Climate change can cause a ‘temporal mismatch’ between interacting species, we learned in our previous article. Here’s a short appendix to that piece, illustrating how simultaneously also a spatial mismatch can develop – further promoting population declines and biodiversity loss, especially in Earth’s temperate climate zones.
A possible spatial mismatch caused by climate change between a European butterfly (purple bog fritillary, black dots) that prefers a cold climate and its host plant (snakeroot, green dots) that prefers a wet natural landscape.
In public communication about the ecological consequences of climate change you may hear the term climate migration: as average temperatures go up, species need to keep up with their respective climate zones (and ecosystems, biomes) by either moving to higher latitudes or to higher altitudes, to a cooler place in short.
You won’t hear ecologists use the word migration to describe this process however. Ecologists talk about species’ dispersal (sometimes ‘biodiversity redistribution‘) – and that’s a lot more accurate, for the simple reason that (unlike humans) plants and other animals do not consciously respond to climate change, first reading the latest IPCC report and evaluating the likelihood of various emissions and warming scenarios before planning a move; but instead rely on their ‘dispersal propensity’ – in short a trial and error process.
Dispersal, moving in any direction to see if environmental conditions (habitat, prey, competition, predators, climate, pollution) will improve, is very dangerous for species – but under continuous build-up of many ecological stressors it can mean the difference between guaranteed extinction and survival, survival in a new home.
Now therefore you may be inclined to think that species that disperse easily have the best chance to adapt to and survive future climate change. But as we’ve tried to illustrate in our special long read about the complex effects of climate change on Earth’s temperate zone biodiversity – nothing is ever that easy in ecology, nothing except the one reason why that complexity exists: the fact that species depend on each other.
In other words, being a very entrepreneurial bird or tree or worm, is of little use if the ecosystem you depend on cannot keep up with your speedy travelling propensity or other rapid climate response trait. This can be illustrated in a temporal mismatch between species (for instance the example of insects responding faster to spring warming than migratory birds that subsequently miss a food peak their successful nesting depends on – see our previous article).
But it can also be illustrated in a spatial mismatch between species, a mismatch that may become even more prevalent under continued climate change, as up to 40 percent of Earth’s biomes may need to switch state – something that will require an immense, coordinated geographical migration of species and their ecosystems.
Here we present an example of a European butterfly species, derived from a publication from 2008 in Ecology, the journal of the Ecological Society of America, with the unmistakable title ‘Climate change can cause spatial mismatch of trophically interacting species’, led by Oliver Schweiger of the Helmholtz Centre for Environmental Research.
Butterflies are fascinating organisms – not only for obvious (esthetical) reasons but also because they have intriguing life cycles. Most butterfly species are highly selective with the plants their caterpillar offspring can feed on – often it’s just one single host plant for an individual butterfly species. Rare butterfly species can therefore be limited by the distribution of their specific host plants.
Video of butterfly biodiversity by WeLoveEarth.org, filmed at botanical gardens of Utrecht University. Butterflies help to illustrate another world of biodiversity that lies underneath: flowering plants. Specific butterflies depend on very specific host plants.
The German researchers studied titania’s fritillary or ‘purple bog fritillary’ (Boloria titania), a cold-loving orange to brown European butterfly that can be found in the Alps and locally in the Baltic region and (above 300 metres altitude) in the Balkans.
Boloria titania depends on the European bistort or snakeroot (Bistorta officinalis/Polygonum bistorta) a 20 to 100 centimetres tall plant with pink flowers that is found in temperate Europe in moist meadows, nutrient-rich wooded swamps, forest edges and other wet natural landscapes.
Now under projected climate change scenarios both Boloria titania and Bistorta officinalis are expected to undergo a change in the geographical distribution of their ecological niche, the Helmholtz ecologists write. However it is possible that a spatial mismatch may develop as the butterfly and its host plant have different abilities to disperse:
“We developed separate ecological-niche models for a monophagous butterfly (Boloria titania) and its larval host plant (Polygonum bistorta) based on monthly interpolated climate data, land-cover classes, and soil data at a 10′-grid resolution. We show that all of three chosen global-change scenarios, which cover a broad range of potential developments in demography, socio-economics, and technology during the 21st century from moderate to intermediate to maximum change, will result in a pronounced spatial mismatch between future niche spaces of these species.”
Apart from the global climate change scenario the severity of the spatial mismatch depends on the dispersal capacity of the host plant predominantly:
“The butterfly may expand considerably its future range (by 124–258%) if the host plant has unlimited dispersal, but it could lose 52–75% of its current range if the host plant is not able to fill its projected ecological niche space, and 79–88% if the butterfly also is assumed to be highly dispersal limited.”
Now of course when you talk about the direct link between two species, you still ignore further ecosystem complexities, as of course both species have many (indirect) links to other species that will also be influenced by future climate change. The butterfly-host plant spatial mismatch is therefore an illustration of broader ecological disruptions caused by climate change:
“These findings strongly suggest that climate change has the potential to disrupt trophic interactions because co-occurring species do not necessarily react in a similar manner to global change, having important consequences at ecological and evolutionary time scales.”
European butterflies meanwhile are not doing well. While the overlying rapid decline of European flying insects is mainly caused by agricultural stressors (insecticide use and landscape factors) a monitored 50 percent decline of European grassland butterflies (between 1990-2011) is also already partly contributed to climate change.
Current and projected spread of the Portuguese dappled white butterfly and its host plants, another European example of a potential spatial trophic mismatch as a result of climate change.
And it’s no different in North America, where for instance the decline of the Mormon Fritillary butterfly, a direct relative of Boloria titania that lives in the Rocky Mountains is linked to earlier spring snowmelt – another climate change factor that decreases grassland flowers.
© Rolf Schuttenhelm | www.bitsofscience.org