Tag Archives: connectivity

On Dispersal, Connectivity and the Will of the Fish

Image Credit: Dennis Jarvis, CC BY-SA 2.0, Image Cropped

Integrating dispersal along freshwater systems in species distribution models (2020) Perrin et. al., Diversity & Distributions, https://doi.org/10.1111/ddi.13112

The Crux

Trying to figure out where a species can comfortably live is one thing, but figuring out which habitats they can actually access is another. I like to think most marsupials would do quite well in South America or Africa, but the fact is that they’re not dispersing across the Atlantic or Pacific anytime soon. However a Species Distribution Model (a statistical model that can be used to predict the likelihood of a species being found somewhere) often requires a more nuanced approach than “big ocean separating these two habitats”.

To integrate a species’ ability to actually access an area into a Species Distributions Model (SDM), we often use the concept of connectivity. Often, this means simply measuring the distance between two populations. But sometimes a species ability to disperse might not reflect something as simple as how far it needs to go. A perfectly good habitat might be only 100 metres away, but cut off by a raging great cliff. Or a road.

In this study, we wanted to see whether we could relate connectivity parameters used in an SDM to the actual ability of the species to disperse.

What We Did

We used two separate study systems here. One consisted of roughly 300 lakes within Northern Norway housed within a single catchment, or watershed, whereby a single path between each lake could be traced. Here we had presence-absence records for two species, the northern pike (Esox lucius) and the European perch (Perca fluviatilis). Both are native to the region, but they are starting to expand into more lakes and have a more severe effect as the climate warms. We used an SDM to investigate which factors determined species presence, including connectivity variables like the length of the rivers between each lake and a downstream population, and the average slope of those rivers.

The second ecosystem was a series of lakes in Sweden which pike and perch had previously occupied, but had been removed from in the 60s and 70s through the use of rotenone, a chemical dumped in small lakes which wipes out fish populations. These were useful, as we knew that the lakes were otherwise suitable for the species given their presence beforehand. As such, here we used a much simpler model to focus on dispersal ability, simply comparing whether or not the species were able to access and then recolonise the lakes from which they had been removed. We compared successful recolonisation from the nearest downstream lake to the same connectivity parameters as in the larger model.

Did You Know: Island Biogeography & Lakes

They obviously don’t look it, but when it comes to biogeography, lakes are essentially a special type of island. Most of the rules of island biogeography apply to them (for fish anyway); larger lakes are more likely to have more species, lakes close to the ocean or other large lakes (the ‘mainland’) are more likely to have those species as well. The big difference between regular islands and lakes is that we can mark pathways between them much more easily. You’d think that would make it easy for us to stop fish spreading into new lakes as the climate warms, but the problem is as always people – people often spread fish from lake to lake, and the rules of island biogeography don’t apply in quite the same way to someone with a car.

What We Found

The slope of the river was a much more important factor in determining a species presence than the actual distance between populations. This makes sense, as a steep slope could make it difficult for a fish to swim up, or could indicate the presence of a waterfall. Furthermore, adding connectivity parameters to our SDM in our first study system did improve our models, but did it represent dispersal accurately?

For pike, the effect of slope was pretty consistent across the two study systems, indicating that the effects of connectivity in a large SDM can mirror a species dispersal ability. However for perch there was some inconsistency across the two study systems, indicating that perhaps there was some other aspect of the rivers between populations that had a larger effect on dispersal.

While European perch might be native to parts of Scandinavia, it is alien to others. If it’s able to freely disperse between lakes, it could be a serious problem as the climate warms (Image Credit: Christa Rohrbach, CC BY-SA 2.0)

Problems?

This study suffers from the same “lab vs. field” pitfalls as any other experiment that compares a complex study system to a smaller, ‘simpler’ one. Here, time is a factor. Our first study system looks at populations that have had centuries, in some cases millenia, to establish, whereas the second one looks at short-term re-establishments. It’s possible that given enough time, pike or perch could have eventually recolonised some of those lakes.

So What?

Having an idea of the effect of how different slope measurements can affect the dispersal of species is a great help, as it lets us know which lakes are protected by natural dispersal barriers, and which are likely to be invaded by species moving from downstream. However the fact that for perch, slope parameters varied in their effects across the study systems is a stern reminder that we need to always be mindful of how connectivity parameters actually relate to dispersal ability.

Sam Perrin is a freshwater ecologist currently completing his PhD at the Norwegian University of Science and Technology who is now completely done with this paper and never wants to look at it again. You can read more about his research and the rest of the Ecology for the Masses writers here, see more of his work at Ecology for the Masses here, or follow him on Twitter here.

On Fish Dispersal and the Perpetual Evil of the Duck

Image Credit: Norbert Nagel, CC BY-SA 3.0, Image Credit

Woe betide my fishy ancestors, for I am come here today to vent my grievances at a paper so dastardly it has cast a tepid patina of anxiety on a LOT of the structured squabbling my colleagues and I call ‘research’.

Actually, I shouldn’t vent too harshly on the sarcopterygiites, those ancient lobe-finned ancestors of ours and their close cousins the regular fish. Birds, as always, are the main culprit here. An abhorrent series of mutations that messed up a perfectly good reptile.

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Water-Based Recreation Can Promote Non-Native Introductions

Image Credit: Manfred Antranias Zimmer, Pixabay licence, Image Cropped

Invasion of freshwater ecosystems is promoted by network connectivity to hotspots of human activity (2019) Chapman et al., Global Ecology and Biogeography, https://doi.org/10.1111/geb.13051

The Crux

The spread of invasive species throughout freshwater ecosystems is a topic we’ve looked at before on Ecology for the Masses. In a previous paper breakdown we talked about how recreational is heavily responsible for the presence of non-native fish at a European scale.

Our paper this week takes a more local approach. Can we predict the presence of non-native birds, invertebrates and fish by looking at the presence of human activity, and where that human activity is present?

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How Does Our Interpretation Of Urbanisation Affect How Damaging It Is?

Increased urbanisation may have a negative effect on the richness of moth species like this Vine’s Rustic, but it depends on what scale we consider richness (Image Credit: Patrick Clement, CC BY 2.0, Image Cropped)

Urbanization drives cross-taxon declines in abundance and diversity at multiple spatial scales (2019) Piano et al., Global Change Biology, https://doi.org/10.1111/gcb.14934

The Crux

You would think that the effect of building a whole lot of stuff on something’s habitat would have a negative effect on just about anything. But building a whole lot of human stuff (maybe let’s retain a modicum of science-ness and call it urbanisation) hasn’t always been shown to be necessarily bad for species. There are a lot of studies out there which show that urbanisation is can be a negative for biodiversity (which makes sense, since for starters it generally breaks up habitat patches and introduces a whole lot more pollutants). But there are also studies showing that urbanisation can increase biodiversity.

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Frivillig vern sin rolle i naturvern

Image Credit: Endre Grüner Ofstad, CC BY-SA 2.0, Image Cropped

Guest post by Endre Grüner Ofstad.

Privately protected areas provide key opportunities for the regional persistence of large‐ and medium‐sized mammals (2018) Clements et al., Journal of Applied Ecology, 56(3), https://doi.org/10.1111/1365-2664.13300

Det Essensielle

Da mennesker slo seg ned i nye områder, bosatte de seg som regel i de mest produktive og artsrike områdene. I dag, mange år senere, er disse områdene fortsatt produktive og i private hender. I dag, derimot, blir flere og flere arter utrydningstruet og vi iverksetter tiltak for å redusere tapet av arter. Et av disse tiltakene er verneområder. Verneområder er områder som er satt til side for å sikre tilstedeværelse av gitte arter eller naturtyper ved å begrense høsting eller annen menneskelig innflytelse. Utfordringen er at dette ofte er kostbart da disse artsrike områdene ofte overlapper med områder som har viktige jordbruk- eller andre naturressursinteresser. Dette resulterer i at vernede områder ofte blir lagt til økonomisk marginale og/eller statseide områder. For å kontre dette kan en inkludere områder tilbudt frivillig av grunneiere. Spørsmålet blir da, hva er verneverdien av de områdene som blir tilbudt? Dette er spørsmålet som Clements og medforfatterne spør seg når jobber med Cape Floraregion i Sør-Afrika .

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The Role of Private Property in Conservation

Image Credit: Endre Grüner Ofstad,CC BY-SA 2.0, Image Cropped

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

Privately protected areas provide key opportunities for the regional persistence of large‐ and medium‐sized mammals (2018) Clements et al., Journal of Applied Ecology, 56(3), https://doi.org/10.1111/1365-2664.13300

The Crux

When humans settle down in new areas, they usually settled in the most productive and species-rich areas. Now, years later, these productive areas are usually still productive, but often still in private hands. However, today more and more species are facing extinction, and many would be helped by the protection of these areas. Protected areas are areas that are set aside to ensure the viability of certain species by limiting human exploitation of the local natural resources. However, this might be costly, and these hot-spot areas likely overlap with agricultural or other natural resource exploitations, with the result that protected areas are often located to economical marginal and state-owned lands. To counter this, one might include lands offered voluntarily by private owners. But are the lands they’re offering of any conservation value?

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Keep Your Eyes Open

Image Credit: ulleo, Pixabay licence, Image Cropped

Natural selection favors a larger eye in response to increased competition in natural populations of a vertebrate (2019) Beston & Walsh, Functional Ecology, doi: 10.1111/1365-2435.13334

The Crux

Studying the evolution of traits in response to selection pressure often helps us understand why species look and act the way they do. Selection pressure can include the need to find food before other members of your species, or the need to escape predation.

But what happens when improving your ability to obtain resources also means you’re more vulnerable to predation? Which will win out? This paper looks at a small species of freshwater fish, Rivulus hartii, and determines which of the two pressures contributes most to the evolution of the size of their eye.

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Shannon McCauley: The Rise of Community Ecology

"...there’s been huge growth in what we can do, but I think there’s been some loss in understanding the behavioural base of biology." (Image Credit: Shannon McCauley)

Image Credit: Shannon McCauley, CC BY-SA 2.0, Image Cropped

Community ecology is one of the more recent ecological disciplines, and has enjoyed a rise in popularity in the last decade. Yet it’s often been criticised as a little obscure, and has had difficulties integrating with other branches of ecology like evolution and population dynamics.

With this in mind, I sat down with Doctor Shannon McCauley of the University of Toronto during her recent visit to the University of Arkansas. Shannon is a community ecologist at the University of Toronto-Mississauga who uses dragonflies and other aquatic insects to answer questions about dispersal, community connectivity, and the effects of climate change. We attempted to put a little more context behind community ecology, and highlighted its relevance in the coming years.

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When the Food Comes to You

A young orca from the southern population chasing its dinner. (Image Credit: JC Winkler, CC BY 2.0, Image Cropped)

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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Between a Dam and a Hard Place

Dams like this change the flow regimes of rivers, and prevent some species from accessing their spawning grounds, lowering population viability. But is removing them completely danger-free? (Image Credit: Notorious4Life, CC0 1.0, Image Cropped)

Anybody who has ever studied freshwater ecosystems will end up having to study dams at some point. And they’ll no doubt learn that dams are the enemy. They fragment ecosystems. They cut fish off from their spawning grounds. They change flow regimes. So it makes sense that the recent trend of dam removal across Europe and the world in general would please ecologists. But there’s a problem with dam removal, and it comes in the form of invasive species.

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