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EMAPI 2015 Bernard-Verdier
- 1. Low abundance effects of alien plants on native plant richness Maud Bernard-Verdier & Philip E. Hulme EMAPi 2015 – September 24th
- 2. Invasion impact assessed at high alien abundances
- 3. Invasion impact assessed at high alien abundances Very abundant or dominant Absent or rare ? Local abundance of the alien plant Native richness
- 4. Native richness and abundance of the alien • At what abundance do alien plants start having an impact? • At the landscape scale, what implications for risk assessment and management? Species A Species B Species C a1 a2 a3 Critical abundance values Local abundance of the alien plant Native richness
- 5. Study of a highly invaded landscape Banks Peninsula New Zealand 40 % plant species are non-native 5 mi
- 6. Study of a highly invaded landscape 5 mi
- 7. Study of a highly invaded landscape
- 8. Extensive vegetation survey Vegetation survey (1982-1985) by Hugh D. Wilson Systematic 1000 x 1000 yards grid 6 x 6 m plots
- 9. Extensive vegetation survey Vegetation survey (1982-1985) by Hugh D. Wilson Systematic 1000 x 1000 yards grid 6 x 6 m plots Abundance scores: 1. Rare 2. Occasional 3. Frequent 4. Common 5. Abundant 6. Dominant
- 10. Identifying gradients of alien abundance 751 grassland plots 466 vascular plant species Species selection criteria: ≥ 3 abundance classes ≥ 5 obs. per class = 55 focal alien species
- 11. At what abundance are alien species associated to a decrease in native richness?
- 12. Native richness along an alien abundance gradientNativeα-richness Contrasts with rare abundances (GLM) = Effect size Local abundance of the alien plant e.g. Lolium perenne
- 13. Assigning critical abundancesEffectsizecomparedtorare (bootstrap95%CI) Critical abundance = lowest abundance at which we observe a significantly negative effect followed by only negative effects e.g. Lolium perenne Occasional Frequent Common Abundant Dominant -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 Local abundance of the alien plant
- 14. 0 10 20 30 40 50 O ccasional FrequentC om m onAbundant D om inant A range of critical abundances 55 Alien species : 11 critical abundances Numberofspecies All species Negative effects Critical abundances • 20% of aliens associated with a decrease in native richness • >80% of critical abundances were below the highest abundance class • Proportionally more frequent toward higher abundances 0.0 0.2 0.4 0.6 0.8 1.0 O ccasional Frequent C om m on Abundant D om inant Proportionperclass
- 15. Occasional Frequent Common Abundant Dominant -3 -2 -1 0 1 2 3 Occasional Frequent Common Abundant Dominant -2 -1 0 1 2 Dactylis glomerata Occasional Frequent Common Abundant Dominant -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 Lolium perenne Low to high critical abundances Achillea millefolium Different shape of relationships between alien abundance and native richness = different mechanisms? High critical abundances are not the general rule Effectsize
- 16. What consequences at the landscape scale ?
- 17. Spread of potential impact across the landscape Achillea millefolium Dactylis glomerata Presence 233 611
- 18. Spread of potential impact across the landscape Achillea millefolium Dactylis glomerata Dominance Presence 233 611 14 15
- 19. Spread of potential impact across the landscape Above critical abundance Dominance Presence 233 611 14 15 171 15 Achillea millefolium Dactylis glomerata Changes ranking of species
- 20. Scaling-up to γ-richness across plots αi αi αi αi αi αi αi αi αi αiαi αi γ γ-richness : total number of unique species across plots How do declines in local richness translate to the regional species pool?
- 21. R are O ccasional Frequent C om m on Abundant D om inant 0 50 100 150 200 γ-richness Trends in native γ-richness Local abundance of the focal species e.g. Lolium perenne Critical abundance for α-richness
- 22. γ-richness R are O ccasional Frequent C om m on Abundant D om inant 0 50 100 150 200 Trends in native γ-richness Expected given the number of plots in each abundance class Local abundance of the focal species Critical abundance for α-richness e.g. Lolium perenne 239 4411664106100
- 23. γ-richness R are O ccasional Frequent C om m on Abundant D om inant 0 50 100 150 200 Trends in native γ-richness Expected given the number of plots in each abundance class Local abundance of the focal species Critical abundance for α-richness e.g. Lolium perenne Effect Size of decrease in γ-richness 239 4411664106100
- 24. Loss in mean α-richness above critical abundances Lossinγ-richness comparedtonullLoss in α vs. γ richness at critical abundance • No correlation • Loss in γ-richness always larger than loss in α-richness
- 25. Conclusions • Negative relationship between native richness and alien abundance for 20% of alien species • Low abundance effects are widespread • Spatial extent is not directly an indicator of impact spread • Species loss at the landscape scale is not proportional to loss at the local scale
- 26. Implications for management • Low abundance alien species may be currently overlooked • We might be underestimating impacts at the landscape scale Prioritizing species based on impact at the landscape scale • low vs. high critical abundances suggest different underlying ecological processes of invasion - Different management targets - Different management approaches
- 27. Bio-Protection Research Centre PO Box 85084 Lincoln University Lincoln 7647, New Zealand P + 64 3 423 0932 F + 64 3 325 3864 www.bioprotection.org.nz Thank you Hugh Wilson Federico Tomasetto Jennifer Bufford Tyler Brummer Will Godsoe