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LB 144: Organismal Biology

Class 2404.14.16

Community Ecology I

Announcements

Readings:Chapter 55, Section 55.1 (pages 1123-1145)

Homework 7 Due Today

You should be able to:1. Describe, compare & contrast, and provide examples of

different types of interspecific interactions and their effects on fitness and short-term ranges and abundances.

2. Explain and give examples of links between current interspecific interactions and evolution (Ex: character displacement, arms races, and fitness effects on interacting species).

Objectives

4

TermsCommunityCommensalismCompetition Consumption Mutualism IntraspecificInterspecificCompetitive exclusion principle NicheFundamental nicheRealized niche

Niche differentiation Character displacementHerbivory Parasitism Predation CarnivoreMimicry Batesian mimicryMullerian mimicry Evolutionary arms race

5

Community EcologyBiological community- all the species that interact in a certain area.

6

Community EcologyAbiotic factors- Non-living factors in the environment that influence an organism’s distribution and abundance

Biotic factors- living factors that (e.g., competition) that influence the distribution and abundance of organisms.

Species interactions

7

Species interactions

Interspecific interactions:

4 Main Types:1. Commensalism2. Competition 3. Consumption 4. Mutualism

Effects on Fitness?+ Positive - Negative 0 None

1) Commensalism

1) Commensalism

1) Commensalism

1) Commensalism Human Commensals Rats (Rattus spp.)House Mice (Mus musculus)Raccoons (Procyon lotor)House Sparrows (Passer domesticusa)Turf Grass (Cynodon dactylon)

Cattle egret (Bubulcus ibis)

2) Competition: INTRA- and INTERspecific

– MANY Types:

• Consumptive

• Preemptive

• Overgrowth

• Chemical

• Encounter

• Territorial

2) Competition:

Interspecific competition:

Ecological niche:

The Consequences of Competition

2) Competition:

2) Competition:

Competitive exclusion occurs when competition is asymmetric.

Re

lati

ve F

itn

ess

Species A Alone

Species B Alone

Species A+B Together

Asymmetric Competition

2) Competition:

Competitive exclusion occurs when competition is asymmetric.

Re

lati

ve F

itn

ess

Species A Alone

Species B Alone

Species A+B Together

Symmetric Competition

2) Competition:

2) Competition:

2) Competition:

2) Competition:

2) Competition:

Competitive Exclusion Principle: A test

Balanus: Upper limit of distribution limited by water levelChthamalus: Lower limit of distribution limited by competition

Figure 19.7

1) A. ricordii

2) A. distichus

3) A. aliniger

4) A. cybotes

7) A. insolitus

6) A. christophei

5) A. etheridgei

A. Distichus – sunny fenceposts

A. Insolitus – shady branches

Resource Partitioning – An example

Fig. 54-4

Los Hermanos

G. fuliginosa G. fortis

Beakdepth

Daphne

G. fuliginosa,allopatric

G. fortis,allopatric

Sympatricpopulations

Santa María, San Cristóbal

Beak depth (mm)

Per

cen

tag

es o

f in

div

idu

als

in

ea

ch s

ize

cla

ss

60

40

20

0

60

40

20

0

60

40

20

08 10 12 14 16

Character displacement

3) Consumption = predation, parasitism, herbivory

Plant defenses against herbivores:

– Chemical toxins

– Spines and thorns

Animal defenses against predators:

– Passive defenses

– Active defenses

Adaptations of the consumed:

3) Consumption

Summary Table 55.1

• Passive camouflage/ cryptic coloration defenses

• Passive mechanical/ chemical defenses (e.g. warning coloration)

Figure 19.10

Figure 19.11

Toxins from: • Synthesis• Acquisition

Passive mimicry defenses = “copycat” adaptation

Batesian mimicry = A palatable/ harmless species mimics an unpalatable/ harmful species

Figure 19.12

Figure 19.13

Müllerian mimicry = >2 unpalatable species resemble each other

3) Consumption

Inducible defenses:– Alarm calls

– Mobbing

– Distraction displays

Figure 19.8

Figure 19.9

3) Consumption

Figure 55.10

Are mussel defenses induced

by the presence of crabs?

Mussels increase investment in defense in the

presence of crabs.

Mussels do not increase investment in

defense in the presence of crabs.

Seawater

Crab

(fed fish, not mussels)No crab

Mussels Mussels

Mussels downstream of the crab tank will have

thicker shells than mussels downstream of the empty tank.

Mussels in the two

tanks will have shells of equal thickness.

Average shell

thickness is

significantly higher

downstream of

the crab

No crab CrabSh

ell th

ic

ke

nss (m

m)

Mussels increase investment in defense when

they detect crabs. Shell thickness is an inducible defense.

Reminder: Practice your scientific

explanations with each data figure: Claim,

evidence, and reasoning

Figure 19.15

Adaptation and arms races

4) Mutualism

Many mutualistic relationships have evolved from predator-prey or host-parasite interactions

Figure 19.16