Category Archives: Paper of the Week

Forecasting Foreign Fishy Futures

Forecasting the future establishment of invasive alien freshwater fish species (2021) Perrin et al., Journal of Applied Ecology, https://doi.org/10.1111/1365-2664.13993

The Crux

I know I write a lot about whether or not we should jump to conclusions about non-native species, but the fact is that there are lots of situations in which invasive species need to GO. Giving them the boot, however, can be a right pain, and more often than not it’s impossible.

But an ounce of prevention is worth a pound of cure (I don’t know the imperial system well so I assume that makes sense), and figuring out where an invader is likely to turn up means you can take measures to stop it happening in the first place. This saves a lot of hassle (and money) down the road.

So how do we figure out where invasives are likely to show up? That’s what this paper, which made up the first chapter of my thesis, aimed to find out, by looking at where invasive freshwater fish species have been popping up in Norway over the last 100 years.

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Location Location Location

Biotic interactions are more often important at species’ warm versus cool range edges, Paquette & Hargreaves, 2021 Ecology. https://doi.org/10.1111/ele.13864

Image credit: Trey Ratcliff, CC BY-NC-SA 2.0

The Crux

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.

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Hungry Hyenas Help Human Health

Image Credit: flowcomm, CC BY 2.0, Image Cropped

Public health and economic benefits of spotted hyenas Crocuta crocuta in a peri-urban system (2021) Sonawane et al., Journal of Applied Ecology, https://doi.org/10.1111/1365-2664.14024

The Crux

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.

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The Effects of Reproduction on Coexistence

Image credit: Charles J. Sharp, CC BY-SA 4.0

When ecology fails: how reproductive interactions promote species coexistence (2021), Gómez-Llano et al., Trends in Ecology and Evolution. https://doi.org/10.1016/j.tree.2021.03.003

The Crux

Scientific literature, like many different aspects of society and culture, goes through periods where a given subject/topic is more prominent in the public conscience than others. Lately, the question of coexistence has been at the forefront of the minds of many community ecologists. Coexistence is the state in which two or more species can each maintain a population in the same habitat as each other, provided that the environmental conditions and species interactions that they experience remain stable. Many studies of coexistence have investigated how differences among coexisting species allow them to maintain their coexistence, which makes sense, as it’s hard to coexist with another species if they require the exact same food or habitat as you do.

Yet there are a lot of examples of coexisting species that seem to be almost identical. Some researchers have suggested that these networks of similar species are unstable and should break down over time. But are these groups of species truly doomed? Or are there other processes maintaining this seemingly unlikely coexistence?

Today’s authors suggest that reproductive interactions among species are what may allow such similar species to continue coexisting. While much of the work in this area is theoretical rather than empirical (see Did You Know?), the authors reviewed what empirical evidence they could. Today’s paper is a review (a paper that summarizes lots of previously published papers with the goal of synthesizing knowledge), so I will briefly touch on the main points as put forward by the authors.

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Charting The Spread Of Invasive Crayfish

Image Credit: Nature.Catcher, CC BY-SA 2.0, Image Cropped

Distribution and establishment of the alien Australian redclaw crayfish, Cherax quadricarinatus, in the Zambezi Basin (2021) Madzivanzira, South et al., Aquatic Conservation, https://doi.org/10.1002/aqc.3703

The Crux

While some of us may love certain seafood, and are willing to carry that seafood all over the globe, often the local species are none to happy about it. Such is the case with the Australian redclaw crayfish, a rare example of Australia finally delivering back to the world that which it has received so many of – an invasive species. The redclaw is actually one of nine crayfish that has been introduced to mainland Africa, and if their record (and the records of other crayfish species) is anything to go by, it could mean everything from the spread of parasites and complete ecosystem upheaval to severe damage to the local fishing industry.

It’s crucial to figure out exactly where invasives have spread to, and how quickly they’ve done it. It allows managers and conservation experts in other areas to prepare, and to keep an eye out. This week’s team tried to determine how quickly the crayfish are spreading from their introduction point in the Zembezi River Basin.

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What’s In A Wolf Scat? New DNA-Based Method To Detect Prey From Carnivore Scats

This is a guest post by Cecilia di Bernardi.

Image Credit: Rick Heeres, CC BY 2.0, Image Cropped

Multiple species-specific molecular markers using nanofluidic array as a tool to detect prey DNA from carnivore scats (2021) Di Bernardi et al., Ecology & Evolution. https://doi.org/10.1002/ece3.7918

The Crux

Studying carnivore diet can be a crucial tool to inform both management and conservation of predators and their prey. If we’re going to ensure a carnivore’s survival, we need to know which species it relies on for food, and in what quantities.

Digging into an animal’s stomach isn’t the nicest way to get the crucial data we’re looking for, so non-invasive sampling of scats (that’s science for poop) has for been a more ideal approach to collecting valuable information on the occurrence, genetics, and diet of animals, especially when dealing with elusive and threatened species. Nowadays, DNA-based analyses of scats are allowing researchers to get more and more high-resolution data on predators’ food habits.

What We Did

We developed a DNA-based method to detect prey from wolf scats, taking advantage of the huge leaps the DNA analysis has been through in recent years. We also made use of nanotechnology (specifically Nanofluidic array technology fromFluidigm Inc.), which has been useful for detecting pathogen species in ticks, or traces of herbivores on browsed twigs, but has never applied to detect prey from predator scats!

Starting from the big bank of DNA sequences available online (GenBank, NCBI), we looked at specific areas of the genome, (the mitochondrial genome), in order to tell apart the different target prey species present in the wolf scat. We developed species-specific molecular markers (see Did You Know?) and tested them with reference tissue samples, kindly provided by the Swedish Museum of Natural History. After the protocol development and optimization, we ended up with a set of 80 markers for our 18 target species. We then applied the newly developed molecular method on a pilot sample of wolf scats collected in the field.

Did You Know: Molecular Markers

Since any species’ genome is an incredibly long sequence, scientists have developed more efficient ways of defining what DNA belongs to which species. The motivation is simple – if you’re trying to tell whether a genome belongs to a human or to a chimpanzee, you don’t want to be looking through the 99% of DNA we have in common, you want to go straight to that 1%. That’s why scientists develop ‘markers’. It helps them narrow down their search and identify species much more quickly.

What We Found

The molecular markers we developed did their job well, correctly detecting the 18 prey species, showing an overall good distinction between the tissue samples of the target and non-target species. In other words, this means that a tissue sample taken from a moose was detected by the moose markers but not by the reindeer markers, which is the sign of a successful marker!

When applied to the pilot of wolf scats collected in the wild, the method detected a total of 16 species, comprising wild ungulates (moose, roe deer, red deer, fallow deer, wild boar), domestic and semi-domestic animals (reindeer, cattle, sheep), small prey species (European badger, European hare, mountain hare, Western capercaillie, black grouse), and other carnivores (Eurasian lynx, wolverine, red fox).

Just because fox DNA turns up in a wolf scat, it doesn’t mean that a wolf has eaten a fox – it could simply mean tha a fox has urinated on the scat! (Image Credit: Joanne Redwood, CC0 1.0)

Problems?

While the method detects the target species as we’d like, it cannot distinguish whether predation, scavenging, or territorial marking has occurred. Detection of fox DNA in wolf scats can mean a wolf predating on a fox, a wolf scavenging on a fox, but also a fox marking with its urine on a wolf scat! To partly disentangle this aspect, we are investigating the contribution of scavenging to wolves diet in Scandinavia, with data from GPS-collared wolves.

So What?

This molecular method, with its high-resolution prey detection, can help better understanding under what circumstances wolves eat certain prey and how that can affect ungulate populations, serving as a valuable complement to the current GPS technology used to investigate wolf predation. Wolf natural expansion is an ongoing and controversial phenomena in the Northern hemisphere, and any technique that tells us more about their impact is a welcome addition to our knowledge base.


Cecilia Di Bernardi is an ecologist who is currently investigating wolf predation ecology within her PhD at the University of Rome La Sapienza in collaboration with SLU Swedish University of Agricultural Sciences. You can follow her on Twitter @c_dibernardi.

Divided and Conquered

Image credit: Alex Proimos, CC BY-NC 2.0, Image Cropped

Experimental habitat fragmentation disrupts nematode infections in Australian skinks (2019), Resasco et al., Ecology. https://doi.org/10.1002/ecy.2547

The Crux

Habitat destruction is an all-too-familiar side effect of human development and expansion. But another prevalent issue is habitat fragmentation, whereby habitat isn’t completely destroyed, but instead broken up into fragments and separated by developed areas. While some may think this is good, because there is still habitat available for wildlife to inhabit, the disconnected nature of what is left makes it very difficult for most wildlife to thrive, as they require much more connected landscapes.

Though fragmentation has been well studied in the past, less is known about how it affects parasites. Because they depend on other organisms for their own survival, parasites in particular are at risk of local or even extinction due to the cascading effects of species loss (i.e., coextinction, see Did You Know?). The complex nature of many parasite life cycles, in addition to a scarcity of experimental studies, makes it difficult to predict what effects that fragmentation will have on parasites. Today’s authors used a long-running, large-scale fragmentation experiment (The Wog Wog Habitat Fragmentation Experiment) to determine how fragmentation affects host-parasite interactions.

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Investigating the Financial Costs of Invasive Species

Economic costs of biological invasions in the United Kingdom (2021) Cuthbert et al., NeoBiota, https://doi.org/10.3897/neobiota.67.59743

The Crux

I write near constantly about non-native species on Ecology for the Masses, but I mainly focus on the negative impacts that many of them have on native ecosystems. Yet often if we want to really kick off initiatives to manage invasive non-native species, we need to point out the financial burden that many of them bring.

Yet obtaining a simple monetary estimate for invasive species is not easy. A few particularly notorious invasives tend to take up a lot of research focus, which mean that there are many species out there for which our cost estimates could be unreliable. Likewise, we’re likely to have a better picture of the impact of non-native species which have been established longer than ones who have just arrived, and haven’t been sufficiently studied or haven’t spread far enough to have had a measurable impact.

But non-native species aren’t slowing down in their spread anytime soon, so it’s important to figure out what the costs of invasive non-native have been and will be, as well as where there are holes in our knowledge that need to be filled. That’s what today’s study set out to do, by looking at invasive species in the United Kingdom.

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What Does it Take to be Indestructible?

The indestructible insect: Velvet ants from across the United States avoid predation by representatives from all major tetrapod clades (2018), Gall et al., Ecology & Evolution. https://doi.org/10.1002/ece3.4123

Image credit: Adam Hasik, image cropped

The Crux

Predation is a selective force that everyone is familiar with. One organism (the predator) kills and consumes another (the prey), and there is usually little nuance to the outcome of this interaction. The prey either escapes and survives, or it is killed and eaten. Due to this extreme pressure, prey organisms have evolved a remarkable array of defensive abilities and behaviors to attempt to reduce predation. Some colorful examples include the pufferfish and its ability to greatly increases its size, the octopus and its ink, or the hilarious (yet effective) behavior whereby the killdeer (a small bird here in North America) will make a lot of noise and fly a short distance before pretending its wing is broken in order to distract a predator from its offspring.

One animal that possesses a suite of such defensive abilities is the velvet ant (Dasymutilla spp.). Despite their name, velvet ants are a group of parasitoid wasps covered in a fine layer of setae (the velvet) where the females are wingless and look like ants. Because these females spend most of their time searching for ground-nesting insects to lay their eggs on/in and cannot fly, one might expect that these insects are particularly vulnerable to predators. But what’s really cool about these insects is just how many defenses that they have to ward off predators. First and foremost, they are brightly colored (just LOOK at that thing, nothing about that insect says “eat me”), which is usually enough of a warning in the natural world. Beyond their coloration, females also possess a venomous sting that is reputed to be one of the most painful stings in the world (see Did You Know?). I mean, that velvet ant in the featured image is colloquially known as the “cow killer” because of its painful sting. Velvet ants also possess a remarkably thick exoskeleton that is difficult to crush, and because it is rounded bites and stings tend to glance off of the abdomen. Today’s authors sought to understand just how effective all of these defenses were for reducing predation.

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