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.