lv competition - only 1 (in 4) solutions yields coexistence – is coexistence the unexpected...

LV Competition

- Only 1 (in 4) solutions yields coexistence – Is coexistence the unexpected outcome?

- Is competitive exclusion random or does the theory indicate some property (not identity) of the competing species that can guide us?

Yes, Intraspecific competition > Interspecific competition

Two species that occupy the same niche (they are identical) cannot coexist = Competitive Exclusion Principle

Seed Size

small large

FrequencyIn the diet

Competition as a structuring force in biological communities

100% Overlap

Medium seed eater

Seed Sizesmall large

FrequencyIn the diet

Small seed specialist

Large seed specialist

Medium seed eater

10% Overlapweak competition

X

Seed Sizesmall large

FrequencyIn the diet

Small seed specialist

Large seed specialist

Seed Size

small large

FrequencyIn the diet

Niche partitioning – there is a limit on the amount of similarity between adjacent species that results in a regular spacing of species’ morphology

Competition works as a biological filter toremove or prevent the invasion of species

into biological communities

Min spacing

Niche partitioning in two desert rodent communities

These coexisting Felids in Israel

Wildcat

Caracal

Wildcat, fem.

Wildcat, male

Jungle cat, fem.

Caracal, fem.

Jungle cat, male

Caracal, male

5mm 9876

Diameters of canines for 3 species of coexisting cats in Israel (after Dayan et al. 1990)

Niche partitioning in the feeding appendages of Felids

Seed Sizesmall large

FrequencyIn the diet

Small seed specialist

Medium seed eater

Large seed specialist

Ghost of Competition Past – Differences in species ecology that reduces competition is due to the action of competitive effects in their evolutionary Past

small large

FrequencyIn the diet

Medium seed eater invades of communityw/o competing species

Niche Expansion – Over time it evolves to fill vacant niches

small large

FrequencyIn the diet

Medium seed eater invades of communityw/ smaller beaked species

small large

FrequencyIn the diet

Character Displacement– Over time it evolves to avoid competition

Medium seed eater invades of communityw/ smaller beaked species

small large

FrequencyIn the diet

ALLOPTARYSmall seed

absent

SYMPATRYSmall seed

present

Differences in species’ morphology will be greater in sympatry than in allopatry

sympatry = occur together allopatry = occur separately

A characteristic of Character Displacement

Differences in species’ morphology will be greater in sympatry than in allopatry

sympatry = occur together allopatry = occur separately

A characteristic of Character Displacement

Character DisplacementIn

Darwin’s Finches

Conclusions:

Competition is a structuring force – dissimilar species can coexist more easily

(1)Niche partitioning – Ecology (2)Niche expansion when there is release from competition - Ecology(3)Ghost of Comp Past & Character Displacement - Evolution

A. In Ecological Time competition is a Species TakerB. But in Evolutionary Time it is a Species Maker

Insufficiencies of LV Competition and the rise of Behavioral Ecology

LV is phenomenological

LV takes the mass-action approach, i.e., organisms are a bunch of molecules that diffuse through space occasionally bumping into one another and when they do, an interaction occurs (whether competition, predation, facilitation).

K (carrying capacity) and α’s (interaction coefficients) are not explicitly defined

Basically, there is a conspicuous absence of REAL BIOLOGY

Heuristically, coexistence requires

Axis of heterogeneity – some “resource” that occurs in variable amounts or states

Tradeoffs, such a species being efficient at utilizing one end of the axis necessitates being poor at utilizing the other end.

These two components make up a Mechanism of Coexistence

Mechanisms of Coexistence between forest tree species: American beech (Fagus grandifolia) and Sugar maple (Acer saccharum)

What’s our axis of heterogeneity?? Sunlight (or shade tolerance)

beech maple oak cherry ash tulip

veryshade

tolerant

Sun loving

What’s the Tradeoff ?? Allocation of Energy

Energy devoted to vertical growth cannot be used for horizontal growth

Mechanisms of Coexistence between forest tree species: American beech (Fagus grandifolia) and Sugar maple (Acer saccharum)

Beech’s Strategy: Allocate growth plenty of energy to horizontal growth (i.e., specialize in light-capturing in the shade)

Large collection surface

Long-horizontal branches seek out light flecks

BeechS. Maple

Maple’s Strategy: Allocate growth plenty of energy to vertical growth (i.e., specialize in fast growth and filling canopy gaps).

Smaller collection surfaceVertical growth into the canopy

Who wins ?? Beech or maple, or can they coexist ??

Beech can persist for a very long time in understory, whereas maple cannot

When a canopy tree eventually fallscreating a light gap it is filled by beech

Who wins ?? Beech or maple, or can they coexist ??

However, if gaps open upfrequently,then small, fast

growing maples can still beat beech to the canopy

Although beech will likely continue to persist

Who wins ?? Beech or maple, or can they coexist ??

Because beech grows better than maple in shade but

Maple grows better in the sun (light gaps)

Canopy dominance depends on the frequency of light gap formation.

e.g., Warren Woods, MI(Poulson and Platt 1996)

1960’s: Tip-overs rare,beech dominated

1980’s: Frequent storms and tornadoes, tip-overs common,

maple began to dominate

beech maple oak cherry ash tulip

veryshade

tolerant

Sun loving

And similarly with the other tree species along the axis, with the more sun loving species

increasingly dependent on gaps

seedlings saplings poles canopy

Black cherryRed oakBeech

353 0 0 1344 0 6 421 16 2 0

Black cherryRed oakBeech

32 0 0 03 0 0 1116 19 28 16

Data: Ecology class 2001, Hopkins Memorial Forest, Williamstown, MA

Bienke stand(old growth)

Rye fieldAbandoned in ~1930

Canopy (light) gaps provide sites for local recruitment of sun-loving species so that coexistence and high diversity of tree species canbe maintained in the forest

Aerial view of a forest

Green Kingfisher (38g) Ringed Kingfisher (300g)

In Panama, 2 species of Kingfishers coexist

Diet is small fish, whichit searches for by

perching near water

Diet is big and small fish,but larger size requires more energy. Perches

high to scan wider area forbig fish but then cannot

see small fish.

Tradeoff between prey size and encounter rate

What are the primary mechanisms of coexistence??

(1) diet choice(2) habitat selection(3) cream skimmers versus crumb pickers(4) competition versus predator avoidance(5) regional (i.e., metapopulation)

(6) Non-EQ processes

How common are the various mechanisms??

The real answer we probably don’t know, but David Lack attempted to answer the question for birds in 1944 (before many mechanisms were proposed)

3 Geographical separation> 18 Separation by habitat2 Different winter ranges (temporal habitat selection)• Separated by feeding habits 5 Size differences (feeding??)

5-7 Apparent overlap

Optimal Foraging Ecology and Diet Choice

-- The need to acquire energy to maintain homeostasis is a universal property of life

-- Natural selection

We expect to see adaptive behaviors that permit individuals to efficiently and effectively acquire and utilize energy

Assumptions

Feeding behavior requires several activities. Consider:

-- search and encounter food, S

-- pursuit and capture of food, P

-- Net energy received, E

Furthermore, adaptive feeding requires an economic goal:

} Costs offoraging

Benefit offoraging

(minus energetic cost to search and pursue it)

Maximize the rate of energy acquisition:Energy Time

Assumptions

Feeding behavior requires several activities. Consider:

-- search and encounter food, S

-- pursuit and capture of food, P

-- Net energy received, E

Furthermore, adaptive feeding requires an economic goal:

} Costs offoraging

Benefit offoraging

(minus energetic cost to search and pursue it)

Develop a scenario - On locating a food item, a forager has 2 choices:

(1) To pursue its prey

or (2) To forgo pursuit and instead search again for a better item and it pursue once encountered

Develop a scenario - On locating a food item, a forager has 2 choices:

(1) To pursue its prey

or (2) To forgo pursuit and instead search again for a better item and it pursue once encountered

The better option is that which yields the greater E/T

Develop a scenario - On locating a food item, a forager has 2 choices:

(1) To pursue its prey

or (2) To forgo pursuit and instead search again for a better item and it pursue once encountered

The better option is that which yields the greater E/T

In other words: a forager should pursue an encountered food itemif and only if it could not BOTH locate and catch something better

Let’s decide which is better …

(1) To pursue prey (that was already encountered):

rate of energy gain = E

P

Let’s decide which is better …

(1) To pursue prey (that was already encountered):

rate of energy gain =

(2) To search for and pursue another prey:

rate of energy gain =

E

P

S +

E

P

Let’s decide which is better …

(1) To pursue prey (that was already encountered):

rate of energy gain =

(2) To search for and pursue another prey:

rate of energy gain =

EP

S +

E

P

If there is one a single food type – then it never pays to refuse a preyitem and search for another – you always pay the extra cost of search

But what if there are two prey (i.e., an axis of heterogeneity) ??

Prey #1 is preferred – by that we mean that

E(1)

P(1)

E(2)

P(2)

If the forager had unfettered access to either prey, prey #1 offers the higher energetic reward per time spent capturing/consuming it

>

Now what does our optimal forager decide ?? To pursue or continue searching ??

Scenario (#1): Forager has encountered its preferred prey, Prey 1.

E(1)

P(1) S +

E

P

Reward if pursues

Reward if Searches/pursues

What is the better option ????

Scenario (#1): Forager has encountered its preferred prey, Prey 1.

E(1)

P(1) S +

E

P

Reward if pursues

Reward if Searches/pursues

What is the better option ????

E(1)

P(1) S +

E

P Is ALWAYS >

E(1)

P(1)Since you can NEVER do better than

Conclusion #1: A forager should always consume its preferred prey

Scenario (#2): Forager has encountered its non-preferred prey, Prey 2.

E(2)

P(2) S +

E

P

Reward if pursues

Reward if Searches/pursues

What is the better option ????

Scenario (#2): Forager has encountered its non-preferred prey, Prey 2.

E(2)

P(2) S +

E

P

Reward if pursues

Reward if Searches/pursues

What is the better option ????

S +

E

P

E(2)

P(2)

IT DEPENDS

>If is small: SKeep searching for preferred prey, do not consume non-preferred prey

Selective Diet

Otherwise: be a generalist and consume all encountered prey

Conclusion #2: A forager is eitherselective on its preferred prey

or it always consumes both its preferred and non-preferred prey

i.e., opportunist

How does diet selection provide a mechanism of coexistence??

Tradeoffs between E’s, S’s or P’s such that 2 (or more) species have distinct prey

preferences and therefore do not share resources

i.e., no resource competition

Serval

Caracal

Cheetah

5 coexisting cats in the Serengeti:

Lion 190 kg wildebeest, zebra 270-690 kg coop. hunting

Leopard 65 kg Impala 60 kg stealth

Cheetah 50 kg Thompson gazelles 25 kg speed

Caracal 20 kg Hyrax, steenbok 5 kg ???

Serval 13 kg birds 100’s g leaping

Species mass preferred prey prey mass behavior