Evaluating the effectiveness of overstory cover as a surrogate for bird community diversity and population trends

Landscape features are often used as surrogates for biodiversity. While landscape features may perform well as surrogates for coarse metrics of biodiversity such as species richness, their value for monitoring population trends in individual species is virtually unexplored. We compared the performance of a proposed habitat surrogate for birds, percentage cover of vegetation overstory, for two distinct aspects of bird assemblages: community diversity (i.e. species richness) and population trends. We used four different long-term studies of open woodland habitats to test the consistency of the relationship between overstory percentage cover and bird species richness across a large spatial extent (>1000 km) in Australia. We then identified twelve bird species with long-term time-series data to test the relationship between change in overstory cover and populations trends. We found percentage cover performed consistently as a surrogate for species richness in three of the four sites. However, there was no clear pattern in the performance of change in percentage cover as a surrogate for population trends. Four bird species exhibited a significant relationship with change in percentage overstory cover in one study, but this was not found across multiple studies. These results demonstrate a lack of consistency in the relationship between change in overstory cover and population trends among bird species, both within and between geographic regions. Our study demonstrates that biodiversity surrogates representing community-level metrics may be consistent across regions, but provide only limited information about individual species population trends. Understanding the limitations of the information provided by a biodiversity surrogate can inform the appropriate context for its application.     

The contribution of different habitat types to species diversity of Baltic uplift islands

Islands are vulnerable ecosystems worldwide, increasingly exposed to human pressure, global climate change and invasive species. Thus, understanding island species diversity is key for nature conservation. Recent studies on insular plant communities indicated that habitat-specific species composition and richness might largely affect diversity patterns observed at the island scale. In consequence, habitat-based approaches are needed to (i) estimate how environmental changes at the habitat scale may affect island diversity, and to (ii) estimate the contribution of different patches of the same habitat to island diversity with respect to habitat-specific environmental constraints.In the present study, we tested these habitat-to-island diversity relationships for shoreline habitats (brackish reeds, salt marsh, rocky shore, tall herbs) and island interior habitats (rocks, semi-natural grassland, pioneer forest, coniferous forest, mixed forest) using 108 islands of three Baltic archipelagos in Sweden. These islands differed in terms of island-scale variables describing effects of island configuration and distance, and habitat-scale variables representing the effects of habitat area, abiotic environment and land-use.The studied habitats differed in their contribution to island species diversity, called habitat specificity. Shoreline habitats shared many common specialist species adapted to extreme conditions like sea salt or bird grazing, while habitats of the island interior harbored mainly species adapted to the specific conditions of a single habitat. We found high variability in habitat specificity as a consequence of habitat-specific environmental factors. Variability was highest for grasslands, where it was related to abandonment and soil fertility, stressing the importance of grassland management for maintaining island biodiversity. Habitats with high habitat specificity through either high species richness or many habitat-specific specialists should be the primary targets for biodiversity management.     

Effects of habitat change and geographical variation on the bird communities of two Indonesian islands

The effects of selective logging and other types of forest exploitation on bird communities are often studied latitudinally, i.e. a contemporaneous comparison of disturbed and pristine areas. Such an approach assumes that before disturbance those areas were equivalent. By comparing communities at a single site before and after disturbance, a so called longitudinal approach does not make that assumption but such studies can be resource intensive. In this study we adopt a latitudinal approach to explore the effects of disturbance on birds, but pay specific attention to whether natural geographically-based variation in the forest ecosystem may be a major contributory factor equal to, or greater than, effects of disturbance. Bird census data were collected from two Indonesian islands, Sumba and Buru. On Sumba the differences between habitat types in terms of species richness, species accumulation rates, and numbers of birds were swamped by simple site differences between the forest blocks sampled. On Buru, disturbed areas were more diverse than mature forest but it was still not possible to discount the effects of natural variation between forest areas. Although the islands support bird faunas which are rather similar in size and origin, local species diversities and abundances were significantly greater on Sumba. Substituting space for time is a common strategy in ecological research but the results of such studies should be viewed with caution.     

Low congruence between the diversity of Waxcap (Hygrocybe spp.) fungi and vascular plants in semi-natural grasslands

The diversity of fungi in semi-natural grasslands is poorly known, partly due to difficulties in species identification in the field but also because there are few specialists available. Diversity assessments of grassland fungi would be facilitated if a potential surrogate group for fungal diversity could be identified. The aim of this study was to assess whether plant diversity patterns in semi-natural grasslands are congruent with diversity patterns of Waxcap (Hygrocybe spp.) fungi. Waxcaps, together with several other groups of fungi (e.g. the genera Entoloma, Dermoloma, Camarophyllopsis, and the families Clavariaceae and Geoglossaceae) have habitat requirements similar to many plants typical for semi-natural grasslands and they are all threatened by ceased management and nutrient enrichment. Diversity data from 31 semi-natural grasslands in southern Sweden were used to examine if there is congruence in species richness, nestedness, β-diversity and species composition between plants and Hygrocybe fungi. Species richness of Hygrocybe was significantly positively correlated with plant richness, although the relationship was not strong (r²=0.14). Both plant and Hygrocybe species composition was significantly nested, i.e. species-poor sites contain a subset of species from species-rich sites, which suggests that rare species mostly occur in the species-rich sites. A species similarity analysis between the grassland sites showed that there is low overlap between species composition of plants and Hygrocybe, indicating that conservation decisions based solely on plants may not fulfil the requirements of the Hygrocybe species. The conclusion is that there is low congruence between plant and Hygrocybe species diversity, making plants a poor surrogate group for Hygrocybe fungi, and probably also for other grassland fungi.     

Effects of habitat management on vegetation and above-ground nesting bees and wasps of orchard meadows in Central Europe

We studied the vegetation, stand structure and communities of above-ground nesting bees and wasps in 45 orchard meadows that were grazed, mown or abandoned (15 of each) in an agricultural landscape near Göttingen, Germany. Total species richness of plants was significantly lower and the proportion of dead wood was significantly higher on abandoned meadows compared to mown or grazed meadows. Species richness of bees, eumenid wasps and sphecid wasps did not differ between the three management types. Abundance of sphecid wasps was significantly higher on abandoned than on managed orchard meadows. Landscape context did not affect management type. The results suggest that management practises affect vegetation more significantly than the studied insect groups.     

Geographic position of sample grid and removal of uncommon species affect multivariate analyses of diverse assemblages: The case of oribatid mites (Acari: Oribatida)

In view of the rapid loss of biodiversity, large-scale environmental monitoring programs are urgently needed, over a range of local, regional and global scales. These programs can be made more efficient and cost-effective through shortcuts such as reduction of sampling effort and the use of low-cost surrogates. We revisited a large-scale dataset composed by 161 species recorded in 72 plots of 250 m, distributed over an 8 m × 8 m sampling grid in the tropical rainforest. Samples of litter and soil were collected and oribatid mites were extracted with a Berlese–Tullgren apparatus. Using a “moving window” procedure, we delimited smaller 5 km × 5 km grids in 16 possible positions within the larger grid. We first evaluated which fraction was more important to explain environmental and spatial patterns in the species composition: known environmental or spatial filters representing unknown causes of aggregation, and the confounded variance that might be associated with either or both. We used soil clay content, litter quantity, soil pH, number of trees, and distance to the nearest stream as environmental predictors. The spatial filters were generated using Moran Eigenvector mapping through the Principal Coordinates of Neighbor Matrices technique. To evaluate the influence of these fractions on the species composition, we used partial Redundancy Analysis. Using Principal Coordinates Analysis for abundance and presence/absence data, we evaluated if reduced matrices, discarding sets of less-frequent species, could identify the relationships captured with the complete dataset. All smaller grids contained more than 100 species. The effect of environmental variables on oribatid-mite community composition was always low, and each smaller grid position produced different results. Soil clay content and pH were the main factors associated with oribatid-mite distributions. The effects of unknown spatial patterns were greater than the environmental ones. Independently of the grid position, similar results were obtained for analyses with all oribatid-mite species, to the results obtained from analyses of only the most frequent species. Sets of more frequent and easily identifiable species proved to be a reliable surrogate for the complete assemblage. Omitting identifications of most species will improve the cost-effectiveness of monitoring programs. More emphasis should be placed on investigating the role of spatial heterogeneity and the effects of grid position in relation to patterns in species associations. Efficient biomonitoring could target surrogate species, to enable rapid tracking of environmental change while enlarging the sampling area to provide data for conservation strategies.     

渤海区无居民海岛植物物种丰富度分布格局

为了解渤海区小型无居民海岛植物物种丰富度的分布格局, 本研究以渤海区9个无居民海岛为研究对象, 基于种-面积关系和种-多度对数正态分布模型探究了无居民海岛植物的物种丰富度分布格局。结果表明: (1)位于温带地区的无居民海岛木本植物相对多度符合对数正态分布特征, 表明海岛木本植物群落中多度较大的物种数较少, 而多度较小的物种甚至是稀有种或罕见种较多; (2)渤海区多数无居民海岛物种数介于60-130之间, 表明总体丰富度较高; (3)通过分析海岛与周边保护区的空间关系发现, 物种丰富度高的海岛基本位于保护区内, 总体上渤海区海岛植物热点区得到了有效保护。综上所述, 种-多度分布模型和种-面积关系均是揭示海岛植物物种丰富度分布的重要手段, 同时可初步推断, 生态位理论对海岛植物物种多样性的维持显得更为重要。     

Bayesian estimation of species richness from quadrat sampling data in the presence of prior information

We consider the problem of estimating the number of species of an animal community. It is assumed that it is possible to draw up a list of species liable to be present in this community. Data are collected from quadrat sampling. Models considered in this article separate the assumptions related to the experimental protocol and those related to the spatial distribution of species in the quadrats. Our parameterization enables us to incorporate prior information on the presence, detectability, and spatial density of species. Moreover, we elaborate procedures to build the prior distributions on these parameters from information furnished by external data. A simulation study is carried out to examine the influence of different priors on the performances of our estimator. We illustrate our approach by estimating the number of nesting bird species in a forest.     

The effect of accidental burning on habitat conditions and species composition of Molinion caeruleae meadows

This study aimed to assess the effects of accidental burning on plant cover and habitat conditions in abandoned Molinion caeruleae meadows. Field studies were conducted in Kraków (Southern Poland) in the years 2017–2019 in two line transects, each with 10 permanent plots established in permanent study plots placed in accidentally burned and unburned patches. In the burned patch, the number of species, as well as Shannon-Wiener, Pielou and Simpson indicators achieved lower values. Moreover, the cover of numerous taxa affiliated with Molinion caeruleae changed remarkably, while taxa representing the alliances Calthion and Filipendulion disappeared. The considerable dominance of hemicryptophytes was observed in burned site, while in unburned place hemicryptophytes and geophytes were represented most abundantly. In the burned patch, anemochorous and autochorous species as well as small-seeded taxa dominated, while in the unburned patch autochorous species and medium-seeded taxa prevailed. The values of Ellenberg indicators in the burned patch achieved greater (light, soil reaction), lower (nitrogen, humidity) or similar (temperature, continentality) values to the unburned patch. The majority of soil properties in the burned and unburned patches were similar with the exception of the significantly greater content of potassium and lower content of magnesium in exchangeable form noticed in the burned patch. The performed investigations showed that, although the accidental fire activity inhibited the secondary succession in Molinion caeruleae meadows, burning cannot replace traditional mowing due to the reduction of species richness and disappearance of characteristic taxa.     

Plants on small islands revisited: the effects of spatial scale and habitat quality on the species–area relationship

Understanding how species diversity is related to sampling area and spatial scale is central to ecology and biogeography. Small islands and small sampling units support fewer species than larger ones. However, the factors influencing species richness may not be consistent across scales. Richness at local scales is primarily affected by small‐scale environmental factors, stochasticity and the richness at the island scale. Richness at whole‐island scale, however, is usually strongly related to island area, isolation and habitat diversity. Despite these contrasting drivers at local and island scales, island species–area relationships (SARs) are often constructed based on richness sampled at the local scale. Whether local scale samples adequately predict richness at the island scale and how local scale samples influence the island SAR remains poorly understood. We investigated the effects of different sampling scales on the SAR of trees on 60 small islands in the Raja Ampat archipelago (Indonesia) using standardised transects and a hierarchically nested sampling design. We compared species richness at different grain sizes ranging from single (sub)transects to whole islands and tested whether the shape of the SAR changed with sampling scale. We then determined the importance of island area, isolation, shape and habitat quality at each scale on species richness. We found strong support for scale dependency of the SAR. The SAR changed from exponential shape at local sampling scales to sigmoidal shape at the island scale indicating variation of species richness independent of area for small islands and hence the presence of a small‐island effect. Island area was the most important variable explaining species richness at all scales, but habitat quality was also important at local scales. We conclude that the SAR and drivers of species richness are influenced by sampling scale, and that the sampling design for assessing the island SARs therefore requires careful consideration.     

The Relationship between Local Species Richness and Species Pool: A Case Study from the High Mountains of the Greater Caucasus

The causes of linear relationships between local species richness and the size of the actual species pool in closed subalpine meadow communities and open plant communities of the alpine stony substrate (the Greater Caucasus Mountains) were analyzed using a computer simulation model. The results demonstrated that this relationship is insufficient evidence for the variation of local species richness among communities is wholly or partly determined by regional processes (the species-pool hypothesis). A relatively proportional ratio between these variables can also arise where local species richness and the size of the species pool both depend on local processes, or where local species richness is determined by local factors alone while the size of the species pool is determined by both local and regional factors.     

Species richness and the proportion of predatory animal species in temporary freshwater pools: relationships with habitat size and permanence

The proportion of predatory animal species is often believed not to vary systematically across communities. However, we predict that larger temporary freshwater pools, and pools that are more permanent, will contain a higher proportion of predatory animal species. In 24 temporary rockpools in Northern Israel (supporting communities dominated by ostracods, copepods, cladocerans, flatworms, dipterans and amphibians), the mean proportion of macroscopic predatory species (averaged over a series of samples) increased with increasing pool area. For the highest possible proportion of predatory species (including microscopic species with uncertain diets), the relationship with pool area was not statistically significant. We did not find significant relationships between permanence and the proportion of either macroscopic or all possible predatory species. Larger pools and pools that were more permanent had more species. Species richness and the proportion of macroscopic predators were positively correlated. These patterns imply that species-poor ecosystems are likely to be functionally different from species-rich systems.     

The role of native forest plantations in the conservation of Neotropical birds: the case of the Andean alder

The gradual increase in reforested areas worldwide, as a strategy for mitigating native forest loss, has stressed the need of assessing their real value as habitat for native species. Forest plantations, particularly those based on native species, could be valuable for conservation purposes, especially in heavily fragmented and disturbed ecosystems. We evaluated the value of a monoculture of a native tree species, the Andean alder (Alnus acuminata), for the conservation of avifauna in the Central Andes region, which is considered a bird species diversity hotspot but also suffers from high anthropogenic disturbance levels. Our results suggest that alder plantations are valuable for conservation from three points of view: (1) they have similar or greater bird species richness and abundance than secondary native forests; (2) low community similarities are found between this type of forest compared to secondary forest stands (with 27 species exclusive to alder plantations); and (3) three near threatened species (Odontophorus hyperythrus, Eriocnemis derbyi, and Cyanolyca viridicyanus). Further, 27 out of the 85 species found at the alder plantations were of least concern but showing decreasing population trends. While forest plantations do not replace native forests, they offer habitat for many bird species, some of them being of conservation concern (i.e., included in an IUCN threat category) or with decreasing populations. Hence establishing native species plantations among native forest remnants – especially in heavily fragmented landscapes – could have a positive effect in the conservation of threatened avifauna.     

Factors influencing vascular plant diversity on 22 islands off the coast of eastern North America

Aim The influence of physiographic and historical factors on species richness of native and non‐native vascular plants on 22 coastal islands was examined. Location Islands off the coast of north‐eastern USA and south‐eastern Canada between 41° and 45° N latitude were studied. Island size ranges from 3 to 26,668 ha. All islands were deglaciated between 15,000 and 11,000 yr bp ; all but the four New Brunswick islands were attached to the mainland until rising sea level isolated them between 14,000 and 3800 yr bp . Methods Island species richness was determined from floras compiled or revised since 1969. Simple and multiple regression and rank correlation analysis were employed to assess the relative influence of independent variables on species richness. Potential predictors included island area, latitude, elevation, distance from the mainland, distance from the nearest larger island, number of soil types, years since isolation, years since deglaciation, and human population density. Results Native vascular plant species richness for the 22 islands in this study is influenced most strongly by island area, latitude, and distance from the nearest larger island; richness increases with island area, but decreases with latitude and distance from the nearest larger island as hypothesized. That a similar model employing distance from the mainland does not meet the critical value of P confirms the importance of the stepping‐stone effect. Habitat diversity as measured by number of soil types is also an important predictor of native plant species richness, but at least half of its influence can be attributed to island area, with which it is correlated. Two historical factors, years since deglaciation and years since isolation, also appear to be highly correlated with native species richness, but their influence cannot be separated from that of latitude for the present sample size. Non‐native vascular plant species richness is influenced primarily by island area and present‐day human population density, although human population density may be a surrogate for the cumulative effect of several centuries of anthropogenic impacts related to agriculture, hunting, fishing, whaling, tourism, and residential development. Very high densities of ground‐nesting pelagic birds may account for the high percentage of non‐native species on several small northern islands. Main conclusions Many of the principles of island biogeography that have been applied to oceanic islands apply equally to the 22 islands in this study. Native vascular plant species richness for these islands is strongly influenced by physiographic factors. Influence of two historical factors, years since deglaciation and years since isolation, cannot be assessed with the present sample size. Non‐native vascular plant species richness is influenced by island area as well as by human population density; human population density may be a surrogate for other anthropogenic impacts.     

The influence of matrix and edges on species richness patterns of ground beetles (Coleoptera: Carabidae) in habitat islands

Aim The aim of this study was to analyse whether, and how, the inclusion of habitat specialists and edge‐preferring species modifies the species–area relationship predictions of the island biogeography theory for an insect group (ground beetles, Coloptera: Carabidae) living in natural fragments. Species–habitat island area relationships applied to terrestrial habitat islands can be distorted by the indiscriminate inclusion of all species occurring in the fragments. Matrices surrounding terrestrial habitat fragments can provide colonists that do not necessarily distinguish the fragment from the matrix and can survive and reproduce there. Edge‐preferring species can further distort the expected relationship, as smaller fragments have larger edge:core ratios. Location Nineteen forest fragments were studied in the Bereg Plain, Hungary, and SW Ukraine. This area contains natural forest patches, mainly of oak and hornbeam, and supports a mountain entomofauna. Methods Ground beetles (Carabidae) present in the 19 forest patches were categorized into generalists, forest specialists and edge‐preferring species. We analysed the relationship between species richness and fragment area using species richness in the different categories. Results The assemblages contained a high share of generalist species (species that occur also in the surrounding matrix). Forest patch size and the number of generalist species showed a marginally significant negative relationship, indicating that generalist species were more important in smaller patches. Forest specialist species richness was correlated positively with patch area. Edge‐preferring species were shown to influence the species–area relationship: the number of edge‐preferring species increased with the edge:area ratio. Main conclusions Both generalist and edge‐preferring species can considerably distort the species–area relationship. Island biogeography theory can be applied to habitat islands only if the habitat islands are defined correctly from the viewpoint of the target species.     

The occurrence and distribution of carabid beetles (Carabidae) on islands in the Baltic Sea: a review

The distribution and occurrence of carabid beetles have been studied extensively in a number of archipelagoes in the Baltic Sea, a ca. 377,000 km², fairly shallow and young sea in northern Europe. This work has revealed some surprising results related to colonisation success and maintenance of populations. Dispersal from the mainland and between islands appears to be relatively easy because inter-island distances are small (tens or hundreds of metres) and the salinity of the Baltic is low, which allows survival during drift. This is reflected in the higher than expected proportion of brachypterous species on small islands. A lack of energetically expensive wings, flight muscles and flight fuel may give brachypterous species an advantage - in terms of resource allocation for survival and fecundity - over macropterous species in the colonisation of an island. Once an island is reached, successful colonisation mainly depends on the presence of suitable habitat. The most abundantly collected carabids on these islands are habitat generalists, but some degree of habitat association exists. Yet, the composition of carabid assemblages differs substantially among islands, possibly a result of chance effects. There is evidence that species on smaller islands occur in a wider variety of vegetation types than species on larger islands. Both habitat diversity and area per se are implicated in the positive species-area relationships found, but the small island effect has been identified as being significant in most of the archipelagoes investigated. Pterostichus melanarius, a eurytopic, wing-polymorphic species abundantly collected on the mainland is, unexpectedly, absent from small islands. Possible reasons for this include; (1) interspecific predation and competition for food by the closely related but slightly larger P. niger, which is dominant on small islands, (2) the apparent inability of P. melanarius to reproduce on small islands, (3) its reduced dispersal power as compared to P. niger and (4) the possible absence of some essential resources from small islands. In conclusion, the conservation value of highly threatened cultural landscapes on Baltic Sea islands, such as species rich wooded meadows, is discussed as well as the possible negative effects of climate change on carabid beetles.     

The link between international trade and the global distribution of invasive alien species

Invasive alien species (IAS) exact large biodiversity and economic costs and are a significant component of human-induced, global environmental change. Previous studies looking at the variation in alien species across regions have been limited geographically or taxonomically or have not considered economics. We used a global invasive species database to regress IAS per-country on a suite of socioeconomic, ecological, and biogeographical variables. We varied the countries included in the regression tree analyses, in order to explore whether certain outliers were biasing the results, and in most of the cases, merchandise imports was the most important explanatory variable. The greater the degree of international trade, the higher the number of IAS. We also found a positive relationship between species richness and the number of invasives, in accord with other investigations at large spatial scales. Island status (overall), country area, latitude, continental position (New World versus Old World) or other measures of human disturbance (e.g., GDP per capita, population density) were not found to be important determinants of a country’s degree of biological invasion, contrary to previous studies. Our findings also provide support to the idea that more resources for combating IAS should be directed at the introduction stage and that novel trade instruments need to be explored to account for this environmental externality.