population ecology ch 53 study of the growth, abundance and distribution of populations
DESCRIPTION
Calculating population size: Mark recapture method Capture and tag a population then release it Recapture a population a count number tagged N-= population size m = #captured and tagged n = #second capture x = #tagged in 2nd capture x/n = m/NTRANSCRIPT
POPULATION ECOLOGYCH 53
Study of the growth, abundance and distribution of populations
I. POPULATION ABUNDANCE AND DISTRIBUTION
A. Population size and density• Population size = N = Total number of
individuals in the population
• Population Density = Number of individuals per unit area
Calculating population size: Mark recapture method• Capture and tag a population then release it• Recapture a population a count number
tagged
N-= population size m = #captured and tagged
n = #second capture x = #tagged in 2nd capture
x/n = m/N
B. Population dispersion: how is the population dispersed in an area
Clumped is often due to availability of resources or social behavior
Uniform is often due to territoriality
Random dispersion is due to no real interaction between members
Age structure • The abundance of individuals of each
age • Pyramid shaped curves indicate a
rapidly growing population • Rectangular shaped curves indicate a
stable population
Survivorship curves • Describes the mortality of individuals
during their lifetime
Type I species: most survive to middle age or older tend to be large mammals that produce few offspring but provide a lot of care
Type II species: length of survival is random. Equal likelihood of death at any age example rodents
Type III species: most of the individuals die young Tend to be organisms that produce a lot of offspring with very little careexample oysters
II. POPULATION GROWTH
Population growth rate N B Dt
1. exponential growth: Maximum growth rate of a species under IDEAL conditionsdN/dt = rmaxNResults in J shaped curveRmax = biotic potential
Factors that affect the rmax of a species • Age at which they reproduce • Average # offspring produced in each
breed • How frequently they reproduce • How long they can reproduce • How many offspring survive to
reproduce
• Greater rmax fly or elephant?
2. Logistic Growth• Exponential growth is often seen in
very small, newly established populations but can’t be sustained for long
• As the population reaches the carrying capacity of the environment, growth decreases and approaches zero
• Represented by the following formula:
dN/dT = rmaxN(K-N/K)
• K = carrying capacity (maximum # individuals environment can support)
• N= #individuals• K-N = #of new individuals the
environment can support• K-N/K = fraction of K that is still
available for population growth
• The smaller N is the closer K-N/K is to 1 and the growth rate approaches the maximum rate (exponential)
• The larger N is the closer K-N/K is to zero and the closer the growth rate approaches zero
• What happens if N>K?
Carrying capacity: • the maximum number of
individuals of a population that the environment can support
• Some populations overshoot carrying capacity before stabilizing at a certain density
• Some populations fluctuate greatly
Factors that limit the carrying capacity and biotic potential of a population • Parasites and disease • Resources • Toxic effects of waste • Stress of too many individuals inhibits
reproduction • predators • These are density dependent. What does
that mean?
III. REPRODUCTIVE PATTERNS ARE THE RESULT OF NATURAL SELECTION
• Any trait that would enhance an organism’s chances to survive and reproduce is favorable
• However, there are tradeoffs between survival and reproduction
• Reproduction requires an investment of energy
• The greater the chance of survival, the more energy can be invested in reproduction
o Species whose young have a high rate of survival like primates tend to produce few larger young and invest energy in their care
The lower the chance of survival the less energy will be invested in reproduction
o Species whose young have a lower chance of survival, like insects, produce a lot of smaller young and don’t invest energy in their care
reproductive strategies can be k-selected or r-selected
K-selected strategies• Tend to operate in a stable environment and is
under the influence of density dependent factors• Selects for traits that are sensitive to population
density
• Organisms that are extreme k-strategists tend to have the following reproductive characteristics:
o Fewer larger offspringo Lots of parental care o Slower maturityoOften reproduce more than onceoMost offspring survive to
reproduce
• Because most offspring survive they can invest a lot of energy in their young
R-selected strategies
• Tend to operate in an unstable environment and subject to density independent factors
• Select for traits that maximize reproduction
• Characteristics of r-strategists:
o many small offspring o little or no parental care o early reproductive age o often reproduce only onceo most offspring die before
they reproduce
• because survival of offspring is low they tend to invest little energy in their young