Author Archives: Adam Hasik

Inbreeding is Depressing

Sex-specific inbreeding depression: A meta-analysis (2021) Vega-Trejo et al., Ecology Letters, https://doi.org/10.1111/ele.13961

Image credit: Monica R., CC BY 2.0, Image Cropped

The Crux

One very basic rule in nature is that it is bad to produce offspring with a close relative. The loss of fitness associated with this sort of breeding is called the inbreeding depression, and it happens because inbreeding leads to a greater chance that recessive or deleterious (i.e., bad) alleles will be expressed. Though inbreeding affects both male and female offspring, it is unknown as to whether or not there is a general rule of it affecting one sex more than another. Today’s authors sought to answer that question by using one of my favorite statistical techniques: the meta-analysis (see Did You Know?).

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Mussel Mass

Facilitation alters climate change risk on rocky shores (2022) Jurgens et al. 2022, Ecology, https://doi.org/10.1002/ecy.3596

Image credit: Paul Asman and Jill Lenoble, CC BY 2.0, Image Cropped

The Crux

Climate change has a marked effect on the environment, and in most cases will be (and already is) devastating to natural systems. However, some areas (and the organisms within them) are less vulnerable to harm than others. Biogenic habitats, or habitats created by a given species which reduce physical stress for other species that live in them (more in Did You Know?), are predicted to reduce the harmful effects of climate change. In particular, they can reduce heat and desiccation.

There have been an abundance of studies on the positive effects of biogenic habitats, but little has been done to explore if these habitats can provide protection against climate change. Today’s authors utilized a marine system to understand how biogenic habitats respond to climate change, allowing for predictions of what will happen to these systems.

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It Takes A Village

Testing the parasite-mediated competition hypothesis between sympatric northern and southern flying squirrels (2022) O’Brien et al. 2022, International Journal for Parasitology: Parasites and Wildlife, https://doi.org/10.1016/j.ijppaw.2021.11.001

Image credit: Stephen Durrenberger, CC BY-NC-SA 2.0, Image Cropped

The Crux

One consequence of climate change is that organisms move to new habitats, as they try and track suitable environmental conditions. This can result in closely related species coming into contact with one another, which in turns drives competition among these organisms. Competition between these organisms can manifest as either direct competition (where two organisms directly compete with one another for food or habitat), but it can also manifest as apparent competition.

Apparent competition happens when species A serves as a food source for predators or parasites, which increases the numbers of predators/parasites in the environment. This increase in predators or parasites then puts more pressure on species B. Apparent competition via parasitism was actually a major driver for the decline of red squirrels in the UK, as the introduced grey squirrel brought along squirrelpox virus that had severe effects on the red squirrels.

If one species is more tolerant to a parasite than another, this can result in competitive exclusion, where one species outcompetes the other species to such an extent that the outcompeted species goes locally extinct. This is particularly important when a climate-mediated range expansion brings two species together that share parasites. Today’s authors sought to quantify how infection by parasites affected a vulnerable population after a range expansion by a potential reservoir species.

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Bigger is Better

Population size impacts host-pathogen coevolution (2021) Papkou et al. 2021, Proc B, https://doi.org/10.1098/rspb.2021.2269

Image credit: Kbradnam, CC BY-SA 2.5, via Wikimedia Commons

The Crux

Host-pathogen interactions are maybe best characterized as a battle – a pathogen (a parasite that causes disease) doing what it can to maximize how much it can get from a given host organism, and a host doing what it can to defend itself from this endless attack. As a result, hosts and pathogens are locked in an endless evolutionary battle, whereby hosts evolve to better defend themselves and pathogens evolve to better attack the host. A key factor in this battle is population size, as this affects the evolutionary potential of a given population of organisms to respond to selection.

The larger a population of hosts, the more novel genetic variants there are, which are simply organisms with different genetic make-ups, which can be the result of mutations popping up or through combinations with other genetic variants within the population. The more variation there is, the more diverse the population is, and the more chance it has of carrying the genes that could help it respond to a new threat, like a pathogen.

This means that a larger host population is more likely to have a genetic variant that is able to defend itself from these pathogens. That variant will then be selected for and the host population will become more resistant to that pathogen over time. While a lot of theory has been dedicated to understanding these coevolutionary battles, actual experimental evidence is lacking. Today’s authors used a model system to conduct evolutionary experiments to test the effect of host population size on host-pathogen coevolution.

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Small Creatures, Large Effects

Arthropod predation of vertebrates structures trophic dynamics in island ecosystems (2021) Halpin et al., The American Naturalist, https://doi.org/10.1086/715702

Image credit: Bernard Dupont, CC BY-SA 2.0, via Wikimedia Commons

The Crux

Predator-prey dynamics are (I think) the most well-known species interaction out there. Not everyone is a scientist, but almost everyone has seen an image of a cheetah running down a gazelle, a great white shark exploding out of the water as it hammers a seal from below, or wolves teaming up on a much larger herbivore.

These interactions are not only fascinating and captivating, they are also key to structuring communities. For example, the damselflies that I worked with during my PhD occur in two different kinds of lakes: fish lakes and dragonfly lakes. The type of predator alters the lake significantly: damselflies that live in fish lakes are adapted to “hide” from their fish predators by not moving. Not moving in a dragonfly lake means that a dragonfly will eat you.

Though these interactions have been (justifiably) studied to an extreme extent, there are still knowledge gaps out there. Of interest for today’s study is the effect of invertebrate predators on vertebrate prey. While these invertebrate predator/vertebrate prey interactions have been studied in marine and freshwater environments, little work has been conducted in terrestrial systems. This is especially hard to do with invertebrate predators of vertebrate prey, because such predators tend to be hard to find, nocturnal, and they also hunt in more “concealed” environments like leaf litter. To overcome these challenges, today’s authors utilized the Phillip Island centipede (Cormocephalus coynei, which is NOT the centipede featured in this post’s image) and stable isotope analyses (see Did You Know) to understand how invertebrate predators structure food web dynamics.

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Started at the Bottom, Now We’re Here…

Predicting how climate change threatens the prey base of Arctic marine predators, Florko et al., 2021 Ecology Letters. https://doi.org/10.1111/ele.13866

Image credit: Kingfisher, CC BY-SA 3.0

The Crux

We are all (unfortunately) very familiar with the effects of climate change on arctic ecosystems. Horrifying images of polar bears on small blocks of ice and the shrinking polar ice caps are but two of the many results of a warming climate, yet a great deal of the work in the realm has focused on the the charismatic, apex species (like the aforementioned polar bear). These are obviously important things to consider, but it is also necessary to look into the effects of climate change on the lower positions within food webs, as any change to these organisms and processes are likely to cascade upwards to effect the upper trophic levels (like our friend the polar bear).

Hudson Bay in North America is one such area impacted by our warming climate. Due to the changes in temperatures, the energy flowing through ecosystems has shifted away from away from species living in the ice and on the bottom. As a result pelagic (free-swimming) species are favored over benthic species (those living on the bottom of the bay), which alters the rest of the food web itself. Specifically, the fish that feed on pelagic species are increasing, while those that feed on benthic species are decreasing. Today’s authors wanted to understand how these changes in fish numbers are will affect Arctic predators, namely the ringed seal (Pusa hispida).

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Bad Neighbors

The disruption of a keystone interaction erodes pollination and seed dispersal networks, Vitali et al., 2021 Ecology. https://doi.org/10.1002/ecy.3547

Image credit: Ennio Nasi, CC BY 4.0

The Crux

Ecological communities are incredibly complex networks, made up of interactions between the species that reside in them. To properly understand how these interactions shape a community, researchers have to employ a variety of analytical methods and modelling approaches. This was something that I had to learn to appreciate in my work, because I always thought that studying ecology would involve a lot of time outdoors working with animals. While that does happen (and I spent months outside during my PhD), most of the ecological research I’m familiar with centers on math and statistics.

Using math and statistics to model ecological communities helps us to break down how various organisms are connected with one another. For example, keystone species are organisms that are connected to so many others within a given ecosystem such that any change to their populations will have consequences for the entire community. Understanding the processes that affect these keystone individuals (and all of the organisms linked to them) is vital to predicting how processes such as climate change and invasive species will affect natural communities in the future.

Today’s authors investigated how disruption of an important species interaction affected pollination and seed dispersal networks in Patagonia. A hummingbird species (Sephanoides sephaniodes) is the main pollinator for a mistletoe species (Tristerix corym-bosus), while the mistletoe provides the hummingbird with nectar in the winter. The colocolo opossum (Dromiciops gliroides) is a small marsupial that is vital for the mistletoe, as mistletoe seeds must pass through the opossum’s gut to trigger their germination. Additionally, the opossums defecate many seeds on branches in a “necklace” arrangement, which likely helps the mistletoe to parasitize their plant hosts. These three species are tightly connected to one another, and any reduction in abundance for one species may affect the other two, and even destroy the entire food web.

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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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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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