Author Archives: Adam Hasik

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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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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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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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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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Measuring Immunity With Transparent Hosts

Host controls of within-host dynamics: insight from an invertebrate system (2021) Stewart Merrill et al., The American Naturalist. https://doi.org/10.1086/715355

This is a guest post by Dr. Tara Stewart Merrill

Image Credit: Per Harald Olsen, NTNU, CC BY 2.0, Image Cropped

The Crux

When it comes to understanding how parasites and pathogens spread, immune defenses may be an especially important factor. The immune system is the gatekeeper for parasites and pathogens (I’ll just use the term “pathogen” from here on out). Whether you are exposed to influenza, a parasitic worm, or a tick-borne bacterium, your immune response will determine the outcome of infection — either you will become infected (which benefits the pathogen’s reproduction) or you will not (which is a barrier to the pathogen’s reproduction). So now, picture a whole population of individuals. A room full of individuals with poor immune responses should result in more infections (and more transmission) than a room full of individuals with strong and robust immune defenses. By shaping the fate of pathogens, host immune defenses can shape transmission.

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Some (Don’t) Like it Hot

Do latitudinal and bioclimatic gradients drive parasitism in Odonata? (2021) da Silva et al., International Journal for Parasitology. https://doi.org/10.1016/j.ijpara.2020.11.008

Image Credit: Adam Hasik, image cropped

The Crux

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).

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Not Giving Into the (Selection) Pressure

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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Incorporating Parasites Into Community Ecology

I’ve said it before and I’ll say it again until I retire*: parasitism is THE most interesting (and arguably the most successful) life history strategy on the planet. Parasites are present in every ecosystem on the planet, and it is incredibly unlikely that any study system or ecological community is parasite-free. So why don’t we talk about them more?

As a disease ecologist, my work focuses on parasites and their place in the natural world, so I think about these organisms a lot. My PhD was centered on incorporating parasites into food webs to understand how they affect species interactions (and how species interactions in turn affect them). Failing to consider parasites can lead scientists to miss important aspects of an ecosystem and draw false conclusions.

Yet most ecological studies – even those which look at entire communities – fail to consider parasites and their effects on other organisms. I can’t blame them, parasite ecology can be difficult to get your head around. So today, I want to try and give ecologists everywhere some tips on incorporating parasites into their work.

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Is the Enemy of My Enemy My Friend?

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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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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