Effects of forest canopy on habitat selection in treefrogs and aquatic insects: implications for communities and metacommunities

The specific dispersal/colonization strategies used by species to locate and colonize habitat patches can strongly influence both community and metacommunity structure. Habitat selection theory predicts nonrandom dispersal to and colonization of habitat patches based on their quality. We tested whether habitat selection was capable of generating patterns of diversity and abundance across a transition of canopy coverage (open and closed canopy) and nutrient addition by investigating oviposition site choice in two treefrog species (Hyla) and an aquatic beetle (Tropisternus lateralis), and the colonization dynamics of a diverse assemblage of aquatic insects (primarily beetles). Canopy cover produced dramatic patterns of presence/absence, abundance, and species richness, as open canopy ponds received 99.5% of propagules and 94.6% of adult insect colonists. Nutrient addition affected only Tropisternus oviposition, as females oviposited more egg cases at higher nutrient levels, but only in open canopy ponds. The behavioral partitioning of aquatic landscapes into suitable and unsuitable habitats via habitat selection behavior fundamentally alters how communities within larger ecological landscapes (metacommunities) are linked by dispersal and colonization.     

A comparison of the responses of two tropical specialist herbivores to host plant patch size

Summary The effects of host plant patch size on the abundances of two specialist herbivores (the chrysomelid beetle, Acalymma innubum and the pentatomid bug, Piezosternum subulatum) were investigated in a natural forest community in the Virgin Islands. Abundances were compared early and late in the season in different sized patches of the cucurbit host plant (Cayaponia americana) growing in open habitat (with no surrounding plant community) and forest habitat (with diverse surrounding plant community). For both herbivore species, adult abundances per patch were positively correlated with patch leaf area, but there was a significant patch size effect (i.e., correlation between herbivore density per unit plant and patch leaf area) only for beetles in the forest habitat. Both herbivore species were significantly affected by surrounding plant diversity, but in opposite ways: beetles were more abundant in open patches whereas bugs were more abundant in forest patches. Relationships between abundance and patch size in open and forest patches changed through the season for both herbivore species. These changing abundance patterns are discussed with respect to (1) increases in the diversity of the plant community surrounding host plant patches, and (2) differences in herbivore movement patterns.     

Short-term response of ground-dwelling arthropods to storm-related disturbances is mediated by topography and dispersal

Wind disturbances and consequent salvage logging lead to drastic changes in forest soil conditions, vegetation and microclimate, potentially affecting arthropod communities. In mountain regions, topography is expected to be particularly important to modulate the effect of canopy removal and soil disturbance potentially amplifying the ecological contrast between forest and disturbed areas. Here, we studied the short-term response of ground beetles (Carabidae), spiders (Araneae), and harvestmen (Opiliones) in wind-damaged spruce forests along statistically orthogonal gradients in elevation, slope, and aspect. We addressed three main ecological questions: (i) Does the effect of wind disturbance on diversity depend on topography? (ii) Are there specific taxon-related responses to disturbances?, and (iii) What is the role of dispersal in shaping species assembly dynamics? We generally observed that increasing slope and elevation amplified the differences between undisturbed forest and windfall areas. On the one hand, the diversity of ground beetles and harvestmen seemed to be negatively affected by wind disturbance, causing a loss of specialized forest species with a low rate of colonization of species typical of open habitats. On the other hand, several novel spider species were able to rapidly colonize windfalls and community composition strongly shifted from forest to disturbed areas. Species with long-range dispersal strategies (e.g. flying and ballooning) were those more likely to colonize windfalls. Our findings suggest that disturbance effects on ground-dwelling organisms were modulated by underlying environmental gradients and that short-term response of different taxa was dependent on their dispersal ability.     

Amphibian species richness across environmental gradients

Large‐scale field patterns are a fundamental source of inferences on processes responsible for variation in species richness among habitats. We examined species richness of larval amphibian communities in 37 ponds over seven years on the Univ. of Michigan's E. S. George Reserve. Ordination of the community incidence matrix indicated a strong major axis of variation in species associations that was correlated with pond hydroperiod, surface area and forest canopy cover. Communities were significantly nested with those species found in ponds with high canopy cover, small area and short hydroperiod being nested subsets of those found in ponds with contrasting characteristics. Presence of fish had strong negative effects on species richness; relaxation of this effect also was apparent when fish were extirpated from ponds by drought. We employed a model selection analysis to identify the most appropriate statistical model for predicting the long‐term average species richness of these ponds from local abiotic and biotic (predator and competitor density) factors. A model including only the abiotic factors was overwhelmingly superior for the anurans; hierarchical partitioning indicated that area and canopy cover alone accounted for over 70% of the independent effects of predictor variables. The global model including both abiotic and biotic factors was the best supported model for the caudates, and correspondingly hierarchical partitioning suggested that area, hydroperiod, invertebrate predators and caudate biomass all accounted for 9–16% of the independent effects. Overall, biotic factors accounted for much less of the variation in species richness than abiotic factors. The patterns in larger, open‐canopy ponds provided little evidence of competitive effects on species richness, though there were patterns consistent with competitive effects in small, closed‐canopy ponds. The unusual temporal and spatial extent of these data enabled us to critically evaluate ideas regarding patterns in larval amphibian communities, and the effects of area, disturbance (hydroperiod) and productivity (canopy cover) on species richness of these communities. These results have important implications to the conservation of amphibian species richness in freshwater wetlands, which are among the most threatened ecosystems worldwide.     

Disturbance regime and limits on benefits of refuge use for fishes in a fluctuating hydroscape

Refuge habitats increase survival rate and recovery time of populations experiencing environmental disturbance, but limits on the ability of refuges to buffer communities are poorly understood. We hypothesized that importance of refuges in preventing population declines and alteration in community structure has a non‐linear relationship with severity of disturbance. In the Florida Everglades, alligator ponds are used as refuge habitat by fishes during seasonal drying of marsh habitats. Using an 11‐year record of hydrological conditions and fish abundance in 10 marshes and 34 alligator ponds from two regions of the Everglades, we sought to characterize patterns of refuge use and temporal dynamics of fish abundance and community structure across changing intensity, duration, and frequency of drought disturbance. Abundance in alligator ponds was positively related to refuge size, distance from alternative refugia (e.g. canals), and abundance in surrounding marsh prior to hydrologic disturbance. Variables negatively related to abundance in alligator ponds included water level in surrounding marsh and abundance of disturbance‐tolerant species. Refuge community structure did not differ between regions because the same subset of species in both regions used alligator ponds during droughts. When time between disturbances was short, fish abundance declined in marshes, and in the region with the most spatially extensive pattern of disturbance, community structure was altered in both marshes and alligator ponds because of an increased proportion of species more resistant to disturbance. These changes in community structure were associated with increases in both duration and frequency of hydrologic disturbance. Use of refuge habitat had a modal relationship with severity of disturbance regime. Spatial patterns of response suggest that decline in refuge use was because of decreased effectiveness of refuge habitat in reducing mortality and providing sufficient time for recovery for fish communities experiencing reduced time between disturbance events.     

Does the composition of Scarabaeidae (Coleoptera) communities reflect the extent of land use changes in the Brazilian Amazon?

Scarab beetles (Coleoptera: Scarabaeidae) have been used to investigate the effects of environmental disturbances on forest structure and diversity. This group is recognized as sensitive to habitat perturbations and ecosystem changes. Here we examine the effects of anthropogenic impacts on Scarabaeidae composition, testing the following hypotheses: (1) Scarab beetle communities react to land use disturbances with predictable trends, (2) disturbed habitats are able to retain only a part of the Scarab beetle community of native forests or late secondary forests; (3) habitats largely differ in terms of species richness, taxonomic diversity and ecological composition, supporting exclusive and indicator species. We selected areas of native forest, agriculture, pasture for extensive livestock and secondary forests in different stages of regeneration. Our results show that the Scarabaeidae species were not indifferent to the gradient of structural changes represented by the studied areas. In fact, their patterns of habitat preference reveals communities more abundant and diverse in pristine habitats. In contrast, disturbed habitats, dominated by agricultural activities and pasture, indicated clear detrimental effects on the abundance of all forest Scarab beetle specialists. On the other hand, the generalist species, mainly associated with open environments, seemed to be favoured by the prevailing conditions induced by agricultural activities. Overall, the composition of the Scarab beetle communities is variable and sensitive to those structural gradients and, therefore, capable of responding as useful ecological indicators for assessing the extent of land use change or degradation.     

小兴安岭森林地表鞘翅目成虫对不同干扰梯度的响应

为探讨小兴安岭凉水自然保护区森林生态系统中地表鞘翅目成虫群落对不同人为干扰梯度的响应,于2015年7月、8月和10月分别对轻度干扰[原始阔叶红松林(KY)和谷地云冷杉林(YL)]、中度干扰[阔叶红松择伐林(ZF)和次生白桦林(BH)]及重度干扰[落叶松人工林(RL)和红松人工林(RHS)]的6个林型进行取样调查。结果表明:(1)整个采样周期共捕获地表鞘翅目成虫879只,隶属9科44物种;其中轻度干扰生境共捕获6科29种251只(KY捕获5科21种150只,YL捕获4科20种101只),中度干扰生境捕获6科27种276只(ZF捕获3科20种144只,BH捕获6科23种132只),重度干扰生境捕获6科29种352只(RL捕获4科22种232只,RHS捕获5科17种120只)。(2)7月和8月步甲科和葬甲科占据数量优势,10月步甲科和葬甲科成虫数量明显减少而隐翅虫科数量占优势;不同林型及不同干扰梯度地表鞘翅目成虫物种总数和总个体数于7、8、10月均表现为下降趋势,且群落多样性也呈不同程度下降。(3)林型和月份对地表鞘翅目成虫群落结构具有显著影响,干扰梯度对群落结构无显著影响;6个林型之间地表鞘翅目成虫个体数量具有显著差异,但在物种组成上无显著差异;不同干扰梯度间地表鞘翅目成虫个体数、物种数无显著差异,且随干扰梯度变化没有明显的梯度性规律;相似性系数和聚类分析表明,属于同一干扰梯度的两个林型没有表现出高度的相似性。本研究表明干扰梯度不是决定各林型间地表鞘翅目成虫群落多样性存在差异的主要原因,凉水森林生态系统地表鞘翅目成虫对不同干扰梯度的响应不符合中度干扰假说,林型和时间则是影响地表鞘翅目成虫群落组成的显著因素,本实验为地表生物多样性保护和森林生态系统管理提供数据支撑。     

Species responses of colonising beetles to variation in patch quality,number, and context in experimental aquatic landscapes

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Dung beetle communities as biological indicators of riparian forest widths in southern Brazil

Riparian forests provide important habitat for many wildlife species and are sensitive to landscape change. Among terrestrial invertebrates, dung beetles have been used to investigate the effects of environmental disturbances on forest structure and diversity. Since many studies demonstrated a negative response of dung beetle communities to increasing forest fragmentation, and that most dung beetle species had a more pronounced occurrence during warmest seasons, three hypotheses were tested: (1) Scarabaeinae richness, abundance, diversity and evenness are lower in thinner riparian zone widths than in wider widths during the warmest seasons; (2) Scarabaeinae richness and abundance are positively influenced by leaf litter coverage and height and canopy cover; and (3) Scarabaeinae composition varies with the reduction in riparian vegetation and among annual seasons. We selected four fragments with different riparian zone widths in three secondary streams in southern Brazil. In each fragment, four sampling periods were carried out seasonally between spring 2010 and winter 2011. We collected dung beetles using pitfall traps with two types of bait. We collected 1289 specimens distributed among 29 species. In spring and summer, dung beetle richness was higher in fragments with the widest riparian zone than in those with a thinner riparian zone, and it did not vary between fragments in fall and winter seasons. Dung beetle abundance did not differ among fragments with different riparian zone widths, but it was higher in spring and summer than fall and winter. Richness and abundance were positively influenced by leaf litter. While dung beetle diversity was higher in fragments with wider riparian zone widths than in those with thinner widths, the evenness was similar among fragments. Dung beetle composition differed between the fragments with the widest and thinnest riparian zones, and it also varied among the seasons. Our results suggest that decreased riparian zones affect negatively to dung beetle community structure in southern Brazil. Fragments with thinner riparian zones had lower beetle richness in warmest seasons and an altered community composition. In this sense, the dung beetles are potentially good indicators of riparian forest fragmentation since some species were indicators of a particular riparian zone width. From a conservation perspective, our results demonstrate that the new Brazilian Forest Code will greatly jeopardize not only the terrestrial and aquatic biodiversity of these ecosystems, but also countless other ecological functions.     

Role of epibiotic diatoms isolated from the barnacle shell in the cyprid metamorphosis of <Emphasis Type="Italic">Balanus amphitrite</Emphasis>

The mechanisms structuring aquatic communities across environmental gradients are often difficult to distinguish from one another and can produce similar patterns of species distributions. In freshwater systems, the amount of canopy cover from surrounding trees is often associated with transitions in local community structure. These community changes could be driven by habitat selection prior to colonization of the aquatic habitat and/or species-sorting post-colonization. To assess the contributions of pre- versus post-colonization processes in structuring larval dragonfly assemblages, we tested the impact of artificial and natural canopy cover on the selection of experimental aquatic mesocosms by adult dragonflies, and monitored the performance (i.e. growth and survival) of larval dragonflies that were placed in mesocosms under a gradient of natural canopy cover. We found that greater levels of canopy cover resulted in fewer adult visits to mesocosms, and more natural canopy cover decreased the species richness of visitors. There were no effects of canopy cover on the growth and survival of larvae added to the mesocosms. Our results suggest that adult habitat selection plays a dominant role in structuring larval dragonfly assemblages across a canopy cover gradient, and that canopy cover can be an important environmental filter on species distributions.     

Effects of flash flooding on mosquito and community dynamics in experimental pools

Pulsed disturbances of larval mosquito sites are likely to have a direct negative effect on mosquitoes but may also have indirect effects due to the alteration of community structure. These altered communities may become attractive to gravid mosquitoes searching for oviposition sites when the disturbances decrease the abundance of mosquito antagonists such as competitors, which often results in an increase in mosquito food resources. However, flash flood disturbances in intermittent riverbeds can also remove mosquito food resources such as algae, so that the net effect of flash floods could be either to increase or decrease mosquito abundance. We conducted an outdoor mesocosm experiment to assess the effects of flash floods on mosquito oviposition habitat selection and larval abundance during the post‐disturbance period of community recovery. Mesocosms were artificially flooded. Mosquito oviposition, immature abundance, invertebrate species diversity, chlorophyll a, and abiotic parameters were monitored. Our results showed that the flash flood negatively affected phytoplankton and zooplankton, leading to a decrease of mosquito oviposition in flooded mesocosms compared to non‐flooded mesocosms. More broadly, this study indicates how disturbances influence mosquito oviposition habitat selection due to the loss of food resources in ephemeral pools, and it highlights the importance of considering the effects of disturbances in management, habitat restoration, and biodiversity conservation in temporary aquatic habitats.     

Matrix context and patch quality jointly determine diversity in a landscape‐scale experiment

The biodiversity of a habitat patch is predicted to be driven in part by interactions between patch quality and landscape context (i.e. type of regional matrix), but these interactions are rarely explored experimentally. Understanding the interaction between patch quality and matrix context can provide insight into the kind of dynamics that best describe a metacommunity and help predict how the diversity of a patch will respond to environmental change at different scales. We conducted a landscape‐scale experiment to examine how regional and local aspects of the terrestrial matrix interact to affect biodiversity within artificial ponds designed to mimic generic features of freshwater ephemeral ponds. We manipulated both the kind of matrix surrounding ponds (open canopy grassland, pine forest, and hardwood forest) and pond quality (three different types of leaf litter substrate). Ponds were left open to natural colonization for three months by aquatic insects and amphibians. The terrestrial matrix had consistent and strong effects on biodiversity throughout the experiment: ponds in open canopy areas had more animal morphotypes than ponds in pine or hardwood forests. Leaf litter type affected biodiversity during the experiment, with more animal morphotypes in ponds with higher quality litter than ponds with lower quality litter, and this effect was stronger in open canopy areas. The effect of leaf litter, however, disappeared by the end of the experiment. Our results suggest that the matrix surrounding patches has strong effects on community dynamics and biodiversity within patches, and conservation efforts aimed at maintaining biodiversity requires simultaneous consideration of both matrix habitats and habitat patches.     

The Response of Ground Beetles (Coleoptera: Carabidae) to Selection Cutting in a South Carolina Bottomland Hardwood Forest

We compared the response of ground beetles (Coleoptera: Carabidae) to the creation of canopy gaps of different size (0.13, 0.26, and 0.50 ha) and age (1 and 7 years) in a bottomland hardwood forest (South Carolina, USA). Samples were collected four times in 2001 by malaise and pitfall traps placed at the center and edge of each gap, and 50 m into the surrounding forest. Species richness was higher at the center of young gaps than in old gaps or in the forest, but there was no statistical difference in species richness between old gaps and the forests surrounding them. Carabid abundance followed the same trend, but only with the exclusion of Semiardistomis viridis (Say), a very abundant species that differed in its response to gap age compared to most other species. The carabid assemblage at the gap edge was very similar to that of the forest, and there appeared to be no distinct edge community. Species known to occur in open or disturbed habitats were more abundant at the center of young gaps than at any other location. Generalist species were relatively unaffected by the disturbance, but one species (Dicaelus dilatatus Say) was significantly less abundant at the centers of young gaps. Forest inhabiting species were less abundant at the centers of old gaps than in the forest, but not in the centers of young gaps. Comparison of community similarity at various trapping locations showed that communities at the centers of old and young gaps had the lowest similarity (46.5%). The community similarity between young gap centers and nearby forest (49.1%) and old gap centers and nearby forest (50.0%) was similarly low. These results show that while the abundance and richness of carabids in old gaps was similar to that of the surrounding forest, the species composition between the two sites differed greatly.     

Nematode community shifts in response to experimental warming and canopy conditions are associated with plant community changes in the temperate-boreal forest ecotone

Global climate warming is one of the key forces driving plant community shifts, such as range shifts of temperate species into boreal forests. As plant community shifts are slow to observe, ecotones, boundaries between two ecosystems, are target areas for providing early evidence of ecological responses to warming. The role of soil fauna is poorly explored in ecotones, although their positive and negative effects on plant species can influence plant community structure. We studied nematode communities in response to experimental warming (ambient, +1.7, +3.4 °C) in soils of closed and open canopy forest in the temperate-boreal ecotone of Minnesota, USA and calculated various established nematode indices. We estimated species-specific coverage of understory herbaceous and shrub plant species from the same experimental plots and tested if changes in the nematode community are associated with plant cover and composition. Individual nematode trophic groups did not differ among warming treatments, but the ratio between microbial-feeding and plant-feeding nematodes increased significantly and consistently with warming in both closed and open canopy areas and at both experimental field sites. The increase in this ratio was positively correlated with total cover of understory plant species, perhaps due to increased predation pressure on soil microorganisms causing higher nutrient availability for plants. Multivariate analyses revealed that temperature treatment, canopy conditions and nematode density consistently shaped understory plant communities across experimental sites. Our findings suggest that warming-induced changes in nematode community structure are associated with shifts in plant community composition and productivity in the temperate-boreal forest ecotones.     

Changes in avian species composition following surface mining and reclamation along a riparian forest corridor in southern Indiana

Data on the response of bird communities to surface mining and habitat modification are limited, with virtually no data examining the effects of mining on bird communities in and along riparian forest corridors. Bird community composition was examined using line transects from 1994 to 2000 at eight sites within and along a riparian forest corridor in southwestern Indiana that was impacted by an adjacent surface mining operation. Three habitats were sampled: closed canopy, riparian forest with no open water; fragmented canopy, riparian forest with flood plain oxbows; and reclaimed mined land with constructed ponds. Despite shifts in species composition, overall bird species richness, measured as the mean number of bird species recorded/transect route, did not differ among habitats and remained unchanged across years. More species were recorded solely on mined land than in either closed forest or forested oxbow habitats. Mined land provided stopover habitat for shorebirds and waterfowl not recorded in other habitats, and supported an assemblage of grassland-associated bird species weakly represented in the area prior to mining. A variety of wood warblers and other migrants were recorded in the forest corridor throughout the survey period, suggesting that, although surface mining reduced the width of the forest corridor, the corridor was still important habitat for movement of forest-dependent birds and non-resident bird species in migration. We suggest that surface mining and reclamation practices can be implemented near riparian forest and still provide for a diverse assemblage of bird species. These data indicate that even narrow (0.4 km wide) riparian corridors are potentially valuable in a landscape context as stopover habitats and routes of dispersal and movement of forest-dependent and migratory bird species.     

Impacts of Small‐scale Clearings due to Selective logging on Dung Beetle Communities

Conservation of biodiversity in production forests is crucial for mitigating biodiversity loss in the tropics. The major ecological impacts of selective logging are often the result of small clearings for skid trails, logging roads, log yards, and logging camps; however, their impacts on forest biodiversity have rarely been examined. The purpose of this study was to assess the impacts of these clearings on a forest‐dependent faunal group, dung beetles, and to identify the environmental factors responsible. Abundance and species richness of dung beetles decreased drastically in clearings, but directly increased in forests with the distance from roads/trails; abundance and species richness at 10 m from roads/trails were almost comparable with those detected in further interior forests. Similarly, species composition was significantly different between forests and clearings (except skid trails) but recovered within a short distance from roads/trails. Canopy openness was the most important environmental factor affecting the abundance, and species richness and composition of dung beetles; most dung beetle species were concentrated under closed forest canopy with less than 10 percent of canopy openness, whereas canopy openness ranged from 16 to 53 percent in clearings. Our study demonstrates that even small‐scale, unpaved clearings affect dung beetle communities through increased canopy openness. Although the effective distance was not very large, a considerable portion of logged areas can be affected when road networks are dense therefore minimizing the density of road networks and enhancing canopy recovery after logging are important for retaining biodiversity in tropical production forests.     

Colonisation of Heliconia caribaea by aquatic invertebrates: resource and microsite characteristics

Abstract.  1. Colonisation of ephemeral aquatic habitats via oviposition by invertebrates may be influenced by a variety of factors, such as the quality of aquatic habitat and the characteristics of the surrounding terrestrial environment. The water-holding bracts of Heliconia caribaea , a subtropical herb that produces ephemeral aquatic habitats, are colonised by a variety of aquatic invertebrates. To date, no experiments have been conducted to identify the cues that affect colonisation patterns via oviposition selection in Heliconia .
2. Artificial bracts were used to assess the influence of two types of resources found in bracts (plant produced carbohydrates and terrestrial snail faeces) on oviposition site-selection by invertebrate taxa via a replicated factorial design at four locations in the Luquillo Experimental Forest of Puerto Rico, U.S.A. Eleven microsite characteristics thought to affect oviposition were measured for each experimental container.
3. Most taxa responded in a minor way to microsite characteristics, whereas site selection by the most numerically dominant groups (e.g. Syrphidae) were influenced principally by resources within artificial bracts. Overall, the greatest response by particular taxa was to the presence of snail faeces. At the community level, total abundance, richness, and evenness of invertebrates increased with increasing biomass of faeces. Variation in sugar produced a more complex response.
4. In general, the terrestrial matrix surrounding these aquatic habitats was only a secondary determinant of population and community attributes; the principal factor affecting site selection was the quality of the aquatic habitat.     

The effects of fire on communities,guilds and species of breeding birds in burnt and control pinewoods in central Italy

Breeding bird communities in burnt and unburnt residual pinewoods were studied over 3 years by line-transect method, following a catastrophic fire event in Castelfusano (Rome, Central Italy; July 2000). We applied bootstrap procedures to evaluate whether the observed data were true or just produced by chance, and then examined the emerging patterns at three levels: community, guild and species levels. At the community level, fire acted on breeding bird communities by altering especially the total abundance patterns: the species abundance decreased in the burnt pinewood compared to the residual one, but other parameters were not significantly affected by fire. As a consequence of fire, the destruction and structural simplification of the canopy and shrubby component, as well as the increase of edge habitat and patchiness at landscape scale, induced a turnover in species between pinewoods. Species turnover was higher at the burnt than at the residual pinewoods, during all the 3 years of study. At the guild level, the forest species decreased strongly in terms of richness and abundance in the burnt pinewoods, contrary to the edge and open habitat species which increased in terms of richness, abundance and evenness. Edge species showed the highest turnover in burnt pinewood during the whole period of study. At species level, after an a priori subdivision (based on bibliographic search) of the various species in two ecological guilds (forest versus edge species), it was found that an a posteriori statistical analysis confirmed the expected trend, i.e. that the species which decreased significantly in burnt pinewood were essentially the forest species, whereas the species which increased were essentially the edge/open habitat ones. Overall, in order to investigate the effects of fire catastrophes on birds, the guild approach seems more exhaustive than the taxonomic community approach, where intrinsic confounding trends are present.     

宁夏黄土丘陵区不同生态恢复生境地表甲虫多样性

为了解宁夏黄土丘陵区不同生境地表甲虫群落多样性变化规律及与环境因子的关系, 并探讨不同生态恢复措施对维持地表甲虫群落多样性的影响, 2013年7-8月, 作者利用陷阱法调查了该区6种生境内的地表甲虫群落多样性。结果表明: 灌草混交林地、乔灌混交林地、生态薪炭林地中地表甲虫物种丰富度和个体数量均较高, 天然封育草地、生态经济林地和水平农田中物种丰富度较低, 生态经济林地和水平农田中甲虫个体数量显著高于天然封育草地。不同生境间, 灌草混交林地、乔灌混交林地与生态薪炭林地之间、生态经济林地与水平农田之间甲虫群落组成相似性较高。多元回归分析表明, 草本层生物量、灌木层盖度及土壤含水量是影响甲虫物种丰富度的决定因素, 林冠层盖度和枯落物厚度是决定地表甲虫个体数量的重要因素。CCA分析表明, 枯落物盖度、枯落物厚度、林冠层盖度及草本层盖度是影响地表甲虫群落组成的重要环境因子。研究表明, 灌草混交林地为地表甲虫群落多样性维持较好的生境类型, 是宁夏黄土丘陵区典型生态恢复的最优模式。     

Interaction between disturbance and primary productivity in determining stream invertebrate diversity

Invertebrate diversity patterns were examined in 10 streams that differed in substrate disturbance rates, in Taranaki, New Zealand, between April 1999 and January 2000. Two sites on each stream were sampled, one under native forest canopy where light was postulated to limit periphyton growth and a similar site 225–3800 m downstream in open grassland. Periphyton biomass was considerably higher at open stable sites than at closed or unstable sites. Associated with the higher algal biomass, species number and total abundance of animals were higher at open canopy sites. Species number exhibited a negative linear relationship with disturbance but only at open sites. In contrast, rarefied species richness exhibited a negative linear relationship with disturbance at both open and closed sites. This was a result of communities at the more disturbed sites being numerically dominated by only a few taxa compared to the more evenly distributed communities at stable sites. The observed patterns provide little support for contemporary diversity disturbance models but suggest diversity of invertebrates in streams is a function of time since the last disturbance, mediated through recovery of the food base in autotrophic streams.