Tag Archives: predator

Don’t Compete If You Don’t Want to Get Eat(en)

Image Credit: Judy Gallagher, CC BY 2.0, Image Cropped

Predators weaken prey intraspecific competition through phenotypic selection (2020) Siepielski, Hasik et al., Ecology Letters, https://doi.org/10.1111/ele.13491

The Crux

We are all familiar with predator-prey relationships in nature, those in which one organism (a predator) kills and consumes another (the prey). Besides these direct effects on prey via consumption, predators can also impose indirect effects on their prey. An indirect effect is one in which the predator changes some aspect of the prey, such as their behavior or the way that they look, but these changes are brought about just by the predator being around. These predator-mediated effects are known to affect the relationships between prey organisms themselves, such as how prey organisms compete with one another, whether its for food, mates, or other resources.

Predators are known to affect how active their prey are, and this selection on activity results in a trade-off between how much prey can grow and their risk of predation. Being more active can allow you to find and eat more food, but that also means that a potential predator is more likely to see you. Today’s paper used larval damselflies and their fish predators to study how selection of fish on their damselfly prey based on the damselfly activity rates affected competition between the damselflies.

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Protection from Two Enemies with One Defense

Image Credit: Connor Long, CC BY-NC-SA 3.0, Image Cropped

Of poisons and parasites—the defensive role of tetrodotoxin against infections in newts (2018) Johnson et al., Journal of Animal Ecology, https://doi.org/10.1111/1365-2656.12816

The Crux

Many organisms in nature produce powerful (and sometimes deadly) toxic substances, often taken as evidence that prey evolved chemical defenses against predators. Interestingly, these chemical defenses are deadly not only to predators, but also to parasites. This complementary defense, in addition to the ubiquity of parasites themselves, indicate that parasites may have had a hand in the evolution of host toxicity.

One particularly potent toxin found in the animal kingdom is tetrodotoxin (TTX). It can cause paralysis, difficulty with breathing, and even death in some cases. Newts in the genus Taricha are notorious for having high concentrations of TTX in their skin and eggs, and this has long been thought to have evolved as a defense against predators. In particular, Taricha newts and garter snakes (Thamnopholis spp.) are a classic example of arms-race dynamics (see Did You Know). Despite this relationship, newt toxicity and snake resistance to the toxin don’t always match up perfectly in nature, suggesting that other factors may influence newt toxicitiy. The goal of today’s study was to study parasitic infection and compare it to variation in toxicity among two newt species, the rough-skinned newt (T. granulosa) and the California newt (T. torosa).

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Brains Over Brawn

Image Credit: Kevin Pluck, CC BY 2.0, Image Cropped

Brain expansion in early hominins predicts carnivore extinctions in East Africa (2020) Faurby et al, Ecology Letters, https://doi.org/10.1111/ele.13451

The Crux

We’ve covered humans and their harmful effects many times here on Ecology for the Masses (see my recent breakdown from last month). Despite all of the colorful examples of our current effects on the wildlife of our planet, a significant amount of research has implicated Homo sapiens as the driver of the extinction of some of the megafauna of the prehistoric world, events that happens millions of years ago. Another possibility is that we as organisms (hominins, not Homo sapiens specifically) have been impacting other species for a very, very long time.

Today, East Africa is home to the most diverse group of large carnivores on the planet (though it is still less diverse than what was once seen in North America and Eurasia). Millions of years ago East Africa had an even more diverse assemblage of large carnivores, including bears, dogs, giant otters, and saber-toothed cats. The change in climate since that time may have caused the decline in large carnivore diversity, but another explanation is the rise of early hominins (our ancestors). Using fossil data, the authors of today’s paper wanted to figure out if it was indeed early hominins that drove many large carnivores extinct.

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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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Outdoor Cats are a Problem

Outdoor cats are a contentious issue for cat-owners, cat-lovers, and those that are concerned about the environment. Like it or not, Fluffy is doing a LOT of damage (Image credit: Cat Outside in Sweden-148884.jpg by Jonatan Svensson Glad, CC BY-SA 4.0, Image Cropped).

I hate to be the bearer of bad news, but domestic cats are bad for the environment. Sure, we as a species have adopted and incorporated them into our society (I live with two, myself), but that doesn’t mean we aren’t responsible for them and their actions.

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Do As I Do

Predators like these Great tits (Parus major) eat a wide variety of insects, but some of those insects are so unpleasant to eat that birds tend to avoid them. How does this trait evolve in prey animals when its maintenance and origin depend on the predators learning by eating them? (Image Credit: Shirley ClarkeCC BY-SA 3.0).

Social information use about novel aposematic prey is not influenced by a predator’s previous experience with toxins (2019) Hämäläinen et al., Functional Ecology, https://dx.doi.org/10.1111/1365-2435.13395

The Crux

Many animals in nature have evolved a defense strategy known as aposematism, meaning that they display warning colors or patterns that tells predators that they are not worth eating due to their toxicity. Predators can learn to avoid aposematic prey by either sampling different prey animals and learning for themselves, or they can watch other predators eat different prey species and, depending on the reaction of that predator, learn what may or may not be good to eat.

The paradox of the evolution of this aposematic trait is that toxic prey species are not only highly visible and easily noticed by predators, but they must be attacked in order for predators to learn that they shouldn’t eat them, meaning that these prey species may not even survive long enough for them to enjoy the benefits of predator avoidance. The question then becomes are aposematic prey able to persist in nature because predator learn to avoid them? The authors of today’s paper wanted to investigate how predators that have learned to avoid toxic prey will watch and learn from other predators eating new, possibly toxic prey.  Read more

The Roles of Aquatic Predators

Image Credit: Neil Hammerschlag, Oregon State University, Image Cropped, CC BY-SA 2.0

Ecosystem Function and Services of Aquatic Predators in the Anthropocene (2019) Hammerschalg et al., Trends in Ecology and Evolution, https://doi.org/10.106/j.tree.2019.01.001

The Crux

Aquatic predators play an important role in many ecosystems, and are often among the more charismatic species in the ecosystem. Because of this, they are often the target of conservation for ocean management bodies worldwide. This paper aims to provide a synthesis of the ecosystem services that aquatic predators provide in marine and freshwater ecosystems worldwide. Below, we’ve chosen 4 of the more interesting and important roles to go into.

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To Blend in or Stand Out?

Body coloration of an animal can be useful for not only attracting prey, but also avoiding being eaten. One important question is whether or not this coloration can simultaneously serve both purposes? (Image Credit: Chen-Pan LiaoCC BY-SA 3.0, Image Cropped).

Multifunctionality of an arthropod predator’s body coloration (2019) Liao et al., Functional Ecology, https://dx.doi.org/10.1111/1365-2435.13326

The Crux

One topic that has interested ecologists for decades is that of animal body coloration, and what function that coloration can serve for the animal. Despite this fascination and the work that has been done to study this aspect of animal biology, the actual mechanisms driving the evolution and maintenance of body color are not well understood. Many different aspects of an organism’s life can shape and affect body color, such as avoiding predators, attracting mates, and whatever resources an organism has available to create specific colors. In addition, many of these aspects often compete with one another, such that a color that is good for attracting mates may also make you more easily-spotted by a predator.

Spiders provide an excellent system in which to study the evolutionary significance of body colors, as previous work has shown that body color affects mate attraction, predator avoidance, and prey attraction. The authors of today’s study wanted to know if these complex color patterns could serve more than one function in the spider’s life.
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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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Are Animals Doing the Wrong Thing?

The great tit (Parus major) needs to gain more than 10 % of its body weight in pure fat every evening, in order to survive a cold winter night (Image Credit: Frank Vassen, CC BY 2.0, Image Cropped)

Short-term insurance versus long-term bet-hedging strategies as adaptations to variable environments (2019). Haaland, T.R. et al., Evolution, 73, 145-157.

The Crux

Why do animals behave the way they do? Behavioral ecology is a field of research trying to explain the ecological rationale of animal decision making. But quite often, it turns out the animals are doing the ‘wrong’ thing. Why don’t all animals make the same choice, when there clearly is a best option? Why do animals consistently do too little or too much of something?

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