mod 8: Populations, Individuals, and Gene Pools Flashcards
population
organisms of a particular species in a particular place at a particular time
what are the three ways the gene pool can be described?
- by genotype frequencies
- by phenotype frequencies
- by allele frequencies
how is frequency calculated?
(subgroup numbers)/(total group numbers), represented by f
Hardy-Weinberg equilibrium (HWE)
a situation where allele frequencies stay the same generation after generation
what are the conditions necessary to maintain Hardy-Weinberg equilibrium (HWE)?
- the population must be closed–there can be no gene flow, no migration
- the population must be large enough that chance events will not alter allele frequencies
- there must be random mating–no picking favourite genotypes or phenotypes as mates
- no net mutations–the mutation rate from b to B must equal that of from B to b
- no natural selection–environment must not favourite survival of one phenotype over the other
gene flow
movement of alleles into or out of populations by immigration or emigration
microevolution
a change in the frequency of alleles in the gene pool that results in the characteristics of the population. does NOT result in new species
how is HWE used?
it is used to test if a population is genetically changing or not. if any one of the five conditions are not present then the population is undergoing microevolution
Hard-Weinberg equations
p + q = 1, where p and q are two different alleles
p^2 + 2pq + q^2 = 1.00
where: p^2 is frequency of homozygous dominant genotype, 2pq is frequency of heterozygous genotype, and q^2 is frequency of homozygous recessive genotype
genetic drift
change in allele frequencies, caused by chance events in a small gene pool, such as inbreeding caused by isolation of a small non-representative group or a few non-breeding individuals (bachelors).
founder effect and bottleneck effect are examples of genetic drift
founder effect
type of genetic drift. occurs when small population that is not representative migrates away, resulting in different allele frequencies in the two groups
bottleneck effect
type of genetic drift. occurs when a natural disaster occurs and thins the population to a small group that happens to be unrepresentative of the original group, resulting in different allele frequencies in the two groups
fecundity
fertility, the ability of an organism to be fertile or reproduce
wildlife corridor
a route used by wildlife to move from one territory to the other. people are building artificial ones–grassy bridges that stretch over highways
parasite
the organism in a symbiotic relationship that benefits by living on or in a host as a source of food or means of reproduction. the host is harmed by this
host
the organism in a symbiotic relationship that provides food or a means to complete reproduction for a parasitic organism of another type of species
symbiotic relationship
any close relationship in which individuals of different species live together in a feeding or protective relationship
mutualism
type of symbiosis where both organisms involved benefit and rely on the relationship to survive
commensalism
type of symbiosis where one species benefits and the other is not affected in any way
protective colouration
body colour as a natural defence mechanism. bright colours (such as black, red, or yellow) that give a warning signal to consumers
Batesian mimicry
when an animal that is not poisonous/venomous relies on looking similar to animals that are, in order to discourage predators
Müllerian mimicry
when two or more animals that are dangerous (unpalatable to predators in some way) use similar colouring to establish a lack of desire in the predator to eat any prey that shares that appearance–since they look similar, predators end up avoiding both species and are discouraged from eating any of them, ensuring the survival of both
intraspecific competition
competition for limited recourses among members of the same species
interspecific competition
competition between two or more populations for limited resources (such as nutrients, light, living space, etc.). it is because of this type of competition that different species cannot occupy the exact same niche
parasitism
a symbiotic relationship where one partner (the parasite) benefits at the expense of its host
parasitoids
organisms that lay their eggs in the larvae of other insects, killing the larvae
competitive exclusion
when one of two populations competing for the same resource is driven to extinction by the other, due to not being as well-adapted
resource partitioning
when species that live close together partition their resources so their niches are slightly different. this decreases competition
how does competition benefit organisms in the long term?
competition encourages the survival of only the healthiest and most well adapted organisms, encouraging co-evolution and improvement of both competing organisms
niche
position or role taken by an organism within its community
structural defences
physical parts of the organism that protect from predators or allow the organism to compete better for scarce resources
chemical defences
chemicals (toxic or bad smelling or tasting) secreted by an organism to discourage/poison consumers or prevent competitors from growing/living nearby
behavioural defences
actions and gestures that let predators know the organism is dangerous or is harmless and not threatening
cryptic colouration
camouflage. colours or patterns that allow an organism to blend into its environment and avoid being seen. used by prey to hide and by predators to sneak up on prey
succession
the sequence of invasion and replacement of species in an ecosystem over time.
what is succession driven by?
abiotic factors such as climate and biotic factors such as interspecific competition for changing available resources
primary succession
begins when there is no soli present (ex: newly formed lava rock). populated by the pioneer community
pioneer community/species
the first species to colonize an area and initiate succession. must be small, opportunistic, and able to withstand harsh environments to survive
climax community
the last new additions to a system undergoing succession before the system becomes relatively stable and stops changing until an ecological disturbance
ecological disturbance
event that changes the structure of a community–sometimes destroying all actively growing organisms. causes a secondary succession
secondary succession
recolonization that occurs after an ecological disturbance. usually proceeds faster than primary succession because ecological disturbances tend to not destroy soil (and therefore not destroy buried roots or seeds)
how can ecological disturbances be important for organisms?
the clearing of other organisms allows new organisms to shine through and survive where they normally would not have been able to. clearing part of a forest (such as due to forest fire) would allow shade-intolerant organisms to grow where there used to be large trees that would block sunlight. some plant species produce seeds that will only germinate after they are exposed to the extreme heat of a forest fire
natality
number of births. tends to increase with food supply and decrease with competition
what are the population determiners?
natality, mortality, immigration, and emmigration
equation for change in population size
∆N = [b + i] – [d + e]
where ∆N is the change in population size, b is births, i is immigration, d is deaths, and e is emigration
equation for growth rate
gr = (∆N) / (∆t)
where gr is growth rate, ∆N is change in population size, and ∆t is a specific time frame
equation for per capita growth rate
cgr = [N final – N] / N
(or cgr = ∆N / N)
where cgr is per capita growth rate, ∆N is the change in population size, and N is the original number of individuals
biotic potential
symbol: r
highest possible per capita growth rate for a population
what factors determine the biotic potential of a species?
- number of offspring per cycle
- offspring survivability
- age of reproductive maturity and number of times individuals reproduce in a life span
- life span
lag stage
the initial stage of population growth, where it grows slowly
stationary phase
when the birth and death rate are equal, usually due to competition or lack of resources slowing down population growth, at the carrying capacity. not present in exponential growth.
logistic growth pattern
when the first portion of the graph is S-shaped due to levelling off to fit within the carrying capacity. birth rate changes over time
exponential growth pattern
occurs when a population is growing at its biotic potential
carrying capacity
symbol: K
theoretical maximum population size that the environment can sustain over a period of time
density-dependent factors
biotic. impact of these increases as population density increases.
density-independent factors
abiotic. entirely separate from population density.
what are two types of factors that limit a habitat’s carrying capacity?
density-dependent and density-independent factors
environmental resistance
combined effects of various interacting limiting factors. prevents a population from growing at biotic potential and determines carrying capacity
population density equation
Dp = N / A
or Dp = N / V
where Dp is population density, N is the number of organisms within A or V, a given area or volume
what are the three theoretical distribution patterns for populations?
uniform–spread out evenly. occurs in artificial environments (agriculture).
random–no pattern exists. occurs in environments with little competition.
clumped–tight groups. occurs in highly competitive environments.
what factors affect distribution patterns?
distribution of resources in a habitat, interactions among members of a population or community, and time of year (in winter, the conditions are more harsh and so animals that don’t normally group together may display a clumped distribution pattern by food or water sources)
random distribution
no discernible pattern. occurs when resources are abundant and population members to not have a need to compete with each other or group together for survival.
(ex: moose during the summer)
clumped distribution
members of a population are found in close proximity to each other in various groups in their habitat. congregation in areas where food, water, or shelter are most abundant. some plants that produce asexually through runners (such as aspens) end up being clumped.
(ex: humans, aspens)
uniform distribution
seen in artificial populations (those cultivated by humans) or in organisms that behave territorially (individuals, not groups) to defend their resources and young.
(ex: golden eagle)
exponential phase
the second phase of a growth graph. significant growth due to limiting factors not being significant yet
r-selected populations
populations that exhibit exponential growth. think: biotic potential is represented by the symbol r, and exponential growth is when a population grows at its biotic potential. FAVOURABLE CONDITIONS
what are the general characteristics of r-selected populations?
they tend to:
- be seasonal
- be small in size
- have a short life span
- produce many offspring (early reproductive age)
- do not take care of young much
K-selected populations
populations that exhibit logistic growth. think: carrying capacity is represented by the symbol K, and logistic growth is growth that is limited and maintained at the stationary phase by the environmental resistance that occurs when breaching the carrying capacity. STABLE CONDITIONS
what are the general characteristics of K-selected populations?
they tend to:
- be large in size
- have a long life span
- have a low reproductive rate (late reproductive age and few offspring)
- care for young
reproductive strategy
strategies used in reproduction to ensure survival of a species. r-selected and K-selected are two different strategies (opposite ends of a spectrum)
