Giant water bugs, typically living in freshwater streams and with a size up to 12 centimeters among the largest of the insects. To smaller insects they are dangerous hunters. But there’s also something sweet to tell. See the water bug on the picture. Those are eggs and he’s the father – who carries them around and protects them from the cold all winter. [(C.C.) picture by NoiseCollusion.]

In the natural world ecological damage does not relate in a linear fashion to environmental stressors. Classically a small disturbance is followed by full recovery. Pass a certain threshold, and suddenly there is collapse.

Ask that emancipated beetle above, who is now disappearing from US aquatic desert ecosystems where it may have lived for thousands of years, say researchers from Oregon State University.

The entangled sustainability crises

Here on Bitsofscience.org we try to shed light on climate change as a driver to biodiversity loss. In August we looked at the really, really macro scale – when through a new Nature publication we learned that if you include intraspecific biodiversity to our planet’s sum total [which makes perfect sense] the projected genetic decline under continued climate change to 2080 may reach a staggering 67 to 84 percent.

To understand how, it is also important to zoom to the absolute micro scale. That’s what we did in June when we read a publication in Proceedings of the Royal Society B about a tiny crustacean that can only raise its heat tolerance by 0.5 degrees Celsius before it reaches genetic boundaries – let’s say the limits of its design – unless we gave it millions of years – which clearly we don’t.

Nothing unimaginable about a dried-out river bed

In their 8-year study the Oregon researchers now add another climate biodiversity case study, and one that does not require trying to think in terms of genes to imagine – drought, thirst, lack of food, no migratory options, death.

In their recent publication in Freshwater Biology, they have examined the effects of a severe drought in 2005 on Arizona’s French Joe Canyon. This drought, although unprecedented, reoccurred in 2008 and 2009. During the episodes the creek that flows through the canyon completely dried out. And although you’d have to be a persevering fieldwork hero to spot the differences, the ecological effects included the local extinction of the giant water bug – and could well be lasting:

“The stream pool communities underwent a catastrophic regime shift after transition to intermittent flow, moving to an alternative stable state with novel seasonal trajectories, and did not recover to pre-drying configurations after 4 years.”

“Six invertebrate species were extirpated by the initial drying event, while other species were as much as 40 times more abundant in post-drying samples. In general, large-bodied top predators were extirpated from the system and replaced with high abundances of smaller-bodied mesopredators.

That last bit is of significance too. If certain species – like top predators – fall out of ecosystems others attain room to expand. That’s another bad thing. It’s how you get plagues. And for biodiversity plagues can finish off what an initial disturbance has started.

New kind of droughts in north and south

Arizona is part of a northern hemisphere arid zone that is likely to become even drier under continued warming. This zone stretches eastwards across the Atlantic over both sides of the Mediterranean and all the way up to Beijing, northeast China.

But don’t think this is exclusive to the northern hemisphere. Want to see another picture about climatic effects on biodiversity? Go take a look at the Amazon, our planet’s richest biodiversity hotspot, earlier this year. Purple is where it hurts most.

© Rolf Schuttenhelm | www.bitsofscience.org