Trends In Species Richness Research Articles

Altitudinal trends in species richness and diversity of Mesoamerican parasitoid wasps (Hymenoptera: Ichneumonidae)

Abstract Utilising short‐term but geographically extensive sampling in Guatemala, Honduras, and Nicaragua, we examined altitudinal trends in species richness and diversity of ichneumonid parasitoid wasps. This study covered 19 subfamilies, including four globally large subfamilies that have not yet been taxonomically revised in the Neotropics. Sampling was done at 25 sites classified into three elevational categories on the basis of the average elevation of traps at each site (low 34–659 m a.s.l., middle 1033–1709 m a.s.l., and high 1930–2565 m a.s.l.). A total of 2847 ichneumonid individuals were captured and sorted into 751 morphospecies, most of which were identified to the genus level. We found a clear compositional gradient in ichneumonid communities along the elevational gradient, as the majority of species were restricted to either one elevational zone or two adjacent zones. In our data, mid‐ and high‐elevation sites had generally higher ichneumonid species richness and diversity than low‐elevation sites. These trends were largely similar to those found in larger scale Mesoamerican ichneumonid studies. Yet, the low ichneumonid richness at low elevations may partly be a sampling artefact. This provides a new piece of evidence for the suggestion that extensive sampling is needed for uncovering the real diversity of ichneumonids in tropical lowland forests, and that the reputation of Ichneumonidae as a notable example of a reversed latitudinal diversity gradient may be undeserved.

The effectiveness of ditch banks as dispersal corridor for plants in agricultural landscapes depends on species’ dispersal traits

The effectiveness of agri-environment schemes (AES) in enhancing biodiversity in agricultural landscapes is still strongly debated. In the Netherlands, one of the most widely implemented AES is the management of ditch banks to enhance plant species diversity. Previous research has shown that this type of AES has not led to increases in plant diversity. However, this work also showed that the success of this type of AES may depend on the presence of source populations in the surrounding areas. In this study we investigated if species-rich nature reserves can act as seed sources for agricultural ditch banks under AES and whether this function of nature reserves differs among plant species with different dispersal capacities. We used data collected by farmers over a 10year period to analyse trends in species richness of target plants and in different dispersal groups in ditch banks under AES at different distances from nature reserves.Our results demonstrate that nature reserves can act as species rich sources in agricultural landscapes and that adjacent AES ditch banks can facilitate the colonisation of the surrounding agricultural landscape. However, the suitability of ditch banks as corridors depends on the dispersal capacity of a species. Particularly water-dispersed species clearly spread from nature reserves into the surrounding agricultural landscape along ditches. In contrast, species without adaptations to disperse over long distances do not show these spatiotemporal patterns.

Transition patterns across an evergreen–deciduous broad‐leaved forest ecotone: the effect of topographies

AbstractQuestionTopography has distinct effects on local‐scale vegetation distribution by creating heterogeneous habitats. In ecotones, which are sensitive to environmental variation, this effect on vegetation differentiation may be magnified at a regional scale. Here, we evaluate vegetation transition patterns across an evergreen–deciduous broad‐leaved forest ecotone (EDF ecotone) in eastern China, to investigate whether the transition pattern differs between two topographic positions with different habitats, and identify underlying environmental mechanisms driving variation in species‐ and trait‐based community structure.LocationAnhui Province, China.MethodsAcross an EDF ecotone, community data were collected in 47 20 × 20‐m plots situated on upper and lower hill slopes. Trait‐based community structure was constructed based on seven functional traits and weighted by species abundance. Environmental variables were grouped into three categories: thermal conditions, water availability and edaphic variables. Trends in species richness and dominance along latitude were evaluated for both evergreen broad‐leaved species (EBT) and deciduous broad‐leaved species (DBT). Variation partitioning analysis was used to distinguish the roles of the three environmental variables in determining transition patterns within the two topographies.ResultsFor both EBT and DBT, species richness showed similar transition patterns along the latitudinal gradient on both the upper and the lower slope. However, species dominance changed more abruptly on the upper than on the lower slope. Compared with edaphic variables, both thermal conditions and water availability had a larger impact on transitions across the EDF ecotone, but their relative roles differed between the upper and the lower slopes. Thermal conditions primarily explained the variation in species‐ and trait‐based community structure on the upper slope, while water availability primarily explained variation on the lower slope.ConclusionsOur results suggest different roles of thermal conditions and water availability in determining transition patterns between the two topographies. Evergreen Castanopsis trees, having less cold tolerance, make transitions on the upper slope more sensitive to thermal conditions. Cyclobalanopsis trees, which prefer wet habitats, make the transition on the lower slope more sensitive to water availability. Based on the present findings, we predict that the EDF ecotone will become narrower and there will be a sharper boundary between the evergreen and deciduous broad‐leaved forests of eastern China under warmer and drier climate conditions.

Garden and landscape-scale correlates of moths of differing conservation status: significant effects of urbanization and habitat diversity.

Moths are abundant and ubiquitous in vegetated terrestrial environments and are pollinators, important herbivores of wild plants, and food for birds, bats and rodents. In recent years, many once abundant and widespread species have shown sharp declines that have been cited by some as indicative of a widespread insect biodiversity crisis. Likely causes of these declines include agricultural intensification, light pollution, climate change, and urbanization; however, the real underlying cause(s) is still open to conjecture. We used data collected from the citizen science Garden Moth Scheme (GMS) to explore the spatial association between the abundance of 195 widespread British species of moth, and garden habitat and landscape features, to see if spatial habitat and landscape associations varied for species of differing conservation status. We found that associations with habitat and landscape composition were species-specific, but that there were consistent trends in species richness and total moth abundance. Gardens with more diverse and extensive microhabitats were associated with higher species richness and moth abundance; gardens near to the coast were associated with higher richness and moth abundance; and gardens in more urbanized locations were associated with lower species richness and moth abundance. The same trends were also found for species classified as increasing, declining and vulnerable under IUCN (World Conservation Union) criteria. However, vulnerable species were more strongly negatively affected by urbanization than increasing species. Two hypotheses are proposed to explain this observation: (1) that the underlying factors causing declines in vulnerable species (e.g., possibilities include fragmentation, habitat deterioration, agrochemical pollution) across Britain are the same in urban areas, but that these deleterious effects are more intense in urban areas; and/or (2) that urban areas can act as ecological traps for some vulnerable species of moth, the light drawing them in from the surrounding landscape into sub-optimal urban habitats.

Mode of larval development as a key factor to explain contrasting effects of temperature on species richness across oceans

AbstractAimIt has been proposed that the mode of larval development (MLD) could explain the exceptions to the latitudinal gradient of species richness exhibited by several groups of marine organisms. We evaluate the generality of the latitudinal patterns of species richness for different MLDs, and analyse the effects of environmental variables on species richness – explicitly considering feeding type during the larval phase – to identify the relevance of the dichotomies between feeding and non‐feeding larvae and between pelagic and non‐pelagic development.LocationSouth America, from 10° to 54° S in the south‐western Atlantic and from 18° to 54° S in the south‐eastern Pacific.MethodsUsing molluscs and crustaceans in two oceans, we deconstructed latitudinal patterns of species richness for three MLDs (planktotrophic, lecithotrophic and direct development). The effects of sea water temperature, chlorophyll a concentration and shelf area on the spatial variation in species richness were analysed for each MLD.ResultsWe found remarkably similar trends in species richness deconstructed by MLD. Planktotrophic species richness decreased polewards, and the converse pattern was observed in direct developers. In the majority of groups with lecithotrophic development, species richness increased from middle to higher latitudes. The main component explaining the variation in species richness was the spatial structure of sea water temperature. Temperature showed positive effects on planktotrophic species and negative effects in almost all lecithotrophic or direct‐developing groups in both oceans and both taxa.Main conclusionsThe similar relationship of temperature with lecithotrophic and direct developers, which contrasts with planktotrophic species, suggests that food availability during planktonic larval development is a critical factor determining species distribution of marine invertebrates. We ruled out the cost of brooding as a single causal factor explaining the poleward increase in diversity of direct developers. Simple linear models can describe changes in the proportion of species with temperature within each MLD.

Spatial patterns of above-ground structure, biomass and composition in a network of six Andean elevation transects

Background: The Amazon to Andes transition zone provides large expanses of relatively pristine forest wilderness across environmental gradients. Such elevational gradients are an excellent natural laboratory for establishing long-term interactions between forest ecosystems and environmental parameters, which is valuable for understanding ecosystem responses to environmental change. Aims: This study presents data on elevational trends of forest structure (biomass, basal area, height, stem density), species richness, and composition from six elevational transects in the Andes. Methods: We analysed the spatial patterns of forest structure, above-ground biomass and composition from 76 permanent plots, ranging from lowland Amazonian rain forest to high-elevation cloud forests in Ecuador, Peru, and Bolivia. Results: Forest above-ground woody biomass stocks ranged from 247 Mg ha−1 (Peru, 210 m) to 86 Mg ha−1 (Peru, 3450 m), with significantly decreasing trends of tree height and biomass and an increasing trend of stem density with increasing elevation. We observed an increase in forest richness at three taxonomic levels at mid-elevation, followed by a decrease in richness within the cloud immersion zone. Conclusions: The transects show an increase in stem density, a decline in tree height and above-ground coarse wood biomass and a hump-shaped trend in species richness with increasing elevation. These results suggest that environmental change could lead to significant shifts in the properties of these ecosystems over time.

Influence of secondary forest succession on plant diversity patterns in a Mediterranean landscape

AbstractAimAs a consequence of multiple cycles of deforestation and reforestation, most forest landscapes in Europe consist of a complex mosaic of patches of different successional ages. Despite the biogeographical distinctiveness of the Mediterranean region, studies on the effects of forest age on plant species diversity and composition are almost lacking for this area. This paper evaluates the influence of forest successional age on plant species richness and composition in various forest types of Mediterranean Italy.LocationThe Natura 2000 network of Siena Province, Tuscany, Italy.MethodsOccurrence data on vascular plant species in 208 forest plots were obtained from a larger data set sampled with a stratified random design. The forest successional age of each plot was quantified through a series of historical maps. Species richness and composition were related to the age of the forest by means ofGIStechniques and univariate and multivariate statistical analyses.ResultsTotal species richness markedly decreased with increasing successional age due to a significant decrease in the richness of open‐habitat species which was not matched by increasing richness of mature forest species. Successional age was the key factor in controlling species richness, while local environmental properties emerged as the main factors shaping community composition. The different forest types showed different temporal trends of species richness and composition and different hierarchies of explanatory factors.Main conclusionsForest successional age emerged as an important factor affecting both species richness and composition, even within the same forest type. Thus, the classification and prioritization of Mediterranean forests exclusively based on present physiognomy or environmental variables causes loss of information about species richness and composition; this could be detrimental for biodiversity conservation.

Global patterns in sandy beach macrofauna: Species richness, abundance, biomass and body size

Global patterns in species richness in sandy beach ecosystems have been poorly understood until comparatively recently, because of the difficulty of compiling high-resolution databases at continental scales. We analyze information from more than 200 sandy beaches around the world, which harbor hundreds of macrofauna species, and explore latitudinal trends in species richness, abundance and biomass. Species richness increases from temperate to tropical sites. Abundance follows contrasting trends depending on the slope of the beach: in gentle slope beaches, it is higher at temperate sites, whereas in steep-slope beaches it is higher at the tropics. Biomass follows identical negative trends for both climatic regions at the whole range of beach slopes, suggesting decreasing rates in carrying capacity of the environment towards reflective beaches. Various morphodynamic variables determine global trends in beach macrofauna. Species richness, abundance and biomass are higher at dissipative than at reflective beaches, whereas a body size follows the reverse pattern. A generalized linear model showed that large tidal range (which determines the vertical dimension of the intertidal habitat), small size of sand particles and flat beach slope (a product of the interaction among wave energy, tidal range and grain size) are correlated with high species richness, suggesting that these parameters represent the most parsimonious variables for modelling patterns in sandy beach macrofauna. Large-scale patterns indicate a scaling of abundance to a body size, suggesting that dissipative beaches harbor communities with highest abundance and species with the smallest body sizes. Additional information for tropical and northern hemisphere sandy beaches (underrepresented in our compilation) is required to decipher more conclusive trends, particularly in abundance, biomass and body size. Further research should integrate meaningful oceanographic variables, such as temperature and primary production, in deciphering latitudinal trends.

Benthic marine biodiversity patterns across the United Kingdom and Ireland determined from recreational diver observations: A baseline for possible species range shifts induced by climate change

Using benthic species abundance records (2003–2009) collected by volunteer divers through ‘Seasearch’, coastal biodiversity patterns around the United Kingdom and Ireland were investigated. The first aim was to assess the utility of volunteer data as a baseline for monitoring environmental change. Separation of the influences of within- and between-surveyor variation from broadscale (year, latitude, longitude) and finer scale (month, depth, local habitat) biogoegraphical factors was achieved using a multilevel mixed effects framework. A high degree of consistency within surveyors was evident and, by modelling between-surveyor variations efficiently, expected trends in species richness and taxonomic distinctness were recovered. Moving from patterns to processes, the second aim was to test the effects of sea surface temperature on prevalence, on a species by species basis. This approach allowed identification of species likely to display range shifts in direct response to future warming trends. Within limitations, volunteer data can provide a valuable contribution to understanding of biodiversity, climate change and aquatic ecosystem health.

Changes in bird community composition in the Czech Republic from 1982 to 2004: increasing biotic homogenization, impacts of warming climate, but no trend in species richness

Recent major environmental changes could lead to homogenization in the composition of plant and animal communities, with generalist species replacing more specialized species, as well as to the increased domination of species adapted to warmer climatic conditions. Using common bird monitoring data, we have tested whether these patterns can be observed in the long-term changes in the structure and species richness of bird communities in the Czech Republic. We focused on a comparison of two time periods (1982–1990 and 1991–2004) that differ in land use (high agricultural intensity in the former, and a drop in agricultural intensity accompanied by forest expansion in the latter). We found that bird communities became less specialized and that this decline in specialization did not change after 1990. In contrast, taxonomic homogenization increased during the first time period but declined at the beginning of the second one. Moreover, the community composition developed towards a dominance of species breeding in warmer climates, and this change coincided with an increase in spring temperatures. Therefore, it would appear that both functional and taxonomic homogenization took place in the 1980s but the latter did not continue in subsequent decades. Species richness of local bird communities did not show any trend over time. We suggest that climate warming might be an important driving force of changes in the bird community composition in the Czech Republic, but the role of land-use changes is less clear, although it is probable that habitat specialists probably did not benefit from lower intensity of agricultural activities and increased forest cover.

Study on Fish Ecology of the Seti Gandaki River Pokhara: II. Spatio-Temporal Variations in Fish Communities

Present paper deals with the spatio-temporal variations in distribution and abundance of fishes along the 30 km stretch of the Seti Gandaki river and its two major tributaries, Mardi Khola and Vijaypur Khola, in Pokhara Valley, Western Nepal. A total of 30 species of fishes belonging to 5 orders, 9 families and 22 genera were recorded from five sites on the river and its tributaries. Cyprinoids were predominant among fishes (17 spp.), siluroids (5 spp.), balitorids and cobitids (4 spp.), channioids (2 spp.), belonoids (one sp.) and mastacembeloids (one sp.). Among cyprinoids, mostly cyprinines were dominant groups (7 spp.) followed by rasborines (7 spp.), garrines (2 spp.) and schizothoracines (one sp.). There was increasing trend of species richness at upstream site (17 spp.). to downstream site (20 spp.) showing a longitudinal pattern. The total fish abundance and family-wise abundance at all the sites observed major peak during the spring and fall during the winter season in both the years of study. The average total density of fishes during the spring peak was highest (51.07/ha) at the upper tributary site and lowest (24.69/ha) at the urban site. According to the distribution pattern and abundance, the population status of the gamefish, mahseer [Tor tor (Ham)] has been endangered (E); that of game fishes [Tor putitora (Ham.) and Chagunius chagunio (Ham.)] and Zebra-fish [Brachydanio rerio (Ham.)] to are vulnerable (V); that of loach [Lepidocephalus guntea (Ham.)], cat-fishes [Myersglanis blythii (Day) and Amblyceps mangois (Ham.)] are rare (R).DOI: http://dx.doi.org/10.3126/njst.v12i0.6523 Nepal Journal of Science and Technology 12 (2011) 350-357

Trait‐dependent occupancy dynamics of birds in temperate forest landscapes: fine‐scale observations in a hierarchical multi‐species framework

AbstractSilvicultural practices lead to changes in forest composition and structure and may impact species diversity from the overall regional species pool to stand‐level species occurrence. We explored to what extent fine‐scale occupancy patterns in differently managed forest stands are driven by environment and ecological traits in three regions in Germany using a multi‐species hierarchical model. We tested for the possible impact of environmental variables and ecological traits on occupancy dynamics in a joint modelling exercise while taking possible variation in coefficient estimates over years and plots into account. Bird species richness differed across regions and years, and trends in species richness across years were different in the three regions. On the species level, forest management affected occupancy of species in all regions, but only 3–5% of the total assemblage‐level variation in occurrence probability was explained by either forest type and successional stage and < 1% by forest edge. On the assemblage level, bird occurrence decreased with body mass in all regions. Species with smaller breeding ranges had lower occurrence probabilities in one region, while later spring arrival decreased occurrence probabilities in the two other regions. Spatial variation in the effect size of trait covariates such as species phylogeny and breeding strata showed that variation in patch occupancy due to fine‐scale differences in forest management is, to some extent, predictable from ecological traits. Our results show that environmental factors and ecological traits jointly predict variation in bird occupancy patterns and their response to forest management. Observations at the fine scale of forest stands, at which conservation efforts can be arranged along with forest management practices in heterogeneous environments, have been shown to provide meaningful insights despite the difficulties involved in monitoring mobile organisms such as birds at the plot level.

We know too little about parasitoid wasp distributions to draw any conclusions about latitudinal trends in species richness, body size and biology.

Much has been written about latitudinal trends in parasitoid diversity and biology, though it is widely recognised that they are a comparatively poorly known group. Here I show that for both braconid and ichneumonid wasps there are highly significant relationships between body size and the mean recorded latitude of species. Numbers of species per genus (surrogates of clades) peaks in the temperate zone for both families contrasting with data from the virtually complete inventories for mammals, birds and monocot plants, suggesting massive under-description of tropical parasitoid faunas. If the ichneumonoids may be expected to show similar trends to mammals, birds and other groups, the implication is that taxonomic work both in terms of active generic revisions, but also likely, the collecting and processing of museum specimens, and selection of taxa for revision, is woefully inadequate to allow latitudinal patterns in biology to be analysed.

Species richness of motile cryptofauna across a gradient of reef framework erosion

Coral reef ecosystems contain exceptionally high concentrations of marine biodiversity, potentially encompassing millions of species. Similar to tropical rainforests and their insects, the majority of reef animal species are small and cryptic, living in the cracks and crevices of structural taxa (trees and corals). Although the cryptofauna make up the majority of a reef’s metazoan biodiversity, we know little about their basic ecology. We sampled motile cryptofaunal communities from both live corals and dead carbonate reef framework across a gradient of increasing erosion on a reef in Pacific Panama. A total of 289 Operational Taxonomic Units (OTUs) from six phyla were identified. We used species-accumulation models fitted to individual- and sample-based rarefaction curves, as well as seven nonparametric richness estimators to estimate species richness among the different framework types. All procedures predicted the same trends in species richness across the differing framework types. Estimated species richness was higher in dead framework (261–370 OTUs) than in live coral substrates (112–219 OTUs). Surprisingly, richness increased as framework structure was eroded: coral rubble contained the greatest number of species (227–320 OTUs) and the lowest estimated richness of 47–115 OTUs was found in the zone where the reef framework had the greatest vertical relief. This contradicts the paradigm that abundant live coral indicates the apex of reef diversity.

Long-term changes in plant diversity of grasslands under agricultural and conservation management

Question In many industrialized countries biodiversity is declining. Although changes in species composition and species richness have been documented for many individual systems, little long-term research has been done on a regional scale. We compared the temporal patterns of plant diversity over the last 30 yr in agricultural grasslands and nature reserves. Location Grasslands scattered over the entire province of South-Holland, the Netherlands. Methods Using data from 403 permanent plots over a period of 30 yr, we analysed temporal trends in species richness, floristic value and indicated nutrient richness and compared these trends between agricultural grasslands and grasslands in nature reserves. Results Expressed as 30-yr averages, species richness and floristic value were much higher in nature reserve grasslands than in agricultural grasslands (an increase of 87% and 78%, respectively), while indicated nutrient richness (determined using indicator values for soil fertility of the species present) was 31% lower. During this 30-yr period, species richness and floristic value significantly increased in nature reserve grasslands (0.186 species·yr-1). For agricultural grasslands, however, no significant changes could be detected. Restricting the analysis to those plots that were already studied before 1990 did reveal significant declines in the agricultural grasslands, indicating a past decrease in species richness that has probably levelled off after 1990. Conclusions These findings imply that the floristic ‘gap’ between agricultural grasslands and grasslands in nature reserves is widening every year. This may have consequences for conservation efforts in both nature reserves and agricultural grasslands. The challenge is to enhance the interaction between nature reserves and agricultural grasslands

Biodiversity and Status of Butterflies in the Vicinity of Mountain View College, Mt. Nebo, Valencia City

To establish a local data base on butterfly composition and richness, biodiversity of species were determined at the Agriculture Garden, Balambangan Area, Hydro II Mini-forest and Malingon Mini-forest sites of Mountain View College using 40 m line transect sampling. BIOPRO software version 2 was used in the analyses. Survey showed 49 species, 33 genera, and 5 families of butterflies. One species (2.0%) was very common, 22 species (44.9%) were common, 10 species (20.4%) were rare, and 16 species (32.7%) were undetermined. From highest to lowest, diversity indices were Malingon Mini-forest (H=1.519), Hydro 2 Mini-forest (H=1.415), Agriculture Garden (H=1.176), and Balambangan Area (H=1.146). Bray-Curtis analysis revealed 2 clusters of habitats. Cluster 1 (81% similarity) at Malingon and Hydro II Mini-forests had dense trees, river systems, and nectar sources which probably favoured the presence of rare and endemic species. Cluster II (73% similarity) at Agriculture Garden and Balambangan Area had human settlements, sparse tree distribution and inhabited by the common species. These results suggest that the highest diversity which includes rare and endemic species could be found in dense forest habitat with presence of water sources and minimal human disturbance. Continued monitoring will establish population and species richness trends and inform ecological measures to preserve endemic and rare species.

Assessing copepod (Crustacea: Copepoda) species richness at different spatial scales in northwestern Romanian caves

The aim of the present study was to assess copepod species richness in groundwater habitats from the Pădurea Craiului Mountains, Transylvania (northwestern Romania). Five species richness estimators (one asymptotic, based on species accumulation curves, and four non-parametric) were compared by testing their performances in estimating copepod species richness at three hierarchical spatial scales: cave, hydrographic basin, and karstic massif. Both epigean and hypogean species were taken in account. Two data sets were used in computing copepod species richness: 1. samples collected continuously during one year (dripping water) and seven months (pools) from five caves, and 2. samples collected from pools in twelve additional caves (data gathered from literature). Differences in copepod species richness among caves and hydrographic basins suggest that local environmental features are important in determining local species richness trends.

Mixed messages from multiple information sources on invasive species: a case of too much of a good thing?

Aim The increasing number and availability of online databases of alien species beg a question of their comparability given most do not adopt standard criteria in the definition of species status or taxonomic treatment and vary in their comprehensiveness. In this study, we compare the consistency of two major European databases for the regions they have in common. We assess whether they use consistent terminology to classify species status, provide similar taxonomic classification and coverage, deliver comparable estimates of alien richness per country and identify comparable correlates of alien richness. Location Northern Europe. Methods Data on the total number of alien species as well as the number of established alien species were extracted from the online databases DAISIE and NOBANIS for 13 European countries and classified into comparable taxonomic groups. Analyses across countries examined trends in alien species richness, correlations among taxonomic groups and the explanatory power of population density, country area and per capita GDP on alien species richness. Results Alien species richness, intertaxon correlations and the significance of individual drivers of invasion were all strongly database dependent. Differences were more marked for total numbers of aliens than established aliens. Over all taxonomic groups, DAISIE had lower species richness and fewer significant intertaxon correlations but presented a greater number of significant explanatory models of alien species richness. Trends in species richness were not generally correlated between the two databases with human population density being a more important driver in DAISIE while country area had greater explanatory power in NOBANIS. Main conclusions Considerable caution should be applied when collating data from different databases because often their underlying structure and content may differ markedly. For Europe, the analysis indicates that having two contrasting databases is not an ideal basis for implementing invasive species policy and moves should be made soon to establish a central pan-European database.

Accounting for detectability improves estimates of species richness in tropical bat surveys

1. Species richness is a state variable of some interest in monitoring programmes but raw species counts are often biased due to imperfect species detectability. Therefore, monitoring programmes should quantify detectability for target taxa to assess whether it varies over temporal or spatial scales. We assessed the potential for tropical bat monitoring programmes to reliably estimate trends in species richness. 2. Using data from 25 bat assemblages from the Old and New World tropics, we estimated detectability for all species in an assemblage (mean proportion of species detected per sampling plot) and for individual species (species-specific detectability). We further assessed how these estimates of detectability were affected by external sources of variation relating to time, space, survey effort and biological traits. 3. The mean proportion of species detected across 96 sampling plots was estimated at 0·76 (range 0·57–1·00) and was significantly greater for phytophagous than for animalivorous species. Species-averaged detectability for phytophagous species was influenced by the number of surveys and season, whereas the number of surveys and sampling methods [ground- or canopy-level mist nets, harp traps and acoustic sampling (AS)] most strongly affected estimates of detectability for animalivorous bats. Species-specific detectability averaged 0·4 and was highly heterogeneous across 232 species, with estimates ranging from 0·03 to 0·84. Species-level detectability was influenced by a range of external factors such as location, season, or sampling method, suggesting that raw species counts may sometimes be strongly biased. 4. Synthesis and applications. Due to generally high species-specific detection probabilities, Neotropical aerial insectivorous bats proved to be well suited for monitoring using AS. However, for species with low detectability, such as most gleaning animalivores or nectarivores, count data obtained in bat monitoring surveys must be corrected for detection bias. Our results indicate that species-averaged detection probabilities will rarely approach 1 unless many surveys are conducted. Consequently, long-term bat monitoring programmes need to adopt an estimation scheme that corrects for variation in detectability when comparing species richness over time and when making regional comparisons. Similar corrections will be needed for other species-rich tropical taxa.

Vegetational dynamics in some tropical abandoned rice fields in the western part of Orissa, India

In many areas of tropics, agroecosystems are developed by clearing the natural forests. Conversion of natural forests to agricultural systems leads to loss of several soil ecological attributes responsible to maintain the soil fertility. Therefore in such converted agroecosystems the soil fertility often declines. In order to meet the deficiency of soil fertility, the farmers adopt the practice of nutrient input to such agricultural systems. However, poor farmers of tropics being unable to adopt such soil management strategy abandon the agricultural systems because of decline in production and leave the fields to remain fallow. The present study examined the vegetational succession and quantitative community characteristics in some abandoned agricultural ecosystems of western part of Orissa, India. The phytosociological attributes in different abandoned rice fields were studied by taking quadrates of suitable sizes (1 ◊ 1, 5 ◊ 5 and 10 ◊ 10 m 2 for herbaceous grass and nongrass, shrubs and tree species respectively). Quantitative community characteristics like frequency, abundance, density of different plant species, diversity and dominance index were examined. Importance Value Index (IVI) was calculated to understand the importance of individual species in a community. The distribution patterns of different species were analyzed by species sequence curve method. Our finding showed that there is decrease in the number of grass stands and increase in the nongrass stands with the increase in the year of fallow periods. The study also indicated an increasing trend of species richness, abundance and diversity with increasing year of abandonment indicating the growth of secondary succession in this region.