POPULATION ECOLOGY

Density and Dispersion What is the density of a population? The number of individuals per unit area Dispersion is how they spread out in that area What are the three patterns of dispersion?

Clumped Clumped dispersion has population occurring in patches Increased concentration of resources leads to clumping Defense against predators e.g. schools of fish

Uniform Even spacing of individuals within the population Diminishes competition Often seen with plants, they secrete chemicals that prevent germination and growth of individuals that may compete for resources.

Random Spacing is varied and unpredictable Occurs in the absence of strong attraction (concentrated resources) or strong repulsion (avoidance of competition) between individuals. This form of dispersal is rare.

Estimating Population Size Mark re-capture method. You capture 200 grasshoppers, mark them all and then release them back into the wild. A few days later you capture 100 grasshoppers and 50 of them were marked. How many grasshoppers do you estimate are in this population? N = # marked x total captured second time number marked recaptures 200 x 100/50 = 400

Density is Dynamic What changes can effect density? Immigration Emigration Births Deaths

Demography What is demography? Study of vital statistics that affects population size age structures - relative numbers of individuals at each age. Used to tell if a population is increasing, decreasing or staying the same birthrate, death rate, generation time and sex ratios, all affect interpretation of age structures

Survivorship Curves What is a survivorship curve? Graphic display of the life table Plot of the numbers of a cohort that are alive at each age. Survivorship curves are generally classified into three types:

Characteristics of The Three Types Seen in Survivorship Curves: Type I : Low death rate in early years. Small clutch sizes and good care for young Type II: constant mortality throughout life Type III: large clutch size, little care for young high mortality rate early on in life.

What sort of life style would show this type of survivorship curve?

Reproductive Table

Life Histories What is the life history of an organism? Traits that affect time of reproduction and death. 1. Clutch size 2. Number of reproductive episodes per lifetime 3. Age at first reproduction

What differences can be found in the life histories of these plants?

Parental Care

Number of reproductive episodes: Large clutch sizes mean one reproductive episode per life. Small clutch sizes means more than one reproductive episode Age at first reproduction is younger in large clutch size reproducers, they invest less energy in their own growth and development.

Models of Population Growth r = reproductive rate, r = b-d/N b = births, d = deaths, N = population size multiply both sides of the equation by N, we get: Nr = b-d, Nr = change in population during a given time interval, =  N/

Models of Population Growth r = reproductive rate, r = b-d/N b = births, d = deaths, N = population size multiply both sides of the equation by N, we get: Nr = b-d, Nr = change in population during a given time interval, =  N/  t = b - d r max = maximal population growth If deaths exceed births r is negative If deaths equal births r is zero (no growth) If births exceed deaths, population is growing.

r max = 1 r max =.5

After Protection From Hunters

Exponential Growth J shaped curve Unlimited population growth, due to unlimited resources. r selected populations favor the exponential growth curve. Seen in areas with little competition Opportunistic species display this pattern, grasses, insects… But all populations eventually have a limit placed on their growth...

Logistic Growth Limiting factors will affect the size of a population Equation becomes: dN/dt = r max N (K-N/K) K = carrying capacity, varies over space and time When the population is low, N is small and K-N/K is large, so r is close to r max As N approaches K, K-N/K approaches zero and therefore r approaches zero and the population is no longer increasing or decreasing in size.

What is occurring here? N is greater than K, so r is negative, deaths exceed births ?

What is occurring here? N is greater than K, so r is negative, deaths exceed births K

Examples of logistic growth: K selected species - likely to be living at carrying capacity, seen in areas with competition

r selected short maturation time short life-span high death rate many offspring/reproduction one reproductive event reproduces early in life small size to offspring no parental care K selected long maturation time long lifespan low death rate few offspring/reproduction several reproductive episodes reproduces later in life large sized offspring parental care for young

Population Limiting Factors Density dependent factors Intensifies as population grows. Density independent factors Affects same number of individuals regardless of population size. A predator is which sort of limiting factor? Density dependent. A hurricane is which sort of limiting factor? Density independent.

–Density-dependent factors increase their affect on a population as population density increases. This is a type of negative feedback. –Density-independent factors are unrelated to population density, and there is no feedback to slow population growth. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig

A variety of factors can cause negative feedback. –Resource limitation in crowded populations can stop population growth by reducing reproduction. 1. Negative feedback prevents unlimited population growth Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig.52.14

What sort of limiting factor is seen here?

Density dependent!

What sort of limiting factor is seen here?

Density independent

Cannibalism of juveniles Only settle in shallow waters. competition

Describe the population shifts seen below:

Are we at carrying capacity?