ecología de comunidades - universidad nacional de · pdf file• dos comunidades...

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Ecología de Comunidades


Qué es una comunidad?

• Una comunidad biológica es un conjunto de poblaciones de distintas especies, conviviendo, que interactúan entre sí.


• Las relaciones entre las poblaciones de distintas especies de una comunidad se denominan interacciones interespecíficas

• Las interacciones interespecíficas afectan la supervivencia y reproducción de las especies

• Ejemplos: competencia, predación, herbivoría, simbiosis (parasitismo, mutualismo, y comensalismo), y enfermedades


Competencia

• Ocurre competencia interespecífica cuando las especies compiten por un recurso limitado


Principio de exclusión competitiva

• Establece que dos especies que compiten por el mismo recurso limitante, no pueden coexistir en el mismo lugar


Nicho Ecológico

• El uso total que una especie hace de los recursos bióticos y abióticos se denomina nicho ecológico de la especie

• Especies ecológicamente similares pueden coexistir en una comunidad si hay una o más diferencias significativas en sus nichos

LE 53-2

Chthamalusfundamental niche

High tide

Low tideOcean

Chthamalusrealized niche

High tide

Low tideOcean

Balanusrealized niche

ChthamalusBalanus


Resource Partitioning

• Resource partitioning is differentiation of ecological niches, enabling similar species to coexist in a community

A. insolitusen ramas sombrías.

A. ricordii

A. insolitus

A. christophei

A. cybotesA. etheridgei

A. alinigerA. distichus

A. distichusen superficiessoleadas.


Character Displacement

• Character displacement is a tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species

• An example is variation in beak size between populations of two species of Galapagos finches

LE 53-4

Beakdepth

Sympatricpopulations

G. fuliginosaG. fortis

Santa María, San Cristóbal40

20

0

Los Hermanos40

20

0

Daphne40

20

0

G. fuliginosa,allopatric

G. fortis,allopatric

Beak depth (mm)161412108

Perc

enta

ge o

f ind

ivid

uals

in e

ach

size

cla

ss


Predación

• Es la interacción en la cual una especie, el predador, mata y se come a la otra, la presa


• Prey display various defensive adaptations

• Behavioral defenses include hiding, fleeing, self-defense, and alarm calls

• Animals also have morphological and physiological defense adaptations


• Cryptic coloration, or camouflage, makes prey difficult to spot

Video: Seahorse CamouflageVideo: Seahorse Camouflage


• Animales con una efectiva defensa química suelen presentar colores de advertencia, o aposemáticos


• In some cases, a prey species may gain significant protection by mimicking the appearance of another species


• In Batesian mimicry, a palatable or harmless species mimics an unpalatable or harmful model

LE 53-7

Hawkmoth larva

Green parrot snake


• In Müllerian mimicry, two or more unpalatable species resemble each other

LE 53-8

Cuckoo bee

Yellow jacket


Herviboría

• Un hervibóro se alimenta de partes de plantas o algas

• Las plantas han desarrollado especializaciones químicas para defenderse de los hervíboros


Parasitismo

• Un organismo, el parásito, obtiene su alimento de otro organismo, su hospedador, que se daña durante el proceso

• El parasitismo ejerce una influencia sustancial sobre las poblaciones y la estructura de las comunidades


Enfermedades

• Producen el mismo efecto que los parásitos

• Los agentes patógenos, que causan la enfermedad, son típicamente bacterias, virus, o protistas


Mutualismo

• La simbiosis mutualística, o mutualismo, es una interacción interespecífica que beneficia a ambas especies

Video: Clownfish and AnemoneVideo: Clownfish and Anemone


Comensalismo

• Una especies se beneficia y la otra aparentemente no es afectada

• Este tipo de interacciones es difícil de documentar en la naturaleza, dado que cualquier interacción estrecha entre dos especie probablemente afecta a ambas


Interspecific Interactions and Adaptation

• Coevolution is reciprocal evolutionary adaptations of two interacting species

• The term is often used too loosely in describing adaptations within a community

• There is little evidence for true coevolution in most interspecific interactions


La especie clave y la dominante, ejercen un fuerte control sobre la estructura de las comunidades

• Dos rasgos fundamentales de la estructura de comunidades son la diversidad de especies y las relaciones de alimentación o tróficas


Diversidad de Especies

• Es la variedad de organismos que componen la comunidad

• Tiene dos componentes: riqueza de especies y abundancia relativa

• Riqueza de especies es el número total de especies de la comunidad

• Abundacia relativa es la proporción que cada especie representa en el total de individuos de la comunidad


• Dos comunidades pueden tener la misma riqueza de especies pero diferente abundancia relativa

• Una comunidad con muchísimas especies es más diversa que otra en la cual una o dos especies son abundantes y las demás son raras

LE 53-11

Community 1

AB

C

D

A: 25% B: 25% C: 25% D: 25%

Community 2A: 80% B: 5% C: 5% D: 10%


Estructura trófica

• Son las relaciones de alimentación entre los organismos de una comunidad

• Es un factor clave en la dinámica de las comunidades

• Las cadenas tróficas unen niveles tróficos desde los productores a los últimos carnívoros

Video: Shark Eating a SealVideo: Shark Eating a Seal

LE 53-12

Quaternaryconsumers

Tertiaryconsumers

Carnivore

Carnivore

Carnivore

Carnivore

Secondaryconsumers

CarnivoreCarnivore

Primaryconsumers

ZooplanktonHerbivore

Primaryproducers

PhytoplanktonPlant

A terrestrial food chain A marine food chain


Redes tróficas

• Es una cadena alimenticia ramificada con interacciones tróficas complejas

LE 53-13

Euphausids(krill)

Carnivorousplankton

Phyto-plankton

Copepods

Squids

Elephantseals

FishesBirds

Crab-eaterseals

Leopardseals

Spermwhales

Smallertoothedwhales

Baleenwhales

Humans


• Food webs can be simplified by isolating a portion of a community that interacts very little with the rest of the community

LE 53-14

Zooplankton

Fish larvae

Fish eggs

Sea nettle Juvenile striped bass


Límites a la longitud de la cadena trófica

• Estas tienen usualmente pocos pasos

• Esto intenta explicarse con dos hipótesis: la hipótesis energética y la hipótesis de la estabilidad dinámica


• La hipótesis energética sugiere que la longitud está limitada por el ineficiente traspaso de energía

• La de la estabilidad dinámica propone que las cadenas largas son más inestables que las cortas

• La mayor parte de los datos soportan la primera hipótesis

LE 53-15

Productivity

Num

ber o

f tro

phic

link

s

Num

ber o

f spe

cies

No. of trophiclinks

No. of species

High(control)

6

5

4

3

2

1

0

6

5

4

3

2

1

0Medium Low


Especies de gran impacto

• Estas especies son muy abundantes o juegan un rol central en la dinámica de la comunidad


Especies dominantes

• Son las más abundantes o las de mayor biomasa

• Ejercen un control poderoso sobre la ocurrencia y distribución de otras especies


• One hypothesis suggests that dominant species are most competitive in exploiting resources

• Another hypothesis is that they are most successful at avoiding predators


Especies clave

• No son necesariamente abundantes en una comunidad

• Ellas ejercen un fuerte control sobre una comunidad por sus roles ecológicos, o nichos


• Estudios en estrellas de mar muestran su rol como especies clave de su comunidad

LE 53-16

Without Pisaster (experimental)

With Pisaster (control)

1963 ’64 ’65 ’66 ’67 ’68 ’69 ’70 ’71 ’72 ’73

20

15

10

5

0

Num

ber o

f spe

cies

pres

ent


• Observation of sea otter populations and their predation shows how otters affect ocean communities

LE 53-17

100

806040

020

Sea otter abundance

Otte

r num

ber

(% m

ax. c

ount

)

400300200

0100

Sea urchin biomass

Gra

ms

per

0.25

m2

10864

02

Total kelp density

Num

ber p

er0.

25 m

2

19971993198919851972Year

Food chain beforekiller whaleinvolvement inchain

Food chain afterkiller whales startedpreying on otters


Ecosystem “Engineers” (Foundation Species)

• Some organisms exert influence by causing physical changes in the environment that affect community structure

• For example, beaver dams can transform landscapes on a very large scale


• Some foundation species act as facilitators that have positive effects on survival and reproduction of some other species in the community

LE 53-19

Num

ber o

f pla

nt s

peci

es

8

6

4

0

2

Conditions

WithJuncus

WithoutJuncusSalt marsh with Juncus

(foreground)


Bottom-Up and Top-Down Controls

• The bottom-up model of community organization proposes a unidirectional influence from lower to higher trophic levels

• In this case, presence or absence of mineral nutrients determines community structure, including abundance of primary producers


• The top-down model proposes that control comes from the trophic level above

• In this case, predators control herbivores, which in turn control primary producers


• Long-term experimental studies have shown that communities can shift periodically from bottom-up to top-down controls

LE 53-20

Perc

enta

ge o

fhe

rbac

eous

pla

nt c

over

100

75

50

0

25

Rainfall (mm)200 300 4000 100


• Pollution can affect community dynamics

• Biomanipulation can help restore polluted communities

LE 53-UN1171

Polluted State Restored State

Fish Abundant Rare

Zooplankton AbundantRare

Algae Abundant Rare


Concept 53.3: Disturbance influences species diversity and composition

• Decades ago, most ecologists favored the view that communities are in a state of equilibrium

• Recent evidence of change has led to a nonequilibrium model, which describes communities as constantly changing after being buffeted by disturbances


What Is Disturbance?

• A disturbance is an event that changes a community, removes organisms from it, and alters resource availability

• Fire is a significant disturbance in most terrestrial ecosystems

• It is often a necessity in some communities

LE 53-21

Before a controlled burn.A prairie that has not burned for several years has a high propor-tion of detritus (dead grass).

During the burn. The detritus serves as fuel for fires.

After the burn. Approximately one month after the controlled burn, virtually all of the biomass in this prairie is living.


• The intermediate disturbance hypothesis suggests that moderate levels of disturbance can foster higher diversity than low levels of disturbance

• The large-scale fire in Yellowstone National Park in 1988 demonstrated that communities can often respond very rapidly to a massive disturbance

LE 53-22

Soon after fire. As this photo taken soon after the fire shows, the burn left a patchy landscape. Note the unburned trees in the distance.

One year after fire. This photo of the same general area taken the following year indicates how rapidly the com-munity began to recover. A variety of herbaceous plants, different from those in the former forest, cover the ground.


Human Disturbance

• Humans are the most widespread agents of disturbance

• Human disturbance to communities usually reduces species diversity

• Humans also prevent some naturally occurring disturbances, which can be important to community structure


Sucesiones ecológicas

• Es la secuencia de cambios de las comunidades y ecosistemas después de un disturbio

• La sucesión primaria se da cuando no hay suelo al comienzo de la sucesión

• La sucesión secundaria comienza en un área donde el suelo permaneció después del disturbio


• Early-arriving species and later-arriving species may be linked in one of three processes:

– Early arrivals may facilitate appearance of later species by making the environment favorable

– They may inhibit establishment of later species

– They may tolerate later species but have no impact on their establishment


• Retreating glaciers provide a valuable field-research opportunity for observing succession

LE 53-23

McBride glacier retreating

CanadaAlaska

1940

1941

1931 1911

19481912

1907

1879 1879

1879

1899

1948

GrandPacific Gl.

1900

1935 194919131892

Riggs Gl.

Muir Gl.Plateau Gl.

McB

ride

Gl.

Case

men

t Gl.

1860Johns Hopkins

Gl.

Pleasant Is.

Reid Gl.1879

GlacierBay

1760

18301780

Miles

15Kilometers

10

105

5

0

0


• Succession on the moraines in Glacier Bay, Alaska, follows a predictable pattern of change in vegetation and soil characteristics

LE 53-24Pioneer stage, with fireweed dominant

Dryas stage

Spruce stageNitrogen fixation by Dryas and alder

increases the soil nitrogen content.

Successional stageDryasPioneer Alder Spruce

Soil

nitr

ogen

(g/m

2 )

60

50

40

30

20

10

0


Concept 53.4: Biogeographic factors affect community diversity

• Two key factors correlated with a community’s species diversity are geographic location and size


Equatorial-Polar Gradients

• Two key factors in equatorial-polar gradients of species richness are probably evolutionary history and climate

• Species richness generally declines along an equatorial-polar gradient and is especially great in the tropics

• The greater age of tropical environments may account for the greater species richness


• Climate is likely the primary cause of the latitudinal gradient in biodiversity

• Two main climatic factors correlated with biodiversity are solar energy and water availability

• They can be considered together by measuring a community’s rate of evapotranspiration

• Evapotranspiration is evaporation of water from soil plus transpiration of water from plants

LE 53-25

Trees

Tree

spe

cies

rich

ness

180

160

140

120

100

80

0

Vert

ebra

te s

peci

es ri

chne

ss(lo

g sc

ale)

200

100

50

10

60

40

20

1,100900700500300100Actual evapotranspiration (mm/yr)

Vertebrates

2,000Potential evapotranspiration (mm/yr)

1,5001,000500


Area Effects

• The species-area curve quantifies the idea that, all other factors being equal, a larger geographic area has more species

• A species-area curve of North American breeding birds supports this idea

LE 53-26

Num

ber o

f spe

cies

(log

sca

le)

1,000

Area (acres)1010109106 107 108103 104 1051 10 100

100

10

1


Island Equilibrium Model

• Species richness on islands depends on island size, distance from the mainland, immigration, and extinction

• The equilibrium model of island biogeography maintains that species richness on an ecological island levels off at a dynamic equilibrium point

LE 53-27

Immigration and extinction ratesNumber of species on island

Equilibriumnumber

Imm

igration

Rat

e of

imm

igra

tion

or e

xtin

ctio

n

Extinc

tion

Effect of island sizeNumber of species on island

Smallisland

Immigration

Rat

e of

imm

igra

tion

or e

xtin

ctio

n

Extin

ctio

n

Largeisland

(large island)

Immigration

(small island)

Extincti

on

(large i

sland)

(sm

all is

land)

Effect of distance from mainlandNumber of species on island

Farisland

Imm

igration

Rat

e of

imm

igra

tion

or e

xtin

ctio

n

Extin

ctio

n

Nearisland

(near island)

Immigration

(far island) Extinctio

n

(near island)(fa

r isla

nd)


• Studies of species richness on the Galápagos Islands support the prediction that species richness increases with island size

LE 53-28

Area of island (mi2)(log scale)

400N

umbe

r of p

lant

spe

cies

(log

sca

le)

1,0001001010.1

200

100

50

25

10

5


Concept 53.5: Contrasting views of community structure are the subject of continuing debate

• In the 1920s and 1930s, two views on community structure emerged: the integrated hypothesis and the individualistic hypothesis


Integrated and Individualistic Hypotheses

• The integrated hypothesis describes a community as an assemblage of closely linked species, locked into association by mandatory biotic interactions

• The individualistic hypothesis proposes that communities are loosely organized associations of independently distributed species with the same abiotic requirements


• The integrated hypothesis predicts that presence or absence of particular species depends on presence or absence of other species

LE 53-29a

Environmental gradient(such as temperature or moisture)

Popu

latio

nde

nsiti

es o

fin

divi

dual

spec

ies

Integrated hypothesis


• The individualistic hypothesis predicts that each species is distributed according to its tolerance ranges for abiotic factors

LE 53-29b

Environmental gradient(such as temperature or moisture)

Popu

latio

nde

nsiti

es o

fin

divi

dual

spec

ies

Individualistic hypothesis


• In most actual cases, composition of communities seems to change continuously, with each species more or less independently distributed

LE 53-29c

Trees in the Santa Catalina Mountains

Num

ber o

fpl

ants

per h

ecta

re

Moisture gradientWet

600

400

200

0Dry


Rivet and Redundancy Models

• The rivet model suggests that all species in a community are linked in a tight web of interactions

• It also states that loss of even a single species has strong repercussions for the community

• The redundancy model proposes that if a species is lost, other species will fill the gap

• Community hypotheses and models represent extremes; most communities probably lie somewhere in the middle

ecología de comunidades - universidad nacional de · pdf file• dos comunidades...

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