The natural world provides as with a laundry list of health services, from cleaning the water we drink to providing blueprints for cutting edge medicine. Yet on this list of ecosystem services, carnivores often get left by the wayside. One such carnivore is the spotted hyena, which can be found roaming the outskirts of many towns in eastern Africa. The hyenas are adept scavengers, and clear away massive amounts of discarded meat every year, potentially preventing the spread of carcass-borne diseases like anthrax and tuberculosis.
Yet as with many predators, hyenas have often been feared, whether as a result of their historical association with evil spirits or more recent unfavourable portrayals. In a world where carnivores like wolves, dingoes and bears are often feared and driven off, providing proof of the benefits they bring is crucial. So that’s what today’s researchers set out to do.
Fire, drought and flooding rains: The effect of climatic extremes on bird species’ responses to time since fire (2021) Connell et al., Diversity and Distributions, https://doi.org/10.1111/ddi.13287
Both bushfires and extreme climate events are capable of shaping not only habitats, but also the number of different species that inhabit them. Yet the interaction between these phenomena can be equally important. For instance, an extreme flood or drought could have a very different impacts on a forest depending on how recently that forest was burned by fire. If a fire tore through recently, an extended period of drought may finish off species already under stress, yet if there has been a longer period of time since the last fire, the ecosystem may be able to tolerate a drought.
Given that climate change is increasing the occurrence of both extreme climate events and bushfires, it’s better to start investigating the effects of these interactions sooner rather than later. This week’s authors looked at the interaction between the two phenomena in south-eastern Australia, an area whose wildlife has come under a lot of pressure recently.
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.
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.
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.
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.
Everything that ecologists do – from saving endangered species to projecting climate change impacts – requires ecological data. Sometimes that data can be hard to come by, like when you’re trying to figure out the range of a rare moss. At other times, that data can be smack bang in front of you, but impossible to measure. The depth of a lake for instance, or the surface area of a tree. Today, we’ll look at how to overcome that second situation, by using other, more easy-to-obtain covariates to provide an estimate of the property you’re looking for.
The challenges and opportunities of coexisting with wild ungulates in the human-dominated landscapes of Europe’s Anthropocene (2020) Linnell, Cretois et al., Biological Conservation, https://doi.org/10.1016/j.biocon.2020.108500
The “land sparing vs land sharing” debate is not new to wildlife conservation and is more relevant now than ever. Land sparing entails creating areas distinctly for wildlife, commonly referred to as Protected Areas. The science of spared landscape is well developed and its principles were fundamental to early conservation biology. On the other hand, the confinement of wildlife into human-free area is possible on a very limited in a highly anthropogenic landscape like Europe. Hence, the coexistence movement, which requires both wildlife and humans to share their landscape, leading to a wide range of interactions between the too. This is especially true when it comes to charismatic large mammals including large carnivores and ungulates, whose range has large overlaps with ours.
We wanted to summarise the knowledge on wild ungulate distributions and examine wild ungulate-human interactions. Ungulates are quite varied in Europe, and this study included species such as the wild boar, European bison, moose and roe deer.
Community ecology, as a relatively new discipline, is fraught with challenges. Here, we look at why an hour spent talking about those challenges may make you feel like the PhD student pictured above (Image Credit: Lau Svensson, CC BY 2.0, Image Cropped)
Anyone who has forayed any small distance into academia will probably understand the following quote by Aristotle.
“The more you know, the more you realize you don’t know.”
According to Stewart Lee, participating in further education means embarking on a “quest to enlarge the global storehouse of all human understanding”. This might be true, yet venturing into academia also means that the more answers you learn to challenging scientific questions, the more questions get opened up. It’s the circle of academic life.
I spent last week up in Tromsø, Norway, for the 4th Conference of the Norwegian Ecological Society. A two-hour flight further north might not seem like a big deal, however if I were a species alone to myself, my northern distribution limit based on temperature would be Trondheim, where I currently reside. It’s just too damn cold for an Australian in the Arctic Circle! Yet Tromso was surprisingly mild last week, coming off the back of a particularly warm winter. And whilst that might sound great, warming temperatures in the Arctic may cause a plethora of negative effects on local wildlife, including starving local reindeer populations and reducing the vital mosquito population.
When species like this toucanet are lost, the interactions that they are a part of are lost too. So how can we restore them? (Image Credit: Jairmoreirafotografia, CC BY-SA 4.0, Image Cropped)
Estimating interaction credit for trophic rewilding in tropical forests (2018) Marjakangas, E.-L. et al., Philosophical Transactions of the Royal Society of Biology, 373, https://dx.doi/10.1098/rstb.2017.0435
We have reviewed more than enough papers on biodiversity loss to entitle us to skip the whole “losing species is bad” spiel (see here, here and here). But what we haven’t talked about is that when some species are lost, specific interactions that those species participate in disappear from an ecosystem. Those interactions range from the minute to the crucial. One such crucial example is that of seed dispersal, whereby specific plants rely on specific animals to disperse their seeds, thus maximising biodiversity in other parts of the forest and creating a positive feedback loop.
Naturally, conservationists will want to reintroduce animals to propagate some of these reactions. But as is always the case in conservation, maximising return is absolutely essential when you’re faced with limited resources and a lot of ground to cover. Today’s authors wanted to develop a system for maximising the effect of species reintroduction.
Spreading of the Australian yabby has led to decreases in other local species. But what happens when these species meet? (Image Credit: Daiju Azuma, CC BY-SA 2.5, Image Cropped)
Insight into invasion: Interactions between a critically endangered and invasive cray fish (2018) Lopez et al., Austral Ecology, doi:10.1111/aec.12654
When we talk about invasive species, often the first thing that pops into our minds are things like feral cats, wild pigs, vicious newcomers that wipe out species or transform vast areas. But often what we focus on less are species which arrive and simply outcompete the locals.
The yabby (Cherax destructor) is one such invader. An Australian species, it has been introduced to new waterways through the country and is now threatening other species, including the Falls Spiny Crayfish (Euastacus dharawalus) in eastern New South Wales, Australia. The introduction of the yabby has resulted in a decreasing habitat range for the crayfish, but what sort of mechanisms are causing this? This experiment aimed to document interactions between the two species.