Chapter 53: Population Ecology
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Transcript of Chapter 53: Population Ecology
Chapter 53: Population Ecology
Essential Knowledge 2.a.1 – All living systems require constant input
of free energy (53.3 & 53.4). 2.d.1 – All biological systems from cells and
organisms to populations, communities, and ecosystems are affected by complex biotic and abiotic interactions involving exchange of matter and free energy (53.1 – 53.5).
4.a.5 – Communities are composed of populations of organisms that interact in complex ways (53.1-53.3, 53.5 & 53.6).
Population Ecology Study of the factors that affect population
size and composition. Population:
Def: Individuals of a single species that occupy the same geographic area
Ex: Humans living in Indianapolis, IN
Important Characteristics1. Density2. Dispersion
Density Number of individuals per unit area or
volume. Ex:
Diatoms - 5 million/m3
Trees - 5,000/km2
Deer - 4/km2
Dispersion Pattern of spacing among individuals. Types:
1. Clumped2. Uniform/Even3. Random
Clumped Dispersion May result form a patchy environment. May increase chances for survival. Ex:
Schooling behaviorFlocks of birds
Uniform Dispersion
Often the result of antagonistic interactions between individuals.
Known as even or regular dispersion
Ex: TerritoriesSpacing between desert plants
Random Dispersion Often the result of the absence of strong
attractions or repulsions between individuals.
Not a common pattern.
Demography The study of the vital statistics that affect
population size. Ex: Birth and Death rates Factors of Demography:
Age structure of populationBirth and death ratesGeneration timeSex ratio and reproductive behavior
Life Tables Mortality summary for a cohort of
individuals. First developed from life insurance studies. What do they show us?
Mortality rate per yearLife span of the organismFecundity (birth rate)
Survivorship Curve Plot of the numbers of a cohort still alive
over time. Curve Types:
Type IType IIType III
Type I Low early deaths. High late deaths. Ex:
HumansOther large
mammals
Type II Constant death rate. Ex:
Annual plantsMany invertebrates
Type III High early deaths. Low late deaths. Ex:
TreesOysters
Comment Curve type may change between young and
adults. Ex: Nestlings - Type III
Adult Birds- Type II
Life History Strategies1. "r" or Opportunistic species2. "k" or Equilibrial species
"r" Species
Increase fitness by producing as many offspring as possible.
Do this by:Early maturationMany reproductive eventsMany offspring
Result Maximize reproduction so that at least a
few offspring survive to the next generation. Most offspring die (Type III curve).
"k" Species
Increase fitness by having most offspring survive.
Do this by:High parental careLate maturationFew reproduction eventsFew offspring.
Result Maximize survivorship of each offspring. Few offspring, but most survive (Type I
curve).
What is the strategy? For a weed? For an endangered species? For Garden Pests?
Population Growth DN/Dt = b - d Where:
N= population sizet = timeb = birth rated = death rate
Rate of Increase r = difference between birth rate and death
rate. r = b - d
Equation with “r”: DN/Dt = rN N = population size t = time r = rate of increase
From Calculus
The equation DN/Dt = rN becomes:dN/dt = rmax Nrmax = intrinsic rate of increase
Exponential Growth
dN/dt = rmax N Characteristic of "r" species. Produces a “J-shaped” growth curve. Only holds for ideal conditions and unlimited
resources.
Logistic Growth dN/dt = rmax N K-N
K K = carrying capacity Result of logistic growth?
“S-shaped” growth curveCharacteristic of “k” speciesCommon when resources are limited
Comment K is not a constant value. Populations often oscillate around “K” as
the environment changes.
Additional Comments Populations often overshoot “K”, then drop
back to or below “K”. AP Exam rarely asks you to work the
equations, but you should be able to give them.
Regulation of Population Size1. Density- Dependent Factors2. Density- Independent Factors
Density-Dependent Affect is related to N As N increases, mortality increases Ex: Food, nesting space, disease
Density-Independent Affect is not related to N Mortality not related to population size Ex: Weather and climate
Population Cycles Cyclic changes in N over time Often seen in predator/prey cycles Ex: Snowshoe Hare – Lynx Causes?
Density dependent factorsChemical cyclesSaturation strategy to confuse predators
Age Structure Diagrams Show the percent of a population in
different age categories Method to get data similar to a Life Table,
but at one point in time
Importance Can be used to predict future population
growth trends, especially for long lived species.
Exponential Growth Produces age structures that are a triangle
or pyramid shape
Logistic Growth Produces age structures that have even
sizes between most age categories
Declining Populations Produce age structures with a narrow base
and wider middles
Summary Identify the difference between population density
and dispersion. Recognize the types of dispersion patterns and the
interactions that lead to them. Identify the types of survivorship curves. Recognize the characteristics of "r" and "k" life history
strategies. Identify the types of population growth models. Identify factors that regulate population size. Recognize how age-structure diagrams relate to
population growth.