In nature, we usually refer to the given area in which a species is found as a species range. The size of these vary, even between species that are very similar in appearance. For example, many of the dragonflies and damselflies I worked with during my PhD research could be found all over the state of Arkansas, but others had more limited ranges, and could only be found in the more southern lakes that I visited. Often, species are limited to these areas because the environmental conditions, such as temperature, are favorable to them, and the change in those conditions beyond the boundaries of their range will lead to them suffering. Knowing which factors limit the range of a given species is important for management policies, as knowing the temperature limits can inform predictions about the effects of climate change, while knowledge of natural enemies (like predators) can help with the containment of invasive species.
Previous work on the constraints experienced by species at their range limits tend to focus on abiotic factors (temperature, precipitation, etc.), as these data are easily quantified and there are very extensive records available. However, biotic factors (interactions with predators/competitors, the availability of prey) can also limit the range of a species. Though biotic factors are important, they are more difficult to quantify than abiotic factors, and are often species-specific. That is, the effect of a competitor on limiting the range of one species won’t be the same on another species. Interestingly, biotic interactions may be more important in warmer range limits, while the abiotic may be more important in the cooler range limits. Today’s authors used data from a number of studies to test just that idea.
Every time fighter jets fly overhead here in Central Norway, either my wife or I nearly always make a dry remark about the Russians finally invading. It’s a slightly dark reference to former Norwegian occupations, but not something that’s likely to occur anytime soon.
Yet this summer, the papers were filled with constant sensational references to very real and ongoing Russian invasions. Luckily, they’re referring to the pink (or humpback) salmon, and not to any human army marching across the borders.
This question comes from Marney Pratt (@marney_pratt) as she noted that a recent paper tracking trends in ecology papers shows the use of Bayesian statistics increasing over time. (Before we get going, if you want a refresher about what exactly Bayesian thought entails, check out this previous post.) Anderson et al. say:
At the start of the pandemic, working from home became essential for many of us – breaking down the physical separation of work and life and instead creating one very long day at the office. For many research groups, this meant having to make key decisions on what to do with vital animals, plants, and tissue cultures. For me, it meant over a year living with hundreds of bush crickets. Now that the summer has returned and more COVID restrictions have been lifted, the insects recently returned to our lab. Here I share some thoughts on this element of the last year, and what I have learnt about time management in academia.
If there is one thing that people know about me and my research it’s that I love parasites. They’re everywhere, and more than half of all animals are parasites. They also make ecosystems more stable and link organisms within food webs to one another. For example, some parasites connect prey animals and their predators by making it easier for the predator to find and/or eat the prey. Though they can be found all over the world, there are a variety of environmental factors that make it more likely for a parasite to be found in a given environment. Today’s study focuses on one particular hypothesis related to the effects of the environment, the latitudinal diversity gradient (LDG, see Did You Know).
Dinosaurs in the arctic – plausible. Dinosaurs thriving in the arctic – absolutely crazy…
The notion that dinosaurs were reptilian-esque, scaly, and cold-blooded creatures has probably played a role in shaping the idea that we shouldn’t expect to find dinosaurs at higher (colder) latitudes. But as our picture of dinosaurs has changed (think feathers and possibly endothermic (warm-blooded)) over time, it is probably not that surprising to learn that dinosaurs may have done well in colder (and darker) latitudes.
The discovery of not only adult dinosaurs but their young up in fossil deposits in Alaska tells us exactly that. This means that these dinosaurs were not just migrants moving through these regions but were able to reproduce. The other cool thing? It wasn’t just one, but a large collection of species that had babies represented in the fossil record. This means that a lot of dinosaurs were actually able to reproduce – which suggests that they were well-adapted to polar regions.
Just another lesson in how much we still have to learn about these beasts from the past.
Simply put, tuna fish would be a good choice if you ever found yourself faced with an underwater drag-race. These predators are designed for both speed and endurance – so much so that they’ve even managed to engage their lymphatic system to help them when chasing down their prey item of choice. The lymphatic system is typically associated with circulation and immunity but the tuna have engineered themselves to use this system to help fine-tune their steering and navigation system.
Much like how the cheetah uses its tail, or planes have adjustable wing-flaps to help execute manoeuvres precisely and accurately, tuna use their fins. The really cool part though? They use their lymphatic system to do the realignment! Researchers found that tuna can use this system to generate hydraulic pressure. This provides fine adjustment of their fins, which helps them become more manoeuvrable.
Perfect for those tight corners out on the course – might even have you considering racing for slips.
I know what you’re thinking: not another virus article! But I want to show you the positive side, the one we all need so badly right now. I want to take you on a journey through the ocean, and show you what good viruses can do for the health of marine environments, as well as how they’ve shaped life as we see it today.
Quantifying 25 years of disease‐caused declines in Tasmanian devil populations: host density drives spatial pathogen spread (2021) Cunningham et al., Ecology Letters, https://doi.org/10.1111/ele.13703
While the Tasmanian Tiger has made news this last month for all the wrong reasons, there’s still another famous species of Tasmanian mammal which deserves just as much attention (probably more given that we can still save this one from extinction). The Tasmanian devil has seen its populations declined considerably over the last three decades, largely due to the emergence of a transmissible facial tumour, the devil facial tumour disease (DFTD).
The way the devils interact mean that even at low densities, the disease can still be transmitted through a population. The aggressive nature of Tasmanian devil mating (which occurs even when there are few devils around) is a big transmission vector. This unfortunately means that extinction due to DFTD was recently thought to be a likely endpoint.
Today’s authors wanted to test to how strongly the devil density influenced the spread of DFTD, and whether the drop in population that the disease causes means that we’re likely to see the disease’s effects wear off at some point, and Tasmanian devil populations stabilise.
What They Did
Long-term data is an absolute must for a study like this. Luckily, the Tasmanian government has run ‘spotlight surveys’ along 172 road transects for the last 25 years. These involve driving slowly along a 10 kilometre stretch of road and recording mammal presence using a handheld spotlight. This was combined with further surveys designed to obtain density at smaller scales to come up with a predictive estimate of devil density in Tasmania from 1985 to 2035.
The team also used occurrence data for DFTD to figure out how quickly it initially spread through Tasmania, and modelled the spread into a new region against the density of the devils in that region.
Did You Know: Devil Reintroduction
The Tasmanian devils are an Australian icon, and a lot of money has been put into figuring out how to save their species. Suggestions have been made to reintroduce DFTD-free population back onto mainland Australia, where their presence may even help reduce the effect of cats and foxes. However it is also possible that the introduction of a new predator could instead put added pressure on mainland species already threatened by invasive predators. Studies into this are ongoing, and you can check out more on them at the articles linked below.
Tasmanian devil density may have played a large role in the initial spread of the disease, explaining why it spread so quickly through certain parts of Tasmania. This isn’t hugely surprising, though the precision with which the authors modelled its spread will be absolutely crucial for effective conservation.
What is really interesting is that the Tasmanian devil population back before the disease struck were probably much lower than initially thought. If this sounds depressing, the other big takeaway is that based on the predictions here, the decline in devil numbers should ease off soon, meaning the disease is unlikely to result in the extinction of Tasmania’s most iconic endemic species.
Normally authors will mention interesting future research which could build on the research they’ve carried out. Standard practice. Here, my ‘problem’ is that the authors mention some research so incredibly tantalising I’m angry at them for bringing it up. What will be important in the future is looking at devil genotypes. The genetic makeup of some devils will make them more resistant to the disease, and identifying and moving these individuals to areas where the disease is rampant could help fight DFTD. Having said that, it could also help produce more aggressive strains of the disease. GIVE ME ANSWERS.
This is a good news story, which often feel quite scant in the world of ecology. But it doesn’t mean the devil is out of the woods yet. Actually the woods themselves are a massive problem, seeing as Australia’s rates of deforestation are among the worst in the world. We need to constantly monitor the population to figure out where local extinctions are likely.
This study is also a fantastic example of how important long-term monitoring is for ecologists. Studies like the one used here are hard to fund (more on that here), but their value to ecologists in allowing us to figure out what drives population fluctuations is enormous.
Sam Perrin is a freshwater ecologist currently completing his PhD at the Norwegian University of Science and Technology who has spent way too much time looking at photos of Tasmanian mammals over the last 2 weeks. You can read more about his research and the rest of the Ecology for the Masses writers here, see more of his work at Ecology for the Masses here, or follow him on Twitter here.
A flatworm (Pseudocerus liparus) crawling on a sponge – passing through a forest of hydroids and tunicates. (Image credit: Christa Rohrbach, CC BY-NC-SA 4.0)
Last week I posted an article about fascinating creatures that escape death almost completely, including the famous “immortal jellyfish” (link below). Yet while the jellyfish’s attitude to aging is awe-inspiring, its existence poses a more obvious, yet perplexing question: why do we age?