Community Ecology
Chapter 56
1
Biological Communities
• Community: all the organisms that live
together in a specific place
– Evolve together
– Forage together
– Compete
– Cooperate
2
Biological Communities
• Individualistic concept: a community is
a group of species that happen to occur
together at one place
– species respond independently to
changing environmental conditions
– The composition of a Community can
change
3
Ecological Niche
• Niche: An Organism’s way of life
– Habitat
– Food
– Temp. range
– Reproduction
4
Ecological Niche
• Fundamental niche: the entire niche that
a species is capable of using.
• Realized niche: actual niche in which the
species can establish a stable population
5
Ecological Niche
study of barnacles
6
Ecological Niche
• causes of niche restriction
– Competition
– Predators
– Absence of pollinators
– Presence of herbivores
Billock
Billock
7
Ecological Niche
Principle of competitive exclusion: no
two species can occupy the same niche
when resources are limited
•Species may divide up the resources,
(resource partitioning)
•natural selection can then lead to
adaptive radiation
8
Resource
partitioning
among
sympatric
lizard
species
9
Ecological Niche
Character displacement in Darwin’s
finches
10
Predator-Prey
• Predation and coevolution
1. Predation provides strong selective
pressure on the prey population
2. Features that decrease the
probability of capture are strongly
favored
3. Predator populations counteradapt
to continue eating the prey
Coevolution race
11
Examples of prey adaptations:
•Chemical defenses
•Camouflage
•Warning coloration
•mimicry
12
Species Interactions
• Symbiosis: two or more kinds of
organisms interact in more-or-less
permanent relationships
• All symbiotic relationships carry the
potential for coevolution
• Three major types of symbiosis
– Commensalism
– Mutualism
– Parasitism
13
Species Interactions
• Commensalism benefits one species
and is neutral to the other
– Spanish moss: an epiphyte hangs
from trees
14
Shark and Pilot Fish
Barnacles and Whales
Species Interactions
• Mutualism benefits both
species
• Coevolution: flowering
plants and insects
Ants and acacias
– Acacias provide
hollow thorns and food
– Ants provide
protection from
herbivores
17
Human Intestine and E.Coli
Zebra and Oxpecker Bird
Species Interactions
• Parasitism benefits one species at the
expense of another
• Can be external or internal parasites
20
Species Interactions
External parasite: the yellow vines are
the flowering plant dodder, it is a parasite
that obtains its food from the host plant it
grows on
21
Heartworm and Dogs
Mistletoe and Mesquite Tree
Species Interactions
• Ecological processes can interact
– Predation reduces competition
• Superior competitors become more
numerous and attract predators
• This allows other species to survive
when they could have been out
competed
24
Species Interactions
Starfish eat barnacles, allowing other species
to thrive instead of being crowded out by the
explosive population of barnacles
25
Species Interactions
• Keystone species: species whose effects
are greater than expected
• Examples:
– Sea star predation on barnacles
– Beaver ponds
– Top predators
26
Species Interactions
Beavers construct dams and transform
flowing streams into ponds, creating new
habitats for many plants and animals
27