Tag Archives: population

Why Warmer Winters Don’t Always Help Geese

Contrasting consequences of climate change for migratory geese: Predation, density dependence and carryover effects offset benefits of high-arctic warming (2019) Layton-Matthews et al., Global Change BiologyDOI: 10.1111/gcb.14773

The Crux

Most of us know that climate change will bring warmer, shorter winters to most parts of the world. For many species in areas like the Arctic, it would be easy to interpret this as a good thing – plants grow earlier, so animals get more food, right? Naturally it’s never that simple. Many herbivorous species have evolved in sync with climate cycles so that their reproduction peaks when food becomes available. If season start dates change, these species may not be able to change their own cycles in time. Additionally, what happens if populations of their predators suddenly boom?

Today’s authors wanted to know what role a warming climate played in the population fluctuations of migratory barnacle geese (Branta leucopsis).

What They Did

The population of barnacle geese studied have their breeding grounds on Svalbard, an island north of mainland Norway that lies deep in the Arctic circle. The geese migrate here from the south (Scotland) every year, hatching around the start of July. Data on bird clutch size and success hatching data was used to determine reproductive success of the geese, whilst mark-recapture data was used to determine their survival chances at different life stages. Data was collected over the last three decades, with over three thousand nests and five thousand individuals monitored in this time.

Survival data was compared to climate data like date of spring onset, average temperature and variation in rainfall, which attempted to capture the likely amount of food the herbivorous geese had access to. Estimates of Arctic fox (Vulpus lagopus) predation at their breeding grounds in Svalbard were also used to see how predator populations affected the geese.

What They Found

Whilst egg production for the geese increased, it was offset by increasing mortality among young geese. This was likely driven by an increase in Arctic fox numbers. Any benefits that increased populations may have had also may have been countered by density-dependent effects during winter in Scotland – when populations increase resources dry up and reproduction rates suffer.

Did You Know: Mark-Capture Data

The survival of every individual in a population is almost always impossible to determine. Ecologists have adapted, and mark-recapture models have become one of the more popular ways to determine the chance of an individual having survived over a time period. It simply involves marking a series of captured individuals of a population, and seeing how many of them were recaptured after a given time. It may sound like a stab in the dark, but modern statistics has made it possible to obtain quite accurate survival data using this technique.

Whilst it may seem intuitive that more resources would increase geese populations, increased Arctic fox populations tend to balance any increase out

Whilst it may seem intuitive that more resources would increase geese populations, increased Arctic fox populations tend to balance any increase out (Image Credit: Eric Kilby, CC BY-SA 2.0)

Problems?

Whilst the researchers did have climate data for the wintering and spring stopover grounds for the geese, the data which came from Svalbard was much more detailed. whilst the results here are quite in-depth, it still remains that there’s a large chunk of very relevant data missing. Getting similar data from spring and winter grounds would naturally make the results more informative, but it would also take an enormous amount of time and resources.

So What?

More resources doesn’t just mean more geese. Areas like Svalbard have fairly simple food webs, with relatively few predator and prey species. But the interactions between these species can still be complex. More reindeer carcasses (another result of climate change, read more about it here) mean more foxes, which means more predation on geese. Less ice also means more polar bears getting stranded on Svalbard, many of which have started preying on goose eggs.

Results like these give much needed insight into how food webs will morph as temperatures increase. If we can develop models for simple ecosystems that are being affected more strongly than others now, it means we can create complex models when climate change starts hitting other regions harder.

Pinning it on the Polar Bear

Image Credit: Christopher Michel, CC BY 2.0, Image Cropped

It’s an image that is ubiquitous in the media when the words ‘climate change’ pop up. The lone polar bear, drifting through the sea on a single ice floe. It is an effective image, evoking emotions like pity, loneliness and general despair for the plight of what has become the flagship species of what seems like the entire Arctic. But is associating the health of an entire ecosystem with one species useful, or dangerous?

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Parrots in Norway

The Norwegian landscape is a beautiful thing. Spruce and pine groves piled on the side of mountains and fjords, moose and deer popping up in backyards, woodbirds flitting about on pristine hiking trails. Parrots screeching bloody murder into your ears as you re-enter the city.

No you did not read that wrong. It’s not happening yet, it in a couple of decades parrots, a type of bird not really associated with the sub-Arctic, could be a regular presence around Norwegian cities. So how could this happen, and why is it really quite concerning?

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Monitoring Freshwater Populations in the Chernobyl Exclusion Zone

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.

What They Did

The researchers sampled populations of the water flea Daphnia pulex (see below) from 8 lakes within the CEZ, all of which had experienced different doses of radiation since the Chernobyl disaster. Information on how much radiation those lakes were subject to was taken from Ukraine’s radiation databases and water samples collected at the site. The 38 types of Daphnia from the 8 lakes were then transported back to a laboratory and bred for three generations. The survival and reproductive success of this third generation was then modelled against radiation dose.

Did You Know: Daphnia as Study Organisms

Some species are frequently used across different ecological disciplines as model organisms. One example is the genus Daphnia, a genus of water fleas. They have a short life cycle, and can reproduce asexually. This means that scientists have the opportunity to disentangle environmental effects on populations of genetically similar individuals, as well as between populations of different genetic backgrounds.

What They Found

Whilst reproductive success and survival varied between the populations of Daphnia at different lakes, this did not seem to occur as a result of radiation dose. Radiation did not have a pronounced effect on any fitness variable.

Problems?

Daphnia_pulex

The water flea Daphnia, here used to test the effects of radiation on populations (Image Credit: Paul Hebert, CC BY 2.5)

Sample size is of course an issue here. Only having 8 lakes to compare the effects of radiation on populations was always going to make an effect of radiation dose hard to find. It was made more difficult by the fact that the effects of one lake were significantly different to the others, skewing results considerably. This is of course no fault of the authors, and hopefully technology in the future will allow us to expand the data used in these projects.

So What?

It’s important to note here that these results do not necessarily mean that radiation has no effect on Daphnia populations. Radiation is known to have negative effects on individual fitness, so what this study could tell us is that we need to view radiation as an environmental process which acts in concert with a variety of other biotic factors. Perhaps a study which takes into account further environmental variables and more lake populations would be able to further advance the work done in this paper.

The Best and Worst Movie Scientists

We look at some of our favourite and least favourite movie scientists. Includes rants about lab coats, self testing and Spiderman.

2:12 – Robert Neville (I Am Legend)
8:32 – Curt Connors (The Amazing Spiderman)
19:38 – Poison Ivy (Batman & Robin)
26:28 – Rhonda LeBeck (Tremors)
30:36 – Victor Frankenstein
34:18 – Ira Kane (Evolution)

You can also find us on iTunes and Google Play.

We also have a bonus episode this week, seeing as we’re on Easter holidays and can’t find the time to record a full one. So please enjoy our analysis of the ecological ramifications of The Snap.

Extreme Warming Events Could Increase Reindeer Population Stability

Extreme warming events may sound like bad news to reindeer, but they could help increase population stability

Extreme warming events may sound like bad news to reindeer, but they could help increase population stability (Image Credit: Christopher Michel, CC BY 2.0)

More frequent extreme climate events stabilize reindeer population dynamics (2019) Hansen et al., Nature Communications, https://doi.org/10.1038/s41467-019-09332-5

The Crux

Whilst climate change has been causing (and will cause) a myriad of environmental problems, it’s important to remember that not all species will be negatively affected by more extreme weather events. One example is reindeer on the Arctic island of Svalbard, according to this week’s paper.

Taken at face value, an increased frequency of extreme warming events may not sound like a good idea for a cold-adapted species. But despite the fact that it can lead to rain falling and freezing over snow, rendering massive patches of food inaccessible, the authors show that this can actually lead to increased population stability.

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