Background: The purpose of this study was an analysis of the impacts of light pollution on benthic microbial populations. The researchers state how these kinds of microbial populations are populous all over the planet and are highly diverse. They hypothesized that artificial light pollution will affect the composition and behavior of these populations and therefore will change ecosystem dynamics, affecting the global carbon cycle. The study was designed to take two similar benthic microbial populations and expose one to artificial light at night for six months and have the other in natural conditions to see whether this was true, and what effects this artificial light would have on the communities and their processes.
Methods: The study was conducted by identifying two sites of benthic microbial organisms, two agricultural drainage ditches. The team verified that moisture levels were near identical for both sites, and also established that the species and populations were biologically similar enough for their study. They did this through DNA metabarcoding and included these results in the study to verify that their two populations were suitable for experimentation. These sites were located in a verified Dark Sky zone to confirm that the control would not experience any artificial light at night. One site was therefore chosen as a control and would receive no treatment, and the other site had artificial lamps installed over it. The lumens of the treatment for this site were also measured and controlled to be similar to the average lumens experienced in other urban settings that experienced artificial light at night. This data was also included in the study to verify that treatment levels were significantly similar to actual experienced light levels. Then, the light was maintained over the treatment site for six months. At the end of this time period, biological information about population composition, cellular respiration, and carbon sinking were recorded.
Results: The study returned results that photosynthetic autotrophic organisms saw statistically significant population growth and comprised a larger percentage of the benthic ecosystem in the site that received treatment than in the one that didn’t. They also detected that cellular respiration levels had decreased. Overall this indicates a decrease in species diversity as the benthic communities were made to shift towards auto phototrophic majority populations, however they did anticipate that this could eventually lead to net positive NEP in these kinds of communities as light levels at night increase over time. This answers one major question of the experiment, which was whether or not light levels at night, significantly lower in intensity than sunlight, would be enough to stimulate photosynthesis for these benthic autotrophic organisms.
Criticisms: I think that this experiment was set up very well. They accounted for many factors that could affect the results of their work and took data measurements to ensure that these factors were mitigated as much as they could be to establish reliable results. The difference in species between locations were accounted for by the DNA metabarcoding to ensure a similarity of species richness. The moisture levels were accounted for by testing to ensure similarity, and the lumen levels of the control site were measured to ensure they met natural dark sky levels to establish significant differences if they appeared. I think that all these precautions show a lot of forethought in the experiment and help to establish credibility of the results. I do think that perhaps they are extrapolating a bit much about the results in the discussion portion. They claim that the results of their experiments are proof that increasing light levels at night in the world will turn benthic organisms into ecosystems of net positive production at night year round, and that this will affect carbon sinking on a global scale. All this experiment really proved is that a long term presence of artificial light at night increased photosynthetic production in this one treatment group. I think these claims they make in their discussion are reasonable hypotheses and absolutely excellent grounds for future experimentation, but not truly establishable from this experiment alone.
The article that I chose to review is “The importance of ponds for the conservation of bats in urban landscapes” by Ancillotto et al. (2019). The study presented in the article discusses research into the importance of urban ponds and how certain qualities can shape how effectively different bat species can survive in their presence. Bats are a vital species when aiding in insect control around urban areas and while many species are heavily impaired in urban environments, there are still those that thrive in these conditions.
The goals of this study were to find how strongly differing levels of vegetation surrounding the ponds had an effect on bat populations. They also sought to record how the surrounding landscape and artificial light presence had a selective impact on bat species. These questions focused on how well bats can feel comfortable avoiding predators in an urban environment as well as how beneficial an area is to their own feeding techniques. These bats rely on lentic habitats for their high water intake so ensuring the area is suitable for preying upon insects is vital to their survival in an urban environment.
Methods
The study was taken place in the municipality of Rome across 35 selected ponds. These ponds were selected to ensure the study encompassed varying pond sizes, riparian vegetation, natural or manmade banks, and surrounding land cover. The ponds were found via satellite images and were only considered if they contained a water surface that was level with the surrounding ground, a perennial history, open air to allow bat access to the pond, the pond was not connected to any other bodies of water, and the water surface was free from vegetation. The ponds’ origins did not have any effect on their selection and for all ponds chosen there were pond management practices taken at least 2 years before the study.
For bat sampling, activity was recorded between June and September 2016-2017. Samples were taken four hours after sunset and only once per site. A manually operated Pettersson D1000X bat detector was used at each site and sampled at a frequency of 384 kHz. Recordings were taken along the banks of each site where there were no obstacles or noises that could block or interfere with readings. Weather and moon illumination were also taken into account when deciding on when to perform sampling events. From here, bat species were identified by their echolocation calls and the most abundant species was used for analysis of bat activity. Bat activity was quantified as bat passes per night with bat passes being counted with 2 or more echolocation calls.
For the second part of the experiment, the landscape and environment was estimated within 50m, 200m, 1000m, and 3000m radii of circular areas around the sampling point. Each distance aided in measuring different categories of environmental features from local to much more broad features of the area. Habitats were to be classified as urban matrix, woodland, open green areas, or intensive farmland. Finally, distance between the pond and other important features was also taken to aid in statistical analysis.
Environmental variable
Description
Unit
woodland1000
Amount of woodland habitat types in a 1000 m radius around sampling point
Percentage
perimeter
Measure of pond perimeter – a proxy of riparian habitat availability
Metres
bank type
Classification of riparian habitat as natural (>75% covered in vegetation) or artificial (>75% made of concrete) – proxy of riparian habitat quality
Categorical
distmargin
Distance between sampling point and closest vegetation edge (hedgerow, tree line, woodland margin)
Metres
distbuilding
Distance between sampling point and closest building
Metres
distlight
Distance between sampling point and closest artificial nocturnal light
Metres
green50
Amount of open green areas (open spaces not including patches of woody vegetation such as natural grasslands, recreational green areas, non-intensive farmland, orchards, private vegetable gardens, small organic farms) in a 50 m radius around sampling point
Percentage
green200
Amount of open green areas (open spaces not including patches of woody vegetation such as natural grasslands, recreational green areas, non-intensive farmland, orchards, private vegetable gardens, small organic farms) in a 200 m radius around sampling point
Percentage
green1000
Amount of open green areas (open spaces not including patches of woody vegetation such as natural grasslands, recreational green areas, non-intensive farmland, orchards, private vegetable gardens, small organic farms) in a 1000 m radius around sampling point
Percentage
green3000
Amount of open green areas (open spaces not including patches of woody vegetation such as natural grasslands, recreational green areas, non-intensive farmland, orchards, private vegetable gardens, small organic farms) in a 3000 m radius around sampling point
Percentage
Results
Of the 2317 recorded bat passes, 94.4% belonged to the species Pipistrellus spp. and Hypsugo savii. The most common bat species that was found at all recorded sites was the P. kuhlii and had a total of 1049 bat passes. The results found from environmental data in addition to this species showed a positive relationship between the bats and the amount of bank habitat alongside the ponds. Another feature that was found to be important was the existence of natural banks over artificial ones. Bats were generally found to be more active around ponds with a majority of natural banks rather than those that were dominated by artificial banks. Distance from the closest building also had a consistently positive effect while distance from closest streetlamp light had varying effects from positive to negative depending on the species. This aids in the notion of how different bat species using different hunting techniques which can be harmed or helped by the presence of light. The amount of open habitat had a varying effect throughout the different species at different ranges while woodland habitat within the 1000m radius was found to have an overall positive effect.
perimeter + distbuilding + distmargin + green50 + bank type
249.60
0.75
5
0.28
Pipistrellus pipistrellus
bank type + distmargin
236.44
0
2
0.63
bank type + distmargin + perimeter
237.31
0.87
3
0.59
bank type + distmargin + perimeter + green3000
238.33
1.89
4
0.11
Pipistrellus pygmaeus
distlight + bank type + woodland1000 + perimeter + distmargin
171.51
0
5
0.49
Critiques/Reflection
As a study, I found this to be an interesting topic to have questions about. Bats have always seemed to me as a species that readily benefits humans as they are a pest control species. One feature I liked about the article was its discussion on how light posed as a detriment to many species of bats while it could prove advantageous to others. The article did discuss how the light was useful in attracting prey and dangerous for revealing bats to predators but it did not give specifics as to why some bats choose to risk it. If there were to be any improvements there I would add what sort of adaptation or improvement some bats have that allows them to make use of well lit areas and reap the benefit of increased food.
For areas that could be expanded upon, the article did a great job at listing other variables that were not included but should be referenced in future studies. One example includes how water quality might have an effect on a pond’s popularity with bats. Since bats use ponds as one of their primary drinking sources, it is important to study what kind of water pH or quality they prefer. This can then be used to determine what water management practices should be taken for urban ponds as well as the vegetation that surrounds them.
A point I would like expanded is the idea that certain ponds might need to focus on benefitting one species over others. In this study, the results were compared to the preferences of the most common species. What if we should then be focusing our efforts on what the minority of species needs to survive? With expanding urbanization, the problems held by those bat species in the minority will only spread and expand their struggles with survival. To properly ensure the protection of all bat species in an area some ponds may need to be specialized to favor certain species over those who have more generalized needs.
While the essay could always be improved by adding more variables to future studies, the authors do a great job in addressing where there is lacking information and next steps that could be taken to improve further.
Reference
L. Ancillotto, L. Bosso, V.B. Salinas-Ramos, D. Russo, The importance of ponds for the conservation of bats in urban landscapes, Landscape and Urban Planning, Volume 190, 2019, 103607, ISSN 0169-2046, https://doi.org/10.1016/j.landurbplan.2019.103607.