ch 15 Flashcards
A population consists of
all the individuals of a species that live together in one place at one time. A population can be widely distributed or confined to a small area.
In the exponential model of population growth, the growth rate remains
constant. Rapid, continuous growth is the result.
In the logistic model of population growth, the growth rate ___ as population size rises. The population stabilizes at the carrying capacity, the maximal population size the environment can sustain.
declines
The population stabilizes at the carrying capacity, the maximal population size the environment can sustain.
Populations of species that are r-strategists are characterized by
exponential growth.
reproduce early in life
have many offspring that are small, mature rapidly, and receive little parental care.
Populations of species that are K-strategists are characterized by
slow population growth.
reproduce late in life
have few offspring that are large, mature slowly, and often receive extensive parental care.
Human populations have evolved with many of the characteristics of ___, however, the human population is now growing ___.
K-strategists
explosively.
The Hardy-Weinberg principle states that
the frequencies of alleles and genotypes in a population remain constant unless evolutionary forces act on them.
This principle holds true only for large populations in which individuals mate randomly and in which forces that change the proportions of alleles are not acting.
The five forces that can cause allele frequencies to change are
mutation, migration, nonrandom mating, genetic drift, and natural selection.
Natural selection reduces the frequency of a harmful recessive allele slowly because
very few individuals are homozygous recessive and express the allele.
Population
all the individuals of a species that live in one place at one time.
Demography
statistical study of populations
Population features:
Size
density
dispersion
Size
number of population
Large populations may be doing well, but
if in small area (high density) may run low on resources and more vulnerable to spread of contagious illnesses and excess waste.
Small Populations - may be in danger of going extinct due to:
Inbreeding (mating with relatives) which increase number of homozygous genotypes. If more homozygous recessives, more change of recessive genetic disorder.
Less genetic diversity therefore less able to survive a new pressure
Difficulty in finding mates if in a large area
Density
number per square unit
Dispersion
pattern of positioning
Types of dispersion
Random
Even
Clumped - most common… can indicate where resources are.
Model
hypothetical population that has key characteristics of a real population uses previous data to predict future trends.
Stage 1 Model:
r (rate of growth) = birth rate – death rate (all per 1000 per year)
Stage 2 Model:
N=current pop.
ΔN (number added) = r x N
Stage 3 (logistic)Model:
K = Carrying Capacity, population size the environment can sustain
ΔN = r x N x (k-n /k)
Logistic model
accounts for decreasing resources available to a population as well as more waste and/or spread of contagious diseases… as population reaches K level.
r-strategists characteristics
large populations due to large # of offspring and/or reach maturity fast,
little care of offspring,
exponential pop. growth,
good in unstable environment BECAUSE of the large population size and/or there quick reproduction cycle they have more genetic variation that enables them to respond to changes - they evolve/adapt quicker.
K-strategists characteristics
small population sizes due to small # of offspring and/or long time to reach maturity,
much care of offspring,
slow pop. growth,
good in stable environments, highly specialized adaptation.
Hardy-Weinberg principle
(in large populations with random mating) the populations do not change unless evolutionary forces act upon them.
Hardy-Weinberg equation:
Allele frequency formula: p + q = 1
p = frequency of dominant allele (# of dominant allele/total pop.) q = frequency of recessive allele (# of recessive allele/total pop.)
Genotype frequency formula:
p2 + 2pq + q2 = 1
Evolutionary forces that can quickly change allele and genotype frequencies:
For SMALL populations:
Migration – individuals (and alleles) moving out or into a population
Genetic Drift – frequency of allele changed by effects of chance event in small populations
Non-random Mating (Inbreeding) is a type of non-random mating that often happens in small populations where organisms have to mate with close relatives.
Disadvantages:
increased homozygous genotypes, less heterozygous…increased homozygous recessive genotypes=more genetic disorders
decreased gene pool=less variation to respond to change
For ALL populations:
Non-random Mating – species members selectively choose mates with specific traits.
Natural Selection – environmental forces select for or against traits. Only works on phenotypes.
Mutation (in gametes)
little or no effect except when combined with natural selection but it IS the ultimate source of variation which enables evolution
· Natural selection operates on
phenotype, not genotype.
· Mutations of alleles mostly
recessive and destructive.
Recessive alleles only expressed if
individual has two recessive alleles(both parents carry at least 1).
Genetic polymorphism
significant frequency two or more types of phenotypes present in a pop.
Polygenic trait
controlled by interaction of several genes. Results in Normal Distribution - “Bell” shaped curve for trait expression.
Normal Distribution
“Bell” shaped curve for trait expression.
growth of human population
10000 years ago - the development of agriculture increases K values
Black Death - increased death rates
1700s - better sanitation decreased death rate
1940s - vaccines & antibiotics decreased death rate
1960s - modern agro-chemical agriculture increases K values
Directional selection
selection against (or for) one end of curve towards other
Stabilizing selection
selection against ends favoring middle of curve.
Disruptive selection
selection against middle favoring ends
