Tag Archives: predation

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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Tool usage – something typically associated with (but definitely not exclusive to) primates. Yet polar bears are also a part of the DIY club and will sometimes turn to using rocks or chunks of ice to help them in taking down their prey. They have (as far as reports go) not yet gotten so far as to use catapults, but who knows…

Although knowledge of this behaviour isn’t really new (it has been observed and noted by Inuit hunters for generations) it does serve as a reminder that other animals can be just as handy should the need arise. Although tool use (or just ‘clever’ behaviour in general, such as tricking their prey to come closer) by bears isn’t something that’s observed often, it does occur and suggests that bears would probably rank high in what we would term ‘intelligence’. That being said, as long as we don’t have polar bears starting to use more ‘refined’ tools to do their hunting I’m happy – the idea of them ‘tossing’ about rocks is scary enough!

The review by Ian Stirling’s team that compiled different accounts of tool use by Polar Bears can be found here: https://doi.org/10.14430/arctic72532

Better Means Faster

Species interactions have predictable impacts on diversification (2021) Zeng and Wiens, Ecology Letters. https://doi.org/10.1111/ele.13635

Image Credit: MacNeil Lyons/NPS, CC BY 2.0

The Crux

No organism on the planet lives in complete isolation from other organisms. Many organisms serve as a food source for others, and even apex predators have to compete for their food. Species interactions like predation, competition, and parasitism directly impact organisms in their daily lives, but there is also a possibility that these same species interactions have had an impact on much longer timescales. That is, species interactions may have had a direct effect on the diversity of life on our planet.

Species interactions have been previously shown to affect diversification rates (see Did You Know?), so the question that today’s authors asked was whether there is a general trend to the effects of species interactions on diversification rates? Specifically, do species interactions with negative fitness (such as being killed by a predator) impacts decrease diversification rates, and do species interactions with positive fitness (such as successfully parasitizing a host) impacts increase diversification rates?

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Risk it for the Biscuit

Environmental controls on African herbivore responses to landscapes of fear (2021) Davies et al., Oikos. https://doi: 10.1111/oik.07559

Image Credit: Olga Ernst, CC BY-SA 4.0, Image Cropped

The Crux

Despite the incredible variation seen in nature when it comes to flora and fauna, it always seems like the two types that most people know are predators and prey. Prey animals being those that eat plants (or other animals), and the predators being those that eat those prey animals. Because prey animals must not only eat food, but try to avoid becoming food for something else, they must always be on the lookout. This watchfulness and awareness is what creates a “landscape of fear” (See Did You Know?), but variation is inherent to the natural world, and there are likely many things that prey animals consider when they pick where they decide to forage. Today’s authors wanted to investigate what factors influence the prey animals choice of foraging areas, and if that selection varies with the environment during the dry season when there isn’t much food available.

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Can A Harsh Climate Create Stronger Interactions Between Species?

Bowler et al. (2020) Impacts of predator-mediated interactions along a climatic gradient on the population dynamics of an alpine bird. Proceedings of the Royal Society B, 287, https://doi.org/10.1098/rspb.2020.2653.

The Crux

Whether or not a species will survive in an area can usually be broken down into two broad categories: how suitable the environmental characteristics of that area are (temperature, elevation, rainfall), and how it interacts with the other species found nearby. Early ecological theory predicted that in harsh environments, how a species interacts with other species wouldn’t matter as much, and would only come into play when the area was easier for the species to inhabit.

Yet more modern work often contradicts this theory. For instance, the Alternative Prey Hypothesis (APH) suggests that in areas where there are relatively few species as a result of harsh climates, interactions between those few species will be relatively strong. For example, if a prey species declines one year, then its usual predator must find an alternative prey species. This creates an indirect interaction between the two prey species, which is particularly strong in harsh environments where there aren’t other species around.

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Sometimes you need to pick your battles….

Dwarfism (or skeletal dysplasia) is a genetic condition rarely found in the wild – and observed in giraffes for the first time in 2017 and again (in a different population) in 2020. The fact that these free-ranging individuals have survived to adulthood (something that about only half of giraffe calves manage to do) suggests that they are still able to overcome threats to their survival (e.g. predation) despite their morphological differences. How they do this is of course of particular interest to researchers.

Read More: Mini Giraffes Spotted In Africa For The First Time Ever

Who knows – maybe they do have an advantage when it comes down to a fight….

Tanya Strydom is a PhD student at the Université de Montréal, mostly focusing on how we can use machine learning and artificial intelligence in ecology. Current research interests include (but are not limited to) predicting ecological networks, the role species traits and scale in ecological networks, general computer (and maths) geekiness, and a (seemingly) ever growing list of side projects. Tweets (sometimes related to actual science) can be found @TanyaS_08.

The Early Mouse Gets the Cheese

For small animals like the mouse, predators are a constant concern (Image Credit: Jess, CC BY-NC 2.0)

Maximising survival by shifting the daily timing of activity (2019) van der Vinne et al., Ecology Letters, https://doi.org/10.1111/ele.13404

The Crux

All animals need to eat food to survive and maintain their energy balance, but unlike us they can’t just order a pizza and have the food brought to them. They must always forage for food themselves, and every time that they do they expose themselves to predators. Small mammals like mice balance this trade-off by foraging for food at night, when their risk of predation is lowest.

One interesting strategy that mice can employ is to switch their foraging from the nighttime to the day, if they cannot get enough resources during the night or if their nighttime predation risk increases. The authors of today’s paper wanted to develop a model to predict under what conditions these temporal switches would occur, a model which they then tested with mice in the field.

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Living Among Beasts: Sharing the Burden of Conservation

African forest elephants populations are declining rapidly due to local human pressures. But is it fair to expect other humans to live among potential threats to their livelihood?

African forest elephants populations are declining rapidly due to local human pressures. But is it fair to expect other humans to live among potential threats to their livelihood? (Image Credit: US Fish and Wildlife Service Headquarters, Public Domain Mark 1.0, Image Cropped)

Some species of animal do a better job of capturing our attention than others. For many of us, the exotic nature of these animals is often the kicker. Think of the majesty of an elephant strolling across the savannah, or the romanticised stalk of the tiger through the jungle. Yet while the public ogles these creatures in the wild or at the local zoo and mourns the decline of their wild populations or the reported deaths of iconic individuals, we often ignore the harsh reality: that there are people who live in close proximity to these animals, to whom they represent a day-to-day threat. So how does our attitudes to charismatic species in places like Africa and Asia here need to shift, and where can we start?

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Keep Your Eyes Open

Image Credit: ulleo, Pixabay licence, Image Cropped

Natural selection favors a larger eye in response to increased competition in natural populations of a vertebrate (2019) Beston & Walsh, Functional Ecology, doi: 10.1111/1365-2435.13334

The Crux

Studying the evolution of traits in response to selection pressure often helps us understand why species look and act the way they do. Selection pressure can include the need to find food before other members of your species, or the need to escape predation.

But what happens when improving your ability to obtain resources also means you’re more vulnerable to predation? Which will win out? This paper looks at a small species of freshwater fish, Rivulus hartii, and determines which of the two pressures contributes most to the evolution of the size of their eye.

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Finished Before You Even Started

Predators are known to affect prey while they are adults and juveniles, but what about when they haven’t even hatched yet?  (Image Credit: Mark Jones, CC BY 2.0, Image Cropped)

Predation risk affects egg mortality and carry over effects in the larval stages in damselflies (2018) Sniegula et al., Freshwater Biology, p. 1-9

The Crux

In the natural world, one of the most dangerous things that a prey animal has to worry about is a predator. These organisms depend on the prey for their sustenance, and as such have become very good at finding ways to eat them. These are known as direct effects, as a predator eating prey is a direct interaction.

Another aspect of the predator-prey relationship is that of indirect effects, or effects that a predator has on prey that don’t involve it eating the prey animal. These can include predator-induced changes in the prey’s behavior, immune function, or even survival. These indirect effects are usually studied in prey species that are adults or juveniles, but the authors of today’s paper were interested in what indirect effects predators had on the eggs of prey species.

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