Download Populations and Communities

FWF 410:
“Populations and Communities”
(Molles 2002 after Gause 1934)
Matthew J. Gray, Ph.D.
College of Agricultural Sciences and
Natural Resources
University of Tennessee-Knoxville
Goal of the Lecture
To familiarize students with
biological organization terms,
population distributions and
growth, and basic concepts in
community ecology.
Reading Assignments:
No Assigned Reading for Lecture
Lecture Structure
I.
Levels of Biological Organization
What is an individual, population and community?
II. Population Distributions and Growth
How are individuals distributed in space and how do populations
fluctuate through time?
III. Community Ecology
What factors influence multiple species assemblages?
1
Levels of Biological Organization
Individual:
A living single or multi-celled organism.
Population:
A collection of individuals of the same species that
have a some probability* of interaction and influence.
Community:
A collection of populations of different species that
have a some probability of interaction and influence.
Population Biology
Introduction
Study of the distribution and abundance of organisms.
Terms
Population:
Group of individuals of the same species that have some probability
to interact and reproduce (without dispersing).
Distribution: The size, shape, and location of the area where a population exists.
Abundance:
Number of individuals in a population per unit time, Nt .
Density:
Number of individuals per unit area (e.g., nt / m2) for a population.
Why Study Populations?
Populations provide an ecological entity of quantification for management & experiments.
•Prudent human natural resource use (harvesting, non-consumptive use)
Evolutionary
Unit
•Human influences on organisms (disturbed vs. undisturbed)
Species of Conservation and Management Interest
•Regulating mechanisms (competition, predation, habitat availability & quality)
Distribution Patterns
Scale & Pattern Types
Scale
Small: Area (e.g., <100 m) over which the environment does not change.
Large: Area (e.g., continent) over which the environment does change.
Pattern
“Home range”
“Sp. Dist.”
1) Random: All locations have equal probability (no biological interaction).
2) Regular: All locations have equal probability (‘−’ biological interaction or
3) Clumped: Locations have unequal probability
uniform resources).
(‘+’ biological interaction or clumped resources).
Important
for
Sampling
Design!
Equal
P[loc]
Small Scale (1−3)
Large Scale (#3)
Antagonistic
Interaction
Clumped
Resources
2
Population Growth
Introduction
Graphical behavior of population abundance over time.
2 Types:
Plankton Blooms
1) Unlimited Population Growth:
a) Geometric
b) Exponential
Rapid increase in population numbers due an abundance of resources
typically at low population numbers.
Adaptation:
1) Colonization of new habitats.
2) Exploitation of transient resources.
3) Recovery from population crash.
2) Limiting Population Growth:
Logistic Growth
Rapid increase in population numbers to a stabilizing, limiting abundance (K).
Carrying Capacity (K): The maximum number of individuals that can
be sustained in an environment at a given time.
Abiotic ⇔ Biotic Factors
A mathematical reality of all biological populations due to a decrease
in available resources necessary for survival and reproduction.
Survival +
Reproduction
Rate of Population Change
(by Age Class)
Survival Rate, lx: proportion of the population surviving to age x.
Fecundity Rate, mx: average number of young produced per individual for age x.
Net Reproductive Rate, R0: average number of young produced by an individual in its
lifetime.
•R0 > 1 ⇒ Population Increasing
n
•R0 ≅ 1 ⇒ Population Stable
R0 = ∑ l x m x
•R0 < 1 ⇒ Population Decreasing
x =0
(
)
Geometric Rate of Increase, λ: rate of change of the population trajectory.
N2 = 25
N1 = 10
o
Sl
λt = N t +1
pe
Generation Time, T :
n
Nt
λ=
25
= 2.5
10
T=
∑ ( xl x m x )
Average Time
from Offspring to
Offspring
x =0
R0
Realized Rate of Increase, r : per capita rate of increase
r=
ln( R 0)
•r > 0 ⇒ Population Increasing
•r ≅ 0 ⇒ Population Stable
•r < 0 ⇒ Population Decreasing
T
Phlox
(births−deaths)
Population Growth
Geometric Growth
Many
Wildlife
Non-overlapping Generations
Conditions:
Recall:
Unlimited population growth by species that produce a single generation per year
(i.e., 1 reproductive event thus population grows in DISCRETE annual pulses).
λ = N t +1 ⇔ N t + 1 = N t λ
Nt
N m = N 1 λm
The abundance at t + 1 can be calculated using the
previous abundance & geometric rate of increase.
Exponential Growth
Overlapping Generations
Conditions:
Unlimited population growth by species that reproduce continuously (i.e., no
discrete annual reproductive event thus population grows CONTINUOUSLY).
Continuous population growth can be represented as a rate of change (i.e., derivative)
f ′(N ) =
dN
= rN
dt
where, r = realized rate of increase (avg. per capita increase)
r = births − deaths (constant!)
Exp Growth Cannot
Notice: as N increases, dN/dt increases
be Sustained
3
Population Growth
Logistic Growth
Overlapping Generations
K
All populations
are governed
by a limiting
distribution &
unable to grow
without bound
indefinitely.
Limiting Growth
b=d
Sigmoidal
Curve
+,∩
K/2
⇔ b−d = 0
⇒r=0
⇒ Nt+1 = Nt
⇒ dN / dt = 0
⎡
⎛
N t⎞⎤
N t +1 = N t ⎢1 + r m ⎜ 1 −
⎟⎥
⎝
K ⎠⎦
⎣
+,∪
discrete
Yeast
•Food Availability
•Space (competition)
•Disease
•Parasitism •Predation
NOTE: K can fluctuate!
Balanus
African Buffalo
Connell
Gause
Waste
Sinclair
Space
Grass
Limits to Population Growth
What affects birth and death rates?
Andrewartha
& Birch
Smith &
Nicholson
Environment vs. Organisms
1) Density-independent Factors:
Food abundance
Abiotic factors (e.g., precipitation, temperature)
that can affect population growth.
Seeds/Caterpillars
2) Density-dependent Factors:
Biotic factors (e.g., competition, predation, disease)
that can affect population growth.
mx
Galápagos Finches: El Niño
Fledglings
Rainfall vs. Nt
4X
b>d
85% (starvation)
b<d
Community Ecology
Introduction
Study of the how abiotic and biotic factors affect the
association and interaction of species in a given area.
Community: An association of interacting species inhabiting some
defined area.
e.g., plant community, amphibian community,
insect community
Community Structure: The assemblage of a community, which includes:
•Number of species (species richness)
•Relative abundance per species (Nti, species abundance)
•Types of species (composition)
Guild:
Plant
Life
Forms
Groups of species exploiting a common resource in a similar fashion
(i.e., have similar ecological roles). e.g., aquatic insect guilds
Complex assembly of component guilds.
Why Study Guilds?
Shredders (CPOM)
Collectors (FPOM)
Grazers (algae)
Predators
1) Focus on functional role 3) Manageable Unit
2) Focus on interaction
4) Basic Building Blocks
4
Species Diversity
A combination of number of species and
their relative abundance.
Species Evenness
1) Species Richness
Components:
2) Species Abundance
A measure (comparison) of abundance among
species. As abundance per species becomes
“more even”, species diversity increases.
B
A
Both
have 5
species
One species comprises 84%
and others 4% of community.
Each species comprises 20%
of community.
Common Misuse
of Terms
Species Diversity is Greater for Community B
MAX ( H ′ ) = ln( SR )
MIN ( H ′ ) = 0
Species Diversity
A common method to calculate species diversity:
pi = proportion of the ith species
Community A
Species
1
2
3
4
5
H A′ = −( −0.662)
Shannon-Wiener Index
Abundance
21
1
1
1
1
= 0.662
s
H B′ = −( −1.610 )
i =1
= 1.610
H ′ = − ∑ p i ln p i
pi
21/25 = 0.84
0.04
0.04
0.04
0.04
ln(pi)
ln(0.84)= −0.174
−3.219
−3.219
−3.219
−3.219
piln(pi)
0.84(−0.174)=−0.146
−0.129
−0.129
−0.129
−0.129
pi
5/25 = 0.20
0.20
0.20
0.20
0.20
ln(pi)
ln(0.20)= −1.609
−1.069
−1.609
−1.609
−1.609
piln(pi)
0.20(−1.609)=−0.322
−0.322
−0.322
−0.322
−0.322
−1.610
25
Community B
Species
1
2
3
4
5
−0.662
Abundance
5
5
5
5
5
25
Environmental Complexity
In general, environmental complexity and species diversity are positively related.
FHD and Bird Species Diversity
FHD = foliage height diversity, where S = # of foliage layers & pi = biomass or volume per layer
Robert MacArthur (1958):
Examined niche partitioning of warblers in Maine.
Found that number of pairs and warbler diversity increased with amount of
vegetation and increasing FHD (increase in K and # of niches [unique habitats]).
Volume of Foliage
Foliage Height Diversity
5
Disturbance & Diversity
Environmental
Complexity
Explains Part
Management
Implications!
Intermediate Disturbance Hypothesis
Equilibrium:
A state when environmental conditions are more or less stable.
Disturbance:
1) A state when environmental conditions are unstable.
“Ecology of Natural
Disturbance”
“Species Dependent”
2) Any discrete event in time that disrupts an ecosystem, community,
or population structure and changes resources, substrate availability,
or the physical environment (White & Pickett, 1985).
26 Major Sources (fire, storms, disease, predation, human-induced)
Hypothesis: Intermediate levels of disturbance (frequency & intensity) will result in the
greatest species diversity.
Too Much: Few species that complete
life cycle between disturbance events.
Too Little: Limited to most effective
competitors (other excluded).
Joseph Connell
Just Right: Sufficient time for a variety
of species to colonize & complete life
yet short enough to prevent exclusion.
High
Science 199:
1302−1310
Low
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