swaay butterfly monitoring analysis
TRANSCRIPT
Butterfly Monitoring: analysis and scientific use of data
Chris van Swaay, De Vlinderstichting / Dutch Butterfly Conservation
Butterfly Conservation Europe (BCE)
Statistics Netherlands (CBS) Thousands of volunteers
Adapted by Martin Wiemers (UFZ, BCE)
What is butterfly monitoring?
“Collect information on the changes in butterfly abundance” We have to follow a protocol to detect real trends Fieldwork • Basis: samples • Regular counts • Fixed method In the Netherlands 400 transects generate 200000
records per year
Products
10
100
1000
1992 1994 1996 1998 2000 2002 2004
Woodland generalistsWoodland specialists
Species trends
Indicators
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100
1000
1992 1994 1996 1998 2000 2002 2004 2006 2008
GeelsprietdikkopjeThymelicus sylvestris
Criteria for indicators
• Scientific sound method • Sensitive • Affordable monitoring, available and routinely collected
data • Spatial and temporal coverage of data • Measure progress towards target • Policy relevance • Broad acceptance
The start
• Ernie Pollard started the first BMS in the UK in 1976
• 1976: start of the first Butterfly Monitoring Scheme in the UK
• Well founded by many scientific papers • Now at least 2500 transects in 14 countries • Every year our European volunteers
count once around the world (40.000 km)!
Butterfly Monitoring available and routinely collected
Butterfly Monitoring Spatial coverage • New countries join in
every year • Most of them done
every year
Butterfly Monitoring Temporal coverage
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1975 1980 1985 1990 1995 2000 2005 2010
Num
ber o
f BM
S
From transects to European indicator
• Location of the transects • Quality of the observer • Quality of the observations • Validation of the observations • Calculating trends • Building indicators
From transects to European indicator
• Location of the transects • Quality of the observer • Quality of the observations • Validation of the observations • Calculating trends • Building indicators
Choice of locations
• Free choice of transects (e.g. in the UK, Netherlands, Germany) – Pro: appealing to volunteers, easy to keep them motivated, rare
species included – Con: data is biased (but can be corrected by weighting)
• (Partly) random (e.g. France) – Pro: less bias – Con: sometimes transects on unattractive sites, no trends of rare
species (often the ones with high conservation value)
• Regular grid (e.g. Switzerland) – Pro: almost no bias – Con: hard to achieve (only on professional basis); no trends of
rare species (often the ones with high conservation value)
From transects to European indicator
• Location of the transects • Quality of the observer • Quality of the observations • Validation of the observations • Calculating trends • Building indicators
Basic idea
• We realise we can’t count all butterflies • But by taking samples we can estimate trends • As a consequence we don’t know the population size • But we can calculate changes in the population size
efficiently • With random or grid sampling transects are properly
distributed over the country • But in many countries recorders have a free choice • Solution: weighting
Why weighting?
• Not all species are equally distributed over the country • Not all transects are equally distributed over the country.
In the Netherlands especially the dunes are ‘oversampled’, agricultural areas in the clay and peat regions are ‘undersampled’.
Weighting by Dutch physical geographic region and main habitat type
Habitat types: • Woodland • Heathland • Agriculture • Open dunes • Urban • Moorland
Distribution of the population over the strata
The distribution of each species per stratum is calculated. For example: Hipparchia semele
Dunes - mainland
Dunes - WaddenseaHeathland - north
Heathland - centre
Heathland - south
Distribution of the transects over the strata
Dunes - mainland
Dunes - WaddenseaHeathland - north
Heathland - centre
Heathland - southdistribution
Big difference between weighted and unweighted indexes
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10
100
1992 1994 1996 1998 2000 2002 2004 2006
WeightedUnweighted
The trend in the dunes is different from the trend on the heathlands
distribution
transects
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100
1000
1990 1993 1996 1999 2002 2005
Heathland Coastal dunes
From transects to European indicator
• Location of the transects • Quality of the observer • Quality of the observations • Validation of the observations • Calculating trends • Building indicators
Grassland Butterfly Indicator: main habitat for European butterflies
• For 57% of the species, grasslands are their main habitat.
Grassland; 280
Woodland and scrub; 153
Heath, bog and fen; 25
others; 31
17 species make the indicator
• 7 widespread species: Ochlodes sylvanus, Anthocharis cardamines, Lycaena phlaeas, Polyommatus icarus, Lasiommata megera, Coenonympha pamphilus Maniola jurtina
• 10 specialist species: Erynnis tages, Thymelicus acteon, Spialia sertorius, Cupido minimus, Maculinea arion, Maculinea nausithous, Polyommatus bellargus, Cyaniris semiargus, Polyommatus coridon Euphydryas aurinia
From national trends to a European trend
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25
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175
1990 1994 1998 2002 2006 2010
Inde
x (fir
st y
ear=
100)
FranceThe NetherlandsSpain - CataloniaUnited Kingdom
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120
1990 1994 1998 2002 2006 2010
Inde
x (19
90=1
00)
+ 9 other countries
European species trends
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120
1990 1994 1998 2002 2006 2010
Inde
x (19
90=1
00)
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120
140
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1990 1994 1998 2002 2006 2010
Inde
x (19
90=1
00)
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1990 1994 1998 2002 2006 2010
Inde
x (19
90=1
00)
European trends
Species Trend in Europe Trend in EU Phengaris nausithous decline decline Erynnis tages decline decline Lasiommata megera decline decline Lycaena phlaeas decline decline Thymelicus acteon decline decline Ochlodes sylvanus decline decline Coenonympha pamphilus decline decline Cupido minimus decline decline Anthocharis cardamines decline stable Polyommatus icarus decline stable Maniola jurtina stable stable Polyommatus coridon stable stable Cyaniris semiargus uncertain stable Polyommatus bellargus uncertain uncertain Spialia sertorius uncertain uncertain Euphydryas aurinia uncertain uncertain Phengaris arion uncertain uncertain
European Grassland Butterfly Indicator
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20
40
60
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120
140
1990 1994 1998 2002 2006 2010
Butterfly Conservation Europe / Statistics Netherlands
Main drivers 1. Intensification
Main drivers 2. Abandonment
Relationships between butterflies and environmental indicators
• Plants: Ellenberg values • Like plants some species have a preference for rich or
wet situations, others for poor or dry places
• Butterfly monitoring gave us info on the presence of butterflies
• We made vegetation surveys at transects and calculated the average Ellenberg value for Nutrient, acidity and moisture.
Field data of occurrence of a species vs soil pH
Logistic regression: sigmoid relationship
Logistic regression: gaussian relationship
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Pro
ba
bil
ity
of
occ
urr
en
ce (%
)
Acidity-value (Ellenberg scale)
Pmax=37%
Tolerance=2.3
Optimum=5.0
Response curve of Araschnia levana for Ellenberg’s acidity-value, showing the Optimum (U), the maximum probability of occurrence (Pmax) and the Tolerance (T).
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Pro
b/Fr
eq o
f occ
urre
nce
(%)
Nutrient-value (Ellenberg scale)
(a) observed
expected
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0 2 4 6 8 10P
rob/
Freq
of o
ccur
renc
e (%
) Nutrient-value (Ellenberg scale)
(b) observed
expected
Two examples of response curves of butterflies on Ellenberg’s nutrient value, showing the calculated logistic regression model (expected) and the observed frequency of the species in the relevés falling in nutrient value classes with a width of 0.25: (a) the unimodal (Gaussian) response of Thymelicus lineola and (b) the sigmoidal response of Ochlodes sylvanus.
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Prob
abili
ty o
f occ
urre
nce
(%)
Nutrient-value (Ellenberg-scale)
(a)
M. alconA. levanaC. seleneP. icarusP. rapae
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0 5 10
Prob
abili
ty o
f occ
urre
nce
(%)
Acidity-value (Ellenberg-scale)
(b)
C. tulliaI. ioE. tagesA. agestisC. pamphilus
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0 5 10
Prob
abili
ty o
f occ
urre
nce
(%)
Moisture-value (Ellenberg-scale)
(c)
V. optilete
M. alcon
E. tages
I. lathonia
L. megera
Use butterfly monitoring results for site information
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1990 1995 2000 2005 2010
Moi
stur
e / N
itrog
en v
alue
Moisture index
Nitrogen index
Luttenbergerven
Multiple relationships
• Give the relationship between the three indicators • When more than one is significant, we get a multi-
dimensional plane or surface • For a site it can give an insight in the effects of a
changing environment on butterflies
Calculate national annual nitrogen index for butterflies
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6.1
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1990 1995 2000 2005 2010
CN
I
Calculate national annual nitrogen index for butterflies
y = 0.0131x - 20.205
5.7
5.8
5.9
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6.1
6.2
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6.5
1990 1995 2000 2005 2010
CN
I
De Vlinderstichting Dutch Butterfly Conservation www.vlinderstichting.nl Statistics Netherlands www.cbs.nl