Self organising vegetation patterns

XXXV CONVEGNO NAZIONALE DI IDRAULICA E COSTRUZIONI IDRAULICHEBologna, 14‐16 Settembre 2016

Niche adaptation in self‐organizingvegetation patterns affects ecosystem

shape and yield in arid land

N. Ursino1 e C. Callegaro2

1Dipartimento ICEA, Università di Padova, [email protected] [email protected]

CRITERI, METODI E MODELLI PER L’ANALISI DEI PROCESSIIDROLOGICI E LA GESTIONE DELLE ACQUE

MODELLAZIONE INTEGRATA DI SISTEMI IDROLOGICI


“Landmanagersshould attemptto mimicsuch bandedvegetationpatterns whenrestoringdegraded aridor semi-aridland andwhen designingwater-harvestingsystems.”

Valentin et al, 1999

Vegetation patterns are natural water-harvesting systems

http://www.pangea-project.org/agricoltura/


Self organizing patterns emerging at field scaleoriginate from positive feedbacks operating at small spatial scale

Time

Steady state and perturmation bands


Differing speciespopulate regular vegetation patterns

Valentin and d’Herbes, 1999

What drives the processby which species from a regional pool colonizeand interact to formlocal communities?


“Community assembly isinfluenced by processesoperating at a wide range ofspatiotemporal scales…

…subpool ofspecies pass through anenvironmental (abiotic) filterand a biotic filter.. Localcommunities reflect the cumulative effects ¨of these processes…

.. the niche of a speciesincludes both its response toand impact on the abiotic and biotic environment”

HilleRisLambers et al., 2012


“When grown in mixtures, relative differences in height and specific leafbetween plantspeciesselected in mixture are greater thanbetween speciesselected in monocultures.”

Zuppinger-Dingleyet al., 2014


Evolutionary and ecosystemprocesses havelong been treated asdistinct.

Thefinding thatinteractions amongplant species cause rapid evolutionarychanges thataffect ecosystemfunction suggeststhat it is time forunification.

Tilman and Snel-Rood, 2014


Niche differences, including variation in rooting depth, cause species to limitindividuals of their ownspecies more than theylimit competitors.

This gives speciesgreater per capita growth rates when theyare rare and theircompetitors are common than when they are common and theircompetitors are rare.

JM Levine & J HilleRisLambers 2009

How niche differences maintain diversity.


COMPLEMENTARY ADAPTATION TO SOIL MOISTURE AVAILABILITY

SOIL MOISTURE CONTENT (w)PER

CA

PITA

GR

OW

T RA

TE

We test the hypothesis thattraitsdifferentiationtranslates intoadaptation toseparate oroverlapping soilmoisture niches

Because of the multiple roles that water plays in biological and geochemical processes, water limitation can impact correlated

processes and other fitness constraints. Harpole, 2016


(a) inter-specific facilitation; (b) intra-specific facilitation.

Coexistence, exclusion and self-organizationmay result fromcomplementaryadaptationstrategies.

When thereis a gap in soilmoistureadaptation (w2> w1) the mostdrought-tolerantspecies tends tobe displaced.

Ursino and Callegaro, 2016


w /w2

w/w1

w /w2w

/w1

x

n1,n

2

xn1

,n2

x

n1,n

2

x

n1,n

2

patterns and exclusionexclusion

coexistence

patterns and coexistence

x

n1,n

2

patterns and exclusion

x

n1,n

2

x

n1,n

2

exclusion

Biomass density (proportional to circle radius) as a function of species adaptation thresholds.


Results

Vegetation patterns are extremely vulnerable to exclusive species adaptation to non overlapping niches.

The higher biomass density is achieved in case of uniform vegetation cover, and the lower when species self-organize in patterns.

Adaptation of one species to a too tight range of extreme conditions does not preserve biodiversity and may rather lead toexclusion.


Conclusions 1/2

“..introducing a second species to a water-limited system dominated by a pattern-forming species leads to stable coexistence … (when) the pattern forming species acts as an ecosystem engineer by concentrating the water resource, while the second species, which is not pattern forming by itself, is a better competitor and (is) characterized by a higher dispersal capability. “

Nathan et al., 2013

Evolution by natural selection and niche differentiation in spontaneousvegetation patterns are an alternative explanation for zonation to previous theories focussing on colonization, competition, facilitation and invasion

Evolutionary and ecosystem processes need unification (Tilman and Snel-Rood, 2014)….


Conclusions 2/2

“Niche differentiation may promote species co-existence because it precludescompetitive exclusion. However, in stressful environments, facilitation maypredominate, and large niche overlaps may result from niche widening and positive spatial associations. “

Martorell et al, 2015(Semi-arid grassland, Oaxaca, Mexico)

Inter-specific and intra-specific net facilitation both lead to vegetation self-organization under resource scarcity, although facilitation needs differentiation and complementarity of traits along an environmental gradient.

Land managers should attempt to mimic such banded vegetation patternswhen restoring degraded land…(Valentin and d’Herbes, 1999)

Education

Self organising vegetation patterns