Communities, ecosystems, and landscapes: Species Interactions

Pine Spruce-Fir Heath Bald Old-growth Hemlock-hardwoods 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 Succession to trees that flowers can’t bloom in the shade of Can’t stand mowers and plowers

Intermediate Disturbance Hypothesis

Most flowers Succession to trees that flowers can’t bloom in the shade of Can’t stand mowers and plowers

Species response to a given disturbance

• Increasers • Decreasers • Invaders • Retreaters • Integrators

The challenge to management!

0

Types of interactions

0 Competition Amensalism Amensalism Neutralism + Predation herbivory parasitism allelopathy Commensalism + Predation herbivory parasitism allelopathy Commensalism Mutualism

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 carnivores (3 o ) Fretwell-Oksanen (1981) 3 o herbivores (2 o ) 2 o 2 o primary producers (1 o ) 1 o 1 o 1 o low medium 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 carnivores (3 o ) Fretwell-Oksanen (1981) 3 o herbivores (2 o ) 2 o 2 o primary producers (1 o ) 1 o 1 o 1 o low medium 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