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Population Biology Chapter 52 U112PP
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Population Biology- Chapter 52 U112PP. Reminder of the population ... Prevalent vegetation type. Stability (ability to resist disturbance) Tropic structure ... – PowerPoint PPT presentation
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Title: Population Biology Chapter 52 U112PP
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Population Biology- Chapter 52 U112PP
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Reminder of the population growth models we have
previously considered
- Exponential
- Under what conditions do we see this growth
pattern? - Logistic
- When do we see this? What is being factored in?
Just how well do these models fit real
populations?
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- We construct the logistic model by starting with
the exponential model - And adding an expression that reduces the per
capita rate of increase as N increases
As N approaches K, r approaches 0). So, even
though the value of r does not change in the
equation, K influences the rate of growth)
Huh? How?
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Some assumptions of logistic population growth
- populations adjust instantaneously to growth and
approach carrying capacity smoothly. - In fact, populations could overshoot their
carrying capacity or could be slow to reproduce - regardless of population density, each individual
added to a population has the same negative
effect on population growth rate. - If population is too small, may have a
detrimental effect (cant find mates, lack of
social behavior). Sometimes, you just NEED
others
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Recall life history traits (evolutionary
trade-offs)
- Life history traits favored by natural selection
- May vary with population density and
environmental conditions (in other words, could
be influenced by population growth)
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r and K selection describe combinations of life
history traits, favored to maximize reproduction
or long-term survival, respectively
- K-selection, or density-dependent selection
- Selects for life history traits that are
sensitive to population density
(slow-reproducing, fewer episodes of
reproduction, larger, parental care)- traits that
would help in high density populations would
maximize each offspring - r-selection, or density-independent selection
- Selects for life history traits that maximize
reproduction (quick reproducing, many episodes of
reproduction, smaller, little parental
care)would maximize the number of offspring
- The concepts of K-selection and r-selection are
somewhat controversial and have been criticized
by ecologists as oversimplifications
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In reality
- Concept 52.5 Populations are regulated by a
complex interaction of biotic and abiotic
influences - There are two general questions we can ask about
regulation of population growth - What environmental factors stop a population from
growing? - Why do some populations show radical fluctuations
in size over time, while others remain stable?
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Population Change and Population Density
Some populations ARE density-dependent regulated
while others are not
- In density-independent populations
- Birth rate and death rate do not change with
population density - In density-dependent populations
- Birth rates fall and death rates rise with
population density
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Determining equilibrium for population density
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Density-Dependent Population Regulation
- Density-dependent birth and death rates
- Are an example of negative feedback that
regulates population growth - Are affected by many different mechanisms
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Competition for Resources
- In crowded populations, increasing population
density intensifies intraspecific competition for
resources (which then lowers birth rate)
Figure 52.15a,b
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Territoriality
- In many vertebrates and some invertebrates
- Territoriality may limit density (not all
individuals can get a territory and reproduce)
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- Cheetahs are highly territorial
- Using chemical communication to warn other
cheetahs of their boundaries
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- Oceanic birds
- Exhibit territoriality in nesting behavior
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Population density matters
- Health
- Can influence the health and survival of
organisms in dense populations, pathogens can
spread more easily - Predation
- Predators may feed preferentially on that species
- Toxic wastes
- Accumulation can contribute to density-dependent
regulation of population size
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Population Dynamics
- The study of population dynamics
- Focuses on the complex interactions between
biotic and abiotic factors that cause variation
in population size
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Stability and Fluctuation
- Long-term population studies
- Have challenged the hypothesis that populations
of large mammals are relatively stable over time
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- Extreme fluctuations in population size
- Are typically more common in invertebrates than
in large mammals
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Population Cycles
- Many populations
- Undergo regular boom-and-bust cycles
- Boom-and-bust cycles
- Are influenced by complex interactions between
biotic and abiotic factors
POPULATIONS INTERACT.?
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- Overview What Is a Community?
- A biological community
- Is an assemblage of populations of various
species living close enough for potential
interaction - Usually characterized by
- Degree of diversity
- Prevalent vegetation type
- Stability (ability to resist disturbance)
- Tropic structure
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