Factors limiting the distribution of deciduous broadleaved trees in warm-temperate mountainous riparian forests

We examined differences in the responses of deciduous and evergreen broadleaved trees to fluvial disturbance and light environment near a river-facing forest edge in order to identify the factors limiting the distribution of deciduous trees, which are important components of warm-temperate mountainous riparian forests. Deciduous trees tended to be distributed on lower terraces of less than 2-m relative elevation from the water level, which corresponded with sites suffering from strong bank erosion due to high flood frequency. On the other hand, evergreen trees showed an opposite trend of distribution, indicating that high flood frequency associated with strong erosion-dominated soil disturbances might be a constraint for their establishment and/or survival. Furthermore, crowns of deciduous trees tended to be in the canopy layer at the forest edge, with fewer individuals observed beneath the canopy of evergreen trees, even at the forest edge. In contrast, evergreen trees were concentrated in the understory of the forest interior. These observations suggested that the light environment is the predominant factor affecting the establishment and survival of deciduous trees in warm-temperate mountainous riparian forests; however, the river-facing forest edge beneath the evergreen canopy is not a suitable habitat for deciduous trees. We concluded that erosion-dominated soil disturbance on lower terraces provides suitable habitats for deciduous trees by facilitating their reaching the canopy layer by limiting the establishment and/or survival of evergreen trees.

     

Legacy forest structure increases bird diversity and abundance in aging young forests

Many studies have demonstrated the importance of early‐successional forest habitat for breeding bird abundance, composition, and diversity. However, very few studies directly link measures of bird diversity, composition and abundance to measures of forest composition, and structure and their dynamic change over early succession. This study examines the relationships between breeding bird community composition and forest structure in regenerating broadleaf forests of southern New England, USA, separating the influences of ecological succession from retained stand structure. We conducted bird point counts and vegetation surveys across a chronosequence of forest stands that originated between 2 and 24 years previously in shelterwood timber harvests, a silvicultural method of regenerating oak‐mixed broadleaf forests. We distinguish between vegetation variables that relate to condition of forest regeneration and those that reflect legacy stand structure. Using principal components analyses, we confirmed the distinction between regeneration and legacy vegetation variables. We ran regression analysis to test for relationships between bird community variables, including nesting and foraging functional guild abundances, and vegetation variables. We confirmed these relationships with hierarchical partitioning. Our results demonstrate that regenerating and legacy vegetation correlate with bird community variables across stand phases and that the strength with which they drive bird community composition changes with forest succession. While measures of regeneration condition explain bird abundance and diversity variables during late initiation, legacy stand structure explains them during stem exclusion. Canopy cover, ground‐story diversity, and canopy structure diversity are the most powerful and consistent explanatory variables. Our results suggest that leaving varied legacy stand structure to promote habitat heterogeneity in shelterwood harvests contributes to greater bird community diversity. Interestingly, this is particularly important during the structurally depauperate phase of stem exclusion of young regenerating forests.     

塔里木荒漠河岸林不同生境群落物种多度分布格局

为解释塔里木荒漠河岸林群落构建和物种多度分布格局形成的机理, 本文以塔里木荒漠河岸林2个不同生境(沙地、河漫滩) 4 ha固定监测样地为研究对象, 基于两样地物种调查数据, 采用统计模型(对数级数模型、对数正态模型、泊松对数正态分布模型、Weibull分布模型)、生态位模型(生态位优先占领模型、断棍模型)和中性理论模型(复合群落零和多项式模型、Volkov模型)拟合荒漠河岸林群落物种多度分布, 并用K-S检验与赤池信息准则(AIC)筛选最优拟合模型。结果表明: (1)随生境恶化(土壤水分降低), 植物物种多度分布曲线变化减小, 群落物种多样性、多度和群落盖度降低, 常见种数减少。(2)选用的3类模型均可拟合荒漠河岸林不同生境群落物种多度分布格局, 统计模型和中性理论模型拟合效果均优于生态位模型。复合群落零和多项式模型对远离河岸的干旱沙地生境拟合效果最好; 对数正态模型和泊松对数正态模型对洪水漫溢的河漫滩生境拟合效果最优; 中性理论模型与统计模型无显著差异。初步推断中性过程在荒漠河岸林群落构建中发挥着主导作用, 但模型拟合结果只能作为推断群落构建过程的必要非充分条件, 不能排除生态位过程的潜在作用。     

Spatial-typological structure of bird communities in coniferous and deciduous forests of the Northern Volga region

Based on materials collected during continuous year-round strip censuses, the spatial heterogeneity of bird communities in coniferous and deciduous forests of the Northern Volga region was analyzed for the first time and the key factors determining it were identified. A spatial-temporal classification of bird communities of the study area was made, and a quantitative estimate of the strength and generality of the relationship between the spatial heterogeneity of bird communities and environmental factors is given. The spatial-temporal structure of bird communities is mainly determined by forest cover, seasonal variation in heat supply, tree species composition, build-up area, and relief.     

Coping with invasive alien species: the Argentine ant and the insectivorous bird assemblage of Mediterranean oak forests

Cork oak forests invaded by the Argentine ant Linepithema humile have a lower abundance and biomass of arthropod prey for birds than uninvaded forests. We studied whether the biomass of breeding insectivorous birds was also lower in invaded areas. We explored this and other possible effects of the ant invasion on the bird community by censusing birds in transects located in four invaded and four uninvaded forest sites in Catalonia (NE Spain) for 3 years. Redundancy analysis showed only slight differences in the community composition between forests. Two insectivorous species, Luscinia megarhynchos and Fringilla coelebs, tended to be less abundant in invaded areas although two others, Phylloscopus bonelli and Sylvia melanocephala, showed the opposite trend. Overall, the differences in prey biomass between invaded and uninvaded areas did not entail a biomass shift in the guild of insectivorous birds, regardless of whether they were shrub or canopy foragers. The main role of the habitat structure in determining bird densities and food resources being non-limiting in the studied forests are two possible non-exclusive explanations for this inconsistency. At today’s levels, the Argentine ant invasion does not appear to have greatly determined the insectivorous bird assemblage of the forests evaluated.     

Fine-scale habitat structure complexity determines insectivorous bird diversity in a tropical forest

Habitat complexity in reforested stands has been acknowledged as a key factor that influences habitat use by birds, being especially critical for habitat disturbance-sensitive species such as tropical understory insectivorous birds. Most studies regarding the relationship between forest structure and species diversity were conducted at the landscape scale, but different diversity patterns may emerge at a finer scale (i.e., within a habitat patch). We examined a tropical reforested area (State of Caldas, Colombia), hypothesizing that insectivorous bird richness, abundance, and foraging guild abundance would increase as intra-habitat complexity increases. We established 40 monitoring plots within a reforested area, measured their structural features, and determined their relationships with species richness, total abundance, and foraging guild abundance, using Generalized Additive Models. We found that the increasing variation in basal area, stem diameter, and number of stems was positively correlated with species richness, total abundance, and foraging guild abundance. Relationships between richness or abundance and structural features were not lineal, but showing curvilinear responses and thresholds. Our results show that heterogeneity on basal area, stem diameter, and the number of stems was more correlated to insectivorous bird richness and abundance than the average of those structural features. Promoting structural variation on reforested areas by planting species with different growth rates may contribute to increase the richness and abundance of a tropical vulnerable group of species such as the understory insectivorous birds.     

天童常绿阔叶林中常绿与落叶物种的物种多度分布格局

物种多度分布是对群落内不同物种多度情况的数量描述, 作为理解群落性质的基石, 其形成机制受到广泛关注。常绿与落叶物种是两类有着不同物候性状与生长策略的物种集合, 它们普遍共存于常绿阔叶林中。在天童20 ha常绿阔叶林动态监测样地内, 虽然常绿物种在物种多度和胸高断面积等指标上占有绝对优势, 但其在物种丰富度上却不及落叶物种。分析两者在常绿阔叶林中的物种多度分布特征, 能够为理解常绿阔叶林内物种多样性的维持机制提供一个全新的视角。为此, 我们基于天童样地的植被调查数据, 一方面利用累积经验分布函数对两类生活型植物的物种多度分布进行描述, 使用Kolmogorov-Smirnov检验(K-S检验)判断其差异性; 另一方面, 采用纯统计模型、生态位模型和中性理论模型对二者的物种多度分布曲线进行拟合, 并基于K-S检验的结果以及AIC值进行最优模型的筛选。结果显示: (1)常绿与落叶物种的物种多度分布曲线间并无显著差异。(2)在选用的3类模型中, 中性理论模型对于两类物种多度分布曲线的拟合效果都最好, 而生态位模型的拟合效果则一般。从上述结果可以看出, 尽管常绿与落叶物种在物种数量和多度等方面均存在差异, 但它们却有着近似的物种多度分布格局以及相近的多样性维持机制。然而, 鉴于模型拟合的结果只能作为理解群落多样性构建机制的必要非充分条件, 故而只能初步判定中性过程对于常绿与落叶物种的物种多样性格局影响更大, 却不能排除或衡量诸如生态位分化等其他过程在两类生活型多样性格局形成中的贡献。     

Species coexistence in temperate, mixed deciduous forests

The response of tree life-history traits to community profiles (horizontal and vertical heterogeneity, disturbances and biotic interactions) determines community assembly rules, which are currently a hot issue in community ecology. Important mechanisms of coexistence differ throughout the developing stages of tree life history. Many processes of niche partitioning and tradeoffs that potentially enable tree coexistence have been reported to be present in temperate forests, although some of these life-history traits are either correlated with each other or are not independent. Not all of the proposed mechanisms explain coexistence equally well; some could predominate in determining the community organization of forest communities. Population studies need to concentrate more on the component species of a target community to detect the ecological assembly rule. These approaches can also address how chance factors contribute to the composition of temperate tree communities, which might be less dependent on chance than are tropical ones.     

Ecosystem functions in degraded riparian forests of southeastern Kenya

Species community structures shape ecosystem functions, which are mostly stronger pronounced in intact than in degraded environments. Riparian forests in semiarid Africa provide important habitats for endangered plant and animal species and provide various ecosystem functions, that is, services to people settling along these streams. Most of these riparian forests are severely disturbed by human activities and dominated by invasive exotic plant species in the meanwhile. Thus, ecosystem functions are negatively influenced. While most studies have analyzed a specific metric to measure the degree of ecosystem function, little is known about how strongly different ecosystem functions respond to anthropogenic disturbances in parallel. In this study, we analyzed a set of four proxies of ecosystem functions, ground‐dwelling arthropod abundances, pollination, seed dispersal, and predation, along a highly disturbed riparian forest in southeastern Kenya. We assessed the land cover and land use manually and with an Unmanned Aerial Vehicle. Our data show that ecosystem functions respond differently to vegetation cover, human disturbances, and the availability of the invasive exotic shrub Lantana camara. The occurrence of representatives from the groups Saltatoria and Formicidae profits from heterogeneous habitat structures and natural riparian forest, while representatives of the Araneae profit from high proportion of agricultural fields. In general, predation is higher in mixed land use and natural riparian forest, while pollination and seed dispersal showed no significant trend in regard on land coverage. Along with this, predation also increased with rising proportion of natural riparian forest, while the proportion of agricultural land negatively affects predation, but in parallel showed a slightly significant positive trend with seed dispersal. Human disturbances and the occurrence of the invasive exotic L. camara shrub did not significantly affect our metrics of ecosystem functioning, except of the negative impact of human disturbances on pollinators. In conclusion, our results underpin that ecosystem functions respond highly variable and individually to environmental changes.     

Severe recent decrease of adult body mass in a declining insectivorous bird population

Migratory bird species that feed on air-borne insects are experiencing widespread regional declines, but these remain poorly understood. Agricultural intensification in the breeding range is often regarded as one of the main drivers of these declines. Here, we tested the hypothesis that body mass in breeding individuals should reflect habitat quality in an aerial insectivore, the tree swallow (Tachycineta bicolor), along a gradient of agricultural intensity. Our dataset was collected over 7 years (2005–2011) and included 2918 swallow captures and 1483 broods. Analyses revealed a substantial decline of the population over the course of the study (−19% occupancy rate), mirrored by decreasing body mass. This trend was especially severe in females, representing a total loss of 8% of their mass. Reproductive success was negatively influenced by intensive agriculture, but did not decrease over time. Interestingly, variation in body mass was independent of breeding habitat quality, leading us to suggest that this decline in body mass may result from carry-over effects from non-breeding areas and affect population dynamics through reduced survival. This work contributes to the growing body of evidence suggesting that declines in migratory aerial insectivores are driven by multiple, complex factors requiring better knowledge of year-round habitat use.     

Ecomorphological relationships in a group of insectivorous birds of temperate forests in winter

We examined the relationships between morphology and foraging behaviour in a group of insectivorous birds wintering in temperate mixed forests in northern Iberia. Using principal components analysis we reduced 11 biometric variables to three major morphological components and 20 foraging categories to four major ecological factors. The relative length of the tarsometatarsus and bill morphology were the most important morphological variables predicting foraging ecology. Birds exploiting distal parts of trees and foliage were generally smaller and had relatively longer tarsometatarsi than those foraging on trunks. Foraging on the ground and branches of medium diameter was associated with bill thickness. Ecomorphological patterns were discernible at the level of substrate use and foraging methods, but bear no relation to selection of tree species or foraging height. Morphology correctly predicted niche breadth and interspecific overlap. In Parus spp. interspecific differences in bill shape could explain 63% of the interspecific segregation according to substrate use (R²= 0.63, p <0.01).     

广西落叶栎林的分类研究

广西的落叶栎林属亚热带落叶阔叶林的一个群系组, 常见有栓皮栎林、麻栎林和白栎林３ 个群系。主要论述其类型划分和生境特点, 为其经营管理和合理利用提供基本材料和依据。     

Ecosystem effects of non-native earthworms in Mid-Atlantic deciduous forests

In many mid-Atlantic forests where both native and non-native earthworms exist, it is the non-native species that are the dominant component of the soil macrofauna. Few earthworm ecology studies, however, focus attention on these forest systems in order to determine the relative ecological roles and potential interactions of the native and non-native earthworms. In a series of field samplings and experimental manipulations we collected data on the effects of earthworms on below-and aboveground ecosystem processes. Earthworm abundance and the ecological processes measured were dynamic in space and time across the range of study sites. Leaf litter decay rates doubled at sites that had abundant non-native earthworms. Earthworms also altered the abundance of soil fungi, the activity of extracellular enzymes, soil respiration, and the growth of tree seedlings but the effects varied among sites depending on differences in land-use history and forest age. Red oak seedling growth was less at sites that had abundant earthworms but tulip poplar and red maple seedlings grew equally well with and without abundant earthworms. These preliminary results suggest that non-native earthworms have significant ecosystem effects, even in forests where native earthworms still occur. Land use history, however, plays an important role in determining what those effects will be, and these effects are likely to be dynamic, depending on the abundance of non-native earthworms.     

Effect of prey availability on the abundance of White‐breasted Wood‐Wrens,insectivorous birds of tropical lowland forests

Some understory insectivorous birds manage to persist in tropical forest fragments despite significant habitat loss and forest fragmentation. Their persistence has been related to arthropod biomass. In addition, forest structure has been used as a proxy to estimate prey availability for understory birds and for calculating prey abundance. We used arthropod biomass and forest structural variables (leaf area index [LAI] and aerial leaf litter biomass) to explain the abundance of White‐breasted Wood‐Wrens (Henicorhina leucosticta), tropical understory insectivorous birds, in six forests in the Caribbean lowlands of Costa Rica. To estimate bird abundance, we performed point counts (100‐m radius) in two old‐growth forests, two second‐growth forests, and two selectively logged forests. Arthropod abundance was the best predictor of wood‐wren abundance (wi = 0.75). Wood‐wren abundance increased as the number of arthropods increased, and the estimated range of bird abundance obtained from the model varied from 0.51 (0.28 – 0.93 [95%CI]) to 3.70 (1.68 – 5.20 [95%CI]) within sites. LAI was positively correlated to prey abundance (P = 0.01), and explained part of the variation in wood‐wren abundance. In forests with high LAI, arthropods have more aerial leaf litter as potential habitat so more potential prey are available for wood‐wrens. Forests with a greater abundance of aerial leaf litter arthropods were more likely to sustain higher densities of wood‐wrens in a fragmented tropical landscape.     

Stream community richness predicts apex predator occupancy dynamics in riparian systems

Streams and adjacent riparian habitats represent linked terrestrial and aquatic ecosystems that exchange materials and energy. Recognized relationships among apex predators and ecosystem biodiversity led us to hypothesize that these predators in riparian‐stream systems were more likely to be found in sites with high stream quality, defined as increased ecosystem function and integrity. In our freshwater study system, river otter Lontra canadensis and mink Neovison vison play critical roles as apex predators. We used multi‐season occupancy modelling across three sampling years (2012–2014) to compare aspects of the stream communities that explain occupancy dynamics of river otter and mink, including their interactions with other semi‐aquatic mammals. We surveyed for semi‐aquatic mammals at 77 sites in 12 major watersheds in southern Illinois, USA (44 526 km²). Naïve occupancy differed among years but generally increased for river otter, and remained high (≥93.5%) for mink. Increasing substrate availability increased detectability of river otter, whereas mink detection varied by survey period. Occupancy of river otter during the initial survey period was higher in sites closer to reintroduction points. Probability of colonization of river otter was positively associated with macroinvertebrate index of biotic integrity, fish species richness, and beaver presence. Sites with high species richness of fish families preferred by river otter also had increased river otter persistence. Mink occupied sites with increased fish richness, muskrat presence and mussel community index. Taken together, our results show occupancy of both mink and river otter were predicted by aspects of prey diversity and presence, indicating the importance of community composition in occupancy dynamics of riparian predators. Ultimately, these relationships suggest that habitat heterogeneity and system stability are important to apex predator site use. However, the relative role of bottom–up and top–down forcing in stream systems remains to be resolved.     

Evolution of chain migration in an aerial insectivorous bird,the common swift Apus apus

Spectacular long-distance migration has evolved repeatedly in animals enabling exploration of resources separated in time and space. In birds, these patterns are largely driven by seasonality, cost of migration, and asymmetries in competition leading most often to leapfrog migration, where northern breeding populations winter furthest to the south. Here, we show that the highly aerial common swift Apus apus, spending the nonbreeding period on the wing, instead exhibits a rarely found chain migration pattern, where the most southern breeding populations in Europe migrate to wintering areas furthest to the south in Africa, whereas the northern populations winter to the north. The swifts concentrated in three major areas in sub-Saharan Africa during the nonbreeding period, with substantial overlap of nearby breeding populations. We found that the southern breeding swifts were larger, raised more young, and arrived to the wintering areas with higher seasonal variation in greenness (Normalized Difference Vegetation Index) earlier than the northern breeding swifts. This unusual chain migration pattern in common swifts is largely driven by differential annual timing and we suggest it evolves by prior occupancy and dominance by size in the breeding quarters and by prior occupancy combined with diffuse competition in the winter.