Category Archives: Paper of the Week

Using Yesterday’s Models for Today’s Conservation

Are polar bear habitat resource selection functions developed from 1985-1995 data still useful? (2019) Durner et. al, Ecology and Evolution, https://doi.org/10.1002/ece3.5401

The Crux

Ecologists often attempt to predict where species are using the spread of the resources that the species depends upon. This is done because often it’s simply easier to monitor the resources than the species. Resource selection functions (RSFs) are a tool which use the likelihood of a resource being used to predict a species distribution. However, if the landscape the resource is found in changes drastically, a resource selection function may start to be less useful.

In the early 2000s, using data collected in the 80s and 90s, US scientists developed RSFs for polar bears, a species which has regrettably become the poster child for the survival of the Arctic ecosystem. Even back then, the bears’ preferred habitat was receding. Now, with human-driven climate change severely reducing sea ice and markedly altering the bears’ habitat, this week’s authors wanted to know how well those RSFs work nowadays.

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Climate Change: Don’t Forget About the Plants!

When we think of global warming, we tend to be a bit selfish and think of how it affects us in our daily lives, but the warming temperatures on our planet have the potential to affect the base of all of our food webs, plants (Image Credit: Matt Lavin, CC BY-SA 2.0).

Phenology in a warming world: differences between native and non-native plant species (2019) Zettlemoyer et al., Ecology Letters, https://dx.doi.org/10.1111/ele.13290

The Crux

The timing of life-history events (such as births, growing seasons, or reproductive period) is called “phenology”, and this aspect of an organism’s life is particularly sensitive to climate change. So much so that changes in the phenology of certain processes are often used as an indicator of climate change and how it affects a given organism.

We’ve talked about the effects of rising temperatures in animals here on Ecology for the Masses, but there is a lot of evidence in the scientific literature for climate change causing a multitude of different changes in the phenology of various plants. Not only does the direction of the change differ (some organisms experience delays in certain events, others have earlier starts), but the size, or magnitude, of the change also differs. The authors of today’s study wanted to examine these changes in the context of an invasive plant species and how it may be able to outcompete a native plant.
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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.

Location Location Location

Deer mice like the one above are small parts of a complex and interconnected world. When two pieces of their world work against them simultaneously, how are these mice affected? (Image Credit: USDA, CC BY 2.0).

Botfly infections impair the aerobic performance and survival of montane populations of deer mice, Peromyscus maniculatus rufinus (2019) Wilde et al., Functional Ecology, https://dx.doi.org/10.1111/1365-2435.13276

The Crux

Parasites are bad news for the organisms that host them. Some parasites are so bad, they can actually make the host kill itself. Despite these clear and obvious costs to infection, the common consensus is that parasites are not too big of a deal for the host, because of how rare parasitic infection is on average. For example, in my research system only one in ten animals have parasites.

But when these ill-effects of parasitism are combined with other detrimental factors, such as a harsh environment, an organism with parasites is forced to deal with not one but two stressors. The authors of today’s paper were interested in how these effects of parasites may change depending on the environment that the host lived in.
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The Hitchhiker’s Guide to the Herbivore

Image Credit: Jorg Hempel, CC BY-SA 2.0

Can plant traits predict seed dispersal probability via red deer guts, fur, and hooves? (2019) Petersen and Bruun, Ecology and Evolution, https://doi.org/10.1002/ece3.5512

The Crux

Large animals are key players in structuring both the physical structure and the species compositions of plant communities. They eat some plants, but not others, they trample vegetation, they deposit nutrients through feces. However, they can also affect plant communities by transporting seeds (a process called zoochory) – either by eating them and defecating later on or by acting as vehicles for seeds stuck in their fur or on their feet. As large plant eaters are found in most of the world, and several populations are actually increasing, a deeper insight into these processes could turn out to be of great importance.

Today’s authors (myself and former colleague Hans Henrik Bruun) looked at the transport of plant seeds by red deer in Denmark: whether the different kinds of seed dispersal are significantly different with regards to what species are transported, and if certain plant and seed traits can be used to predict whether a seed is more likely to be found on the outside or inside of a deer.

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It’s Not How You Get There, But When

When migrating, animals like the great white pelican have to walk the fine line between saving time and saving energy. (Image Credit: Ray in Manila, CC BY 2.0, Image Cropped).

Landscape-dependent time versus energy optimisations in pelicans migrating through a large ecological barrier (2019) Efrat et al., Functional Ecology, https://dx.doi.org/10.1111/1365-2435.13426

The Crux

We have all seen the amazing scenes in nature documentaries of the great seasonal migrations undertaken by many different species on this planet. By migrating between two different habitats, migrating animals are thought to maximize both how many resources they have access to, and to minimize their exposure to harsh environmental conditions.

Despite these benefits gained by migrating animals, there are risks associated with these seasonal, long-distance travel events. Migrating animals, like the great white pelican (Pelecanus onocrotalus), have to decide what is better: traveling for a shorter distance or using less energy by taking a less strenuous – but longer – path. Today’s authors tracked the great white pelican during its seasonal migration over the Sahara to study how these birds made decisions about their travel.
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Killing 2 Million Cats: When Broad Targets Aren’t Enough

Image Credit: Joey Doll, CC BY 2.0, Image Cropped

Conservation or politics? Australia’s target to kill 2 million cats (2019) Doherty et al., Conservation Letters, https://doi.org/10.1111/conl.12633

The Crux

We’ve talked a lot lately about competition between causes on Ecology for the Masses. Often when extra attention is given to one cause over another equally valid cause, it’s a product of social trends coinciding at the right time, sudden events capturing the public interest (think the Notre Dame fire) or a particularly effective marketing campaign. But sometimes a cause or a conservation target can be used to deliberately distract the public from another cause, and it’s a potential example of this that we’re looking at today.

Australia has long had an issue with cats. They’ve decimated populations of native species, playing a large hand in the extinction of many species found nowhere else. So it makes sense that part of Australia’s first Threatened Species Strategy would be to minimise the impact of cat populations on local wildlife. The strategy included a target of 2 million cats being killed between 2015 and 2020. Whilst this might sound like a reasonable goal, this paper argues that the actual scientific evidence supporting the target is pretty weak, and goes into some alternatives and motives.

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