[Syrphidae] FW: FW: Re: FW: Syrphidae alert
Francis Gilbert
Francis.Gilbert at nottingham.ac.uk
Thu Jun 11 09:25:47 BST 2020
-----Original Message-----
From: Roger Morris [mailto:syrphid58 at gmail.com]
Sent: 11 June 2020 09:24
To: Francis Gilbert <plzfg at exmail.nottingham.ac.uk>; Stuart Ball <stuart.ball54 at gmail.com>
Subject: Re: [Syrphidae] FW: Re: FW: Syrphidae alert
Hi Francis
I'm not sure if I responded directly that this would circulate relevant
people, so perhaps you can circulate as you just have with Bastian's
comments. I have the following thoughts:
1. We have some evidence that the numbers of hoverflies present do drop
during periods of extreme heat and drought - there is a basic analysis
in Dipterists Digest but it must be accompanied by suitable caveats -
the data used are not structured and making parallels with aggregations
of previous years' data makes some assumptions that can be challenged.
Nevertheless, with data collected in a similar manner over a sequence of
years it may be possible to detect basic patterns but probably not
conclusive evidence.
2. For all effects we must consider that there are two or more variables
that may be responsible for localised differences in perceived
abundance. Firstly, a drop in abundance may be a response to a previous
season rather than the season under observation. We have some evidence
that incremental impact of climate change may affect subsequent
generations using Rhingia campestris, and we did try to publis a paper
on Leucozona glaucia that got comprehensively trashed by reviewers
(criticisms included that the reason for decline was simply agricultural
impacts and pesticide use - wrong but difficult to counter without a
long wrangle and no point when the paper has been rejected).
3. To stand any chance of a realistic analysis one needs an awful lot of
records! The HRS now generates about 60-70k records a year, but for most
species the absolute numbers are low because the data are always
dominated by the obvious, charismatic and readily identified species.
Thus, once one starts to look at individual species within more
challenging taxa such as Pipiza, Cheilosia and Eumerus, the volumes of
data are very limited and do not stand up well to detailed scrutiny. I
would not consider modelling these genera because the data are far too
weak and unreliable. So, the best one might do is to think about
different guilds - how do stem feeders, root feeders, saproxylic root
feeders, rot hole feeders etc fare as a guild? I suspect that if the HRS
lacks adequate data then the same will obtain across Europe and may be
even more restricted in many places.
4. Making links to actual weather patterns is often problematic too. We
see a regular pattern in our data with vastly more records emerging at
weekends. BUT there are supplementary patterns that seem to reflect
separate weather events - a High or Low pressure system can be detected
in the gross number of records, and after a particular hot or cold
episode the following days can be very weak for records. So, it is
likely that existing generations are suppressed and new waves reflect
the emergence of new generations.
5. We know precious little about differentials in phenology across
Europe. What Stuart and I have found in the UK is that there are strong
regional differences across both lonitude and latitude. I suspect that
with enough data we might be able to develop a regional picture for
Europe for a few distinctive and responsive species. The species I would
use is Epistrophe eligans, which is suitable because it is both abundant
and easily identified, as well as being very widespread. Maybe a dataset
could be assembled to create the equivalent of a seasonal 'pressure map'
for Europe. However, there is a need for a huge volume of data and we
know that this species' phenology has changed massively in the past 40
years.
So, my feeling is that making any link between this spring and perceived
abundance of hoverflies is unlikely to be possible with current levels
of recording effort. I think there is a small chance of picking up
signals from some big extremes in the future providing data are
collected with this in mind. There is obviously potential for setting up
a collaborative project to look at such matters on a European scale, but
looking at GBIF I think that there is such massive variation in
recording activity that many of the signals will be lost in the
graininess of the data. A run of several years of effort would be
needed. For the last couple of years I have pushed my efforts onto
detailed daily recording, but even that is scuppered because I have
nipped up to Scotland in June and of course my data then come from a
completely different geographic zone, making them quite unsuitable for
analysis.
Hope thios provides some food for thought
Roger
On 11/06/2020 06:55, Francis Gilbert wrote:
>
> -----Original Message-----
> From: Bastiaan [mailto:bastiaan at wakkie.org]
> Sent: 10 June 2020 21:14
> To: Leendert-Jan van der Ent <ljvanderent at planet.nl>
> Cc: Hoverfly discussion list <Syrphidae at lists.nottingham.ac.uk>
> Subject: Re: [Syrphidae] Re: FW: Syrphidae alert
>
> Hi,
>
> First of, I was sitting most of the time home, so no time to look
> really. I guess that has an effect too this year?
> Also I have the 'feeling/hunch' a lot of species start earlier, the last
> years I always seam to mis the Melangyna's for example.
>
> I guess fixed monitoring (grid) across Europe can really prove something
> in the future.
>
> Cheers,
> Bastiaan
>
>
> Leendert-Jan van der Ent schreef op 10-06-2020 21:53:
>> Hi all,
>>
>> Similar in The Netherlands.
>> Low number of specimens of most species and low numbers regarding
>> species in forest areas on sandy soils.
>> We have had the thirth dry and warm spring in a row and probably also
>> will get a dry and hot summer again.
>> This is going to be devestating to populations of quite some forest.
>> and also natural dry grassland an Heather, species.
>> The number of species that I usually see around the place where I do
>> live every year but the past few years not anymore is growing.
>> If this continuous we will get mediteranean climate conditions in The
>> Netherlands .
>> Good for some interesting _Pipizella_ and _Paragus_ species, maybe
>> also _Merodon_, but bad for the North European and Central European
>> hilly area and mountain species.
>>
>> Maybe an idea that those of us who have similar findings tries to
>> quantify this downgrade of species and specimens numbers and put these
>> information together to find out which species are influenced the
>> most. I will do this at the end of the season.
>> Right now we are busy with the Red Listing of Eurpean hoverfly
>> species.
>> Climate change - influenced by humans or not - might become a bigger
>> threat to hoverfly species than habitat destruction has been in the
>> past. And this effects most species of hoverflies and not only those
>> who are living in threathened habitat types.
>>
>> Let's hope that in other parts of Europe hoverflies are doing better!
>>
>>
>> Regards,
>>
>> Leendert-Jan van der Ent
>>
>>> Op 10 juni 2020 om 6:57 schreef Francis Gilbert
>>> <Francis.Gilbert at nottingham.ac.uk>:
>>>
>>> FROM: stiller3 [mailto:stiller3 at xs4all.nl]
>>> SENT: 09 June 2020 20:56
>>> TO: Ante Vujić <ante.vujic at dbe.uns.ac.rs>
>>> CC: Hoverfly discussion list <Syrphidae at lists.nottingham.ac.uk>
>>> SUBJECT: Re: [Syrphidae] Syrphidae alert
>>>
>>> Hi Ante,
>>>
>>> I kind of experience the same here where I have spent almost 2
>>> months now, in the SW of France.
>>> Low numbers of most taxa, also of many Syrphini, except some.
>>> Sphaerophoria scripta in very large numbers last week.
>>> But, compared to last year 2019, my impression is that this year is
>>> much poorer, despite the mild winter they had here.
>>>
>>> But 'a hunch' is no proof.
>>>
>>> cheers, André
>>>
>>> Ante Vujić schreef op 09-06-2020 09:59:
>>>
>>>> Dear all,
>>>>
>>>> I would like to share with you field experience from this season
>>>> in Serbia. We have less than 50% of species usual for this time of
>>>> year in flight and most of present species are with very small
>>>> populations. Aphidofagous species are most numerous, especially
>>>> Syrphus. Very low number of Cheilosia and Merodon. This can be
>>>> related to long period without rain during spring, but still.
>>>> During my 40 years experience in field work, this is the strangest
>>>> season.
>>>>
>>>> Best regards,
>>>>
>>>> Ante
>>>>
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>> Met vriendelijke groet,
>> Leendert-Jan van der Ent
>>
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