Seeing the trees

Cox, D.T.C., Bennie, J., Casalegno, S., Hudson, H.L., Anderson, K. & Gaston, K.J. 2019 Skewed contributions of individual trees to indirect nature experiences. Landscape and Urban Planning 185, 28-34.

Exposure to nature is associated with a broad range of benefits to human health. Whilst there has been exploration of how these experiences vary amongst people, the converse – how different individual organisms contribute to human nature experiences – has largely been overlooked. The most common way that people experience nature occurs indirectly, when they are in a room with a natural view. Here, we estimate variation in how individual trees provide indirect nature experiences in an urban human population. As a proxy for its contribution towards indirect nature experiences, within an extended urban area in southern England, UK (n=612,920) we calculated the number of buildings with line of sight to each tree. We then modelled each tree’s contribution towards these experiences against potential predictors, namely tree height, land ownership, social deprivation, while controlling for human population density. We demonstrate that a small number of trees contribute disproportionately towards indirect nature experiences, with individual trees in socio-economically deprived high density housing falling within the viewscape of significantly more buildings. Further, trees in private gardens were generally more important for providing indirect nature experiences than those in public green spaces. This novel study demonstrates the skewed contribution of different organisms to human population indirect nature experiences. This approach can be applied more broadly to understand how individual organisms provide indirect, incidental and intentional nature experiences. Understanding the ecology behind human nature experiences is an important step towards linking urban design and policy for maximising the health benefits from nature.

Scanning the horizon for global conservation

Sutherland, W.J., Broad, S., Butchart, S.H.M., Clarke, S.J., Collins, A.M., Dicks, L.V., Doran, H., Esmail, N., Fleishman, E., Frost, N., Gaston, K.J., Gibbons, D.W., Hughes, A.C., Jiang, Z., Kelman, R., LeAnstey, B., le Roux, X., Lickorish, F.A., Monk, K.A., Mortimer, D., Pearce-Higgins, J.W., Peck, L.S., Pettorelli, N., Pretty, J., Seymour, C.L., Spalding, M.D., Wentworth, J., & Ockendon, N. 2019. A horizon scan of emerging issues for global conservation in 2019. Trends in Ecology and Evolution, in press. 

We present the results of our tenth annual horizon scan. We identified 15 emerging priority topics that may have major positive or negative effects on the future conservation of global biodiversity, but currently have low awareness within the conservation community. We hope to increase research and policy attention on these areas, improving the capacity of the community to mitigate impacts of potentially negative issues, and maximise the benefits of issues that provide opportunities. Topics include advances in crop breeding, which may affect insects and land use; manipulations of natural water flows and weather systems on the Tibetan Plateau; release of carbon and mercury from melting polar ice and thawing permafrost; new funding schemes and regulations; and land-use changes across Indo-Malaysia.

Urbanising doses of nature

Cox, D.T.C., Shanahan, D.F., Hudson, H.L., Fuller, R.A. & Gaston, K.J. 2018. The impact of urbanisation on nature dose and the implications for human health. Landscape and Urban Planning 179, 72-80. 

The last 100 years have seen a huge change in the global structure of the human population, with the majority of people now living in urban rather than rural environments. An assumed consequence is that people will have fewer experiences of nature, and this could have important consequences given the myriad health benefits that they can gain from such experiences. Alternatively, as experiences of nature become rarer, people might be more likely actively to seek them out, mitigating the negative effects of urbanisation. In this study, we used data for 3,000 survey respondents from across the UK, and a nature-dose framework, to determine whether (a) increasing urbanisation is associated with a decrease in the frequency, duration and intensity of nature dose; and (b) differences in nature exposure associated with urbanisation impact on four population health outcomes (depression, self-reported health, social cohesion and physical activity). We found negative exponential relationships between nature dose and the degree of urbanisation. The frequency and duration of dose decreased from rural to suburban environments, followed by little change with further increases in urbanisation. There were weak but positive associations between frequency and duration of dose across all four health domains, while different dimensions of dose showed more positive associations with specific health domains in towns and cities. We show that people in urban areas with a low nature dose tend to have worse health across multiple domains, but have the potential for the greatest gains from spending longer in nature, or living in green areas.


Top-down and bottom-up lighting effects

Bennie, J., Davies, T.W., Cruse, D., Inger, R. & Gaston, K.J. 2018. Artificial light at night causes top-down and bottom-up trophic effects on invertebrate populations. Journal of Applied Ecology 55, 2698-2706.

1. Globally, many ecosystems are exposed to artificial light at night. Nighttime lighting has direct biological impacts on species at all trophic levels. However, the effects of artificial light on biotic interactions remain, for the most part, to be determined.
2. We exposed experimental mesocosms containing combinations of grassland plants and invertebrate herbivores and predators to illumination at night over a three-year period to simulate conditions under different common forms of street lighting.
3. We demonstrate both top-down (predation controlled) and bottom-up (resource controlled) impacts of artificial light at night in grassland communities. The impacts on invertebrate herbivore abundance were wavelength dependent and mediated via other trophic levels.
4. White LED lighting decreased the abundance of a generalist herbivore mollusc by 55% in the presence of a visual predator, but not in its absence, while monochromatic amber light (with a peak wavelength similar to low pressure sodium lighting) decreased abundance of a specialist herbivoraphid (by 17%) by reducing the cover and flower abundance of its main food plant in the system. Artificial white light also significantly increased the food plant’s foliar carbon to nitrogen ratio.
5. We conclude that exposure to artificial light at night can trigger ecological effects spanning trophic levels, and that the nature of such impacts depends on the wavelengths emitted by the lighting technology employed.
6. Policy implications. Our results confirm that artificial light at night, at illuminance levels similar to  roadside vegetation, can have population effects mediated by both top-down and bottom-up effects on ecosystems. Given the increasing ubiquity of light pollution at night, these impacts may be widespread in the environment. These results underline the importance of minimising ecosystem disruption by reducing light pollution in natural and semi-natural ecosystems.

Personalising ecology

Gaston, K.J., Soga, M., Duffy, J.P., Garrett, J.K., Gaston, S. & Cox, D.T.C. 2018. Personalised ecology. Trends in Ecology and Evolution, in press. 

The field of ecology has focused on understanding characteristics of natural systems in a manner as free as possible from biases of human observers. However, demand is growing for knowledge of human–nature interactions at the level of individual people. This is particularly driven by concerns around human health consequences due to changes in positive and negative interactions. This requires attention to the biased ways in which people encounter and experience other organisms. Here we define such a ‘personalised ecology’, and discuss its connections to other aspects of the field. We propose a framework of focal research topics, shaped by whether the unit of analysis is a single person, a single population, or multiple populations, and whether a human or nature perspective is foremost.

Alien abundances dominate

Blackburn, T.M. & Gaston, K.J. 2018. Abundance, biomass and energy use of native and alien breeding birds in Britain. Biological Invasions 20, 3563-3573. [Photo: T.M. Blackburn]

We quantify the contribution of alien species to the total breeding population numbers, biomass and energy use of an entire taxonomic assemblage at a large spatial scale, using data on British birds from 1997 and 2013. A total of 216 native and 16 alien bird species were recorded as breeding in Great Britain across the two census years. Only 2.8-3.7% of British breeding bird individuals were alien, but alien species co-opted 11.9-13.8% of the energy used by the assemblage, and contributed 19.1-21.1% of assemblage biomass. Neither the population sizes nor biomasses of native and alien species differed, on average, in either census, but alien species biomass is higher than native species biomass for a given population size. Species richness underestimates the potential effects of alien bird species in Britain, which have disproportionately high overall biomass and population energy use. The main driver of these effects is the ring-necked pheasant (Phasianus colchicus), which comprised 74–81% of alien biomass, yet the breeding population of this species is still only a small fraction of the estimated 35 million birds released in the UK in autumn. The biomass of this release exceeds that of the entire breeding avifauna, and suggests that the pheasant should have an important role in structuring the communities in which it is embedded.


Daylength changes community dynamics

Kehoe, R., Cruse, D., Sanders, D., Gaston, K.J. & van Veen, F.J.F. 2018. Shifting daylength regimes associated with range shifts alter aphid-parasitoid community dynamics. Ecology and Evolution, online early. 

1. With climate change leading to poleward range expansion of species, populations are exposed to new daylength regimes along latitudinal gradients. Daylength is a major factor affecting insect life cycles and activity patterns, so a range shift leading to new daylength regimes is likely to affect population dynamics and species interactions; however, the impact of daylength in isolation on ecological communities has not been studied so far.

2. Here, we tested for the direct and indirect effects of two different daylengths on the dynamics of experimental multitrophic insect communities. We compared the community dynamics under “southern” summer conditions of 14.5‐hr daylight to “northern” summer conditions of 22‐hr daylight.

3. We show that food web dynamics indeed respond to daylength with one aphid species (Acyrthosiphon pisum) reaching much lower population sizes at the northern daylength regime compared to under southern conditions. In contrast, in the same communities, another aphid species (Megoura viciae) reached higher population densities under northern conditions.

4. This effect at the aphid level was driven by an indirect effect of daylength causing a change in competitive interaction strengths, with the different aphid species being more competitive at different daylength regimes. Additionally, increasing daylength also increased growth rates in M. viciae making it more competitive under summer long days. As such, the shift in daylength affected aphid population sizes by both direct and indirect effects, propagating through species interactions. However, contrary to expectations, parasitoids were not affected by daylength.

5. Our results demonstrate that range expansion of whole communities due to climate change can indeed change interaction strengths between species within ecological communities with consequences for community dynamics. This study provides the first evidence of daylength affecting community dynamics, which could not be predicted from studying single species separately.

Artificial nighttime light drives evolution

Hopkins, G.R., Gaston, K.J., Marcel E. Visser, M.E., Elgar, M.A. & Jones, T.M. 2018. Artificial light at night as a driver of evolutionary change across the urban-rural landscapes. Frontiers in Ecology and the Environment, online early. 

Light is fundamental to biological systems, affecting the daily rhythms of bacteria, plants, and animals. Artificial light at night (ALAN), a ubiquitous feature of urbanization, interferes with these rhythms and has the potential to exert strong selection pressures on organisms living in urban environments. ALAN also fragments landscapes, altering the movement of animals into and out of artificially lit habitats. Although research has documented phenotypic and genetic differentiation between urban and rural organisms, ALAN has rarely been considered as a driver of evolution. We argue that the fundamental importance of light to biological systems, and the capacity for ALAN to influence multiple processes contributing to evolution, makes this an important driver of evolutionary change, one with the potential to explain broad patterns of population differentiation across urban–rural landscapes. Integrating ALAN’s evolutionary potential into urban ecology is a targeted and powerful approach to understanding the capacity for life to adapt to an increasingly urbanized world.