Study Questions--Week 7

1.Give a conceptual and an empirical definition of a population. How do these two definitions differ?

Conceptual definition: A population is a group of individuals of the same species that (potentially) interbreed with one another, and are more or less isolated from other such groups of the same species.

Empirical defintion: A population is a group of individuals of the same species living in a specified area, exposed to the same environment, using the same resources, and involved in the same ecological processes.

2.What are Life History Characteristics and what are the three components of LHC’s?

LHC’s are the properties of individuals that, when expressed in populations, affect the distribution and abundance of populations. The three components of LHC’s are: evolutionary constraints, adaptations, and ecological responses.

3.What is meant by the term demography?

Demography: The study of processes affecting the structure and growth of populations. In other words what makes dN/dt not equal to zero (+ or – population growth, not ZPG)?

4.What are some characteristics of an individual that do not translate over into the population level (for example, the body size of an individual does not determine the numbers of individuals within a population, or the population density).

Other examples include: the growth of an individual (in size) does not determine the growth of the population as a whole (in numbers); the number of births in a population is not the same as the founding of a population; the death of an individual does not determine the extinction of a population.

5.Draw a graph illustrating the three types of survivorship curves found in most organisms. Give an example of an organism that exhibits each of the survivorship

curves. Why does the measure of survivorship always decrease over time?

account the proportion of individuals that have died since time 0 to time x. Since individuals that die cannot be brought back into the population after death, the proportion of individuals left surviving from generation to generation must decrease.

6.What do semelparity and iteroparity mean?

Semelparity: the reproductive strategy where individuals reproduce only once during their lifetime.

Iteroparity: the reproductive strategy where individuals reproduce several times throught their lifetime.

7.What are the differences between absolute and relative densities? What are five ways to measure density?

Absolute density ( Na ): This is a precise quantitative measure of the numbers of individuals (e.g. rabbits: n km-2; snails: n m-2; bacteria n mm-3). This is possible only when the area or volume can be defined accurately, and individuals can be detected and counted accurately.

Relative density ( Nr ): This is some index of biological activity of the population that is known or assumed to be proportional to the absolute density (i.e. Nr = cNa ). Assuming that the value of "c" is constant (although) usually unknown, proportional changes in Nr should be identical to those in Nc.

Five ways to measure density are: census, sampling (point, transects, quadrats), and mark-release-recapture.

8.Distinguish between sychronous/asynchronous and discrete/continuous mating strategies.

Synchronized breeding: All females breed at the same time

Non-synchronized breeding: Females breed independently of others

Continuous breeding: Each female breeds frequently (without seasonality)

Discrete breeding: Each female has distinct breeding / non-breeding seasons

9.How do uniform, random, and clumped dispersions tend to vary as a function of density and of scale?

Uniform: common at high densities because this dispersion permits the maximum number of individuals to occupy space; also at low densities when availability of limiting resource does not vary (e.g. desert plants limited by soil and water).

Clumped: resource is patchy; behavioral reasons (i.e. social animals- safety in numbers).

Random: at intermediate densities and when resources are not limiting.

10.What are lx and bx?

lx is the term for survivorship; bx is the term for fecundity.

11.Describe a life table. What is it used for?

A table which lists age (or age class), age-specific survival, fecundity, mortality, and age-specific future contribution (survivorship to age x multiplied by fecundity at age x). Used by insurance companies to estimate life expectancies of clients when setting premiums. Also used to calculate exponential growth rates and stable age distributions of populations.

12.Define "intrinsic rate of increase" and list the conditions under which it will be observed.

This is the maximum possible per capita growth rate that is constant and independent of population density (i.e. in exponential growth). It is observed when the environment is constant and resources are constant, lx and bx are constant, and the population had a stable age distribution.

13.Why do we often use per capita population growth rates rather than total population growth rates?

Per capita growth rates allow us to compare rates of change of population size independently of their absolute sizes; they allow us to express frowth rates of very different organisms and life histories in the same units.

14.What conditions are necessary to establish a stable age distribution in a population?

Constant lx and bx curves; constant environment.

15.When does natural selection occur, and what life history characters are favored in (A) an r-selected species? and B) a K-selected species?

Natural selection occurs when there is a limiting resource (food, space….). When a population is below its carrying capacity (K), it ideally has logistic growth…….thus the species is "r-selectd". Life histories that favor this stage of growth (or species that almost exclusively exploit resource unlimited situations) include, semelparity, many small eggs, short life span, early age of reproduction, no parental care…. On the other hand, species that are near their K are no longer in logistic growth……these species are "K-selected". Life history characteristics that favor K-selection are iteroparity, smaller clutches, well provisioned offspring, lateer reproductive age, longer life span…..