Tag Archives: variation

The Water of Life

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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).

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Monitoring Freshwater Populations in the Chernobyl Exclusion Zone

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Radiation can have extremely negative effects on an individual. But is it as easy to measure its effects on an entire population? (Image Credit: Hnapel, CC BY-SA 4.0, Image Cropped)

Variation in chronic radiation exposure does not drive life history divergence among Daphnia populations across the Chernobyl Exclusion Zone (2019) Goodman et al., Ecology and Evolution, DOI: 10.1002/ece3.4931

The Crux

As anyone who has recently watched HBO’s Chernobyl can tell you, large doses of radiation are capable of doing some pretty serious damage to an organism. But whilst examining the effect of radiation on an individual might be simple, monitoring those effects on a population can be difficult. Whilst radiation negatively effects fitness, it can also help individuals with higher radiation tolerance to reproduce and dominate within the population of a single species, making it difficult to monitor the exact effects of radiation on that population. If a population is filled with only those who were strong enough to survive, you don’t get an idea of the variation in the radiation’s effects.

This week’s researchers tried to break through that problem by looking at different populations of a water flea in Chernobyl’s Exclusion Zone (CEZ) – the area still barred from entry in eastern Europe.

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Are Animals Doing the Wrong Thing?

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The great tit (Parus major) needs to gain more than 10 % of its body weight in pure fat every evening, in order to survive a cold winter night (Image Credit: Frank Vassen, CC BY 2.0, Image Cropped)

Short-term insurance versus long-term bet-hedging strategies as adaptations to variable environments (2019). Haaland, T.R. et al., Evolution, 73, 145-157.

The Crux

Why do animals behave the way they do? Behavioral ecology is a field of research trying to explain the ecological rationale of animal decision making. But quite often, it turns out the animals are doing the ‘wrong’ thing. Why don’t all animals make the same choice, when there clearly is a best option? Why do animals consistently do too little or too much of something?

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Battle of the Sexes

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If male and female predators like this newt hunt in different places, they may have different effects on prey communities. (Image Credit: Dave Huth, CC BY 2.0, Image Cropped)
Sexual dimorphism in a top predator (Notophthalmus viridescens) drives aquatic prey community assembly (2018) Start & De Lisle, Proceedings B, doi:10.1098/rspb.2018.1717

The Crux

Ecology is a scientific discipline focused on the interactions between the biotic (living) and abiotic (non-living) parts of the environment, and within ecology the subdiscipline of community ecology focuses on how these biotic and abiotic parts interact to determine what species live where. When researchers investigate these relationships, they tend to only consider differences between species, instead of differences within a single species. This means that we are missing a big part of the picture, as differences within a single species can outnumber those between multiple species.

One of the most common differences within a species are those between males and females. Depending on the species in question, one sex can be bigger, eat more, live longer, or eat different things, and this can have an effect on the community that the species in question lives in. Despite these many differences between the sexes, there weren’t any direct empirical examples in the scientific literature of these differences affecting community dynamics. The authors of this paper were the first to use an experiment to investigate this phenomenon, using the red-spotted newt (Notophthalmus viridescens), which is an important predator in aquatic communities.

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