How general are global trends in biotic homogenization? Floristic tracking in Chile,South America

Aim   To quantify the occurrence of floristic change in the vascular flora of Chile. We test whether continental areas have experienced floristic modification leading to either homogenization, differentiation or tracking.
Location   Continental Chile.
Methods   On the basis of the geographical distribution of native (1806 species) and naturalized plants (552 species) in continental Chile, we quantified change between two floristic stages: (1) pre-European flora, including native extant and extinct species; and (2) current flora, including native and naturalized species, but excluding extinct plants. We compared changes in compositional similarity (calculated by Jaccard's index, Δ J ) between pairs of regions, and similarity decay with respect to geographical distance. Additionally, by means of Whittaker's index, we examined species turnover, distinguishing between native and naturalized plants.
Results   Between floristic stages (pre-European vs. current flora) no significant changes in floristic similarity were noted at national or regional scales. Similarity decay showed no statistical differences between pre-European and current flora. Analysing patterns of geographical turnover, we found that species turnover of naturalized plants over their geographical range is similar to that of native plants.
Conclusions   The composition of the continental flora of Chile does not show significant modifications in similarity patterns after considering naturalized species, thus indicating floristic tracking. The causes of this phenomenon may be related to the current geographical distribution of naturalized plants, which closely parallels that of native plants. Our results differ from those obtained in Northern Hemisphere continents, thus indicating that trends of biotic change may differ between hemispheres.     

Distribution patterns of the small mammals (Insectivora and Rodentia) in a transitional zone between the Eurosiberian and the Mediterranean regions

To determine, by means of quantitative analyses, the distribution patterns of the insectivores and rodents in Catalonia using physiographical regions as Operative Geographical Units (OGUs). Catalonia (north‐eastern Iberian Peninsula). Based on the presence/absence of twenty‐five small mammals in thirteen physiographical regions, which were used as OGUs, the following aspects were studied: (a) identification of biotic boundaries; (b) determination of chorological association of species; (c) climatic characterization of the biotic regions and the chorotypes. Groups of biotic regions and species were established, and their statistical significance was tested. The possible effect of several climatic factors on these groupings was studied using discriminant analyses. A significant biotic boundary was found to separate the central and eastern Pyrenees from the remaining physiographical regions. The climatic variables that defined this boundary were related to the severity and the availability of environmental energy. Four chorotypes were identified. One chorotype was constituted by Pyrenean or Pre‐Pyrenean species, an association determined by their mid‐European requirements; another chorotype was formed by Eurosiberian species, but showed a variable degree of tolerance to Mediterranean conditions; a third chorotype included species with a wide distribution that are Mediterranean, anthropic, generalist or have very specific habitats; and finally the fourth chorotype was constituted by a strictly Mediterranean species. The climatic factors that accounted for the distribution of these chorotypes were the mean July temperature and the mean annual precipitation. We conclude that the axial zone of the Pyrenees, except the coastal portion, determines two biotic regions in Catalonia. As for the classification of species, using quantitative techniques for the first time, we offer a new biogeographicalal configuration for the small mammals in this temperate‐Mediterranean transition.     

Taxonomic homogenization of woodland plant communities over 70 years

Taxonomic homogenization (TH) is the increasing similarity of the species composition of ecological communities over time. Such homogenization represents a form of biodiversity loss and can result from local species turnover. Evidence for TH is limited, reflecting a lack of suitable historical datasets, and previous analyses have generated contrasting conclusions. We present an analysis of woodland patches across a southern English county (Dorset) in which we quantified 70 years of change in the composition of vascular plant communities. We tested the hypotheses that over this time patches decreased in species richness, homogenized, or shifted towards novel communities. Although mean species richness at the patch scale did not change, we found increased similarity in species composition among woodlands over time. We concluded that the woodlands have undergone TH without experiencing declines in local diversity or shifts towards novel communities. Analysis of species characteristics suggested that these changes were not driven by non-native species invasions or climate change, but instead reflected reorganization of the native plant communities in response to eutrophication and increasingly shaded conditions. These analyses provide, to our knowledge, the first direct evidence of TH in the UK and highlight the potential importance of this phenomenon as a contributor to biodiversity loss.     

浙江钱江源-百山祖国家公园庆元片区叶附生苔多样性及其时空变化

叶附生苔是苔藓植物中特有率最高的一个类群, 特殊的生理生态特性使其对气候变化及人为干扰极为敏感, 成为苔藓植物中最需要关注和保护的一个类群。为了解叶附生苔物种多样性及组成随时间变化的规律, 我们以钱江源-百山祖国家公园庆元片区为研究对象, 针对该区域内有叶附生苔历史调查记录且物种较为丰富的3个保护点(百山祖、十九源、五岭坑)进行叶附生苔类植物调查, 比较并分析这3个保护点叶附生苔类植物的物种丰富度、分类β多样性及功能β多样性在时间(1990-2020年)和空间两个维度上的变化。结果表明, 该片区共有叶附生苔类植物4科10属31种。与历史数据相比, 本次调查新增叶附生苔7种, 但有14种未采集到。在所调查的3个保护点中, 仅五岭坑的物种数上升, 百山祖和十九源的物种数均下降。30年来, 各保护点的叶附生苔总的功能丰富度都呈下降趋势, 百山祖的物种分类β多样性及功能β多样性在3个保护点中最高; 物种分类β多样性主要是由周转组分构成, 相反, 功能β多样性主要是由嵌套组分构成。与30年前相比, 3个保护点之间的物种分类β多样性及功能β多样性均呈上升趋势, 表明物种异质化现象有增加的趋势。鉴于叶附生苔物种组成随时间的明显变化, 以及不同地区之间物种组成差异随时间的加剧情况, 建议在我国其他叶附生苔分布中心开展类似的调查和比较研究, 以期及时更新物种名录, 同时结合国家公园的建设契机, 加强对叶附生苔不同分布点之间的联通保护。     

Do biotic interactions modulate ecosystem functioning along stress gradients? Insights from semi-arid plant and biological soil crust communities

Climate change will exacerbate the degree of abiotic stress experienced by semi-arid ecosystems. While abiotic stress profoundly affects biotic interactions, their potential role as modulators of ecosystem responses to climate change is largely unknown. Using plants and biological soil crusts, we tested the relative importance of facilitative–competitive interactions and other community attributes (cover, species richness and species evenness) as drivers of ecosystem functioning along stress gradients in semi-arid Mediterranean ecosystems. Biotic interactions shifted from facilitation to competition along stress gradients driven by water availability and temperature. These changes were, however, dependent on the spatial scale and the community considered. We found little evidence to suggest that biotic interactions are a major direct influence upon indicators of ecosystem functioning (soil respiration, organic carbon, water-holding capacity, compaction and the activity of enzymes related to the carbon, nitrogen and phosphorus cycles) along stress gradients. However, attributes such as cover and species richness showed a direct effect on ecosystem functioning. Our results do not agree with predictions emphasizing that the importance of plant–plant interactions will be increased under climate change in dry environments, and indicate that reductions in the cover of plant and biological soil crust communities will negatively impact ecosystems under future climatic conditions.     

Ribbing patterns in the brachiopod Diceromyonia

Ribbing patterns in two collections of the Ordovician brachiopod Diceromyonia from central North America are compared using the system invented by Bancroft (1928; Manchester Memoirs 72 ) for naming ribs. Simple and nearly symmetric arrangements of frequently occurring branches characterize both collections, with much of the complexity evident in larger valves due to irregular occurrence of low-frequency branches on either side of major ribs. Examination of median sectors reveals little support for Bancroft's derivation of the rhipidomelloid midrib from isorthoid forms, and an alternative non-evolutionary interpretation is proposed in which median patterns appear as predictable outcomes of a simple space-filling process. The approximately 2500 ribs identified in this study are treated as a population in their own right: orderly patterns which emerge are not inferred but are simple summaries of complete counts, obtained by hand. This approach is quick and painless compared to methods using order relations to assess ribbing differences in dalmanellid brachiopods. For this reason, it may encourage systematic study of ribbing patterns among these taxa and lead ultimately to better understanding of the utility of ribbing in their taxonomy.     

Combined effects of climate and biotic interactions on the elevational range of a phytophagous insect

1. The ranges of many species have expanded in cool regions but contracted at warm margins in response to recent climate warming, but the mechanisms behind such changes remain unclear. Particular debate concerns the roles of direct climatic limitation vs. the effects of interacting species in explaining the location of low latitude or low elevation range margins. 2. The mountains of the Sierra de Guadarrama (central Spain) include both cool and warm range margins for the black-veined white butterfly, Aporia crataegi, which has disappeared from low elevations since the 1970s without colonizing the highest elevations. 3. We found that the current upper elevation limit to A. crataegi's distribution coincided closely with that of its host plants, but that the species was absent from elevations below 900 m, even where host plants were present. The density of A. crataegi per host plant increased with elevation, but overall abundance of the species declined at high elevations where host plants were rare. 4. The flight period of A. crataegi was later at higher elevations, meaning that butterflies in higher populations flew at hotter times of year; nevertheless, daytime temperatures for the month of peak flight decreased by 6.2 degrees C per 1 km increase in elevation. 5. At higher elevations A. crataegi eggs were laid on the south side of host plants (expected to correspond to hotter microclimates), whereas at lower sites the (cooler) north side of plants was selected. Field transplant experiments showed that egg survival increased with elevation. 6. Climatic limitation is the most likely explanation for the low elevation range margin of A. crataegi, whereas the absence of host plants from high elevations sets the upper limit. This contrasts with the frequent assumption that biotic interactions typically determine warm range margins, and thermal limitation cool margins. 7. Studies that have modelled distribution changes in response to climate change may have underestimated declines for many specialist species, because range contractions will be exacerbated by mismatch between the future distribution of suitable climate space and the availability of resources such as host plants.     

Paleobiogeographic significance of a new ozawainelloid fusulinid Pseudoacutella partoazari n. sp., from the Asselian (lowermost Permian) of Gaduk (Central Alborz,Iran)

The uppermost Carboniferous–Lower Permian Dorud Group that crops out at the Gaduk section of Central Alborz is over 44 m thick and includes thick sequences of conglomerate, quartzarenite, calcareous sandstone, oncolitic fusulinid limestone, sandy limestone, sandstone and shale. The Toyeh, Emarat and Shah Zeid formations of this Group were dated as latest Gzhelian to Early Sakmarian. A review of the Asselian fusulinids and smaller foraminifers of Iran emphasizes (1) how the foraminiferal assemblages of Alborz and central Iran differ; (2) why non-Pseudofusulina cannot be a nomen substitutum to Pseudofusulina (even if this latter was often misinterpreted in the Tethyan regions). A new smaller fusulinid Pseudoacutella partoazari n. sp. is described from the Emarat Formation (Asselian) that crops out in the Gaduk area. The palaeobiogeographic significance of Pseudoacutella is discussed, because this genus, which was cosmopolitan from Late Bashkirian to Moscovian, became rare in the Upper Pennsylvanian of the USA and the Carnic Alps, and then, very rare in Lower Permian of Texas, Arizona and Iran.     

A soft-bodied lophophorate from the Silurian of England

Soft-bodied taxa comprise an important component of the extant lophophorate fauna, but convincing fossils of soft-bodied lophophorates are extremely rare. A small fossil lophophorate, attached to a brachiopod dorsal valve, is described from the Silurian (Wenlock Series) Herefordshire Lagerstätte of England. This unmineralized organism was bilaterally symmetrical and comprised a subconical body attached basally to the host and partially enclosed by a broad ‘hood’; the body bore a small, coiled lophophore. Where the hood attached laterally, there is a series of transverse ridges and furrows. The affinities of this organism probably lie with Brachiopoda; the hood is interpreted as the homologue of a dorsal valve/mantle lobe, and the attachment as the homologue of the ventral valve and/or pedicle. The ridges are arranged in a manner that suggests constructional serial repetition, indicating that they are unlikely to represent mantle canals. Extant brachiopods are not serially structured, but morphological and molecular evidence suggests that their ancestors were. The new organism may belong to the brachiopod stem group, and might also represent a significant element of the Palaeozoic lophophorate fauna.     

Fish introductions reveal the temperature dependence of species interactions

A major area of current research is to understand how climate change will impact species interactions and ultimately biodiversity. A variety of environmental conditions are rapidly changing owing to climate warming, and these conditions often affect both the strength and outcome of species interactions. We used fish distributions and replicated fish introductions to investigate environmental conditions influencing the coexistence of two fishes in Swedish lakes: brown trout (Salmo trutta) and pike (Esox lucius). A logistic regression model of brown trout and pike coexistence showed that these species coexist in large lakes (more than 4.5 km²), but not in small, warm lakes (annual air temperature more than 0.9–1.5°C). We then explored how climate change will alter coexistence by substituting climate scenarios for 2091–2100 into our model. The model predicts that brown trout will be extirpated from approximately half of the lakes where they presently coexist with pike and from nearly all 9100 lakes where pike are predicted to invade. Context dependency was critical for understanding pike–brown trout interactions, and, given the widespread occurrence of context-dependent species interactions, this aspect will probably be critical for accurately predicting climate impacts on biodiversity.