Communities, ecosystems, and
landscapes:
Species Interactions
Pine
Old-growth
Spruce-Fir Hemlock-hardwoods
Heath Bald
YBirch
Pine
Oak
Oak
Farming/Settlement
The Goldilocks problem
• Not too hot, not too cold, but just right
• Species have ranges of tolerance and
optima for given environmental
parameters
• Species tend to have different set points
• A particular change in the environment
or conservation strategy will be good for
some species and bad for others
Pure Effects of Diversity:
Niche division, Niche overlap
• Complementarity
• Redundancy
Hemlock
Beech
Tuliptree
Then now is the chance for flowers
That can’t stand mowers and plowers.
It must be now, though, in season
Before the not mowing brings trees on,
…The trees are all I’m afraid of,
That flowers can’t bloom in the shade
of…
The Last Mowing, 1928
Intermediate Disturbance
Hypothesis
Most
flowers
Can’t stand
mowers and
plowers
Succession to
trees that flowers
can’t bloom in the
shade of
Intermediate Disturbance
Hypothesis
Most
flowers
Can’t stand
mowers and
plowers
Succession to
trees that flowers
can’t bloom in the
shade of
Species response to a given
disturbance
•
•
•
•
•
Increasers
Decreasers
Invaders
Retreaters
Integrators
The challenge to management!
Types of interactions
-
0
+
- Competition Amensalism
Predation
herbivory
parasitism
allelopathy
0 Amensalism Neutralism
Commensalism
+ Predation
Mutualism
herbivory
parasitism
allelopathy
Commensalism
Figure 8.6
Ficus carica – Edible Fig
So, naturalists observe, a flea
hath smaller fleas that on him prey,
and these have smaller fleas to bite ‘em,
and so proceed, ad infinitum.
--Jonathan Swift
Trophic Structure:
Cascading effects
“Just as a deer herd lives in mortal
fear of its wolves, so does a mountain
live in mortal fear of its deer.”
Aldo Leopold, Think like a mountain
The enemy of my enemy is my friend…
predators as the friend of plants
Hairston, Smith and Slobodkin (1960)
‘HSS model’
Why is the world green?
1. Decomposers are limited by their food
(otherwise fossil fuels would build up
quickly)
2. Plants are limited by their resources
(as they are not all eaten up by the
herbivores)
3. Herbivores are not limited by their
food (because they are only seen to
eat all their food plants when, rarely,
they are ‘protected’ by ‘human’ or
‘natural events’). Therefore, herbivores
are limited by predators.
4. Carnivores are limited by their food
(since predators are controlling prey,
they must be limited by prey).
Hairston NG, Smith FE, Slobodkin LD (1960) Community structure poplation control and
competition. American Naturalist 94:421-425.
Oksanen L, Fretwell SD, Arruda J, Niemela P (1981) Exploitation ecosystems in gradients of
primary productivity. AmNat 118:240-261
HSS
Fretwell-Oksanen (1981)
o
carnivores (3 )
3
o
2
herbivores (2 )
o
primary producers (1 )
1
o
1
o
o
low medium
o
2
1
o
o
high
PRODUCTIVITY
Hairston NG, Smith FE, Slobodkin LD (1960) Community structure poplation control and
competition. American Naturalist 94:421-425.
Oksanen L, Fretwell SD, Arruda J, Niemela P (1981) Exploitation ecosystems in gradients of
primary productivity. AmNat 118:240-261
HSS
Fretwell-Oksanen (1981)
o
carnivores (3 )
3
o
2
herbivores (2 )
o
primary producers (1 )
1
o
1
o
o
low medium
o
2
1
o
o
high
PRODUCTIVITY
Chemical defense in plants is big
business
Popular drugs & spices:
Nicotine, caffeine, capsasins
Spices more abundant in tropical cultures
Addictive drugs
morphine, coca, marijuana
Medicinal drugs
Taxus bark; aspirin; penicillin
Changes in metabolism of predators
Are the estimates accurate?
Did the deer population irrupt?
Was it reduction in predators or hunting (top
down control)?
Was it reduction in livestock use in the late
1800s, thus reduced competition for food
(bottom up control)?
When the deer population crashed:
Was it overgrazing?
Was K reduced?
Binckley et al. 2006
Was Leopold right about the Kaibob deer herd?
Ecosystems 9:227-241.
• The deer herd did irrupt from late 1910s through 1920s,
though numbers imprecise
• The early phase of this, at least, was coincident with
increased livestock, so reduction in livestock competition not
a viable explanation
• Livestock reductions in fine fuels probably underlie
reduction in surface fires leading to increase in aspen, the
preferred deer food, which supported an increase in deer;
but later changes in deer and aspen are unrelated to fire
(fire absent)
• When deer populations were high, food sources were
drastically reduced, a change correlated with deer but not
climate
• No evidence of reduction in deer K, recovery rapid as deer
population fell
• The two major irruptions of deer followed periods of
reduced predation and/or reduced hunting
• Deer population under top down control when small, bottom
up control when large
Lake Guri: Terborgh &
collaborators 2001, 2006
Lake Guri: Terborgh &
collaborators 2001, 2006
• Small islands
– <15 ha
• Increased
–
–
–
–
Iguanas
Howler Monkeys
Leaf-cutter ants
Diet broadened
• Decreased
– Pumas, jaguars,
anacondas, eagles…
– Saplings