Transcript Island biogeography II: the application

Island biogeography II:
the application
Bio 415/615
Questions
1. Why would one large reserve be
better than small ones of equal total
area?
2. How are spatial grain and extent
related to the SLOSS debate?
3. How does distance decay of similarity
apply to SLOSS?
4. How do properties of species
contribute to SLOSS?
IBT & Design (Diamond)
•
•
•
•
A. Large is better than small
B. Undivided is better than divided
C. If divided, close is better than far
D. If divided, distances should be
equal
• E. Corridors are better than no
corridors
• F. Circular is better than narrow (low
perimeter to area ratio)
Size
Better
Worse
Fragmentation
Better
Worse
Distance
Better
Worse
Clustered
Better
Worse
Connectivity
Better
Worse
Shape
Better
Worse
The
SLOSS Debate
Single Large
Or
Several Small
of the same total area
Megareserves for large predators
>106 ha
100 km linear extent
Simberloff & Abele 1976
•
•
•
•
Island A becomes Archipelago A
Island B becomes Archipelago B
For A, SS > SL
For B, SL > SS
Simberloff & Abele 1976
Area m2
Spp
A
475
77
-------------------------------A1
119
51
A2
133
48
A3
80
47
A4
102
50
Archipelago A
434
81
81 > 77!!
Simberloff & Abele 1976
Area m2
Spp
B
168
56
-------------------------------B1
71
36
B2
87
32
Archipelago B
158
47
47 < 56!!
Immediate Complaints
Diamond, Terborgh, Whitcomb
• Not all spp equal
– Some extinction prone, Total Spp not the
best measure of success
– Large predators need 100s-1000s km2
– Colonial nesters, Migrating spp, Spp
dependent on core
• Small reserves lose the same Spp, so
become more similar to each other,
more overlap, spp lists are nested
Species are Not Equal:
Incidence functions -- Diamond
Nested Species Lists
• Deterministic extinctions
– Sites lose species in a predictable
sequence based on site area
• Area sensitivity
– Small areas all lose the same species
– Sites lose species in a predictable
sequence based on isolation
• Isolation sensitivity
• Nesting of species lists reduces
distance decay and SL > SS
Biological Dynamics of Forest
Fragments Project
• Manaus, Brazil, est. 1979
11 fragments:
1 ha
10 ha
100 ha
avg. 280 tree
species per ha
(~200 in NY!)
Biological Dynamics of Forest
Fragments Project
Biological Dynamics of Forest
Fragments Project
• Results: complex!
• Some species suffered immediately:
– Large mammals, primates, understory birds,
certain large-range insects (beetles, ants,
termites, bees, butterflies)
• Some species unaffected regardless of
fragment size
– Small mammals, frogs
Biological Dynamics of Forest
Fragments Project
• EDGE EFFECTS
• Microclimate changes impacted species
in smallest fragments (esp. plants,
insects, understory birds); favored
other ‘gap species’
• Matrix matters: patches surrounded by
cattle pastures more affected than
those surrounding by regrowth forests
Single Large
vs. 2 Half Reserves
• A = 1 vs. A = ½ A
• Z = .263
• SH = c (A/2)z = Az/1.2 = .83 SL
• If total overlap, 2 * SH = .83 SL
– SL WINS!
• If no overlap, 2 * SH = 1.66 SL
– SH WINS!
Estimation of critical similarity
for SLR>THR as a function of z
90%
Single Large Reserve
75%
R=1.0
2 Half
Reserves
.1
.3
Bell & Boecken 1990
z (log-log slope of the species-area relation)
2 Kinds of
Diversity
Inventory
Diversity
α, γ, δ
Differentiation
Diversity
β
β diversity measures
• β = γ / α, β = γ – α
α
γ
• β = (log [sim0] – log [simmin])/ log 2
– Half change beta
β diversity measures
• β = γ / α, β = γ – α
• β = the distance decay of similarity
Similarity
a
c
b
d
• Differentiation diversity (β)
– Jaccard’s Index
– Sørensen’s Index
– Matching Coefficient
β diversity measures
• β = γ / α, β = γ – α
• β = the distance decay of similarity
Similarity
a
c
b
d
The first law of geography:
the similarity between two observations
decreases or decays with distance
Sd = S0 e-cd, d is distance, c is the rate
of distance decay, S0 is the initial
similarity
Circumpolar Boreal Forest
Plants on 300 x 300 m plots
Upland spruce forest
(LaRoi 1966)
Rate of decay: Nut/berry>Mosses, Small, Wind
C=-0.25
Plumose
C=-0.43
Nut/berry
C=-0.23
Spore/micro
C=-0.27
Other
Distance decay in
Spruce-fir forests along
the Appalachians is 2.7x
the Boreal forest rate
C=-0.25
C=-0.67
What causes distance decay?
The rate of distance decay, c, varies with
Two traits of environment &
Two traits of organisms:
Environment
Organism traits
Adaptation
Gradients
Niche
Movement
Resistance
Vagility
SLOSS?? It depends!
Several Small
Species overlap (similarity) among islands
Simberloff & Abele 1972
Rate of distance decay of similarity
Nekola & White 1999, 2002
Body size, vagility, gene flow
Nestedness
Boecklen 1997
CONSERVATION STRATEGY
Both grain and extent are critical!
Grain: Ecological integrity, Population viability
Hydrology, Black bears, Vagile species
Extent: variation in environment and history
Local endemics, Poorly dispersed species
Representativeness
SLOSS is here to stay because grain &
extent maximize different contributions to
biodiversity