NEU Ecology Fall 2013 Lec set 6

This is the number of organisms per unit area or volume

Population density

Natality (the reproductive output of a population), mortality, immigration and emigration are all factors that can do what?

Cause changes in population density

What are life tables in the grand scheme of demography?

They describe the mortality schedule in a population and are an age-specific summary or the mortality rates operating on a cohort of individuals

The most frequently used part of the life tables is the (blank) column, the (blank)

nx, number of survivors at age x

How are per capita rates of change measured in survivorship curves: on an absolute numerical curve or on a logarithmic scale?

Logarithmic scale

Humans are an example of a type 1 survivorship curve. Provide the basic details behind this kind of survivorship curve

Populations have low per capita mortality for most of their life span and then high losses of older organisms

Birds are prime examples of the type 2 survivorship curve model. Provide the basic details of this model

A linear survivorship curve indicates a constant per capita rate of mortality that is independent of age

Fishes and marine invertebrates are prime examples of the type 3 survivorship curve. Provide the basic outline of this model type

There is a high per capita rate of mortality early in life followed by much less and constant mortality thereafter

This is one form of life table and is common and easy to produce, focuses on a cross section of a population at a specific time and assumes that there are static/stationary populations

This is a static life table

This is one type of life table and follows a cohort of organisms throughout their life, is difficult to make because birth and death rates can vary from year to year but is much more dynamic that its counterpart

These are cohort life tables

This follows the overall survival of a large cohort born at the same time throughout its existance to directly generate cohort life tables


What two factors are often used to generate life tables?

The number of overall individuals that are alive over the course of time and mortality rates vs age in years

Fertility, the speed of individual development and longevity are all key factors that play into what?

The intrinsic capacity for increase

What must we know in order to estimate changes in population size with respect to natality and death rates?

We must know how natality and death rates change with age

What is the fertility schedule?

It is the number of female offspring produced per female per unit time

What is the net productive rate, how is it calculated and what does its result mean?

The net reproductive rate is the sum of the female offspring produced per female divided by the survivorship up to the critical age (in this case, reproduction capacity). R=1 means that the population is replacing itself exactly at a 1:1 ratio, R<1 means the population is shrinking and R>1 means the population is growing

What do we expect about mortality rates and female production rates for humans?

We assume that these values remain constant and that there is no limit placed on population growth. Ex: if the whole population were over 50, it would not increase

Given the differences in mortality and female production with age, one would think that we need to specify the age distribution of the population but this was shown by Lotka to not be true. Why is this not true?

Because a population with a constant schedule of natality and mortality rates will eventually approach a stable age distribution and maintain it indefinitely

What is the integral equation for the population size increase?

Nt=N0ert where Nt = the number of individuals at time T, N0 = the number of individuals at time 0, r = the intrinsic capacity for increase in a given environment and t = unit time

What is the N(t)=N(0)e^rt equation called?

It is the geometric growth pattern. On a logarithmic scale, the line is linear in shape

This is the mean period of time elapsing between the birth of parents and the birth of their offspring; also, how is this calculated?

Mean generation length; this is taken as the sum of Ixbxx all divided by R0

In the N(t)=N(0)e^rt equation, how do you calculate r?


Do moisture content and temperature of an environment impact the intrinsic capacity for increase, r?


Reduction in the age at first reproduction, an increase in the number of progeny in each reproductive event and an increase in the number of reproductive events will all serve what purpose?

They will all increase the r value (intrinsic capacity for increase)

What is a good general rule to follow regarding the r value, or intrinsic capacity for increase?

The earlier the peak in reproductive output, the larger the r value

Pacific salmon serve as a prime example of Big Bang reproduction. How does this method work?

An organism reproduces once and then dies shortly thereafter

How does the process of repeated reproduction work?

An organism reproduces several times throughout its life

What reproductive methods will be used when reproductive efforts are either high or low?

In the case of high effort, big bang reproduction will take place. In the case of low effort, repeated reproduction will occur

Both lobelia telekii and lobelia keniensis are giant rosette plants that grow on Mount Kenya in Africe. Why does telekii prefer semelparity and why does keniensis prefer iteroparity?

Telekii quickly dies off after its flowering event whereas keniensis can survive after flower events

How can reproduction actually hurt an individuals chance of survivorship?

There’s a possibility that an individual can actually put too much effort into reproduction (such as lactating) to the point where they may no longer be able to produce sufficient energy for themselves