Communities, Communities, ecosystems, and ecosystems, and

landscapes:landscapes:Species InteractionsSpecies Interactions

Farming/Settlement

PinePine

Spruce-Fir

YBirchHeath Bald

Old-growth Hemlock-hardwoods

Oak Oa

k

The Goldilocks problemThe Goldilocks problem• Not too hot, not too cold, but just rightNot too hot, not too cold, but just right• Species have ranges of tolerance and Species have ranges of tolerance and

optima for given environmental optima for given environmental parametersparameters

• Species tend to have different set Species tend to have different set pointspoints

• A particular change in the environment A particular change in the environment or conservation strategy will be good or conservation strategy will be good for some species and bad for othersfor some species and bad for others

Pure Effects of Diversity: Pure Effects of Diversity: Niche division, Niche Niche division, Niche

overlapoverlap• ComplementarityComplementarity• RedundancyRedundancy

HemlockBeech

Tuliptree

Then now is the chance for flowersThen now is the chance for flowers

That can’t stand mowers and plowers.That can’t stand mowers and plowers.

It must be now, though, in seasonIt must be now, though, in season

Before the not mowing brings trees on,Before the not mowing brings trees on,

……The trees are all I’m afraid of, The trees are all I’m afraid of,

That flowers can’t bloom in the That flowers can’t bloom in the shade ofshade of……

The Last Mowing, 1928The Last Mowing, 1928

Intermediate Intermediate Disturbance HypothesisDisturbance Hypothesis

Succession to Succession to trees that trees that flowers can’t flowers can’t bloom in the bloom in the shade ofshade ofCan’t Can’t

stand stand mowers mowers and and plowersplowers

Most Most flowersflowers

Intermediate Intermediate Disturbance HypothesisDisturbance Hypothesis

Succession to Succession to trees that trees that flowers can’t flowers can’t bloom in the bloom in the shade ofshade ofCan’t Can’t

stand stand mowers mowers and and plowersplowers

Most Most flowersflowers

Species response to a Species response to a given disturbancegiven disturbance

• IncreasersIncreasers• DecreasersDecreasers• InvadersInvaders• RetreatersRetreaters• IntegratorsIntegrators

The challenge to management!The challenge to management!

-- 00 ++

-- CompetitioCompetitionn

AmensalismAmensalism PredationPredation

herbivoryherbivory

parasitismparasitism

allelopathyallelopathy

00 AmensalisAmensalismm

NeutralismNeutralism CommensalisCommensalismm

++ PredationPredation

herbivoryherbivory

parasitismparasitism

allelopathyallelopathy

CommensalisCommensalismm

MutualismMutualism

Types of Types of interactionsinteractions

Figure 8.6Figure 8.6

Ficus carica – Edible FigFicus carica – Edible Fig

So, naturalists observe, a fleahath smaller fleas that on him prey,and these have smaller fleas to bite ‘em,and so proceed, ad infinitum.--Jonathan Swift

Trophic Structure: Trophic Structure: Cascading effectsCascading effects

““Just as a deer herd lives in mortal Just as a deer herd lives in mortal fear of its wolves, so does a fear of its wolves, so does a mountain live in mortal fear of its mountain live in mortal fear of its deer.”deer.”

Aldo Leopold, Think like a Aldo Leopold, Think like a mountainmountain

The enemy of my enemy is my The enemy of my enemy is my friend… predators as the friend of friend… predators as the friend of plantsplants

Hairston, Smith and Slobodkin (1960)Hairston, Smith and Slobodkin (1960)‘‘HSS model’HSS model’

Why is the world green?Why is the world green?

1. Decomposers are limited by their food1. Decomposers are limited by their food (otherwise fossil fuels would build up(otherwise fossil fuels would build up quickly)quickly)2. Plants are limited by their resources2. Plants are limited by their resources (as they are not all eaten up by the(as they are not all eaten up by the herbivores)herbivores)

3. Herbivores are not limited by theirHerbivores are not limited by their food (because they are only seen tofood (because they are only seen to eat all their food plants when, rarely,eat all their food plants when, rarely, they are ‘protected’ by ‘human’ orthey are ‘protected’ by ‘human’ or ‘ ‘natural events’). Therefore, herbivoresnatural events’). Therefore, herbivores are limited by predators.are limited by predators.4. Carnivores are limited by their food4. Carnivores are limited by their food (since predators are controlling prey,(since predators are controlling prey, they must be limited by prey).they must be limited by prey).

HSS Fretwell-Oksanen (1981)

carnivores (3o)

herbivores (2o)

primary producers (1o)

PRODUCTIVITY

low medium high

1o 1o 1o

2o 2o

3o

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)

carnivores (3o)

herbivores (2o)

primary producers (1o)

PRODUCTIVITY

low medium high

1o 1o 1o

2o 2o

3o

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

Chemical defense in plants is big business

Popular drugs & spices: Nicotine, caffeine, capsasinsSpices more abundant in tropical

cultures

Addictive drugs morphine, coca, marijuana

Medicinal drugs Taxus bark; aspirin; penicillinChanges 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. 2006Binckley et al. 2006Was Leopold right about the Kaibob deer Was Leopold right about the Kaibob deer

herd?herd?Ecosystems 9:227-241.Ecosystems 9:227-241.

• The deer herd did irrupt from late 1910s through 1920s, The deer herd did irrupt from late 1910s through 1920s, though numbers imprecisethough numbers imprecise

• The early phase of this, at least, was coincident with The early phase of this, at least, was coincident with increased livestock, so reduction in livestock increased livestock, so reduction in livestock competition not a viable explanationcompetition not a viable explanation

• Livestock reductions in fine fuels probably underlie Livestock reductions in fine fuels probably underlie reduction in surface fires leading to increase in aspen, reduction in surface fires leading to increase in aspen, the preferred deer food, which supported an increase in the preferred deer food, which supported an increase in deer; but later changes in deer and aspen are unrelated deer; but later changes in deer and aspen are unrelated to fire (fire absent)to fire (fire absent)

• When deer populations were high, food sources were When deer populations were high, food sources were drastically reduced, a change correlated with deer but drastically reduced, a change correlated with deer but not climatenot climate

• No evidence of reduction in deer K, recovery rapid as No evidence of reduction in deer K, recovery rapid as deer population felldeer population fell

• The two major irruptions of deer followed periods of The two major irruptions of deer followed periods of reduced predation and/or reduced huntingreduced predation and/or reduced hunting

• Deer population under top down control when small, Deer population under top down control when small, bottom up control when largebottom up control when large

Lake Guri: Terborgh & Lake Guri: Terborgh & collaborators 2001, 2006collaborators 2001, 2006

Lake Guri: Terborgh & Lake Guri: Terborgh & collaborators 2001, 2006collaborators 2001, 2006• Small islandsSmall islands

– <15 ha<15 ha

• IncreasedIncreased– IguanasIguanas– Howler MonkeysHowler Monkeys– Leaf-cutter antsLeaf-cutter ants– Diet broadenedDiet broadened

• DecreasedDecreased– Pumas, jaguars, Pumas, jaguars,

anacondas, eagles…anacondas, eagles…– SaplingsSaplings