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 ( , 53.5 & 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 Characteristics 1. Density 2. Dispersion

Density  Number of individuals per unit area or volume.  Ex: Diatoms - 5 million/m 3 Trees - 5,000/km 2 Deer - 4/km 2

Dispersion  Pattern of spacing among individuals.  Types: 1. Clumped 2. Uniform/Even 3. Random

Clumped Dispersion  May result form a patchy environment.  May increase chances for survival.  Ex: Schooling behavior Flocks of birds

Uniform Dispersion  Often the result of antagonistic interactions between individuals.  Known as even or regular dispersion  Ex: Territories Spacing 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 population Birth and death rates Generation time Sex 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 year Life span of the organism Fecundity (birth rate)

Survivorship Curve  Plot of the numbers of a cohort still alive over time.  Curve Types: Type I Type II Type III

Type I  Low early deaths.  High late deaths.  Ex: Humans Other large mammals

Type II  Constant death rate.  Ex: Annual plants Many invertebrates

Type III  High early deaths.  Low late deaths.  Ex: Trees Oysters

Comment  Curve type may change between young and adults.  Ex: Nestlings - Type III Adult Birds- Type II

Life History Strategies 1. "r" or Opportunistic species 2. "k" or Equilibrial species

"r" Species  Increase fitness by producing as many offspring as possible.  Do this by: Early maturation Many reproductive events Many 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 care Late maturation Few reproduction events Few 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   N/  t = b - d  Where: N= population size t = time b = birth rate d = death rate

Rate of Increase  r = difference between birth rate and death rate.  r = b - d

Equation with “r”:   N/  t = rN  N = population size  t = time  r = rate of increase

From Calculus  The equation  N/  t = rN becomes: dN/dt = r max N r max = intrinsic rate of increase

Exponential Growth  dN/dt = r max N  Characteristic of "r" species.  Produces a “J-shaped” growth curve.  Only holds for ideal conditions and unlimited resources.

Logistic Growth  dN/dt = r max N K-N K  K = carrying capacity  Result of logistic growth? “S-shaped” growth curve Characteristic of “k” species Common 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 Size 1. Density- Dependent Factors 2. 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 factors Chemical cycles Saturation 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.