Breeding success at the range margin of a desert species: implications for a climate‐induced elevational shift

If the breeding range of a species is limited by biotic or abiotic environmental factors that depress breeding success at the range margin, then range expansion is expected when those limiting factors are alleviated. Over a three‐year period, we measured breeding success of a desert species, black‐throated sparrow Amphispiza bilineata, along a steep elevation gradient between the Peninsular Mountains and Colorado Desert (San Diego County, California) that is undergoing a warming trend. We compared breeding success at geographically marginal locations (higher‐elevation chaparral sites) to more central locations (lower‐elevation desert scrub sites) only a short distance apart. Breeding success was measured at the nest level, territory level, and population level. At each level measured, breeding success tended to be greater at higher‐elevation chaparral sites at the distribution margin compared to lower‐elevation sites where the bird was more common. Black‐throated sparrows had 100% reproductive failure at lower‐elevation sites during the two driest years of our study (2006–2007), but did relatively well at higher‐elevation sites. Only in a wetter year (2008) was breeding success improved at lower‐elevation sites. Surprisingly, there was no evidence of an upward elevational shift in distribution over a 26‐year period despite a clear warming trend and drier conditions. Greater territory density at lower‐elevation sites with reproductive failure during dry years suggests the possibility of an ecological trap in this system, which could prevent or delay climate‐induced range shifts. A common presumption has been that desert species will undergo relatively mild negative impacts due to a warming climate, but it is possible that some desert species are already at or near their temperature and aridity tolerance limits within their current range and shifts may not always be possible.     

岷山黑熊生境选择的初步分析

1998 年3 月末至9 月, 作者在岷山山系对黑熊的生境选择进行了研究。野外工作中共设置了40 个20 ×20 m²样方和15 个生态因子, 以此为基准进行了定量分析。黑熊生境喜好程度分析表明, 黑熊喜欢选择向阳、坡度较大、避风性适中、郁闭度在30 %～50 %之间的山嵴或山坡面, 选择乔木密度和灌木密度适中、倒木密度和树桩密度较小的生境, 其他如乔木距离、灌木距离、倒木距离和树桩距离以适中为准。主成分分析表明,影响黑熊生境选择的主要因子有5 种, 依次为: 食物丰富度因子(包括乔木密度、灌木密度、乔木距离和灌木距离) 、干扰因子(包括倒木密度、树桩密度、倒木距离和树桩距离) 、地形因子(包括郁闭度、地理性和坡位) 、气候因子(包括避风性和坡向) 和海拔因子。其最适生境状况为: 乔木密度为1 226～1 625根/ hm², 灌木密度为1 425～1 976 根/ hm², 倒木密度为120～240 根/ hm² , 树桩密度为110～230 根/ hm² , 郁闭度为3519 %～4315 % , 地理性为0.6～0.7 (山坡面) , 坡位为0.5～0.7 (中坡位) , 避风性为0.4～0.7 (适中) , 坡向为49.8°～153°(东坡) , 海拔高度为1 993～2 276 m (阔叶林和针阔混交林带) 。     

Dry Season Den Use by Pygmy Spotted Skunk (Spilogale pygmaea) in a Tropical Deciduous Forest of Mexico

Dry season den use by the pygmy spotted skunk Spilogale pygmaea , an endemic and threatened species of western Mexico, was evaluated at the micro and macrohabitat level, in the tropical deciduous forest of Chamela, Jalisco, Mexico. During the dry seasons of 1997, 1998, and 2000, 79 skunk den sites (29 for females and 50 males) were located using Radiotelemetry. Dens were underground excavations with one to five access points, located mostly on open ground or under live or dead trees. Skunks exhibited a continued reuse of dens but evidence of simultaneous occupation by two or more skunks was not found. Microhabitat den-site analysis showed that skunks showed flexibility and individual variation in usage of the microhabitat surrounding den sites inside the forest. Macrohabitat den-site analysis showed that skunks were not selecting either tropical deciduous or tropical semideciduous forest; however, no dens were located outside the forest in transformed habitats, strengthening the hypothesis of the association of this species with the tropical deciduous forests on the Pacific coast of Mexico. The current deforestation rates of the tropical deciduous forest in the coast of Jalisco could be reducing the potential den sites for pygmy spotted skunks and exposing them to adverse environmental conditions and predation.     

Estimating population size and density of a low-density population of black bears in Rocky Mountain National Park, Colorado

Rocky Mountain National Park (RMNP) is home to a low-density black bear (Ursus americanus) population that exists at >2,400?m with a very limited growing season. A previous study (1984–1991) found bear densities among the lowest reported (1.37–1.52 bears/100?km²). Because of concerns of viability of this small population, we assessed population size and density of black bears from 2003 to 2006 to determine the current status of RMNP’s bear population. We used three approaches to estimate population size and density: (1) minimum number known, (2) occupancy modeling, and (3) catch per unit effort (CPUE). We used information from capture and remote-triggered cameras, as well as visitor information, to derive a minimum known population estimate of 20–24 individuals and a median density estimate of 1.35 bears/100?km². Bear occupancy was estimated at 0.46 (SE?=?0.11), with occupancy positively influenced by lodgepole pine stands, non-vegetated areas, and patch density but negatively influenced by mixed conifer stands. We combined the occupancy estimate with mean home-range size and overlap for bears in RMNP to derive a density estimate of 1.44 bears/100?km². We also related CPUE to density estimates for eight low-density black bear populations to estimate density in RMNP; this estimate (1.03 bears/100?km²) was comparable to the occupancy estimate and suggests that this approach may be useful for future population monitoring. The use of corroborative techniques for assessing population size of a low-density black bear population was effective and should be considered for similar low-density wildlife populations.     

A Multiscale Assessment of Den Selection by Black Bears in Louisiana

ABSTRACT Understanding den selection for the federally threatened Louisiana black bear (Ursus americanus luteolus) will assist managers in effectively managing bear populations and the landscapes they inhabit. We assessed den selection of 72 female Louisiana black bears at multiple spatial scales in northern and central Louisiana, USA. We used 230 den-years to examine den type preference, microhabitat characteristics of dens, and effects of landscape characteristics on den selection. We also evaluated reuse of tree dens and their availability across several study areas. Bears selected tree dens more frequently (65%) than ground dens. Most (55%) ground dens were associated with standing or downed trees, and most tree dens were in baldcypress (Taxodium distichum; 86%) or surrounded by water (80%). Selection of ground dens was positively associated with landscape metrics related to presence of water, whereas selection of tree dens was positively associated with proximity to edge and greater proportions of swamp and areas containing water. Reuse of tree dens averaged 15% (range = 0–20%) across study areas and our estimates of tree-den availability indicated that tree dens were not a limiting resource for Louisiana black bears in the northern or central portions of Louisiana. Although Louisiana black bears demonstrated plasticity in den selection, we recommend managers use forest management practices that conserve appropriate tree dens and create ground-denning opportunities, because both would promote the recovery of Louisiana black bear populations.     

A predictive spatial model for gray wolf (Canis lupus) denning sites in a human-dominated landscape in western Iran

Predictive models of species denning habitat are useful for understanding distribution of core use areas and identifying areas with potential conflicts. Wolf den site selection in unmanaged areas with dominance of agriculture-lands and human disturbance is not completely understood. We used a GIS multivariate model based on the Mahalanobis distance statistic and 11 digital habitat layers to evaluate gray wolf denning site suitability in Hamedan province (HP), western Iran. Results showed that >74 % of dens occurred in potential denning sites that occupied 14 % (2,785 km²) of the study area. Based on sensitivity analysis with ROC, we found that the distance to rangelands, elevation, and distance to roads, human settlements and streams were the most predictive variables. Our potential distribution model of wolf den sites showed a very good overall performance according to classification accuracy and discrimination capacity. Denning in elevated rugged terrains adjacent to rangelands and away from roads and villages revealed that wolf den distribution in HP is highly influenced primarily by factors associated with human disturbance. The derived predicted distribution map can be used to prioritize areas for conservation, identify areas with potential conflicts, and to implement adaptive management in regions beyond wilderness and protected areas.     

Within-Stand Selection of Canada Lynx Natal Dens in Northwest Maine,USA

Abstract Canada lynx (Lynx canadensis) were listed as threatened in the contiguous United States under the Endangered Species Act in March 2000. Little information on lynx ecology at the southern extent of their range was available at the time of listing, and no ecological studies had been conducted in the eastern USA. Between 1999 and 2004, we investigated habitat selection at natal dens in northern Maine to address questions on the importance of forest conditions to denning requirements. We compared within-stand characteristics of 26 den sites to general characteristics of the stands containing dens. We used logistic regression to identify components within stands that distinguished natal dens from the residual stand and used the information-theoretic approach to select models that best explained lynx den-site selection. The top-ranked model had 2 variables: tip-up mounds of blown-down trees and visual obscurity at 5 m from the den (w_i = 0.92). Within-stand structure was useful for predicting lynx den-site selection in managed forests in Maine and suitable denning habitat did not appear to be limiting.     

Despotism and risk of infanticide influence grizzly bear den-site selection

Given documented social dominance and intraspecific predation in bear populations, the ideal despotic distribution model and sex hypothesis of sexual segregation predict adult female grizzly bears (Ursus arctos) will avoid areas occupied by adult males to reduce risk of infanticide. Under ideal despotic distribution, juveniles should similarly avoid adult males to reduce predation risk. Den-site selection and use is an important component of grizzly bear ecology and may be influenced by multiple factors, including risk from conspecifics. To test the role of predation risk and the sex hypothesis of sexual segregation, we compared adult female (n = 142), adult male (n = 36), and juvenile (n = 35) den locations in Denali National Park and Preserve, Alaska, USA. We measured elevation, aspect, slope, and dominant land cover for each den site, and used maximum entropy modeling to determine which variables best predicted den sites. We identified the global model as the best-fitting model for adult female (area under curve (AUC) = 0.926) and elevation as the best predictive variable for adult male (AUC = 0.880) den sites. The model containing land cover and elevation best-predicted juvenile (AUC = 0.841) den sites. Adult females spatially segregated from adult males, with dens characterized by higher elevations ( = 1,412 m, SE = 52) and steeper slopes ( = 21.9°, SE = 1.1) than adult male (elevation:  = 1,209 m, SE = 76; slope:  = 15.6°, SE = 1.9) den sites. Juveniles used a broad range of landscape attributes but did not avoid adult male denning areas. Observed spatial segregation by adult females supports the sex hypothesis of sexual segregation and we suggest is a mechanism to reduce risk of infanticide. Den site selection of adult males is likely related to distribution of food resources during spring.     

Population genetic structure of a rare high-elevation black fly, Metacnephia coloradensis, occupying Colorado lake outlet streams

1. Using a portion of the mitochondrial cytochrome oxidase I gene, we evaluated the population genetic structure of a geographically rare black fly (Metacnephia coloradensis) that is a habitat specialist in outlet streams of large, productive, alpine lakes in Colorado, U.S.A. Given its rarity and life history traits that restrict dispersal, we hypothesised that genetic structure would show a signature of allopatric fragmentation associated with climatic warming since Pleistocene glaciations. 2. We tested for genetic isolation by distance (IBD) and applied nested clade analysis (NCA) to ask whether current genetic structure is primarily a consequence of historic fragmentation or if there is evidence of ongoing gene flow. 3. Only four populations were located despite a thorough search of potential sites, and they demonstrated a significant degree of genetic structure (F_ST = 0.17). However, there was some evidence of IBD in a plot of genetic versus geographic distance, and NCA further supported IBD and restricted ongoing gene flow in clades at all nested levels. Compared with a more widespread alpine black fly (Prosimulium neomacropyga) in the same region, M. coloradensis demonstrated significantly less population genetic structure. 4. Although these results counterintuitively implicate limited ongoing gene flow driving current population structure, significant IBD may be a signature of historic gene flow, especially if migration–drift equilibrium has not yet been reached since a late‐Pleistocene fragmentation event. Extraordinarily dense local populations probably allowed M. coloradensis to maintain large effective population sizes and minimise genetic drift rates. 5. Despite large local populations, M. coloradensis is vulnerable to continued rapid environmental change because of its limited geographic distribution and high habitat specificity.     

Radial growth of Fraxinus nigra in a Canadian boreal floodplain in response to climatic and hydrological fluctuations

Abstract. Stands of Fraxinus nigra (black ash) near Lake Duparquet (Abitibi region, NW Québec) are affected each year by spring or early summer flooding. The relationship between environmental factors and radial growth was studied in 50 100-m² quadrats laid out in five Fraxinus-dominated stands. Response function coefficients showed that the weather in the year before growth, i.e. in the time of bud formation, had a strong influence on radial increment. Temperatures in April of the year before (year i-1) and May (i- 1) were positively correlated with growth, while precipitation in April (i-1), May (i-1) and June (i-1) were negatively correlated. Climatic factors positively associated with growth during the year of bud expansion were April (i) temperature and June (i) precipitation. Redundancy analysis showed that radial growth in Fraxinus nigra responded to variation in elevation and geomorphological landform. These differences in stand location and elevation were also related to different responses to climate. The sites most exposed to flooding responded much more to the negative impact of spring precipitation, while the more elevated sites were more responsive to summer precipitation. This study showed that black ash could be used for long term reconstruction of climatic and hydrological fluctuations.     

天山盘羊夏季采食地和卧息地生境选择

2010年7-8月采用样线调查法及直接观察法对天山中部古仁郭楞高山区的盘羊天山亚种采食地和卧息地生境进行了研究。共调查5条沟系的12条样线,测量天山盘羊147个采食地和136个卧息地样方,分析了13类生态因子对天山盘羊采食地和卧息地选择的影响。研究结果表明,天山盘羊夏季采食地与卧息地在坡位、坡向、地貌类型、海拔高度、距最近家畜距离、距道路距离和距居民点距离差异极显著（P < 0.01）,植被高度差异显著（P < 0.05）,而其它生态因子差异性不显著（P > 0.05）;相对卧息地的选择而言,夏季盘羊采食地的选择更偏爱海拔较低,植被高度低,距离道路、居民点和最近家畜距离近的半阴半阳坡,山体中下位的高山草甸缓坡生境。逐步判别分析表明,距道路距离、距居民点距离、植被高度、距家畜距离4个生态因子可以用于判别夏季天山盘羊采食地与卧息地生境,正确区分率达到90.6%。     

Patterns of β‐diversity in a Mexican tropical dry forest

Abstract. Patterns of β‐diversity in a highly diverse tropical dry forest tree community are described; the contribution of environmental heterogeneity and distance to β‐diversity was assessed. Significant differences in elevation, insolation, slope and soil water holding capacity (p < 0.01), variables related to water availability, were found among 830 m × 100 m transects laid along contrasting slopes of a system of three parallel microbasins. A gradient in elevation and insolation was found within north‐facing transects, among 10 m × 10 m sites; south‐facing transects showed an elevation gradient while crest transects showed a gradient in water holding capacity. In total 119 species were registered, with 27 to 64 species per transect, and 4 to 16 species per site. A large β‐diversity was found among and within transects; two indices of β‐diversity consistently showed a higher β‐diversity within transects than among them. Among transects, 64% of the variance in species composition could be attributed to the environmental variables; an additional 22% to the spatial distribution of sites. Within transects, 42% of the deviance in β‐diversity values was explained by insolation, and 19% by distance. β‐diversity increased with distance and with difference in insolation among sites; north‐facing transects, those with most contrasting insolation conditions, had the steepest increase in β‐diversity with distance. Such increase was clearly associated with changes in species composition, not with changes in species richness.     

The limits to biogeographical distributions: insights from the northward range extension of the marine snail, Kelletia kelletii (Forbes, 1852)

Aim The development of accurate models predicting species range shifts in response to climate change requires studies on the population biology of species whose distributional limits are in the process of shifting. We examine the population biology of an example system using the recent northward range expansion of the marine neogastropod Kelletia kelletii (Forbes, 1852). Location This is a marine coastal shelf neogastropod species whose range extends from Isla Asuncion (Baja California, Mexico) to Monterey (CA, USA). Research sites spanned the extent of the range. Methods We examine abundance distributions and size frequency distributions of K. kelletii for evidence of factors determining historic and contemporary distributional patterns. Population studies were supplemented by historic and contemporary hydrographic data, including seawater temperature data from California Cooperative Oceanic Fisheries Investigations (CalCOFI ) and National Data Buoy Center (NDBC), and seawater circulation data. Results The structure of recently established populations varied dramatically from that of historic populations. Markedly low densities and irregular size frequency distributions characterized recently established populations and suggested only occasionally successful recruitment. The point of transition between historic and recently established populations also corresponded to the location of a gradient in seawater temperature and the confluence of two major oceanic currents. The accumulated data suggest that temperature and/or barriers to dispersal could have set both contemporary patterns in population structure as well as the former northern range limit. Main conclusions Early life stages play a critical role in determining distributional patterns of K. kelletii. Dispersal barriers and temperature limitation are two plausible mechanisms that could determine both contemporary and historic distributional patterns. Future studies on this species should attempt to tease apart the relative importance of these factors in maintaining the populations at the northern edge of the range.     

Habitat use by desert bighorn sheep during lambing

Habitat used for predator escape may be a factor limiting restoration of desert bighorn sheep (Ovis canadensis mexicana) in small mountain ranges in New Mexico. Female bighorn sheep seek isolation in discrete areas for parturition. Although parturition sites are used only for <3 days they play an important role in neonate survival. We compared habitat characteristics at pre-parturition (n = 21), parturition (n = 38), random (n = 38), and post-parturition sites (n = 21). At each site we calculated distance to steep terrain, elevation, ruggedness, slope, and visibility. Parturition and post-parturition sites were higher in elevation and more rugged than sites used during pre-parturition. Post-parturition sites were closer to terrain with 100% slope than the pre-parturition or parturition sites. Post-parturition sites had higher visibility and steeper slopes than the pre-parturition sites. Parturition sites were steeper, higher in elevation, more rugged, and had lower visibility than the random sites. Fidelity to parturition sites was observed on 1 of 38 occasions. Because lambing sites are used for short periods they are poorly understood and often ignored by land managers. Additional research is recommended in other desert bighorn sheep populations to understand better and predict habitat use during the lambing period.     

小兴安岭黑河胜山林区冬季驼鹿的生境选择

2002年、2003年和2004年的12月至3月,在小兴安岭黑河胜山林场开展了驼鹿生境选择的研究。研究中选择了9类与驼鹿生境选择相关的生态因子：植被型、离公路距离、离采伐点距离、平均雪深、隐蔽程度、坡向、坡位、坡度、海拔,运用SPSS软件进行交叉汇总定量分析。结果表明,胜山驼鹿冬季以落叶阔叶林、灌丛为主要生境,影响驼鹿分布的主要生态因子为隐蔽程度、坡位,其次为雪深、坡向、离采伐点距离、离公路距离,坡度、海拔对驼鹿分布的影响不明显。     

Gene flow in complex landscapes: testing multiple hypotheses with causal modeling

Predicting population-level effects of landscape change depends on identifying factors that influence population connectivity in complex landscapes. However, most putative movement corridors and barriers have not been based on empirical data. In this study, we identify factors that influence connectivity by comparing patterns of genetic similarity among 146 black bears (Ursus americanus), sampled across a 3,000-km(2) study area in northern Idaho, with 110 landscape-resistance hypotheses. Genetic similarities were based on the pairwise percentage dissimilarity among all individuals based on nine microsatellite loci (average expected heterozygosity=0.79). Landscape-resistance hypotheses describe a range of potential relationships between movement cost and land cover, slope, elevation, roads, Euclidean distance, and a putative movement barrier. These hypotheses were divided into seven organizational models in which the influences of barriers, distance, and landscape features were statistically separated using partial Mantel tests. Only one of the competing organizational models was fully supported: patterns of genetic structure are primarily related to landscape gradients of land cover and elevation. The alternative landscape models, isolation by barriers and isolation by distance, are not supported. In this black bear population, gene flow is facilitated by contiguous forest cover at middle elevations.     

Understory vegetation indicates historic fire regimes in ponderosa pine‐dominated ecosystems in the Colorado Front Range

Question: Can current understory vegetation composition across an elevation gradient of Pinus ponderosa‐dominated forests be used to identify areas that, prior to 20th century fire suppression, were characterized by different fire frequencies and severities (i.e., historic fire regimes)? Location: P. ponderosa‐dominated forests in the montane zone of the northern Colorado Front Range, Boulder and Larimer Counties, Colorado, USA. Methods: Understory species composition and stand characteristics were sampled at 43 sites with previously determined fire histories. Indicator species analyses and indirect ordination were used to determine: (1) if stands within a particular historic fire regime had similar understory compositions, and (2) if understory vegetation was associated with the same environmental gradients that influence fire regime. Classification and regression tree analysis was used to ascertain which species could predict fire regimes. Results: Indicator species analysis identified 34 understory species as significant indicators of three distinct historic fire regimes along an elevation gradient from low‐ to high‐elevation P. ponderosa forests. A predictive model derived from a classification tree identified five species as reliable predictors of fire regime. Conclusions: P. ponderosa‐dominated forests shaped by three distinct historic fire regimes have significantly different floristic composition, and current understory compositions can be used as reliable indicators of historical differences in past fire frequency and severity. The feasibility demonstrated in the current study using current understory vegetation properties to detect different historic fire regimes, should be examined in other fire‐prone forest ecosystems.     

广西凭祥不同年龄红椎林林下植物物种多样性及其环境解释

林下植被作为森林生态系统的重要组成部分,其在调控森林群落结构和功能上发挥着至关重要的作用。从揭示人工林林下植物物种组成的关键控制因素的目标出发,以不同年龄红椎林灌木层和草本层的植物群落作为研究对象,采用野外调查和室内分析相结合的方法,重点探究林下植物物种组成与环境因子之间的关系及其关键控制因子。研究结果表明:不同年龄红椎林的林下植物物种组成存在明显差异;RDA结果表明,胸高断面积是影响灌木层物种组成的最主要因子,胸高断面积、坡度和海拔能显著影响影响草本层的物种组成;方差分解结果表明,所调查的生物和非生物因子分别解释灌木层和草本层物种组成变异的63%和47%,微环境和植物之间的相互作用是影响林下植物群落物种变异的最主要因素,而土壤与微环境、土壤与植物两者之间,以及微环境、植物和土壤三者之间的相互作用对林下植物群落的物种组成的影响较小,甚至无影响,微环境的独立效应对林下植物物种组成的影响高于植物或土壤因素。     

A humped latitudinal phylogenetic diversity pattern of orchid bees (Hymenoptera: Apidae: Euglossini) in western Amazonia: assessing the influence of climate and geologic history

Amazonian rainforests are among the most species‐rich terrestrial habitats on Earth. The aim of this study was to analyze phylogenetic diversity (PD) patterns of orchid bee assemblages along a latitudinal gradient of 15° from northern Peru to central Bolivia and to relate them to climatic factors and geological history. We expanded an existing phylogeny of orchid bees and analyzed the PD of 15 orchid bee assemblages along a latitudinal gradient using mean pair‐wise phylogenetic distance. The resulting pattern was correlated to climatic factors and elevation. We found a hump‐shaped pattern of PD that peaked in central Peru and decreased towards the equatorial and especially towards the southern, subtropical sites. The decrease in PD towards higher latitudes is a common pattern found in many taxa, which in our case correlates with increasing climatic seasonality. However, the decrease towards the equatorial sites is unusual and may be related to a particular historic event: the northern sites with low PD are situated in the area of the former Lake Pebas, which covered western Amazonia until 3 mya. After the lake disappeared orchid bees mainly belonging to two distantly related species groups apparently colonized the region and diversified, which led to the comparatively low observed PD. In contrast, in central Peru, no in situ radiations were detected, hence the assemblages were composed of species from diverse phylogenetic lineages. Additionally, we identified multiple phylogenetically independent radiations of regionally restricted Euglossa species along the latitudinal gradient that, according to a published, dated phylogeny, diversified roughly 3–1 mya. The hump‐shaped latitudinal pattern of PD of the orchid bees of western Amazonia thus appears to have resulted from a preponderance of early divergent lineages in central Peru and of young radiations from distantly related clades colonizing higher latitudes, possibly triggered by historic climate fluctuations and major geological events.