Category Archives: Paper of the Week

A ‘Stepping-Stone’ Approach to Endangered Species Release

Image Credit: Guy Monty, Image Cropped, CC BY-NC-SA 2.0

Optimizing release strategies: a stepping-stone approach to reintroduction (2019) Lloyd et al., Animal Conservation, 22.

The Crux

Restoring endangered species through breeding the species in captivity has become common practice over the last century, and has led to the successful recovery of many species. But the process is complicated, as there are always dangers inherent in releasing species that have become used to captivity back into the wild.

This week’s researchers wanted to test a new approach: rather than releasing species directly back into an area where they have disappeared from, they wanted to first release individuals into an already-occupied habitat patch, where predators and prey were present but the species had a high survival probability. This would be a stepping stone before a second release, intended to restore a population in a new area.

What They Did

The species here is the Vancouver Island marmot (Marmota vancouverensis), found only in the mountains of Vancouver Island, Canada. Conservation breeding started in 1997, with the wild population dropping below 30 in 2003. Marmots from four different Canadian institutions were transferred to one of the institutions, the Mt. Washington Marmot Recovery Centre, to undergo a period of quarantine before release.

Some of these marmots were then released for a year into a safe area on Mount Washington, Vancouver Island – the ‘stepping stone’. They were then released into a more challenging area on Vancouver Island, along with captive marmots who had not been exposed to the stepping stone, and wild marmots translocated from Mount Washington. These groups enabled the researchers to compare survival.

The researchers then modelled the survival of each marmot group against the release type, as well as the year and location of release.

Did You Know: Species Tracking

GPS technology has come a long way in recent years, and it has benefited ecologists enormously. This study utilised radio tracking on the miniscule marmot. But the size of radio trackers in the past often made them unethical. Australian Rakalis were notorious for being able to remove almost any radio tracker. However with advances in technology have come significant advances in our understanding of animal movement. Sirtrack in New Zealand are now able to place a radio tracker on a dragonfly.

What They Found

Marmots released into the stepping stone environment had high survival rates initially. These dropped when they were translocated to the wild, but rebounded after a year, coming close to the other wild marmots. Captive marmots released directly into the wild, however, had low survival rates for the first two years before rebounding, suggesting that there is potentially a two year acclimation period for the species.

Problems?

The experiment required a very specific type of habitat. It needed to have predators and prey, but not so many that the marmots are likely to be hunted at natural levels. In this experiment, human activities on Mount Washington kept predator levels low. This sort of habitat is not always possible to locate, especially for larger species.

So What?

Being able to increase the survival rates of captive-bred species is obviously a huge boost. As highlighted above though, this method is not simply possible for all species. However it does give conservationists a clear avenue forward for further research.

And lastly, studies like this really highlight the role human land use clearance plays in lowering species survival rates. The larger the suitable habitat area for a species, the more likely we are to be able to find suitable stepping stone environments for them.

How Different is Too Different?

This Peruvian warbling-antbird must walk a fine line between being different enough from its competitors to reproduce successfully, while staying similar enough to be able to recognize and outcompete the same competitors (Image Credit: Hector Bottai, Image Cropped, CC BY-SA 4.0).

Range-wide spatial mapping reveals convergent character displacement
of bird song (2019)
Kirschel et al., Proc B, https://dx.doi.org/10.1098/rspb.2019.0443

The Crux

In nature, many different organisms can be found in a single location, and sometimes those organisms are closely related to one another. When this happens, classical evolutionary theory predicts that these closely related species should differ in some ways, so as to differentiate members of their own species from others and avoid the costs associated with breeding with a mate that will not produce any viable offspring. This is called character displacement, and there are many examples of this in nature where two different species may be very similar when they live in different places (allopatry), but when they live in the same place (sympatry) they will differ in appearance, behavior, or the exact part of the local habitat that they live in (see Niche Partioning below).

A specific form of character displacement, called agonistic character displacement, occurs when traits or behaviors associated with competition differ between closely related species living in the same area. This is thought to reduce the costs of wasting energy on competing with an organism that you don’t really “compete” with. Agonistic character displacement can, however, result in greater similarity of traits when similar species live together, but previous studies in this area have not accounted for other causes of this similarity. Today’s authors wanted to do just that. Read more

Why are animals where they are?

Guest post by Endre Grüner Ofstad. Norwegian version available here.

Use, selection, and home range properties: complex patterns of individual habitat utilization (2019) Endre Ofstad et al., Ecosphere, 10(4), https://doi.org/10.1002/ecs2.2695

The Crux

The areas in which we find an animal is often called its ‘habitat’. Yet it’s a fairly ambiguous term. Where animals are found is usually the outcome of a range of considerations, primarily foraging, predator avoidance and mating opportunities. Animals trade-off among these in order to maximise their contribution to future generations (i.e. ‘fitness’).

When considering which habitats we most likely find animals one often works with habitat selection. Habitat selection is how much a certain habitat type is used compared to its availability, i.e. what is the relative probability that an animal will use a given habitat upon encounter. The amount of time an individual spends (or density of individuals) in a habitat is usually a good proxy for the importance the habitat to the animals. Therefore we often use this to evaluate which areas to target for management and conservation efforts.

Read more

Does Invading Change You?

The red lionfish, an aggressive, fecund, and competitive species invasive to the Atlantic Ocean (Image Credit: Alexander Vasenin, CC BY-SA 3.0).

The genomics of invasion: characterization of red lionfish (Pterois volitans) populations from the native and introduced ranges (2019) Burford Reiskind et al., Biological Invasions, https://doi.org/10.1007/s10530-019-01992-0(0123456789

The Crux

Invasive species are one of the most destructive forces and largest threats to native ecosystems, second only to habitat loss. The “how” and “when” of a species invading new habitats is obviously important, and as such many studies focus on if invasive species are present and if they are spreading. Yet these studies often disregard the mechanisms behind why a species is spreading or succeeding in these new environments. The mechanisms are important here, because by and large most invasive organisms will have very small populations sizes, leaving them vulnerable to stochastic events like environmental flux, disease, and inbreeding depression.

Two key paradoxes of invasive species are that these small groups of invasive organisms tend to not only have more genetic diversity than the native species (making them more adaptable to environmental change), but they are also able to outcompete the native organisms, despite having evolved in and adapted to what may be a completely different environment. The authors of this study used genomic approaches to address and try to understand these paradoxes.  Read more

Re-Analysing Forest Biodiversity

The Gribskov Forest in Denmarkj, where this study took place (Image Credit: Malene Thyssen, CC BY-SA 3.0)

Biodiversity response to forest structure and management: Comparing species richness, conservation relevant species and functional diversity as metrics in forest conservation (2019) Lelli et al., Forest Ecology and Management, https://doi.org/10.1016/j.foreco.2018.09.057

The Crux

The classification of biodiversity is something that has become more and more relevant as the term ‘biodiversity’ has worked its way into the public’s vernacular. How we measure biodiversity can vastly influence our perception of it, and whilst we’ve previously looked at spatial interpretations of biodiversity on EcoMass, today I’m examining a paper that looks at interpretations of biodiversity by species groups.

Species richness (how many species are present in a given place) is often the go-to measurement for biodiversity. But it doesn’t always help when trying to conserve an ecosystem. For instance, we may wish to focus on certain types of species which are rare, or that preserve certain ecosystem functions. This paper looks at the differences in the effect of management on biodiversity, depending on which approach to biodiversity you take.

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Can Scavengers Actually Reduce Disease Transmission?

Many organisms are vulnerable to a wide array of diseases and parasites throughout the course of their lives, but could scavengers help reduce that vulnerability? (Image Credit: The High Fin Sperm Whale, CC BY-SA 4.0)

Do scavengers prevent or promote disease transmission? The
effect of invertebrate scavenging on Ranavirus transmission (2019) Le Sage et al., Functional Ecology, https://doi.org/10.1111/1365-2435.13335

The Crux

As intimate as the host-parasite relationship is, it is important to keep in mind that it is embedded within a complex web of other interactions within the local ecological community. To add to this complexity, all of these interactions can feed back on and effect the host-parasite relationship. One ubiquitous part of all communities is the scavenger, an organism that feeds on dead and decomposing organisms. The authors of this paper wanted to investigate how scavengers affect disease transmission in local communities.

This question in interesting because it can easily go either way, depending on the community in question. Scavengers could lower disease transmission by eating infected organisms, thus removing contagious elements from the environment. However, scavengers could also increase transmission by promoting the spread of contagious elements in the community via their own waste after they consume infected tissues.

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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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