Functional complement of biogenic structures produced by earthworms, termites and ants in the neotropical savannas

Soil-engineering organisms (earthworms, termites and ants) affect the soil and litter environment indirectly by the accumulation of their biogenic structures (casts, pellets, galleries, crop sheetings nests…). An enzymatic typology was conducted on six types of biogenic structures: casts produced by two earthworms (Andiodrilus sp. and Martiodrilus sp.), a nest built by a soil-feeding termite (Spinitermes sp.), crop galleries built by another soil-feeding termite (Ruptitermes sp.) and soil pellets produced by two species of leaf-cutting ant (Acromyrmex landolti and Atta laevigata) and an control soil from a natural Colombian savanna. A total of 10 enzymes (xylanase, amylase, cellulase, α-glucosidase, β-glucosidase, β-xylosidase, N-acteyl-glucosaminidase, alkaline and acid phosphatases and laccase) were selected to characterize the functional diversity of the biogenic structures. Our results showed that (i) Martiodrilus casts were characterized by a broad enzymatic profile that was different from that of the soil. (ii) A. laevigata pellets and termite structures had a profile broadly similar to the soil only with some enzymes (iii) Andiodrilus casts had an enzyme profile very similar to that of the soil. These results suggest that the functional diversity of these structures is related to differences between species and not to differences between taxonomic groups. For the first time, we evaluated differences in enzyme typology between biogenic structures collected on the same site but produced by different organisms. These differences suggested species dependent pathways for the decomposition of organic matter.     

Different effects of earthworms and ants on soil properties of paddy fields in North-East Thailand

As soil engineers, earthworms and ants play major roles in soil functioning, especially in modifying soil physical and chemical properties. This study was conducted in a very constraining environment, i.e., paddy fields which have anoxic conditions (approximately four months per year), and which are affected by soil salinisation during the dry period (approximately eight months per year). This study points out that despite those very adverse conditions, soil invertebrates must be taken into account in the dynamic of soil organic and mineral properties in paddy fields. The effects of one earthworm species, Glyphodrillus sp., and an ant species, Epelysidris sp., on soil physical and chemical properties were determined through elemental soil physical and chemical properties (texture, pH, conductivity, C and N contents) and near infrared reflectance spectroscopy (NIRS) in order to evaluate their ability to influence soil organic matter quality. PCA processed with NIRS data clearly showed that biogenic structures (ant sheetings and earthworm casts) were separated from the control surrounding soil. Earthworms and ants affected differently soil properties. Glyphodrillus sp. increased the SOM content and decreased the pH on the surface of the soil. These effects were attributed to an increase in fine particle content (clay). Conversely, Epelysidris sp. only increased the content of coarse particles (sand) and did not influence either soil pH or SOM content. Soil conductivity was found to be very variable but was not significantly affected by soil invertebrates. These results show the potential of soil macro-fauna to create heterogeneity at small spatial scale and to modify the quality of surface soils even under adverse conditions like saline paddy fields.     

云南热带亚热带退耕山地中蚂蚁对舞草种子的影响研究

舞草为云南热带、亚热带山区刀耕火种轮歇地的一种常见多年生先锋植物。野外调查表明蚂蚁与舞草具有互惠共生关系。在舞草群落地，蚂蚁会将舞草种子搬运到蚁巢。本文研究了刀耕火种过程中蚂蚁对舞草种子的影响，结果表明：地表面的舞草种子火烧5min后，已完全丧失了生活力，而埋在地下5、10cm的种子，经5、30、60、90、120min火烧处理后与对照相比，都显著提高了种子的萌发率。离地表5cm处的种子其萌发率明显高于10cm处的种子，萌发时间则短于10cm处的种子。蚂蚁搬运舞草种子能使其免遭于火烧毁伤，使舞草种群得以恢复与扩散，从而有助于森林植被的演替。这可以视为舞草与蚂蚁的互惠共生。     

河南洛阳地区蚂蚁种类和分布调查

蚂蚁是土壤中大型动物的优势类群,种群数量庞大,分布较广。通过调查获得洛阳地区蚂蚁包括5亚科,13属,31种。优势种为铺道蚁、粗面收获蚁、日本弓背蚁,且不同生境、不同地域内的蚂蚁种类和分布都有差异。根据调查资料分析了该地区6种生境中蚂蚁种群的结构及多样性特征,以及人为干扰和生境异质性对蚂蚁群落的影响,结果表明:6种生境中蚂蚁群落种类、组成和多样性等指标均不相同。人为干扰越强的生境,蚂蚁种群多样性指数越低;生境质量和异质性越高,蚂蚁种群多样性指数越高。     

Proximity to the forest edge affects the production of sexual offspring and colony survival in the red wood ant Formica aquilonia in forest clear-cuts

Abstract

Red wood ants of the Formica rufa group, as well as their nests, form a vital part of the ecosystems of both European and Siberian boreal and temperate forests. It has been well documented that the nests of red wood ants in clear-cuts do not perform as well as those deeper in the forest. However, clear-cuts may not be a homogeneously poor habitat for such forest-dwelling ants because the distance of the nest site to the edge of the remaining forest may be a significant factor affecting the nest performance. In this study, I compared the probability of nest survival and sexual offspring production between the nests of Formica aquilonia (Yarrow, 1955) in a forest edge zone (distance to the forest edge <9.2 m) and a clear-cut centre zone in 18 different clear-cut areas. Although the nests were generally smaller, the probability of sexual offspring production and nest survival was higher among those nests in the edge compared to the centre zone. Since the proximity to the forest edge increased the performance of a nest, selective logging and smaller scale clear-cuts may not be as harmful to red wood ants as clear-cutting over a large area.     

Ant community responses to experimental fire and logging in a eucalypt forest of south-eastern Australia

Sustainable forest management requires a sound understanding of the impacts of forestry management practices, especially prescribed fire and timber harvesting, on biodiversity. Many studies have examined the impacts of fire and logging separately, but few have considered them together. Here we describe the combined effects of selective logging and repeated prescribed fire on ants in eucalypt forest near Eden in south-eastern Australia. The study was conducted within 18 experimental coupes comprising three replicates of each of six treatments, representing combinations of two logging (selectively logged and unlogged) and three prescribed burning (unburnt, routine and high fire frequency over 20 years) practices. Ants were sampled using terrestrial and arboreal pitfall traps in two plots within each of the 18 coupes. A total of 92 species from 35 genera were recorded, with ant species richness increasing with both increasing fire frequency and selective harvesting. We also found significant differences in ant species composition between management treatments; however, these differences were rather modest, and apparent only between extremes of fire and harvesting combinations. Logging on its own was not a significant factor contributing to variation in ant species composition. However, the responses of two common species and a key functional group to fire depended on logging treatment; in each case their abundance decreased with increasing fire frequency at unlogged sites, but increased at logged sites. The general resilience of ant communities suggests that forests remain in good functional health even when subject to a combination of selective logging and frequent burning. However, our study under-sampled species with specialist microhabitat requirements, and these might have been more heavily impacted. We have also revealed some significant interactions between the effects of fire and logging, which highlights the importance of considering combined impacts of forest management practices.     

Cross-taxon surrogacy of biodiversity in the Indian Garhwal Himalaya

Biodiversity surveys were conducted in 13, 10×50 m² plots located between 1400 to 3700 m above mean sea level in a range of habitats in temperate mixed Oak and Coniferous forests through sub-alpine to the alpine grasslands in Chamoli district of Uttaranchal state in the Indian Garhwal Himalaya. Cross-taxon congruence in biodiversity (α-diversity and β-diversity) across macrolichens, mosses, liverworts, woody plants (shrubs and trees) and ants was investigated, so as to examine the extent to which these groups of organisms can function as surrogates for each other. Although woody plants provided a major substrate for macrolichens and mosses, there was no species-specific association between them. Woody plant species richness was highly positively correlated with mosses (r²=0.63, P<0.001), but the relationship was not particularly very strong with lichens and liverworts. While there was a significant correlation in the species turnover (β-diversity) of macrolichens with mosses (r²=0.21, P<0.005), the relationship was relatively poor with the woody plants. On the other hand, negative correlations emerged in the species richness of ants with those of macrolichens, mosses and woody plants (r²=−0.44, P<0.05), but most of the complementarity (turnover) relationships among them were positive. Since diversity between taxonomic hierarchies within the group was consistently significantly positively correlated in all these taxa, the higher taxonomic categories such as genus and family may be employed as surrogates for rapid assessment and monitoring of species diversity. Although no single group other than macrolichens has emerged as a good indicator of changes in species richness in all other groups, some concordant relationships between them conform to the hypothesis that species assemblages of certain taxonomic groups could still be used as surrogates for efficient monitoring of species diversity in other groups whose distribution may further predict the importance of conserving overall biodiversity in landscapes such as the Garhwal Himalaya.     

Edge effects of an invasive species across a natural ecological boundary

Natural habitats adjacent to human-modified areas often suffer edge effects stemming from physical disturbance, elevated predator densities, or invasive species. Although seldom documented, detrimental edge effects can also occur at natural ecological boundaries. Here I examine the spatial pattern and ecological effects of a biological invasion at well-delineated and abrupt edges between riparian corridors and coastal sage scrub at 10 sites in southwestern California. The invasive Argentine ant Linepithema humile thrives in moist riparian corridors but decreases greatly in number with increasing distance into adjacent dry scrub habitats. As L. humile numbers decrease, both the number of native ant workers and the number of native ant species captured in pitfall traps increase. Argentine ants appear to suppress native ants within at least 50 m of riparian corridors, but these effects diminish to undetectable levels by 200 m. At comparable uninvaded sites neither the number of native ant workers nor the number of native ant species captured in pitfall traps varies significantly across riparian-scrub edges. Areas subject to this edge effect may be sinks both for native ants and for organisms that depend on them for food or services. In general edge effects occurring at natural boundaries should receive increased attention as they might disrupt ecosystems not greatly altered by human activity.