Tag Archives: ecology

It’s Who and Where You Are

A role for the local environment in driving species-specific parasitism in a multi-host parasite system (2022) Hasik & Siepielski, Freshwater Biology, https://doi.org/10.1111/fwb.13961

Image credit: Adam Hasik, image cropped

The Crux

Parasites are an ever-present part of every ecological community on Earth, yet there are some species that harbor more parasites than others. In systems where parasitism is density-dependent, meaning parasitism increases with host density, the most common/numerous species will harbor the greatest amount of parasites. Yet there are also cases of species-specificity, whereby parasites specifically target a single host species. In other host-parasite systems, local-adaption plays a role in parasitism dynamics, whereby parasites are better at attacking their local hosts than they are attacking foreign hosts and/or hosts are better at defending themselves from local parasites than foreign parasites.

With all of these different factors affecting how host-parasite systems operate, it is important to identify when and if each one is operating within specific ecological communities. This is especially necessary when ecological communities are comprised of multiple host species and multiple parasite species, all of which can/do interact with one another.

To investigate the above factors, we first conducted a survey of parasitism in damselflies (Enallagma spp.) and their water mite parasites (Arrenurus spp.). From there, we then carried out to field experiments to understand why parasitism operates the way it does within this system.

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My Enemy is Not the Enemy of My Other Enemy

Do predators keep prey healthy or make them sicker? A meta- analysis (2022) Richards et al., Ecology Letters, https://doi.org/10.1111/ele.13919

Image credit: Angah hfz, CC BY-SA 4.0, via Wikimedia Commons

The Crux

Ecology is all about understanding how the various parts of the natural world interact with one another. While we tend to think about things like predators, competitors, and parasites as separate entities that have their own effects, it is important to remember that these species interactions can interact with one another. Such interactions will have implications for the dynamics of natural populations.

Of interest is how predators and parasites interact with one another through their shared resources, prey/host species. Specifically, the Healthy Herds Hypothesis (HHH, see Did You Know?) predicts that predators reduce parasitism within the populations of their prey. While the HHH was based on a mathematical model, other theoretical models predict a range of effects, from predators decreasing parasitism to actually increasing parasitism. Because the empirical results from experimental studies show similar variation in their results, today’s authors wanted to determine if there is indeed a consistent, overall effect of predators on the parasitism of their prey.

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Your Immune Defenses Are What You Eat

Condition‐dependent immune function in a freshwater snail revealed by stable isotopes (2022) Seppälä et al., Freshwater Biology, link to article

Image credit: Bj.schoenmakers, CC0, via Wikimedia Commons

The Crux

There are myriad factors at play when it comes to parasitic infections, but the primary physiological barrier for the parasite is the immune function of host organisms. Despite its importance and usefulness, the immune function is costly to maintain. Building and effectively using immune defenses relies on the host being able to secure enough food to properly fuel its defenses. As a result, individuals in poor condition are more susceptible to parasites. Building off of that, if the conditions in a given area are poor/worsening, then an entire population of organisms may be vulnerable to disease outbreak.

Many studies have investigated the dependence of immune function, including one of my own, but many of those studies take place in lab settings where the food given to a host is carefully controlled. While there are obvious benefits to controlling experimental conditions, it can be hard to generalize the findings of a lab study to the natural settings that organisms actually live in. Today’s authors utilized an observational study of a freshwater snail (Lymnaea stagnalis) to better relate host condition in nature to immune function.

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Getting Hot Hot Hot

How melanism affects the sensitivity of lizards to climate change (2022) Mader et al. , Functional Ecology, https://doi.org/10.1111/1365-2435.13993

Image credit: Tony Rebelo, CC BY-SA 4.0, via Wikimedia Commons

The Crux

Climate change is a fact of life. Every day we uncover more of the negative effects it will have on the various animals, plants, and fungi in the natural world. Species range contractions are one such effect, and they occur when the area that a given species normally occupies shrinks. They are directly linked to a species’ risk of extinction, with this risk growing as a species inability to adapt to new environments grows. Though the theory sounds logical, many of the exact mechanisms behind range contractions are still unknown.

Ectotherms are organisms that depend on the surrounding environment to regulate their own body temperature, making them particularly vulnerable to climate change. Many different biological mechanisms are involved in regulating temperature, but the ability to reflect solar radiation is a key player. Indeed, the ability of organisms to reflect solar radiation (aka energy from sunlight) is part of the thermal melanism hypothesis (see Did You Know?). Melanistic (darker) organisms may be favored under climate change, due to the protection against UV radiation provided by melanin. However, melanistic individuals are more prone to increased heating, which can be bad. Today’s authors sought to understand how climate change would affect melanistic organisms.

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Why Are There So Many Species?

The causes and ecological context of rapid morphological evolution in birds (2022) Crouch & Tobias, Ecology Letters, https://doi.org/10.1111/ele.13962

Image credit: Andrej Chudý , CC BY-NC-SA 2.0

The Crux

One of the biggest questions facing evolutionary ecologists is why some groups of organisms contain SO MANY species, while others are relatively sparse in comparison. We’ve discussed adaptive radiations on Ecology for the Masses before, which is when a burst of speciation occurs within a group, with new species adapting to fill new ecological niches. It could be that the reason for such uneven groups is that some clades, or related groups of organisms, are more prone to such adaptive radiations than others. If this is true, it would mean that such clades experience not only an increase in the number of lineages (species) that they contain, but also the number of traits they exhibit.

Increases in the speciation rate and trait evolution are the hallmarks of adaptive radiations, but they may not occur at the same time, which can lead to some different outcomes. Clades may diversify rapidly, without really evolving new traits, and this is known as a “non-adaptive radiation“. In contrast, a lineage may quickly evolve new traits without speciating, which is known as an “adaptive non-radiation“. To understand the causes and context of such evolutionary scenarios, today’s authors studied the history of bird evolution.

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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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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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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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