Bird diversity patterns in Neotropical temperate farmlands: The role of environmental factors and trophic groups in the spring and autumn

Productivity, habitat heterogeneity and environmental similarity are of the most widely accepted hypotheses to explain spatial patterns of species richness and species composition similarity. Environmental factors may exhibit seasonal changes affecting species distributions. We explored possible changes in spatial patterns of bird species richness and species composition similarity. Feeding habits are likely to have a major influence in bird–environment associations and, given that food availability shows seasonal changes in temperate climates, we expect those associations to differ by trophic group (insectivores or granivores). We surveyed birds and estimated environmental variables along line‐transects covering an E‐W gradient of annual precipitation in the Pampas of Argentina during the autumn and the spring. We examined responses of bird species richness to spatial changes in habitat productivity and heterogeneity using regression analyses, and explored potential differences between seasons of those responses. Furthermore, we used Mantel tests to examine the relationship between species composition similarity and both the environmental similarity between sites and the geographic distance between sites, also assessing differences between seasons in those relationships. Richness of insectivorous birds was directly related to primary productivity in both seasons, whereas richness of seed‐eaters showed a positive association with habitat heterogeneity during the spring. Species composition similarity between assemblages was correlated with both productivity similarity and geographic proximity during the autumn and the spring, except for insectivore assemblages. Diversity within main trophic groups seemed to reflect differences in their spatial patterns as a response to changes between seasons in the spatial patterns of food resources. Our findings suggest that considering different seasons and functional groups in the analyses of diversity spatial pattern could contribute to better understand the determinants of biological diversity in temperate climates.     

Summer vegetation, deglaciation and the anomalous bird diversity gradient in eastern North America

Aim Geographic variation in the species richness of birds has been shown to be strongly associated with annual water and energy levels (actual evapotranspiration, AET) at the global scale. However, the gradient in eastern North America appears to be anomalous, because richness is greatest around the Great Lakes, whereas AET is highest in the south‐eastern US. Here I examine if birds may be responding to vegetation produced during the breeding season rather than to annual production. Location North America east of longitude 98° W. Methods The bird richness pattern was examined using climatic variables, remotely sensed estimates of annual and seasonal plant biomass, and time since areas were exposed by the retreating Laurentide ice sheet from 20,000 to 6000 yr bp . Results Average summer GVI (Global Vegetation Index, derived from NDVI) was found to be positively linearly associated with richness, explaining 82% of the variance, whereas the relationships between richness and annual measures of both AET and GVI were curvilinear. The pattern of retreat of the Laurentide ice sheet explained an additional 6% of the variance in richness, consistent with a previous analysis of Canadian birds. Main conclusions In eastern North America, a seasonal variable associated with plant production explains the diversity gradient rather than the annual measures, but it does not undermine a general conclusion that bird diversity is closely linked with plant biomass. Further, both contemporary and historical factors appear to influence the gradient, and an association between bird richness and the geographic pattern of glacial retreat is detectable in both climatic and plant‐biomass models of bird diversity.     

Filling in the GAPS: evaluating completeness and coverage of open‐access biodiversity databases in the United States

Primary biodiversity data constitute observations of particular species at given points in time and space. Open‐access electronic databases provide unprecedented access to these data, but their usefulness in characterizing species distributions and patterns in biodiversity depend on how complete species inventories are at a given survey location and how uniformly distributed survey locations are along dimensions of time, space, and environment. Our aim was to compare completeness and coverage among three open‐access databases representing ten taxonomic groups (amphibians, birds, freshwater bivalves, crayfish, freshwater fish, fungi, insects, mammals, plants, and reptiles) in the contiguous United States. We compiled occurrence records from the Global Biodiversity Information Facility (GBIF), the North American Breeding Bird Survey (BBS), and federally administered fish surveys (FFS). We aggregated occurrence records by 0.1° × 0.1° grid cells and computed three completeness metrics to classify each grid cell as well‐surveyed or not. Next, we compared frequency distributions of surveyed grid cells to background environmental conditions in a GIS and performed Kolmogorov–Smirnov tests to quantify coverage through time, along two spatial gradients, and along eight environmental gradients. The three databases contributed >13.6 million reliable occurrence records distributed among >190,000 grid cells. The percent of well‐surveyed grid cells was substantially lower for GBIF (5.2%) than for systematic surveys (BBS and FFS; 82.5%). Still, the large number of GBIF occurrence records produced at least 250 well‐surveyed grid cells for six of nine taxonomic groups. Coverages of systematic surveys were less biased across spatial and environmental dimensions but were more biased in temporal coverage compared to GBIF data. GBIF coverages also varied among taxonomic groups, consistent with commonly recognized geographic, environmental, and institutional sampling biases. This comprehensive assessment of biodiversity data across the contiguous United States provides a prioritization scheme to fill in the gaps by contributing existing occurrence records to the public domain and planning future surveys.     

Changes in the diversity structure of avian assemblages in North America

Aim To determine the major patterns of change in avian diversity structure over space and time at a local resolution and continental extent in non‐urban areas in North America. Location The contiguous United States and southern Canada. Methods We used 1673 North American Breeding Bird Survey (BBS) routes containing 547 terrestrial and aquatic species to estimate four diversity components: species richness, individual abundance, taxonomic distinctness and species evenness. We implemented three levels of analysis to examine changes in diversity structure on a yearly basis from 1968 to 2003: (1) a canonical analysis of discriminance, (2) a univariate analysis across BBS routes, and (3) a univariate analysis at individual BBS routes. We estimated changes in similarity in species composition over time between 470,730 BBS route pairs. We also estimated the level of human activity at BBS routes using three spatial anthropogenic databases. Results BBS routes were located in non‐urban areas in association with low nighttime light activity and moderately low human population densities. The analysis of diversity structure indicated the presence of two independent patterns: (1) a temporally consistent pattern defined by increasing species richness (12% increase from 1968 to 2003) associated with limited gains in taxonomic distinctness, and (2) an association between species abundance and evenness related to variability in abundance associated with the most abundant species. The similarity analysis indicated that BBS routes located closer to the Atlantic and the Pacific coasts of the United States experienced the strongest patterns of homogenization of species composition. Main conclusions Our results suggest that avian diversity structure has changed at the local scale in non‐urban areas in North America. However, there was no evidence for a consistent continent‐wide pattern. Instead, the evidence pointed to the presence of regional factors influencing diversity patterns. This study provides a foundation for more detailed investigations of the spatiotemporal and taxonomic details of these general patterns.     

Bird diversity and environmental gradients in Britain: a test of the species–energy hypothesis

1.  We tested the species diversity–energy hypothesis using the British bird fauna. This predicts that temperature patterns should match diversity patterns. We also tested the hypothesis that the mechanism operates directly through effects of temperature on thermoregulatory loads; this further predicts that seasonal changes in temperature cause matching changes in patterns of diversity, and that species' body mass is influential.
2.  We defined four assemblages using migration status (residents or visitors) and season (summer or winter distribution). Records of species' presence/absence in a total of 2362, 10 × 10-km, quadrats covering most of Britain were used, together with a wide selection of habitat, topographic and seasonal climatic data.
3.  We fitted a logistic regression model to each species' distribution using the environmental data. We then combined these individual species models mathematically to form a diversity model. Analysis of this composite model revealed that summer temperature was the factor most strongly associated with diversity.
4.  Although the species–energy hypothesis was supported, the direct mechanism, predicting an important role for body mass and matching seasonal patterns of change between diversity and temperature, was not supported.
5.  However, summer temperature is the best overall explanation for bird diversity patterns in Britain. It is a better predictor of winter diversity than winter temperature. Winter diversity is predicted more precisely from environmental factors than summer diversity.
6.  Climate change is likely to influence the diversity of different areas to different extents; for resident species, low diversity areas may respond more strongly as climate change progresses. For winter visitors, higher diversity areas may respond more strongly, while summer visitors are approximately neutral.     

The effect of habitat on the range expansion of a native and an introduced bird species

Aim Range expansion across a heterogeneous landscape may depend on the habitat selected and used by the expanding species. If habitat selection influences range expansion then localities colonized by a species should contain a greater proportion of favoured habitat (and less non‐habitat) than other nearby localities not colonized. White‐winged doves (Zenaida asiatica) and Eurasian collared doves (Streptopelia decaocto) are two bird species that provide an excellent opportunity to test this hypothesis, because the geographic ranges of both species have been expanding in North America for more than two decades. Location Continental USA. Methods We used distribution data from the North American Breeding Bird Survey to test whether the landscapes occupied by each species contained a greater proportion of favoured habitat (urban land, grassland/pasture, shrub land and cropland) and a lower proportion of non‐habitat (forest land) than landscapes where doves were not found. We tested each species separately in each of three broad expansion areas, namely East, Central and West. We also compared rates of spatial spread between expansion areas and between the two species. Results As predicted, both species tended to occupy landscapes with greater proportions of urban land, shrub land and cropland but with less forest land compared with landscapes without doves, in all three expansion areas. Contrary to prediction, occupied landscapes tended to have slightly less grassland/pasture than unoccupied landscapes. Rates of spread differed between the two species and among expansion areas. Main conclusions Range expansion and the extent to which a species fills or saturates its range are influenced by the habitat ecology of the expanding species. Species colonize localities based on the availability of suitable habitat. However, the role of habitat in a species’ range expansion does depend somewhat on the greater geographical setting. Over large regional and geographical scales, range expansion (rate of spread and saturation) may proceed unevenly, suggesting that range expansion is a very dynamic and context‐specific process.     

New York's nature: a review of the status and trends in species richness across the metropolitan region

Aim The world's population is urbanizing, yet relatively little is known about the ecology of urban areas. As the largest metropolitan area in the USA, New York City is an ideal location to study the effects of urbanization. Here, we aim to produce a better understanding of the state of the research for species richness of flora and fauna across the New York metropolitan region. Location New York metropolitan region, USA. Methods We conducted a review of the published and grey literature, in which we targeted studies of species richness, and categorized each study by habitat, location and taxonomic group. Results We found 79 studies reporting location‐specific species richness data, resulting in 261 location‐taxonomic group records. Of these, 26 records had data from multiple time periods; 17 showed decreases in species richness, six reported increases and three showed stable species richness. Of these 26 records, most declines were attributed to anthropogenic causes, such as habitat loss/degradation and invasive species, while most increases reflected recovery from major habitat loss or increases in exotic species. Overall, most records (84) were terrestrial, followed by those in freshwater (72) and mixed habitats (61). When parsed by taxonomic group, the most commonly studied groups were plants (76) and mammals (48). Main conclusions In general, we discovered fewer studies than expected reporting species richness, especially studies reporting species richness for more than one point in time. Most studies that did contain data over time reported declines in species richness, while several studies reporting increasing or stable species richness reflected increases in exotic species. This survey provides a crucial first step in establishing baseline ecological knowledge for the New York metropolitan region that should help prioritize areas for protection, research and development. Furthermore, this research provides insights into the impacts of urbanization across the USA and beyond and should help establish similar frameworks for ecological understanding for other metropolitan regions throughout the world.     

Plant composition and diversity in a semi-natural Mediterranean island landscape: the importance of environmental factors

Abstract

Islands crucially contribute to the Mediterranean Basin’s high floristic diversity, which, however, is at risk facing climate and land-use changes. Besides the identification of highly diverse areas, the knowledge about factors favouring diversity is of great importance. We analysed plant species diversity and composition related to environmental factors over varied vegetation units on a former Italian prison island in the northwest of Sardinia. Due to a long history of land use with grazing and later abandonment the nowadays protected island features a semi-natural landscape and can serve as an example for strongly anthropogenic altered insular ecosystems. Floristic composition, soil properties, microclimate and ungulate abundance were assessed. Relationships of vegetation composition and diversity with abiotic variables were examined by Canonical Correspondence Analysis, which indicated the importance of air temperature, soil moisture, slope gradient and C/N ratio for floristic differentiation. Most important abiotic factors for plant species richness were relative air humidity and soil moisture, while floristic diversity was mainly determined by air temperature and pH. Furthermore, observation data pointed to an adverse influence of ungulate abundance for plant species diversity. Regarding nature conservation, grazing intensity thus must be critically taken into account, especially for sensitive vegetation units like the coastal garrigue.     

Host range validation,molecular identification and release and establishment of a Chinese biotype of the Asian leaf beetle Lilioceris cheni (Coleoptera: Chrysomelidae: Criocerinae) for control of Dioscorea bulbifera L. in the southern United States

Dioscorea bulbifera, an Asian vine, is invasive in the southeastern USA. It rarely flowers but propagates from potato-like bulbils formed in leaf axils, which persist into the subsequent growing season. Lilioceris cheni Gressitt and Kimoto, a foliage-feeding beetle (Coleoptera: Chrysomelidae: Criocerinae) from Nepal, had been tested, proven to be a specialist and approved for release as a biological control agent. Regulatory delays, however, resulted in the demise of quarantine-held colonies, and acquisition of new Nepalese stock proved untenable. Searches then undertaken in southern China resulted in the collection of over 300 similar beetles. Two Chinese Lilioceris species were identified: one confirmed to be L. cheni and the other identified as Lilioceris egena (Weise). Mitochondrial analysis revealed an exact DNA match between some Chinese and one of the two Nepalese c oxidase subunit I haplotypes and all Chinese L. cheni haplotypes clustered as a single species but the comingling of the two species aroused concerns over possible hybridisation. These concerns were allayed by nuclear D2 analysis showing the absence of dual parental sequences. Nonetheless, diligence was exercised to ensure that the Chinese strains were safe to release. Abridged host testing using critical test species verified specificity. Caged releases during autumn 2011 documented the ability of adult beetles to overwinter in south Florida despite a prolonged lack of foliage. Open releases the following year produced vigorous populations that caused extensive defoliation. Preliminary observations indicate that L. cheni now contributes to the control of D. bulbifera and the bulbil-feeding L. egena should complement these effects if its host range proves appropriate.