1. Matthew P. Hill and John S. Terblanche
Do niche shifts explain the recent range expansion and invasion of Bactrocera invadens into South Africa?
©Kaja Raghunath
Matthew P. Hill and John S. Terblanche
@InsectEcology

2. Niche Shifts Ecological Niche Models
Broennimann et al. (2007) Ecol. Letters
Fitzpatrick et al. (2006) Global Ecol. Biogeog.
Ecological Niche Models

3. Niche Shifts ISSUES Rapidly changing realised niche
Non-equilibrium with environment
Modelling caveats
Background selection
Multicolinearity
Transferability
Taxonomic identification

4. Bactrocera (Diptera: Tephritidae)
Over 500 species
75 in Bactrocera dorsalis complex
Bactrocera dorsalis s.s Asia
Significant quarantine pests
Disrupt free and fair trade
of fruit and vegetables
© USDA

5. Bactrocera invadens 2003 detected in Kenya Likely origin Sri Lanka
Polyphagous (mango, banana, citrus, stone)
Spread rapidly throughout Africa
© IITA

6. Distribution (De Meyer et al. 2010)
2003 first detection
Native Range

7. Distribution 2012

8. 2013 – South Africa
Recent interception

9. Range expansion hypotheses
Niche shift
i.e. physiological, host plants, resistance
adaptation
Propagule pressure
Filling ‘realised’ or ‘potential’ niche
i.e. non-equilibrium distribution
© USDA
© IAEA.org
© IITA

10. Or.. Conspecific invaders? © IAEA.org © IAEA.org B. invadens
B. dorsalis
Conspecific invaders?

11. Khamis et al. 2012
COI data
supported

12. Tan et al. 2011
Phenylpropanoid volatiles

13. Hypotheses Conspecific species (B. invadens & B. dorsalis)
Combined data better explain understand range expansion
Considering as single species will give better predictions of global invasion potential
© USDA
© IAEA.org
© IITA

14. Methods Four Bactrocera species Climate zones Niche exploration tools
Ecological Niche Models
© USDA
© IAEA.org
© IITA

15. Bactrocera distributions

16. GEnS 38 B. dorsalis 31 B. invadens 6 B. phillipiensis 8 B. papayae
Metzger et al Glob. Ecol. Biogeog.

17. Predictor Variables 2 sets 1. “Expert”
8 variables describing temperature and precipitation
2. Ecological Niche Factor Analysis
Best subset of 35 variables
Ranked on Marginality
© USDA
© IAEA.org
© IITA

18. Principle Components Analysis
ENFA-derived
Expert

19. Principle Components Analysis
ENFA-derived
Expert

20. Ecological Niche Models
MaxEnt (presence-background)
Backgrounds * Predictor variable sets * model fitting complexity (β)
AICc and AUCTEST to find ‘best’ models
Projections
Reciprocal Distribution Models
© USDA
© IAEA.org
© IITA

21. B. dorsalis
B. invadens

22. Do ENMs support a single species?
High overlap in E-space and G-space
B. dorsalis able to project to B. invadens
B. invadens not able to project to northern parts of B. dorsalis range
Still undergoing range expansion
© USDA
© IAEA.org
© IITA

23. Range Expansion

24. Range Expansion
B. dorsalis better predicts recent invasion through southern Africa
Niche shift?
Expanding to fill the niche of a single global invader
© USDA
© IAEA.org
© IITA

25. Global Invasion Potential

26. ENMs drive recommendations
B. invadens and B. dorsalis to be considered a single species “functionally”
Risk assessment and global trade management of Bactrocera dorsalis complex reviewed
© USDA
© IAEA.org
© IITA

27. Thank you Matthew Addison Mark Shutze Mark De Meyer Andrea Stephens
© IAEA.org