Horizon scanning for urban ecosystems

Stanley, M.C., Beggs, J.R., Bassett, I.E., Burns, B.R., Dirks, K.N., Jones, D.N., Linklater, W.L., Macinnis-Ng, C., Simcock, R., Souter-Brown, G., Trowsdale, S.A. & Gaston, K.J. (2015) Emerging threats in urban ecosystems: a horizon scanning exercise. Frontiers in Ecology and the Environment 13(10): 553–560. (Image from Shutterstock) shutterstock_115045105

As urbanization intensifies, urban ecosystems are increasingly under pressure from a range of threats. Horizon scanning has the potential to act as an early warning system, thereby initiating prompt discussion and decision making about threat mitigation. We undertook a systematic horizon scanning exercise, using a modified Delphi technique and experts from wide-ranging disciplines, to identify emerging threats in urban ecosystems. The 10 identified threats were generally associated with rapid advances in technology (eg solar panels, light-emitting diode lights, self-healing concrete) or with societal demands on urban nature (eg green prescriptions). Although many of the issues identified are also technological opportunities with recognized environmental benefits, we have highlighted emerging risks so that research and mitigation strategies can be initiated promptly. Given the accelerated rate of technological advancement and the increasing demands of urbanized populations, horizon scanning should be conducted routinely for urban ecosystems.

192 Words

Songbirds and connecting people to nature

Cox, D.T.C. & Gaston, K.J. (2015) Likeability of Garden Birds: Importance of Species Knowledge & Richness in Connecting People to Nature. PLoS ONE 10(11), e0141505. (Image from Shutterstock) shutterstock_149233118

Interacting with nature is widely recognised as providing many health and well-being benefits. As people live increasingly urbanised lifestyles, the provision of food for garden birds may create a vital link for connecting people to nature and enabling them to access these benefits. However, it is not clear which factors determine the pleasure that people receive from watching birds at their feeders. These may be dependent on the species that are present, the abundance of individuals and the species richness of birds around the feeders. We quantitatively surveyed urban households from towns in southern England to determine the factors that influence the likeability of 14 common garden bird species, and to assess whether people prefer to see a greater abundance of individuals or increased species richness at their feeders. There was substantial variation in likeability across species, with songbirds being preferred over non-songbirds. Species likeability increased for people who fed birds regularly and who could name the species. We found a strong correlation between the number of species that a person could correctly identify and how connected to nature they felt when they watched garden birds. Species richness was preferred over a greater number of individuals of the same species. Although we do not show causation this study suggests that it is possible to increase the well-being benefits that people gain from watching birds at their feeders. This could be done first through a human to bird approach by encouraging regular interactions between people and their garden birds, such as through learning the species names and providing food. Second, it could be achieved through a bird to human approach by increasing garden songbird diversity because the pleasure that a person receives from watching an individual bird at a feeder is dependent not only on its species but also on the diversity of birds at the feeder.

332 Words

LiDAR for vegetation modelling

Anderson, K., Hancock, S., Disney, M. & Gaston, K.J. (2015) Is waveform worth it? A comparison of LiDAR approaches for vegetation and landscape characterization. Remote Sensing in Ecology and Conservation, in press. (Image from Shutterstock) shutterstock_95030080

Light Detection and Ranging (LiDAR) systems are frequently used in ecological studies to measure vegetation canopy structure. Waveform LiDAR systems offer new capabilities for vegetation modelling by measuring the time-varying signal of the laser pulse as it illuminates different elements of the canopy, providing an opportunity to describe the 3D structure of vegetation canopies more fully. This article provides a comparison between waveform airborne laser scanning (ALS) data and discrete return ALS data, using terrestrial laser scanning (TLS) data as an independent validation. With reference to two urban landscape typologies, we demonstrate that discrete return ALS data provided more biased and less consistent measurements of woodland canopy height (in a 100% tree covered plot, height underestimation bias = 0.82 m;SD = 1.78 m) than waveform ALS data (height overestimation bias = −0.65 m; SD = 1.45 m). The same biases were found in suburban data (in a plot consisting of 100% hard targets e.g. roads and pavements), but discrete return ALS were more consistent here than waveform data (SD = 0.57 m compared to waveform SD = 0.76 m). Discrete return ALS data performed poorly in describing the canopy understorey, compared to waveform data. Our results also highlighted errors in discrete return ALS intensity, which were not present with waveform data. Waveform ALS data therefore offer an improved method for measuring the three-dimensional structure of vegetation systems, but carry a higher data processing cost. New toolkits for analysing waveform data will expedite future analysis and allow ecologists to exploit the information content of waveform LiDAR.

277 Words

IUCN Red List assessment: Cactaceae

Goettsch, B., Hilton-Taylor, C., Cruz-Piñón, G., Duffy, J.P., Frances, A., et al. (2015) High proportion of cactus species threatened with extinction. Nature Plants 1, 15142. (Image from Shutterstock) shutterstock_134963513

A high proportion of plant species is predicted to be threatened with extinction in the near future. However, the threat status of only a small number has been evaluated compared with key animal groups, rendering the magnitude and nature of the risks plants face unclear. Here we report the results of a global species assessment for the largest plant taxon evaluated to date under the International Union for Conservation of Nature (IUCN) Red List Categories and Criteria, the iconic Cactaceae (cacti). We show that cacti are among the most threatened taxonomic groups assessed to date, with 31% of the 1,478 evaluated species threatened, demonstrating the high anthropogenic pressures on biodiversity in arid lands. The distribution of threatened species and the predominant threatening processes and drivers are different to those described for other taxa. The most significant threat processes comprise land conversion to agriculture and aquaculture, collection as biological resources, and residential and commercial development. The dominant drivers of extinction risk are the unscrupulous collection of live plants and seeds for horticultural trade and private ornamental collections, smallholder livestock ranching and smallholder annual agriculture. Our findings demonstrate that global species assessments are readily achievable for major groups of plants with relatively moderate resources, and highlight different conservation priorities and actions to those derived from species assessments of key animal groups.

244 Words

Artificial light and food webs

Sanders, D., Kehoe, R., Tiley, K., Bennie, J., Cruse, D., Davies, T.W., van Veen F.J.F. & Gaston, K.J. (2015) Artificial nighttime light changes aphid-parasitoid population dynamics. Scientific Reports 5, 15232.shutterstock_312278753
(Image from Shutterstock)

Artificial light at night (ALAN) is recognized as a widespread and increasingly important anthropogenic environmental pressure on wild species and their interactions. Understanding of how these impacts translate into changes in population dynamics of communities with multiple trophic levels is, however, severely lacking. In an outdoor mesocosm experiment we tested the effect of ALAN on the population dynamics of a plant-aphid-parasitoid community with one plant species, three aphid species and their specialist parasitoids. The light treatment reduced the abundance of two aphid species by 20% over five generations, most likely as a consequence of bottom-up effects, with reductions in bean plant biomass being observed. For the aphid Megoura viciae this effect was reversed under autumn conditions with the light treatment promoting continuous reproduction through asexuals. All three parasitoid species were negatively affected by the light treatment, through reduced host numbers and we discuss induced possible behavioural changes. These results suggest that, in addition to direct impacts on species behaviour, the impacts of ALAN can cascade through food webs with potentially far reaching effects on the wider ecosystem.

209 Words

Land-sparing, land-sharing and use of urban greenspace

Soga, M., Yamaura, Y., Aikoh, T., Shoji, Y., Kubo, T. & Gaston, K.J. (2015) Reducing the extinction of experience: Association between urban form and recreational use of public greenspace. Landscape and Urban Planning 143, 69-75.shutterstock_309919712
(Image from Shutterstock)

Halting the ‘extinction of experience’, the progressive disengagement of people with the natural world, is vital to human health and wellbeing and to public support for global biological conservation. Home to the majority of humanity, urban areas are the key for engaging people with nature, raising the crucial question of how cities should best be designed to facilitate these experiences. For the purposes of maintaining local biodiversity, intensive development within a small area (land sparing) has been shown to be better than extensive development over a large area (land sharing). Here, we investigated for the first time how different city forms affect people’s experience of nature, measured in terms of their use of greenspaces. We selected five pairs of land-sharing and land-sparing study regions with different coverage by greenspaces within the city of Tokyo, central Japan and used a questionnaire survey to determine the use residents made of these spaces. We found the frequency of people’s recreational use of urban greenspaces was higher in urban land-sharing than land-sparing regions. Moreover, satisfaction with local green environments was also higher in land-sharing regions. This suggests a potential conflict in the design of cities between the urban form that is most desirable for the direct protection of regional biodiversity, and that which best promotes people’s nature experiences and the support for its wider protection. A strong emphasis on the advantages of land sparing may increase the separation of humans from nature, and further reduce public interest in, and awareness of, biodiversity and its benefits.

287 Words

Land-sparing for urban ecosystem services

Stott, I., Soga, M., Inger, R. & Gaston, K.J. (2015) Land sparing is crucial for urban ecosystem services. Frontiers in Ecology and the Environment 13: 387–393.shutterstock_85565086
(Image from Shutterstock)

The world’s cities must grow to accommodate an increasing urban population, and achieving this with minimal impact on ecosystem structures and functions is a major challenge. At opposite ends of a possible development spectrum are “land sharing” – extensive sprawling urbanization where built land and natural space are interspersed – and “land sparing” – intensive and extremely compact urbanization alongside separate, large, contiguous green space. Using case studies across urbanization gradients, we demonstrate that land sparing is crucial for sustaining a majority of ecosystem services. Conversely, some land sharing may also be necessary to ensure that people benefit from urban green space. Future urban development should carefully consider green space provision, to maximize the services provided by urban ecosystems. This can be achieved by optimizing distributions of development intensity across cities by means of top-down, policy-led approaches.

160 Words

Macrophysiology: A review

Chown, S.L & Gaston, K.J. (2015) Macrophysiology – progress and prospects. Functional Ecology, DOI: 10.1111/1365-2435.12510.shutterstock_274637654
(Image from Shutterstock)

1. Macrophysiology is the investigation of variation in physiological traits over large geographic and temporal scales and the ecological implications of this variation. It has now been undertaken, as a defined field, for a decade.
2. Here, we overview its conceptual foundations, methodological approaches and insights, together with challenges the field is facing currently.
3. Macrophysiology builds on approaches that investigate the ecological and evolutionary significance of physiological trait variation and feedbacks in these processes. One of its key strengths is its ability to provide a basis for examining interactions among the intraspecific, interspecific and assemblage levels.
4. Macrophysiology is distinct from and typically concerns larger spatial and temporal scales than conservation physiology, whereas it is in several respects similar to, but antecedes, functional biogeography. Contrary to some claims, macrophysiology is not concerned only with the implications for geographic ranges of physiological trait variation.
5. Several insights, which would not otherwise have been achieved, have arisen from the field, notably the understanding of variation in global patterns of upper and lower lethal temperature limits and organism performance, which have important implications for forecasting the impacts of climate change.
6. Ten major challenges are identified for the field of macroecology, including better integration of approaches and information for plants and animals. Nonetheless, the prospects for macrophysiology as a significant way to understand our world remain bright.

236 Words

Mammals and artificial light

Duffy, J.P., Bennie, J., Duràn, A.P. & Gaston, K.J. (2015) Mammalian ranges are experiencing erosion of natural darkness. Scientific Reports 5, 12042.shutterstock_212529835
(Image from Shutterstock)

The continuous increase in the intensity and extent of anthropogenic artificial light has significantly shaped Earth’s nighttime environment. This environmental change has effects across the natural world, with consequences for organismal physiology and behaviour and the abundances and distributions of species. Here, we evaluate for the first time the relations between the spatio-temporal patterns of anthropogenic nighttime light and the distribution of terrestrial mammals, one of the most endangered species groups and one that expresses varying time partitioning strategies. Using descriptive statistics, trend tests and spatial prioritization analysis we show that in most places on earth there is a terrestrial mammal species whose range is experiencing detectable artificial light. For most species this tends only to be for small parts of their range, and those affected across large parts are typically rare. Over time (1992–2012), an increase in mean light intensity was found for the ranges of the majority of species, with very few experiencing a decrease. Moreover, nocturnal species are more likely to experience an increase in light within their ranges. This is of conservation concern as many terrestrial mammals are nocturnal and therefore often particularly vulnerable to a pressure such as artificial light at night.

222 Words

Estimating return energy of waveform lidar

Hancock, S., Armston, J., Li, Z., Gaulton, R., Lewis, P., Disney, M., Danson, F.M., Strahler, A., Schaaf, C., Anderson, K. & Gaston, K.J. (2015) Waveform lidar over vegetation: An evaluation of inversion methods for estimating return energy. Remote Sensing of Environment 164, 208-224.Screen Shot 2015-07-12 at 13.59.43

Full waveform lidar has a unique capability to characterise vegetation in more detail than any other practical method. The reflectance, calculated from the energy of lidar returns, is a key parameter for a wide range of applications and so it is vital to extract it accurately. Fifteen separate methods have been proposed to extract return energy (the amount of light backscattered from a target), ranging from simple to mathematically complex, but the relative accuracies have not yet been assessed. This paper uses a simulator to compare all methods over a wide range of targets and lidar system parameters. For hard targets the simplest methods (windowed sum, peak and quadratic) gave the most consistent estimates. They did not have high accuracies, but low standard deviations show that they could be calibrated to give accurate energy. This may be why some commercial lidar developers use them, where the primary interest is in surveying solid objects. However, simulations showed that these methods are not appropriate over vegetation. The widely used Gaussian fitting performed well over hard targets (0.24% root mean square error, RMSE), as did the sum and spline methods (0.30% RMSE). Over vegetation, for large footprint (15 m) systems, Gaussian fitting performed the best (12.2% RMSE) followed closely by the sum and spline (both 12.7% RMSE). For smaller footprints (33 cm and 1 cm) over vegetation, the relative accuracies were reversed (0.56% RMSE for the sum and spline and 1.37% for Gaussian fitting). Gaussian fitting required heavy smoothing (convolution with an 8 m Gaussian) whereas none was needed for the sum and spline. These simpler methods were also more robust to noise and far less computationally expensive than Gaussian fitting. Therefore it was concluded that the sum and spline were the most accurate for extracting return energy from waveform lidar over vegetation, except for large footprint (15 m), where Gaussian fitting was slightly more accurate. These results suggest that small footprint (≪ 15 m) lidar systems that use Gaussian fitting or proprietary algorithms may report inaccurate energies, and thus reflectances, over vegetation. In addition the effect of system pulse length, sampling interval and noise on accuracy for different targets was assessed, which has implications for sensor design.

395 Words