Lighting invertebrates

Lockett, M.T., Jones, T.M., Elgar, M.A., Gaston, K.J., Visser, M.E. & Hopkins, G.R. 2021. Urban street lighting differentially affects community attributes of airborne and ground-dwelling invertebrate assemblages. Journal of Applied Ecology, in press.

1. The introduction of artificial light at night (ALAN) into natural and urbanised landscapes is a known and highly pervasive disruptor of invertebrate communities. However, the effect of variation in intensity and spectra of ALAN on invertebrate communities inhabiting different spatial niches is little understood. Further, the remarkable ability of ALAN to continue to disrupt biodiversity even in chronically illuminated urban landscapes is not often acknowledged.

2. Here, we simultaneously sampled airborne and ground-dwelling invertebrate assemblages under and between urban street lights to explore the effects on community composition and abundance of (a) proximity to decadal (i.e. long-illuminated) nocturnal street lighting and (b) variation in the spectral output of light.

3. The two assemblages responded differently. For airborne invertebrates, night-time abundance doubled, and night-time assemblage composition was significantly different for traps under, compared with between, street lights. These differences in abundance were not affected by street light intensity, and were absent in day samples, suggesting that even weak ALAN may be causing short-term redistribution of nocturnal invertebrates. Further, the abundance (but not composition) effects of ALAN on airborne invertebrates increased when the street lights emitted a higher proportion of short-wavelength light.

4. In contrast, for ground-dwelling invertebrates, we found only marginal effects of proximity and spectrum of lighting on abundance and no effect on assemblage composition. However, more intense street lighting reduced abundance and altered composition at traps both under and between lights.

5. Synthesis and Applications. Public lighting managers must consider ALAN impacts on invertebrate communities not only when introducing ALAN to naïve environments, but also when changing lighting in areas that are highly urbanised and exposed to decades of ALAN. Further, lighting proposals and environmental monitoring of invertebrate communities must take into account the effects on both ground-dwelling and airborne assemblages, as these may respond very differently to the presence, intensity and spectrum of ALAN.

When the sampling stops

Zhang, W., Sheldon, B.C., Grenyer, R. & Gaston, K.J. 2021. Habitat change and biased sampling influence estimation of diversity trends. Current Biology, in press.

Recent studies have drawn contrasting conclusions about the extent to which local-scale measures of biodiversity are declining and whether such patterns conflict with the global-scale declines that have attracted much attention. A key source of high-quality data for such analyses comes from longitudinal biodiversity studies, which sample a given taxon repeatedly over time at a specific location. There has been relatively little consideration of how habitat change might lead to biases in the sampling and continuity of biodiversity time series data, and the consequent potential for bias in the biodiversity trends that result. Here, based on analysis of standardized routes from the North American Breeding Bird Survey (3,014 routes sampled over 18 years), we demonstrate that major local habitat change is associated with an increase in the rate of survey cessations. We further show that routes that were continued despite major habitat changes show reduced diversity. By simulating potential rates of loss, we show that the underlying real trends in taxonomic, functional, and phylogenetic diversity can even reverse in sign if more than a quarter of diversity is lost from routes that ceased and are thus no longer included in surveys. Our analyses imply that biodiversity loss can be underestimated by biases introduced if continued sampling in longitudinal studies is influenced by local change. We argue that researchers and conservation practitioners should be aware of the potential for bias in such data and seek to use more robust methods to evaluate biodiversity trends and make conservation decisions.

Cities and climate change

Lin, B.B., Ossola, A., Alberti, M., Andersson, E., Bai, X., Dobbs, C., Elmqvist, E., Evans, K.L., Frantzeskaki, N., Fuller, R.A., Gaston, K.J., Haase, D., Jim, C.Y., Konijnendijk, C., Nagendra, H., Niemelä, J., McPhearson, T., Moomaw, W.R., Parnell, S., Pataki, D., Ripple, W.J. & Tan, P.Y. 2021. Integrating solutions to adapt cities for climate change. The Lancet Planetary Health 5, e479-486.

Record climate extremes are reducing urban liveability, compounding inequality, and threatening infrastructure. Adaptation measures that integrate technological, nature-based, and social solutions can provide multiple co-benefits to address complex socioecological issues in cities while increasing resilience to potential impacts. However, there remain many challenges to developing and implementing integrated solutions. In this Viewpoint, we consider the value of integrating across the three solution sets, the challenges and potential enablers for integrating solution sets, and present examples of challenges and adopted solutions in three cities with different urban contexts and climates (Freiburg, Germany; Durban, South Africa; and Singapore). We conclude with a discussion of research directions and provide a road map to identify the actions that enable successful implementation of integrated climate solutions. We highlight the need for more systematic research that targets enabling environments for integration; achieving integrated solutions in different contexts to avoid maladaptation; simultaneously improving liveability, sustainability, and equality; and replicating via transfer and scale-up of local solutions. Cities in systematically disadvantaged countries (sometimes referred to as the Global South) are central to future urban development and must be prioritised. Helping decision makers and communities understand the potential opportunities associated with integrated solutions for climate change will encourage urgent and deliberate strides towards adapting cities to the dynamic climate reality. 

Morning bees

Hall, K., Robert, T., Gaston, K.J., Hempel de Ibarra, N. 2021. Onset of morning activity in bumblebee foragers under natural low light conditions. Ecology and Evolution 11, 6536-6545.

Foraging on flowers in low light at dusk and dawn comes at an additional cost for insect pollinators with diurnal vision. Nevertheless, some species are known to be frequently active at these times. To explore how early and under which light levels colonies of bumblebees, Bombus terrestris, initiate their foraging activity, we tracked foragers of different body sizes using RFID over 5 consecutive days during warm periods of the flowering season. Bees that left the colony at lower light levels and earlier in the day were larger in size. This result extends the evidence for alloethism in bumblebees and shows that foragers differ in their task specialization depending on body size. By leaving the colony earlier to find and exploit flowers in low light, larger-sized foragers are aided by their more sensitive eyes and can effectively increase their contributions to the colony’s food influx. The decision to leave the colony early seems to be further facilitated by knowledge about profitable food resources in specific locations. We observed that experience accrued over many foraging flights determined whether a bee started foraging under lower light levels and earlier in the morning. Larger-sized bees were not more experienced than smaller-sized bees, confirming earlier observations of wide size ranges among active foragers. Overall, we found that most foragers left at higher light levels when they could see well and fly faster. Nevertheless, a small proportion of foragers left the colony shortly after the onset of dawn when light levels were below 10 lux. Our observations suggest that bumblebee colonies have the potential to balance the benefits of deploying large-sized or experienced foragers during dawn against the risks and costs of foraging under low light by regulating the onset of their activity at different stages of the colony’s life cycle and in changing environmental conditions.

Abundance and aesthetics

Soga, M., Fukano, Y., Koyanagi, T.F. & Gaston, K.J. 2021. Species abundance as a determinant of aesthetic values of flowering plant communities. Urban Forestry & Urban Greening 63, 127194.

Both the conservation of biodiversity and the maintenance of ecosystem services are important and fundamental goals in response to the current biodiversity crisis. Cultural ecosystem services – the non-material benefits people derive from their interactions with nature – are an important component of ecosystem services. However, determining the contributions of different components of biodiversity to these benefits has proven more challenging than for other ecosystem services. Here, we determine the relative contributions of diversity (measured as cultivar richness) and abundance (number of individuals) to the aesthetic value of flowering plant communities, using sunflowers as a model organism. We created grassland vegetation plots consisting of different numbers of sunflower cultivars and individuals, presented these treatments to people, and measured their aesthetic preferences (both self-reported and objective behavioural measures) towards them. We found that people’s aesthetic preferences were unrelated to differences in the cultivar richness of the plots but increased substantially with the number of individuals. More importantly, these preference patterns did not differ with a participants’ nature orientation, ecological knowledge, or gender, suggesting the generality of the results. Our findings indicate that the abundance of wildlife can play a crucial role in shaping the cultural services provided by ecosystems. Researchers and policy-makers should therefore pay more attention to the role of abundance in maintaining ecosystem services. 

On the verge

Phillips, B.B., Navaratnam, A., Hooper, J., Bullock, J.M., Osborne, J.L. & Gaston, K.J. 2021. Road verge extent and habitat composition across Great Britain. Landscape and Urban Planning 214, 104159.

 There is growing societal and scientific interest in enhancing road verges for nature and the environment. This is partly because they are estimated to cover large areas in some regions. Yet, to our knowledge, there has been no quantitative assessment of national road verge extent, or of the habitats they encompass. We present a novel method for characterising and classifying road verges remotely. We use this to evaluate the extent and habitat composition of road verges across Great Britain, and to identify opportunities for improving verges for nature and the environment.

We use stratified random sampling of freely-available road maps combined with satellite (Google Earth) and ground-level imagery (Google Street View). Overall, we estimate that there are 2,579 km2 (2,149-3,010 km2) of road verges across Great Britain, equivalent to 1.2% of land area, of which 707 km2 (27.47%) is short, frequently-mown grassland, 1,062 km2 (40.87%) is regular grassland, 480 km2 (18.73%) is woodland, and 272 km2 (10.66%) is scrub. By comparison, we estimate that there are 3,694 km2 of hard road surfaces across Great Britain, equivalent to 1.8% of land. Only 27% of frequently-mown grassland verges contained trees, indicating potential for planting trees and shrubs to provide environmental benefits.

Our findings suggest that there are significant opportunities to enhance (i) verges along major roads, because these constitute a disproportionately large area of road verge and have the widest verges, and (ii) frequently-mown grassland verges for example by, where appropriate, reducing mowing frequencies and/or planting trees. Our method can be used, adapted and further developed by others, for 

People, nature and COVID-19

Soga, M., Evans, M.J., Cox, D.T.C. & Gaston, K.J. 2021. Impacts of the COVID-19 pandemic on human-nature interactions: pathways, evidence and implications. People and Nature [online early].

1. The coronavirus (COVID-19) pandemic and the global response have dramatically changed people’s lifestyles in much of the world. These major changes, as well as the associated changes in impacts on the environment, can alter the dynamics of the direct interactions between humans and nature (hereafter human–nature interactions) far beyond those concerned with animals as sources of novel human coronavirus infections. There may be a variety of consequences for both people and nature.

2. Here, we suggest a conceptual framework for understanding how the COVID-19 pandemic might affect the dynamics of human–nature interactions. This highlights three different, but not mutually exclusive, pathways: changes in (a) opportunity, (b) capability and (c) motivation.

3. Through this framework, we also suggest that there are several feedback loops by which changes in human–nature interactions induced by the COVID-19 pandemic can lead to further changes in these interactions such that the impacts of the pandemic could persist over the long term, including after it has ended.

4. The COVID-19 pandemic, which has had the most tragic consequences, can also be viewed as a ‘global natural experiment’ in human–nature interactions that can provide unprecedented mechanistic insights into the complex processes and dynamics of these interactions and into possible strategies to manage them to best effect.

Lighting Madrid’s night sky

Robles, J., Zamorano, J., Pascual, S., Sánchez de Miguel, A., Gallego, J. & Gaston, K.J. 2021. Evolution of brightness and color of the night sky in Madrid. Remote Sensing 13, 1511.

Major schemes to replace other streetlight technologies with Light-Emitting Diode (LED) lamps are being undertaken across much of the world. This is predicted to have important consequences for nighttime sky brightness and color. Here, we report the results of a long-term study of these characteristics focused on the skies above Madrid. The sky brightness and color monitoring station at Universidad Complutense de Madrid (inside the city) collected Johnson B, V, and R sky brightness data, Sky Quality Meter (SQM), and Telescope Encoder Sky Sensor-WiFi (TESS-W) broadband photometry throughout the night, every night between 2010-2020. Our analysis includes a data filtering process that can be used with other similar sky brightness monitoring data. Major changes in sky brightness and color took place during 2015-2016, when a sizable fraction of the streetlamps in Madrid changed from High-Pressure Sodium (HPS) to LEDs. The sky brightness detected in the Johnson B band darkened by 14% from 2011 to 2015 and brightened by 32% from 2015 to 2019.

Road pollution – no getting away

Phillips, B.B., Bullock, J.M., Osborne, J.L. & Gaston, K.J. 2021. Spatial extent of road pollution: a national analysis. Science of the Total Environment 773, 145589.

Roads form vast, pervasive and growing networks across the Earth, causing negative environmental impacts that spill out into a ‘road-effect zone’. Previous research has estimated the regional and global extent of these zones using arbitrary distances, ignoring the spatial distribution and distance-dependent attenuation of different forms of road environmental impact. With Great Britain as a study area, we used mapping of roads and realistic estimates of how pollution levels decay with distance to project the spatial distribution of road pollution. We found that 25% of land was less than 79 m from a road, 50% of land was less than 216 m and 75% of land was less than 527 m. Roadless areas were scarce, and confined almost exclusively to the uplands (mean elevation 391 m), with only ca 12% of land in Great Britain more than 1 km from roads and <4% of land more than 2.5 km from roads. Using light, noise, heavy metals, NO2, and particulate matter PM2.5 and PM10 as examples, we estimate that roads have a zone of influence that extends across >70% of the land area. Potentially less than 6% of land escapes any impact, resulting in nearly ubiquitously elevated pollution levels. Generalising from this, we find that, whilst the greatest levels of road pollution are relatively localised around the busiest roads, low levels of road pollution (which may be ecologically significant) are pervasive. Our findings demonstrate the importance of incorporating greater realisminto road-effect zones and considering the ubiquity of road pollution in global environmental issues. We used Great Britain as a study area, but the findings likely apply to other densely populated regions at present, and to many additional regions in the future due to the predicted rapid expansion of the global road network.

Artificial light and lockdown

Bustamante-Calabria, M., Sánchez de Miguel, A., Martín-Ruiz, S., Ortiz, J-L., Vílchez, J.M., Pelegrina, A., García, A., Zamorano, J., Bennie, J. & Gaston, K.J. 2021. Effects of the COVID-19 lockdown on urban light emissions: ground and satellite comparison. Remote Sensing, 13, 258.

‘Lockdown’ periods in response to COVID-19 have provided a unique opportunity to study the impacts of economic activity on environmental pollution (e.g., NO2, aerosols, noise, light). The effects on NO2 and aerosols have been very noticeable and readily demonstrated, but that on light pollution has proven challenging to determine. The main reason for this difficulty is that the primary source of nighttime satellite imagery of the earth is the SNPP-VIIRS/DNB instrument, which acquires data late at night after most human nocturnal activity has already occurred and much associated lighting has been turned off. Here, to analyze the effect of lockdown on urban light emissions, we use ground and satellite data for Granada, Spain, during the COVID-19 induced confinement of the city’s population from 14 March until 31 May 2020. We find a clear decrease in light pollution due both to a decrease in light emissions from the city and to a decrease in anthropogenic aerosol content in the atmosphere which resulted in less light being scattered. A clear correlation between the abundance of PM10 particles and sky brightness is observed, such that the more polluted the atmosphere the brighter the urban night sky. An empirical expression is determined that relates PM10 particle abundance and sky brightness at three different wavelength bands.