Microhabitat preference constrains invasive spread of non-native natal grass (<Emphasis Type="Italic">Melinis repens</Emphasis>)

Preventing the establishment of a non-native species is critical for ensuring the species does not become invasive, yet most non-native species will have little impact on their environment. Despite this, little is known about what influences whether a species will remain relatively benign, or whether it will cause economic or ecological harm. Understanding a plant’s microhabitat provides insight into the necessary conditions for establishment and the current distribution limitations of a population. We investigated microhabitat preference of the non-native natal grass (Melinis repens (Willd.) Zizka) in Florida scrub using microhabitat sampling to measure vegetation composition. We examined the extent to which microhabitats were associated with natal grass presence and biomass in invaded disturbed scrub and roadside plots using backwards stepwise logistic regression and general linear models to identify significant microhabitat variables. We further compared these plots with those in undisturbed, uninvaded scrub to characterize vegetation across habitat types, and used our model to predict the probability of natal grass invasion in undisturbed scrub. Natal grass preferred microhabitats with high litter volume and distance to shrubs and intermediate cactus, graminoid, and vine cover. Roadside natal grass achieved higher biomass and was less microhabitat limited than disturbed scrub natal grass. We determined that undisturbed scrub plots represent distinct microhabitats that natal grass is unlikely to invade. Microhabitat sampling provides land-managers a non-intrusive technique to assess potential habitat suitability based non-native plant preferences before a costly invasion occurs.     

Feeding guild structure of beetles on Australian tropical rainforest trees reflects microhabitat resource availability

1.?We tested the hypotheses that feeding guild structure of beetle assemblages changed with different arboreal microhabitats and that these differences were consistent across rainforest tree species. 2.?Hand collection and beating techniques were used from the gondola of the Australian Canopy Crane to collect beetles from five microhabitats (mature leaves, flush leaves, flowers, fruit and suspended dead wood) within the rainforest canopy. A simple randomization procedure was implemented to test whether the abundances of each feeding guild on each microhabitat were different from that expected based on a null hypothesis of random distribution of individuals across microhabitats. 3.?Beetles from different feeding guilds were not randomly distributed, but congregated on those microhabitats that are likely to provide the highest concentrations of their preferred food sources. Herbivorous beetles, in particular, were over-represented on flowers and flush foliage and under-represented on mature leaves and dead wood. Proportional numbers of species within each feeding guild were remarkably uniform across tree species for each microhabitat, but proportional abundances of feeding guilds were all significantly non-uniformly distributed between host tree species, regardless of microhabitat, confirming patterns previously found for arthropods in trees in temperate and tropical forests. 4.?These results show that the canopy beetle community is partitioned into discrete assemblages between microhabitats and that this partitioning arises because of differences in feeding guild structure as a function of the diversity and the temporal and spatial availability of resources found on each microhabitat.     

Microhabitat effects on bryophyte species richness and community distribution on exposed rock outcrops in Portugal

Background: Rock outcrops have been shown to provide specific conditions for bryophyte communities, but no studies have focused on the importance of microhabitats on such communities.

Aim: To analyse the distribution pattern of bryophyte species from granite and schist outcrops in three microhabitats (rock surfaces, fissures and cavities) in Portugal.

Methods: Sample plots were established in fissures, cavities and on rock surfaces of rock outcrops in north and central Portugal. Micro-scale variables, such as exposure and slope were assessed for each microhabitat.

Results: The microhabitats most different in species composition were surfaces versus cavities and surfaces versus fissures, both on granite and schist. Short-lived shuttle species tended to be associated with surfaces, and perennial species were more frequent in cavities and fissures. Both on granite and schist, the number of species found in each microhabitat was highest in cavities, followed by fissures and rock surfaces. The most relevant predictors of bryophyte richness were microhabitat type, exposure and rock type.

Conclusions: This investigation confirmed that rock microhabitats play an important role in bryophyte diversity by promoting habitat heterogeneity. In addition, our results clearly suggest local explanations for variation in bryophyte species richness and communities.     

Fine‐scale drivers of beetle diversity are affected by vegetation context and agricultural history

Environmental gradients have been shown to affect animal diversity, but knowledge of fine‐scale drivers of insect diversity is, in many cases, poorly developed. We investigated the drivers of beetle diversity and composition at different microhabitats, and how this may be mediated by past agricultural activities. The study was undertaken in temperate eucalypt grassy woodland near Canberra, south‐eastern Australia, with a 200‐year history of pastoral land use. We sampled beetles using pitfall traps at three microhabitats (open grassland, logs and under trees). We analysed the effects of soil properties, vegetation structure, and plant composition on beetle composition, and compared beetle responses among the microhabitats. We found that microhabitat was a strong determinant of the way beetle communities responded to their environment. Soil nutrients (C, N and P) were the strongest drivers of beetle species richness, abundance and composition at open and log microhabitat, however vegetation structure (tree basal area) was more important for beetle richness, abundance and biomass under trees. We also found significant differences in beetle composition among distinct ground‐layer plant communities at log and tree microhabitat. We show that prior agricultural land use, particularly fertilization, has altered soil and plant communities, and that these effects continue to flow through the system affecting beetle assemblages. These findings have implications for future management of microhabitat structures in temperate grassy woodlands with a history of agricultural use.     

济南地区直翅目昆虫群落多样性

济南地区位于鲁中丘陵山区和黄河冲积平原交接地带 ,境内生境丰富多样。研究不同生境中直翅目昆虫群落的组成及多样性既有重要的理论意义又有现实的应用价值。近来对该地区直翅目昆虫的研究成果已有报道[2 ,3 ,6 ],但有关多样性的工作还少有研究。作者于 1 994年对本地区的直翅目昆虫做了较为全面的调查 ,应用生境型的概念[9,13],将直翅目昆虫分布的 1 3种生境划分为 5个生境型[2 ]。在此基础上本文着重研究了直翅目昆虫群落的多样性及环境等因素与群落多样性的关系。1　自然条件概况济南位于山东省中部 ,整个地势南高北低。南部为鲁中丘陵…     

Identification of key microhabitats for fish assemblages in tropical Brazilian savanna streams

The habitat use by stream fish can provide an understanding of this important component of species niches, and the changes in the availability of certain structures of instream habitats have a strong influence on the occurrence and abundance of fish species. In this study, we identified the interaction networks between fish and microhabitats in 19 streams of three watersheds from the Brazilian savanna, known as the “Cerrado”. We also investigated whether the connectance between fish species and microhabitats depends on either the species abundance or availability of microhabitats and verified whether the use of stream microhabitats vary among watersheds. The data for the fish were obtained using standardized fish collections and underwater (snorkeling) observations to record the association of fish species with 11 stream microhabitats. We used the incidence data to calculate the connectance of species with different microhabitats, a Spearman correlation analysis to test the dependence of the connectance to the species abundance and microhabitat availability, and an Analysis of Similarity to test whether the use of stream microhabitats by fish can vary among watersheds. In all of the watersheds, the tetras of the family Characidae used the largest number of microhabitats. The most‐used microhabitats by the fish watersheds were the lateral surface, column surface, and unconsolidated substrate, which were differentially used by the fish in each watershed, indicating the variable importance of microhabitats. Despite this observation, the fish occurred more frequently in the lateral microhabitats. When the data for all of the streams were combined, the species connectance was correlated with the species abundance. We also discuss the consequences of the elimination of certain bottom structures in the context of siltation, which is the main issue in the studied region. The results of our study allowed the detection of key microhabitat structures and can be used for the aquatic ecosystems restoration. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Bottom-up control of carabid beetle communities in early successional wetlands: mediated by vegetation structure or plant diversity?

Two hypotheses of bottom-up control that predict that the species richness of Carabidae will depend either on the taxonomic diversity of plants ("taxonomic diversity hypothesis") or on the structural heterogeneity of the vegetation ("structural heterogeneity hypothesis") were tested. Plant species were classified into nine plant structural groups through cluster analysis of morphological traits (e.g. total height) at 30 early successional temporary wetlands in the east-German agricultural landscape. In a linear regression analysis, the heterogeneity of vegetation structures explained 55% of the variation in carabid beetle diversity. According to a partial correlation analysis, plant taxonomic diversity did not have a significant effect, consistent with the "structural heterogeneity hypothesis," and contradicting previous studies which concluded that plant taxonomic diversity would be the most important factor in early successional habitats. An experimental study was used to test hypotheses on the processes underlying this bottom-up control by vegetation structure: the "hunting efficiency hypothesis," the "enemy-free space hypothesis," and the "microhabitat specialization hypothesis." The composition of plant structural groups in 15 vegetation plots (1 m(2)) was manipulated, creating a gradient from dense vegetation to open plots. Subsequent pitfall catches revealed significant differences in the activity-abundances of the carabid species. Large species preferred dense vegetation plots, consistent with the enemy-free space hypothesis that large species are more vulnerable to predation on the open plots and prefer dense vegetation to escape from natural enemies. The results indicate that bottom-up control is not mediated only by plant taxonomic or functional group diversity and that vegetation structures may be more important than previously suggested.     

The microhabitat distribution of two Dactylogyrus species parasitizing the gills of the barbel, Barbus barbus

The microhabitat distribution of two congeneric species Dactylogyrus carpathicus and D. malleus (Monogenea) parasitizing the gills of the barbel (Barbus barbus L.) was investigated. We tested whether congeneric species exhibited microhabitat preference and whether interspecific interactions could be attributed to the microhabitat segregation of congeners. The outlying mean index method was used to evaluate species microhabitats. Gill variables (different microhabitats within gills) were used as environmental factors characterizing the gills. When abundances of both species were highest, and no significant difference was found between the abundance of the two species, the gill segments and gill areas were the most important factors segregating the Dactylogyrus species on the gills. Niche overlap was low within each of the four gill arches, and parasites were segregated in the same microhabitats within each gill arch. When abundances of both species were low, each monogenean species was segregated at the level of the gill arches. When abundances of both species increased, the niche and overlap between species increased. The distribution of both congeneric species confirmed microhabitat preference within the gills. The results suggest that microhabitat preference is dependent on species abundances, species being segregated in the case of low abundance, possibly to increasing mating opportunities. Both niche and overlap between species increased with species abundance. In the case of the high abundance of both species, microhabitat preference seems to be related to interspecific interactions between monogenean species, as previously found for endoparasitic species.     

Soil heterogeneity effects on canopy structure and composition during early succession

Early succession from annuals to herbaceous and woody perennials on abandoned fields and grasslands is marked by vegetation heterogeneity; i.e., variation in canopy composition and structure over the field through time. Soil resource heterogeneity could promote vegetation heterogeneity. We created soil resource patchiness on two newly ploughed fields by establishing two types (fertilized, unfertilized) of checkerboard plots with two, four, or eight subplots (trenched, untrenched) to test effects of soil fertility heterogeneity scale on vegetation heterogeneity during early succession. Canopy composition and structure were censused in years 2, 4 and 6. On both fields, soil resource heterogeneity did not affect canopy composition or structure. Differential abundance of dominant species, Ambrosia trifida on one field and Solidago altissima on the other, between fertilized and unfertilized plots led to decreased vegetation heterogeneity among subplots within plots and increased vegetation heterogeneity among plots. Soil enrichment promoted taller and layered, but species-poor, canopy. In general, soil fertility effects on abundance, expansion, and dominance of individuals of dominant species promoted variation in canopy composition and structure, or vegetation heterogeneity, among plots on the two fields.     

Microhabitat specialization in a species-rich palm community in Amazonian Ecuador

1 Relationships between microhabitat variables (altitude, inclination, topographic position, drainage, canopy height) and the distribution and abundance of palms and palm-like plants in 50 ha of old-growth terra firme rain forest in the Yasuní National Park, lowland Amazonian Ecuador, were examined using 118 20 × 20 m plots laid out in a stratified random design.
2 If microhabitat niche differentiation is important for maintaining the species richness of the community, then (i) the distribution of the palms will be strongly influenced by microhabitat heterogeneity and (ii) palms of similar growth form will show antagonistic microhabitat relationships.
3 Mantel and cluster analyses showed that palm species distributions were strongly structured by topography. The main difference in species composition was between plots in the bottomland and plots on the upper slopes and hill tops.
4 Logistic and logit analyses showed that 20 of the 31 palm and palm-like taxa analysed had distributions that were significantly related to the microhabitat variables measured, mainly to topography but also to drainage and canopy height.
5 Spatial autocorrelation in the overall community structure was not explained by the microhabitat variables. Analyses of distributions or abundances of single species showed neighbourhood effects for seven taxa.
6 Antagonistic patterns of microhabitat preferences were recognizable among some species pairs of small palms, medium-sized palms and palm-like plants, but not among canopy palms.
7 It is concluded that microhabitat specialization is an important factor in maintaining the diversity of this palm community, while mass effects might also be important.     

Oribatid mite communities in the canopy of montane Abies amabilis and Tsuga heterophylla trees on Vancouver Island, British Columbia

To study the oribatid mite community inhabiting microhabitats in the canopy of montane Abies amabilis [(Douglas ex D. Don) Lindl.] and Tsuga heterophylla [(Raf.) Sarg] tree species across five elevational sites, we collected 180 branch tips and 180 foliose/crustose lichen samples over three time periods. Thirty-three species of oribatid mites were identified from the study area. Mite species richness and abundance was significantly affected by microhabitat, and this association was independent of sampling time. At the microhabitat scale, distinct species assemblages were associated with lichen and branch tip habitats, and to a lesser degree, tree species. Conifer specificity was most apparent in the closely related species of Jugatala, where Jugatala tuberosa Ewing was only found on branch tips from A. amabilis and Jugatala sp. was primarily found on branch tips from T. heterophylla. Microhabitat specificity was most pronounced in Dendrozetes sp. where most individuals were found on branch tips and Anachiperia geminus Lindo et al. that occurred primarily on lichens. Principal components analysis of oribatid mite community composition further showed a high degree of association with microhabitat and tree species. Habitat profiles are difficult to discern for many species because tree, microhabitat, and elevation preferences confound distribution patterns. Given the significant tree-microhabitat associations in species composition in this montane canopy study, we suggest that sampling multiple microhabitats across elevations to look for patterns in community structure offers opportunities to explicitly test organizing principles in community ecology.     

不同喀斯特小生境中土壤丛枝菌根真菌的遗传多样性

为探明西南喀斯特地区小生境土壤中丛枝菌根真菌(AMF)的遗传多样性特征, 利用巢式PCR和变性梯度凝胶电泳相结合的分子生物学方法, 对茂兰3种植被类型下的小生境(石缝、石沟、土面) AMF遗传多样性进行了研究。结果发现: 各类小生境都含有丰富的AMF遗传多样性, 灌木林土面的多样性指数和物种丰富度最高, 为4.06和68; 次生林石缝的最低, 为3.16和29, 所研究的9个小生境多样性指数和物种丰富度的平均值分别高达3.67和48, 高于同类研究在其他地区的结果, 这可能主要与喀斯特生态系统复杂的结构和较高的植物多样性有关; 聚类分析显示各类小生境间的AMF群落结构差异显著, 相似性指数最高仅为0.45, 说明小生境所带来的空间异质性对AMF的遗传多样性产生了显著影响; 基因测序显示球囊霉属(Glomus)极有可能是喀斯特地区AMF的优势菌属, 在以后筛选喀斯特地区的高效生态恢复菌种时可重点考虑球囊霉属的一些菌种。     

Biodiversity impacts of an invasive grass: ant community responses to <Emphasis Type="Italic">Cenchrus ciliaris</Emphasis> in arid Australia

Buffel grass (Cenchrus ciliaris) is a highly invasive species that thrives in semi-arid environments and has the capacity to transform native vegetation outside its native range. However, there is limited information on the effects of buffel grass invasion on native fauna. We used an experimental approach to investigate the impact of buffel grass on the native ant fauna near Alice Springs in semi-arid central Australia. A series of plots where buffel grass was removed and native vegetation had regenerated (B?), paired with adjacent control plots heavily invaded by buffel grass (B+), were used to assess the impact of buffel grass on ant diversity and composition, and on rates of seed dispersal by ants. Differences in ant diversity were also compared between two microhabitat types: bare ground and under cover, to examine the extent to which any impacts were a simple function of change in vegetation cover. Ant abundance and richness were approximately 50 % higher in B? compared with B+ plots, and higher abundance was especially pronounced for the very thermophilic Hot-Climate Specialists. Ant species composition varied significantly between plot types. B? plots supported more species and individuals in both bare and covered microhabitats, which suggests that the differences in ant diversity was not simply through changes in vegetation cover. Rates of seed removal by ants were marginally higher in B? plots. Our findings indicate that buffel grass has a major impact on a dominant faunal group of arid Australia, and possibly reduces the delivery of an important ecosystem service. In addition, our study demonstrates the potential for ecosystem recovery following effective buffel grass management.     

Food resource matching by foraging tits Parus spp. during spring-summer in a Mediterranean mixed forest; evidence for an ideal free distribution

We analysed whether patterns of microhabitat use by Blue Tits Parus caeruleus , Great Tits Parus major and Crested Tits Parus cristatus inhabiting a mixed forest consistently matched the patterns of food availability experienced by foraging birds during spring-summer. The use of five microhabitats by each bird species (the foliage of three tree species, shrubs and ground) and the availability of food in trees during the prebreeding, breeding and post-breeding periods of the birds' annual cycle were measured. All three tit species foraged mainly in the outer part of tree canopies (small branches and leaves or needles). Tit distributions between tree species matched food resource distributions irrespective of overall food resource levels, which varied four-fold between the study periods, and tit species. Tits also exploited secondary microhabitats (shrubs and ground) in periods of low food availability; Blue Tits tended to use shrubs, whereas Great and Crested Tits foraged on the ground. Between-trees distributions fitted that expected from an ideal free distribution, suggesting that food availability and intraspecific exploitative competition were the main factors governing tree use by tits. In contrast, patterns of use of secondary microhabitats (shrubs and ground) seemed to indicate a role for the species-specific morphological configurations of each tit species since Blue Tits are better adapted to hang and tended to forage in shubs, whereas Great and Crested Tits are better adapted to feed on horizontal surfaces and tended to forage on the ground. No evidence of interspecific interactions was observed. Overall, the results pointed to an independent exploitation of Mediterranean mixed forest by each bird species, food availability and food accessibility being the main factors affecting microhabitat use by foraging tits.     

Inter and intraspecific variation in fish body size constrains microhabitat use in a subtropical drainage

Microhabitat characteristics are expected to influence the distribution of stream fish species at fine spatial scales (e.g., within riffle segments). Body size is probably the most important trait that constrains microhabitat occupation by fish, but the effect of intraspecific variation has been understudied. We investigated how physical microhabitat characteristics affect species and body size distribution of fish within a stream riffle segment in a coastal subtropical drainage of Brazil. Fishes were sampled by electrofishing 56 riffle plots along a 730-m long stream segment. Species composition was significantly related to four microhabitat characteristics: substrate size, flow velocity, distance to margin and depth. In addition, mean body size increased with increasing substrate size and depth of microhabitat sampling plots. However, when including species identity in linear mixed-effects models (LMM), we observed a different relationship between body size and microhabitat characteristics, but most of the variation was explained by species identity. Thus, we fitted LMMs separately for each species and found species-specific relations between intraspecific variation in body size and microhabitat characteristics. The low variation explained in the models suggests that other fine scale factors, such as biotic interactions and dispersal from adjacent habitat patches, should be incorporated in modeling microhabitat use by stream fish. Our findings suggest that body size is important by itself, but intraspecific variation in body size also constrains microhabitat use differently for each species, which may depend on other species-specific traits, such as morphology, behavior and life history.     

Bryophyte diversity and distribution along an altitudinal gradient on a lava flow in La Réunion

Non‐vascular plant distribution patterns were examined in three microhabitats along an altitudinal gradient on a recent lava flow of the Piton de la Fournaise volcano (La Réunion, Mascarene archipelago). The uniform nature of the lava flow provides an excellent system to study the relationship between altitude and species diversity and distribution, and at the same time avoiding confusing multiple effects of substrate and vegetation heterogeneity. Non‐vascular plants were surveyed with quadrats within an altitudinal range from 250 m to 850 m a.s.l. Fine‐scale variations in bryophyte communities between three ecological microhabitats (the ground and on the rachises of two fern species) were investigated. Three specific questions were addressed: (1) What is the species diversity of bryophyte communities on a 19‐year‐old lava flow? (2) How does altitude influence the diversity and distribution of bryophytes on a lava flow? (3) Does microhabitat variation control bryophyte diversity? In our study, bryophyte diversity increased with altitude. Unexpectedly, species richness was very high; 70 species of bryophytes were recorded including nine new records for the island. Diversity was also controlled by ecological microhabitats. Bryophyte species were structured into six categories according to altitude and microhabitat preferences. Results suggested that the high diversity of these cryptic organisms on this lava flow is fostered in part by their host substrate and their adaptative strategies on new substrates. On a broader scale, it was concluded that lava flows as primary mineral environments are important to conserve, as they support a high diversity of pioneer organisms that constitute the early stages of the development of La Réunion's remnant lowland rainforest.     

Vegetation patterns at the alpine treeline ecotone: the influence of tree cover on abrupt change in species composition of alpine communities

Aims: The upper elevation limit of forest vegetation in mountain ranges (the alpine treeline ecotone) is expected to be highly sensitive to global change. Treeline shifts and/or ecotone afforestation could cause fragmentation and loss of alpine habitat, and are expected to trigger considerable alterations in alpine vegetation. We performed an analysis of vegetation structure at the treeline ecotone to evaluate whether distribution of the tree population determines the spatial pattern of vegetation (species composition and diversity) across the transition from subalpine forest to alpine vegetation. Location: Iberian eastern range of the Pyrenees. Methods: We studied 12 alpine Pinus uncinata treeline ecotones. Rectangular plots ranging from 940 to 1900 m² were placed along the forest‐alpine vegetation transition, from closed forest to the treeless alpine area. To determine community structure and species distribution in the treeline ecotone, species variation along the forest‐alpine vegetation transition was sampled using relevés of 0.5 m² set every 2 m along the length of each plot. Fuzzy C‐means clustering was performed to assess the transitional status of the relevés in terms of species composition. The relation of P. uncinata canopy cover to spatial pattern of vegetation was evaluated using continuous wavelet transform analysis. Results: Vegetation analyses revealed a large degree of uniformity of the subalpine forest between all treeline ecotone areas studied. In contrast, the vegetation mosaic found upslope displayed great variation between sites and was characterized by abrupt changes in plant community across the treeline ecotone. Plant richness and diversity significantly increased across the ecotone, but tree cover and diversity boundaries were not spatially coincident. Conclusions: Our results revealed that no intermediate communities, in terms of species composition, are present in the treeline ecotone. Ecotone vegetation reflected both bedrock type and fine‐scale heterogeneity at ground level, thereby reinforcing the importance of microenvironmental conditions for alpine community composition. Tree cover did not appear to be the principal driver of alpine community changes across the treeline ecotone. Microenvironmental heterogeneity, together with effects of past climatic and land‐use changes on ecotone vegetation, may weaken the expected correlation between species distribution and vegetation structure.     

Relationship Between Microhabitat Structure and Distribution of Mouse Lemurs (Microcebus spp.) in Northwestern Madagascar

Understanding processes affecting the distribution and abundance of organisms is a central issue in ecology and conservation biology. In northwestern Madagascar, we found an uneven distribution pattern of the golden-brown mouse lemur (Microcebus ravelobensis) and the grey mouse lemur (M. murinus). In one area (JBA) the two species lived sympatrically, whereas in another forest area (JBB) Microcebus ravelobensis occurred exclusively. To investigate whether differences in forest structure may explain this uneven distribution, we conducted a microhabitat analysis and related it to specific distribution. In JBA the habitat of Microcebus ravelobensis was characterized by a higher percentage of trees with many lianas and a higher cover of the herb layer, whereas that of M. murinus had a higher number of trees with a diameter at breast height (DBH) >10 cm. The comparison of the forest structure of the microhabitats of the two species between JBA and JBB revealed further differences. The cover of the overstory, the percentage of trees without lianas and the number of larger trees (DBH >10 cm) among the microhabitats were higher for Microcebus murinus in JBA than for M. ravelobensis in JBB whereas the microhabitats of M. ravelobensis at the two sites did not differ concerning these vegetation structures. Differences between the two species coincide with those of resources important for survival. Our results indicate the importance of microhabitat analyses for the understanding of distribution patterns of species and for successful conservation planning.