wildlife passages – how to evaluate their effectiveness? edgar van der grift...
TRANSCRIPT
![Page 2: Wildlife passages – How to evaluate their effectiveness? Edgar van der Grift Edgar.vandergrift@wur.nl](https://reader035.vdocument.in/reader035/viewer/2022062619/55165a9a550346b2068b5c76/html5/thumbnails/2.jpg)
Worldwide many wildlife passages in all forms/sizes, but….
Dassentunnel
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…do they work?
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Much baseline information about passage
performance available!
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Knowledge gab 1
Many studies about passage use…
But little knowledge about passage effectiveness!
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Knowledge gab 2
Some studies address effectiveness…
But in most of them the effectiveness of wildlife passages on population
persistence remains unclear!
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Wildlife passage use
Studying use is not useless!
However:
• Use ≠ Effectiveness
• Use does not provide evidence for effects of wildlife passages on population persistence !
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Use ≠ Effectiveness
3 x 1 badger?
Research:
3 crossings of badger per time period T
But: what does it mean?
1 x 3 badgers?
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Use ≠ Effectiveness
After road construction:
Before road construction:
3 x 3 badgers
1 x 3 badgers
Usually no monitoring “before” !
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Wildlife passage effectiveness
Definition:
The extent to which the objectives (= desired effect) for a wildlife passage are reached
no objective = no effectiveness
(And: no problem = no objective)
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Setting “SMART” objectives
S = Specific What are we going to do?M = Measurable How much?A = Acceptable Is there enough support?R = Realistic Is it possible what we want to
do?T = Time frame When are we finished?
Objective for each project must be specific to the location, species of concern and nature of the problem
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Does it meet our objectives?
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Working out a monitoring approach
• What are suitable research species?
• What are suitable research sites?
• What is the best study design (options)?
• Which research methods (surveys/analyses) are most promising?
• What measurement schemes should be used?
• What are the estimated costs?
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Choose appropriate research species
• Species is (highly) vulnerable for road impacts
• Proven use of wildlife passages
• Road impact is measurable
• Species allows for study design with high inferential strength
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Choose appropriate research sites
Select locations where wildlife passages are expected to make a large difference (e.g. by modeling population
viability)
Species X: not viable viable highly viable
with infra without infra
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Choose appropriate study design: (B)BACI, BA or CI
Before road Before Afterconstruction mitigation
mitigation
Impact
Control 1
Control 2
(Roedenbeck et al., 2007)
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Study design in literature review (n=123 studies):
• Before-After (BA) comparison approach: n=15• Use of controls in <10 studies• Most studies retrospective: only survey of crossing
structures after construction
In practice: trade-offs between perfect study design and reality!
• “Before” situation already in the past• No controls, no replication• Randomisation not feasible• Limited budget• ….
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Do not only include the wildlife passage in your study design!
• <50% studies in literature review incorporated assessment of presence/abundance target species around wildlife crossing
• Not measuring the population adjacent to road may result in wrong conclusions about wildlife passage performance
Example:• Reduction in roadkill does not necessarily mean the
crossing structure is effective
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Importance of population surveys
BEFORE AFTEREffect
Example 1:Roadkill 10 5 50% ↓
Population size 100 20 15% ↑
Example 2:Roadkill 10 10 0%
Population size 100 200 50% ↓
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Relate to abundance of animals in adjacent habitat
Wildlife overpass: August-December 2007
020406080
100120140160
Nu
mb
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wildlife overpass
adjacent habitat
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Select appropriate research methods
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Monitoring!
Photo: Bart Siebelink
Photo: Bart Siebelink
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Review:
• Tracking pads (n=74)• Video / infra-red still cameras (n=36)• Collection/identification scats (n=16)• Direct observations (n=13)• Trapping (n=12)• Collection/identification hair (n=8)• Radio-tracking (n=7)• Trail monitors/wildlife counters (n=6)• Other (including dusting with fluorescent pigment)
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Select appropriate research methods
Go (sometimes) off the beaten track!
Large species over-represented in existing studies, partly because of chosen research methods
New techniques in development: e.g. genetics, PIT tags
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Wildlife overpass “Groene Woud”
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21
Droge zone Natte zone
Poel W-2Poel W-1
Poel O-1 Poel O-2
1
4041
60
2061
80
21
Droge zone Natte zone
Poel W-2Poel W-1
Poel O-1 Poel O-2
1
4041
60
2061
80
Wetland zone
Dry zone
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0
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Number of observations 2006-2007
adults/juveniles (n=968)
Wildlife overpass
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
Distribution amphibians across overpassCommon toad
Common frog
Smooth newt
Crested newt
Green frog
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Significant more amphibians in wetland zone
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Nu
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M A M J J A S O N TOT
Dry zone
Wetland zone
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Efficiency method “artificial refugia”
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Sector
Sheet
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Crested newts: Belly patterns
Identification of individuals and individual movements across the overpass
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Crested newts: Belly patterns
Identification of individuals and individual movements across the overpass
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Appropriate measurement scheme
• Appropriate monitoring period (review: 4 nights – 8 yrs)
• Appropriate frequency of measurements within period(review: 1/day – 1/week)
• Appropriate number of impact and control sites
Recommendation: Assessment of measurement scheme on the basis of dynamic population model
simulations of monitoring
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Appropriate measurement scheme
Monitoring changes in populations
dassen alpha startyear=1, nrobj=10
0
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0 10 20 30 40 50
nr observation year%
sig
%sigAlp1-6
%sigAlp2-6
%sigAlp3-6
%sigAlp4-6
%sigAlp5-6
dassen startyear=1, nrobj=1 alpha
0
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0 10 20 30 40 50
nr observation years
%si
gn
%sigAlp1-6
%sigAlp2-6
%sigAlp3-6
%sigAlp4-6
%sigAlp5-6
Survey: 26 years
Survey: 12 years
1 study site 10 study sites
100%
80%
60%
40%
20%
100%
80%
60%
40%
20%
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Maximize inferential strength (validity)
Inferential strength= high probability and low uncertainty that research
result is true
Dependent on:• Number of competing hypotheses tested• Extent of extrapolation• Study design• Measurement scheme
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Implications
• Without studies with high IS it will be difficult to prove the effectiveness of defragmentation programs and to justify investments
• Correlation between increasing IS and increasing costs
However: investment in a few good but costly experiments should be prefered above numerous poor experiments at low costs
• Experiments with high IS carried out over the relevant temporal and spatial time scales may not be feasible in isolated studies, but may be conducted in collaborative (international) networks of researchers
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Complex problem: time for collaboration...!
This badger gate is for
94.68% effective!
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Use ≠ Effectiveness
Questions and discussion