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Population Ecology

Group 3 - Sarah Rios, David Jung, Steven Lee

Key Concepts

Density and Dispersion (pg 1137-1139)

-Density is the number of individuals in a certain area. Dispersion is the pattern of spacing between individuals of the species.

Dispersion Types:





Organisms are evenly spaced



Organisms are spaced randomly, with no apparent system



Organisms are found in groups.

Wolves, Human

Image: examples of uniform, random

, and clumped dispersion.

Demography (pg 1137- 1141)

Demography is the study of population statistics and how they change over time. Shown using life tables following a cohort (group or individual of the same age), or a survivorship curve.

    Types of  Survivorship Curves:                                                                        

 I: Rate of death increases as the individuals get older. Organisms get lots of parental care

II: An intermediate curve between types I and III.

III: Rate of death decreases as the individuals get older. Organisms get little to no parental care.  

Life History Traits are Producers of Natural Selection (pg1141)

An organism’s traits reflect evolutionary history and the development, physiology, and behavior of the species. Life history is made up of the schedule of reproduction of an organism, such as how many offspring are produced. 

Life History Diversity (pg 1141-1142)

There are two types of Reproduction.

-Semelparity “Big Bang Reproduction”: When an organisms reproduces only once, but produces a large amount of offspring.

-Iteroparity: “Repeated Reproduction”: When an organism produces multiple times during its life, but produces one of few offspring each time.

''Tradeoffs" and Life Histories (pg 1112-1143)

Organisms have finite resources, and limited resources such as nutrients and energy mean trade-offs. Age at maturity, brood size, and level of parental care depend on the environment. For example, plants and animals with high mortality rates tend to produce more offspring in hopes some will survive. 

Per Capita Rate of Increase (pg 1143-1144)

If immigration and emigration is ignored, changes in population during a period of time can be summed up as this: 
Change in population size during time interval= Births during time interval- Deaths during time interval

Exponential Growth (pg 1144-1145)

Exponential Growth represents the potential growth without taking resource restrictions and carrying capacity into consideration. This model is shown using a J shaped curve, and predicts a larger rate of growth the larger the population is.

 Equation: dN = change in population, dt= change in time, r= maximum rate for the species, N = population  

The Logistic Growth Model Includes the Concept of Carrying Capacity (pg 1145)

Logistic Growth incorporates (K), carrying capacity because exponential growth cannot continue forever. All populations are limited by the amount of resources in their environment.

The Logistic Growth Model (pg 1145-1146)

In the logistic growth equation, population is known to ‘level off’ and grow much more slowly as it approaches carrying capacity.

Equation: Similar to exponential growth model, but now includes K which = carrying capacity

The Logistic Model and Real Populations (pg 1146)

In logistic growth models, the population growth will slow down as soon as it approaches carrying capacity. In a real population, there is usually a delay and it may exceed carrying capacity for a short time before correcting itself. Overall, the logistic model is an accurate approximation of the growth of a population.

The Logistic Model and Life Histories (pg 1147)

Logistic growth is affected by life histories, which are defined as a series of events from birth through reproduction and death. Two life history traits include K- selection, which is dependent on density and r- selection which is density independent.

Population Change and Population Density (pg 1148)

Population density can affect the regulation of that population. Density independent populations have birth and death rates that do not change with population density. In density dependent populations the birth or death rate rises or falls with a change in population density.

Density Dependent Population Regulation (pg 1148-1150)

Density dependent rates of birth and death is a type of negative feedback, or a regulation mechanism to turn a process on or off. This is due in part to several factors such as competition for resources like food and space to live, increased predators, increased risk of health problems like infection, and the buildup of toxic wastes.  

Population Dynamics (pg 1150-1151)

The study of population dynamics focuses on the abiotic and biotic factors that cause changes in population size. Temperature and environmental fluctuations can cause dramatic change in even stable populations. Population size is also affected by emigration and immigration, especially in metapopulations, which are made of several populations linked together.                                                        

Population Cycles (pg 1151- 1152)

Image: Population cycles of snowshoe hares and lynx. 
Populations go through 'boom and bust' cycles of regular highs and lows. Cycles vary from 3 to 4 year cycle in lemmings and voles, to a 10 year cycle of snowshoe hare and lynx. These cycles are influenced by both biotic and abiotic factors. 

The Global Human Population (pg 1152-1155)

The human population has grown exponentially since 1650, when there was 500 million people. The population reached 1 billion within the next 2 centuries, and 2 billion between the years of 1850 and 1930. The annual rate of growth has been slowing since the 1960's, at it's highest it was 2.19% and is now 1.16%. It is predicted by 2050 the rate of growth will drop to 0.4%. Rates of infant mortality and life expectancy differ between developed and developing nations. 

Global Carrying Capacity (pg 1155-1156)

There are several different estimates for global carrying capacity ranging from less than 1 billion to a trillion people, the average of them is somewhere between 10 to 15 billion. Ecological footprint is the concept of calculating carrying capacity by finding the aggregate land and water area to sustain the people of a nation. Ecological capacity varies by nation, and is defined as the ability of an ecosystem to maintain it's condition and produce goods. The world is already exceeding ecological capacity.