Species interactionsCommunity
“The number of bumblebees in any district depends in a great
measure upon the number of field-mice, which destroy their combs
and nests”. “[Because] the number of mice is largely dependent, as
everyone knows, on the number of cats . . . It is quite credible that the
presence of a feline animal in large numbers in a district might
determine, through the intervention first of mice and then of bees, the
frequency of certain flowers in that district!”
Charles Darwin: The Origin of Species by means of Natural Selection, 6th Edition, 1859
Plants Bumblebees
Mice
Cats
Plants Bumblebees
Mice
Cats Species 1
Species interaction grid
Species 2
+ -
-
+
MutualismPredationHerbivoryDisease
PredationHerbivoryDisease
Competition
Species 1
Species interaction grid
Species 2
+ -
-
+
Plants Bumblebees
Mice
CatsPredation
Plants Bumblebees
Mice
Cats
Mutualism
Competition
Plants Bumblebees
Mice
Cats Hawks
Plants Bumblebees
Mice
Cats
Indirect effect
Examples of species interactions: Competition
House gecko introduced to Pacific islands where there is a native gecko (mourning gecko)
Examples of species interactions: Mutualism
fig trees – fig wasps750 species of figs most with a single
species of pollinator
Examples of species interactions: Predation
Wolves increased since reintroduction
Elk
Pronghorn
Coyotes
Wolves
Plants
Effect of introduction of wolves on plants and elks?
Keystone species
Species with a disproportionate effect on community structure
Total effect
Abundance
Keystone
Dominant
Keystone species can influence diversity
Equilibrium theory of island biogeography
What explains the total diversity in a community?Island biogeography
Theory describing the diversity in a community as a function of extinction and colonization
Mainland Island
Number of species = P Number of species = S
Rate
Number of island species
Colonization, the rate at which new species
are gained
Extinction, the rate at whichisland species are lost
Colonization versus Extinction
Equilibrium island species
number
0 S
Island biogeography Metapopulations
Balance of E and C Balance of E and C
Number of species in a patch
Number of patches occupied
Island biogeography and metapopulations
Area effects
P
Ss
Sl
How does island area affect the number species on the island?
C Es
El
Island species number
Rate
How does size affect extinction rate?
Area effects
P
Ss
Sl
How does island area affect the number species on the island?
C Es
El
Island species number
Rate
Sl
Ss
How does size affect extinction rate?
Ssmall
< Slarge
Area effects
P
Ss
Sl
How does island area affect the number species on the island?
Cs
Es
El
Island species number
RateC
l
How does size affect colonization rate?
Ss
Sl
Ssmall
< Slarge
Bird species in the Lesser Antilles (D. Lack's data)
Distance effectsHow does distance from the mainland affect
the number species on the island?How does size affect colonization rate?
P
Sn
Sf
Cf
E
Cn
isn
Rate
Sf
Sn
Sfar
< Snear
S
Bird species in the Lesser Antilles (D. Lack's data)Dan Simberloff
(a former FSU Biology Sciences member)
Experimental Zoogeography of Islands: The Colonization of Empty Islands, by Daniel S. Simberloff, Edward O. Wilson Ecology © 1969
Test of theEquilibrium theory of island biogeography (ETIB)
E2: closest to mainland
E1: farthest from mainland
Contribution of ETIB for conservation biology
Reserve = island
Rules for reserve design
Hanski, I. A., and G. M.E., editors. 1996. Metapopulation biology: ecology, genetics, and evolution. San Diego, CA: Academic Press. 512 p.
Island Biogeography and Reserve rules: IUCN, UN,WWF
Bigger is better
better worse
Connectivity is good
One large is better than several small
Less edge is better
What explains total diversity in a community?
Keystone species can influence diversity
Equilibrium theory of island biogeography
Disturbance
Disturbance
An event that moves the community
away from its equilibrium state
Disturbance events can be caused by biotic (e.g. disease) and abiotic factors (e.g. fire)
An event that moves the community
away from its equilibrium state
Disturbance
Equilibrium state?
In Southeast = long-leaf pine forest In Midwest = tall grass prairie
Disturbance vs. Equilibrium
When disturbances are very frequent, then
equilibrium may never happen.
Some species specialize on disturbance
Furbish"s lousewort
Succession
the process by which a community moves towards
its equilibrium state following a disturbance
What is the relationship between disturbance and species diversity?
How does diversity vary with the frequency of ! !
! disturbance?
How does species diversity vary with the time since disturbance?
How does species diversity vary with the magnitude of disturbance?
Intermediate disturbance hypotheses
Num
ber
of sp
ecie
s
- Disturbance ratefrequentshortly after
large
infrequentlong after
small
Intermediate disturbance hypotheses
Num
ber
of sp
ecie
s
- Disturbance ratefrequent infrequent
Community is a
mosaic of patches at
different stages of
succession
Community is
dominated by
a few superior
competitorsCommunity is
dominated by a
few colonizing
species