Do ecohydrology and community dynamics feed back
to banded-ecosystem structure and productivity?
Callegaro* C. and Ursino* N.
*: University of Padova, Dept. of Civil, Environmental and Architecture Engineering, Padova – Italy.
ECOHYDROLOGY AND COMMUNITY DYNAMICS OF BANDED ECOSYSTEMS
Species act as ecosystem engineers when they
can feed the typical water source-sink system
formation.
Relevant processes leading to vegetation patterning do
not change with root architecture (Ursino, 2009)
Ecosystem engineers and non ecosystem
engineers may both lead to self-organized
vegetation patterns in arid lands.
However, the root/shoot ratio may reverse the correlation
between soil moisture and biomass distribution (Gilad et
al., 2007), affecting the engineering behaviour.
The biomass growth rate dependence on
biomass density
determines:
i) whether a plant acts as an ecosystem
engineer or not;
ii) which hydrological process enable
vegetation pattern initiation.
A pattern-forming species modulates the soil moisture
distribution, that in turn mediates competition and allows
the coexistence of different species. Long-range
dispersal may penalize the fastest disperser, as
reproductive efforts occurring outside of the islands of
resource abundance are wasted (Nathan et al., 2013).
What happens if species with
the same traits evolve within the
pattern by niche differentiation?
MODELLING ATTEMPT:
- space-explicit dynamical system
- two vegetation species, and water
resources
- restriction of biomass growth to
SPECIFIC WATER CONTENT NICHES
MODELLING CASE 1: ECOSYSTEM ENGINEERS
Ecosystem engineers accumulate soil moisture where the vegetation density is higher.
SEPARATE NICHES
the positive feedback
between
infiltration and biomass
density leads the formation of
patterns of POSITIVELY
correlated soil moisture and
vegetation
(HilleRisLambers et al., 2001)
x
0
w1
w2
1
COMPLEMENTARY NICHES
0
w1=w2
1
OVERLAPPING NICHES
0
w2
w1
water content, w
1
MODELLING CASE 2: NON ECOSYSTEM ENGINEERS
w2
1
COMPLEMENTARY NICHES
w2/w0
0.5
INTRA-SPECIFIC
FACILITATION:
each species growth
function is proportional
to specific
biomass density
0.5
0.3
0.3
0.1
0.1
0.3
0.5
w1/w0
0.7
0.1
0.9
0.9
0.7
0.7
0.5
0.3
0.1
0.1
0.5
w1/w0
0.7
0.9
0.1
ECOSYSTEM
PRODUCTIVITY
0
w1=w2
1
0.3
RESULTS
0.5
w1/w0
n1,n2
n1,n2
1
0.7
0.9
0
bare soil
uniform cover and exclusion, species 2 only
patterns and exclusion, species 2 only
uniform cover and exclusion, species 1 only
uniform cover and coexistence
patterns and exclusion, species 1 only
patterns and coexistence
0.3
3.0
X
productivity
X
X
n1,n2
n1,n2
w2
w1
water content, w
0.9
ECOSYSTEM
STRUCTURE
OVERLAPPING NICHES
0
0.7
0.5
0.3
0.3
0.5
w /w
1
0.9
0.1
0.3
n1,n2
w1
0.7
n1,n2
0
0.7
X
X
n1,n2
SEPARATE NICHES
0.9
w2/w0
x
0.9
0.1
w2/w0
Soil moisture redistribution
leads to the formation of
patterns of NEGATIVELY
correlated soil moisture and
vegetation
(Klausmeier, 1999)
INTER-SPECIFIC
FACILITATION:
equal growth functions
of both species, which
are only dependent on
the total local biomass
w2/w0
Non-ecosystem engineers deplete the soil moisture in the root zone and lead to counter phase soil moisture and biomass density spatial
X
X
CASE 1: evolution by niche differentiation of species behaving as ecosystem engineers leads to bare soil when the plant growth is restricted to a limited niche.
CASE2: evolution by niche differentiation of non engineer species favours biodiversity in vegetation patterns, which rely on inter-specific facilitation mechanisms,
unless one species adaptates to extremely harsh conditions; in that case, adaptation leads to exclusion.
Gilad E., von Hardenberg J., Provenzale A., Shachak M. and E. Meron (2007) A mathematical model of plants as ecosystem engineers, Journal of Theoretical Biology, 244, 680-691
HilleRisLambers, R., Rietkerk M., van den Bosch F., Prins H. H. T. and H. de Kroon (2001), Vegetation pattern formation in semi-arid grazing systems. Ecology, 82(1), 50-61.
Klausmeier CA. (1999), Regular and irregular patterns in semiarid vegetation. Science 284, 1826-1828.
Nathan J., von Hardenberg J., Meron E. (2013), Spatial instabilities untie the exclusion-principle constraint on species coexistence. Journal of Theoretical Biology 335, 198-204.
Ursino N. (2009), Above and below ground biomass patterns in arid lands. Ecological Modelling, 220, 1411-1418.
Ursino N. and C. Callegaro (2016), Diversity without complementarity threatens vegetation patterns in arid lands. Ecohydrology, DOI: 10.1002/eco.1717