Tag Archives: city

Predators Under Nightlights

This is a guest post by Dr. Mark Ditmer.

Streetlights like these have meant that for some animals, hiding in the dark is now increasingly difficult (Image Credit: ME Stoner, CC BY 2.0, Image Cropped)

Artificial nightlight alters the predator–prey dynamics of an apex carnivore (2020) Ditmer et al., Ecography, https://doi.org/10.1111/ecog.05251

The Crux

The earth is no longer dark at night – artificial lighting has degraded the dark nighttime conditions that many species have evolved with throughout their evolutionary history. This change is only accelerating, with human expansion and intensity of radiance continuing to increase annually. We already know that elevated light levels can disrupt ecological processes like pollination or migration, as well as have a litany of negative effects on individual species, from physiological stress to predation risk. But it’s hard to get an idea of how the increase in ‘light pollution’ affects free-roaming wildlife, especially large mammals, and especially at scales relevant for making conservation policy.

In areas like the American west, the rapid growth of urban areas and the accompanying spread of light pollution create a rapidly changing ecosystem, one that sees many conflicts between humans and wildlife. One particularly species of particular interest is the mule deer (Odocoileus hemionus), which seeks out sources of forage on the edges of and within towns and cities (e.g. parks, farms), especially in arid regions. The primary predator of mule deer – the cougar (Puma concolor) – also navigates and hunts near human development where their prey congregate, but tend to avoid human presence more so than deer.

Today’s authors wanted to assess how artificial lighting, both where it occurs and its intensity, can shape the behaviors and predator-prey interactions of these species across the American West ranging from the edges of bright urban regions, such as Salt Lake City (Utah) and Reno (Nevada), to areas receiving minimal light pollution like Grand Canyon National Park.

What They Did

The authors used a massive dataset that included GPS-locations from 263 mule deer, 56 cougars, and 1,562 locations where cougars successfully killed mule deer. The resulting location data were combined with estimates of anthropogenic light pollution (more on this in Did You Know?).

Several different analyses were performed on the combined light and GPS-location data, along with other variables representing environmental (e.g., snow cover, land cover, terrain) and human factors (e.g., distance to roads, housing density). The aim was to figure out whether A) light has any influence on the behavior of each species, B) cougars avoid areas with high light pollution, allowing deer to forage freely wherever and whenever they want (the ‘predator shield hypothesis’), or C) cougars exploit the higher densities of deer seeking forage around areas with elevated light pollution (e.g., parks, golf courses, agriculture; the ‘ecological trap hypothesis’).

Did You Know: A Space Agency’s Ecological Impact

In this study we used remote sensing data to determine the amount of light pollution in a given environment. Yet the sensors only pick up the total amount of light, and can’t tell us what is a product of our activity and what is a natural source of light. To separate the two, we used light data which was recently developed by the U.S. National Aeronautics and Space Administration (NASA). This dataset removes the contributions of natural sources of light (e.g., moonlight, fire, atmospheric spray) from our data and results in values of just the human-created nighttime light emissions.

What They Found

The behaviors of both species changed greatly with levels of light pollution, as did the predation risk for deer. The behaviour changed across different scales as well. Cougars killed deer in study sites with the high amounts of light pollution, but within those sites (e.g., edge of Salt Lake City, Utah) cougars selected to hunt and kill in the relatively darkest locations. In contrast, in the darker study areas, cougars killed deer in areas with the relatively more light pollution than the surrounding area. However, even though cougars killed deer in the darkest spots within the bright urban interface, those locations generally had much higher levels of light pollution than the brightest kill sites in the low light pollution study areas.

The study found that cougars made kills in bright regions, but generally only within the darker parts of those regions (Image Credit: ME Stoner, CC BY 2.0)

Deer living in brighter urban areas tended to forage at night, potentially to avoid direct human interactions. This shift might have benefited deer by avoiding humans, but as they sought out more natural and dark locations in these areas, cougars would wait in ambush.

In the end, the authors concluded that their findings fell in a gray zone between the predator shield and ecological trap hypotheses dependent on scale. Areas with high levels of light and subsequent human activities provide excellent foraging opportunities for ungulates (as this study measured as well), but adaptable predators can follow and take advantage – at least in environments that they feel are safe enough.

Problems

This is an observational study, so it’s hard to fully tease apart what effects are driven by light and what are driven by other human factors. We did our best to account for the other more traditional sources of the human footprint, reporting effect sizes for each, but there’s always a chance we’re attributing some effects to light pollution that could be caused by some other aspect of our presence.

So What?

Work like this shines a light on (pun intended) how different species will respond to the ongoing urbanization trends humans are driving in much of the planet.

Although many wildlife ecology studies consider various human alterations to habitats and the consequent changes in animal behavior, most studies fail to consider the sensory environment and the pollutants (e.g., noise, light) that can impact wildlife populations in their analyses. How wildlife use an ecosystem can impact everything from human-wildlife interactions to pulses of nutrients to the soil based on shifting areas of kill sites/carcasses.

Dr. Mark Ditmer is a post-doctoral researcher at the Centre for Human-Carnivore Co-Existence and Wittemyer Lab at Colorado State University. You can read more about him at his profile here or follow him on Twitter @MDitmer.

Rebuilding Our Relationship With Urban Rivers With Dr. Cecilia Medupin

Rivers have played a monumental role in determining where people live. Their importance in providing water, transportation and a raft of other ecosystem services has meant that even today most of the world’s largest cities are situated close to a major source of freshwater, from Sydney to Delhi, Quebec to Karachi.

Yet despite their role in our history, urban rivers today are often facing increasing levels of pollution as a result of human activity. As well as often being a huge tourist drawcard, and an ongoing resource for fishers, joggers and portable BBQ toters, freshwater ecosystems carry a disproportionate number of aquatic species, which makes this trend increasingly worrying.

After meeting at last year’s British Ecological Society Annual Meeting, I got in touch with Dr. Cecilia Medupin, a freshwater ecologist at the University of Manchester. Cecilia works to increase peoples understanding of rivers, including the project Our Rivers, Our City. I asked Cecilia abut our connection with rivers, the challenges they face, and how to inspire research and change in urban rivers.

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Appreciating the Nature On Our Doorstep With Kelly Brenner

Image Credit: Kelly Brenner, CC BY 2.0, Image Cropped

Over the last few months, extenuating circumstances have confined us to our homes, and the areas immediately surrounding them. For those who love nature, being trapped in the city or suburbs might seem like we’ve lost our daily opportunity to explore the ecosystems around us. Yet over recent years, the push to appreciate urban ecosystems and the species that flourish in them has grown. The exploration of urban ecosystems makes up the lion’s share of my PhD. With the increasing urbanisation seen worldwide, we are at risk of getting alienated from nature, unless we actively make an effort to stay in touch – the phrase: “You can’t save what you don’t love, and you can’t love what you don’t know” comes to mind. Urban ecosystems can offer the opportunity to reconnect with nature without having to travel far and wide to find a patch of green.

With this in mind, Sam and I recently had the chance to sit down and talk to author Kelly Brenner. Kelly, whose book Nature Obscura chronicles the many fascinating lives of urban species, has been leading the charge for renewed appreciation of the nature that is available right outside our doorstep, or in the backyards of those fortunate enough to have them. We spoke with Kelly about her new book, our attitudes toward urban nature, and even how useful Pokemon Go is in an urban nature context.

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The Big Challenge: Increasing City Biodiversity

Image Credit: GuoJunjun, CC BY-SA 3.0 NO, Image Cropped

The Big Challenge Science Festival is currently in Trondheim, bringing a host of celebrities, scientists and futurists together. Their goal is to present solutions for the challenges the planet currently faces, and get people thinking about how they can adjust their lives to help the planet. While there are some big names in attendance, there are also a large number of local students and scientists working tirelessly on stands, and it’s them that I spent yesterday working alongside.

There’s some fantastic stuff on display. I was particularly impressed by the use of VR in a couple of exhibitions. One stand presented a worst case scenario for warming planet, with one of Trondheim’s most famous laneways submerged in water (although the man clinging to a floating car tire waving for assistance may somewhat disturb the kids). Nearby was another VR experience where you could shoot cars, carbon molecules and chimneys, transforming them into bikes, trees and solar panels respectively. The tent next to us had a great range of displays, presenting practical and simple options for living sustainably and also letting you snack on insects and other arthropods!

Our own stand was part of the Futurum exhibition, which postulated how Trondheim may look in 2050. It focussed on biodiversity, and how Trondheim’s wildlife will change over the next 30 years with increasing urbanisation and a warming climate. On loan from the Natural History Museum was a selection of species that could conceivably arrive in Trondheim with a 1-2 degree temperature increase. It was fun to see kids’ faces contort at the thought of a parrot being a common presence in Trondheim, but with Ring-Neck parrots already as far north as Brussels, it could happen within their lifetime.

I was pleasantly surprised at the willingness of some children to accept that new species weren’t necessarily a good thing. Most of them were entranced by the sight of a grey squirrel, but readily understood that it could mean the demise of the red squirrel and some local bird life. Likewise, I was surprised at how many parents could immediately recognise the species likely to disappear from Trondheim, and acknowledge how many more Black-Headed Gulls and Northern Lapwings they could see only twenty years ago.

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NTNU’s Tanja Petersen explains how species life the Pacific Oyster or the Grey Squirrel could be in Trondheim within 30 years (Image Credit, Øystein Kielland, CC BY 2.0)

It was also encouraging to see how many people have started to let portions of their garden grow wild in an effort to allow insects, and thus birds and mammals make their way back into urban areas. The exhibition had 2 fantastic videos compiled by Øystein Kielland focussing on the difference between a green area and a biodiverse one, and how fragmentation has devastated local plant and insect populations. So the number of adults who had already started letting areas around their house grow unchecked was encouraging. Two particular highlights were the couple who eagerly showed us the badger who had recently taken up residence in their backyard, and the girl who nodded eagerly and started telling me all about her insect hotels.

One thing I always struggle with in these situations is communicating uncertainty. Whilst it’s fun to see jaws drop at the thought of parrots in Norway, it’s difficult to communicate the ‘maybe’ factor in the amount of time it takes to engage someone in these issues. The point of the Big Challenge is to get people to act, so I hope that people walk away thinking that if they don’t start living more sustainably there could be huge species’ turnover, but I don’t want to present a worst case scenario, or talk in absolutes about issues that are very much only possibilities. So any success stories you’ve had communicating uncertainty in these scenarios would be very much welcome below!

I’ll be back at the Futurum exhibit at Krigseilerplass near the Royal Garden today. If you’re in Trondheim, I highly recommend stopping by. You can read more about the event here.

The Ecology of Pokemon

Image Credit: Detective Pikachu (2018)

Over 2 weeks, we go into the physiology of everyone’s favourite (or at least the one your parents know) Pokemon, Pikachu, and look at the horrifying world they inhabit. How would people evolve on this world? Is Pikachu a carnivore? What the hell is up with animal ethics here?

The World of Pokemon

01:46 – Obligatory Sonic the Hedgehog Thoughts
04:35 – The World of Pokemon
41:14 – Riddick on the World of Pokemon

The Physiology of Pikachu

01:52 – The Physiology of Pikachu
27:30 – Vet’s PSA (Neutering Your Pets)