Climax communities

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Climax communities Main climatic determinants of biomes

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Climax communities Main ecological determinants of biomes

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0.00

0.01

0.10

1.00

rank

Log

rela

tive

abun

danc

e

1 yr

40 yr

25 yr 15 yr

4 yr

logarithmic

lognormal

Brocken-stick

Community structure change during succession Years after farmland abandonment

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N o

f spe

cies

time

P1 P2 p3

P1 P2 P3 P4

m1 m2 P4

m1 m2 m3 m4 c2 c3

c4 c1 c2 c3

c4 c1

pioneers pioneer-intermediate climax

Biodiversity change during succession

Max diversity

r K

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Biodiversity change during succession D

iver

sity

Frequency of disturbance

Low

Medium

High

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Biodiversity change during succession

Intermedium disturb

Frequency of disturbance

Div

ersi

ty

high medium high

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smaller medium larger

Bebbles-stones dimension

0 1

2

3

4

5

N a

lgal

spe

cies

Bebble-stony beach

Biodiversity change during succession

Intermedium disturb (Sousa experiment)

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Biodiversity change during succession

Frequency of wildfires

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Biodiversity change during succession

Intensity of grazing

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Climate-Fire-Grazing interactions

climate

enhances depress Fire

Herbivores Vegetation

affects

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Human impact

climate

enhances depress Fire

Humans

Herbivores Vegetation

affects

Climate-Fire-Grazing interactions

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However formed, communities must have an internal, functional consistency to persist within an ecosystem, or to develop coherently Each species must find its own functional, ecological space to be a stable member of a given community Species are “packaged” within communities according to their ecological prophyle (e.g. trophic prophyle, sustainable interactions with other species in terms of predation, competition, mutualism etc.)

Community as a functional system

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A description of the trophic relationship within the community

Trophic web

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Primary producers

Herbivores

Carnivores

Top predators

Trophic levels

Vertical stratification of the community (Food chain)

Mat

ter/E

nerg

y tra

nsfe

r

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Assessment of the “vertical position” of each species along the trophic chain

A) Ethological assessment: direct observations of the foraging behaviour of the single species B) Dietary assessment: analysis of gut content, faeces content, discarded items etc. C) Isotopic assessment: sorting of different stable isotopes of N and C

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Predatory birds’ pellet analysis Dietary assessment of the position along the trophic chain

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Trophic position (N isotopes)

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Trophic position (C isotopes)

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C = Consumed

A = Assimilated

S = Discarded

U = Utilized

Es = Escreted

P = Allocated into “production” (Growth + Reproduction)

M = Spent for Metabolism biosyntesis concentration mobility

Se = Secreted

E = Energy available (per unit space and time)

Not intercepted

P / A = Net coefficient of production

Biomass/Energy transfer at each step of the food chain

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Bottom PP

C1 Herbivores

C2 Carnivores

Top Predators-Parasites

Trop

hic

Leve

ls

1

2

3

4

Taxa

Reduction of the total biomass/energy with increasing level of the food web

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1

.15

.02

.003

Phytoplancton

Carnivore zooplancton

Anchovetas

Herbivore zooplancton

Relative biomass per habitat unit

Oceanic trophic chain (off Peru coast)

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1 10

100 1000

10000

1 10

100 1000

0

BN

PP

AN

PP

Mammals Birds Insect

Artrhropods Nematodes

BPC

APC

BSC

ASC

kcal·m

-2·y

-1

Above- and below-ground energy allocation in mixed (savannah like) ecosystem

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A B C D E

A 0 0 0 1 0

B 1 0 1 1 1

C 1 0 0 1 0

D 0 0 0 0 0

E 1 0 1 1 0

A consumes E

B is consumed by D

A does not consume D

Consumer

Con

sum

ed

D is not consumed by D

Consumption matrix

Ø  Direct observation in field or in the laboratory Ø  Indirect assessment (gut content, faeces etc.)

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Consumption matrix

Sp1 Sp2 Sp3 Sp4 Sp5 Sp1 0 1 1 1 1 Sp2 0 0 1 1 1 Sp3 0 0 0 1 1 Sp4 0 0 0 0 1 Sp5 0 0 0 0 0

Trophic Cascade

Consumer

Con

sum

ed

Sp1 Sp2 Sp3 Sp4 Sp5 Sp1 1 1 1 1 1 Sp2 0 0 1 1 1 Sp3 1 0 0 1 1 Sp4 0 0 0 1 1 Sp5 0 0 0 0 1

Cannibalism + Circularity

Consumer

Con

sum

ed

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Biodiversity within trophic webs

Horizontal biodiversity (Taxa within each level)

Verti

cal b

iodi

vers

ity

(Num

ber o

f lev

els)

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Biodiversity within trophic webs

Ø Horizontal diversity

is controlled by demographic interactions between species of the same trophic level (competition, mutualism) Ø Vertical diversity

is controlled by prey-predators interactions (energy flow, structural and behavioural characteristics of both)

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11

−⋅= nn EE η

( ) ( )( )ηLog

ELogELogn 1min1 −+=

Energy available at nth level

Energy available at the basal level

Energy conversion coefficient

Minimun energy to sustain a level

Number of permitted levels

Energetic control of vertical biodiversity

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Biomass/Energy

Primary production control of vertical biodiversity

Higher Primary production

Biomass/Energy

Lower Primary production

This is not a general effect because:

ü  Increased mass production can impair the functionality of organisms at higher levels of the trophic chain (e.g. hypoxia)

ü  Vertical packaging depends also on morpho-functional & behavioural hierarchy

Low

er v

ertic

al d

iver

sity

Hig

her v

ertic

al d

iver

sity

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Competition links Lc

Predation links Lp

Taxa

Connectedness: Lc+Lp Connectance: Connectedness/Possible links

Community connectedness (connectance)

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0 10 20 30 40 50 60 Number of species (S)

0

0.2

0.4

0.6

0.8

1.0 Co

nnec

tanc

e (C

)

S·C=2

( )1−⋅=

SSLC

Connectance in real (benthonic) communities

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0

0.20

0.40

0.60

0.80

1.00

0 0.2 0.4 0.6 0.8 1 Connectance

Sta

bilit

y

S = 4

S = 7

S = 10

Stability vs connectance in simulated communities

S = number of species

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Propagation of demographic disturbance

Top-down (predation)

Bottom-up (production)

increase

decrease

increase

increase

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Propagation of demographic disturbance

Ø  Top-down progagation prevails in communities where classic predator-prey relationships are dominant

Ø  Bottom-up prevails where donor-controlled relationships

are common (e.g. in scavenger dominated communities)

Predator

Prey

Consumer

Producer

Consumed stuff (e.g. dead organic matter)

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Bottom-up biomagnification of POP Top-down propagation of demographic disturbance

Biomagnification Demographic disturbance

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DDD treatment of Clear Lake (California) to eliminate the non biting dipteran Chaoborus astiptocus Diclorodifenildicloroetano

Grebe disappearence

0.02 ppm

5 ppm

10 ppm

1500 ppm

1600 ppm

1949-51

1954

Biomagnification of persistent pollutants and community disruption

Flint & van der Bosch, 1981 in Begon et alii, 1990

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Propagation of demographic disturbance

Top-down

Taxonomic horizontal diversity is a buffer for top-down demographic disturbance propagation Reducing horizontal diversity reduces the community resilience to demographic fluctuations

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Non-trophic relationships within communities

Members of a community (different species) may establish relationships different from predation and competition: Mutualism/Commensalism – Reciprocal or directional trophic exchange between species Facilitation – Non-trophic reciprocal or directional benefits (e.g. modification of abiotic components of the environment which “facilitate” the presence of another species) Ecological engineering - When one species modifies the abiotic/biotic structure of an ecosystem in such a way that this reshape the environment and makes it suitable for survival-reproduction of other species Niche construction – When protracted and profound niche construction leads to selection of new traits (genetic-phenotipic) in the constructor species and in other species which became “entrapped” into the constructed niche (one extreme case is domestication)

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PP DOM

H S Dc

TP

C

Energy transfer Matter transfer Heat loss

PP primary production DOM dead organic matter H herbivores S scavengers Dc decomposers C carnivores TP top predators

Schemes of energy/matter circulation in communities

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PP DOM

P Dv

B)

PP DOM

P Dv

C)

I

PP DOM

P Dv

A)

E

Schemes of energy/matter circulation in communities

PP primary production DOM dead organic matter P predators Dv detritivores Energy transfer Matter transfer Heat loss

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Sagittaria & other macrophytes periphyton

Crostaceans Chironomids Tricoptera Gastropods Herb. fish

Celenterati Macroinvertebrates Carn. Fish

Top predator fish

Bacteria Crustaceans

Biomass (100 gps·m-2)

Stream community (USA) Standing biomass

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Stranded seaweeds and macroalgae

Phyt

opla

ncto

n

Stra

nded

ani

mal

res

idua

ls

Isopods Coleopters

Birds

Moll. scs Coleopt Diptera

larvae

Amphipods

6·103

10·103 141·103 584·103

2146·103

1198·103

1903·103

356·103

4·103

3·103 16·103

Releaseed to the sea and interstitial system

Fluxes: Kj · m-2 · y-1

Sandy beach community Energy flows

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Source-sink coupled ecosystems

Rocky shores

Sea currents

Seagrass beds

Sandy beach

Stranded organic materials

Rivers

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