Jon P. Sadler

Changing Bee and Hoverfly Pollinator Assemblages along an Urban-Rural Gradient

Background The potential for reduced pollination ecosystem service due to global declines of bees and other pollinators is cause for considerable concern. Habitat degradation, destruction and fragmentation due to agricultural intensification have historically been the main causes of this pollinator decline. However, despite increasing and accelerating levels of global urbanization, very little research has investigated the effects of urbanization on pollinator assemblages. We assessed changes in the diversity, abundance and species composition of bee and hoverfly pollinator assemblages in urban, suburban, and rural sites across a UK city. Methodology/Principal Findings Bees and hoverflies were trapped and netted at 24 sites of similar habitat character (churchyards and cemeteries) that varied in position along a gradient of urbanization. Local habitat quality (altitude, shelter from wind, diversity and abundance of flowers), and the broader-scale degree of urbanization (e.g. percentage of built landscape and gardens within 100 m, 250 m, 500 m, 1 km, and 2.5 km of the site) were assessed for each study site. The diversity and abundance of pollinators were both significantly negatively associated with higher levels of urbanization. Assemblage composition changed along the urbanization gradient with some species positively associated with urban and suburban land-use, but more species negatively so. Pollinator assemblages were positively affected by good site habitat quality, in particular the availability of flowering plants. Conclusions/Significance Our results show that urban areas can support diverse pollinator assemblages, but that this capacity is strongly affected by local habitat quality. Nonetheless, in both urban and suburban areas of the city the assemblages had fewer individuals and lower diversity than similar rural habitats. The unique development histories of different urban areas, and the difficulty of assessing mobile pollinator assemblages in just part of their range, mean that complementary studies in different cities and urban habitats are required to discover if these findings are more widely applicable.

Interdisciplinary investigations of the end of the Norse Western Settlement in Greenland

The loss of the Norse Western Settlement in Greenland around the mid-fourteenth century has long been taken as a prime example of the impact of changing climate on human populations. This study employs an interdisciplinary approach combining historical documents, detailed archaeological investigations, and a high-resolution proxy climate record from the Greenland Ice Sheet Project 2 (GISP2) to investigate possible causes for the end of this settlement. Historical climate records, mainly from Iceland, contain evidence for lowered temperatures and severe weather in the north Atlantic region around the mid-fourteenth century. Archaeological, palaeoecological and historical data specifically concerning the Western Settlement suggest that Norse living conditions left little buffer for unseasonable climate, and provide evidence for a sudden and catastrophic end around the mid-fourteenth century. Isotopic data from the GISP2 ice core provide annual- and seasonal-scale proxy-temperature signals which suggest multiyear intervals of lowered temperatures in the early and mid-fourteenth century. The research synthesized here suggests that, while periods of unfavourable climatic fluctuations are likely to have played a role in the end of the Western Settlement, it was their cultural vulnerabilities to environmental change that left the Norse far more subject to disaster than their Inuit neigh bours.

Exploring the role of private wildlife ranching as a conservation tool in South Africa: stakeholder perspectives

Rich in biological diversity, South Africas natural habitats are internationally recognized as a conservation priority. Biodiversity loss continues, however, and limited scope to enlarge the state- protected areas, combined with funding shortages for public parks, means that conservationists are increasingly turning to private landowners for solutions. The recent boom in privately owned wildlife ranches in South Africa has the potential to contribute to conservation in South Africa. This paper explores the benefits, limitations, and challenges of private wildlife ranching as a tool for conservation in South Africa through interviews with key stakeholders working within conservation and wildlife ranching, and through case studies of threatened species programs. Respondents suggested that wildlife ranches contribute to conservation positively by maintaining natural areas of habitat and by providing resources to support reintroduction programs for threatened species. However, they reported a number of limitations centered on three themes that generally arise due to the commercial nature of wildlife ranching: (1) tourist preferences drive the industry, (2) predators are persecuted to protect valuable game, and (3) inadequate resources are made available for professional conservation management and planning on ranches. In addition to challenges of combining economic gain with conservation objectives, ranchers face a number of challenges that arise because of the small, enclosed character of many ranches in South Africa, including the need to intensively manage wildlife populations. In order to enhance the role of wildlife ranching within conservation, clear guidance and support for ranchers is likely to be required to boost endorsement and minimize economic loss to ranchers.

The influence of artificial light on stream and riparian ecosystems: questions, challenges, and perspectives

Artificial light at night is gaining attention for its potential to alter ecosystems. Although terrestrial ecologists have observed that artificial light at night may disrupt migrations, feeding, and other important ecological functions, we know comparatively little about the role artificial light might play in disrupting freshwater and riparian ecosystems. We identify and discuss four future research domains that artificial light may influence in freshwater and associated terrestrial ecosystems, with an emphasis on running waters: (1) dispersal, (2) population genetics and evolution, (3) ecosystem functioning, and (4) potential interactions with other stressors. We suggest that future experimental and modeling studies should focus on the effects of different spectral emissions by different light sources on freshwater organisms, the spatial and temporal scale over which artificial light acts, and the magnitude of change in light at night across the landscape relative to the distribution of running and standing waters. Improved knowledge about the effects of artificial light on freshwater ecosystems will inform policy decisions about changes to artificial light spectral emissions and distributions.

Carabid beetle assemblages on urban derelict sites in Birmingham, UK

Brownfield sites are thought to support a minimum of 12–15% of Britains nationally scarce and rare invertebrates. The amount of derelict land in Britain is set to decrease dramatically under current home-building and regeneration policies. There is therefore a pressing need for research into the potential importance of brownfield sites for invertebrates. In this study we sampled the carabid fauna of 26 sites, with ages varying between 2–20 years since their formation, to assess whether vegetation succession was an important determinant of invertebrate diversity the West Midlands of England. The work was carried out over the course of one growing season (in 1999), with concurrent surveys of the soil characteristics, vegetation type and land-use history. 63 carabid species were found including 2 nationally scarce species. The most species rich assemblages are found on early successional sites, which persist for 6 years on graded sites and up to 20 years on compacted substrates.

Condition-dependent dispersal of a patchily distributed riparian ground beetle in response to disturbance

In common with many habitat elements of riverine landscapes, exposed riverine sediments (ERS) are highly disturbed, naturally patchy and regularly distributed, whose specialists are strongly adapted to flood disturbance and loss of habitat due to succession. Investigations of dispersal in ERS habitats therefore provide an important contrast to the unnaturally fragmented, stable systems usually studied. The present investigation analysed the three interdependent stages of dispersal: (1) emigration, (2) inter-patch movement and (3) immigration of a common ERS specialised beetle, Bembidion atrocaeruleum (Stephens 1828) (Coleoptera, Carabidae), in a relatively unmodified section of river, using mark–resight methods. Dispersal was correlated with estimates of local population size and density, water level and patch quality in order to test for condition-dependent dispersal cues. Flood inundation of habitat was found to increase strongly the overall rate of dispersal, and the rate of emigration was significantly higher from patches that were heavily trampled by cattle. Strongly declining numbers of dispersers with distance suggested low dispersal rates during periods of low water level. Dispersal in response to habitat degradation by cattle trampling would likely lead to a higher overall population fitness than a random dispersal strategy. Dispersal distances were probably adapted to the underlying habitat landscape distribution, high-flow dispersal cues and ready means of long-distance dispersal through hydrochory. Species whose dispersal is adapted to the natural habitat distribution of riverine landscapes are likely to be strongly negatively affected by reduced flood frequency and intensity and habitat fragmentation through flow regulation or channelisation.

The invertebrate fauna of a physically modified urban river

The typical urban river is affected by various factors relating to water quality problems, physical habitat modification (for flood prevention) and flashy flows. These restrict macroinvertebrate biodiversity such that a few tolerant taxa may dominate and more sensitive organisms may be completely absent. This paper presents the findings of a year long, macroinvertebrate survey of an urban river catchment and investigates the effects of physical habitat modification on macroinvertebrates using various analytical tools. It is demonstrated that considerable variation in invertebrate species, abundance, diversity and tolerance exists between different urban rivers, sites on the same river and individual sites at different sampling times. Analysis of paired sites with similar water quality, but contrasting physical habitat, indicates that less modified sites support a slightly higher quality macroinvertebrate fauna (defined by biotic score and beta diversity) than heavily engineered sites. It is concluded that water quality is the primary limiting factor of invertebrate biodiversity in the heavily urbanized River Tame catchment. The removal of heavy engineering structures may facilitate improvements to invertebrate fauna in urban rivers only in conjunction with improvements to water quality.

Habitat composition and connectivity predicts bat presence and activity at foraging sites in a large UK conurbation.

Background Urbanization is characterized by high levels of sealed land-cover, and small, geometrically complex, fragmented land-use patches. The extent and density of urbanized land-use is increasing, with implications for habitat quality, connectivity and city ecology. Little is known about densification thresholds for urban ecosystem function, and the response of mammals, nocturnal and cryptic taxa are poorly studied in this respect. Bats (Chiroptera) are sensitive to changing urban form at a species, guild and community level, so are ideal model organisms for analyses of this nature. Methodology/Principal Findings We surveyed bats around urban ponds in the West Midlands conurbation, United Kingdom (UK). Sites were stratified between five urban land classes, representing a gradient of built land-cover at the 1 km2 scale. Models for bat presence and activity were developed using land-cover and land-use data from multiple radii around each pond. Structural connectivity of tree networks was used as an indicator of the functional connectivity between habitats. All species were sensitive to measures of urban density. Some were also sensitive to landscape composition and structural connectivity at different spatial scales. These results represent new findings for an urban area. The activity of Pipistrellus pipistrellus (Schreber 1774) exhibited a non-linear relationship with the area of built land-cover, being much reduced beyond the threshold of ∼60% built surface. The presence of tree networks appears to mitigate the negative effects of urbanization for this species. Conclusions/Significance Our results suggest that increasing urban density negatively impacts the study species. This has implications for infill development policy, built density targets and the compact city debate. Bats were also sensitive to the composition and structure of the urban form at a range of spatial scales, with implications for land-use planning and management. Protecting and establishing tree networks may improve the resilience of some bat populations to urban densification.

The ecological impact of city lighting scenarios: exploring gap crossing thresholds for urban bats

Abstract As the global population urbanizes, dramatic changes are expected in city lighting and the urban form, which may threaten the functioning of urban ecosystems and the services they deliver. However, little is known about the ecological impact of lighting in different urban contexts. Movement is an important ecological process that can be disrupted by artificial lighting. We explored the impact of lighting on gap crossing for Pipistrellus pipistrellus, a species of bat (Chiroptera) common within UK cities. We aimed to determine whether the probability of crossing gaps in tree cover varied with crossing distance and lighting level, through stratified field surveys. We then used the resulting data on barrier thresholds to model the landscape resistance due to lighting across an entire city and explored the potential impact of scenarios for future changes to street lighting. The level of illumination required to create a barrier effect reduced as crossing distance increased. For those gaps where crossing was recorded, bats selected the darker parts of gaps. Heavily built parts of the case study city were associated with large and brightly lit gaps, and spatial models indicate movement would be highly restricted in these areas. Under a scenario for brighter street lighting, the area of accessible land cover was further reduced in heavily built parts of the city. We believe that this is the first study to demonstrate how lighting may create resistance to species movement throughout an entire city. That connectivity in urban areas is being disrupted for a relatively common species raises questions about the impacts on less tolerant groups and the resilience of bat communities in urban centres. However, this mechanistic approach raises the possibility that some ecological function could be restored in these areas through the strategic dimming of lighting and narrowing of gaps.

Selling conservation? Scientific legitimacy and the commodification of conservation tourism.

Conservation tourism is a rapidly growing subsector of ecotourism that engages paying volunteers as active participants in conservation projects. Once the preserve of charities, the sector now hosts a proliferation of private companies seeking to make money by selling international conservation work to tourists as a commodity. The commodification of conservation depends upon balancing the scientific legitimacy of projects against the need to offer desirable tourist experiences. Drawing on interviews with UK tour operators and their counterparts in South Africa who run the conservation projects, we explore the transnational geography of commercial conservation tourism, charting how scientific legitimacy is constructed and negotiated within the industry. Although conservation tourism makes trade-offs between scientific rigor and neoliberal market logic, it is a partial and plural process that resists simple categorization. We conclude by considering the difference that commodification makes to conservation science, and vice versa.