NEIGHBORHOOD FUNCTIONS ALTER UNBALANCED FACILITATION
IN AN ALPINE TREELINE SIMULATION
Problem: Treelines
Malanson, George P.(1), Resler, Lynn M.(2)
(1) University of Iowa & NSF
(2) Virginia Tech
george-malanson@uiowa.edu
Facilitation & SGH
Spatial effects of neighbors
 Range limits
 1o impact:
biodiversity?
Why do treelines respond to
climate change – or not?
What can we learn about
ecological relations?
Malanson et al. 2011, AAAR
Alpine Treelines

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Pioneer
Keystone
Foundation
Unbalanced
facilitation?
 Spatially
explicit
feedbacks
Pinus albicaulis
Resler & Tomback 2008 AAAR; Tomback et al.
2014, AAAR
Newer question: how do neighbors
create stress-gradient interaction
intensity?
Newer model:
Delete pathogen, climate change
Focus on neighbor relations (linear,
logarithmic, unimodal) in stressgradient hypothesis
 Stress gradient correlated facilitation
(SGCF) boosts edges and mean
facilitation
 SGCF increases populations in the
area of higher stress
 SGCF increases the beneficiary species
relative to even facilitation
 Unimodal functions of facilitation for
neighbor density magnify all above
effects; important in ecotones with
patchy patterns
Malanson & Resler 2014, JTB
Facilitation vs Competition
1‐neutral, 2‐positive, 3‐negative
4‐ stress gradient hypothesis
5000
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4000
3000
H1X
2000
1000
H2X
H3X
Coexistence
 Climate effects
questionable?
Negative Interaction
with Climate Change
3000
2000
H
3…
1000
H4X
Newest question: how do contrasting
neighbor interactions affect
coexistence with climate change?
Newest model (w/climate change):
3 types of interaction:
 negative, competitive
 positive, facilitative
 stress-gradient switch
Funding:
0
0
1
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601
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 Stress-gradient
hypothesis?
Extensions of an Agent-Based Model
Smith-McKenna et al. 2014, EM&S
Environmental
gradient
Establishment
seeds, seedlings
Growth
branches
Mortality
age class
Pathogen
blister rust
Climate change
amelioration
Coexistence
 Fundamental
niche?
Latest results: for 3 species on a
hierarchical competition niche gradient:
 facilitation decreases coexistence,
sharpens boundaries
 competition has strong transient effects
with climate change and leads to long
term coexistence
 effects are shifted spatially in the stress
gradient case