Tag Archives: food

When the Food Comes to You

A young orca from the southern population chasing its dinner. (Image Credit: Oregon State University via Flickr, CC BY-SA 2.0)

A young orca from the southern population chasing its dinner. (Image Credit: Oregon State University via Flickr, CC BY-SA 2.0)

Long-distance migration of prey synchronizes demographic rates of top predators across broad spatial scales (2016) Ward et al, Ecosphere, DOI: https://doi.org/10.1002/ecs2.1276

The Crux

Populations that experience some kind of connection are classified as “meta-populations”, as they are all interconnected in some way and can influence one another. Although these populations may be geographically and reproductively isolated, meaning that they are in different places and the organisms from the different populations don’t breed with one another, certain environmental factors may cause these populations to grow or shrink in similar ways.

The key to understanding how this synchrony between the varying populations happens is understanding what connects them. Killer whale (orca) populations in the northeast Pacific Ocean inhabit three distinct areas, with orcas from the northern and southern populations never coming into contact with one another. They do, however, feed on the same salmon populations that migrate from where the southern population lives to the where the northern lives. The authors wanted to find out if this connection via a food source could result in the demographic rates of these distant populations syncing up.

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Whom to Blame – Cats or Rats?

Feral cats are responsible for the decline of many endemic species worldwide. But will removing them boost rat populations, causing more potential harm?

Feral cats are responsible for the decline of many endemic species worldwide. But will removing them boost rat populations, causing more potential harm? (Image Credit: Brisbane City Council, CC BY 2.0)

Trophic roles of black rats and seabird impacts on tropical islands: Mesopredator release or hyperpredation? (2015) Ringler et al., Biological Conservation, https://doi.org/10.1016/j.biocon.2014.12.014

Guest post by Bart Peeters

The Crux

For centuries, rats have been portrayed as carriers of diseases and death; whereas our feline friends, worshipped by the ancient Egyptians, will definitely make your YouTube video go viral (a quick Google search of “cat video” shows 1 310 000 000 results). Both have been introduced, either accidentally or deliberately, to islands where endemic species have evolved and adapted to an environment without these generalist predators. So how do you know if eradicating one of them will make things better for the native wildlife?

Before taking radical conservation actions, it may be a good idea to understand how feral cats (the apex predator), rats (the mesopredator) and their common prey are affecting each other. Namely, if you kill all the cats, will there be more rats to prey on seabirds? On the other hand, will killing all the rats really reduce the predation by cats on seabirds?

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The Pacific Oyster

The Pacific oyster could make its way further north as the Arctic and sub-Arctic regions warm

Last Monday, I wrote about how climate change can facilitate the spread of non-native and invasive species. Today, we look at a species that whilst problematic now, could spread further throughout Norwegian waters as temperatures rise.

The last time we looked at an ocean-dweller in this series, we saw that while some species may not be great for ecosystems, they can provide an obvious benefit to other aspects of the region, in this case the fishing industry. The Pacific oyster (Crassostrea gigas) was also introduced intentionally for cultivation and is now on the verge of becoming a major problem in Norwegian waters.

What are they?

Because of its tolerance of most environments, the Pacific oyster has become the most widely cultivated oyster in the world, and thus one of the most widely distributed alien species in the world. Originating from the North-West Pacific, around Japan, it’s sometimes referred to as the Japanese oyster. There is some confusion regarding its taxonomy, with it also sometimes referred to as the Portuguese oyster, though it’s possible the two are separate species. They are large, jagged oysters, and occur in marine coastal waters.

How did they get here?

The oysters were imported into waters throughout Scandinavia and most of Northern Europe to replace dwindling stocks of native oysters at various points through the 20th century. Naturally, they eventually established wild populations as well, and are now abundant along Norway’s southern coast. Whilst they have taken over coastlines through much of Europe, their dislike of colder waters means that for now, their local populations are largely constrained to the south of Norway. But increases in temperature, which will occur at an accelerated rate in the Arctic and sub-Arctic, mean that the oyster could spread further north in the coming decades.

1200px-Pacific_oysters

Whilst the Pacific oyster’s place in novel marine food webs is still not particularly well understood, these specific oysters place in their immediate food web is very obvious (Image Credit: Wikipedia Commons)

What do they do?

Much like the Red King Crab, they transform the local ecosystem into a homogenous mass. They can transform substrate from soft bottomed and muddy to filled with rocks and other oysters and mussels, also paving the way for other alien species, and lowering regional biodiversity by outcompeting and displacing local species. Interestingly though, presence of oysters can often improve water quality in the surrounding regions and heighten ecosystem productivity, though the position of the oyster in novel food webs is not particularly well understood. They also have negative effects for local human populations, making certain areas impossible to use for recreation, as they’re extremely sharp.

How do we stop them?

In other countries, attempts to eradicate wold populations by harvesting them have proved futile, and a 2005 study showed the oyster eradication would also cause substantial harm to the local ecosystem. Warming seas will mean the expansion of the oyster’s range, however this is likely to happen very slowly, so by focusing on the ranges edges it may be possible in the future to limit expansion.

For more information on the oyster, we recommend that you read the following articles:

Invasive Alien Species Fact Sheet – Crassostrea gigas by the Online Database of the North European and Baltic Network on Invasive Alien Species

Crassostrea gigas – Cultured Aquatic Species Information Program by the Fisheries and Aquaculture Department of the United Nations