The range expansion of the silver-spotted skipper butterfly: lessons for conservation under climate change
BENNIE, J.J.1, THOMAS, C. D.2, LAWSON, C.1, HODGSON, J.2, WILSON, R.J.1 (1 University of Exeter, 2 University of York) Warren et al, 2001 Nature 414,65-69 “
To maintain biodiversity, species need to shift through fragmented” habitat Key issue in conservation under climate change
Concentrate resources on maintaining, improving and/or enlarging existing high-quality habitat (Hodgson 2009, Falcy 2007)? Or create connectivity along major environmental gradients (Krosby 2010)? There is a lack of empirical examples of successful range shifts to inform policy Photo: Zoe Davies Silver spotted skipper - Hesperia comma Thermophilic species - at northern limit of range in South East of England Breeding habitat in UK is short-turfed calcareous grassland with Festuca ovina. Severe decline in UK during 20th Century – due to agricultural intensification, decline of extensive grazing on chalk downs and myxomatosis. Photo: Zoe Davies Silver spotted skipper - Hesperia comma Major surveys of existing populations and suitable habitat in SE England were carried out in 1982, 1991, 2000 and 2009 Silver spotted skipper national index
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-20 Percentage change in national index in index national change Percentage -30 13 14 15 16 17 18 19 20 Mean August temperature in current year (oC) Central England Temperature (CET) record for August Parker, D.E., T.P. Legg, and C.K. Folland. 1992. A new daily Central England Temperature Series, 1772- 1991. Int. J. Clim., Vol 12, p317-342, DOI: 10.1002/joc.3370120402 Temperature at 10 cm in Festuca ovina grassland on two opposing slopes of Beacon Hill, Hampshire, 9/9/09 to 12/9/09 As the climate warms, species may occupy previously sub-optimal habitat (eg. north- facing slopes; Wilson et al, 2010)
Wilson, R. J., Davies, Z. G. and Thomas, C. D. 2010. Linking habitat use to range expansion rates in fragmented landscapes: A metapopulation approach. - Ecography 33: 73-82 120
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Temperature profiles in Festuca ovina grassland in south-facing swards of contrasting height, Beacon Hill, Hampshire, 3pm 02/09/09 2009 Exeter University survey
• 15 surveyors across 5 habitat networks in SE England. • Aimed to survey all grassland patches with >5% F. ovina within 30 km of an existing population. • 940 habitat patches surveyed for adults eggs and habitat quality • 303 populations recorded, either through observing adults during the flight season, or egg searches. Surrey Sussex North
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Surrey - Core area of south-facing slopes along North Downs brought in to conservation management - Stable system of good quality sites with limited potential to expand into new habitat Sussex
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Sussex - Rapid expansion wetwards along South Downs from core area. - Recent local extinctions in cooler years – mostly poor quality sites – although expanding front continues What determines colonisation and survival of breeding habitat patches during range expansion?
Using logistic regression predicts the probability of a) Empty patches being colonised and b) Occupied patches surviving across all 5 networks during the period 2000 2009.
Model selection through AICc with forward stepwise procedure; minimum adequate models presented here. What determines colonisation and survival of breeding habitat patches during range expansion?
6 Parameters included in models:
• Connectivity to patches occupied in 2000 (edge to edge connectivity as parameterised in Wilson et al 2010)
• Connectivity to patches unoccupied in 2000
• Solar radiation index (calculated using ArcGIS hillshade function; solar azimuth 180° alt 60° - median value extracted for each patch)
• Area of grassland <10cm (ha)
• %age cover of foodplant
• %age cover of bare ground What determines colonisation and survival of breeding habitat patches during range expansion?
Survival Minimum adequate model: •Connectivity to occupied patches (+) •Solar index (+) •Area < 10cm (+) •Foodplant cover (+) R2 = 0.17 What determines colonisation and survival of breeding habitat patches during range expansion?
Colonisation Minimum adequate model: •Connectivity to occupied patches (+) •Connectivity to unoccupied patches (+) •Foodplant cover (+) R2 = 0.14 Management implications at expanding ranges
Manage for colonisation Monitor Increase landscape connectivity? Introduction programmes?
Low priority Manage for survival Improve habitat quality? Probability of survival
Probability of colonisation
Conclusions – some lessons from the silver spotted skipper
•On short timescale climate fluctuations mean that managing to prevent local extinctions is important even for expanding species.
•Habitat shifts – for example north-to-south facing slopes, sward heights – may be as important as range shifts. Conservation management strategies may need to take this into account. •“Connectivity” or “complexity”? Managing sites for heterogeneity – in topography and/or vegetation structure – may promote resilience and buffer against local extinctions. •Management of existing sites is still important – the recovery of the silver spotted skipper has been due to both reintroduction of grazing and climate warming. Conclusions – some lessons from the silver spotted skipper
•Modelling results are broadly consistent with metapopulation theory and the known ecology of the species – colonisation is dependent on connectivity and foodplant availability; survival is dependent on area, microclimate and habitat quality.
•Over a 9 year period there is evidence for both a “rescue” effect (extinctions are less likely in connected landscapes).
•Managing for survival (through habitat management at existing sites) will be often the most effective strategy at expanding range margins
•Managing for colonisation (through enhancing landscape connectivity, introductions, or increasing food plant abundance) may be most effective in isolated areas where some good habitat exists.
•Sites with high probability of survival and high probability of (re-) colonisation may act as refuges and/or source populations - should be monitored. Acknowledgements
Field surveyors
• Phil Budd • Rachel Hoyes • Crispin Holloway • Jenna Poole • Alice Daish • Tracy Gray • Helen Silver •Bonnie McBride • Mark Edwards • Tim Bernhard • Tim Yardley
Centre for Ecology and Hydrology •David Roy Butterfly Conservation • Tom Brereton • Ian Middlebrook • Richard Fox