Transcript B. dorsalis
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 Niche Shifts Broennimann et al. (2007) Ecol. Letters Fitzpatrick et al. (2006) Global Ecol. Biogeog. Ecological Niche Models Niche Shifts ISSUES • Rapidly changing realised niche • Non-equilibrium with environment • Modelling caveats – Background selection – Multicolinearity – Transferability – Taxonomic identification 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 Bactrocera invadens • • • • 2003 detected in Kenya Likely origin Sri Lanka Polyphagous (mango, banana, citrus, stone) Spread rapidly throughout Africa © IITA Distribution (De Meyer et al. 2010) 2003 first detection Native Range Distribution 2012 2013 – South Africa Recent interception 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 Or.. © IAEA.org © IAEA.org B. invadens B. dorsalis Conspecific invaders? Khamis et al. 2012 COI data supported Tan et al. 2011 Phenylpropanoid volatiles 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 Methods • Four Bactrocera species • Climate zones • Niche exploration tools • Ecological Niche Models © USDA © IAEA.org © IITA Bactrocera distributions GEnS 38 B. dorsalis 31 B. invadens 6 B. phillipiensis 8 B. papayae Metzger et al. 2013 Glob. Ecol. Biogeog. 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 Principle Components Analysis Expert ENFA-derived Principle Components Analysis Expert ENFA-derived 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 B. dorsalis B. invadens 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 Range Expansion 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 Global Invasion Potential 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 Thank you • • • • Matthew Addison Mark Shutze Mark De Meyer Andrea Stephens © IAEA.org