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.     

Nest site selection by the Argentine ant and suitability of artificial nests as a control tool

The Argentine ant is an invasive species that has been introduced worldwide causing devastating effects on entire ecosystems. Control strategies might be focused on slowing its rate of spread to limit its establishment inside yet non-invaded areas. For this, a better knowledge about nest selection is necessary to identify rapidly and accurately nest locations where to apply control measures. Herein, nest site selection by the Argentine ant, nests’ physical characteristics and their longevity were studied in three invaded cork oak secondary forest. Results showed that this species shifts nest locations seasonally to keep appropriate microclimatic conditions, nesting mainly underneath rocks during cold and rainy months and in tree bases during warmer periods. The terrain features at micro-scale (orientation and slope) were found to influence the distribution of the Argentine ant nests beneath rocks. Additionally, artificial nests used as a control tool were tested, finding that their use may be suitable if they are set in appropriate locations and before the ants start migrating to winter aggregations.     

Comparison of the initial demographies of pine and oak populations in rural pine forests in Korea and Japan

In order to understand the human impact upon demographic change in plant population in rural forests, we examined the population trends ofPinus densiflora andQuercus serrata inP. densiflora forests viewing their seedlings and saplings in rural Korea and Japan. The most prominent factor affecting the regeneration of the pine and oak was the intensity of management activity which controlled the vegetation stratification and its light environment. Open spaces, such as graveyard or cleaned area that allow the long-term direct daylight in dry season to accelerate the surface heat of soil, were unfavorable habitats for germination and growth of both species. The negative effects of the presence of litter and evergreen trees were related to the failure of early seedling and sapling growth of pine. Cover of litter is, especially, another factor related to the growth of pine saplings. It is considered that successful germination and sapling growth of pine and oak in early successional stages is determined by vegetation structures and light condition.     

Patterns and ecological consequences of abiotic heterogeneity in managed cork oak forests of Southern Spain

Spatial heterogeneity of abiotic factors influences the structure and function of forests and must be taken into account for their conservation and sustainable management. In this study, we evaluate the heterogeneity of abiotic environmental variables in managed cork oak (Quercus suber L.) forests in southern Spain at patch, site and regional scales. The extent of spatial heterogeneity depended on the environmental variable examined and the scale considered. For example, soil Mn and P and light availability in the understorey were very heterogeneous at the regional scale, while soil N had low regional heterogeneity, but high spatial variability, at patch scale, attributed to open overstorey and grazing disturbance. There was a general trend of increasing heterogeneity with spatial scale. We also study the effects of a silvicultural practice—shrub clearing on the forest environment and its consequence for spatial heterogeneity. Shrub clearing increased understorey light and decreased its spatial heterogeneity with idiosyncratic effects on soil properties and their spatial heterogeneity at each site. Finally, we compare the heterogeneity (estimated by the coefficient of variation) obtained in these cork oak forests with a database compiled from published studies on other forest environments. The comparison revealed a remarkable extent of abiotic heterogeneity in the cork oak forests studied, suggesting that a sustainable management of these forests should combine intrinsic and human induced abiotic heterogeneity to preserve crucial ecological processes and to maintain high levels of biodiversity.     

Diversity in the cork oak forests of the northern Straits of Gibraltar Region (Southern Spain)

Several components of diversity (ecological, taxonomic, chorological and morphological– functional) were studied in the woody vegetation of the cork oak forests in the northern Straits of Gibraltar Region, and their relationship to the two main environmental gradients (one mainly climatic—precipitation, fog—and another secondary related to the disturbance and hydric stress associated with hillslope orientation). An inventory of the woody species and their cover measure was carried out on 94 plots. The relationship between the components of diversity and the main environmental gradients was analysed by means of regression analysis. Decreases of species richness, Shannon diversity index, Western Mediterranean species cover, percentage of endemism and the share of the Herrera Syndrome I in diversity were related to the increase of the precipitation and the fog. However, the cover and percentage of species of the Circum-Mediterranean and Mediterranean-Eurosiberian chorological groups increase with the precipitation and the fog. Disturbance and hydric stress associated with hillslope orientation, have a negative effect on specific richness of the Mediterranean-Eurosiberian chorological group and taxonomic singularity, but its have a positive effect on the share of the Herrera Syndrome I in diversity. The number of edaphic endemisms is associated mainly with disturbance. In the cork forests does not exist an inverse relationship between the number of endemisms and floristic richness, as it happens in other Mediterranean areas. It has suggested that this pattern is due to effect of competitive exclusion associated with disturbance in vegetation on relatively fertile substrate.     

Exploitative strategies of the invasive Argentine ant (Linepithema humile) and native ant species in a southern Spanish pine forest

The Argentine ant, Linepithema humile (Mayr, 1868), is displacing native ant species in Do?ana National Park (Spain). This paper discusses the results of experiments aimed at analyzing exploitation competition between the invading species and other ant species in a park community. The Argentine ant was found to implement several strategies favoring its success in exploitation competition: mass recruitment, use of various microhabitats (on the ground and in trees), and activity over a wide range of temperatures. Although these strategies were not exclusive to L. humile, their joint use, together with the large number of workers forming each "unicolony," conferred a clear advantage for resource exploitation. Some native species were more severely affected than others by the presence of L. humile in terms of both abundance and behavior. The worst affected species were those whose ecological characteristics were similar to those of the Argentine ant, e.g., Pheidole pallidula (Nylander, 1849); the species least affected was Cataglyphis floricola Tinaut, 1993, possibly because of its subordinate and thermophilous nature (little overlap of daily activity rhythms with the exotic species).     

Impact of vegetation removal on the temperature and moisture content of red wood ant nests

We studied the influence of vegetation growing on red wood ant, Formica polyctena, hills and its removal, by cutting, on the temperature and moisture content of the nests. Vegetation was removed from half of nests (n = 10) in June and August. Generally, ant hills were small (0.1–1.1 m³) and their daily temperature fluctuations and moisture (16–38%) were low. The centre temperature of ant hills was positively correlated with ambient air temperature. Daily temperatures peaked at 13:00 and slowly decreased until 09:00 then increased again until 13:00. Nest moisture content was not related to nest volume. All the ant hills were covered with Reed Grass (Calamagrostis arundinacea) that grows through nests and reaches about 185–1085 g/dcm² of dry matter. Dry vegetation matter (g/dcm² of anthill surface) was the same on cut and uncut nests as well because all ant hills were under long-term management (vegetation removal) for at least 10 years. Although vegetation removal did not result in an immediate increase in the temperature of denuded ant hills removal did results in higher daily and night temperatures during the July-September period. The moisture content of nests with undisturbed and intact vegetation was the same. The dry matter content of vegetation strongly affected their moisture content. However, temperature at the inside centre of nests decreased as vegetation dry matter increased, i.e. there was a statistically negative correlation between temperature and moisture. The results support removing grass as a suitable management tool to facilitate the survival of wood ants. Received 30 December 2007; revised 22 April 2008; accepted 10 June 2008.     

八仙山不同类型松栎林群落主要特征分析

为探究八仙山保护区不同类型森林群落的更新潜力、多样性程度以及稳定性水平,阐明三者间的关系,该文以保护区内油松林、蒙古栎林和油松-栓皮栎混交林(松栎混交林)3种不同类型天然次生林为对象,调查建群种径级结构和更新潜力,计算不同层次群落多样性,测定M.Godron稳定性,并采用主成分法建立评价模型.结果表明:(1)油松种群径...     

The role of abiotic conditions in shaping the long-term patterns of a high-elevation Argentine ant invasion

Analysis of long‐term patterns of invasion can reveal the importance of abiotic factors in influencing invasion dynamics, and can help predict future patterns of spread. In the case of the invasive Argentine ant (Linepithema humile), most prior studies have investigated this species’ limitations in hot and dry climates. However, spatial and temporal patterns of spread involving two ant populations over the course of 30 years at a high elevation site in Hawaii suggest that cold and wet conditions have influenced both the ant's distribution and its rate of invasion. In Haleakala National Park on Maui, we found that a population invading at lower elevation is limited by increasing rainfall and presumably by associated decreasing temperatures. A second, higher elevation population has spread outward in all directions, but rates of spread in different directions appear to have been strongly influenced by differences in elevation and temperature. Patterns of foraging activity were strongly tied to soil temperatures, supporting the hypothesis that variation in temperature can influence rates of spread. Based on past patterns of spread, we predicted a total potential range that covers nearly 50% of the park and 75% of the park's subalpine habitats. We compared this rough estimate with point predictions derived from a degree‐day model for Argentine ant colony reproduction, and found that the two independent predictions match closely when soil temperatures are used in the model. The cold, wet conditions that have influenced Argentine ant invasion at this site are likely to be influential at other locations in this species’ current and future worldwide distribution.     

Species and structural diversity affect growth of oak,but not pine,in uneven-aged mature forests

The effects of mixing tree species on tree growth and stand production have been abundantly studied, mostly looking at tree species diversity effects while controlling for stand density and structure. Regarding the shift towards managing forests as complex adaptive systems, we also need insight into the effects of structural diversity. Strict forest reserves, left for spontaneous development, offer unique opportunities for studying the effects of diversity in tree species and stand structure. We used data from repeated inventories in ten forest reserves in the Netherlands and northern Belgium to study the growth of pine and oak. We investigated whether the diversity of a tree's local neighbourhood (i.e., species and structural diversity) is important in explaining its basal area growth. For the subcanopy oak trees, we found a negative effect of the tree species richness of the local neighbours, which – in the studied forests – was closely related to the share of shade-casting tree species in the neighbourhood. The growth of the taller oak trees was positively affected by the height diversity of the neighbour trees. Pine tree growth showed no relation with neighbourhood diversity. Tree growth decreased with neighbourhood density for both species (although no significant relationship was found for the small pines). We found no overall diversity-growth relationship in the studied uneven-aged mature forests; the relationship depended on tree species identity and the aspect of diversity considered (species vs. structural diversity).     

Diameter of downed woody debris does matter for saproxylic beetle assemblages in temperate oak and pine forests

Deadwood is widely recognized to be an important issue for biodiversity conservation in forest ecosystems. Establishing guidelines for its management requires a better understanding of relationships between woody debris characteristics and associated species assemblages. Although deadwood diameter has been identified as an important factor predicting occurrence of many saproxylic species, the boundary between small and large diameter has not yet been precisely defined. In commercial forests, it is also of critical importance to know which diameter is large enough to host the beetle species associated with large logs in order to ensure cost-effectiveness of biodiversity conservation measures. We investigated the differences in saproxylic beetle assemblages among four different diameter classes of downed woody oak and maritime pine debris, in France. Beetles were sampled using in situ emergence traps. The diameter of deadwood pieces ranged from 1 to 40 cm. No patterns of nestedness associated with the gradient of diameter size were identified for either tree species. More indicator saproxylic species were observed in large logs and branches than in small logs. A clear distinction appeared in assemblage composition around the 5-cm diameter threshold whereas no similar pattern occurred around the 10 cm value, i.e. the classical threshold used in forestry to distinguish fine woody debris from coarse woody debris. For both tree species, the mean body length of beetles increased with the diameter of deadwood suggesting that the quantity of available resources per piece may constitute a limiting factor for large beetle species. This study confirms that not only large deadwood pieces are relevant for saproxylic biodiversity conservation but also the smallest pieces. Therefore, forest managers would be well advised to maintain a high diversity of deadwoods to maintain saproxylic biodiversity.     

Diversity and structure of ant communities associated with oak,pine, eucalyptus and arable habitats in Portugal

Summary In central Portugal, 28 species of ants were found in oak, 25 in pine, 35 in eucalyptus and 12 in arable habitats, a total of 43 species. They include five numerically dominant species, the exotic Argentine ant.Linepithema (Iridomyrmex) humile and four native species,Crematogaster scutellaris, Pheidole pallidula, Tapinoma nigerrimum andTetramorium hispanicum. L. humile occurred in 34% of sampled sites. When present, it was abundant in all three arboreal habitats, where it was associated with strikingly decreased ant species richness and equitability. Such diversity was greater inL. humile-colonised arable habitats, where the ant was much less abundant than in the arboreal habitats.WhereL. humile was absent,C. scutellaris andP. pallidula were usually co-dominants in oak and pine, andT. nigerrimum andT. hispanicum in the arable habitat, but all were absent or rare in eucalyptus. Ants were numerically least abundant in eucalyptus but, in the absence ofL. humile, species richness was greater and the community more equitable than in the other habitats.L. humile-absent arable habitats supported the poorest and least equitable ant community.     

Hyperdiversity of ectomycorrhizal fungus assemblages on oak seedlings in mixed forests in the southern Appalachian Mountains

Diversity of ectotrophic mycobionts on outplanted seedlings of two oak species (Quercus rubra and Quercus prinus) was estimated at two sites in mature mixed forests in the southern Appalachian Mountains by sequencing nuclear 5.8S rRNA genes and the flanking internal transcribed spacer regions I and II (ITS). The seedlings captured a high diversity of mycorrhizal ITS-types and late-stage fungi were well represented. Total richness was 75 types, with 42 types having a frequency of only one. The first and second order jackknife estimates were 116 and 143 types, respectively. Among Basidiomycetes, tomentelloid/thelephoroid, russuloid, and cortinarioid groups were the richest. The ascomycete Cenococcum geophilum was ubiquitously present. Dominant fungi included a putative Tuber sp. (Ascomycetes), and Basidiomycetes including a putative Craterellus sp., and Laccaria cf. laccata. Diversity was lower at a drier high elevation oak forest site compared to a low elevation mesic cove--hardwood forest site. Fungal specificity for red oak vs. white oak seedlings was unresolved. The high degree of rarity in this system imposes limitations on the power of community analyses at finer scales. The high mycobiont diversity highlights the potential for seedlings to acquire carbon from mycelial networks and confirms the utility of using outplanted seedlings to estimate ectomycorrhizal diversity.     

胜山阔叶红松林蚂蚁巢穴对其他地表节肢动物多样性的影响

为了阐明蚂蚁巢穴对其他地表节肢动物群落组成和多样性的影响,于2019年在胜山自然保护区的原始阔叶红松林内开展实验,并采用陷阱法收集地表节肢动物.共捕获地表节肢动物92266只,分别为蜈蚣目、盲蛛目、马陆目、蜘蛛目,大头蚁属和步甲科、隐翅虫科、葬甲科这8个类群;蚂蚁巢穴存在及到蚂蚁巢穴的不同距离对其他地表节肢动物个体数量...     

凋落物处理和氮添加对松栎混交林土壤生态酶化学计量的影响

全球变化会引起凋落物质量和数量的变化以及氮沉降增加,从而影响土壤养分循环。土壤生态酶化学计量可以揭示微生物生长和代谢过程的养分限制,但目前温带混交林土壤生态酶化学计量对凋落物输入和氮添加同时改变的响应还不清楚。通过凋落物处理和氮添加实验设计,探讨温带松栎混交林生态酶化学计量的响应以及影响生态酶化学计量的主要因子。结果表明:(1)凋落物处理和氮添加无显著交互作用,土壤生态酶化学计量在氮添加处理下差异不显著,在凋落物处理下差异显著,表现为叶凋落物加倍(L)和混合凋落物加倍(LB)处理高于枝果凋落物加倍(B)和去除凋落物处理(N)。不同凋落物和氮添加处理下,土壤生态酶化学计量均未明显偏离1∶1∶1的关系。(2)土壤微生物碳利用效率(CUE_C∶N和CUE_C∶P)表现为叶凋落物加倍和混合凋落物加倍处理低于枝果凋落物加倍和去除凋落物处理,在氮添加处理下差异不显著。土壤微生物氮利用效率(NUE_N∶C)和微生物磷利用效率(PUE_P∶C)在不同凋落物和氮添加处理下差异均不显著。TER_C∶N在不同...     

Assessment and management of old-growth forests in south eastern Australia

Abstract

Old-growth forests in south eastern Australia are important for biodiversity conservation, recreation, carbon storage, social values and, to a declining extent, for timber production. Developing a comprehensive definition of old-growth forest that can apply across all Australian vegetation types has been challenging. Old growth can be viewed from ecological and social perspectives. For policy and management purposes old growth has been defined as a growth stage in forest development, incorporating ecological maturity and lack of evidence of past disturbance. Classification and assessment of old growth has largely been restricted to those areas covered by regional forest agreements (RFAs) between different states and the Federal Government. Old growth can be impacted by wildfire, timber harvesting, insect pests, diseases and other disturbances. Climate change will also present challenges for the future management of old-growth forests. There is increasing scientific understanding of the relationships between species, forest growth stage and old-growth forest attributes. To meet biodiversity conservation objectives, the management focus is shifting from assessing and protecting old-growth forests, to providing for forests across the landscape with old-growth attributes. This approach may be at odds with other conceptions of old growth based on notions of undisturbed systems free of human influence.     

Intraspecific competition influences the symmetry and intensity of aggression in the Argentine ant

Cooperative social groups rely on the ability to distinguishmembers from nonmembers. Accordingly, social insects have evolveda variety of systems that allow discrimination of nest matesfrom non–nest mates. In this study, we show that experiencecan modify patterns of intraspecific aggression in Argentineants (Linepithema humile). In laboratory experiments, we foundthat aggression between colonies was often asymmetrical, butin all five cases, this asymmetry shifted to symmetrical aggressionafter contact with a hostile colony. Moreover, in the field,aggression between workers collected from colony borders wassymmetrical, whereas polarized aggression occurred between workerscollected 500 m away from colony borders. Coinciding with thisshift in aggression symmetry, we also observed an increase inboth the overall level of aggression and the frequency of aggressionin both the field and laboratory bioassays. We found littleevidence for colony-level competitive asymmetries stemming frompolarities in aggression at the worker level, either in thelaboratory or in the field. These results illustrate that recognitionsystems in Argentine ants are surprisingly dynamic and provideexperimental evidence for how recognition can be adjusted inresponse to specific circumstances—in this case the presenceof intraspecific competitors.     

Allozyme variation in cork oak (Quercus suber L.): the role of phylogeography and genetic introgression by other Mediterranean oak species and human activities

 Genetic variation in the cork oak (Quercus suber L.) was investigated using 11 loci from seven enzyme systems in 40 populations sampled over the entire distribution of this species in the western Mediterranean Basin. Mean heterozygosity values over the polymorphic loci (Ho=0.283), the percentage of polymorphic populations (M=0.76), and the total genetic diversity (Ht=0.31) from which 11% was accounted for among-population variation, are among the highest recorded in oak species. In contrast to previous results in holm oak (Q. ilex L.), another evergreen species in the same area, cork oak possessed a smaller allele pool and a lower average number of alleles per locus and per population (A=2.0). More particularly, very few low-frequency alleles were observed in cork oak except for eight populations in which allozyme polymorphism at locus Pgi 1, diagnostic between both species, indicates that these low-frequency alleles are introgressed from holm oak. On the basis of the genetic distance estimated from allozyme frequencies, 32 of the 40 cork oak populations studied were classified into two very distinct sets which also corresponded to distinct geographic areas. One set gathered together the 18 populations from the Iberian peninsula and two adjacent areas in France, i.e. the centre of origin of cork oak, according to paleobotanical data. This set was characterized by a larger allele pool, a higher within-population genetic diversity and a lower differentiation between populations than was observed in the other set, which comprised the populations from North Africa, Sicily, Sardinia, Corsica, continental Italy and the region of Provence (southeastern France). In these more southern and eastern disjunct areas, cork oak migration from Iberia may have occurred at different periods since the end of the Tertiary. The possible effect of human activity on cork oak genetic structure, i.e. the selection of good-quality cork, acorn over-use for animal food, and even human nutrition, is discussed. Received: 3 March 1998 / Accepted: 19 March 1998     

Factors influencing the distribution of nests of the Argentine ant Linepithema humile Mayr (hymenoptera: formicidae), in a foothills ecosystem of the central zone of Chile

The purpose of this research was to demonstrate the dependant relationship between the Argentine ant Linepithema humile Mayr, plant coverage, and human settlements. A method was designed in order to sample the presence of the Argentine ant and other ant species that may had influenced L. humile distribution, under different types of vegetation and percentages of plant coverage, taking in consideration the distance from human settlements. Eight sample stations were established. Four of these stations were found on a dwelling home and the other four were found on similar areas, but far from human settlements. Three transects were established from the center of each sampling station (Tt1, shrublike vegetation, Tt2, herblike vegetation and Tt3, no vegetation). Transects were compound by 10 m side quadrants. A negative correlation was found between nest number of L. humile and human settlement distance, therefore nests were not found at distances higher than 80 m, in all studied areas. There was a positive and significant correlation between nest number of L. humile and plant coverage percentage, regardless the type of vegetation found. The same trend was found for other ant species studied in the area. Finally, it was proved that the distribution of L. humile nests is not influenced by other ant species.