandy soils are caused by increasing number of records of nitrophilous species, both invasive and native. These two processes have different spatial patterns caused by varying levels of geochemical buffer capacity and should be considered separately. Fragmentary historical data on Vladimir Oblast flora agrees with the overall European picture of eutrophication in the twentieth century.

Clonal ability, height and growth form explain species’ response to habitat deterioration in Fennoscandian wooded meadows

Fennoscandian calcareous wooded meadows have high conservation value due to very high diversity which has been maintained by consistent mowing, but undergo species loss when this management is abandoned. We compared species richness and composition of regularly mown and abandoned wooded meadows in Estonia and established species groups with respect to their response to abandonment. These meadows were very species rich with a maximum of 43 species per 0.25 m2. Species whose populations are maintained by mowing constituted >60 % of the floristic diversity of the mown wooded meadows. Abandonment suppressed species with a preference for dry infertile open habitats. Response to abandonment was related to clonality, height and growth form. The greatest negative response was associated with low graminoids, short-lived and non-clonal species, rosette and semi-rosette growth form. Weak competitors with low height and light seeds exhibited a slow decline; perennial life span and clonality enable a delay in local extinction of these species. Response groups had similar persistence at a national level, revealing that earlier assessment of species dynamics at larger spatial scales could underestimate the number of threatened species. Application of restoration measures could avoid local extinctions of many mowing-supported species, whereas some of the mowing-dependent species likely need reintroduction.

Linking indices for biodiversity monitoring to extinction risk theory.

Biodiversity indices often combine data from different species when used in monitoring programs. Heuristic properties can suggest preferred indices, but we lack objective ways to discriminate between indices with similar heuristics. Biodiversity indices can be evaluated by determining how well they reflect management objectives that a monitoring program aims to support. For example, the Convention on Biological Diversity requires reporting about extinction rates, so simple indices that reflect extinction risk would be valuable. We developed 3 biodiversity indices that are based on simple models of population viability that relate extinction risk to abundance. We based the first index on the geometric mean abundance of species and the second on a more general power mean. In a third index, we integrated the geometric mean abundance and trend. These indices require the same data as previous indices, but they also relate directly to extinction risk. Field data for butterflies and woodland plants and experimental studies of protozoan communities show that the indices correlate with local extinction rates. Applying the index based on the geometric mean to global data on changes in avian abundance suggested that the average extinction probability of birds has increased approximately 1% from 1970 to 2009.Conectando Índices para el Monitoreo de la Biodiversidad con la Teoría de Riesgo de ExtinciónResumenLos índices de biodiversidad combinan frecuentemente los datos de diferentes especies cuando se usan en los programas de monitoreo. Las propiedades heurísticas pueden sugerir índices preferidos, pero carecemos de medios objetivos para discriminar a los índices con propiedades heurísticas similares. Los índices de biodiversidad pueden evaluarse al determinar qué tan bien reflejan los objetivos de manejo que un programa de monitoreo busca apoyar. Por ejemplo, la Convención sobre la Diversidad Biológica requiere reportar las tasas de extinción, así que los índices que reflejan el riesgo de extinción serían valiosos. Desarrollamos 3 índices de biodiversidad que se basan en modelos sencillos de viabilidad de población y que relacionan el riesgo de extinción con la abundancia. Basamos el primer índice en la media geométrica de la abundancia de especies, y el segundo en una media de poder más general. En el tercer índice integramos la media geométrica y la tendencia. Estos índices requieren los mismos datos que índices previos, pero también se relacionan directamente con el riesgo de extinción. La información de campo sobre mariposas y plantas de bosque, y los estudios experimentales de comunidades protozoarias, muestran que los índices se correlacionan con las tasas locales de extinción. Al aplicar el índice basado en la media geométrica sobre los datos globales de los cambios en la abundancia de aves, sugirió que la probabilidad de extinción promedio de aves ha incrementado aproximadamente 1% desde 1970 hasta 2009.Palabras ClaveÍndice de biodiversidad, media geométrica, medida de la biodiversidad, riesgo de extinción

Extinction debt of cities and ways to minimise their realisation: a focus on Melbourne

The formation and growth of cities sets in train a slow process of local species extinction, although it can take a long time for that extinction to be realised. Using Melbourne as an example, the authors ask ‘What plant species are potentially at risk and what strategies and actions could minimise the predicted negative outcomes?’

Topo‐climatic microrefugia explain the persistence of a rare endemic plant in the Alps during the last 21 millennia

Ongoing rapid climate change is predicted to cause local extinction of plant species in mountain regions. However, some plant species could have persisted during Quaternary climate oscillations without shifting their range, despite the limited evidence from fossils. Here, we tested two candidate mechanisms of persistence by comparing the macrorefugia and microrefugia (MR) hypotheses. We used the rare and endemic Saxifraga florulenta as a model taxon and combined ensembles of species distribution models (SDMs) with a high-resolution paleoclimatic and topographic dataset to reconstruct its potential current and past distribution since the last glacial maximum. To test the macrorefugia hypothesis, we verified whether the species could have persisted in or shifted to geographic areas defined by its realized niche. We then identified potential MR based on climatic and topographic properties of the landscape and applied refined scenarios of MR dynamics and functions over time. Last, we quantified the number of known occurrences that could be explained by either the macrorefugia or MR model. A consensus of two or three SDM techniques predicted absence between 14-10, 3-4 and 1 ka bp, which did not support the macrorefugia model. In contrast, we showed that S. florulenta could have contracted into MR during periods of absence predicted by the SDMs and later re-colonized suitable areas according to the macrorefugia model. Assuming a limited and realistic seed dispersal distance for our species, we explained a large number of the current occurrences (61-96%). Additionally, we showed that MR could have facilitated range expansions or shifts of S. florulenta. Finally, we found that the most recent and the most stable MR were the ones closest to current occurrences. Hence, we propose a novel paradigm to explain plant persistence by highlighting the importance of supporting functions of MR when forecasting the fate of plant species under climate change.

Non‐interactive effects of plant invasion and landscape modification on native communities

AbstractAimBiological invasions and anthropogenic habitat modification are considered to be the leading drivers of global environmental change, yet their synergistic impacts on native communities remain poorly understood. We tested the effects of an invasive grass,Stenotaphrum secundatum, on an endangered coastal swamp forest community across an anthropogenic land use gradient. We also investigated the relative importance of landscape versus local community attributes in mediating the effects ofS. secundatuminvasion on the community.LocationFour hundred kilometres of the coastline of south‐eastern Australia.MethodsWe compared the diversity, composition and recruitment of resident vegetation in 32 invaded and 32 non‐invaded forest stands across an anthropogenic land use gradient. Local disturbance and environmental attributes of the forest (e.g. fire severity, litter abundance, canopy openness, vegetation structure) and adjacent landscape matrix (e.g. cover of forest, urban and agricultural land) were measured in detail at each site.ResultsInvasion was associated with substantial local extinctions of native plant species (i.e. 83% fewer species in invaded sites), altered community compositions and an 85% reduction in rates of woody plant recruitment. Local disturbances and environmental attributes of forest stands and adjacent landscape matrix were similar between invaded and native sites. Invasion caused a twofold increase in litter biomass, which we hypothesize is the primary mechanism by which the invader excludes native species. Landscape modification had no effect on the diversity of adjacent swamp forest. There was no interactive effect of landscape modification and invasion on the native community; species losses in response to invasion were high regardless of the condition of the adjacent matrix.Main conclusionsWe show that impacts of non‐native species are not dependent on landscape context and, unexpectedly, that invasion by an alien plant poses a greater threat to diversity of endangered swamp forests than modification of the adjacent matrix.

养分资源脉冲供给对几种微藻种间竞争的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 养分资源脉冲供给对几种微藻种间竞争的影响 DOI: 10.5846/stxb201306281795 作者: 作者单位: 西南林业大学 作者简介: 通讯作者: 中图分类号: 基金项目: 云南省教育厅科学研究基金理工类重点项目（2012Z069） The effect of resource pulse supply on interspecific competition of a few algal species Author: Affiliation: Southwest Forestry University 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:以淡水生态系统常见的5种微藻为研究对象，通过稳态条件下单一培养的方式获取各微藻在氮素或磷素缺乏条件下对应的生长特征参数和R*值，同时将5种微藻在养分资源脉冲供给的方式下进行混合培养，进而检测养分资源脉冲供给对几种微藻种间竞争的影响作用，并与基于稳态条件下所预测的微藻种间竞争结果进行比较。研究结果显示，在稳态条件下具有最小R*值的纤细角星鼓藻在与其它微藻的种间竞争过程中始终保持优势地位，而其余4种微藻在混合培养状态下的相对比重亦与其稳态条件下的R*值紧密相关。然而，资源脉冲供给条件下的竞争优势种纤细角星鼓藻能与其它种群数量较小的微藻共存。此外，在氮素和磷素的不同供给比例情况下，对应微藻群落的结构也会发生相应的变化。实验养分资源脉冲作用下多种微藻的共存现象与自然水体中的观测现象相一致，显示了资源脉冲可能是维持生物多样性水平的一个重要机制。 Abstract:Resource competition theory predicts that under equilibrium conditions, algal species with a minimal requirement for a specific limiting factor, or, in other words, algal species with the lowest R* value for that limiting factor would become the superior competitor and assert its dominance. In contrast, algal species with higher R* values would be out-competed by the superior competitor and thus undergo local extinction due to competitive exclusion. However, observations from natural aquatic ecosystems have repeated shown the fact that dominant algal species could coexist with algal species with small population size. Resource pulses of limiting nutrients might reduce competition intensity among algal species, and thus help solve this discrepancy between theoretical predictions and field observations. However, due to the existence of other confounding factors, such as regional species pool and spatial heterogeneity, our understanding of the effect of resource pulses on alleviating algal competition intensity and altering competitive outcome has been hindered. This study applied microcosms assembled with five algal species that are commonly found in natural freshwater ecosystem to test the effect of resource pulses on algal competitive outcome. Several growth parameters, including the half-saturation constant and the maximum specific growth rate, were determined using Monod model when individual algal species were grown as monocultures on a gradient of limiting nitrogen or phosphorous. Also, the R* value of each algal species was calculated to predict the competitive outcome when algal species were grown as polycultures under non-equilibrium conditions when limiting nutrient resources were supplied as fluctuation forms. To reduce confounding effect, spatial heterogeneity effect was reduced by shaking microcosms frequently, and regional species pool effect was minimized by assembling all microcosms with same algal species with equal abundance initially. Therefore, the non-equilibrium conditions in studied microcosms are directly caused by resource pulse supply, and the effect of resource pulses on algal competitive outcome could be strictly tested. Also, the observed results under non-equilibrium conditions could be compared with theoretical predictions based on equilibrium state assumption, and the validity of resource competition theory would be further assessed. The results showed that one green algal species, Staurastrum gracile, had the lowest R* value under either nitrogen- or phosphorous-limiting conditions. According to the resource competition theory under equilibrium settings, this algal species should be the superior competitor that would outcompete other algal species when grown together, ultimately resulting in the local extinction of other algal species due to competitive exclusion. In the present study, when resource pulses of limiting nutrients were supplied to simulate non-equilibrium conditions and when all five algal species were grown together, Staurastrum gracile remained the best competitor that was found in every microcosm with absolute dominance as predicted. However, this superior competitor coexisted with other algal species under resource pulse supply conditions. Clearly, resource pulses had lowered down algal competitive intensity and thus greatly reduced the possibility of competitive exclusion as long as resource pulse supply could persist. Additionally, for microcosms receiving different nitrogen to phosphorous ratios, corresponding community structure also varied in terms of species composition and identity. Our empirical result that multiple algal species could coexist with resource pulse supply is thus in line with many observational studies on natural aquatic ecosystem, indicating that resource pulse supply represents one of important mechanisms for the maintenance of biodiversity. 参考文献 相似文献 引证文献

Species abundance patterns of supratidal sandy grassland along China’s Shandong Peninsula and their responses to human disturbances

Aims Supratidal zones of sandy coastlines are occasionally influenced by storm surges, and they contain distinctive plant communities and some unique species. Our objective was to solve the questions: 1) how sandy coast plants are grouped into plant communities and 2) how such anthropogenic disturbances as tourist trampling and pond fishery affect such communities. Methods Three long sandy coasts were investigated for species composition and abundances, representing three typical states of human disturbances: nearly original state, tourist trampling and pond fishery. Each coast was investigated with 20 sampling lines of 50 m. Their species abundance patterns were compared and analyzed via four classic models of species abundance patterns: the neutral theoretical model, geometric series model, overlapping niche model and broken stick model. Important findings The neutral theoretical and geometric series models fit the species abundance patterns of the coastal plant communities well, and the broken stick and overlapping niche models were not reliable. The disturbances could decrease vegetation cover and cause local extinction of some rare species. Some evidence suggests that plant species on sandy coasts are variable, thus that stochastic establishment of plant individuals may well play a major role in community assembling, as the neutral theory describes. However, these species have very small differences in their traits and resource capturing, and their integrative effects are supposed to take many years to accumulate for ultimately causing evident differences, which can be fitted via the geometric series model at times. Local governments ought to control anthropogenic disturbances, so as to conserve the rare plants.

The richness–heterogeneity relationship differs between heterogeneity measures within and among habitats

The positive monotonic relationship between habitat heterogeneity and species richness is a cornerstone of ecology. Recently, it was suggested that this relationship should be unimodal rather than monotonic due to a tradeoff between environmental heterogeneity and population sizes, which increases local species extinctions at high heterogeneity levels. Here, we studied the richness–heterogeneity relationship for an avian community using two different environmental variables, foliage‐height diversity and cover type diversity. We analyzed the richness–heterogeneity within different habitat types (grasslands, savannas, or woodlands) and at the landscape scale. We found strong evidence that both positive and unimodal relationships exist at the landscape scale. Within habitats we found positive relationships between richness and heterogeneity in grasslands and woodlands, and unimodal relationships in savannas. We suggest that the length of the environmental heterogeneity gradient (which is affected by both spatial scale and the environmental variable being analyzed) affects the type of the richness–heterogeneity relationship. We conclude that the type of the relationship between species richness and environmental heterogeneity is non‐ubiquitous, and varies both within and among habitats and environmental variables.

Climate-induced range shifts and possible hybridisation consequences in insects.

Many ectotherms have altered their geographic ranges in response to rising global temperatures. Current range shifts will likely increase the sympatry and hybridisation between recently diverged species. Here we predict future sympatric distributions and risk of hybridisation in seven Mediterranean ischnurid damselfly species (I. elegans, I. fountaineae, I. genei, I. graellsii, I. pumilio, I. saharensis and I. senegalensis). We used a maximum entropy modelling technique to predict future potential distribution under four different Global Circulation Models and a realistic emissions scenario of climate change. We carried out a comprehensive data compilation of reproductive isolation (habitat, temporal, sexual, mechanical and gametic) between the seven studied species. Combining the potential distribution and data of reproductive isolation at different instances (habitat, temporal, sexual, mechanical and gametic), we infer the risk of hybridisation in these insects. Our findings showed that all but I. graellsii will decrease in distributional extent and all species except I. senegalensis are predicted to have northern range shifts. Models of potential distribution predicted an increase of the likely overlapping ranges for 12 species combinations, out of a total of 42 combinations, 10 of which currently overlap. Moreover, the lack of complete reproductive isolation and the patterns of hybridisation detected between closely related ischnurids, could lead to local extinctions of native species if the hybrids or the introgressed colonising species become more successful.