Today’s Lecture
• Communities
• Ecosystems
Community Ecology
Communities are
populations that live and
interact in the same place at
the same time.
Smaller communities are
nested within larger
communities.
Communities
– spatial scales
- a specific group
• Cliff dwelling birds
• Microbial
communities
• Plant communities
Communities
• Organisms do not
live in isolation
– Associations can be
based on need
• Butterflies and plants
• Parasites and hosts
• Flowers and
pollinators
– Associations can
also be due to
sharing similar
requirements
• Soil types
• moisture
Niche
• All the biotic and
abiotic resources a
species needs to
survive, remain
healthy and reproduce
– Light
– Temperature
– Moisture
– Food…
Fundamental vs realized
niche
No two species can have identical niches!
Limiting resources
• Any environmental
resource that restricts
the ecological niche of
a species
Species’ Interactions: Competition,
Symbiosis, Predation
• Intraspecific
• Interspecific
Factors Limiting Distribution
Biotic
Competitive exclusion –
a species is
prevented from
occupying an area
due to a competitive
interaction with
another
Biotic and abiotic factors can
restrict niches
Fig. 54-3
EXPERIMENT
Chthamalus
Balanus
High tide
Chthamalus
realized niche
Balanus
realized niche
Ocean
Low tide
RESULTS
High tide
Chthamalus
fundamental niche
Ocean
Low tide
Competitive exclusion – a species is prevented from occupying
an area due to a competitive interaction with another
Gallium ssp.
Reducing Competition – Niche partitioning
• Temporal
– nocturnal vs diurnal
– Predatory mammals
– Woodland flowers
• Spatial – species use
different microhabitats
– Wading birds
– Fish
Reducing Competition
Frequency
Green
sunfish
Largemouth
bass
Bluegill
Prey size
Werner, 1977
Amer. Nat. 111:553
Reducing Competition
Frequency
Green
sunfish
small
Largemouth
bass
Bluegill
Prey size
Werner, 1977
Amer. Nat. 111:553
Reducing Competition
med
Frequency
Green
sunfish
small
Largemouth
bass
Bluegill
Prey size
Werner, 1977
Amer. Nat. 111:553
Reducing Competition
med
Frequency
Green
sunfish
small
Largemouth
bass
Bluegill
Prey size
Werner, 1977
Amer. Nat. 111:553
Prey size
small
large
inshore
Green
sunfish
Microhabitat
Bluegill
Largemouth
bass
Deep,
open
water
Werner, 1977
Amer. Nat. 111:553
Character displacement reduces
interspecific competition
On islands where 2
species of finches do
not co-occur, birds
have similar beak
depths
On islands where they
are both found beak
depths differ
Predation
Predation strategies
include speed,
ambush and lures
Predation avoidance strategies
include cryptic and aposomatic
coloration
Fig. 54-5
(a) Cryptic
coloration
Canyon tree frog
(b) Aposematic
coloration
Poison dart frog
(c) Batesian mimicry: A harmless species mimics a harmful one.
Hawkmoth
larva
Green parrot snake
(d) Müllerian mimicry: Two unpalatable species
mimic each other.
Cuckoo bee
Yellow jacket
Fig. 53-8, p. 1154
Herbivory
• Herbivory (+/– interaction) refers to an
interaction in which an herbivore eats parts
of a plant or alga
• It has led to evolution of plant mechanical
and chemical defenses and adaptations by
herbivores
Symbiosis
• Symbiosis is a relationship where two or
more species live in direct and intimate
contact with one another
– Parasitic
– Mutualistic
– Commensal
Fig. 54-1
Fig. 54-7
(a) Acacia tree and ants (genus Pseudomyrmex)
(b) Area cleared by ants at the base of an acacia tree
Fig. 54-8
Diversity vs Richness
• Diversity is about number of species AND
species evenness
• Richness is only number of species
• Two communities with 100 individuals and
10 species:
– First on has 91 individuals of one species and
1 of all the others
– Second has 10 individuals in 10 species
– Which is more diverse?
Fig. 54-9
A
B C D
Community 1
A: 25% B: 25% C: 25% D: 25%
Community 2
A: 80% B: 5% C: 5% D: 10%
California Floristic Province
2,124 endemic plant species
Community Dynamics
• Trophic structure
– Food chains
– Food webs
•
•
•
•
Community Dominants
Ecosystem Engineers
Keystone Species
Facilitators
Food
chain
Quaternary
consumers
Carnivore
Carnivore
Tertiary
consumers
Carnivore
Carnivore
Secondary
consumers
Carnivore
Carnivore
Primary
consumers
Herbivore
Zooplankton
Primary
producers
Plant
Phytoplankton
A terrestrial food chain
A marine food chain
Food
Web
Humans
Smaller
toothed
whales
Baleen
whales
Crab-eater
seals
Birds
Leopard
seals
Fishes
Sperm
whales
Elephant
seals
Squids
Carnivorous
plankton
Euphausids
(krill)
Copepods
Phytoplankton
Community Dynamics
• Trophic structure
– Food chains
– Food webs
•
•
•
•
Community Dominants
Ecosystem Engineers
Keystone Species
Facilitators
Fig. 54-22d
4
Spruce-dominated forest – Community Dominants
Ecosystem Engineers
RESULTS
Number of species
present
Keystone
Species
EXPERIMENT
20
15
With Pisaster (control)
10
5
Without Pisaster (experimental)
0
1963 ’64 ’65 ’66 ’67 ’68 ’69 ’70 ’71 ’72 ’73
Year
Number of plant species
Fig. 54-18
8
6
4
2
0
(a) Salt marsh with Juncus
(foreground)
(b)
With Juncus
Without Juncus
Diversity in time
Succession– directional change in community
structure through time, but outcome is
unpredictable
Fig. 54-22-4
Early successional species– rapid
colonization and/or growth
1941
1907
2
1
Pioneer stage, with
fireweed dominant, low N, OM
0
1860
Dryas stage
5 10 15
Kilometers
Glacier
Bay
Alaska
1760
4
Spruce stage –
invades Alder
Late successional
species– slow
colonization
and/or growth
3
Alder stage symbiosis with nodule
forming bacteria
– but reaching equilibrium doesn’t mean that the community is
static
- A forest is a mosaic of successional stages (sensu Forman)
Secondary succession
– Gaps from, trees dying, ice, windfall
Final successional stage is a state of flux, a mosaic of patches
-Landscape ecology, patch dynamics
Ecosystem Ecology
Study of the ecological significance of the flow of energy and matter
Ecosystems
• Ecosystems include the
community and the
physical environment
– Community: focus is
on species interactions
– Ecosystem: focus is on
functional aspects
• Functional aspects
include:
– Energy flow
– Nutrient Cycling
Decomposers/
detritivores – feed on
bits not consumed or
that die naturally
Decomposition
connects all trophic
levels
• Energy flow is linear, from sun to producer to consumer to
decomposer (with some systems receiving energy from another
source!)
• A lot of energy is converted to heat, and is lost as it moves from
one organism to another
Energy that reaches the predators has passed through
many organisms and feeding levels.
Energy is lost at each
transfer so energy
available to the top is
limited relative to those at
lower trophic levels
• Disturbance
• Components of
Stability
-Resistance
-Resilience
Ecosystem structure and function
Stability and Diversity
Time
Time
Stability and Diversity
• In the 1950s
ecologists proposed
that more complex
systems should be
more stable
– Simple systems more
prone to outbreaks
– Simple models of
predator/prey systems
tend to oscillate
– More pathways for
energy flow
Nutrient Cycling
• From nutrient “pools”
• Nutrients are passed from
organisms to organism
• All organisms eventually die and
become food for decomposers
• Nutrients then return to the
nutrient pool
• Unlike energy, nutrients are
recycled.
• Limiting nutrients often
determine ecosystem dynamics
Biogeochemical Cycles
• Gaseous carbon, oxygen, sulfur, and
nitrogen occur in the atmosphere and cycle
globally
• Less mobile elements such as phosphorus,
potassium, and calcium cycle on a more
local level
• A model of nutrient cycling includes main
reservoirs of elements and processes that
transfer elements between reservoirs
• All elements cycle between organic and
inorganic reservoirs
• In studying cycling of water, carbon,
nitrogen, and phosphorus, ecologists focus
on four factors:
– Each chemical’s biological importance
– Forms in which each chemical is available or
used by organisms
– Major reservoirs for each chemical (pools)
– Key processes driving movement (flux) of each
chemical through its cycle
97% oceans
2% glaciers
1% lakes, rivers,
streams
Transport
over land
Solar energy
Net movement of
water vapor by wind
Precipitation Evaporation
over ocean
from ocean
Precipitation
over land
Evapotranspiration
from land
Percolation
through
soil
Runoff and
groundwater
Effects of altered water cycle
on ecosystems - Global
Glacier melting
- Influx of fresh water
- Rise in sea level
- Change of coastline
- More inland lakes
- Less circulation
Fig. 55-14b
CO2 in atmosphere
Photosynthesis
Photosynthesis
Cellular
respiration
Burning of
fossil fuels Phytoand wood plankton
Higher-level
consumers
Primary
consumers
Carbon compounds
in water
Detritus
Decomposition
Effects of change in C cycle
•
•
•
•
Plants grow faster
Hotter, wetter climate
Ocean acidification
Change in phenology and migration
Fig. 55-14c
N2 in atmosphere
Assimilation
NO3–
Nitrogen-fixing
bacteria
Decomposers
Ammonification
NH3
Nitrogen-fixing
soil bacteria
Nitrification
NH4+
NO2–
Nitrifying
bacteria
Denitrifying
bacteria
Nitrifying
bacteria
Eutrophication
• Eutrophication is the
transformation of an
ecosystem from low to
high nutrient levels
• Increase in nutrient
loads can lead to rapid
increases in the amount
of algae and aquatic
plants and reduced
water clarity
Fig. 55-14d
Precipitation
Geologic
uplift
Weathering
of rocks
Runoff
Consumption
Decomposition
Plant
uptake
of PO43–
Plankton Dissolved PO43–
Uptake
Sedimentation
Soil
Leaching
Fig. 55-1