Biodiversity Theory Presentation

7/26/2019 Biodiversity Theory Presentation

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Chapter 8 Biodiversity theories

Any mechanisms that promote speciescoexistence in a given community are

biodiversity maintenance mechanisms, orcommunity assembly rules.

There are two types of mechanismsstabili!ation and e"uali!ation or niche andneutral theories.

Connell, #. $. %&'8. (iversity in tropical rain forests and coral reefs. )cience%&&%*+-%*%+.

Chesson, . +++. /echanisms of maintenance of species diversity. Annu. 0ev. 1col.

)yst. +++. *%*2*-33. )iepiels4i, A./. and /cee4, /.A. +%+. 5n the evidence for species coexistence a

criti"ue of the coexistence program. 1cology &%*%6*-*%32.


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inal proEect

0eview 2 of these mechanisms

$istorical note @origination,/odel description$ow the mechanisms contribute to speciesdiversity

Comparison of the mechanismsTheoretical:empirical evidence(iscussion

ndproEectCompare the additive and multiplicative partition ofbiodiversity @9ande %&&3 vs #ost ++' papers.5r model BC? )A( and )A0 it logseries andlognormal distribution to BC? )A( and


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%. The 9ot4a-olterra

competition model


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opulationdynamics

K

xKrx

dt

dx =

rxdt

dx =

1xponential growth

9ogistic growth

(ensity-dependence

Accelerating growth

?n the above e"uation, r intrinsic growth rate and K carryingcapacity

The evolutionary strategies of r-Kspeciesrspecies exploit empty niches, and produce many ospring,low probability to surviving to adulthood.Kspecies strong competitors, and invest more heavily in much


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)peciescompetition

1. Intraspecifc competition:competition between individuals of thesame species.

Scramble competition:a


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The 9ot4a-olterra competitionmodel

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9ot4a-olterramodel

121/K

2K

212/K

1K

n2

n1

Condition for stable equilibrium (speciescoexistence): Intraspecific competition stronger

than interspecific competition:

21

1

2>

K

K

12

2

1>

K

K

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Lotka-Volterra Competition o!el

I t"is con!ition is #iolate!$competiti#e excl%sion t"en"appens.


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. 9imiting similarity:Hause=s principle

The notion behind the niche hypothesis is Flimiting similarityG, i.e.,there must be a limit to the similarity of coexisting competitors inutili!ing a


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. (e


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*. $abitat niche diversi


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2. 0>theory

(iagram illustrating competition for potassium andnitrogen between two plant species, using thegraphical approach of Tilman @%&8. The solid curveslabeled LLA== and LLB== are resource dependent !ero

net-growth isoclines for )pecies A and B. These showthe soil solution concentrations of nitrate andpotassium at which the growth of a species exactly balances all sourcesof loss and mortality to that species. CAand CBare vectors that show the

amounts of ; and M consumed by )pecies A and B. These de


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6. #an!en-Connell spacinghypothesis

#an!en-Connell model @#an!en %&'+, Connell %&'%. The x-axisrepresents distance from the focal tree, and the y-axis represents thedensity of seeds falling to the ground @seed shadow or the proportionof seeds surviving to maturity @escape curves.

Terborgh, #. et al. ++8. Tree recruitment in an empty forest. 1cology


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3. ?ntermediate disturbancehypothesis

?($ is a non-e"uilibrium process

re"uent disturbances prevents competitiveexclusion

/id-domain hypothesis @my alternativehypothesis

)ousa, 7. . %&'&. 1xperimental investigations of disturbance and ecological succession in aroc4y intertidal algal community. 1cological /onographs 2&'-62.

)heil, (. and Burslem, (..0.. ++*. (isturbing hypotheses in tropical orests. Trends in 1cology


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3. ?ntermediate disturbancehypothesis

)pecies richness of the - to %+-cm dbh tree communities in the && aracou2++ mterra rme"uadrats, as a function of the percentage of pioneer stems @N) or heliophilicstems @N$) in the same dbh class. )pecies richness per "uadrat O1@)2+P is

calculated using $urlbert=s rarefactionmethod for a standard sample si!e n Q 2+. @* 1@)2+ as a function of N). @+

1@)2+ as a function of N$). Kpper and lower curves are regression lines formaxima and minima in steps of 6N $) @n 6 %3. @C )ame as @B, but "uadrats

/olino, #.-. and )abatier, (.. ++%. Tree diversity in tropical rainforests A validation of the intermediate disturbance hypothesis.


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8. Competition-coloni!ationtradeo

$astings, A. %&8+. (isturbance, coexistence, history, and competition for space.Theoretical opulation Biology %8*3*-*'*.Tilman, (. %&&2. Competition and biodiversity in spatially structured habitats.

/etapopulation dynamic model

The superior competitor is not aected by the inferior species.

The inferior can coloni!e only sites in which both it and thesuperior are absent @the term %-p%-p. $owever, species % can

invade into and displace species @the term c%p%p. ?f the

species have identical mortality rates, any two speciese"uilibrium is globally stable. This occurs because species %

grows logistically and approaches its e"uilibrium. 5nce the %st

species is at e"uilibrium, species then grows logistically to itse"uilibrium.

These are the necessary andsuScient conditions for thestable coexistence of the twospecies. 7hen m%Qm, cc%

because c%m%.


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&. )ource-sin4 eects:/ass eect@immigration

ulliam, $.0. %&88. )ources, sin4s, and population regulation. Am ;at %*36-33%.)hmida, A. and 7ilson, 7.. %&86. Biological determinants of species diversity. #

/any species, especially rare species, are thought to not be self-

sustaining, and these species are locally maintained in a givencommunity only by constant immigration from source populationslocated outside the community @ulliam %&&8. ?n discretelydistributed metapopulations, immigration plays a vital role inrescuing rare populations.

,esc%e eect: opulationson islands that are lessisolated are less li4ely to goextinct because individualsfrom the source population

and other islands canimmigrate and FrescueG thepopulation from extinction.


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%+. Theory of islandbiogeography

Small island

Extinction

rates

Large island

%mber o species on islan!

Immi/ra

tionrates

ear mainland

!ar mainland

S2 S1

U The number of speciesoccurring on an island@or a habitat isdetermined byrecurrent immigrationof new species onto theisland, and recurrentextinction of residentspecies.

U 7hen the immigrationand extinction rates aree"ual, the number ofspecies is at ane"uilibrium.


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%%. $istorical and regionaleects

?t stresses the importance of historical events and regionalspecies pool to the assembly of species at localcommunities. )pecies diversity can dier betweencomparable habitats in regions that have dierent historiesor geographical con


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+io/eo/rap"ical ori/in: @a phylogenetic

clustering due to local speciation ofallopatric cladesW @b phylogeneticoverdispersion due to allopatric speciationof two ancestral sympatric species causedby the same biogeographical barrier.

Ecolo/ical ori/in: @c phylogeneticclustering due to habitat


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%. luctuatingrecruitment:)torage eect

The mechanism hypothesi!es that if there is an asynchronousvariability in relative recruitment rates between common andrare species, then rare species are at advantage, therebypromoting coexistence @Chesson and 7erner %&8%. The strengthof this eect depends on the degree of reproductive asynchronyand the degree to which rare species are not limited by dispersaland maximal fecundity. The test of this hypothesis clearlyre"uires long-term data on production of seeds and recruitmentsof seedlings and growth of saplings.

9ottery model @Connell=s e"ual chance hypothesis )pecies have

e"ual chance to coloni!e empty sites, hold them againstinvaders and survive any environmental adversaries. 0esourcesare captured at random by recruits from a larger pool ofpotential colonists. The species composition at any site would beunpredictable, depending upon the history of chance

coloni!ation )ale, .. %&''. /aintenance of high diversity in coral reef


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%*. 0ecruitmentlimitation

This hypothesis states that coexistence is promoted bythe failure of species to recruit seedlings in allmicrosites favorable for their germination, growth andsurvival, so that those vacant sites could be occupiedby other species @$urtt and acala %&&6.

$urtt, H. C. and ). 7. acala. %&&6. The conse"uences of recruitment limitationreconciling chance, history, and competitive dierences between plants. #ournal


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%2. ;eutral

theory

I t t i ? N b t


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Is nature symmetric? No, but. . . .

Photo by Cristian Ziegler

$ d i ti i itI


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$ow good an approximation is itI


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7hat is symmetric neutral theoryI

)ymmetric neutral theory as4s To what extent are theproperties of ecological communities due to speciessimilaritiesrather than to species dierencesI

Current theory is limited to communities of trophicallysimilar species, li4e tree species in a forest, not tigers and

trees.)ymmetry is the assumption that the population dynamicsof species @demographic parameters on the per capita basisin such communities are statistically identicalYat least to a


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Contrast with mainstreamtheory

U The mainstream theoretical paradigm asserts thatecological nature is fundamentally asymmetric. ?temphasi!es the inherent uni"ueness of species inecological communities @i. e., niche-assembly theory.

U According to this largely deterministic perspective,competing species co-exist in closed, e"uilibrium, ornear-e"uilibrium assemblages by partitioning limitingresources through niche dierentiation.

U ?n contrast, in neutral theory, a stochastic perspective,communities are open, non-e"uilibrium assemblageswhose stability arises only from the inertia of large

numbers.U ;iche theory tends to be parameter-rich, complex, and

prediction-poor, whereas neutral theory is parameter-poor, simple, and prediction-rich.


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0ecipe for neutral theory

)tart simply, add complexityreluctantly, 4ic4ing and screaming,

only as needed, stir vigorously


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arameters of symmetric neutral theory

Metacommunity(Size JM)

One of manylocal communities(each of size J)

JQ local community si!e

JM Q metacommunity si!e

mQ probability of immigration

@dispersal that a death in the local community is replaced by immigrant from metacommunity

n Q probability of a

speciation event per birth

c Q density dependenceparameter

@units individuals.

b, dQ per capita birth, deathrates


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$ow communities and the biodiversity

therein are formed and maintainedI

The traditional paradigm 1nvironmental


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%bbell0s ,%les o Comm%nit*ssembl

,an!om alk (!rit3!ensit !epen!ent!rit)

4ispersal limitation (immi/ration)

Speciation


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,an!om 5alk (Ecolo/ical 4rit): 7hathappens if two competing species have

identical competition abilityI

121/K

2K

212/K

1K

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n1

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4rit: Coexistence o

e%tral Species


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S%mmar: obio!i#ersit is

maintaine! innat%re6

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Biodiversity Theory Presentation