Competition - PowerPoint Presentation

Slide1

Competition

Mutually negative interaction between two species in the same guild or trophic levelChanges in abundance, fitness, or some fitness component (growth, feeding rate, body size, survival)Slide2

Topics for today

Mechanisms and models of competitionEvidence for competitionExperiments (lab, field)Observational (competitive exclusion, character assortment or displacement)

Latest advances in the study of competitionGenetic diversity/distance and competitionFunctional trait complementarity and competition

Habitat filtering vs. competitive exclusion using phylogenetic methodsSlide3

Schoener (1983): Mechanisms

ConsumptionPre-emptionOvergrowthChemical interactions

TerritorialityEncounter competitionCan we think of other sorts?Slide4

Schoener

1983Slide5

Lotka-Volterra

models of competitionBased on estimates of logistic population growth, and how this differs in monoculture vs. mixturesSlide6
Slide7

Values

of population sizes of two species, N1 and N2, that result in positive, negative, or zero population growth for

interacting species. The

zero growth isoclines are shown as a solid line for species 1 and a dashed line for species 2.

[from Morin 1999]

K is carrying capacity;

dN/dt is population growth rate; a is competition coefficient with a

12

being effect of sp. 2 on sp.1Slide8

Figures from

Gotelli

, “A Primer of Ecology”

Species 1

Species 2Slide9

...of species 2 by species 1

...of species 1 by species 2

Competitive Exclusion

Figs from

GotelliSlide10

Equilibrium: stable coexistence vs. unstable competitive exclusion

coexistence

“winner” depends on priority effects

Figs from

GotelliSlide11

Tilman’s

mechanistic model

R

2

R

1

R

1

A

R

1

B

R

2

B

R

2

ASlide12

Tilman’s model

If ZNGI’s overlap, we add consumption vectors (C) to illustrate how each species uses resourcesIf each species consumes more of the resource that limits itself, get coexistenceIf each species uses more of the resource that limits the other species, outcome is unstableSlide13

Tilman’s model

R

2

R

1Slide14

Tilman’s model

R

2

R

1Slide15

Experimental evidence

supporting

Tilman’s

modelSlide16

Competitive ability can be measured by species traits in monoculture

R*: the amount of resource left when a population of a single species reaches equilibrium densitySpecies with lowest R* should competitively exclude all othersSlide17

Evidence for competitive ability:

Tilman’s

measure of R*

Tilman and Wedin 1991

Poor competitors remove less N

Good competitors remove more N

Roots are the foraging organ: mass correlated with N assimilationSlide18

Tilman’s

field expt.Wedin and

Tilman 1993.Slide19

Chthamalus stellatus

Balanus balanoides

Nucella

= Thais lapillus

Connell’s barnacle experimentSlide20
Slide21
Slide22

Hairston’s salamanders

Hairston 1980Slide23

Low overlap as a consequence of competitionSlide24

Anoles in the Lesser Antilles

Anolis

wattsi

Similar body size and perch height

Little overlap in size or perch height

Anolis

gingivinus

Anolis

bimaculatusSlide25

High body size and perch height overlap

results in competition

Treatments with “W”: competing with A.

wattsiPacala and

Roughgarden 1982Similar

nicheDifferent nicheSlide26

Patterns from field experiments

Are there traits that predict who ‘wins’?Are there traits or patterns that predict where competition is more intense?Slide27

Observational evidence

for competitive exclusion: MacArthur’s WarblersSlide28

Galapagos finch bill sizes differ more in

sympatry

than

allopatrySlide29

Strong et al 1979

But differences in bill size between co-occurring pairs no different than expected by chance??Slide30

Yet the Grants showed that evolution did indeed occur

Large-beaked

G. fortis (A) and

G. magnirostris (B) can crack or tear the woody tissues of T. cistoides

mericarps (D), whereas small-beaked G. fortis (

C) cannot. Slide31

magnirostris

introduced: has really large beak

Drought causes competition: selects for divergent (small) beaks in

fortis

Drought selects for larger beaks in

fortis

(only large seeds available)

Grant and Grant 2006Slide32

Desert cats DO show character displacement when tested against null models

Dayan et al 1990

Canine size for each species/sex in two locationsSlide33

And so do bat-pollinated

BurmeisteraMuchhala and Potts 2007Slide34

All images from http://www.bio.miami.edu/muchhala/home.htmlSlide35
Slide36

Current areas of inquiry

Is competition stronger for closely related species? And, can we infer whether competitive exclusion has occurred using phylogenetic methods?Is competition stronger for species in the same functional group?Slide37

Darwin 1859

“As species of the same genus have usually, though by no

means invariably, some similarity in habits and constitution, and always in structure, the struggle will generally be more severe between species of the same genus

, when they come into competition with each other, than between species of distinct genera.”Slide38

If habitats select for particular traits, and related species share traits, expect

phylogenetic

clustering (“habitat filtering”)If competition or other density-dependent factors are stronger between relatives than between distant relatives, expect phylogenetic overdispersionSlide39

Webb 2000: evidence for habitat filtering in tropical trees

Two different estimates of relatedness

NRI: species more related than expected (clustering); NTI: not different from random (do NOT see

overdispersion)Slide40

Cavender

-Bares et al 2004: evidence for competitive exclusion in oaksSlide41

Using experimental estimates of competition, closely related species do not compete more intensely

Cahill et al 2008

These are correlations between competitive effect and

phylogenetic distance.

What do you expect this correlation to be if closely related things compete more intensely?Slide42

The Cedar Creek Biodiversity PlotsSlide43

In general....

Productivity is greater in plots with higher species richnessIs this because competition is lower in diverse plots (more functional groups present)?Slide44

Two hypotheses

Niche Complementarity: different functional groups use resources differently (in “complementary” ways), so greater efficiency

Selection Effect: with higher diversity, greater chance of “selecting” a competitive dominant in a plot (ie species that grow large over time)

Fargione et al 2006Slide45

Net effect:

Difference between total biomass in a plot and average biomass of monocultures increases over time

Selection:

if positive would mean that species with high monoculture biomass are competitive dominants, and when present (by chance) create more total biomass in diverse plots

Complementarity: when positive (as here) means species have higher than expected yield in mixture (attributed to N-fixers and C4 species presence in high-diversity mixtures)

Fargione et al 2006Slide46

Cadotte

et al 2009

Is it really about functional group diversity, or another diversity metric?Slide47
Slide48

Main points

Models as a way to think about what we can measure in the fieldExperiments can show patterns of functional traits that are importantPhylogenetic inference can provide new insight for experimentally intractable systems, and new interpretation of data from othersSlide49

Reading for next week

Connell 1961Slide50

Booth, R. E., and J. P. Grime. 2003. Effects of genetic impoverishment on plant community diversity. Journal of Ecology

91:721–730.Cadotte, M. W., J. Cavender-Bares, D. Tilman

and T.H. Oakley. 2009. Using phylogenetic, functional and trait diversity to understand patterns of plant community productivity. PLoS ONE 4(5): e5695. Cavender

‐Bares, J., D. D. Ackerly, D. A. Baum, F. A. Bazzaz. 2004. Phylogenetic Overdispersion

in Floridian Oak Communities. Am Nat 163:823-843Connell, J. H. 1961. The influence of interspecific competition and other factors on the distribution of the barnacle Chthamalus

stellatus. Ecology 42: 710-723. Connell

, J. H. 1980. Diversity and the Coevolution of Competitors, or the Ghost of Competition Past. Oikos 35:131-138.

Dayan, T. , D.

Simberloff

. 2005

Ecological and community-wide

character displacement

: the next generation

. Ecology Letters 8: 875-894.

Dayan, T., D.

Simberloff

, E.

Tchernov

, Y Yom-

Tov

. 1990. Feline canines: community-wide character displacement among the small cats of Israel. Am. Nat. 136: 39-60.

Fargione

, J.;

Tilman

, D. 2006. Predicting relative yield and abundance in competition with plant species traits. Functional Ecology 20:533-450.

Gause

G. F. 1934. The struggle for existence. Williams & Wilkins

.

Grant, P.R. and B. R. Grant. 2006. Evolution of character displacement in Darwin’s finches. Science 313: 224-226.

Hairston N. G. 1980a The experimental test of an analysis of field distributions: competition in terrestrial salamanders. Ecology 61: 817-826.

JF Cahill, SW

Kembel

, EG Lamb, and PA

Keddy

.  2008.  Does

phylogenetic

relatedness influence the strength of competition among vascular plants?  Perspectives in Plant Ecology, Evolution, and

Systematics

10:41-50.

Macarthur R.H. 1958. Population ecology of some warblers of northeastern coniferous forests. Ecology 39: 599-619.

Muchhala

, N. And M. D. Potts. 2007. Character displacement among bat-pollinated flowers of the genus

Burmeistera

: analysis of mechanism, process and pattern. Proc Roy Soc B 274: 2731-2737

Schoener

T. W. 1983. Field experiments on

interspecific

competition. Am Nat 122: 240-285.

Strong, D. R., L. A.

Szyska

, D.

Simberloff

. 1979. Tests of community-wide character displacement against null hypotheses. Evolution 33: 897-913.

Tilman

, D. and D.

Wedin

. 1991.

Plant traits and resource reduction for five grasses growing on a nitrogen gradient Ecology 72: 72:685-700

Webb CO. 2000. Exploring the

phylogenetic

structure of ecological communities: an

example for rain forest trees.

Am. Nat. 156:145–

55

Wedin

D. And D.

Tilman

. 1993.

Competition

Among Grasses Along a Nitrogen Gradient: Initial Conditions and Mechanisms of Competition. Ecological Monographs 6:3 199-229