Ecology of Animal Populations:
Theory, Application, and Estimation
“There is something fascinating
about science. One gets such a
wholesale return of conjecture
out of a trifling investment of fact.”
Mark Twain
What is Population Ecology?
The understanding of patterns of population change, either
numerically or genetically.
• “… the branch of ecology that studies the structure and
dynamics of populations” (Sharov)
• “… the study of the sizes (and to a lesser extent the
distributions) of plant and animal populations, and of the
processes, … which determine these sizes” (Begon et al. 1996)
• “… the study of the distribution of the individuals in a
population over time and space. … asking how and why a
population changes (Williams et al. 2001)
From Chitty 1996: Do lemmings commit
suicide? Beautiful hypotheses and ugly
facts.
Population Ecology as a Central Theme in Ecology
Population
Genetics
Ecosystem
Physiology
Ecology
Population
Ecology
Behavioral
Landscape
Ecology
Ecology
Community
Ecology
Vs the individual ???
but is this practical?
Modified from Sharov
Central Theme in Population Ecology:
relate the characteristics of individuals to the dynamics of the
population and their response to biotic and abiotic
environmental properties
Ind. Characteristics
Age
Stage
Size
Sex
Behavior
Ind. Processes
Development
Growth
Feeding
Reproduction
Death
Pop. Characteristics
Density
Age/Stage distribution
Sex ratio
Spatial distribution
Pop. Processes
Pop. growth/stability
Dynamics of age dist
Patterns of survival
Modified from Sharov
What is A Population?
“The definition of a population represents a fundamental
problem for understanding ecological dynamics and it has wide
application for applied issues such as management and conservation”
Camus and Lima 2002
Berryman (2002) and Camus and Lima (2002)
shed some light:
• Traditional definition:
•group of individuals of the same species living together in
a particular place
• Ambiguity largely due to lack of definition of “place”
• “…natural area of sufficient size that reproduction and
survival maintains the population….” Huffaker et al. 1999.
•“… made up of many interbreeding local populations …”
such that dispersal among local populations is expected but
dispersal among “natural” populations is “non-existent or
negligible…” = = geographical isolates
Andrewartha and Birch 1984
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Thus, spatial identity important in identifying
the “natural” (rather than “local”) population
If so, then population changes are not dependent on movement, as
all movement is within the population and birth and death process
are fully sufficient in describing the dynamics of the population
Following this logic, a more restrictive definition is in order:
Leading to Berryman’s definition of a population:
“ a group of individuals of the same species that live together in an
area of of sufficient size to permit normal dispersal and or migration
behavior and in which numerical changes are largely determined by
birth and death processes”
Population dynamics is the study of birth and death processes
NOT redistribution processes (immigration and emigration)
whereas local dynamics must consider movements.
Therefore,
the spatial identity (or “population area”) must be large enough
that immigration and emigration are rare.
Camus and Lima add to this:
• “local” poorly defined and out of convenience, thus
making it a “non-concept” of population ecology
• Scales used by ecologists tend to be small, researchers
usually are actually working with fragments of populations
And End with :
“ We do propose that unambiguous conceptualizations about
what is a population and how to determine the proper scale
of population dynamics continue to be central issues for
improving understanding of ecological systems”
• “…investigators feel comfortable with textbook definitions
… because it accurately reflects the way the work is done in
in the field”
Is Population Ecology all about about mathematical models?
But theory can guide us and avoid mountains of “factoids”
that seem unconnected and provide little future guidance in
our thinking
B 316 B B 316
15 D 31615D 15
D
Z
Z
Z
F
F
FB
B
LB
L
B
AL B
B
A
A
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Why “Theory, Application, and Estimation”:
Some Initial Thoughts
“Every scientific discipline is founded on an operational theory,
which provides a conceptual framework through which the world is
observed and facts about the world are discerned” Williams et al. 2001
Why “Theory, Application, and Estimation”:
Some Initial Thoughts
• Theoretical Ecology is the study of how nature might work and
provides useful constructs but does not provide a basis
for scientifically sound application.
Theoretical Ecology = Mathematical Ecology
•Empirical studies grounded in an a priori hypothesis framework
allow theory to be amended and provide a basis for application.
• Biological models provide one tool for linking theory and
empirical studies, and provide a means for scientifically-based
resource management.
• Specific hypotheses and predictions can be evaluated through
estimation of model parameters.
N = B + D + I + E
E=f(inbreeding)
Predictions
+ Experiment
Learn from
the study and
amend model
Leaving the Population Definition in Fair Standing
A few final thoughts about last week’s discussion on population:
Berryman’s “last words”:
1.
Argues population is the central concept and thus “the concept
requires a precise and unambiguous meaning”
2.
Argues his definition has these qualities
3.
“Place” important but requires definition and biological consideration
4.
Inclusive study of population (as he defines it) is not Berryman’s point:
“This is not to say that studies of reproductive success in the north,
or over-winter survival in the south, are meaningless, only that the
investigators need to realize that they are not studying the true
population” (p. 441)
5.
This class will hopefully be a fun exploration into the myriad
avenues of Population Ecology
“Finally (but not exhaustively), the ultimate goal of ecology is to
elucidate general principles or laws….” (p. 442)
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