Moving soil, moving plants

Robinson, B.S., Bennie, J. Inger, R., Early, R. & Gaston, K.J. 2018. Sweet flowers are slow and weeds make haste: anthropogenic dispersal of plants via garden and construction soil. Journal of Urban Ecology, in press.

Anthropogenic activities are increasingly responsible for the dispersal of plants. Of particular concern is anthropogenic dispersal of problematic invasive non-native plants. A common dispersal vector is the movement of soil containing seeds or rhizomes. Housing development and domestic gardening activities cause large quantities of soil to be moved, and understanding the role of these activities is critical for informing policy and management to reduce the spread of problematic plants. Here, by collecting soil samples being moved for housing development and domestic gardening, and observing the species that germinated from these samples, we determined the quantities and invasive status of plants moved. From our samples nearly 2000 individuals representing 90 species germinated. Our results suggest that given the quantity of topsoil needed to cover an average-sized UK garden (190m2), there could be 2.2 million and c.2 million viable seeds in soil sourced from housing developments and gardens, respectively. In both housing development and garden samples, native species were more abundant and species-rich than non-native naturalised and invasive species. Buddleia (an invasive) was the most common species overall and in garden samples; this is likely due to multiple traits that adapt it to dispersal, such as prolific seed production. The abundance of invasive and naturalised species was significantly higher in garden than in housing development samples, suggesting that informal movement of soil between gardens poses a greater risk of spreading invasive plants than commercial sources. Consequences for models predicting future distributions of plants, and strategies to mitigate anthropogenic dispersal of problematic plants are considered.

Throwing light on communities

Sanders, D. & Gaston, K.J. 2018. How ecological communities respond to artificial light at night. Journal of Experimental Zoology Part A: Ecological and Integrative Physiology, in press [online early].

Many ecosystems worldwide are exposed to artificial light at night (ALAN), from streetlights and other sources, and a wide range of organisms has been shown to respond to this anthropogenic pressure. This raises concerns about the consequences for major ecosystem functions and their stability. However, there is limited understanding of how whole ecological communities respond to ALAN, and this cannot be gained simply by making predictions from observed single species physiological, behavioral, or ecological responses. Research needs to include an important building block of ecological communities, namely the interactions between species that drive ecological and evolutionary processes in ecosystems. Here, we summarize current knowledge about community responses to ALAN and illustrate different pathways and their impact on ecosystem functioning and stability. We discuss that documentation of the impact of ALAN on species interaction networks and trait distributions provides useful tools to link changes in community structure to ecosystem functions. Finally, we suggest several approaches to advance research that will link the diverse impact of ALAN to changes in ecosystems.
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Shifting norms

Soga, M. & Gaston, K.J. 2018. Shifting baseline syndrome: causes, consequences and implications. Frontiers in Ecology and the Environment, in press [online early].

With ongoing environmental degradation at local, regional, and global scales, people’s accepted thresholds for environmental conditions are continually being lowered. In the absence of past information or experience with historical conditions, members of each new generation accept the situation in which they were raised as being normal. This psychological and sociological phenomenon is termed shifting baseline syndrome (SBS), which is increasingly recognized as one of the fundamental obstacles to addressing a wide range of today’s global environmental issues. Yet our understanding of this phenomenon remains incomplete. We provide an overview of the nature and extent of SBS and propose a conceptual framework for understanding its causes, consequences, and implications. We suggest that there are several self reinforcing feedback loops that allow the consequences of SBS to further accelerate SBS through progressive environmental degradation. Such negative implications highlight the urgent need to dedicate considerable effort to preventing and ultimately reversing SBS.

Declining nature experiences in childhood

Soga, M., Gaston, K.J. & Kubo, T. 2018. Cross-generational decline in childhood experiences of neighborhood flowering plants in Japan. Landscape and Urban Planning 174, 55-62.

People (especially children) are becoming less likely to experience nature, as we become an increasingly urban society. This progressive disengagement of humans from the natural world, “extinction of experience”, has been viewed both as a key public health issue and one of the most fundamental obstacles to halting global environmental degradation. However, while the existence and significance of the phenomenon are generally agreed upon, it remains surprisingly poorly documented, particularly at large scales and over the longer-term. Here, we report the findings from a web-based questionnaire survey (n = 1,147) to determine the extent to which levels of childhood experiences with neighborhood flowering plants have changed over the generations in Japan. Results showed that people’s levels of childhood experiences with neighborhood flowering plants were positively related to their age: older participants, compared to younger ones, reported higher frequencies of childhood experiences with neighborhood flowering plants. The reported number of neighborhood flowering plant species that participants have directly experienced during childhood was also higher for older participants. Among the 21 flowering plant species we investigated, temporal decline in direct experiences during childhood was observed for 9 species, particularly for those that depend on grasslands (an ecosystem that is in dramatic decline). Participants’ age and childhood environment (urban vs. rural settings) also had significant effects on their levels of childhood nature experiences. Overall, our results suggest that children’s direct connection to neighborhood biodiversity is indeed progressively dwindling, which can have serious implications for public health and biodiversity conservation.

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.