Gradient structure of forest vegetation in the central Washington cascades

Summary Forest vegetation located in three areas of the central Washington Cascades, arrayed along a gradient of increasing continentality and decreasing rainfall, were compared using ordination methods. Within each region, lower and upper elevation sites were analyzed separately and for each set of sites, trees and ground story vegetation were analyzed independently. Principal components analysis, reciprocal averaging, weighted averaging, and polar ordination were applied to each set. The characteristics of the data determined which method gave the most readily interpretable results, but RA and WA usually best ordered the stands along a complex, combined coenocline, while PO often decomposed the gradient into moisture and temperature components. PCA was of little use, even with relatively low beta diversity.Results are presented in the form of stand by species tables for each data set and the most appropriate two dimensional ordination. Both are correlated to the classification. A mosaic diagram for each region is synthesized from these analyses and habitat data. These diagrams indicate that community types occupy a smaller portion of the habitat as continentality increases.The ordination results were in close agreement with our earlier classification of these stands. The maritime (west) region contains stands of low richness and with relatively little coenocline differentiation. In contrast, the continental (east) region has high alpha and beta diversity. Species in the west tend to occupy a broad portion of the available habitat range, while species in the east do not. The analyses reveal that ordinations by different strata may produce similar stand sequences if both strata are responding directly to the same factors, but that the correspondence degenerates where the understory responds primarily to the nature of the canopy dominant species. Thus stand sequence correlations are highest in the lowland eastern region and lowest in the lowland western region.This study demonstrates that none of these metric ordination methods is fool-proof and that none should be used exclusively or in isolation. RA and PO are demonstrated to be useful general methods; WA gave results similar to those of RA. PCA never produced uniquely superior results. Analyses with too few species and moderate beta diversity often produce distortions as pronounced as those with many species and high beta diversity.Nomenclature follows Hitchcock & Conquist (1973).Funds provided by the Graduate School Research Fund, University of Washington and by grants GB-20963 and GB-36810X to the Coniferous Forest Biome, U.S.I.B.P. This is contribution # 318 to the Coniferous Forest Biome. M.F. Denton, R.S. Fleming, A.R. Kruckeberg, and R.H. Whittaker each made significant suggestions. We thank R.S. Fleming, S.G. Fleming, C. Brewer, B.C. Cannon, K.E. Wade, K. Loughney, and J.E. Canfield for their assistance with field work and data analysis.     

Genetic architecture of the marbled goby Pomatoschistus marmoratus (Perciformes, Gobiidae) in the Mediterranean Sea

The marbled goby Pomatoschistus marmoratus, a species inhabiting coastal Mediterranean lagoons, has been studied by measuring its mitochondrial DNA variation. This analysis revealed a Mediterranean west vs east split and, subsequently, an eastern differentiation among the Libyan-Tunisian Gulf, the Adriatic Sea and the Aegean Sea. The high cohesion between the samples collected in the vast area of western Mediterranean contrasts with the genetic mosaic of the more sub-structured eastern Mediterranean. This western homogeneity can not yet be fully explained even if a human-mediated migratory flow, due to a maritime traffic, has been posited. The pattern in the eastern basin revealed a genetic architecture possibly due to the non-migratory habit of the gobid. Within this perspective, the role of the Mediterranean lagoon habitat should be related to how much it amplifies the effects of historical (e.g. past sea-level changes) and environmental (e.g. present-day hydrographic regime) processes as regards the genetic structure of the inhabiting species.     

Forest complexity drives dung beetle assemblages along an edge-interior gradient in the southwest Amazon rainforest

1. The habitat heterogeneity hypothesis predicts that heterogeneous habitats may provide more niches and diverse ways of exploiting environmental resources, thereby allowing more species to coexist, persist and diversify. 2. We aimed to investigate how an edge-interior gradient related to forest complexity influences species composition, abundance and richness of dung beetles in the western Amazon rainforest. We expected dung beetle abundance and richness to increase along the forest edge-interior gradient, in accordance with the habitat heterogeneity hypothesis. We also expected strong changes in species composition driven by species turnover in the forest interior and nestedness along the forest edges. We sampled dung beetles using baited pitfall traps across an edge-interior gradient. We also assessed the variation in forest features along the edge-interior gradient to identify changes in forest complexity. 3. Both species richness and abundance of dung beetles increased along the forest edge-interior, following the gradient of forest complexity. The Sorensen dissimilarity of dung beetle assemblages was higher among sampling units placed near the forest edge, although neither turnover, nor nestedness was different between the extremes of the forest edge-interior gradient. There was a clear compositional change along the edge-interior gradient mostly driven by species turnover. Individual indicator value analysis revealed that species were strongly associated with the forest interior conditions. 4. The simplification of the Amazon rainforest near clearings causes compositional changes in dung beetle assemblages. These changes are characterised by species-poor and low-abundance assemblages and may impair dung beetle ecological functions and therefore forest recovery.     

POLLINATION OF ANGIOSPERMS IN CONTRASTING CONIFEROUS FORESTS

We studied the distributions of flower color, flower morphology, and putative pollinators in eight communities in the western Cascades of Washington and 14 communities in the eastern Cascades. These two forested regions differ in the proportions of species in each flower color and morphological type such that the eastern region is more complex. The putative pollinators of each species were determined from morphological and color properties of the flowers and from the recent, extensive literature. The floristic complement of the western region appears to be serviced by a collection of pollinators that is less diverse than that of the east. In each region there is a strong positive correlation between species richness and flower color diversity, floral morphology diversity, and putative pollinator diversity, respectively. These comparisons suggest the competition for pollinators has led to greater niche differentiation in the eastern regions and that this factor, combined with greater habitat complexity, results in the far greater species richness of the eastern region.     

三种嵩草群落中若干植物种的生态位宽度与重叠分析

本文利用Levins和Pianka公式,在多维生态因子梯度上测定了海北地区高寒草甸三种嵩草(Kobresia)群落中若干植物种的生态位宽度和生态位重叠。结果表明：三种嵩草群落中优势种群的生态位宽度都较大,其中小嵩草(K,pygmaea)在土壤水势、光照强度和坡向等三维因子上的生态位宽度分别是0.918、0.896和0.910;矮嵩草(K．humilis)和藏嵩草(K．tibetica)在土壤水势维上的生态位宽度分别是0.875和0.866;植物种如具有较大的生态位,则种间的生态位重叠亦较高;植物种对间若有相似的生物学—生态学特征,生态位重叠有降低的趋势;小嵩草和矮嵩草在三维上的重叠值分别是0.671、0.719和0.686;某些杂类草与优质牧草之间存有较大的重叠,这主要与长期过度放牧、优良牧草受到抑制以及生境退化有关。     

Red panda fine‐scale habitat selection along a Central Himalayan longitudinal gradient

Red panda Ailurus fulgens, an endangered habitat specialist, inhabits a narrow distribution range in bamboo abundance forests along mountain slopes in the Himalaya and Hengduan Mountains. However, their habitat use may be different in places with different longitudinal environmental gradients, climatic regimes, and microclimate. This study aimed to determine the habitat variables affecting red panda distribution across different longitudinal gradients through a multivariate analysis. We studied habitat selection patterns along the longitudinal gradient in Nepal's Himalaya which is grouped into the eastern, central, and western complexes. We collected data on red panda presence and habitat variables (e.g., tree richness, canopy cover, bamboo abundance, water availability, tree diameter, tree height) by surveys along transects throughout the species’ potential range. We used a multimodal inference approach with a generalized linear model to test the relative importance of environmental variables. Although the study showed that bamboo abundance had a major influence, habitat selection was different across longitudinal zones. Both canopy cover and species richness were unimportant in eastern Nepal, but their influence increased progressively toward the west. Conversely, tree height showed a decreasing influence on habitat selection from Eastern to Western Nepal. Red panda's habitat selection revealed in this study corresponds to the uneven distribution of vegetation assemblages and the dry climatic gradient along the eastern‐western Himalayas which could be related to a need to conserve energy and thermoregulate. This study has further highlighted the need of importance of bamboo conservation and site‐specific conservation planning to ensure long‐term red panda conservation.     

The latitudinal gradient of species diversity among North American grasshoppers (Acrididae) within a single habitat: a test of the spatial heterogeneity hypothesis

Abstract. The spatial heterogeneity hypothesis predicts a positive relationship between habitat complexity and species diversity: the greater the heterogeneity of a habitat, the greater the number of species in that habitat. On a regional scale, this hypothesis has been proposed to explain the increases in species diversity from the poles to the tropics: the tropics are more diverse because they contain more habitats. On the local scale, the spatial heterogeneity hypothesis suggests that the tropics are more diverse because they contain more microhabitats. The positive relationship between habitat heterogeneity and species diversity, on the local scale, is well documented. In this paper, we test whether habitat heterogeneity on the local scale can explain the latitudinal gradient of species diversity on the regional scale. We determined the latitudinal gradient of species diversity of 305 species of North American grasshoppers using published distribution maps. We compared the slope of this multihabitat (regional-scale) gradient with the slope of a within-habitat (local-scale) gradient in the prairie grasslands. Our results show no significant difference between the slopes at the two scales. We tested the generality of our results by comparing multi- and within-habitat latitudinal gradients of species diversity for ants, scorpions and mammals using data from the literature. These results are in accordance with those from grasshoppers. We can therefore reject the local-scale spatial heterogeneity hypothesis as a mechanism explaining the regional-scale latitudinal gradient of species diversity. We discuss alternative mechanisms that produce this gradient.     

Pointer years in tree-ring width and earlywood-vessel area time series of Quercus robur—Relation with climate factors near its northern distribution limit

For a long time, radial growth of pedunculate oak (Quercus robur) in relation to environmental factors has been studied in Central Europe. However, there is insufficient information on oak growth in the Baltic region. Climate–growth interactions have been mostly investigated by correlation/response analysis between ring width and climatic factors. Other wood anatomical proxies, and also pointer year analysis, which focuses on weather extremes, can be sources of additional information. Wood samples were taken from 40 sites across Latvia. Tree-ring width (TRW) and mean area of earlywood vessels (EVA) were measured. To assess differences in wood formation among sites, a PCA was performed based on pointer year series of TRW and EVA per site. The relation with climate was assessed by Pearson's correlation. Patterns of wood formation differed along west/east gradient, so that two regions (western and eastern) of Latvia were distinguished. Pointer year values were higher for TRW than for EVA and higher in the eastern than in the western region. However, the pointer year values were moderate, suggesting that there was no strict limiting factor for their formation. Pointer years of EVA were strongly related with temperature during the dormant period in both regions; June precipitation had a significant effect in the eastern region. Pointer years of TRW were correlated with spring and summer temperature in the western region and with February temperature in the eastern region; precipitation in autumn showed a negative effect. These differences can be explained by a gradient from maritime to continental climate, leading to shifts in the growth limiting factors. Extremely cold winters resulted in most of the negative pointer years of TRW and EVA.     

Taxonomic diversity of the terrestrial bird and mammal fauna in temperate and boreal biomes of the northern hemisphere

Abstract. Using comprehensive range information of northern Hemisphere birds and mammals, we assessed the taxonomic diversity of these two groups in four different regions: Europe, east Asia, and western and eastern North America. East Asia is the richest region in the number of bird and mammal species, genera, families and orders, except that mammal species richness is highest in western North America. Eastern North America is taxonomically the poorest region, but when only forest-associated taxa were considered in mammals taxonomic diversity is equally low in Europe and in eastern North America, and in birds, Europe is the least diverse region. Patterns in endemic taxa follow overall taxonomic diversity. The proportion of shared taxa between regions is higher among boreal species and genera than among all taxa. A comparison with tree species diversity underpins the role of east Asia as the most diverse of all northern biota. Largely congruent patterns at different taxonomic levels emphasizes the role of historical processes, such as differential extinction rate in response to paleoenvironmental fluctuations, in producing these patterns, but we stress the need for more research on the coevolution of species diversity and habitat diversity.     

Annual temperature variation influences the vulnerability of montane bird communities to land‐use change

Understanding how and why species respond to land‐use change is one of the central challenges in conservation biology, yet the causes of variation in the responses of species to land‐use change remain unclear. We tested whether adaptation to different abiotic environments influenced the vulnerability of bird communities to agricultural expansion in the Himalayan mountain range, which exhibits a strong east–west gradient in annual temperature variation. We did so by surveying bird communities in forest and agriculture at opposite ends of that gradient. We contrasted metrics of species richness, diversity, community composition and forest dependency across land‐use types and regions, and tested whether species’ thermal sensitivity influenced their response to the replacement of forest with agriculture. Agricultural land in the relatively aseasonal east harboured significantly fewer bird species than did forests, a pattern that is starkly reversed in the highly seasonal west. For species common to both regions, eastern populations used forest ~35% more than did western populations. While western species were less constrained by temperature than eastern species, western species with narrow thermal tolerances were also more forest dependent. Selection across a stark environmental gradient on a common species pool appears to have altered the vulnerability of Himalayan birds to forest loss, with communities in the relatively aseasonal east much more sensitive to forest conversion than those in the west. Adaptation to local environmental conditions appears to mediate species’ responses to land use change, with thermal specialists more vulnerable to forest loss than species with greater thermal tolerances. Species’ responses to global change may differ predictably along abiotic gradients even within a single region or biodiversity hotspot, and such variation must be addressed in conservation planning.     

Regional variation in abundance and response to fire by Henslow's Sparrows in Louisiana

ABSTRACT Wintering Henslow's Sparrows (Ammodramus henslowii) are generally associated with open grasslands. Results of small‐scale, regionally specific studies have not revealed larger‐scale abundance patterns, but they have shown regional differences in habitat selection. Our objective was to quantify Henslow's Sparrow abundance and vegetation associations across Louisiana, an area that includes multiple types of grassland habitats. Bird densities in longleaf pine savannas of eastern and western Louisiana were over 1.5 times higher than in northern prairies and over 13 times higher than at a site in southwestern Louisiana. The responses of Henslow's Sparrows to fire differed between eastern and western savannas, with abundance increasing three fold over the first 3 yrs after fire in the west, and decreasing three fold over that interval in the east. In both areas, habitat became unsuitable by about 5 yrs after fire, probably due to woody encroachment and loss of herbaceous plants. For sites that contained Henslow's Sparrows at least once during our study, habitat modeling revealed that neither vegetation structure nor plant species composition was important in predicting the occurrence of Henslow's Sparrows within sites or abundance among sites throughout the state, perhaps due to the variety of habitats sampled. Our results suggest that longleaf pine savannas are the most important grasslands for wintering Henslow's Sparrows in Louisiana and that overwintering habitat is probably selected based on regionally specific vegetation features. Optimal fire intervals may vary regionally, particularly between mesic flatwoods savannas and drier upland savannas, perhaps due to different rates of biomass accumulation. Management for Henslow's Sparrows should be based on region‐specific studies, recognizing that appropriate fire regimes may vary among regions.     

Habitat heterogeneity, richness and structure of assemblages of dung beetles (Scarabaeidae: Scarabaeinae) in areas of cerrado in the Chapada dos Parecis, Mato Grosso state, Brazil

Ecological theory of habitat heterogeneity and limited niche-similarity assumes that more heterogeneous environments provide a greater amount and diversity of resources than simple environments, resulting in a greater diversity of species. This study aimed to evaluate the effect of the habitat heterogeneity on the richness of dung beetles and to examine the spatial patterns of assemblage structure in relation to patterns of habitat heterogeneity. Dung beetles were collected using pitfall traps without bait in 30 points distributed in an area of cerrado sensu lato, in the region of Tangará da Serra, MT, Brazil, including areas of cerrado sensu stricto, campo sujo, cerrad?o and gallery forest. A total of 1,291 dung beetles were collected, distributed in 16 genera and 29 species. Overall habitat heterogeneity exerted a negative effect on patterns of dung beetles richness. Higher levels of species richness were observed in areas of cerrado campo sujo, while the areas of gallery forest were the most species poor. Regarding assembly structure, it was found that the dung beetles were separated into two major groups, one formed by the presence of specialized species in forest areas and other composed of species that occurred predominantly in cerrado. In conclusion, it was found that habitat complexity influenced the distribution of dung beetles, but the level of turnover in species composition along the heterogeneity gradient was relatively weak.     

The influence of substrate type on macroinvertebrate assemblages within agricultural drainage ditches

Artificial drainage ditches are common features in lowland agricultural catchments that support a wide range of ecosystem services at the landscape scale. Current paradigms in river management suggest activities that increase habitat heterogeneity and complexity resulting in more diverse floral and faunal assemblages; however, it is not known if the same principles apply to artificial drainage ditch systems. We examined the effects of four artificial substrates, representing increasing habitat complexity and heterogeneity (bricks, gravel, netting and vegetation), on macroinvertebrate community structure within artificial drainage ditches. Each substrate type supported a distinct macroinvertebrate community highlighting the importance of habitat heterogeneity in maintaining macroinvertebrate assemblages. Each substrate type also displayed differing degrees of community heterogeneity, with gravel communities being most variable and artificial vegetation being the least. In addition, several macroinvertebrate diversity metrics increased along the gradient of artificial substrate complexity, although these differences were not statistically significant. We conclude that habitat management practices that increase habitat complexity are likely to enhance macroinvertebrate community heterogeneity within artificial drainage channels regardless of previous management activities.

     

Diffusion of nuclear and mitochondrial genes across a zone of secondary contact in the maritime shrew, Sorex maritimensis: implications for the conservation of a Canadian endemic mammal

The maritime shrew, Sorex maritimensis, is a Canadian endemic species with a limited distribution in two provinces in eastern Canada. Phylogeographic analysis of mitochondrial DNA control region and cytochrome b sequences revealed two clades, one found in New Brunswick and the other primarily in Nova Scotia, Canada. We propose that these clades have come back into secondary contact following the Wisconsin glaciation via wetlands on the narrow Isthmus of Chigneto that connects these provinces. Despite evidence of an historic separation of maritime shrew subpopulations in Nova Scotia and New Brunswick, we conclude that shrews in these two regions should be considered a single evolutionary significant unit but separate, semi-isolated management units that should be recognized as such for conservation purposes. The susceptibility of this stenotopic species with limited dispersal capabilities raises concerns about its long-term persistence if climate-change induced habitat fragmentation increases. Maintenance of contiguous wetland habitats is needed to ensure connectivity and gene flow among populations of the maritime shrew.     

Vegetation responses along environmental gradients on the Ordos plateau, China

The Ordos plateau is a unique ecotone and is a focal region for the campaign to reduce or reverse desertification in China. This paper explores the relationship between vegetation and environmental gradients on the Ordos plateau based on a field survey of species distribution, vegetation distribution patterns, plant community structure, ecophysiological properties, and soil water content along an environmental gradient. The vegetation on the Ordos plateau may be divided into three types from east to west: steppe (eastern part), desert steppe (middle part) and steppe desert (western part). From east to west, precipitation declines significantly (from 400 mm to 150 mm). The spatial distribution pattern of vegetation at different sites was random. The density of shrub islands decreased from east to west, and their height and diameter were negatively correlated with precipitation. From east to west, the transpiration rate increased as temperature increased. Stomatal conductance was positively correlated with percentage of sunshine hours and negatively correlated with temperature. Water-use efficiency was positively correlated with average annual precipitation but negatively correlated with increasing percentage of sunshine hours. The results suggest that for effective revegetation, highly drought-tolerant species, such as Caragana tibetica and C. stenophylla, should be used and a lower percentage of vegetation cover expected (30–40%) in the western half of the Ordos plateau. In the eastern half, moderately drought-tolerant species, such as Artemisia ordosica and C. korshinskii, could be used and a higher percentage vegetation cover expected (40–50%).     

Cattle grazing in CRP grasslands during the nesting season: effects on avian abundance and diversity

The Conservation Reserve Program (CRP) is a primary tool for restoring grassland in the United States, in part as wildlife habitat, which has benefited declining grassland bird populations. Among potential mid-contract management practices used to maintain early-successional CRP grasslands, cattle grazing had been prohibited and is currently disincentivized during the primary nesting season for birds (much of the growing season), despite the important role that large herbivores historically played in structuring grassland ecosystems. Conservative grazing of CRP grasslands could increase spatial heterogeneity in vegetation structure and plant diversity, potentially supporting higher densities of some grassland bird species and higher bird diversity. Our objective was to determine the effect of experimental cattle grazing on species-specific relative abundance and occupancy, species diversity, and community dissimilarity of grassland birds on CRP grasslands across the longitudinal extent of Kansas, USA (a 63.5-cm precipitation gradient) during the 2017–2019 avian breeding seasons. Fifty-three of 108 fields were grazed by cattle during the growing seasons of 2017 and 2018 and all fields were rested from grazing in 2019. For all analyses, we examined separate model sets for semiarid western versus more mesic eastern Kansas. Using data from line transect surveys, we modeled relative abundances of 5 songbird species: grasshopper sparrow (Ammodramus savannarum), dickcissel (Spiza americana), eastern meadowlark (Sturnella magna), western meadowlark (Sturnella neglecta), and brown-headed cowbird (Molothrus ater). Grazing had delayed yet positive effects on abundances of grasshopper sparrow in western Kansas, and eastern meadowlark in eastern Kansas, but negative effects on dickcissel abundance in western Kansas and especially on burned fields in eastern Kansas. Somewhat counterintuitively, brown-headed cowbirds in western Kansas were more abundant on ungrazed versus grazed fields in the years after grazing began. In addition, we modeled multi-season occupancy of 3 gamebird species (ring-necked pheasant [Phasianus colcicus], northern bobwhite [Colinus virginianus], mourning dove [Zenaida macroura]) and Henslow's sparrow (Centronyx henslowii); grazing did not affect occupancy of these species. In eastern Kansas, species diversity was highest in grazed, unburned fields. In western Kansas, bird communities in grazed and ungrazed fields were dissimilar, as determined from multivariate analysis. Though regionally variable, conservative stocking of cattle on CRP grasslands during the nesting season as a mid-contract management tool might increase bird species diversity by restructuring habitat that accommodates a greater variety of species and decreasing abundances of species associated with taller, denser stands of vegetation.     

The influence of agricultural land-use intensity on bryophyte species richness

This study is a quantitative approach to the estimation of bryophyte species richness in relation to land-use intensity at three spatial scales in highly cultivated areas. A total of 460 randomly selected habitats and their various substrates within 29 study sites were investigated with regard to their land-use intensity and their bryophyte species richness in an agricultural region of eastern Austria. On bare soils (substrate-scale), low but regular disturbance increases bryophyte diversity in comparison to lower land-use intensity. However, more frequent disturbance (e.g. ploughing more than two times a year) dramatically reduces species richness at these sites, with more than 50% of these sites showing no bryophytes. The production of reproductive units (sporophytes and vegetative units) is highest at an intermediate disturbance regime. On the habitat, as well as on the landscape-scale, there is a significant increase in total bryophyte species number as well as in the number of threatened species with decreasing land-use intensity. This is mainly due to habitat and structural diversity, which increases with decreasing land-use intensity. There are significant correlations between landuse intensity, structural diversity and species richness at the habitat as well as on the landscape scale.     

The brighter side of climate change: How local oceanography amplified a lobster boom in the Gulf of Maine

Ocean warming can drive poleward shifts of commercially important species with potentially significant economic impacts. Nowhere are those impacts greater than in the Gulf of Maine where North America's most valuable marine species, the American lobster (Homarus americanus Milne Edwards), has thrived for decades. However, there are growing concerns that regional maritime economies will suffer as monitored shallow water young‐of‐year lobsters decline and landings shift to the northeast. We examine how the interplay of ocean warming, tidal mixing, and larval behavior results in a brighter side of climate change. Since the 1980s lobster stocks have increased fivefold. We suggest that this increase resulted from a complex interplay between lobster larvae settlement behavior, climate change, and local oceanographic conditions. Specifically, postlarval sounding behavior is confined to a thermal envelope above 12°C and below 20°C. Summer thermally stratified surface waters in southwestern regions have historically been well within the settlement thermal envelope. Although surface layers are warming fastest in this region, the steep depth‐wise temperature gradient caused thermally suitable areas for larval settlement to expand only modestly. This contrasts with the northeast where strong tidal mixing prevents thermal stratification and recent ocean warming has made an expansive area of seabed more favorable for larval settlement. Recent declines in lobster settlement densities observed at shallow monitoring sites correlate with the expanded area of thermally suitable habitat associated with warmer summers. This leads us to hypothesize that the expanded area of suitable habitat may help explain strong lobster population increases in this region over the last decade and offset potential future declines. It also suggests that the fate of fisheries in a changing climate requires understanding local interaction between life stage‐specific biological thresholds and finer scale oceanographic processes.     

石鸡繁殖期栖息地的特征

2005年4~7月,对甘肃西部(东阿尔金山地区和西祁连山地区)和东南部(西秦岭地区)的石鸡(Alectoris chukar)种群栖息地选择进行了调查。主成分分析表明,草本密度、地面异质性和草本盖度是栖息地选择的主要影响因子;方差分析表明,甘肃西部(东阿尔金山和西祁连山)的石鸡种群在海拔、坡度和小石块数目的选择上差异显著。甘肃西部和东南部的石鸡种群在栖息地选择上存在显著的地理变异,西秦岭种群选择海拔低、坡度大、坡位偏上、草本密度低和草本高度高的栖息地。栖息地选择差异可能是在不同的选择压力下,经过长期的隔离进化形成。     

Genetic variability and the effect of habitat fragmentation in spotted suslik Spermophilus suslicus populations from two different regions

Endangered species worldwide exist in remnant populations, often within fragmented landscapes. Although assessment of genetic diversity in fragmented habitats is very important for conservation purposes, it is usually impossible to evaluate the amount of diversity that has actually been lost. Here, we compared population structure and levels of genetic diversity within populations of spotted suslik Spermophilus suslicus, inhabiting two different parts of the species range characterized by different levels of habitat connectivity. We used microsatellites to analyze 10 critically endangered populations located at the western part of the range, where suslik habitat have been severely devastated due to agriculture industrialization. Their genetic composition was compared with four populations from the eastern part of the range where the species still occupies habitat with reasonable levels of connectivity. In the western region, we detected extreme population structure (F _ST = 0.20) and levels of genetic diversity (Allelic richness ranged from 1.45 to 3.07) characteristic for highly endangered populations. Alternatively, in the eastern region we found significantly higher allelic richness (from 5.09 to 5.81) and insignificant population structure (F _ST = 0.03). As we identified a strong correlation between genetic and geographic distance and a lack of private alleles in the western region, we conclude that extreme population structure and lower genetic diversity is due to recent habitat loss. Results from this study provide guidelines for conservation and management of this highly endangered species.