Tag Archives: alien

Where the Wild Things Are

Urban aliens and threatened near-naturals: Land-cover affects the species richness of alien- and threatened species in an urban- rural setting (2020), Petersen et al., Scientific Reports, https://doi.org/10.1038/s41598-020-65459-2

The Crux

Land-use changes (in particular, urbanisation and everything related to it) have huge effects on biodiversity patterns – some habitats can support populations of many different species, others cannot. This seems intuitive on a large scale (think a rainforest vs. a large, industrialised city) and on a small scale (a small patch of concrete vs. a patch of soil in a forest), but what about on a medium scale, more relevant to management organisations? How different species of plants, animals and fungi are distributed in space on such a meso-scale is far more relevant to everyday management, compared to say a global distribution, or the organisation of a 10 x 10 metre quadrant.

Today’s authors (myself and my current supervisors) looked at how species richness changes with land-cover on a municipality scale. We also looked at whether these patterns differ if one considers the total number of species, threatened- or alien ones, and whether animals, plants and fungi react to concrete vs. forests in the same way.

What They Did

We used species records from the Global Biodiversity Information Facility (GBIF) and digitised land-cover maps (find out more about them in last week’s post) to make statistical models to investigate if and how species richness among different groups of organisms (plants, fungi, birds and other animals) differed between the different land-cover types in 500 x 500 metre grid cells in Trondheim Municipality (Norway). The land-cover in each grid cell was classified based on the dominant, fine-scale land-cover within the grid cell – some examples are “Urban/developed area”, “Cultivated land”, “Coniferous forest” and “Open marsh”.

We included data on whether the observed species were registered on the Norwegian Red List or Alien Species List, to test if these groups (or all species in total) react to different land-cover types in the same way.

What They Found

Threatened species, alien species and overall species richness do not depend on the same land-cover types, and they are not distributed similarly across space. The mechanisms determining total species richness in an area turned out to be highly complex, depending both on land-cover, the heterogeneity of land-covers in a grid cell, and whether the ground faced north or south. Additionally, the response to these variables differed depending on what kind of organism was in question. As an example, the number of bird and plant species responded positively to grid cells with heterogenous land-cover, whereas the opposite was the case for non-avian animals and fungi. Generally, urban/highly developed areas showed lower biodiversity than did more natural areas.

The number of threatened species depended on the land-cover type in a grid cell, with near-natural areas having the highest number of species for all organism groups. Surprisingly, none of the land-cover variables could help predict where the most alien species were found, meaning that the number of alien species (on this spatial scale) is only determined by where they were first introduced.

Did You Know?

“Everything is related to everything else, but near things are more related than distant things” (Tobler, 1970).

This is Tobler’s First Law of Geography and it describes what is known as Spatial Autocorrelation. Whenever scientists are making statistical tests or –models (whether that is correlating people’s height to their bodyweight, or the number of species observed in a grid cell on a map), the most fundamental assumption required by these tests is that the observations are independent of each other. As an example: Person A’s height and weight are not influenced by (i.e. dependent on) the height and weight of Person B. However, once we start working with either time or space, this becomes a problem. If you find many species in one grid cell, you are likely to find many species in the neighbouring grid cells as well – not necessarily because these grid cells are “better” than grid cells far away, but simply because teleportation still only exists in science fiction. This breaks with the fundamental assumption of most statistics, and researchers have to be very careful to account for this effect whenever they make statements about anything involving spatial (or temporal) aspects.


Using species occurrence records from online portals is always tricky – these are a mix of observations by laymen, museum specimens collected in structured surveys by professors, and everything in between. This makes the quality of the datasets highly fluctuating. Likewise, some areas have been investigated a lot more closely than others: easily accessible areas close to people’s homes have a lot more records than do remote, inaccessible areas. This could potentially over- and underestimate the importance of these areas and habitats, respectively.

The lack of correlation between any land cover types and where alien species pop up make tracking their introduction crucial to preventing their spread (Image Credit: Tanja Kofod Petersen, CC BY 2.0)

The lack of correlation between any land cover types and where alien species pop up in cities like Trondheim make tracking their introduction crucial to preventing their spread (Image Credit: Tanja Kofod Petersen, CC BY 2.0)

So What?

Where we find high (and low) numbers of species, and why we find them there is obviously important, especially as cities and other human constructs have a major impact on these patterns. Investigating patterns of biodiversity on a spatial scale relevant for managers could help them make better, informed decisions on how to deal with these issues.

The most surprising and important finding of this study is the lack of correlation between any of the included predictors and the number of alien species in a grid cell; it seemingly only matters where they were first introduced. As urban areas are generally acknowledged to be hotspots of alien introductions (see some of the other posts on alien species here on the blog), this makes the need for proper monitoring and management of urban areas even more important.

Tanja Petersen s a PhD candidate at the Norwegian University of Science and Technology. She studies the effects of urbanisation, land-use and land-use changes on biodiversity, focussing on threatened and alien species. She uses records from the Global Biodiversity Information Facility (GBIF) and offical land-cover maps to track the patterns and changes over time and in space. Check out her previous articles at her Ecology for the Masses profile here or follow her on Twitter @NeanderTanja.

Title Image Credit: Tanja Kofod Petersen, CC BY 2.0 (Image Cropped)

Introduced Species Might Restore Ecological Functions Lost During The Ice Age

Image Credit: hbieser, Pixabay Licence, Image Cropped

Introduced herbivores restore Late Pleistocene ecological functions (2020) Lundgren et al., PNAS, https://doi.org/10.1073/pnas.1915769117

The Crux

The fauna of the Pleistocene (also known as the Ice Age) was not that dissimilar to the communities of animals which inhabit our planet now. However, many more large land mammals inhabited all kinds of ecosystems. By the end of the Pleistocene, many of them were extinct, mainly due to climate change impacts (glaciers got larger and restricted their ragne) and prehistoric human impacts like over-hunting, habitat alteration, and introduction of new diseases. The decline of large-bodied herbivores in the Late Pleistocene (LP from here on) led to many ecological changes including reduced nutrient cycling and dispersal, reduced primary productivity, increased wildfire frequency and intensity, and altered vegetation structure. These changes have become our norm.

Scientists usually study species introduction under the premise that they are ecologically novel. However, the introduction of large herbivores has been found to drive changes in the environment, potentially restoring or introducing novel ecological functions similar to pre-extinction Late Pleistocene conditions. This week’s researchers wanted to investigate what sort of role introduced mammals played in restoring ecological interactions by investigating their functional similarity with LP species.

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Breaking Down the Social Stigma of Invasive Species with Professor Helen Roy

I sat down with leader of the UK Ladybirds Survey Helen Roy to talk about the stigma surrounding invasive species like this Harlequin Ladybird (Image Credit: PJ Taylor, Pixabay Licence, Image Cropped)

I sat down with leader of the UK Ladybirds Survey Helen Roy to talk about the stigma surrounding invasive species like this Harlequin Ladybird (Image Credit: PJ Taylor, Pixabay Licence, Image Cropped)

While climate change and habitat loss seem to keep making all the headlines when it comes to environmental damage, invasive species are still chugging along comfortably as the second biggest threat to our planet’s biodiversity. New cases are popping up all the time, with the Burmese python, Crucian carp and the emerald ash borer beetle recently reaching new levels of notoriety.

Yet the negative impact that many non-native species have on the habitats they move into have often led to stigmatisation of anything new. This can be counter-productive, as the majority of newcomers into an ecosystem won’t have a pronounced negative effect. And whilst it may seem like a smart piece of preventative management to maintain an ecosystem’s status quo by preventing species introductions, it’s often just not feasible.

With this in mind, I sat down at the recent British Ecological Society’s Annual Meeting with Professor Helen Roy of the UK Centre for Ecology and Hydrology. Helen has studied the impacts of non-native species the world over, from the UK to smaller island nations like St. Helena, and has led several projects for the European Commission on non-native species. We spoke about the importance of distinguishing between invasives and non-natives, the impact of climate change on invasive biology, and the social and cultural significance of both native and non-native species.

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Fishing for Invaders

Image Credit: California Department of Fish and Wildlife, CC BY 2.0, Image Cropped

Angling as a source of non-native freshwater fish: a European review (2019) Carpio, De Miguel, Oteros, Hillstrom & Tortosa, Biological Invasions, doi.org/10.1007/s10530-019-02042-5

The Crux

People love fishing. It’s an intrinsic part of some people’s lives, whether as a livelihood or a past-time. People who have grown up fishing often have specific species that they enjoy fishing for. Nothing wrong with that.

Yet people’s desire to go after one fish species will often lead them to move that species around. This can happen on a small scale, with people moving a species from one lake to another slightly closer to their homes. Or it can happen on a massive one, with a species being transported to new continents.

This has shaped entire freshwater communities in modern-day Europe, where 195 species now reside that have no natural range in the continent. Most of these have been introduced since the nineteenth century, which is around the time that fishing became a popular recreational activity. This week’s authors wanted to find out what the role of recreational fishing was in shaping the make-up of today’s invasive freshwater fish populations in Europe.

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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 LavinCC 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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Parrots in Norway

Image Credit: Sandeeep Handa, Pixabay licence, Image Cropped

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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The Ecology of a Big Gorilla Wolf Motherf***er

Image Credit: Attack the Block, 2011

We examine the ecology of the BGWMs of 2011’s Attack the Block. Sexual ecology has never been more furry. Or glow-in-the-dark. Actually sexual ecology can get pretty furry. Also we have two fights this week.

3:05 – The Chimera in Cinema
11:41 – Ecology of a BGWM
38:38 – BGWMs vs. Liam Neeson from The Grey

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