Thomas J. Matthews

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.

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.

Oceanic island biogeography through the lens of the general dynamic model: Assessment and prospect

The general dynamic model of oceanic island biogeography (GDM) has added a new dimension to theoretical island biogeography in recognizing that geological processes are key drivers of the evolutionary processes of diversification and extinction within remote islands. It provides a dynamic and essentially non‐equilibrium framework generating novel predictions for emergent diversity properties of oceanic islands and archipelagos. Its publication in 2008 coincided with, and spurred on, renewed attention to the dynamics of remote islands. We review progress, both in testing the GDMs predictions and in developing and enhancing ecological–evolutionary understanding of oceanic island systems through the lens of the GDM. In particular, we focus on four main themes: (i) macroecological tests using a space‐for‐time rationale; (ii) extensions of theory to islands following different patterns of ontogeny; (iii) the implications of GDM dynamics for lineage diversification and trait evolution; and (iv) the potential for downscaling GDM dynamics to local‐scale ecological patterns and processes within islands. We also consider the implications of the GDM for understanding patterns of non‐native species diversity. We demonstrate the vitality of the field of island biogeography by identifying a range of potentially productive lines for future research.

Mapping Lightscapes: Spatial Patterning of Artificial Lighting in an Urban Landscape

Artificial lighting is strongly associated with urbanisation and is increasing in its extent, brightness and spectral range. Changes in urban lighting have both positive and negative effects on city performance, yet little is known about how its character and magnitude vary across the urban landscape. A major barrier to related research, planning and governance has been the lack of lighting data at the city extent, particularly at a fine spatial resolution. Our aims were therefore to capture such data using aerial night photography and to undertake a case study of urban lighting. We present the finest scale multi-spectral lighting dataset available for an entire city and explore how lighting metrics vary with built density and land-use. We found positive relationships between artificial lighting indicators and built density at coarse spatial scales, whilst at a local level lighting varied with land-use. Manufacturing and housing are the primary land-use zones responsible for the city’s brightly lit areas, yet manufacturing sites are relatively rare within the city. Our data suggests that efforts to address light pollution should broaden their focus from residential street lighting to include security lighting within manufacturing areas.

Neutral theory and the species abundance distribution: recent developments and prospects for unifying niche and neutral perspectives

Published in 2001, The Unified Neutral Theory of Biodiversity and Biogeography (UNTB) emphasizes the importance of stochastic processes in ecological community structure, and has challenged the traditional niche-based view of ecology. While neutral models have since been applied to a broad range of ecological and macroecological phenomena, the majority of research relating to neutral theory has focused exclusively on the species abundance distribution (SAD). Here, we synthesize the large body of work on neutral theory in the context of the species abundance distribution, with a particular focus on integrating ideas from neutral theory with traditional niche theory. First, we summarize the basic tenets of neutral theory; both in general and in the context of SADs. Second, we explore the issues associated with neutral theory and the SAD, such as complications with fitting and model comparison, the underlying assumptions of neutral models, and the difficultly of linking pattern to process. Third, we highlight the advances in understanding of SADs that have resulted from neutral theory and models. Finally, we focus consideration on recent developments aimed at unifying neutral- and niche-based approaches to ecology, with a particular emphasis on what this means for SAD theory, embracing, for instance, ideas of emergent neutrality and stochastic niche theory. We put forward the argument that the prospect of the unification of niche and neutral perspectives represents one of the most promising future avenues of neutral theory research.

REVIEW: On the species abundance distribution in applied ecology and biodiversity management

Summary 1. The species abundance distribution (SAD) is an important concept in ecology, and much work has focused on the SAD in a theoretical context. However, less focus has been placed on the utility of SADs in applied ecology and biodiversity management, which therefore forms the focus of the present article. We illustrate that study of the SAD allows inferences beyond those that flow from many simple diversity indices, enabling workers to identify patterns in the commonness and rarity of species in a community. 2. First, we discuss how incorporating SAD analyses into the study of ecological communities can generate useful information for the management of biodiversity. In particular, we argue that deconstructing ecological assemblages into various subsets and analysing how each subset contributes to the overall SAD can reveal patterns of interest to managers. Secondly, we review the many applications of SADs in applied ecological fields, including disturbance ecology, conservation planning and conservation biological control. 3. Using examples we show that the SAD can be useful in applied ecology as it is visually intuitive, easy to implement in a broad variety of ecological contexts, and does not require substantial species-specific data. We provide a summary of the various methods available for plotting the SAD and illustrate how each method provides information of value for applied ecologists. 4. Using empirical and simulated data, we show that the SAD can provide early warning of the effects of disturbance on ecological communities and that a number of SAD models represent useful tools for comparing communities in a management context. 5. Synthesis and applications. Applied ecologists require tools that allow for relatively quick assessments of ecosystem health and/or the success of management prescriptions aimed at ameliorating the effects of disturbance. We demonstrate that that the methods reviewed herein provide such tools and that the species abundance distribution (SAD) has additional applied uses beyond traditional applications in disturbance ecology. We hope that this synthesis will provide a catalyst for advancing a more utilitarian SAD research agenda.

Integrating Geoconservation and Biodiversity Conservation: Theoretical Foundations and Conservation Recommendations in a European Union Context

Nature conservation has become synonymous with biodiversity conservation and despite recent acknowledgements of the importance of geodiversity it is unrealistic to believe current European geoconservation efforts are either equal to those focused on biodiversity conservation, or sufficient to effectively conserve Europe’s geodiversity. This is despite the multitude of studies reporting the inherent linkages between geodiversity and biodiversity and, in particular, the role geodiversity performs in determining biotic species richness patterns. Thus, there is an urgent need to accentuate the principle that natural diversity is composed of both geodiversity and biodiversity, and that proficient conservation requires a holistic approach that views nature as a complex interaction of biodiversity and geodiversity pattern and process. This paper identifies a three-tiered conceptual framework for achieving integrated nature conservation in a European context. The primary in situ conservation method proposed is an integrated European protected area network aimed at representing all aspects of unique geodiversity and biodiversity. Regarding nature conservation as a whole, the benefits of a geo-ecological approach, that is, a conservation approach focused on the interlinked nature of biological and geological processes, landscape functionality, and the inevitably of environmental change, as opposed to individual landform and species conservation, are discussed. As a separate but linked concept, the issue of reducing confusion surrounding terminology in the geoconservation and biodiversity conservation literature is also explored.

Island biogeography: Taking the long view of nature’s laboratories

Dynamics of island biodiversity Fifty years ago, MacArthur and Wilson published their influential book, The Theory of Island Biogeography. This work provided a quantitative framework for understanding the ecological processes governing the diversity of species on oceanic islands. Whittaker et al. review the subsequent progress in the field, focusing particularly on the integration of the ecological model with island geophysical dynamics. Recent work is showing how immigration, speciation, and extinction respond to the phases of emergence, development, and submergence in oceanic islands. Science, this issue p. eaam8326 BACKGROUND Ever since Darwin, natural scientists have turned to islands for inspiration and for model systems. For the past half century, they have done so largely within the paradigm established by Robert H. MacArthur and Edward O. Wilson’s Theory of Island Biogeography, which provided a quantitative, dynamic framework, based upon assumptions of geographically predictable patterns of immigration, extinction, and speciation. Although this approach has proven productive, its application to remote archipelagos and evolutionary time scales has been hampered by a rather static view of islands themselves, despite mounting evidence of their dynamism as platforms. We review recent progress in integrating the largely ecological thinking of their theory with insights on the longer-term dynamics of both the islands and their biotas. ADVANCES Classification and analysis of marine islands by their geophysical dynamics, and of their species by how they colonized, provides a step toward a more nuanced biogeography out of which new insights are already emerging. This perspective is exemplified by the general dynamic model of oceanic island biogeography, which predicts how immigration, speciation, and extinction respond to the typical life cycle of hotspot islands, with phases of emergence, development, and submergence. The model successfully predicts such emergent patterns as the occurrence of peak diversification on youthful, expanding islands with maximum vacant niche space. Diversity patterns analyzed for large numbers of data sets have confirmed the importance of in situ evolutionary dynamics on remote archipelagos, which typically possess steep island species–area relationships, especially for endemic taxa. We may infer that variations in propagule flow among islands within archipelagos are important in modulating these emergent diversity patterns. There is, for example, good support for an “island progression rule” in which older land masses donate colonists to younger islands (consistent with the generalization of islands as “sinks”), but there is also increasing evidence of “reverse colonization,” including from islands to continental regions. Advances are also being made in linking such island biogeographical models with the classic traits and syndromes of insular species, although this first demands that previous generalizations are rigorously reexamined using expanded data sets and modern techniques of analysis. A classic insular syndrome is the loss of dispersability of formerly dispersive species following island colonization, for which there is now good evidence for several taxa, including many genera of land birds. Yet, paradoxically, and perhaps controversially, it has also been inferred that many species of plants lacking specialized dispersal adaptations can colonize quite remote islands, often by nonstandard means of transport. Unfortunately, island evolutionary syndromes, such as loss of flight in birds, frequently predispose species to heightened extinction risk when islands are colonized and transformed by humans, as we also document. OUTLOOK Developments in theory and in analytical and modeling capabilities within biological and Earth system science, and the pooling of large numbers of data sets, enhancing statistical power, collectively hold the promise of a new synthesis in island biogeography. This synthesis will need to accommodate evidence of the long-term dynamics of remote island systems, whereby some lineages persist far longer than any particular island platform, while others founder as their sole island home sinks under the waves. The promise is of a biogeography in the tradition of the MacArthur–Wilson theory, generating and testing predictive models, but extended to accommodate a more sophisticated suite of insular geological and environmental dynamics, combined with a fuller understanding of patterns and processes of gene flow within and between archipelagos. Islands provide model systems for the investigation of the fundamental biogeographical processes of migration, diversification, and extinction, as discussed herein with emphasis on long-term dynamics. Islands provide classic model biological systems. We review how growing appreciation of geoenvironmental dynamics of marine islands has led to advances in island biogeographic theory accommodating both evolutionary and ecological phenomena. Recognition of distinct island geodynamics permits general models to be developed and modified to account for patterns of diversity, diversification, lineage development, and trait evolution within and across island archipelagos. Emergent patterns of diversity include predictable variation in island species–area relationships, progression rule colonization from older to younger land masses, and syndromes including loss of dispersability and secondary woodiness in herbaceous plant lineages. Further developments in Earth system science, molecular biology, and trait data for islands hold continued promise for unlocking many of the unresolved questions in evolutionary biology and biogeography.

Are Protected Areas Required to Maintain Functional Diversity in Human-Modified Landscapes?

The conversion of forest to agriculture across the world’s tropics, and the limited space for protected areas, has increased the need to identify effective conservation strategies in human-modified landscapes. Isolated trees are believed to conserve elements of ecological structure, providing micro-sites for conservation in matrix landscapes, and facilitating seed dispersal and forest restoration. Here we investigate the role of isolated Ficus trees, which are of critical importance to tropical forest ecosystems, in conserving frugivore composition and function in a human-modified landscape in Assam, India. We surveyed the frugivorous birds feeding at 122 isolated Ficus trees, 33 fruit trees, and 31 other large trees across a range of 32 km from the nearest intact forest. We found that Ficus trees attracted richer and more abundant assemblages of frugivores than the other tree categories. However, incidence function estimates revealed that forest specialist species decreased dramatically within the first kilometre of the forest edge. Despite this, species richness and functional diversity remained consistent across the human-modified landscape, as habitat generalists replaced forest-dependent frugivores, and accounted for most of the ecological function found in Ficus trees near the forest edge. We recommend that isolated Ficus trees are awarded greater conservation status, and suggest that their conservation can support ecologically functional networks of frugivorous bird communities.