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Species interactions
Community
Cats
“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!”
Mice
Plants
Bumblebees
Charles Darwin: The Origin of Species by means of Natural Selection, 6th Edition, 1859
Species interaction grid
Species 1
Cats
+
-
+
Mice
Species 2
Plants
Bumblebees
Species interaction grid
Species 1
+
+
-
Mutualism
Predation
Herbivory
Disease
Predation
Cats
Mice
Species 2
-
Predation
Herbivory
Disease
Competition
Plants
Bumblebees
Competition
Cats
Cats
Mice
Mice
Hawks
Mutualism
Plants
Indirect effect
Bumblebees
Cats
Plants
Bumblebees
Examples of species
interactions: Competition
House gecko introduced to
Pacific islands where there is a
native gecko (mourning gecko)
Mice
Plants
Bumblebees
Examples of species
interactions: Mutualism
fig trees – fig wasps
750 species of figs
most with a single
species of pollinator
Examples of species
interactions: Predation
Wolves increased since reintroduction
Keystone species
Wolves
Species with a disproportionate
effect on community structure
Coyotes
Elk
Total effect
Pronghorn
Keystone
Dominant
Plants
Effect of introduction of wolves on plants and elks?
Abundance
What explains the total diversity in a community?
Island biogeography
Keystone species can influence diversity
Equilibrium theory of island biogeography
Theory describing the diversity
in a community as a function of
extinction and colonization
Colonization versus Extinction
Island
Mainland
Rate
Extinction, the rate at which
island species are lost
Colonization, the rate
at which new species
are gained
Equilibrium
island species
number
0
Number of species = P
Number of species = S
Number of island species
Island biogeography and
metapopulations
Island biogeography
S
Area effects
How does island area affect the number
species on the island?
How does size affect extinction rate?
Metapopulations
Ss
Balance of E and C
Balance of E and C
Number of species in
a patch
Number of patches
occupied
C
Es
Rate
El
P
Sl
Island species number
Area effects
Area effects
How does island area affect the number
species on the island?
How does size affect extinction rate?
How does island area affect the number
species on the island?
How does size affect colonization rate?
Ssmall < Slarge
Ssmall < Slarge
Ss
C
Rate
Ss
Es
El
P
Cs
P
Sl
Sl
Ss
Island species number
Cl
Rate
Es
El
Sl
Sl
Ss
Island species number
Distance effects
Bird species in the Lesser Antilles (D. Lack's data)
How does distance from the mainland affect
the number species on the island?
How does size affect colonization rate?
Sfar < Snear
Sn
Rate
E
Cn
Cf
Sn
P
Sf
Bird species in the Lesser Antilles (D. Lack's data)
Test of the
Equilibrium theory of island biogeography (ETIB)
Experimental Zoogeography of Islands: The Colonization of Empty Islands, by Daniel S. Simberloff, Edward O. Wilson Ecology © 1969
isn
S
Sf
Dan Simberloff
(a former FSU Biology Sciences member)
Contribution of ETIB for
conservation biology
E2: closest to mainland
Reserve = island
Rules for reserve design
E1: farthest from mainland
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
better
What explains total diversity in a
community?
worse
Bigger is better
Connectivity is good
One large is better
than several small
Keystone species can influence diversity
Equilibrium theory of island biogeography
Disturbance
Less edge is better
Disturbance
Disturbance
An event that moves the community
away from its equilibrium state
An event that moves the community
away from its equilibrium state
Equilibrium state?
In Southeast = long-leaf pine forest
Disturbance
events can be
caused by biotic
(e.g. disease) and
abiotic factors
(e.g. fire)
In Midwest = tall grass prairie
Succession
Disturbance vs. Equilibrium
the process by which a community moves towards
its equilibrium state following a disturbance
When disturbances are very frequent, then
equilibrium may never happen.
Some species specialize on disturbance
Furbish"s lousewort
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
Number of species
What is the relationship between
disturbance and species diversity?
frequent
shortly after
large
Number of species
Intermediate disturbance hypotheses
frequent
Community is a
mosaic of patches at
different stages of
succession
Community is
dominated by a
few colonizing
species
- Disturbance rate
Community is
dominated by
a few superior
competitors
infrequent
- Disturbance rate
infrequent
long after
small