Chapter 53 Part 1 Population: density, dispersion, survivorship

Concept 53.1

Biological processes influence population density, dispersion, and demographics

Population

group of individuals of single species living in the same general area

How are populations described?

By their boundaries and size

Density

number of individuals per unit area or volume

Dispersion

pattern of spacing among individuals within boundaries of the population

Most cases, is it practical or possible to count all individuals in a population?

No

What are sampling techniques used for?

estimate densities and total population sizes

Examples of sampling techniques

Extrapolation from small samples

Index of population size

Mark-recapture method

Overview of Mark-Recapture Method

1. Capture, Tag, Release random sample of individuals (s) in population

2. Marked individuals are given time to mix back into population

3. Capture second sample (n) see how many are marked (x)

4. Pop size (N) is determined by N = (sn)/x

How does density come to be?

Interplay between processes that add and remove individuals to and from population

Immigration

influx of new individuals from other areas

Emigration

movement of individuals out of a population

Main 2 processes ADD to population

Births and Immigration

Main 2 processes REMOVE from population

Death and Emigration

Generally (2) what influences spacing of individuals in population?

Environmental and social factors

Clumped Dispersion

individuals aggregate in patches

What influences clumped dispersion

resource availability and behavior

3 types of dispersion

Clumped, Uniform, Random

Uniform Dispersion

individuals are evenly distributed

What influences uniform dispersion

social interactions ex: territoriality

Territoriality

defense of bounded space against other individuals

Random Dispersion

Position of each individual is independent of other individuals

Why does random dispersion occur

Absence of strong attractions of repulsions

Demography

study of the vital statistics of a population and how they change over time

What are of particular interest to demographers

Birth rates and death rates

Survivorship curve

graphic way of representing data in a life table, number of survivors as a function of time (age)

Ex: what does the survivorship curve for Belding's ground squirrels show

Relatively constant death rate

3 types of survivorship curves

Type I

Type II

Type III

Type I S.Curve

low death rates during early and middle life > increase in death rates among older age groups

Type II S. Curve

Constant death rate over organism's lifespan

Type III S. Curve

High death rates for young, lower death rate for survivors

Do most species follow S. Curves exactly?

No, most are intermediates of the curves

For species that sexually reproduce, what do demographers focus on?

Females of the population

Many approaches exist to find out what about reproductive rates?

Estimate the number of breeding females

Ex: DNA profiling for reproductive rates

DNA from turtle eggs amplified by PCR, trace back to which mom laid which eggs

Reproductive Table

fertility schedule, age-specific summary of reproductive rates in population

What do reproductive tables describe

Reproductive patterns of a population