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Is there a mechanism deficit in ecology? INTECOL 2013.

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Presentation on theme: "Is there a mechanism deficit in ecology? INTECOL 2013."— Presentation transcript:

1 Is there a mechanism deficit in ecology? INTECOL 2013

2 Agenda Macroecology is mechanism-less? Mechanism in ecology Mechanism in physics Example 1 – distribution & abundance Example 2 - biogeography

3 Macroecology – a mechanism deficit? “If you can do a regression and pull data out of a journal you can do macroecology” Machine Learning p<0.05I did science! ?

4 Agenda Macroecology is mechanism-less? Mechanism in ecology Mechanism in physics Example 1 – distribution & abundance Example 2 - biogeography

5 Reductionism Sadava et al Causality Biology is hierarchical reified Causality moves up Mechanism comes from below Ricklefs Potochkin & McGill 2012

6 Generalized Lotka Volterra

7 But does it work? McGill 2013 (in The Balance of Nature and Human Impact ed. Rohde)

8 The equilibrial target is always moving!

9 Agenda Macroecology is mechanism-less? Mechanism in ecology Mechanism in physics Example 1 – distribution & abundance Example 2 - biogeography

10 Physics 1687 Newton: 1. F=Ma 2. F=GM 1 M 2 /d 2 3. Inertia & equal/opposite reactions Descartes clockwork universe

11 Physics 2013 Quantum mechanics Statistical mechanics

12 Mechanism in physics Practical If you have an equation that is useful/predictive you have a mechanism (or maybe you’re just done and don’t care about mechanism?) Laddered Quantum mechanics gives Bohr atom Physical chemistry gives multi-atom systems Ideal gas law/statistical mechanics gives relation of macro- properties Statistical Quantum mechanics Statistical mechanics (avoids intermediate numbers problem) As general as possible Only occasionally reductionist (more often self-contained) Context aware (external forcing, environment)

13 Conclusion Macroecology Doesn’t have a mechanism deficit Has a mechanism recognition deficit Mechanisms in ecology: AWOL or Purloined Letter. Towards a practical view of mechanism McGill & Nekola

14 Agenda Macroecology is mechanism-less? Mechanism in ecology Mechanism in physics Example 1 – distribution & abundance Example 2 - biogeography

15 A thought experiment – sampling from the region Region Small local community N=2, S=2 Larger local community N=4, S=3

16 We can write sampling idea as equations S, N, N i, A from region are inputs Pivotal idea is sampling function: P=  (n i |N i,a,A,  ) McGill 2011 American Journal Botany Also see: Etienne & Alonso 2005 Green & Plotkin 2007 He & Legendre 2002 Dewdney 1998 Pielou multiple

17 How are we doing? Surprisingly not too bad, but we’re missing something (too much , not enough  )

18 Need another assumption Have been using sampling function, , as spatially random (binomial or Poisson form) We know clumped in nature Clumping would fix problems (reduce , increase  ) More individuals from same species in sample lowers  More individuals from same species in one sample, likely to be underrepresented in other sample increases  Condit et al 2000

19 Clumping fixes it!  =Finite Negative Binomial (Zillio & He 2010)

20 Sampling works at small scales Scale-break 100km X 100km Deterministic absences Moving out of range Stochastic absences Sampling

21 Spatially explicit, larger scale version WIDTH A B ii RADIUS i EXTENT Abundance Spatial extent MVP i Range Boundary  ii N i (X)=NMAX i exp(||X-  i || 2 /  2 ) X McGill & Collins 2003 Also see Gauch & Whittaker 1972 Allen & White 2003

22 3 assumptions common to many theories 3 Assumptions 1. Species abundance varies logarithmically 2. Individuals in 1 species are clumped 3. All else can be random McGill Ecology Letters 2010

23 Agenda Macroecology is mechanism-less? Mechanism in ecology Mechanism in physics Example 1 – distribution & abundance Example 2 - biogeography

24 Back to Leibig’s Law? Gause Leibig biogeographic law Any one variable sets an upper limit according to a Gause’s law (Gaussian bell-curve) But most sites at the optimum are limited by something else

25 It appears to be very general

26 It appears very general

27 Bruce Martin Wikimedia under CCA

28 In the lab can home in on limiting factor Cristian Solari

29 Environment and Organisms What Dozens of GIS layers of climate that are biologically relevant for use in distribution modelling Bioagricultural (e.g. degree days, frost free days, drought) Extreme events (10-year coldest day, 50 year drought) Topographic (slope, aspect, moisture indices) Landcover Traditional climate Publically served, global 1km co-registered Status Funding from 3 organizations, >30 people involved Pieces starting to become publically available

30 Non-stationarity is now helpful

31 Can do predictions

32 Summary Mechanism is not deterministic and reductionist Mechanism is often stochastic, self- referential, context-sensitive, more general than biology Macroecology already has many mechanisms! Sampling w/ clumping Gause’s normal curve & Liebig’s Law


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