Colonisation by a dominant ant facilitated by anthropogenic disturbance: effects on ant assemblage composition, biomass and resource use

Dominant species are thought to regulate species composition and assemblage structure. Invasion by a dominant species is thus likely to alter assemblages and anthropogenic disturbance often facilitates such invasions. In this study we examined the association of a dominant ant, Iridomyrmex purpureus , native to south-eastern Australia, with fire trails in national parks and its effects on ant assemblages. Association with fire trails was examined by comparing the numbers of I. purpureus nests on transects along fire trails with those in transects through surrounding vegetation. Ant assemblages and habitat characteristics of eight sandstone outcrops that supported colonies of I. purpureus were compared with those on eight that did not in summer and autumn 2000. We examined ant species richness, abundance, composition and biomass using quadrats, and resource use with Acacia botrycephalus seeds placed on rock and in vegetation. I. purpureus nests were considerably more common along fire trails than in surrounding vegetation. Sites with I. purpureus had similar species richness to those without, but a lower abundance and biomass of other ants and a different assemblage composition. These differences could not be attributed to any differences in measured habitat characteristics. Ecologically similar species, particularly other species of Iridomyrmex , were less abundant in areas with I. purpureus . While the biomass of other species was suppressed in areas with I. purpureus , the biomass of the dominant was several times that of the assemblage of other ants, a pattern shared with assemblages invaded by exotic species. In areas with I. purpureus , seeds were removed more rapidly from rock, but not vegetation, indicating that resources on rock may be under-exploited by other species. Regulation of invaded ant assemblages by this dominant ant is thus limited to functionally similar species, and this may be due to its use of resources that are unexploited in its absence.     

Scale dependence of diversity measures in a leaf-litter ant assemblage

A reliable characterization of community diversity and composition, necessary to allow inter‐site comparisons and to monitor changes, is especially difficult to reach in speciose invertebrate communities. Spatial components of the sampling design (sampling interval, extent and grain) as well as temporal variations of species density affect the measures of diversity (species richness S, Buzas and Gibson's evenness E and Shannon's heterogeneity H). Our aim was to document the small‐scale spatial distribution of leaf litter ants in a subtropical dry forest of the Argentinian Chaco and analyze how the community characterization was best achieved with a minimal sampling effort. The work was based on the recent standardized protocol for collecting ants of the leaf litter (“A.L.L.”: 20 samples at intervals of 10 m). To evaluate the consistency of the sampling method in time and space, the selected site was first subject to a preliminary transect, then submitted after a 9‐month interval to an 8‐fold oversampling campaign (160 samples at interval of 1.25 m). Leaf litter ants were extracted from elementary 1 m² quadrats with Winkler apparatus. An increase in the number of samples collected increased S and decreased E but did not affect much H. The sampling interval and extent did not affect S and H beyond a distance of 10 m between samples. An increase of the sampling grain had a similar effect on S than a corresponding increase of the number of samples collected, but caused a proportionaly greater increase of H. The density of species m^?2 varied twofold after a 9‐month interval; the effect on S could only be partially corrected by rarefaction. The measure of species numerical dominance was little affected by the season. A single standardized A.L.L. transect with Winkler samples collected <45% of the species present in the assemblage. All frequent species were included but their relative frequency was not always representative. A log series distribution of species occurrences was oberved. Fisher's α and Shannon's H were the most appropriate diversity indexes. The former was useful to rarefy or abundify S and the latter was robust against sample size effects. Both parametric and Soberón and Llorente extrapolation methods outperformed non‐parametric methods and yielded a fair estimate of total species richness along the transect, a minimum value of S for the habitat sampled.     

The spatial variation in ant species composition and functional groups across the Subantarctic-Patagonian transition zone

The role of ecotones in the maintenance of species diversity is rather controversial; they may represent either biodiversity hotspots with unique and rare forms, or be transitional areas that hold marginal populations of species. We analyse the taxonomic and functional composition of ant species assemblages across the Subantarctic-Patagonian transition to evaluate the role that transitional shrublands may play in the maintenance of the taxonomic and functional differentiation. We collected ants using 450 pitfall traps within a ~150 × 150 km area. Species were classified into functional groups in relation to stress and disturbance, and in foraging groups according to their foraging behavior. An indicator value for each species in each habitat was calculated. The steppes and the forests strongly differed in ant species and functional composition. Climatic effects combined with structural components of plant environment explained about 23–27 % of the variation in ant composition. The shrublands did not show a distinctive fauna, and show greater similarity in ant species composition and in the proportional occupancy of functional groups to the steppes than to the forests. They harbor neither rare nor indicator species, except for Lasiophanes valdiviensis, and thus this reinforces the idea that they are not a habitat source of species, but an area of encounter between two distinct forest- and steppe- ant faunas, where a high number of local distributional limits of ant species overlap.     

海州湾蟹类群落种类组成及其多样性

本研究根据2011年3月、5月、7月、9月和12月在海州湾海域进行的渔业资源底拖网调查数据,采用Margalef种类丰富度指数(D)、Shannon-Wiener多样性指数(H′)和Pielou均匀度指数(J′)等分析了该海域蟹类群落种类组成及其多样性的时空变化。结果表明,本次调查共捕获蟹类34种,隶属于18科27属,其中玉蟹科种数最多,有3属4种。从适温属性来看,主要以暖水种(16种)和暖温种(15种)为主,冷温种3种。蟹类群落各多样性指数的月际间变化较大,其中物种丰富度指数(D)3月最高,12月最低;多样性指数(H′)和均匀度指数(J′)均在7月最高,12月最低。多样性指数的空间分布呈现一定的月变化:在3月、5月、7月均表现为北高南低;9月为中部低,南、北部海域较高;12月均呈南高北低的趋势。蟹类单位网次渔获尾数空间分布格局呈现明显的月变化;平均单位网次渔获尾数呈现一定的月变化,总体上表现为3月、5月、12月高于7月和9月。Pearson相关分析结果表明,在5月,多样性指数(H′)和均匀度指数(J′)与底层水温呈显著负相关,与底层盐度呈极显著正相关,多样性指数还与水深呈显著正相关;12月均匀度指数与底层水温和水深均呈极显著负相关,与底层盐度呈显著负相关;在3月、7月和9月,各多样性指数与底层水温、底层盐度及水深均无显著相关性。海州湾蟹类种类组成及多样性的时空变化主要与海州湾地处温带海域、水温等海洋环境因子的季节变化以及优势种的数量分布有关。     

Functional and genetic diversity changes through time in a cloud forest ant assemblage

Climate change in the Neotropics is causing upslope range shifts. We used arrays of ant species collected in a cloud forest at 1,500 m in Área de Conservación Guanacaste (ACG), northwestern Costa Rica, collected in two time periods (1998–2000 and 2008–2011) to measure changes in species richness and diversity over a decade. Using metrics of community structure, we found that the species assemblage in the collections from the 1990s was significantly phylogenetically clustered and functionally less diverse as compared to collections from the early 2000s. At both time points, the assemblages were significantly phylogenetically clustered and while the difference in functional diversity between the time points was not significant, the ant assemblage has become lighter in color (on average) over time. When individual species are considered, the overall pattern of replacement is consistent with the cloud forest ant assemblage being colonized by arrivals from lower elevation forests. The invertebrate communities on cloud forested mountain tops are especially vulnerable to a changing climate as there are two factors working together; no higher terrain to which they can move and the invasion of more and more taxa from lower downslope. This vulnerability is already measurable.     

Mutualistic rhizobia reduce plant diversity and alter community composition

Mutualistic interactions can be just as important to community dynamics as antagonistic species interactions like competition and predation. Because of their large effects on both abiotic and biotic environmental variables, resource mutualisms, in particular, have the potential to influence plant communities. Moreover, the effects of resource mutualists such as nitrogen-fixing rhizobia on diversity and community composition may be more pronounced in nutrient-limited environments. I experimentally manipulated the presence of rhizobia across a nitrogen gradient in early assembling mesocosm communities with identical starting species composition to test how the classic mutualism between nitrogen-fixing rhizobia and their legume host influence diversity and community composition. After harvest, I assessed changes in α-diversity, community composition, β-diversity, and ecosystem properties such as inorganic nitrogen availability and productivity as a result of rhizobia and nitrogen availability. The presence of rhizobia decreased plant community diversity, increased community convergence (reduced β-diversity), altered plant community composition, and increased total community productivity. These community-level effects resulted from rhizobia increasing the competitive dominance of their legume host Chamaecrista fasciculata. Moreover, different non-leguminous species responded both negatively and positively to the presence of rhizobia, indicating that rhizobia are driving both inhibitory and potentially facilitative effects in communities. These findings expand our understanding of plant communities by incorporating the effects of positive symbiotic interactions on plant diversity and composition. In particular, rhizobia that specialize on dominant plants may serve as keystone mutualists in terrestrial plant communities, reducing diversity by more than 40 %.     

Spatial and functional structure of an entire ant assemblage in a lowland Panamanian rainforest

Ants are a major ecological group in tropical rainforests. Few studies in the Neotropics have documented the distribution of ants from the ground to the canopy, and none have included the understorey. A previous analysis of an intensive arthropod study in Panama, involving 11 sampling methods, showed that the factors influencing ant β diversity (i.e., changes in assemblage composition) were, in decreasing order of importance, the vertical (height), temporal (season), and horizontal (geographic distance) dimensions. In the present study, we went one step further and aimed (1) to identify the best sampling methods to study the entire ant assemblage across the three strata, (2) to test if all strata show a similar horizontal β diversity and (3) to analyze the functional structure of the entire ant assemblage. We identified 405 ant species from 11 subfamilies and 68 genera. Slightly more species were sampled in the canopy than on the ground; they belonged to distinct sub-assemblages. The understorey fauna was mainly a mixture of species found in the other two strata. The horizontal β diversity between sites was similar for the three strata. About half of the ant species foraged in two (29%) or three (25%) strata. A single method, aerial flight interception traps placed alongside tree trunks, acting as arboreal pitfall traps, collected half of the species and reflected the vertical stratification. Using the functional traits approach, we observed that generalist species with mid-sized colonies were by far the most numerous (31%), followed by ground- or litter-dwelling species, either specialists (20%), or generalists (16%), and arboreal species, either generalists (19%) or territorially dominant (8%), and finally army ants (5%). Our results reinforce the idea that a proper understanding of the functioning of ant assemblages requires the inclusion of arboreal ants in survey programs.     

Organic mulches in highbush blueberries alter beetle (Coleoptera) community composition and improve functional group abundance and diversity

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Changes in woody community structure and composition under constrasting landuse systems in a semi-arid savanna, South Africa

We aimed to explore the farm scale effects of three landuse types, communal grazing, wildlife management and commercial cattle farming, on the woody vegetation of a semiarid savanna. Location The study farms were located within a single bioclimatic zone in semiarid savanna, South Africa. Methods The species composition and structure of woody vegetation on three farms of each of three landuse types were sampled. Results We found that communal grazing land sites were classified outside the topland-bottomland vegetation dichotomy characteristic of this region. Comparisons of size class distributions showed the communal grazing lands had fewer small and large individuals; suggesting both lower levels of regeneration and regenerative capacity in the communal grazing lands. The species richness and biomass of woody plants was lower on communal grazing lands than on private game reserves and commercial cattle farms. The longevity of tree species explains the observed lag between changes in abundance and species loss; we consequently predict that there will be future losses of species in the communal grazing lands. By classifying species into a range of use-categories we showed that utilization and species loss was not limited to certain plant use categories. Higher levels of wood harvesting measured in the communal grazing lands are likely to be responsible for the observed differences. Main conclusions It is concluded that communal grazing management at this study site has substantially changed the composition and structure of woody plant communities, and that these changes have reduced the current availability of natural resources and will reduce resource production in the future.     

Changing phosphorus concentration and subsequent prophage induction alter composition of a freshwater viral assemblage

1. The effects of nutrients on the temporal variation in viral assemblage composition, and in particular the occurrence of temperate phages, were assessed in mesotrophic Lake Erken over 5 months of the ice‐free period. The percentage of the bacterial community that contained inducible prophages (lysogenic bacteria, LB) changed over the season, being lowest in late spring and highest in early autumn. The most important variables for predicting LB were concentrations of total nitrogen (TN), total phosphorus (TP) and temperature. 2. The viral assemblage composition, as determined by pulsed‐field gel electrophoresis (PFGE), also changed over the season. Prophages were induced by incubations with mitomycin C and we show, for the first time for natural communities, that the resulting temperate phages could be detected using PFGE. 3. A substantial fraction (19%) of the number of detected operational taxonomic units (OTUs: defined as unique genome sizes) appeared unique to temperate phages and 41% of OTUs increased in relative abundance after treatment with mitomycin C. 4. Different viral OTUs were induced at different times during the season. The most important environmental factor covarying with viral assemblage composition over the period of study, as determined by multivariate analysis, was concentration of TP. In re‐growth cultures with natural bacteria and lowered viral abundance (VA) (decreased virus to bacteria ratio), addition of PO₄‐P induced prophages and resulted in subsequent production of temperate phages, as indicated by a decreased percentage of LB and increased VA. Incubations of natural bacterial communities with mitomycin C (field data) or PO₄‐P (experiment) changed the viral assemblage composition at a similar rate as the observed monthly changes in the lake.     

Identifying the scales of variability in stream macroinvertebrate abundance, functional composition and assemblage structure

1. Many natural ecosystems are heterogeneous at scales ranging from microhabitats to landscapes. Running waters are no exception in this regard, and their environmental heterogeneity is reflected in the distribution and abundance of stream organisms across multiple spatial scales. 2. We studied patchiness in benthic macroinvertebrate abundance and functional feeding group (FFG) composition at three spatial scales in a boreal river system. Our sampling design incorporated a set of fully nested scales, with three tributaries, two stream sections (orders) within each tributary, three riffles within each section and ten benthic samples in each riffle. 3. According to nested anova s, most of the variation in total macroinvertebrate abundance, abundances of FFGs, and number of taxa was accounted for by the among‐riffle and among‐sample scales. Such small‐scale variability reflected similar patterns of variation in in‐stream variables (moss cover, particle size, current velocity and depth). Scraper abundance, however, varied most at the scale of stream sections, probably mirroring variation in canopy cover. 4. Tributaries and stream sections within tributaries differed significantly in the structure and FFG composition of the macroinvertebrate assemblages. Furthermore, riffles in headwater (second order) sections were more variable than those in higher order (third order) sections. 5. Stream biomonitoring programs should consider this kind of scale‐dependent variability in assemblage characteristics because: (i) small‐scale variability in abundance suggests that a few replicate samples are not enough to capture macroinvertebrate assemblage variability present at a site, and (ii) riffles from the same stream may support widely differing benthic assemblages.     

Australian ant research: fabulous fauna, functional groups, pharmaceuticals, and the Fatherhood

Abstract   Apart from flies, ants are Australia's most noticeable and studied insects. In addition to their sheer abundance and ubiquity in most terrestrial ecosystems, they are also exceptionally diverse. Here, we outline the history of describing the Australian ant fauna and document the resources that are available for identifying and researching them. Unusual patterns in chromosome numbers in individual species are discussed, and the rediscovery of an ancient ant is described. A framework for understanding the dynamics of Australian ant communities is outlined, and the functional groups that fall within this framework are documented. The predictability of responses of ant communities to stress and disturbance has enabled a protocol for using ants as bioindicators of environmental health and integrity to be developed. This has been exported and adapted to other regions of the world. Australian ant research has also lead to promising sources of biopharmaceuticals. As well as describing these two practical applications of Australian ant research, this review looks at some of the future directions that studies on Australian ants might take.     

植物功能多样性与功能群研究进展

综述了植物功能多样性与功能群研究的最新进展。介绍了植物功能群的定义及植物功能群的划分方法。在功能多样性与生态系统资源动态关系方面．抽样效应和生态位互补效应用来解释植物多样性在生态系统资源动态中的作用。功能多样性与生态系统的稳定性间的关系可以用生态冗余或生态保险概念来解释,这两个概念是一个问题的两个侧面,是多样性与生态系统功能争论的焦点。     

Impact of secondary forest management on ant assemblage composition in the temperate region in Japan

In Japan, the impacts of human disturbance on ant assemblages have been intensively studied mainly in suburban areas. In contrast, the impact on ant assemblages of long-term human management and abandonment of forests is not well studied even though forestry is viewed as a process that seriously impacts ant assemblages. Besides, the studies focused on the relationship between secondary forest management for producing the firewood and charcoal which is considered to be characteristic of Japan and ant assemblage is not well studied. Do the long-term impacts on the secondary forest alter the ant composition? The effects of forest management on ant assemblages were studied through comparisons of managed, unmanaged and clear cut forest plots in secondary tree stands that had been used previously for producing firewood and charcoal. Ant species richness did not differ among forest categories, but ant species composition varied among forest categories. The absence or presence of openland and woodland ant specialist species is considered a good indicator for secondary forest management.     

Functional significance of ungulate diversity in African savannas and the ecological implications of the spread of pastoralism

The African savanna biome supports a higher diversity of ungulate species than is found in any other biome or continent. This exceptional faunal diversity and herbivore biomass density is directly linked to the high spatial heterogeneity of African savanna ecosystems. The dependence of herbivore dietary tolerance on body size translates into important size-related differences between savanna ungulate species in terms of habitat specificity, geographical range, and the share of community resources exploited. Intact savanna ungulate communities, with species distributed across body size classes and feeding guilds (grazer/browser), have strong regulatory influences on savanna ecosystem structure and function. Replacement with livestock systems of low diversity and high biomass density within a narrow body size range has occurred through the removal of competitors, pathogens, and predators, and the widespread provisioning of water. Overgrazing by livestock, coupled with episodic droughts, has caused widespread rangeland degradation and loss of floristic and faunal diversity which, by current models, is unlikely to recover to 'climax conditions even with destocking. In selected regions where potential still exists, African savanna biodiversity and human economic development will both be best served by the integration of sustainable wildlife utilization into multispecies animal production systems.     

Changes in functional composition and diversity of waterbirds: The roles of water level and submerged macrophytes

1. Water level and submerged macrophytes are critical players for the functioning of shallow lake ecosystems; understanding how waterbird communities respond to changes in both can have important implications for conservation and management. Here, we evaluated the effects of changes in water level and submerged macrophyte status on wintering waterbird community size, functional group abundances, functional diversity (FD), and community assembly by using a dataset compiled over 50 years.
2. We built generalised linear models to evaluate the effects of water level and submerged macrophyte status on the above-listed attributes of the waterbird communities by using mid-winter waterbird censuses, water level measurements, and submerged macrophyte surveys, along with submerged macrophyte macrofossil records from two shallow lakes in Turkey. Using a relevant set of functional traits, we defined functional groups, calculated four FD measures, and simulated null distributions of the FD measures for assessing assembly rules.
3. We found that macrophyte-dominated years had significantly higher abundances of waterbirds in one of the study lakes, and had more diving herbivores and omnivores in both lakes, while diving/scooping fish-eating waterbird abundance was lower in macrophyte-dominated years. Community size in Lake Beyşehir exhibited a negative association with water level; surprisingly, however, none of the functional group abundances and FD indices were significantly related to water level.
4. In our study communities, standardised effect sizes of functional richness and functional dispersion—two indices that are particularly sensitive to community assembly processes—were mostly lower than those of randomly assembled communities, which implies functional clustering. Shifts to a scarce-macrophyte state were associated with increases in these two indices, possibly due to either changes in the relative strength of environmental filtering and limiting similarity in community assembly or sampling of transitional communities. Further studies covering a wider range of the trophic/macrophyte status spectrum are needed to be certain.
5. The results of this study indicate that shifts between abundant and scarce-macrophyte states can have significant effects on wintering waterbird abundances, FD and community assembly. The results also suggest that shallow lakes in macrophyte-dominated states can support more wintering waterbirds, especially diving omnivores, some of which are globally threatened.