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The Water of Life

Posted on October 5, 2022 by Adam Hasik Leave a comment

Image credit: Muséum de Toulouse, CC BY-SA 4.0, via Wikimedia Commons

Top-down response to spatial variation in productivity and bottom-up response to temporal variation in productivity in a long-term study of desert ants (2022) Gibb et al., Biology Letters, https://doi.org/10.1098/rsbl.2022.0314

The Crux

Ecosystem productivity can tell us a lot about how an ecosystem functions. The more productive an ecosystem is, the more life it can support. But productivity doesn’t just affect the diversity or number of species within an ecosystem, it affects how those species interact, from the large carnivores you find at the upper levels, to the plants and bacteria down the ‘bottom’.

Within ecosystems, the strength of a top-down process (something influencing those upper levels) vs. a bottom-up process (something influencing the lower levels) depends on how much primary productivity there is. Primary production occurs when a species makes its own energy instead of eating something else, and when there is a lot of it going around, it often allows the carnivores at the upper trophic levels to suppress the population numbers of herbivores. That means that while a bottom-up process may end up affecting the herbivores, a top-down process (like the hunting of carnivores) might impact the entire ecosystem.

On the other side of the spectrum, when there is little primary productivity, there aren’t usually as many carnivores suppressing the herbivore populations. A bottom-up process will increase herbivore numbers, making these bottom-up processes more important in these low-productivity systems. This is known as the Exploitation Ecosystem Hypothesis (EEH).

My Enemy is Not the Enemy of My Other Enemy

Posted on June 23, 2022 by Adam Hasik Leave a comment

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.

Can You Afford to be Picky?

Posted on April 27, 2022 by Adam Hasik Leave a comment

The better, the choosier: A meta-analysis on interindividual variation of male mate choice (2022) Pollo et al. , Ecology Letters, https://doi.org/10.1111/ele.13981

Image credit: barloventomagico, CC BY-NC-ND 2.0

The Crux

Choosing who to reproduce with (mate choice – see Did You Know?) is a major player when it comes to the evolution of a species, yet it can be tough to know when individuals (and which individuals) should be choosy in their partners. A general trend is that when there are a plethora of potential mates available, too many for a given animal to mate with, they must make decisions on who to mate with. For many species, females tend to be the choosy sex, given the limited number of reproductive resources that are available to them (i.e., eggs) and how many males are usually available to mate.

Despite this commonality of female mate choice, male mate choice is also widespread in the animal kingdom. It is therefore important to know how different factors affect how a male chooses his mates. One factor that may play a key role is male quality, or the ability of a male to acquire mates. It could be that males that vary in their quality also vary in how picky they are. Today’s authors used a meta-analysis, or a “study of studies”, to understand how males make their decisions.

Sunstruck

Posted on April 7, 2022 by Tanya Strydom One comment

Viruses are weird – they are non-living, yet still contain genetic information and are dependent on a live host to actually replicate and survive. Unlike many other parasites, since viruses are basically just a string of DNA or RNA, they actually need to actually get inside the cells of their host and hijack some of the components of these cells to allow them to replicate. After infection they are (at least partially) in the driving seat and can control and manipulate how some cells behave.

This means that viruses often have the capacity to also alter the behaviour of their host – which can be particularly beneficial to help ensure that the virus can also spread from one host to another. A good example is rabies, whereby the virus triggers infected individuals to become exceptionally aggressive – a surefire way to probably lead to them biting another individual and allowing infection to occur via the bite wound.

Sometimes the behavioural changes can be more nuanced – in this case caterpillars infected by a baculovirus start perceiving then sun in a positive light (pun definitely intended). Infected caterpillars become attracted to sunlight and feel compelled to move towards it (this process is known as phototaxis). Unfortunately in this case is is drawing them to an untimely death. Having the caterpillars die near the tree canopy is beneficial for the virus, as its a better scouting ground for newer hosts.

Tanya Strydom is a PhD candidate at the Université de Montréal, mostly focusing on how we can use machine learning and artificial intelligence in ecology. Current research interests include (but are not limited to) predicting ecological networks, the role species traits and scale in ecological networks, general computer (and maths) geekiness, and a (seemingly) ever growing list of side projects. Tweets (sometimes related to actual science) can be found @TanyaS_08.

Uncategorized

The Lazy Bird Gets the Worm

Posted on March 3, 2022 by Adam Hasik Leave a comment

A fine-scale analysis reveals microgeographic hotspots maximizing infection rate between a parasite and its fish host (2021) Mathieu-Bégné et al., Functional Ecology, https://doi.org/10.1111/1365-2435.13967

Image credit: Viridiflavus via Wikimedia Commons, CC BY-SA 3.0

The Crux

Interactions between hosts and parasites can be broken down into two broad stages: the encounter filter and the compatibility filter. The encounter filter determines whether a parasite actually comes in contact with a host, through either a spatial or temporal overlap. After the encounter filter comes the compatibility filter, the stage at which a parasite either successfully infects a host and takes the resources needed, or is successfully repelled by the host. Though the encounter filter must come before the compatibility filter, most studies tend to focus on the compatibility filter. Yet for a parasite to successfully encounter a host, many obstacles must first be overcome.

Parasites tend to be very small, and hosts tend to be rare. Furthermore, many hosts move around the environment and/or are only available to a parasite at specific times of the year. Finally, in many cases the environment that a single host can occupy is huge. With all of these difficulties facing parasites, it is not surprising that they have evolved many different strategies to effectively find hosts.

However, some species don’t appear to display these strategies. For them to succeed, it is possible that they distribute themselves in a non-random (see Did You Know?) fashion in the environment, clumping together to form “hot-spots” of infection. Other studies have investigated this “hot-spot” phenomenon before, but tended to focus on larger spatial scales, anywhere from hundreds to thousands of meters. Today’s authors wanted to understand if investigations at much smaller spatial scales (i.e., ~10 meters or less) could provide further insight into the spatial aggregation of parasites.

Mainstream

Posted on February 25, 2022 by Tanya Strydom One comment

Bird and whale song are a way for males to attract members of the opposite sex, and (as the variety of bird calls you might hear out in the garden indicates) these songs vary between species. Similar to how people can have different tastes in music, there is also variation in the the style of the songs between individuals of the same species. This can lead to ‘cultural revolutions’ where some individuals can influence and change the mating calls of the other individuals in the population if they want to stay relevant.

This poses an interesting question of if and how animals value and appreciate aesthetic beauty and how similar that is to how humans view ‘aesthetic beauty’ – and of course implies that bird and whales must have some kind of Billboard 100 chart floating around!

The idea of cultural evolution in non-human animals is a growing topic of discussion but if you want to know more about how whale songs change check out the link below.

Location Location Location

Posted on October 14, 2021 by Adam Hasik Leave a comment

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.