Tag Archives: competition

The Ramifications of Clashes Between Wolves and Bears

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Image Credit: Yellowstone National Park, CC BY 2.0, Image Cropped

Of wolves and bears: Seasonal drivers of interference and exploitation competition between apex predators (2021) Tallian et al., Ecological Monographs, https://doi.org/10.1002/ecm.1498

The Crux

I’ve written a lot about our relationship with top predators like bears and wolves on Ecology for the Masses, but their relationship with each other is also capable of having a big impact on their surroundings. When bears live in the same regions as wolves, predation levels are generally higher, but how much higher really depends on how much competition takes place between the two species.

Competition can take two forms out in the wild: interference competition, in which a bear might drive wolves away from a kill they’ve made, and exploitation competition, in which wolves have to search longer because bears have reduced the number of prey species in their area. Since both bears (through hibernation) and their prey species (through fixed mating cycles) vary in their behaviour throughout the year, could the type of competition that wolves face vary throughout the year as well? That’s what today’s authors wanted to find out.

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Not Giving Into the (Selection) Pressure

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A common measure of prey immune function is not constrained by the cascading effects of predators (2021) Hasik et al., Evolutionary Ecology. https://doi.org/10.1007/s10682-021-10124-x

Image Credit: Adam Hasik, Image Cropped

The Crux

The immune function is a critical component of an organism’s ability to defend itself from parasites and disease. Without it, we would be in much worse shape when we got sick. Despite this usefulness, the immune function is costly to use as organisms have to consume enough food to have the energy needed to mount an immune response. This is easier said than done, however, and there are often many factors that come into play when it comes to acquiring energy.

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Is the Enemy of My Enemy My Friend?

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Natural enemies have inconsistent impacts on the coexistence of competing species (2021) Terry et al., Journal of Animal Ecology. http://doi.org/10.1111/1365-2656.135434

Image Credit: Alandmanson, CC BY 4.0

The Crux

In nature, organisms are often competing with other organisms for food, mates, or even just for a place to call home. This competition comes in two forms: interspecific competition (meaning competition between two different species) and intraspecific competion (meaning competition within the same species). These two forms of competition play into the phenomenon known as mutual invasibility (see Did You Know), which is a necessary component of coexistence. If two organisms coexist, one species will not outcompete the other and drive it extinct, and thus the two species will coexist over time.

Because competition plays such a strong role in species coexistence, any factor that affects competition between two species has the potential to also affect coexistence. Today’s authors wanted to ask how an antagonistic species interaction (specifically, interactions with a parasitoid) affected coexistence in rainforest flies.

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New Neighbors

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Interspecific competition slows range expansion and shapes range boundaries (2020) Legault et al., Proceedings of the National Academy of Sciences, https://doi.org/10.1073/pnas.2009701117

Image Credit: CISRO, CC BY 3.0

The Crux

Climate change has resulted in multifarious changes in the natural world, not the least of which being where one can find a given species. Because areas are growing warmer, some species are shifting their habitats to stay within the type of environment that they like. The thing about shifting habitats though is that a species that shifts is likely to run into/need to compete with another species that is already there. Competition affects the growth and dispersal of organisms, so it follows that this should have an effect on the ability of a given species to shift or expand its range. However, most studies do not take competition into account when predicting range expansion.

A classic example in the scientific literature that did take competition into account was that of the gray squirrel invasion of Britain. Gray squirrels invaded and subsequently displaced the native red squirrels, but competition appeared to have no influence. Instead, a pathogen appeared to be the likely cause of the contraction of the red squirrel range. This example, however, comes from an observational study of a single replicate. Today’s authors instead conducted a manipulative lab experiment to test for the effects of competition on range expansion.

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The Healthy Male Wins the Mate

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Guest post by Miguel Gómez-Llano (Image Credit: Sharp Photography, CC BY-SA, Image Cropped)

Male-Male Competition Causes Parasite-Mediated Sexual Selection for Local Adaptation (2020) Gómez-Llano et al., The American Naturalist, https://doi.org/10.5061/dryad.cjsxksn35

The Crux

The natural world changes constantly: temperatures fluctuate, predators and parasites enter into the ecosystem, and the landscape itself could change (looking at you, Yellowstone). These changes mean that organisms are under a constant pressure to adapt to local conditions. Due to this pressure, one of the biggest questions for conservation biology is if species are able to adapt fast enough to keep up with environmental changes. Sexual selection is thought to promote rapid adaptation to such environmental changes, but most of the evidence comes from laboratory studies.

Our study looked at adaptation to one of nature’s ubiquitous pressures: parasitism. We were interested in the strength of selection by parasites and if there was subsequent adaptation by the host in a wild population.

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

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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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The Kids Are Not OK: Causes of Infanticide in Female Mammals

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The Bonnet Macacque, one of the 89 species in which females have been shown to commit infanticide (Image Credit: Vino Rex, CC BY 2.0, Image Cropped)

The evolution of infanticide by females in mammals (2019) Lukas & Huchard, Philsophical Transactions of the Royal Society – Biological Sciences, https://doi.org/10.1098/rstb.2018.0075

The Crux

The practice of male mammals killing their rival’s cubs has been well-documented by wildlife biologists. The image of a male lion striding away from a pride with a dead cub in his mouth is quite haunting (spare a though for Scar’s kids when Simba takes over again). But infanticide by female mammals has received less attention.

Whilst males generally only kill young to ensure they have more access to mates, the motivations behind infanticide in females are more complex. It ultimately comes down to resource competition, but the resources themselves are myriad – milk, availability of space, care from more than one ‘parental’ figure (allocare), and social status. These four resources make up the competing hypotheses as to why females commit infanticide. This week’s researchers wanted to know what factors of a species biology increased the likelihood of a mother to kill an infant of the same species.

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The Roles of Aquatic Predators

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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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How Different is Too Different?

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This Peruvian warbling-antbird must walk a fine line between being different enough from its competitors to reproduce successfully, while staying similar enough to be able to recognize and outcompete the same competitors (Image Credit: Hector Bottai, Image Cropped, CC BY-SA 4.0).

Range-wide spatial mapping reveals convergent character displacement
of bird song (2019) Kirschel et al., Proc B, https://dx.doi.org/10.1098/rspb.2019.0443

The Crux

In nature, many different organisms can be found in a single location, and sometimes those organisms are closely related to one another. When this happens, classical evolutionary theory predicts that these closely related species should differ in some ways, so as to differentiate members of their own species from others and avoid the costs associated with breeding with a mate that will not produce any viable offspring. This is called character displacement, and there are many examples of this in nature where two different species may be very similar when they live in different places (allopatry), but when they live in the same place (sympatry) they will differ in appearance, behavior, or the exact part of the local habitat that they live in (see Niche Partioning below).

A specific form of character displacement, called agonistic character displacement, occurs when traits or behaviors associated with competition differ between closely related species living in the same area. This is thought to reduce the costs of wasting energy on competing with an organism that you don’t really “compete” with. Agonistic character displacement can, however, result in greater similarity of traits when similar species live together, but previous studies in this area have not accounted for other causes of this similarity. Today’s authors wanted to do just that. Read more

Keep Your Eyes Open

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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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