Wednesday, 28 November 2012

Synchronisation

Each year, species come and go with the seasons: in spring we have the early flowers, such as Snowdrops and Primroses. In summer we see a wide profusion of insect life, and in autumn we find fruits and fungi. On this grand scale things are pretty much set: we won't find many butterflies in mid-winter and few fungi are seen in spring. But within this fixed schedule there is much fine-tuning: each year has different weather, leading to different temperature and humidity on any particular day in different years. This difference can cause annual variations in flowering and emergence dates, so although the general trend is predictable, the precise dates of first (or last) sightings are not: each year is different. Within this variable environment, however, all is not random: we have synchronisation to consider. Synchronisation is a fundamental driving force in our wildlife: when there is a strict dependency between two (or more!) species, they must be together at the correct time. For example, if a larva eats the leaves of a particular plant, then the larva needs to hatch when the leaves are available. The larvae of many moths and butterflies fit into that category. This synchronisation can be quite 'soft' - a few days won't make much difference to availability of the correct food - but other species need a much tighter synchronisation. If a parasitic wasp lays its eggs into the larvae of flies that eat particular fungi, then:


  • the fungus needs to be in place
  • the fly needs to have laid its eggs in the fungus and 
  • the larva must be nearing full size.


Considering that the life of a particular mushroom specimen can be as short as a few days, we can see that the synchronisation required for this parasitic wasp to be successful is extremely tight: its annual opportunity is measured in hours.

So what governs this synchronisation? On the grand scale, we have the year: the amount of time it takes for our planet to go once round the sun. Most lifecycles are governed by this unit of measure. Then we have the day: the amount of time it takes the planet to turn once on its axis. These units of measure are absolutely consistent (within the lifetime of our observations). But what is much more variable is day length. The shortest day is 21st December, with the longest being 21st June. The day length follows a sinusoidal curve between those dates and is the major indication of time of the year. If you know the day length, you know that it can only fall on two particular days of the year. And it's this dual identity that leads me on to the first of today's pictures.

In springtime, I expect to see Celandines and Willow catkins as the first signs that a new year has begun. Over the past few years, I have seen Celandines in late November. This is clearly the wrong time of year, since winter is just arriving: ice is imminent, which will cause flower damage and there will be no insects to help with pollination. But if you look at the 'proper' flowering time (February around here), you will see that the 'proper' flowering date and the 'wrong' flowering date are an equal distance from the shortest day: the day length is roughly the same in each case. So the plants have detected that the day length is correct, but have failed to notice that the overall trend of day length is decreasing rather than increasing. Something is causing confusion.

When I find the early Willow catkins, the first pollinators to be seen are queen bumblebees and early solitary bees such as Andrena clarkella. These bees need Willow pollen to get their annual nests started: their larvae will feed on this pollen, so the bees are stocking up from the only pollen supply that is available. (I should point out that Andrena clarkella is a prime example of synchronisation: the female gathers only Willow pollen, so she can be seen only during the Willow pollen season, which is around 60 days long. When it comes to the bumblebee, the synchronisation is tight for the queen, but more relaxed for the workers, since many flowering plants will be available when they hatch.)

I previously mentioned that I had seen a queen Bombus terrestris gathering pollen on two occasions recently, and wondered where her workers were going to get pollen over the winter. This weekend, I found out:

Willow catkins


Willow catkin opening
I have never seen Willow catkins opening before February, so this was a huge surprise. Queen Bombus terrestris have been known to make overwintering nests in the south of England, but I was still very surprised to make two sightings of a working queen this far north in late October and mid November. It appears that both the bumblebee and the Willow have been triggered by the same stimulus and have both synchronised at the wrong time. It will be interesting to see how this all develops.

Moving on to things at the 'right' time: now is a good time to look at mosses. Most mosses need microscopy to identify for the first time, but once the initial identification has been made, most species can be readily identified in the field. I spent some time photographing specimens on an old wall at the south of the town.

Homalothecium sericeum can be identified by the pale, pointed growing tips:

Homalothecium sericeum

Tortula muralis can be found growing on wall tops:


Tortula muralis (with Grimmia pulvinata in background)
The setae ('stalks' that hold up the capsules) catch the light very well. I'd love to think that they act as light pipes to drive sunlight deep into the base of the plant. I have previously covered the complex lifecycle of mosses, (here and here) but for now I'll point out that the setae and capsule are not wholly from the original plant, but are partly a junior generation that is parasitic on an older generation.

Most mosses have setae that carry capsules well clear of the parent plant in order to maximise the opportunities for spore dispersal. Grimmia pulvinata continues to puzzle me by its insistence on burying its capsules under the leaves of the parent plant:

Grimmia pulvinata showing 'drooped' capsules
Orthotrichum anomalum can be tricky to identify due to its extreme similarity to other mosses, and also due to a high degree of variability when wet or dry:
Orthotrichum anomalum
Growing on the same wall, I found:

The lichen Caloplaca flavescens, which normally dies away in the centre, although I think this specimen has had some assistance from molluscs:

Caloplaca flavescens
And Ivy-leaved Toadflax, which I think flowers here all-year round, now:

Ivy-leaved Toadflax


Just to add to the absurdity of the flowering Willow, here is a shot of Galerina clavata taken on the same day on my lawn:

Galerina clavata with frost





2 comments:

Gill said...

That's a wonderful page - can I ask that you put in a link to your previous page on the life-cycle of mosses?

As for the Grimmia: do the spore-cases always hang/point down? If so I'd suggest the spores may have evolved to spread by "swimming" in water - raindrops wash them out and they then run away rather than blowing in the wind as I imagine other spores do.

Your ivy-leaved toadflax is much bluer than mine.

stuart dunlop said...

"can I ask that you put in a link to your previous page on the life-cycle of mosses?"

Done.

"As for the Grimmia: do the spore-cases always hang/point down?"

The book says that they are 'held erect in dry weather', but I have never seen this. Your suggestion about swimming spores is almost certainly correct, but then we have to wonder about how they manage to appear on wall-tops. I suppose they must be carried on birds' feet, or perhaps even the feet of insects. I certainly think that some lichens are spread in a similar fashion.