Transcript Slide 1

Population growth and regulation
— in a stable population inputs (natality and growth) are
balanced by outputs (harvest and natural mortality)
— if
inputs are higher then population grows, if outputs are
higher then population declines
— only a certain biomass can be supported by a particular
area; some limiting factor (food, shelter, water, etc.) will stop
population growth
— sometimes species in new environment will increase at an
exponential rate, J-curve; this can only continue as long as
no limiting factors are reached
— when this happens the growth curve flattens to an S-curve
or logistic growth curve
this happens at carrying capacity (k), the max biomass of
a population that can be sustained within a defined area for
a given amount of time
—
inflection point is where population starts increasing at a
decreasing rate
—
— managers may consider k to be at a level where the
population does not severely damage the habitat;
management practices can change k for a pop in a given
area by improving habitat
Examples:
- increasing cover and food for quail to increase
- removing roosting habitat for blackbirds to decrease
— biotic potential - max rate of population increase under
ideal conditions
— environmental resistance - biotic and abiotic factors that
limit population growth; includes predators, food, water,
nesting sites, similar competitors, etc.
— combination of biotic potential (increases #) and
resistance (decreases #) is ultimately what sets k
— many times we see a cyclic pattern; environmental factors
change and this effects population size
Example:
as the population increases the habitat is degraded and
fewer individuals can be supported so #’s drop; as #’s drop,
the habitat improves and can support more individuals so k
and #’s goes up
Production and yield
— production - biomass, living and dead, accumulated by a
population during a year
— surplus production - portion that can be removed from
population by natural causes or harvest w/out adversely
affecting future populations; part we take is yield
— we try for maximum sustained yield (MSY) – we consider
ecological and socioeconomic factors when deciding where
to hold a population; usually between inflection point and k
Ecological:
– population size that is not harmful for target species with
regard to disease, body condition, sustained yield
– must not overload habitat and degrade it for future animals
(overgrazing or overbrowsing)
Socioeconomic:
– How many animals do the public want to see?
– Do they want trophy size animals?
– Is the population causing undue risk and/or cost to the
public? traffic accidents, agricultural damage/economic loss
Genetics
– genes - segments of hereditary material that are positions
on chromosomes
– chromosomes - structures that carry genes and are in the
nuclei of every cell of an organism
– most vertebrates are diploid - have 2 sets of chromosomes
that are paired; get one copy from mother and one from
father; each copy has every gene and known as alleles;
humans get 23 chromosomes from each parent (46 total)
– alleles occur on the same area, called a locus, of the
chromosome and there may be alternative forms of the same
gene; we get one allele from each parent
– genotype – all genetic information possessed by individual
– phenotype - actual physical expression of traits; genotype
reacting with environment; you can have same genotype
and 2 phenotypes or vice versa
– individuals with 2 copies of the same allele is homozygous
and those with 2 different alleles are heterozygous
– can have dominant and recessive alleles; dominants are
expressed over recessives
– can have incomplete dominance where one allele is
expressed a little more over another or co-dominance where
both are expressed equally
– gene pool of a population - all the alleles present within all
the individuals in the population
– in general, the less diverse the gene pool the less a
population will be able to adapt to changing environmental
conditions; variety is better
– evolution - changes in the gene pool over time that lead to
adaptation to the environment; products of evolution are
genetically new organisms