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Invasion by e xotic species

Invasion by e xotic species. A possible mechanism that allows competitive coexistence between native and exotic plants. Augustina di Virgilio Ewaldo L. de O. Júnior João Pinheiro Neto Luiz H. de Almeida Melina O. Melito Pedro G. A. Alcântara. Invasions. -. Resources consumption

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Invasion by e xotic species

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  1. II Southern-Summer School on Mathematical Biology Invasion by exotic species A possible mechanism that allows competitive coexistence between native and exotic plants. Augustina di Virgilio Ewaldo L. de O. Júnior João Pinheiro Neto Luiz H. de Almeida Melina O. Melito Pedro G. A. Alcântara

  2. II Southern-Summer School on Mathematical Biology Invasions - Resources consumption Disease transmission - + Exotic bumblebee Native bumblebee “Steals” nectar Native plants

  3. II Southern-Summer School on Mathematical Biology Relevance • Worldwide phenomena. • Invasion can have strong effects on the environment. • Diversity of species could be at risk. • Conservation polices have to take this into account.

  4. II Southern-Summer School on Mathematical Biology Competition • A basic competition dynamics should eventually force the elimination of the weaker competitor (CompetitiveExclusionPrinciple). • However, there is no evidence to suggest that this is a common occurrence. (Lonsdale 1999;Stohlgrenetal. 1999) • The species forge a kind of coexistence.

  5. II Southern-Summer School on Mathematical Biology So how can there be coexistence? • There must be mechanisms regulating the interactions. • What could they be? • Predator, niche, space, delay for predators to attack (enemy release), or many other possibilities. • It could even be that the timescale in which the elimination happens is just too large for we to observe

  6. II Southern-Summer School on Mathematical Biology Predator hypothesis • Could predators act as a mechanism promoting equilibrium? • Two competitive preys one predator. • Trade-off: competitive ability X susceptibility to predation?

  7. II Southern-Summer School on Mathematical Biology Study system • Estuarial plant communities in New England • Similar native and exotic plants • Herbivory by insects Native species Exotic species (Heard &Sax, 2012)

  8. II Southern-Summer School on Mathematical Biology Dynamics – Model 1 Herbivores Native plants Exotic plants

  9. II Southern-Summer School on Mathematical Biology Assumptions • Natives and Exotics - different growth rates • Herbivore rates are different for exotics and natives • Competitive strength is not symmetrical • Capture rate (), conversion rate (), and the parameter D are the same for both species

  10. II Southern-Summer School on Mathematical Biology First model

  11. II Southern-Summer School on Mathematical Biology No predators Coexistence No exotics

  12. II Southern-Summer School on Mathematical Biology Population size Natives Exotics Predators

  13. II Southern-Summer School on Mathematical Biology Dynamics – Model 2 Herbivores Native seedlings Exotic seedlings Native adults Exotic adults

  14. II Southern-Summer School on Mathematical Biology Second model

  15. II Southern-Summer School on Mathematical Biology No predators No exotics No natives Coexistence

  16. II Southern-Summer School on Mathematical Biology Robustness of the models

  17. II Southern-Summer School on Mathematical Biology Comparison between models

  18. II Southern-Summer School on Mathematical Biology General conclusions • Both models fit the observations. • Predator dynamics could act as a mechanism to promote coexistence between competitors. • A basic trade off in adaptability and susceptibility to predators could explain coexistence without loss of biodiversity. • We must remember they may not be the only mechanism at work.

  19. II Southern-Summer School on Mathematical Biology References: [1] Heard, M.J. and Sax, D.F. , Coexistence between native and exotic species is facilitated by asymmetries in competitive ability and susceptibility to herbivores. Ecology Letters 16 (2013) 206. [2] Adler,P.B. et alli, Coexistence of perennial plants: an embarrassment of niches. Ecology Letters 13 (2010) 1019. [3]Keane, R.M. and Crawley, M.J.  Exotic plant invasions and the enemy release hypothesis. Trends in Ecology and Evolution 17 (2002) 164. [4] Davis, M.A. et alli.  Don't judge species on their origins. Nature 474 (2011) 153. [5] Stromberg, J.C. et alli.  Changing Perceptions of Change: The Role of Scientists in Tamarix and River Management.  Restoration Ecology 17 (2009) 177 Images from: • http://ian.umces.edu/ • Augustina di Virgilio - Argentina Special thanks to group 6 for their work on preferences, it was very useful.

  20. II Southern-Summer School on Mathematical Biology Parameters – Model 1 Saciation coefficient Predators mortality rate Conversion coefficient Natives growth rate Exotics growth rate Natives carrying capacity Exotics carrying capacity Competition coefficient Feeding efficiency Natives herbivore rate Exotics herbivore rate

  21. II Southern-Summer School on Mathematical Biology Parameters range – Model 1

  22. II Southern-Summer School on Mathematical Biology Parameters range – Model 2

  23. II Southern-Summer School on Mathematical Biology Experimental observations • Results (Heard & Sax, 2012):

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