Ecological impacts of light from vehicles

Gaston, K.J. & Holt, L.A. 2018. Nature, extent and ecological implications of nighttime light from road vehicles. Journal of Applied Ecology, in press [online early view].

1. The erosion of night-time by the introduction of artificial lighting constitutes a profound pressure on the natural environment. It has altered what had for millennia been reliable signals from natural light cycles used for regulating a host of biological processes, with impacts ranging from changes in gene expression to ecosystem processes.
2. Studies of these impacts have focused almost exclusively on those resulting from stationary sources of light emissions, and particularly streetlights. However, mobile sources, especially road vehicle headlights, contribute substantial additional emissions.
3. The ecological impacts of light emissions from vehicle headlights are likely to be especially high because these are (i) focused so as to light roadsides at higher intensities than commonly experienced from other sources, and well above activation thresholds for many biological processes; (ii) projected largely in a horizontal plane and thus can carry over long distances; (iii) introduced into much larger areas of the landscape than experience street lighting; (iv) typically broad ‘white’ spectrum, which substantially overlaps the action spectra of many biological processes; and (v) often experienced at roadsides as series of pulses of light (produced by passage of vehicles), a dynamic known to have major biological impacts.
4. The ecological impacts of road vehicle headlights will markedly increase with projected global growth in numbers of vehicles and the road network, increasing the local severity of emissions (because vehicle numbers are increasing faster than growth in the road network) and introducing emissions into areas from which they were previously absent. The effects will be further exacerbated by technological developments that are increasing the intensity of headlight emissions and the amounts of blue light in emission spectra.
5. Synthesis and applications. Emissions from vehicle headlights need to be considered as a major, and growing, source of ecological impacts of artificial night-time lighting. It will be a significant challenge to minimize these impacts whilst balancing drivers’ needs at night and avoiding risk and discomfort for other road users. Nonetheless, there is potential to identify solutions to these conflicts, both through the design of headlights and that of roads.

Where birds and people meet

Cox, D.T.C., Hudson, H.L., Plummer, K.E., Siriwardena, G.M., Anderson, K., Hancock, S., Devine-Wright, P. & Gaston, K.J. 2018. Covariation in urban birds providing cultural services or disservices and people. Journal of Applied Ecology, in press [advance articles].

1. The spatial distributions of biodiversity and people vary across landscapes, and are critical to the delivery of ecosystem services and disservices. The high densities of people, and often of birds, in urban areas lead to frequent human-avian interactions, which can be positive or negative for people’s well-being. The identities of the bird species providing these services or disservices tend to be quite different, however it is unclear how their abundance and richness covary with human population density, and hence with potential recipients of these services and disservices.
2. We surveyed bird populations in 106 tiles (500×500 m) across the 174 km2 of an extended urban area in southern England. From the literature, we identified two groups of species: those associated with positive interactions for human well-being, and those that display behaviours that are negative for human well-being. We estimated the abundance (adjusted for detection probability) and richness of each group, and modelled how they covary with human population density.
3. Aggregation of population estimates for the 35 service and nine disservice species observed revealed 593,128 (95% confidence interval: 541,817-657,046) and 225,491 (200,134-235,066) birds, respectively. Across the surveyed tiles there were 1.09 service, and 0.42 disservice birds per person.
4. There was a peaking quadratic relationship between service abundance and human population density, but a negative linear relationship between richness and human density. Conversely, there were positive linear relationships for both abundance and richness of disservice species with human density. The ratio of service to disservice birds shifted from 3.5 to 1 at intermediate human densities to 1 to 1 in more densely populated areas.
5. Synthesis and applications. Differences in the distributions of service and disservice species, and the extremely low ratios of birds to people particularly in socioeconomically deprived areas, mean that people there have few opportunities for contact with birds, and the contact that they do have is equally likely to be negative as positive for human well-being. We recommend spatial targeting of improvements in green infrastructure, combined with the targeted provisioning of food and nesting places for service species, to promote positive interactions between birds and people.

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Cacti losing darkness

Correa-Cano, M.E., Goettsch, B., Duffy, J.P., Bennie, J., Inger, R. & Gaston, K.J. 2018. Erosion of natural darkness in the geographic ranges of cacti. Scientific Reports 8, 4347.

Naturally dark nighttime environments are being widely eroded by the introduction of artificial light at night (ALAN). The biological impacts vary with the intensity and spectrum of ALAN, but have been documented from molecules to ecosystems. How globally severe these impacts are likely to be depends in large part on the relationship between the spatio-temporal distribution of ALAN and that of the geographic ranges of species. Here, we determine this relationship for the Cactaceae family. Using maps of the geographic ranges of cacti and nighttime stable light composite images for the period 1992 to 2012, we found that a high percentage of cactus species were experiencing ALAN within their ranges in 1992, and that this percentage had increased by 2012. For almost all cactus species (89.7%) the percentage of their geographic range that was lit increased from 1992-1996 to 2008-2012, often markedly. There was a significant negative relationship between the species richness of an area, and that of threatened species, and the level of ALAN. Cacti could be particularly sensitive to this widespread and ongoing intrusion of ALAN into their geographic ranges, especially when considering the potential for additive and synergistic interactions with the impacts of other anthropogenic pressures. Download pdf

Providing for wildlife

Cox, D.T.C. & Gaston, K.J. 2018. Human-nature interactions and the consequences and drivers of provisioning wildlife. Philosophical Transactions of the Royal Society B 373, 20170092.

Many human populations are undergoing an extinction of experience, with a progressive decline in interactions with nature. This is a consequence both of a loss of opportunity for, and orientation towards, such experiences. The trend is of concern in part because interactions with nature can be good for human health and wellbeing. One potential means of redressing these losses is through the intentional provision of resources to increase wildlife populations in close proximity to people, thereby increasing the potential for positive human-nature experiences, and thence the array of benefits that can result. In this paper we review the evidence that these resource subsidies have such a cascade of effects. In some westernised countries, the scale of provision is extraordinarily high, and doubtless leads to both positive and negative impacts for wildlife. In turn, these impacts often lead to more frequent, reliable and closer human-nature interactions, with a greater variety of species. The consequences for human wellbeing remain poorly understood, although benefits documented in the context of human-nature interactions more broadly seem likely to apply. There are also some important feedback loops that need to be better characterised if resource provisioning is to contribute effectively towards averting the extinction of experience. Download pdf

More birds, more service

Gaston, K.J., Cox, D.T.C., Canavelli, S.B., García, D., Hughes, B., Maas, B., Martínez, D., Ogada, D. & Inger, R. Population abundance and ecosystem service provision: the case of birds. BioScience 68, 264-272.

Whilst there is a diversity of concerns about recent persistent declines in the abundances of many species, the implications for the associated delivery of ecosystem services to people are surprisingly poorly understood. In principle, there are a broad range of potential functional relationships between the abundance of a species or group of species and the magnitude of ecosystem service provision. Here we identify the forms these relationships are most likely to take. Focusing on the case of birds, we review the empirical evidence for these functional relationships, with examples of supporting, regulating and cultural services. Positive relationships between abundance and ecosystem service provision are the norm (although seldom linear), we found no evidence for hump-shaped relationships, and negative ones were limited to cultural services that value rarity. Given the magnitude of abundance declines amongst many previously common species, it is likely that there have been substantial losses of ecosystem services, providing important implications for the identification of potential tipping points in relation to defaunation resilience, biodiversity conservation and human wellbeing. Download pdf

Droning on about invasive grasses

Sandino, J., Gonzalez, F, Mengersen, K. & Gaston, K.J. 2018. UAVs and machine learning revolutionising invasive grass and vegetation surveys in remote arid lands. Sensors 18, 605.

The monitoring of invasive grasses and vegetation in remote areas is challenging, costly, and on the ground sometimes dangerous. Satellite and manned aircraft surveys can assist but their use may be limited due to the ground sampling resolution or cloud cover. Straightforward and accurate surveillance methods are needed to quantify rates of grass invasion, offer appropriate vegetation tracking reports, and apply optimal control methods. This paper presents a pipeline process to detect and generate a pixel-wise segmentation of invasive grasses, using buffel grass (Cenchrus ciliaris) and spinifex (Triodia sp.) as examples. The process integrates unmanned aerial vehicles (UAVs) also commonly known as drones, high-resolution red, green, blue colour model (RGB) cameras, and a data processing approach based on machine learning algorithms. The methods are illustrated with data acquired in Cape Range National Park, Western Australia (WA), Australia, orthorectified in Agisoft Photoscan Pro, and processed in Python programming language, scikit-learn, and eXtreme Gradient Boosting (XGBoost) libraries. In total, 342,626 samples were extracted from the obtained data set and labelled into six classes. Segmentation results provided an individual detection rate of 97% for buffel grass and 96% for spinifex, with a global multiclass pixel-wise detection rate of 97%. Obtained results were robust against illumination changes, object rotation, occlusion, background cluttering, and floral density variation.

Outdoor lighting continues increase

Kyba, C.C.M., Kuester, T., Sánchez de Miguel, S., Baugh, K., Jechow, A., Hölker, F., Bennie, J., Elvidge, C.D., Gaston, K.J. & Guanter, L. 2017. Artificially lit surface of Earth at night increasing in radiance and extent. Science Advances 3, e1701528.

A central aim of the “lighting revolution” (the transition to solid-state lighting technology) is decreased energy consumption. This could be undermined by a rebound effect of increased use in response to lowered cost of light. We use the first-ever calibrated satellite radiometer designed for night lights to show that from 2012 to 2016, Earth’s artificially lit outdoor area grew by 2.2% per year, with a total radiance growth of 1.8% per year. Continuously lit areas brightened at a rate of 2.2% per year. Large differences in national growth rates were observed, with lighting remaining stable or decreasing in only a few countries. These data are not consistent with global scale energy reductions but rather indicate increased light pollution, with corresponding negative consequences for flora, fauna, and human well-being.

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Time and time again

Gaston, K.J., Davies, T.W., Nedelec, S.L. & Holt, L.A. 2017. Impacts of artificial light at night on biological timings. Annual Review of Ecology, Evolution and Systematics 48, 49-68.

The use of artificial lighting to illuminate the night has provided substantial benefits to humankind. It has also disrupted natural daily, seasonal, and lunar light cycles as experienced by a diversity of organisms, and hence it has also altered cues for the timings of many biological activities. Here we review the evidence for impacts of artificial nighttime lighting on these timings. Although the examples are scattered, concerning a wide variety of species and environments, the breadth of such impacts is compelling. Indeed, it seems reasonable to conclude that the vast majority of impacts of artificial nighttime lighting stem from effects on biological timings. This adds support to arguments that artificial nighttime lighting has a quite pervasive and marked impact on ecological systems, that the rapid expansion in the global extent of both direct illuminance and skyglow is thus of significant concern, and that a widespread implementation of mitigation measures is required.

Risk from alien plants

Robinson, B.S., Inger, R. & Gaston, K.J. 2017. Drivers of risk perceptions about the invasive non-native plant Japanese knotweed in domestic gardens. Biological Invasions, in press.

How people perceive risks posed by invasive non-native plants (INNP) can influence attitudes and consequently likely influence behavioural decisions. Although some drivers of risk perception for INNP have been identified, research has not determined those for INNP in domestic gardens. This is concerning as domestic gardens are where people most commonly encounter INNP, and where impacts can be particularly acute. Using a survey approach, this study determined the drivers of perceptions of risk of INNP in domestic gardens and which risks most concern people. Japanese knotweed Fallopia japonica, in Cornwall, UK, where it is a problematic INNP in domestic gardens, was used as a case study. Possible drivers of risk were chosen a priori based on variables previously found to be important for environmental risks. Participants perceived Japanese knotweed to be less frequent on domestic property in Cornwall if their occupation involved the housing market, if they had not had Japanese knotweed in their own garden, if they did not know of Japanese knotweed within 5 km of their home, or if they were educated to degree level. Participants who thought that the consequences of Japanese knotweed being present on domestic property could be more severe had occupations that involved the housing market, knew of Japanese knotweed within 5 km of their home, or were older. Although concern about the damage Japanese knotweed could do to the structure of a property was reported as the second highest motivation to control it by the majority of participants, the perception of threat from this risk was rated as relatively low. The results of this study have implications for policy, risk communication, and garden management decisions. For example, there is a need for policy that provides support and resources for people to manage INNP in their local area. To reduce the impact and spread of INNP we highlight the need for clear and accurate risk communication within discourse about this issue. The drivers identified in this study could be used to target awareness campaigns to limit the development of over- or under-inflated risk perceptions.

Streetlighting impacts on vegetation

Bennie, J., Davies, T.W., Cruse, D., Bell, F. & Gaston, K.J. 2018. Artificial light at night alters grassland vegetation species composition and phenology. Journal of Applied Ecology 15, 442-450.

1. Human settlements and transport networks are growing rapidly worldwide. Since the early 20th century their expansion has been accompanied by increasing illumination of the environment at night, a trend that is likely to continue over the decades to come. Consequently, a growing proportion of the world’s ecosystems are exposed to artificial light at night, profoundly altering natural cycles of light and darkness. While in recent years there have been advances in our understanding of the effects of artificial light at night on the behaviour and physiology of animals in the wild, much less is known about the impacts on wild plants and natural or semi-natural vegetation composition. This is surprising, as effects of low-intensity light at night on flowering, phenology and growth form are well known in laboratory and greenhouse studies.
2. In a long-term experimental field study we exposed a semi-natural grassland to artificial light at intensities and wavelengths typical of those experienced by roadside vegetation under street lighting.
3. We found that lighting affected the trajectory of vegetation change, leading to significant differences in biomass and plant cover in the dominant species.
4. Changes in flowering phenology were variable between years, with grass species flowering between 4 days earlier and 12 days later under artificial light.
5. Policy implications. Our results demonstrate that artificial light, at levels equivalent to those in street-lit environments, can affect species composition in semi-natural vegetation. This highlights the importance of considering artificial light as a driver of vegetation change in urban, suburban and semi-natural ecosystems, and where possible, of minimising or excluding artificial light from habitats of conservation importance.