Term
|
Definition
| selective pressures from environment resulting in adaptation. |
|
|
Term
| Why is natural selection good? |
|
Definition
-Organisms behave and function like their parents
-Chance variations exist among individuals, some variations are
heritable
-Some individuals have physical or behavioral characteristics that give
them a better chance at surviving and reproducing (passing on genes) compared to other individuals
-Varying survival based on traits (phenotypes) produces changes in
populations over time. |
|
|
Term
|
Definition
| different versions of a gene. |
|
|
Term
|
Definition
| all of the alleles in a population |
|
|
Term
|
Definition
| organism has same alleles (BB) |
|
|
Term
|
Definition
| organism has different alleles (Bb) |
|
|
Term
|
Definition
| Phenotypic variation can be broken up into variation due to genetic variation and variation due to environmental effects |
|
|
Term
|
Definition
–proportion of phenotypic variation that is
attributable to genetics
-h^2 = VG/(VG + VE)
VG = variation due to genetics
VE = variation due to environmental effects |
|
|
Term
| Why color difference for same organism in different environments? |
|
Definition
| Organisms take on different phenotype color forms so predators wouldn't get to them, based off of environmental conditions. |
|
|
Term
How do we determine environment vs. genetic
based phenotypic variation? |
|
Definition
| Common garden experiments |
|
|
Term
| Common garden experiments |
|
Definition
| Put individuals from multiple populations that vary in phenotype into a common environment and observe phenotypic response. |
|
|
Term
| What would you expect if phenotypic variation is mostly due to genetics? |
|
Definition
| small bodied deer would stay the same or get bigger, if lines don't overlap, it's due to genetics. |
|
|
Term
| What would you expect if phenotypic variation is mostly due to environmental effects? |
|
Definition
| small bodied deer would stay the same |
|
|
Term
|
Definition
| changes in gene frequencies over time |
|
|
Term
| Hardy-Weinberg Equilibrium |
|
Definition
– If a population is mating at random in the absence of evolutionary forces, allele frequencies will remain constant.
-therefore changes in allele frequencies can help ID evolutionary pressures (This is what evolutionary ecologists study)
- At a locus with two alleles, the three genotypes will appear in the following
frequencies: p2 + 2pq +q2
• p2 is the expected frequency of the CRCR genotype
• 2pq is the expected frequency of the CRCW genotype
• q2 is the expected frequency of the CWCW genotype |
|
|
Term
| Principles of Hardy-Weinberg Equilibrium |
|
Definition
1. Random mating – nonrandom or selective mating can result in allele frequency differences that are greater or less than predicted
2. No mutations – mutations add or change alleles
3. Large population size – Small population sizes increase the probability of allele frequency changes due to chance.
Genetic drift-change in allele frequency due to chance
4. No immigration – immigrants can add new alleles or change allele frequencies
5. All genotypes have equal fitness.
Fitness-genetic contribution of individuals to future generations
-Therefore….Hardy-Weinberg equilibrium rarely observed in nature |
|
|
Term
| So why is the H-W Equilibrium important? |
|
Definition
• It demonstrates that the potential for evolutionary change is high!
• It represents an “ideal” model that the effects of evolutionary influence can be tested against.
• E.g., Statistically test if allele frequencies violate any of the H-W
principles |
|
|
Term
| Types of Natural Selection |
|
Definition
1. Stabilizing selection – selection that
impedes change in a population
2. Directional selection – selection that favors an extreme phenotype
3. Disruptive selection – selection for
two or more extreme phenotypes |
|
|
Term
|
Definition
• Fitness is highest for average individuals
• What does this mean?
-Average traits more likely to be
passed on to future generations
• Extreme phenotypes selected against
• Example: Stabilizing selection for egg size in Ural Owls
-very small and very large eggs hatch
at a lower rate compared to average- size eggs
-females that produced very small or
very large eggs produce fewer fledglings over lifetime |
|
|
Term
|
Definition
• Leads to change in average phenotype over time
• Example: Soapberry bugs feed on seeds from Sapindaceae plants in southern US
• Non-native Sapindaceae introduced to southern US, have smaller fruit radiuses than native Sapindaceae
• Soapberry bugs pierce fruit to get to seeds
• Since non-native Sapindaceae had smaller fruit radius, didn’t need as long of beak
• Directional natural selection led to Soapberry bugs with smaller beak |
|
|
Term
|
Definition
• Leads to population dominated by two or more
phenotypes; multimodal
• Example: Darwin’s finches in Galapagos
-Dominated by two groups: large beaks
and small beaks
-Average-size beak individuals had higher
mortality (likely due to inappropriate food
types for finches with avg. size beaks or
competition with more abundant small-beaked
and large-beaked individuals)
-Small beaks preferentially mated with
small beaks (create more small beaks)
-Large beaks preferentially mated with
large beaks (create more large beaks) |
|
|
Term
|
Definition
Genetic change due to chance (e.g., an allele drifts out of the population by chance)
• Reduces variation in a population’s genetics
• Most effective at changing gene frequencies in small populations
-Greater chance for an allele to “drift” out of a small population
• Where do we find small populations of organisms?
• How do humans isolate populations?
• What are the implications of anthropogenic related isolation of
populations?
-lower genetic variation = lower potential for evolutionary response to environmental change |
|
|
Term
|
Definition
• Polymerase Chain Reaction
• Makes many copies of DNA from a small sample
• DNA can then be used in genetic analysis
• Primary tool for genetic analysis |
|
|
Term
|
Definition
• Structured = genetically different populations
• Isolated populations will not freely interbreed
• Genetic composition (allele frequencies) will differ over time
• Changes in allele frequencies due to chance or natural selection |
|
|
Term
|
Definition
• FST = measure of genetic differentiation between two populations
(oldest and most widely used)
-compares observed vs. expected heterozygosity (based on random mating within the total population; Hardy-Weinberg Equilibrium)
-What is heterozygosity?
-ranges from 0 – 1:
0 = two populations interbreeding freely
1 = no interbreeding of populations, 100% frequency of different alleles
• Differences between populations detected by differences in allele frequencies
-Global scale- whole pop. in both oceans.
-Close scale- animals travel to another place to breed |
|
|
Term
| Why do we care about population structure? |
|
Definition
• Genetically distinct populations might have local adaptations for the
environment they live in
• Managing organisms that are genetically distinct as one population
could result in loss of subpopulations
• Lack of knowledge of stock structure could result in overharvest of
certain populations in commercial fisheries |
|
|
Term
|
Definition
– maintaining genetic diversity is important for species survival and persistence during environmental or biological challenges
-E.g., genetic make-up of some
individuals may allow them to be more
resilient to warming water temperatures
-E.g., resistance to and recovery from
disease
• Pacific salmons managed as Evolutionary
Significant Units
• Allows individual runs of salmon to be
protected under the ESA |
|
|
Term
|
Definition
• Genetic diversity is related to the effective population size (Ne)
-Ne = number of individuals contributing genes to next
generation (successful spawners)
-Greater Ne = higher diversity
-Low Ne can result in inbreeding depression |
|
|
Term
|
Definition
-breeding between close relatives results in
negative effects on fitness
-Direct evidence of inbreeding depression is rare for wild populations
-Statistical methods can be used to estimate the population size necessary to minimize risks of inbreeding depression |
|
|
Term
|
Definition
–Reproduction with an individual from
another population leads to reduced fitness of offspring. |
|
|
Term
Why should fisheries managers consider
inbreeding and outbreeding depression when
stocking fish?
produced offspring that were not as reproductively successful in the
wild as fish offspring from fish that performed poorly in the hatchery.
• Authors concluded this was evidence for domestication |
|
Definition
• Christie et al. (2012) found that captive born fish produce more
offspring than wild fish in a hatchery setting
• However, fish that were reproductively successful in the hatchery
produced offspring that were not as reproductively successful in the
wild as fish offspring from fish that performed poorly in the hatchery.
• Authors concluded this was evidence for domestication
• Inbreeding and outbreeding often a concern when using stocking to enhance or restore endangered populations |
|
|
Term
| Genetics in Fisheries Management |
|
Definition
• Can be used to identify effects of stocking on fish populations
• Identify populations that have large proportion of native genes
remaining and can be used for restoration |
|
|
Term
|
Definition
• Group of individuals from a single species living in a specific area (or
areas if referring to a migratory species)
Ex. Black Hills, SD population of mountain lions
• Populations are best defined by natural boundaries, but frequently defined by political boundaries |
|
|
Term
| Why is it better to define populations by natural instead of political boundaries? |
|
Definition
| Organisms don't really know political boundaries. |
|
|
Term
| Three main characteristics |
|
Definition
1. Distribution
2. Density
3. Abundance |
|
|
Term
|
Definition
-Size, shape, and location of the area a population occupies
• Area inhabited by population can 10’s of square meters (Devil’s Hole pupfish) or millions of square km (gray whale) |
|
|
Term
| Distribution and the Niche |
|
Definition
| Distribution of organisms constrained by its’ Niche and barriers to dispersal (e.g., mountain range, water fall) |
|
|
Term
|
Definition
“n-dimensional hypervolume where n equals the number of abiotic and biotic factors to survival and reproduction of a species”
(Hutchinson 1957)
• The niche is a founding concept of ecology |
|
|
Term
|
Definition
“n environmental factors permitting a species to survive and reproduce” (i.e. The physical conditions that allow an
organism to exist; where it can live in the absence of interaction with other species) |
|
|
Term
|
Definition
| “the actual niche of a species whose distribution is limited by biotic interactions such as competition, predation, disease, and parasitism.” All of the biotic and abiotic factors |
|
|
Term
|
Definition
• In northern area lives throughout boreal forests
• In the southern part of its range limited to high mountain coniferous
forests and meadows |
|
|
Term
| What is the niche of Beetle? |
|
Definition
colder temperatures in the South up top because its warm in the South, but colder in higher elevations.
North is colder so they are widespread throughout the north |
|
|
Term
| Distribution of Barnacles |
|
Definition
• Organisms living in different areas of the intertidal zone have evolved
different tolerances for drying
• Barnacles are common intertidal organisms
• Connell (1961a, 1961b) studied barnacle distributions in Scotland
• Chthamalus stellatus found in upper levels of intertidal zone
• Balanus balanoides limited to lower and middle intertidal zones
• During a very low tide period he examined mortality of exposed
barnacles
• Balanus (lives in areas less frequently exposed to air compared to
Chthamalus) experienced higher mortality |
|
|
Term
| What is the fundamental niche of Cthalamus? |
|
Definition
| -competition is limiting thalmus |
|
|
Term
| What is the realized niche of Cthalamus? |
|
Definition
|
|
Term
| Distribution of Organisms |
|
Definition
• Populations can be studied on a variety of spatial scales
• At SMALL scales three common patterns of distributions observed:
1. Random distribution - neutral interaction
2. Regular distribution- antagonistic interaction
3. Clumped distribution - attraction
• Distributions determined by biotic interactions, the spatial arrangement of
habitats in the environment, or a combination of both |
|
|
Term
| Distribution Patterns at Large Scales |
|
Definition
• On a large scale, the distribution pattern of organisms within a species is clumped.
- mechanism against predation, or kill prey. |
|
|
Term
| Distribution of American Crows |
|
Definition
| •Distributed widely, but in winter, birds are clumped in one area. |
|
|
Term
| Relationship Between Population Density and Body Size |
|
Definition
• Population density decreases with increasing body size
• Damuth (1981) examined this relationship based on 307 species of herbivores
• Animal sizes ranged from 10 g for small rodents 1,000 kg for rhinos |
|
|
Term
|
Definition
Based on the work of Damuth (1981; 1987) and Carbone and Gittleman (2002) density inversely related to mass by:
D=αM-0.75
D = Density (individuals/km2)
M= Mass in (g)
Brown et al. (2004) found a similar
relationship
- As density decreases, animal increases. Inverse relationship
- Birds tend to exist at lower densities because they can fly and search for habitat in wider areas than terrestrial vertebrates.
- Aquatic species generally exist at higher densities than terrestrial species. Cyr et al. (1997) hypothesized that this was mostly due to aquatic herbivores consuming 3x the proportion of primary production consumed by terrestrial herbivores |
|
|
Term
|
Definition
• Rabinowitz (1981) developed a classification system for commonness and
rarity based on
1. Geographic range of species (broad vs. restricted; e.g.,
American crow vs. Devil’s Hole pupfish)
2. Habitat tolerance (generalist vs. specialist; e.g., coyote vs. koala)
3. Local population size (large vs. small; e.g., gray squirrel vs. bald
eagle)
• Seven combinations of these factors
• |
|
|
Term
| What types of organisms are most vulnerable to extinction based on these combinations? |
|
Definition
| Large organisms with a low population in a restricted area. |
|
|
Term
|
Definition
– study of factors affecting changes in
populations
-estimate abundance or density of organisms for a snapshot of time. |
|
|
Term
| Why is study of population dynamics important? |
|
Definition
-understand factors affecting endangered species populations and use that information to prevent extinction
-understand factors affecting invasive species populations and use that information to control those species
-managing game and fish species
- Bald eagles increase, we wouldn't know this without tracking them without tracking it. |
|
|
Term
|
Definition
• Generally not continuous
• Often broken up into subpopulations
-E.g., Subpopulations of sockeye salmon in Bristol Bay |
|
|
Term
|
Definition
– subpopulations that are connected through exchange of individuals
-E.g., Subpopulations of sockeye salmon in Bristol Bay form a metapopulation |
|
|
Term
| How can population size be summarized with a basic equation? What are the basic things that affect population change? |
|
Definition
• Nt = Nt-1 + B + I – D – E
Nt
= number at time “t”
Nt-1 = number at time “t”-1
B = births
I = immigration
D = deaths
E = emigration |
|
|
Term
Dispersal (Immigration or Emigration)
• What are some mechanisms of dispersal? |
|
Definition
• Can lead to immigration or emigration
-Water currents (fish larvae drifting)
-Wind (seed dispersal)
-Seed dispersal by animals
-Active dispersal |
|
|
Term
| Larval Transport and Movement |
|
Definition
Many marine fishes spawn offshore
(sometimes >100 km), but nursery
grounds nearshore
-Transported by wind-driven ocean
currents to shore
• Coral reef larvae dispersed by ocean
currents
• Some will join parent population, others
will join other populations
-remember marine fishes are the
least genetically structured! |
|
|
Term
|
Definition
• Female lions disperse (emigrate) from pride if pride gets too large.
• Form new prides
• Males immigrate into prides
• Per capita reproductive rates highest when three females in a pride
• Mediated by habitat (more dispersal in sparsely populated plains) |
|
|
Term
| Dispersal in Response to Changing Food or Water Supply |
|
Definition
Frequently observed throughout
history of humans and other animals
• Emigrate from areas of low resources
per capita; immigrate to areas of
higher resources per capita
• Predator: long-lived (compared to prey), low reproductive rate
• Prey: short-lived, high reproductive rate with boom and bust cycles
• Because predator is long-lived with a
low reproductive rate Korpimaki and
Norrdahl (1991) concluded that changes in kestrel and owl abundance
was sue to dispersal (i.e., Kestrels and
owls moved in and out of the areas
they studied based on the vole
population). |
|
|
Term
|
Definition
– Organisms expand range through natural movements
• Areas adjacent to current range become suitable
-Change in climate (retreat of glaciers during last ice age)
-Decreased competition
-Increased food resources
-Removal of barrier (storm and flooding creates a new connection
between two lakes or rivers)
-Transport by other animals
-- Northward dispersal of maple and hemlock trees coinciding retreat of
glaciers during the last |
|
|
Term
|
Definition
– Humans moving organisms around (intentional and unintentional)
-Stocking of recreational game and fish species (pheasants in North
America, rainbow trout in New Zealand and South America)
-Escape of captive animals (Asian carps in Mississippi and Illinois Rivers)
- “Hitchhiking” in goods or vessels used for transportation
--• ~182 species have invaded the Great Lakes
• Majority of invaders due to shipping
-65% since opening of the St. Lawrence Seaway in 1959 |
|
|
Term
| Natural AND Human-assisted Range Expansion |
|
Definition
• Example – coyotes
• Historically found on prairies
• Could not compete with
wolves in forest areas
• Wolf populations dramatically
decreased due to hunting
• Coyotes have higher
reproductive rate and can feed
on a greater variety of prey
than wolves
• Lack of competition with
wolves allowed for expansion
of coyote populations
• Change in Environment - Increase in farmland and
abandoned farmland in early
successional stages may also
have facilitated range
expansion |
|
|
Term
| Populations Also Contract |
|
Definition
• Grizzly Bears in the lower 48
• Only occupy 2% of historic range
• Humans like to kill large predators they fear and compete with |
|
|
Term
|
Definition
• Some species produce few young and invest a lot (energy, resources)
in their care. Other species produce many young (>100k) and provide
no parental care.
1 calf, 22 month pregnancy,
care for 5-6 years
--High survival rate to maturity
~120,000 eggs, external
fertilization, no parental care
--low survival rate to maturity. |
|
|
Term
|
Definition
• Biologists use life tables to keep track of survivorship and deaths
(mortality) in a population
• Can be used to estimate the probability of survival to a given age |
|
|
Term
| Three main ways of estimating survival patterns |
|
Definition
-1 type of cohort life table; 2 types of static life tables
-Static life tables – examine a cross section of the population
with individuals from multiple generations
1. Age distribution analysis (static life table) – Look at the proportion
of individuals of different ages
2. Age of death analysis (static life table) - record the age of death for
a large number of individuals in a population
3. Cohort analysis – track abundance of a group of organisms that are
born, hatch, or germinate at the same time |
|
|
Term
| Age Distribution Analysis – Static Life Table |
|
Definition
-Measure abundance of individuals of all
ages during a sampling event(s).
-This if often done for animals
harvested during hunting, or
scientific or commercial fisheries
sampling
• Average the abundance estimates for
each age across the years sampled (best
to have multiple years)
• Can calculate mortality or survival |
|
|
Term
| Plots based on Age Distribution Data |
|
Definition
To estimate mortality, abundance is log transformed. Why?
can easily be transformed back to normal units of mortality.
Z = instantaneous mortality
e-Z = annual survival
1-e-Z = annual mortality |
|
|
Term
| Age of Death – Static Life Table |
|
Definition
• Use the age of death for individuals
from many cohorts to calculate
mortality or survival
• Use the number of deaths at 1, 2, 3,…..
to determine the proportion of the
population surviving to age 1, 2,
3….etc. |
|
|
Term
| Assumptions of Static Life Tables |
|
Definition
Constant birth and mortality rate if only data
collected during a single year (rarely happens)
• Birth rate that varies randomly (i.e., patterns of
increasing or decreasing population size violate
this assumption)
-See ages 2 and 3 for organisms sampled in
1996 on slide 8
-If a population is increasing, then older
age classes will be under-represented in a static life table.
-If a population is declining, then older age classes will be over-represented in a static
life table.
-If data is averaged over many years it
alleviates the affects of non-constant birth
rates on mortality estimates
• Immigration and emigration are equal if the
population is open or the population is closed
(individuals cannot enter or exit the population
through dispersal)
• Mortality is constant among age classes when plotted on a log scale
--Population increase, older individuals under represented.
--Population decrease, older individuals over represented. |
|
|
Term
|
Definition
Work well if assumptions of constant recruitment and log-constant
mortality are violated
• Track cohorts over time – keep track of abundance from birth (or age when
organisms can be reliably collected) to death
-How can we keep track of abundance from birth to death?
-sometimes young individuals are not fully recruited to the gear
used to catch them (i.e., the gear used to sample organisms does not
effectively collect young (small) individuals). See ages 1 and 2 for
1998 cohort on next slide.
• Estimate survival (or mortality) for each cohort examined
• Average values for multiple cohorts
• What are some issues or potential problems of cohort analysis?
-must collect data for a long time if organism is long-lived
-must sample frequently for short-lived species |
|
|
Term
|
Definition
• Cohort life tables can be used to create survivorship curves, by
plotting number of individuals surviving over time!
• Describe general types of pattern in survival from young to old.
• Type I – high rate of survival among young and middle-aged, high
mortality among old – humans, large mammals with high parental
care
• Type II – constant rate of survival throughout life – American robins,
common mud turtles
• Type III – Extremely high mortality among young, followed by
relatively high survival – trees, many fishes, marine invertebrates
• Most natural populations do not strictly follow these curves and
display intermediate characteristics |
|
|
Term
| Importance of Age Estimation |
|
Definition
• Estimating mortality rate for some organisms relies on knowing ages
of individuals in a population
• How do we estimate the age of an organism?
-mark with a unique ID tag during first year of life (often done
with large mammals)
-monitor individuals throughout life (sometimes done in
protected areas)
-use body structures from the organism to estimate age
- can tell when an organisms had offspring.
- can tell the age by counting rings. |
|
|
Term
| ID’ing causes of mortality as a conservation issue |
|
Definition
• Often we do not understand all of the factors affecting population
dynamics of wild organisms
• Understanding causes of can be a major issue for conserving organisms
• Moose are an iconic species in northern MN. Recently the population has
declined for unknown reasons (declined 55% in last 10 years)
• Researchers are using high tech GPS systems to better understand
mortality
-Must get to recently deceased moose to do an autopsy before the moose is consumed by wolves.
Mortality Implant Transmitter –
implanted in moose digestive system |
|
|
Term
|
Definition
Can be used to determine if a population is stable or if there is cause
for concern
-If you looked a chart of age distribution, when would you be
concerned?
- If younger organisms are more than older organisms.
• Studies of age distribution can be used to identify periods of high or
low reproduction, and high or low mortality. |
|
|
Term
| Age Distribution Over Time |
|
Definition
• Can be used to examine patterns in age structure over time
• Identify issues |
|
|
Term
| Year Class Strength Analysis |
|
Definition
• Used to identify factors related to strong, weak, or average year
classes from a population
• Use statistical models to relate abundance of a certain standardized
age of individuals to environmental (e.g., temperature, rain) and
biotic factors (e.g., prey availability, predator abundance)
-The age examined may be determined by when an organism is
first recruited to the gear used to sample that organism
-For organisms that display a Type III survivorship curve the age
used should occur after the time period of extremely high
mortality has ended. Why?
-- see some stability and start sampling there. Sample once there starts stability, rather than the end where mortality is. |
|
|
Term
| Rates of Population Change |
|
Definition
• Life tables combined with a fecundity schedule can be used to estimate:
R0 = net reproductive rate (avg number of offspring produced by an
individual over their lifetime)
λ = geometric rate of increase (ratio of population sizes at two points in time)
T = generation time
r = per capita rate of increase
Birthrate = number of young born per female in a period of time
-plants = number of seeds produced or shoots produced in asexual
reproduction
-birds, fish, reptiles = number of eggs produced
-mammals = number of young born |
|
|
Term
|
Definition
-table of birthrates for females of different ages (birthrate for many organisms changes with age). What would this look like
for humans? What about fish? |
|
|
Term
| Calculating Net Reproductive Rate |
|
Definition
• R0 = avg number of (sometimes only female) offspring produced by a female over her lifetime
-accounts for mortality (i.e., weights calculation based on the
proportion of population surviving until the next year)
-Why would biologists choose to only track female production?
R0 = Σl
xmx (Σ means “sum”)
l
x = proportion of population surviving to day x
mx = average number of eggs or offspring (that are female) or seeds produced by each individual during a time interval (e.g., 1 year)
R0 > 1 = population is increasing
R0 < 1 = population is decreasing
• Assumes the population has a stable age distribution (l x and mx are constant for each age class) |
|
|
Term
| Calculating Geometric Rate of Increase |
|
Definition
• λ = the ratio of population size at two points in time
λ = Nt+1/Nt
Nt+1 = number at time t + 1
Nt = number at time t
• Assumes generations do not overlap |
|
|
Term
| Calculating Generation Time and Per Capita Rate of Increase |
|
Definition
• T = average time between two consecutive generations in a lineage
(average age of reproduction)
T = Σxlxmx/R0
x = age in years
l
x = proportion of population surviving to year x
mx = average number of eggs or offspring (that are female; i.e., daughters) or
seeds produced by each individual during a time interval (e.g., 1 year)
• r = per capita rate of increase (essentially births-deaths)
r = ln R0/T
r > 1 = population is increasing
r = 0 population stable
r < 1 = population is decreasing |
|
|
Term
|
Definition
• Many populations, especially for short-lived organisms have a
tremendous capacity to grow (and decline)
-boom and bust of vole populations
• Major fluctuations in populations the result of environmental or
biotic changes
• Ecologists use a variety of mathematical equations to model
population growth
• We will discuss the: geometric, exponential, and logistic growth
models |
|
|
Term
|
Definition
• Used to model populations with discrete
annual pulses
-annual plants
-many insects
• Indefinite growth unrealistic because
pop. will eventually be limited by
environmental or biotic conditions
• Successive generations differ in size by a constant ratio |
|
|
Term
|
Definition
• Looks similar to geometric growth but population growth is
continuous
-i.e., Not a function of discrete annual generations like Phlox
example
• In an unlimited environment exponential growth rate modeled as:
dN/dt = rN
dN/dt = change in numbers with change in time
r = per capita rate of increase
N= population size
• r is constant, but N changes
• As N increases the rate of population increase (dN/dt) increases
-Model can be used to calculate population size. |
|
|
Term
| Exponential Growth part 2 |
|
Definition
• Often observed when an organism first
occupies suitable habitat
• Exponential growth cannot be
continued indefinitely because at some
point organisms will become limited by
something necessary to sustain life
(nutrients, energy, light, etc.)
• We use the logistic model to
incorporate complexity of
environmental limits on population
growth |
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Term
| Logistic Population Growth Model |
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Definition
• Resources are not unlimited (as is assumed for exponential growth)
• Growth eventually slows and levels off at carrying capacity, K
• K = number of individuals in a population that the environment can
support
• At K, the population size is approximately constant
• Represented by a sigmoidal curve produced by the logistic model |
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Term
| Logistic Population Growth Model part 2 |
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Definition
• Developed to mathematically account for slowing of population
growth as resources available to each individual in the population
become depleted
• Limits to growth frequently due to availability of food and space, or
disease and parasitism or interactions among these variables |
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Term
| What would limit growth of a population of yeast (hint: think about the beverages we use yeast to make)? |
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Definition
Low Density= yeast population grows at a high rate.
High Density= yeast population slows and then levels off
-Yeast produce alcohol, the alcohol would eventually kill the yeast because alcohol conc. gets too high. |
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Term
| What would limit barnacle population growth? |
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Definition
-settlement rapidly increased barnacle density.
- Then at about 2 weeks the population levels off because of space and competition. |
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Term
| The Math Behind the Model |
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Definition
• Recall the rate of change for the exponential growth model = rN (realized
per capita rate of increase x number of individuals in the population)
• Need to add something to the equation to account for slowed growth
• Logistic growth model gives the rate of population change as a function of:
rmax (intrinsic rate of increase) = maximum rate of per capita rate of increase
N = population size
K = carrying capacity
• Assumes birth rates, death rates, and age structure are stable.
-At K/2, you run out of resources. |
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Term
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Definition
• Population growth highest when N = K/2
• Population growth decreases when N > K/2
• Growth rate increases or decreases based
on balance between two parts of the
equation
-N x rmax increases with increasing N
-However, as N increases the 1-(N/K)
portion of the equation decreases
-once N > K/2 balances shifts to slow
the growth rate |
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Term
| Density-dependent factors |
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Definition
• effects of biotic factors are often influenced by population density (e.g., disease)
• Density-dependence can be positive or
negative
• When would positive density dependence
be observed?
-benefits of protection by the herd
outweigh resource limitations (e.g.,
fish schooling) |
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Term
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Definition
• Related to density dependence
• At low densities organisms may compensate through increased fitness, growth, or survival
-may help to increase population when population is low and vice versa
-at low densities potential for abundant resources per capita and vice versa
• This (and other reasons) is why stocking fish is not always the answer for increasing fish
populations
-as density increases, fewer resources, which may lead to decreased overall survival |
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Term
| Density dependent mortality |
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Definition
• At a certain densities mortality rate
increases
• The density at which this is first
observed depends on the availability of
resources (food, space)
• Understanding these relationships are
important for understanding
population dynamics and determining
stocking density of fishes
• What are the implications of this
relationship for stocking over top of
naturally reproducing populations? |
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Term
Limits to Population Growth
Density-independent factors |
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Definition
| • effects of abiotic factors such as floods, fires, and drought are often independent of population density |
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