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