Termite diversity along a land use intensification gradient in a semi-arid savanna

Disturbance, particularly agricultural expansion is one of the major threats to the biodiversity and ecological functions of tropical and sub-tropical ecosystems. In this regard, we examined changes in the species richness, abundance, and diversity of termites across different disturbance treatments in a sub-tropical semi-arid savanna in south eastern Zimbabwe. Nine transects (100?×?2 m) representing three habitat disturbance treatments (primary woodland; grazing area; agricultural field) were sampled for termites using a rapid biodiversity assessment protocol. Termites were more abundant and species-rich in primary woodland and grazing area than in the agricultural field. Twelve termite species from three sub-families were present, with Microtermes sp. constituting 35% of the identified termite species. Termite feeding group structure differed significantly among land-use types, and of all termites present, wood-feeding termites were the most abundant while soil-feeders were rare in the agricultural field. In conclusion the observed pattern in termite species richness and relative abundance indicates that termites are very resilient to natural disturbance and might actually benefit from some natural disturbances like they did in the grazing area of this study, but they are not resilient to extreme anthropogenic disturbance. Although there was no notable difference in termite species richness and relative abundance between agricultural field and primary woodland, the pattern observed across the three sites may be potential support for the IDH suggesting that intermediate levels of physical disturbance intensity influence the structure and functioning of termite assemblages in semi-arid savanna.     

Responses of mammalian carnivores to land use in arid savanna rangelands

Shrub encroachment due to heavy grazing has led to dramatic changes in arid savanna landscape structure worldwide. It is considered to be one of the most threatening forms of rangeland degradation altering plant diversity. However, possible impacts of shrub encroachment on species diversity at higher trophic levels remain poorly understood. Additionally, indirect effects, such as changes of trophic interactions, are often ignored when trying to understand changes in biodiversity patterns. In this study, conducted in the southern Kalahari, we explored how the diversity of small carnivores and their prey is affected by shrub encroachment. We analysed the relationships between abundance and diversity of small carnivores, the availability of their main prey groups (coleopterans, termites, grasshoppers, rodents) and the structural diversity of the landscape (shrub, grass and herb cover). Eight hundred track surveys were conducted to determine carnivore abundance on 20 rangeland habitats, which represented a gradient of grazing intensity. Prey availability was surveyed for each study site and related to vegetation cover.

Results show a significant impact of shrub cover on abundance and diversity of carnivores and their prey. The diversity of both, carnivores and their prey, showed a hump-shaped response to increasing shrub cover whereas relative carnivore abundance decreased. Availability of prey groups was affected differently by shrub cover increase. Diversity of carnivores was best predicted by shrub cover (R²>0.7, p<0.001) indicating the overriding role of habitat structure as compared to prey availability. We conclude that intermediate shrub cover values enrich structural diversity of savanna landscape and in consequence sustain diversity of small carnivores and their prey in arid and semiarid ecosystems.     

Presence of Cuckoo reliably indicates high bird diversity: A case study in a farmland area

Here we studied the occurrence of Cuckoo Cuculus canorus and top predators as indicators of biodiversity in agro ecosystems of Western Poland, to identify local hotspots. Bird species richness and land-use diversity were used as measures of biodiversity. The relationship between the presence of Cuckoos and four avian top predators with biodiversity measures were examined using Generalized Linear Mixed Models.Cuckoos were mainly distributed on sites with greater species richness, but were absent from the low species richness sites, while the top predators were distributed uniformly. The performance of the best models using the presence of Cuckoo was 27% higher than the best models using top predators. Our results highlight the predictive capacity of Cuckoos as an indicator of bird species richness than top predators and the usefulness of this species in biodiversity studies. The cookoo is charismatic, widespread across the main types of landscapes, and is easy to detect from its song. Importantly, our findings propose that cookoo can be used as effective and cheap tool to monitor the high bird diversity in different European countries.     

Changes in plant species diversity along a chronosequence of vegetation restoration in the humid evergreen broad-leaved forest in the Rainy Zone of West China

Plant species diversity has been recognized as one of the vital attributes for assessing vegetation restoration. Changes in the diversity may be related to different stages of succession. In this study, 54 sites of humid, evergreen, broad-leaved forest were selected in the Rainy Zone of West China. A chronosequence of the sites was used to study the successive patterns of the diversity in the forest that had undergone natural regeneration for 5 to 350 years and to test the hypothesis that the diversity is maximized in mid-succession. Data were collected simultaneously at different stages of succession, and four α-diversity indices (species richness, Margalef index, Shannon-Wiener index, Pielou Evenness index) and two β-diversity indices (Whittaker index, Sørensen’s index) were calculated for each stratum in each plot. A total of 394 vascular plant species were recorded. From the β-diversity indices, the forest succession may be divided into the early-successional stage (before 50 years), mid-successional stage (from 50 to 300 years), and late-successional stage (after 300 years). In this community, the species diversity and richness were found to be the greatest at the mid-successional stage, followed by the late- and early-successional stages. The results of regression analysis indicated that the richness and Margalef index peaked around the 175th and 165th year, respectively. Shannon-Wiener index values also appeared to follow an approximately humped pattern of succession and were maximal around the 100th year. However, the species evenness did not show any significant relationship with successional age. Our results demonstrate (1) forest restoration is a long-term process and the formation of climax forest requires at least 300 years and (2) the forest has a strong capacity for restoration. Our results also suggest Lindera limprichitii and Machilus pingii as ideal tree species for afforestation because of their wide niche.     

Testing indicators of epiphytic lichen diversity: a case study in N Italy

The predictability of a standardized and widely used biomonitoring method for estimating total lichen diversity on trunks (LDV-index) was tested. The study was carried out in Veneto (NE Italy), on 34 randomly selected trees in five sites in different landscape contexts. Two sets of biodiversity data were obtained from each tree: (1) the LDV index based on species frequency within a standard sampling grid positioned on a limited part of the trunks only (2) the total number of species found on the trunks. Total species richness on trunks is significantly related with the LDV index, which suggests that the LDV standard methodology can be used also for estimates of lichen diversity. Even a LDV index based on macrolichens, or on large-lobed foliose lichens only, still permits reliable estimates of total diversity on the trunks.     

A minimum data set and soil quality index to quantify the effect of land use conversion on soil quality and degradation in native rangelands of upland arid and semiarid regions

Conversion of native rangelands to croplands potentially influences soil functions and quality. The aim of the current study was to assess soil quality (SQ) after rangeland conversion and degradation for more than 40 years using an indexing framework and integrated approach. Fifteen soil attributes were measured at two sampling depths (0–20 and 20–40 cm) of paired native undisturbed and adjacent cultivated rangelands at three rangeland sites. The soil organic carbon (OC), electrical conductivity (EC) and arylsulphatase (ARY) activity were found to be the key indicators of the minimum data set and these indicators greatly affected the computed soil quality index (SQI), particularly in the soil surface. The contribution of OC, EC and ARY to the overall SQI was 77, 13 and 10%, respectively. Although rangeland conversion reduced other soil attributes (including aggregate stability, available water capacity, cation exchange capacity, microbial biomass, microbial activity and the activities of urease and invertase enzymes), in particular at the 0–20 cm depth, these variables did not contribute to the estimated SQI values because of their high correlation with OC contents (i.e., strong interdependency). Cultivated rangelands were characterized by a low soil OC content, EC and ARY activity, and consequently a low SQI. A significant decline in SQI value (29–47%) was observed as a result of rangeland conversion to croplands, depending on soil depth considered and scoring function used to compute the SQI. Overall, converting native rangelands to croplands decreased SQ to 52–64% of their potential capacity using a non-linear scoring method. In summary, soil OC, EC and ARY are the most important indicators, which can be used to monitor and asses the degradation of rangeland SQ after conversion to croplands in these arid and semiarid upland environments. This finding is of especial importance because the assessment of SQ allows the successful and straightforward discrimination between rangeland and cropland ecosystems or to quantify land use conversion effects on SQ. It is concluded that the rate of soil changes can be assessed and compared more accurately in the studies of land use conversions in native rangeland ecosystems using the current indexing framework due to its simplicity and quantitative flexibility.     

Changes in traits of shrub canopies across an aridity gradient in northern Patagonia, Argentina

Low and highly variable precipitation pulses exert a strong selective pressure on plant traits and this might provide axes of ecological differentiation among plant species in arid ecosystems. We asked whether aridity contributes to maintain high diversity of species and morphotypes in shrub canopies. We selected eleven study sites evenly distributed across a 400-km transect in northern Patagonia, Argentina. Precipitation is low and highly variable within and between years but almost homogeneous across the transect (125–150 mm). Mean annual temperature varied, however, ranging from 8 °C (west) to 13.5 °C (east) creating a west–east gradient of aridity (aridity index from 3.7 to 7.3, respectively). Sheep grazing commenced in the early 1900s at a similar intensity across the transect. We recorded the richness and cover of shrubs by species and by morphotypes (drought deciduous tall shrubs, evergreen tall shrubs, medium shrubs, and dwarf shrubs), and further calculated the species and morphotype Shannon diversity index at each site. We assessed the presence of spiny leaves, leaf pubescence, thorny stems, and photosynthetic stems in shrub species of all morphotypes and collected green leaves of the dominant shrub species (more than 80% of the total shrub cover) to assess the leaf area, leaf mass per unit area, N-, lignin- and soluble phenolic-concentrations per species at each site. Richness and diversity of shrub species and morphotypes were positively associated with aridity. The richness and diversity of shrub species with pubescent leaves and thorny stems, and nitrogen concentration in green leaves of dominant shrubs increased with increasing aridity. We conclude that our findings on increased diversification in life history traits, species and morhotypes in shrub canopies with increasing aridity support the hypothesis that variability in aridity provides axes of ecological differentiation among shrub species facilitating their coexistence.     

Patterns in the structure of grassland butterfly communities along a gradient of human disturbance: further analysis based on the generalist/specialist concept

Kitahara and Fujii, in 1994, analyzed the butterfly communities along a gradient of human disturbance by applying the generalist/specialist concept. Butterfly species were classified into generalist or specialist species based on their voltinism (seasonal time dimension) and potential larval resource breadth (food dimension). The community structure and species composition showed the systematic changes along the gradient. To verify the generality of those trends, we monitored five grassland butterfly communities with varying degrees of human disturbance twice a month during 1985 by the line transect method at the foot of Mt. Fuji, central Japan, and analyzed their structure in a manner similar to that employed by Kitahara and Fujii. Most results were consistent with the patterns recognized by Kitahara and Fujii. The route (community) order based on increasing human disturbance was strongly and negatively correlated with butterfly species richness but with neither butterfly species diversity (H′) nor evenness (J′). Also, the degree of human disturbance was significantly and negatively correlated with the number of specialist species, but not with that of generalists, in a community. Butterfly species richness was more strongly correlated with the number of specialist species than with that of generalists. Our analyses also showed that the generalist species were distributed more widely over the communities than were the specialists. However, in contrast to the trend revealed by Kitahara and Fujii, there was no significant difference in the population densities and in the spatial population variability between the two species groups. As a whole, our analyses confirmed the consistency of most community patterns detected by Kitahara and Fujii. The causes of the inconsistencies in some patterns were thought to be mainly the present habitat conditions with a relatively short growing season at high altitudes. Received: October 19, 1999 / Accepted: June 5, 2000     

Trait variation and functional diversity maintenance of understory herbaceous species coexisting along an elevational gradient in Yulong Mountain,Southwest China

Characterizing trait variation across different ecological scales in plant communities has been viewed as a way to gain insights into the mechanisms driving species coexistence. However, little is known about how changes in intraspecific and interspecific traits across sites influence species richness and community assembly, especially in understory herbaceous communities. Here we partitioned the variance of four functional traits (maximum height, leaf thickness, leaf area and specific leaf area) across four nested biological scales: individual, species, plot, and elevation to quantify the scale-dependent distributions of understory herbaceous trait variance. We also integrated the comparison of the trait variance ratios to null models to investigate the effects of different ecological processes on community assembly and functional diversity along a 1200-m elevational gradient in Yulong Mountain. We found interspecific trait variation was the main trait variation component for leaf traits, although intraspecific trait variation ranged from 10% to 28% of total variation. In particular, maximum height exhibited high plasticity, and intraspecific variation accounted for 44% of the total variation. Despite the fact that species composition varied across elevation and species richness decreased dramatically along the elevational gradient, there was little variance at our largest (elevation) scale in leaf traits and functional diversity remained constant along the elevational gradient, indicating that traits responded to smaller scale influences. External filtering was only observed at high elevations. However, strong internal filtering was detected along the entire elevational gradient in understory herbaceous communities, possibly due to competition. Our results provide evidence that species coexistence in understory herbaceous communities might be structured by differential niche-assembled processes. This approach--integrating different biological scales of trait variation--may provide a better understanding of the mechanisms involved in the structure of communities.     

Species richness and cover along a 60-year chronosequence in old-fields of southeastern Spain

We analyse changes in plant cover and species richness along a 60-year chronosequence in semi-arid Mediterranean old-fields of southeastern Spain. The objectives were: (i) to study patterns of species richness along the abandonment gradient in semi-arid conditions (e.g., to test the “humped-back model” in our system); (ii) to test whether different broad life forms (annuals, forbs, grasses and woody species) showed different patterns along the abandonment gradient, and (iii) to examine to what extent plants with different dispersal strategies dominate at different stages of succession. The explained variance of the regression relating species richness to years since abandonment is improved when considering different life forms. The results suggest that cover and richness of different functional groups show a non-linear unimodal (often positive-skewed) pattern along the gradient (age since abandonment). Maximum total richness is found at young stages of abandonment (<20 years), when most life forms and dispersal strategies coexist. Annuals and perennial forbs reached their maximum richness during the first 10 years of abandonment. About 45% of total woody species richness is reached at this time as a consequence of early colonization of zoochorous shrubs. While the results showed a tendency towards a life-form replacement sequence, the pattern is not so clear when looking at the different dispersal strategies. The results complement previous results in Mediterranean conditions and emphasise the importance of considering different functional types when studying successional patterns. This revised version was published online in June 2006 with corrections to the Cover Date.     

Macrolichen diversity as an indicator of stand age and ecosystem resilience along a precipitation gradient in humid forests of inland British Columbia,Canada

The distributional ecology of 87 macrolichens is reported from 14 unmanaged mid-seral and old forest stands along a precipitation gradient in south-central British Columbia. We used a combination of univariate and multivariate statistics to investigate the role of forest structure and stand age in the distribution of epiphytic macrolichens in interior cedar-hemlock forests. Old forests support a higher number of species; although mean species richness is not significantly different between the two age classes. Terricolous and epixylic community structure is correlated with stand age and log characteristics, but the epiphtytic community is not. Epiphytic community structure is strongly associated with precipitation in the old stands, but not in the mid-seral stands. Old forests at the wetter end of the precipitation gradient contained several old-growth associated species, all of which are hygrophytic. Most epiphytic macrolichens associated with old forests are not dependent on specific structural attributes. However, western red cedar (Thuja plicata Donn ex D. Don) harbors the greatest number of arboreal macrolichen species by far in these unmanaged stands and should, therefore, be considered a key indicator in managed forests. Our study suggests that most macrolichen species found in old forests can also occur in 70- to 165-year-old forests dating from stand-replacing fires. Old forests, however, clearly provide important habitat for oceanic epiphytes at the edge of their ecological range in the interior of British Columbia. Our findings illustrate that the macrolichen flora in wet toe-slope stands in humid inland British Columbia has a high level of resilience following disturbance under natural succession conditions. It also underlines the point that some species, like Lobaria pulmonaria, are good indicators of old-growth forests in certain regions but not in others, suggesting a careful use of the term old-growth dependence.     

森林草原过渡带持久土壤种子库沿降水梯度的格局

为了解全球气候变化背景下森林草原过渡带持久土壤种子库对未来降水减少的响应,本研究以呼伦贝尔森林草原过渡带为研究区域,沿降水梯度采集0～10 cm土层的持久土壤种子库样本,研究种子库密度、物种组成、多样性及其与地上植被的关系,并利用结构方程模型研究年降水量对持久土壤种子库的直接影响及其通过地上植被和土壤有效氮、有效磷、土壤pH值产生的间接影响。结果表明: 随着降水量的降低,种子库密度和物种丰富度有增加趋势,森林草原过渡带草地土壤种子库物种多样性高于森林。土壤种子库与地上植被相似性整体较低。结构方程模型结果显示,年降水量对种子库的密度和物种丰富度的总效应为负效应,标准路径系数为-0.051和-0.122。年降水量对种子库的密度和物种丰富度的直接效应为正效应,降水量通过土壤全氮对种子库密度和物种丰富度产生显著的间接正效应,通过土壤pH和土壤有效磷对种子库物种丰富度产生显著的间接负效应,通过土壤pH对种子库密度产生显著的间接负效应。气候变化下降水减少会改变植物应对风险的策略,森林草原过渡带的持久土壤种子库对应对未来可能发生的降水减少具有一定的缓冲作用。     

Community assembly along a species pool gradient: implications for multiple-scale patterns of species diversity

Various ecological processes influence patterns of species diversity at multiple spatial scales. One process that is potentially important but rarely considered is community assembly. I assembled model communities using species pools of differing size to examine how the history of community assembly may affect multi-scale diversity patterns. The model contained three scales at which diversity could be measured: local community, metacommunity, and species pool. Local species saturation occurred, as expected from the competition and predation built in the model. However, local communities did not become resistant to invasions except when the species pool was very small. Depending on dispersal rate and trophic level, the larger the species pool, the harder it was to predict which species invades which local community at a given time. Consequently, local-community dissimilarity maintained by assembly history increased linearly with pool size, even though local diversity was decoupled from pool size. These results have two implications for multi-scale diversity patterns. First, assembly history may provide an explanation for scale-dependent relationships between local and regional diversity: assembly causes the relationship to be curvilinear at one scale (local community), while linear at another (metacommunity). Second, assembly history influences how -diversity is partitioned into - and -diversity: assembly causes the relative contribution of to increase with pool size. Overall, this study suggests that community assembly history interacts with species pool size to regulate multi-scale patterns of species diversity.     

Nutrient recycling by fish in streams along a gradient of agricultural land use

Nutrient recycling is an essential ecosystem process provided by animals. In many aquatic systems, fish have been identified as important in ecosystem nutrient recycling; however, this importance can vary widely between systems. The factors controlling intersystem variation in animal‐mediated nutrient cycling have rarely been examined and as such it remains unclear what impact human landscape changes will have upon these processes. Here we examined rates of nutrient recycling for temperate stream fish assemblages along a gradient of agricultural land use (proportion cropland in the watershed: 1–59%). We quantified nutrient excretion rates of both ammonium–N (NH₄⁺–N) and phosphate (as soluble reactive phosphate: SRP) for fish assemblages at eight streams in southern Ontario, Canada with species‐specific excretion measurements and quantitative assemblage sampling. For both nutrients, total assemblage excretion exhibited a strong positive relationship with riparian cropland. The distance required for fish assemblages to turn over ambient nutrient pools was shorter for cropland systems, indicating that the relative importance of excreted nutrients was higher in these systems. Based on measured uptake rates of NH₄⁺–N in two streams (one higher cropland and one low cropland) and on modeled uptake rates for all streams, the proportion of ecosystem demand that can be satisfied by excretion is generally higher in the more agricultural streams. These patterns appear to be driven largely by disproportionate increases in fish assemblage biomass with increasing stream nutrient concentrations.     

The determinants of land snail diversity along a tropical elevational gradient: insularity,geometry and niches

Aim We investigated the patterns of species richness in land snails and slugs along a tropical elevational gradient and whether these patterns correlate with area, elevation, geographic constraints, and productivity. We did so both at the scale at which land snail population processes take place and at the coarser scale of elevational zones. Location Mount Kinabalu (4096 m) and the adjacent Mount Tambuyukon (2588 m) in Kinabalu Park, Sabah, Malaysian Borneo. Methods We used an effort‐controlled sampling protocol to determine land snail and slug species richness in 142 plots of 0.04 ha at elevations ranging from 570 to 4096 m. Extents of elevational ranges were determined by interpolation, extended where appropriate at the lower end with data from lowlands outside the study area. We used regression analysis to study the relationships between species density and richness on the one hand and elevation and area on the other. This was done for point data as well as for data combined into 300‐m elevational intervals. Results Species density (based on the individual samples) showed a decline with elevation. Elevational range length profiles revealed that range lengths are reduced at greater elevations and that a Rapoport effect is absent. Diversity showed a mild mid‐domain effect on Kinabalu, but not on Tambuyukon. When the data were combined into 300‐m elevational intervals, richness correlated more strongly with elevation than with area. Ecomorphospace was seen to shrink with increasing elevation. Main conclusions The elevational species richness patterns show the combined effects of (1) reduced niche diversity at elevations with lower productivity and (2) historical events in which the upward migration of lowland species as well as the speciation of highland endemics took place.     

The diversity of soil mites (Acari: Mesostigmata) in yellow ant (Lasius flavus) nests along a gradient of land use

Mesostigmatid mites communities in yellow ant (Lasius flavus) hills and phoresis of mites on this ant species were analysed in the Wielkopolska Region, Central Poland. Samples were collected from ant nests located along a gradient of four different types of land use: forest, ecotone, meadow and garden. In total, 132 mites were collected in ant nests among which 26 species were identified. The highest total abundance of mites was observed in the ecotone. Moreover, 14 mite specimens were found on L. flavus workers bodies. These are the first records of phoresis of mesostigmatid mites on this ant species.