Tag Archives: food web

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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Making Food Webs Out Of (Almost) Nothing At All

Food web reconstruction through phylogenetic transfer of low-rank network representation (2022) Strydom and Bouskila et al., Methods in Ecology and Evolution, https://doi.org/10.1111/2041-210X.13835

The Crux

Understanding food webs (and more generally how different species interact) is important in helping us to understand ecological processes, but sampling (observing) interactions in the field is pretty challenging. Observing a parrot? Simple. Observing a possum? No problem. Observing a parrot evicting a possum from a tree-hollow? Rarer.

This means that data on species interactions is sparse. But we do have data for some regions, and things like computers and fancy maths (think machine learning) at our disposal. Which leads to the question: can we learn something from the places for which we do have interaction data and ‘transplant’ this knowledge and create an interaction network for a region with no data at all?

The focus here is to try and use predictive methods to help and at least give us a idea of who might potentially be eating who and use this to construct a metaweb (a full list of potential interactions) for a region that has plenty of species data, but no species interaction data.

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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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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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How Influential is the Platypus in Freshwater Dynamics?

Image Credit: Maria Grist, CC BY-SA 4.0, Image Cropped

Platypus predation has differential effects on aquatic invertebrates in contrasting stream and lake ecosystems (2020) McLachlan-Troup, Scientific Reports, https://doi.org/10.1038/s41598-020-69957-1

The Crux

A trophic cascade occurs when a predator’s effects of its prey goes on to affect ‘lower’ levels of that ecosystem. A great example is the effect that sea otters have on kelp: the sea otters prey extensively on sea urchins, which in turn increases the populations of kelp, which the sea urchins prey on. While this is a result of direct predation by otters, often this can occur through a prey species changing its behaviour to avoid the predators.

Yet most ecosystems are more complex than a simple three-level trophic system. Cascades are therefore more likely to occur when the ecosystem is less complex, or when there are well-defined relationships between species, as a result of a predator having preferred prey species or only a few groups of species making up an ecosystem.

This week’s authors investigated how the platypus (our recently-found-to-be-fluorescent friend) influences the abundance and species richness of invertebrates across both rivers and lakes, and whether it’s capable of affecting an ecosystems algae and sediments as well.

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Consider the Copepod: Researching the Base of the Food Web (with Dr. Nancy Mercado-Salas)

Image Credit: Andrei Savitsky (left and right), CC BY-SA 4.0 ; Uwe Kils (centre), CC BY-SA 3.0

The deep sea is a wondrous world of biodiversity, darkness, and mysteries we still know very little about. Despite the fact that we rely on the deep sea as a sink for carbon dioxide – and increasingly as a source of natural gases and minerals – we have very little understanding of how our actions will affect its intricate food web.

Near the base of the food web sits an incredibly diverse group of animals called copepods. They are so abundant and have such sweeping variety that we are still struggling to come up with a way to classify them. Dr. Nancy Mercado-Salas has worked with these tiny creatures since her bachelor’s thesis, both in freshwater and in marine ecosystems, and her message is clear: We need to increase our knowledge on this group of animals before it is too late.

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It’s EVERYWHERE: The true extent of microplastics

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

Quantitative analysis of selected plastics in high-commercial-value Australian seafood by pyrolysis gas chromatography mass spectrometry (2020) Ribeiro et al., Environmental Science & Technology, https://doi.org/10.1021/acs.est.0c02337

The Crux

Plastic is one of those things that we hear about all the time these days. More specifically, we hear about how there is an absolute ton of it in the environment thanks to human negligence and the lack of concern that a large amount of people have for where their plastic goes when they are finished with it. Plastic isn’t like paper or metal, it takes a long, LONG time for it to break down. Plastic bags take anywhere from 10-20 years, but the normal time it takes for most plastic waste to decompose is about 1000 years. To put that into perspective, Leif Erikson led an expedition from Greenland to the coast of what is now North America in the year 1002. If his crew had some plastic with them and left it in the places they visited (typical tourists) there’s a good chance that it would STILL be there today.

I hope I’ve convinced you why plastic is bad, but another danger that plastics pose are microplastics, small bits of plastic that have come from a larger piece, all of which are less than 5mm in size. Our environment is full of them, and the ocean in particular has been saturated with microplastics. In 2014 a research expedition sailed from Bermuda to Iceland (a trip of 2500 miles/4023 km) and found microplastics in every single sample they took. And that was just plastic in the environmental samples they took, the real threat to marine life comes from what happens to all of that microplastic.

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How Form Defines Function

Image Credit: Francesco Veronesi, CC BY-SA 2.0, Image Cropped

Macroevolutionary convergence connects morphological form to ecological function in birds (2020) Pigot et al, Nature Ecology & Evolution, https://doi.org/10.1038/s41559-019-1070-4

The Crux

There are an astounding amount of different forms that the animals on our planet take. Likewise, there are a multitude of diverse functions that animals serve in the environment, such as that of a herbivore, a predator, or scavenger. In some cases it’s a clear link between the form of a given animal and its function in the environment, like that of the beak of a hummingbird that allows it to feed on nectar and their role as a pollinator. But whether or not there is a reliable way to predict the function of an animal based off of its form is has been the subject of considerable controversy.

Deciding on how many morphological traits to use to predict ecological function is a difficult prospect. One could argue that it’s impossible to pick a finite number of traits, as there are infinite possible niches that organisms can fill so there’s no way that a set of traits could fill those infinite possible niches. Mapping animal form to function has major implications for quantifying and and conserving biodiversity, and the authors of today’s paper wanted to to determine just how many traits are needed to do that.

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