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