Change is afoot, but not always how you expect

Biodiversity is changing all the time, but not necessarily in headline catching ways

Hi folks,

Just a quick one before I get into things. We’ve reached 10,000 subscribers! Unreal. 😱🤯🎉🙌 I thought I’d celebrate with a new feature.

The Predirections chat is growing and becoming quite active. So, in the next few days I’ll be launching something extra for paid subscribers—a dedicated Ask Me Anything (AMA) thread where you can ask me about anything related to the newsletter or more. This could include:

• The latest in biodiversity, freshwater and climate research and policy

• My research process and what’s on my radar

• Future topics I’m exploring for the newsletter

• Anything else related to the biodiversity-climate nexus and freshwater

For now, I’ll be answering questions on a rolling basis, so if you’re a paid subscriber, drop your questions anytime! Look out for an email invite to the AMA in the next few days.

But remember, other chat threads are completely free, so don’t hesitate to jump in. I want this to be a welcoming and active community of people.

And just in case you’re lost, we have a chat feature on Substack for more wide-ranging conversation than we can have in the comments. Think of it like a forum where a bunch of folks are interested in the same thing and I’m active on there responding to your questions/perspectives.

Another benefit for paid subscribers is getting to direct the discussions by having the ability to start new threads and shape the direction of the conversation.

Cheers,

Jono

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Our beautiful little solitary native bees in New Zealand are under threat from a variety of stressors, like introduced bees, land use change, and climate change. Image credit: Esta Tonkin.

Have you ever started a new post-holiday season fitness regime only to find your weight hasn't changed despite weeks of toil? This is all too common. Well it may be that you're losing fat and gaining muscle. That is, your composition is changing despite no change in the "emergent property" of your total weight.

Similarly, your neighbourhood doesn’t just disappear overnight, but over time, new residents move in—longtime ones leave, and businesses change. The character of the neighbourhood shifts—not necessarily for the worse, just different. And the same number of people still live there.

The same thing can happen to biodiversity. And, in fact, it is. All over the place!

We often see headline-topping news stories about the loss of species or "insectageddon". (Remember the good old days when your car would be splattered with dead bugs after a long drive? And how that doesn't happen anywhere near as much these days? But I digress.)

However, biodiversity change can be much more insidious than this. A lot of the important changes go unnoticed.

I could write a book about this topic. But I'm just going to pick a few examples to demonstrate the type of thing I'm talking about. There'll be many follow-up posts with specific examples. So this isn't meant as exhaustive coverage of this topic.

So yes, we may not see species disappearing completely, but change is definitely afoot. And much more widely than you may expect.

I'll start with something right in my wheelhouse: rivers.

Reshuffling the decks

Although species richness (the number of species at a location) may not be declining through time, the identity of the species at that location can be changing. Here, species richness is an emergent property of the ecological community (a group of species that share a space and interact). And it can remain fixed despite considerable reshuffling of who is in the community.

A study from a friend of mine in Italy, Stefano Larsen, demonstrated this nicely. He examined invertebrate communities living in the bed of streams and found no change in the number of species through time over a 30-year period. But, when looking more closely, despite this lack of change in richness, he found that the communities were getting gradually more different through time. That is, they were changing in their composition.

I know there's a lot going on here, so I included the original caption in the screenshot. I'll try to translate it for you. Just focus on the left y axis and the blue lines. Panel 'a' is just the number of taxa (a general term to represent species, genus, sub-family, family etc.; here it's either species or whatever level they could consistently identify the invertebrates to: often a combination of species, genus and subfamily level). In this panel, it is mean richness per stream site across ten streams in a long-term observatory in Wales. Panel 'b' is the number of taxa combined across all sites in the region (58 sites across Wales). Both of these panels show there has been no change in the number of invertebrate taxa over the past 30 years. Panel 'c' is where it gets interesting: this is a measure of how dissimilar the invertebrate communities are in the panel 'a' data to the first communities sampled back in the '80s. It shows that the communities are getting more dissimilar through time, indicating a gradual replacement of the species that are present. In summary, while the diversity of species isn't changing, the composition is. Source: Larsen et al. (2020).

In work led by Peter Haase during my postdoc in Germany, we found that cold-dwelling river specialist invertebrates were declining through time across thousands of sites across Germany over a 25-year period. They were being replaced by species that prefer warmer temperatures. This is all despite not much going on in terms of overall numbers.

Changes in invertebrate community composition in German streams over 25 years. a: Abundance, b: Taxonomic richness. Different colours represent different components of the invertebrate communities, pink: warm-dwelling taxa, orange: medium-temperature-dwelling taxa and blue: cold-dwelling taxa. Essentially, cold-dwelling species are declining and being replaced by warm- and medium-temperature-dwelling species through time. Source: Haase et al. (2019).

So there's some reshuffling the decks going on here, where species are dropping out for certain reasons. In the case of the German streams, it's likely warming temperatures, which we found to be increasing too.

The reshuffling of the decks can be even more nuanced than this. Species can even reorganise within their existing habitats, and this can have major impacts on the dynamics of ecosystems, including disrupting important interactions among species.

One major study examined four decades of data with 1,478 species, including birds, mammals, butterflies, moths, plants, and phytoplankton, across Finland. They found little change in which species were present across the study period, but where species were relative to their preferred climatic conditions shifted considerably. This is important as species performance tends to decline as they move away from their preferred conditions, which might have implications for important functions like carbon sequestration or nutrient cycling. And, as climate change progresses, these 'reshufflings' of species within their existing habitats might be precursors to more major changes.

Such changes can be abrupt, with ecosystems rapidly shifting between completely different states. The most well known of these is the flip from clear water states to turbid states in shallow lakes. But while these appear to be rapid transitions, they are often preceded by early warning signs like 'flickering' where an ecosystem can flicker between two states temporarily, indicating instability before a full regime shift. Alternatively, 'critical slowing down' can happen, where an ecosystem becomes slower to recover from small disturbances, indicating that it is losing resilience and nearing a tipping point.

Suffice to say that rapid transitions can occur but there are often subtle signs indicating a change ahead of time.

Connections everywhere

Coming back to streams for a minute, I want to describe a really neat study showing clear changes in species phenology: the study of cyclic and seasonal natural events, like when flowers bloom or birds migrate, particularly in relation to things like seasonal weather cycles or light.

The Breitenbach Stream. © Freak-Line-Community / Wikimedia Commons

Near where I worked in Germany for a couple of years sits the Breitenbach stream. This has been the focus of a very long-term, high intensity monitoring programme for several decades. A recent study showed that, over a 42-year period, the phenology of species of mayflies, caddisflies and stoneflies have changed considerably. These insects spend part of their lives in streams (as juveniles) and then metamorphose and emerge as adults that fly around outside of the stream. The authors found that the amount of time the insects spent out of the water flying around increased by 15 days over the study period, and the date of peak of emergence arrived 13 days earlier.

Changes in the phenology (timing of events like when flowers bloom or birds migrate) of 31 species of mayflies, stoneflies and caddisflies. Here, peak date of emergence and the duration of emergence are shown. Source: Baranov et al. (2020).

These are substantial changes. You only need to think about other species that rely on these insects for sustenance to realise it can have major knock-on effects. For instance, birds, bats, and beetles all consume considerable amounts of aquatic prey. If they depend heavily on these species for their diet, this could slow down their conditioning and delay key life history events like migration. Then the impacts are no longer just local but potentially global.

Such shifts are called ‘phenological mismatches’, where species that depend on each other, like pollinators and plants or predators and prey, become out of sync, disrupting ecosystems and food webs, and potentially having cascading effects on things like agriculture.

These examples really highlight the interconnectedness of natural systems. Ever since Darwin's vision of the entangled bank, we've realised ecosystems are interconnected, complex systems.

Ecosystems aren’t just made up of species. The tight connections among species is what holds them together. But these interactions are unravelling.

An unravelling network of interactions among species. Without going into the details too deeply (just to demonstrate the point of unravelling networks of interactions), this is an assemblage of riparian plants (the nodes/points) that are competing for space with each other (the links/arrows). The five networks unravel in response to projected increases in drought. Adapted from Tonkin et al. (2018).

Any number of drivers can be responsible for these changes in interactions. It might be that a flower opens too late for a specialist butterfly to pollinate it, due to later onset of warmer weather. It could be competition with introduced bees driving our lovely solitary bees in New Zealand (pictured at the top) to find new sources of food. Or it might be that a frugivorous bird shifts its range further north due to temperature increases, leaving its preferred fruit tree behind, and resulting in reduced seed dispersal for the tree and lower regeneration rates.

Each of these cases could be precursors to profound and sustained ecosystem-level and associated impacts, such as carbon sequestration declining, soil erosion increasing due to different root structures of plants, or the loss of a key food resource for a local village.

Conclusions

I think that's enough for now! I've bombarded you with enough examples of subtle changes in biodiversity that are happening all around the world, often unnoticed. This is just a very small snapshot of examples to indicate the broad suite of subtle biodiversity changes going on around us all the time. I'll share many more of these separately in future more in-depth posts. But, for now, hopefully you’ve learned something new.

If you got to this point, and you’re wondering, why even care about biodiversity, go check this post out.

Let me know your thoughts in the comments. And have a great weekend!

PS: Thanks to those who suggested things to cover in this post in the chat! I didn’t get anywhere near to covering them all, but I tried to incorporate a couple.

PPS: if you’re in the US, hang in there. You’re doing it tough at the moment. We’re thinking of you.

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