Island Biogeography

1
(No Transcript)
2
Island Biogeography

• Explore the relationships of I and E rates and S
  to island area and distance
• Observe the accumulation of sp on an island, and
  the approach of I and E rates and S values to
  equilibrium
• Find equilibrium values of I and E and sp
• Understand species-area curves and the underlying
  mathematical relationships
• Explore interaction effects of A D

3
Island Biogeography

• Larger islands and closer islands support a
  greater number of species than smaller or more
  distant islands
• These relationships can be described as
  species-area or species-distance
• These patterns not only hold for true oceanic
  islands, but also mountain tops, lakes, and other
  habitat islands

4
Island Biogeography
5
Island Biogeography

• So what mechanism (or process) generates this
  pattern?
• MacArthur and Wilson (1967) modeled species
  richness as the result of two processes I and E
• Equilibrium theory of island biogeography

6
Island Biogeography

• I rate is determined by 3 factors
• Distance, sp remaining in mainland pool,
  probability a given sp will disperse
• E rate is determined by 3 factors
• Island area, of sp on island, probability that
  a given sp will go extinct

7
Island Biogeography

• In the simplest version of the model, all sp have
  equal probability of I E
• Realistically, I should be inversely related to D
• Iimm rate, Pmainland sp pool, Sisland
  richness, Ddistance, ccolonization probability,
  fscaling factor for distance (which have been
  estimated c0.1, f0.01)

I c (P-S) / f D
8
Island Biogeography

• Consider E
• Eextinction rate, Ssp richness on island,
  Aarea, qextinction probability, mpower factor
  scaling for area
• Values for q and m must be derived from the data
  ((q0.20, m0.25)

E qS / Am
9
Island Biogeography

• Consider Eq. 1, you can see species accumulate on
  an island, I will decrease
• Conversely, as S increases, E increases
• At some intermediate value, I and E will become
  equal and the S will be in equilibrium

I c (P-S) / f D
E qS / Am
10
Graphical model of one variation of
MacArthur-Wilson Dynamic Theory of Island
Biogeography
11
Island Biogeography

• 2nd important point, the equilibrium point of S
  is a dynamic equilibrium
• At this point, IE, but neither is 0 and
  consequently, there is turnover

12
Graphical model of one variation of
MacArthur-Wilson Dynamic Theory of Island
Biogeography
Turnover Rate
13
Island Biogeography

• This model has been widely adopted for
  conservation purposes, but do you see any
  potential flaws?

14
Island Biogeography

• The rate at which species are accumulated by
  increasing area is the slope
• All else being equal, more sp on a given area of
  mainland supports more than same area of island

15

Z-values (slope in species-area curve) tend to be
lower in groups that disperse well (such as
birds, graph b) than in groups that show more
effect of isolation (such as mammals, graph c)
16
Island Biogeography

• Lets look at the model graphically and consider
  a few special cases

17
Effect of island area, distance held constant
18
Effect of island distance (isolation), area held
constant
19
Final pattern Isolation effect, shown by fewer
species on isolated islands, in species-area
curve for birds of warm ocean regions red
triangles represent isolated islands (gt300 km
from next largest land mass) (from Paul Slud)
Cocos Island, Costa Rica
20
Both isolation (distance) effects on immigration,
and island size (area) effects on extinction,
combined into one model--showing different
predicted equilibrium species richness values
21
Target Effect of island area, distance held
constant
L Is
22
Rescue Effect of island distance (isolation),
area held constant
S EL
23
Island Biogeography