Midterm 2 (Lectures 10-20) Flashcards
Individuals and Evolutionary Ecology
- individuals are the units of evolution
- how individuals maximize fitness and adapt to their environment over generations
Individuals and Physiological Ecology
how individuals respond to environmental conditions (abiotic)
Individuals and Behavioural Ecology
how individuals respond to other organisms (biotic)
Populations and Evolutionary Ecology
evolutionary change occurs at the population level
Population ecology
processes of birth, death, migration influence the abundance/distribution patterns of groups of organisms
What three characteristics define Population structure?
1) spatial structure
2) age/size structure
3) genetic structure
Spatial structure
how individuals organize themselves in space
○ geographic distribution/range (large scale)
○ patterns of dispersal
○ patterns of dispersion (small scale)
○ population size
What are examples of small and large scale spatial structure in populations?
Small scale=patterns of dispersion
Large scale=geographic distribution/range
Age/size structure
number of individuals in each age/size class
-demographic rates (births, deaths, migration) of individuals change throughout their lifetime
Genetic structure
genetic composition of all individuals combined within the population
What determines population size (number of individuals in a population)?
- demographic processes: birth rates, death rates, migration rates (can add or remove individuals from the population)
- These demographic processes will be influenced by abiotic and biotic factors
Demographic processes
- birth rates, death rates, migration rates
- can add or remove individuals from the population
Population
-a group of individuals of one species living together
represent the ecological unit within which individuals mate and offspring are produced
What two types of individuals make up a population?
1) unitary individuals
2) modular individuals
Unitary individuals
- physically and genetically distinct individuals each arising from a genetically distinct zygote (e.g. humans, dogs)
- genets = genetically distinct individuals, each derived from a single zygote (sexual reproduction)
Genets vs ramets
Genets = genetically distinct individuals, each derived from a single zygote (sexual reproduction)
Ramets = Modules with the potential to exist separately, are genetically identical; asexual reproduction
Modular individuals
- genetically identical individuals
- consist of many interconnected units derived from the same zygote (e.g. plants, corals, sponges), by clonal or asexual reproduction
- Modular individuals can exist separately and be physiologically independent
- Modules with the potential to exist separately are ramets (= genetically identical; asexual reproduction)
What is an example of both a ramet and genet?
-Aspen tree (Genus Populus)
□ a tree develops from a seed (zygote)
□ reproduces asexually via underground horizontal roots
□ gives rise to what appears to be another individual tree
□ Each tree produced is a ramet, while all trees together are a genet
For natural selection to occur, what must happen?
Genetic variation
If a population of of ramets occurs, what is the risk?
if a population of ramets → no genetic variation → less likely to adapt to environmental changes → high risk of extinction
What is the Pando Clone?
- Entire forest is one genet, multiple ramets
- Oldest genetically distinct individual
- Individual ramets will die out, but the genet lives on
What type of individual are corals?
- Modular individual
- Reproduce by cloning or asexually
- At risk of extinction due to bottom trawling
- Most diverse ecosystem on the planet
Geographical distribution/range
- geographical area in which a species occurs
- determined by presence of suitable environmental conditions & resources
- large area containing the habitat patches with various populations
- the large habitat patch is the source, and the smaller ones where populations move around are the sinks (to and from source)
- Habitat patches can be heterogeneously distributed over the range, separated by unsuitable habitat (remember environmental heterogeneity) results in many local populations of a species within a range
Habitat patch
- an area of homogeneous environmental conditions
- contains suitable conditions and resources needed to sustain a population
- Habitat patches can be heterogeneously distributed over the range, separated by unsuitable habitat (remember environmental heterogeneity) results in many local populations of a species within a range
The geographical range of local populations of a species can expand or shrink due to what?
-environmental conditions (environmental heterogeneity)
If ideal conditions exist in a geographical range, does this mean you will find a species living there?
No
- must account for the colonization abilities of ancestral species
ex) polar bears do not live in Antarctica because their ancestors did not colonize there
Metapopulation
collection of local populations interacting within the geographical range
How do local populations interact within a geographical range?
1) dispersal
2) emigration
3) immigration
Dispersal
movement of individuals away from place of birth or areas of high population density
Emigration
movement of individuals out of a population
Immigration
movement of individuals into a population
Because local populations do not function in isolation, the size of a metapopulation depends on?
Population size (# of inds) within a local population and among all populations
The degree of interaction among local populations depends on?
1) Ability of individuals to disperse between habitat patches
2) Habitat patch size and quality
The ability of individuals to disperse between habitat patches will depend on?
- distance between habitat patches
- suitability of environmental conditions & resource abundance between patches
- barriers (eg. mountain, ocean)
The habitat patch size and quality will depend on?
- larger/higher quality patches tend to support more individuals
- higher number of individuals immigrate to smaller/lower quality local populations with fewer individuals (lowers intraspecific competition)
Rescue effect *on exam
- Source populations in high-quality habitat allow sink populations to exist in inferior habitat
- Sinks can’t support a population, you need a source patch
How do plants do dispersal?
- Plants tend to move at the level of seed
- Dispersal of seeds involves gravity, wind, water and animals
Which adaptations do plants have designed for increased dispersal?
- Release of fluid pressure allows some plants to physically eject seeds a considerable distance
- Morphological adaptations (ie. Hooks on burrs) that exploit animals for seed dispersal
- Sugar incentives for consumption, but seed passes through digestive system intact (ex-berries and corn) of the animal
How do animals do dispersal? Passive and active means?
active:physical movement to disperse
passive:
- Wind carries the young of spiders and moths
- Larval forms of many invertebrates are carried downstream by currents
Dispersion
spacing of individuals with respect to one another
Dispersion vs dispersal *on exam
Dispersion: spacing of individuals with respect to one another
Dispersal: movement of individuals away from place of birth or areas of high population density
Name three general patterns of dispersion.
1) clumped
2) even
3) random
Patterns of dispersion: Clumped
- in discrete groups
- Heterogeneous distribution of suitable conditions/resources
- Social attraction (eg. flocking)
- Offspring remain near parents
Patterns of dispersion: Even
- regularly/uniformly spaced
- competitive interactions among individuals (eg. plants for light)
Patterns of dispersion: Random
- without regard to others
- rare
- used to compare against other dispersion patterns
What influences dispersion patterns at different spatial scales?
environmental conditions and resources
Why is it critical to define the spatial scale when talking about dispersion patterns in the Northern Gannet example?
Large scale: Clumped dispersion pattern (breeding habitat), but zoom in on one clump…
Moderate scale: Clumped dispersion pattern (predator avoidance), but zoom in again…
Small scale: Even dispersion pattern (competition)
Local density
number of individuals per unit area
How do patterns of dispersion of local population density affect the measures of total population size
Can be misleading when trying to give an accurate estimate of total population size
What are different methods used to estimate population sizes?
1) quadrat sampling
2) line transects
3) mark-recapture
4) removal method
Quadrat sampling method
- estimates population sizes by choosing a certain amount of samples (quadrats) where you count the number of individuals in those quadrats to make a total population size estimation
- best on sessile/immobile organisms due to counting
Line transects method
- estimates population sizes by measuring a distance to observed specimens while walking a straight line
- Use of formulas to estimate pop. size
Mark-recapture method
- estimates population sizes to create an identifiable mark on all specimens captured in first sample
- Sample again and estimate pop. size based on the proportion recaptured
- ex) whales have unique markings on their tales, so they can use these markings to identify the whales recaptured
What are the assumptions made in the mark-recapture method? *on exam
1) captures are random
2) marks are not lost
3) individuals can’t leave
4) behaviour is not affected by marking (‘trap happy, shy’)
5) marks do not cause higher mortality
_________ is concerned with how the processes of births, deaths, and migrations (also known as ________) influence the abundance of individuals within a population, whether they are genetically distinct (______) or not genetically distinct (________) individuals
Population ecology
demographic processes
genets
ramets
Population structure is characterized by its _______ characteristics, which include ________, _________, _______, and _________
spatial geographic range patterns of dispersion dispersal population size
Patterns of dispersion (_____, ______, ______) vary with spatial scale.
clumped
even
random
________ and ________ must be integrated to accurately estimate total population size.
Geographic range
patterns of dispersion
Age structure
-the number of different age classes and the number of individuals in each age class
Age class
- a discrete group of individuals born at the same time
- different age classes have different birth and death rates
- age classes contribute different number of offspring to the population
Cohort
Individuals that make up an age class
Birth rate
- the number of female offspring produced per female in a particular age class
- number of offspring produced will differ among age classes (eg. age at sexual maturity, senescence)
Why are we concerned primarily with females in the birth rates?
1) birth rate is limited by the number of females (egg more energy costly than sperm)
2) difficult to quantify the contribution of each male
Death rate
- the number of females that die per age class in the population
- number of individuals dying will differ among age classes
Survivorship curves
- number of individuals alive (log scale) versus age
- 3 hypothetical curves (few populations fit one precisely)
- # of individuals alive vs age (axes)
What are the three types of survivorship curves?
Type I - low mortality when young (eg. humans) *k-selected, curve is an upside down bell curve with high survivorship in young ages and low survivorship in old ages
Type II – equal survival through life (eg. birds), straight line that decreases at constant rate
Type III – high mortality when young (eg. fish, marine invertebrates) *r-selected, bell curve
What happens to the size of a population if there is the same number of individuals in all age classes?
population size increases since births>deaths
What happens to the size of a population if there are only pre-reproductive adolescents and adults too old to breed?
population size decreases since deaths>births=0
Life table
- a tabulation of births and deaths of each age class in a population
- allows us to quantify whether the size of a population is increasing, stable or decreasing from one generation to the next
What are the two types of life tables?
-two types: cohort (dynamic) life tables and static (time-specific) life tables
Cohort (dynamic) life tables
- follow one cohort (individuals within an age class) from birth to death
- determine deaths and births in each age class
- Eg. plants, sessile animals, mobile animals where dispersal is limited
- Difficult for highly mobile animals (cannot track them easily)
- Can take a long time to collect data (depends on lifespan)
Static (time-specific) life tables
- snapshot of the population at one point in time
- estimated by determining the age-specific survival independently for each age class at a specific time
- Eg. highly mobile animals
- Difficult to determine the ages of all individuals
- can use stage or size classes if age cannot be determined
- Ignores variation in births and deaths among individuals in an age class (eg. size, competitive ability, social status, genotype)
What is an important underlying assumption made in static (time-specific) life tables?
stable age structure (=number of individuals in each age class) remains the same through time
How do biologists age organisms?
- In some birds, the feathers will help determine which age class they are in
- In some mammals, bone ossification could indicate age, but need to do in lab, and the specimen would already be dead
- In trees, they have rings that represent a year of growth in their trunk
- In lions, the canine teeth could also determine its age with rings on them, but would have to be dead to count them
- In fish, scales could indicate how many rings they have when dead and then classify them in age groups
Important variables in cohort life tables: x
age class
*0-1 year old, then 1-2 so once the individual turns 1 they are part of the second age class
Important variables in cohort life tables: nx
- total number of individuals at each age class (x)
- need to go out every year to count the number of individuals remaining from the original cohort (follow them from birth to death)
- age class 0 is young of the year (or number born into original cohort)
- can see until what age individuals live up to
Important variables in cohort life tables: Fx
- total number of offspring produced during each age class (x)
- highest fecundity? (F)
- tells us the age of sexual maturity (biggest number between the age classes)
What is the goal of the cohort life table?
To see if a population is going extinct or increasing in size
Important variables in cohort life tables: lx
- proportion of the original cohort surviving from birth to age x
- survivorship
lx=nx/no (original cohort)
Important variables in cohort life tables: dx
- proportion of the original cohort dying during each age class
- sum=1
- provides the highest proportion of cohort death
- provides various proportions (ex-5%) by adding the various proportions from a range of cohorts
dx=lx - lx+1 (of next age class) OR
dx=individuals that died/original cohort
Important variables in cohort life tables: qx
- proportion of the original cohort dying versus surviving
- age-specific mortality rate
- indicates the intensity of mortality at a particular age
- sum does not = 1
- gives the cohort with the highest proportion of age-specific mortality rate
qx=dx/lx (dying/surviving)
Important variables in cohort life tables: bx
- individual fecundity or birth rate
- age specific birth rate
- the mean number of offspring produced per surviving individual
- make sure that if decimal given you round down (can’t have a partial baby)
- gives the cohort with the highest proportion of age-specific fecundity
bx=Fx/nx
Important variables in cohort life tables: Ro
- net reproductive rate
- the sum of mean number of offspring produced per original individual during each age class before death
- tells us whether a population increased or decreased from one generation to the next
- may change for different generations
Ro=sum of lx*bx If: Ro<1=population declines Ro=1=population is stable (each female replaces herself) Ro>1=population increases
Using the cohort life table, how would we determine population size changes in the long-term?
many generations of data are required!
The _______ of a population is characterized by the number of individuals in each age class, combined with age-specific birth and death rates.
age structure
_________(____________) indicate general patterns of the number of individuals surviving to each age class.
Survivorship curves
type 1, 2, 3
______ are tabulations of age-specific birth and death rates of each age class in a population.
Life tables
Two different types of life tables (_______, _______) can be constructed depending on the type of data collected.
cohort
static
_______ can be useful to describe many life history traits of a population (ex-age of sexual maturity).
life tables
Life tables can be used to determine the growth of a population between two generations using ___________.
Ro or Net reproductive rate
Genetic structure * on exam
- a description of the genetic variation among individuals within a population
- genetic variation is important since it reflects the capacity of a population to respond/adapt to environmental change
Gene flow
- the exchange of genetic material among populations resulting from dispersal)
- important to increase/maintain genetic variation
Genetic variation is dependent on what acting on individuals within a population?
- on the number and variability of selection pressures
- Few selection pressures with low variability=low variation
- Many selection pressures with high variability=high variation
How can you quantify the level of genetic variation in a population?
- level of heterozygosity (prop. of heterozygotes in the population)
- the more alleles in the gene pool → more possible combinations of alleles → higher genetic variation
What is the general pattern regarding populations and genetic diversity? *on exam
Smaller populations tend to have lower genetic diversity (variation) than larger populations
What two mechanisms operate to decrease genetic diversity over time?
1) genetic drift
2) inbreeding
Genetic drift
- random changes in allele frequencies within a population due to chance
- Genetic drift occurs in all populations and is a mechanism of evolution
- In small populations, genetic drift occurs at a faster rate and is more likely to result in the loss of an allele
- Genetic variation decreases more rapidly in a small population!
Random vs chance in allele frequencies within a population
random: no discrimination between (or ‘selection of’) individuals with favourable or unfavourable traits
chance: unpredictable change in environmental conditions
Inbreeding
- mating between relatives
- In small populations the choice of mates can be limited, resulting in increased probability of mating with relatives
- Inbreeding tends to increase homozygosity and decrease heterozygosity
- Eventually populations can become exclusively homozygous
- can cause risk of extinction due to decrease in genetic diversity
- If rare, recessive genes are harmful, homozygosity for recessive genes can result in reduced fitness and increased mortality
Inbreeding depression
loss of vitality and increased incidence of disease due to the expression of deleterious recessive alleles when genetic diversity decreases
What is a good example of a species that is experiencing inbreeding depression?
-New Zealand Birds=Black Robin
-populations reduced significantly
-5 individuals were remaining, one female
-Lower fitness = 30% hatching failure (usually ~ 10%)
-Cause? A good proportion of the sperm are abnormal (non-motile)
so eggs are never fertilized….(low fertilization success)
What population size is needed to maintain genetic diversity?
- Difficult to determine because all species are different
- must be large enough to cope with chance variations in environmental conditions that cause genetic drift and changing demographic processes (increasing deaths, decreasing births)
Name two key concepts when talking about the population size needed to maintain genetic diversity?
1) Effective Population Size
- the subset of males and females within a population that successfully breed
- Defines the number of individuals passing genes to successive generations
- Ex) mating systems (polygyny)
2) Minimum Viable Population
- number of individuals necessary to ensure the long-term survival of a species
- Critical in Conservation Biology ,allows us to calculate how large a population of a particular species should be to assure its long-term survival
Polygyny
males defend harems of females
Population viability analysis (PVA) * on exam
-Inputs: detailed information on the species’ biology
integrate all to determine population growth
1) population structure (spatial structure, age structure, age structure, genetic structure)
2) life history traits
3) behavioural ecology
-Output: the minimum population size needed for the species to have a 95% chance of persisting for 500 yrs (long-term survival)
-Simulate population trajectories → different values of b, d → estimate risk as the fraction of simulations where extinction occurred
-Problem: limited information available for input into PVAs
What were the observations and results that came from population viability analysis (PVA) of the killer whale populations?
- no gene flow
- many small populations=inbreeding
- threats are less prey (salmon), more noise, pollution = most contaminated marine mammal in the world since concentration of contamination increases as you go up the food chain
- results: population is likely to disappear in 90 years (45 to 140 years from now) without human intervention
Quantify the level of genetic variation by the proportion of _________ in the population.
heterozygosity
_________ and _______ operate to reduce genetic diversity in populations.
genetic drift
inbreeding
Genetic diversity decreases ______ (more or less) rapidly over time in small populations compared to large populations.
more
2 key concepts involved in determining the population size needed to maintain genetic diversity : ________ and _________
effective population size
minimum viable population
To determine the chances of long-term survival of a species, we can conduct a ____________
population viability analysis
Inputs of Population viability analysis (PVA)
1) population structure (spatial structure, age structure, genetic structure)
2) life history traits
3) behavioural ecology
Main output of population viability analysis (PVA)
- the minimum population size needed for the species to have a 95% chance of persisting for 500 yrs (long-term survival)
- Simulate population trajectories → different values of b, d → estimate risk as the fraction of simulations where extinction occurred
Generalized population growth
-Imagine a closed population ○ no immigration ○ no emigration ○ Births increase the population ○ Deaths decrease the population -To determine a change in population size (N) from one point in time to sometime later: N (later) = N (now) + Births – Deaths
Population growth models
- are used to estimate population size many generations in the future
- two types of growth models:
1) Geometric model
2) Exponential model
Geometric model
-Assumes discrete breeding
-population only grows during the breeding season
Typical pattern of growth: population size in the future (Nt) will depend on the growth rate of the population (Lambda) and the size sometime in the past (No)
Geometric model equation
Nt=(lambda^t)(No)
Geometric model variables: Nt
- Population size at some time interval (t) in the future
- population size in the future (Nt) will depend on the growth rate of the population (Lambda) and the size sometime in the past (No)
Geometric model variables: lambda
- Average number of offspring left by an individual during one time interval
- growth rate of the population
- assumed to be constant over successive generations
- the factor by which the population increases or decreases during each time unit
- Increase in landba means an increase in the exponential rate of the population size
- Decreasing in lambda means a decrease in the exponential rate of the population size
Geometric model variables: t
Number of time intervals or generations
Geometric model variables: No
Number of individuals in the population at time zero
Exponential model
- Assumes continuous breeding
- population grows continuously throughout the year
- Atypical pattern of growth: the population size in the future (Nt) will depend on the growth rate of the population (r) and the size sometime in the past (No)
Exponential growth equation
Nt= (e^rt)(No)
Exponential growth variables: Nt
- population size in the future (Nt) will depend on the growth rate of the population (r) and the size sometime in the past (No)
- Population size at some time interval (t) in the future
Exponential growth variables: e^rt
- e^r is the factor by which the population increases during each time unit, the exponential growth rate (constant), *the difference between geometric and exponential model
- t=the number of time interval
- r=exponential growth rate (assumed to be constant over generations)
- e=base of the natural logarithm (2.72)
Exponential growth variables: No
- Number of individuals in the population at time zero
- initial population size at t=0
Geometric vs exponential model (comparing lambda and r) *on exam
- direct relationship between lambda and r = intrinsic rate of increase of a population
- lambda = e^r AND ln(lambda) = r
- increasing graph= r is positive and lambda larger than 1
- decreasing graph= r is negative and lambda smaller than 1
- constant graph= r is 0 and lambda is 0
What are the underlying assumptions made by the exponential model?
1) All individuals have the same average birth(b) and death(d)rates
2) births and deaths are constant through time
3) Births and deaths occur continuously (not discrete)
4) No migration (Immigration or Emigration), the population is closed
5) Resources are unlimited!
Exponential Model: How quickly is the population increasing or decreasing?
- use the derivative of the exponential equation to determine the slope (rise over run) of a curved line
- The rate of change in population size over a specific time period (ΔN/Δt = dN/dt) is equal to the average birth rate (b) minus the average death rate (d) multiplied by the number of individuals in the population (N) at the start of the time period (t0)
Derivative of the Exponential Equation variables
dN/dt = (b-d) N
dN/dt = rN
dN/dt=rate of change in population size over a specific time period, slope of population growth curve at a particular point in time
b=average birth rate
d=average death rate
N=number of individuals in the population at the start of the time period (t=0)
b-d in the derivative of the exponential equation can be replaced by which variable?
r=b-d
- r is the exponential growth rate of the population between time 0 and time t
- an instantaneous rate of increase
- r is the individual or ‘per capita’ contribution to population growth
What are the underlying principles of the intrinsic rate of increase (r)?
a. r is the individual or ‘per capita’ contribution to population growth
b. dN/dt varies in direct proportion to N at that instant
c. r is constant through time
Do we observe exponential population growth in nature?
Not normally since… They typical pattern observed is…
1) when population size is low (r>0):
- no competition (resources are unlimited)
- population grows at the intrinsic rate of increase, r (exponential growth = highest growth potential)
2) when population size is high (r=0):
- competition increases (resources become limited)
- population size levels off and r=0
* ***breaks assumption that r is constant
What are the underlying assumptions in exponential growth that are violated in nature?
a. Different age classes generally have different births & death rates
b. populations rarely have constant birth and deaths because:
- age distribution of a population changes through time
- environmental conditions change through time and continuously influence births, deaths and r
- Therefore, consider r the highest growth rate that the population has potential to achieve if the population has a stable age distribution and b & d remain constant over time
c. Populations are rarely closed (except in the laboratory, in a Petri Dish)
d. Resources are usually limited!
How does intraspecific competition affect r?
- Resources may become limited as individuals of the same species gather in an area due to increased Intraspecific Competition
- Low competition=Reduced Growth
- Moderate competition=Reduced Growth, Reproduction (Decreased births=decreasing r since r=b-d)
- High competition=Reduced Growth, Reproduction, Survival (Decreased births, Increased deaths, so r decreases)
Density-dependence
- Intraspecific Competition influences births & deaths as the number of competitors (or N) increase
- intensity of reduction is related to the density of individuals
Why are Harp seals of Newfoundland a good example of exponential growth?
- 1500s - traditional hunt
- 1950-1969 – large-scale commercial harvesting (removed 50-60% of N)
- 1970s – regulated harvest and protests, got population’s attention
- increased from 2 → 9 million seals
- Exponential increase in their population due to protection efforts
- Enough resources to increase so much! Hasn’t levelled off yet
Why are humans a good example of exponential growth?
- 1600 – rapid growth
- 1800 - 1 billion
- 1930 - 2 billion
- 1975 - 4 billion
- 2000 - 6 billion (5 billion < 200 years)
- 2050 – 10 billion
- Human population dramatically increases in year 2000s
- Major issue is that resources will be limited at some point
- Scientists say that we have already hit carrying capacity
Why has the human population size NOT leveled off?
a) Modern medicine (medical advances)
- Lowers our death rates substantially
- Increased lifespan (decreased deaths)
- Increases birth rates (b)
b) Technological advances
- Industrialized agriculture and aquaculture
- Increasing our resources
- Unlimited food supply
- Manufacturing food products
What are the limitations to population growth?
- Resources can never truly be unlimited (even at extreme cases)
- Universe is limited to 10^80 atoms
We can determine whether a population grows from one generation to the next using age-specific survival and fecundity data from _______.
life tables
To determine population size many generations in the future, we must use ____________.
Mathematical models
The exponential (and geometric) models require the knowledge of ___________, ______________, and ____________.
average birth rates
average death rates
population size
Most species violate the assumptions of the exponential model for many reasons: a) b) c) d)
a) births and deaths vary through time
b) populations are rarely closed
c) resources are rarely unlimited
d) individuals do not have the same births and deaths rates
Exponential growth rates, or ______________, will only be accurate over the long-term if ________ and ___________.
intrinsic rates of increase (r)
age distributions are stable
birth and death rates do not vary
Population regulation: How does a population grow?
- Populations grow when # of births+immigration»_space;deaths+emigration
- input»_space;output
What factors reduce inputs (births and immigration) relative to outputs (deaths and emigration)?
- Biotic
- interactions among organisms (eg. competition)
- Intensity of reduction is related to the density of individuals = Density-Dependent - Abiotic
- fluctuations in environmental conditions (eg. temp)
- Intensity of reduction is unrelated to the density of individuals = Density-Independent
- Biased, reduce fitness (selective for favourable traits)
- Unbiased, random mortality (eg. Severe storms) (unselective for favourable traits)
Density-dependent vs Density-independent
Density-dependent: Intensity of reduction is related to the density of individuals
Density-independent: intensity of reduction is unrelated to the density of individuals
Biased vs unbiased abiotic factors
Biased=reduce fitness, selective for favourable traits
Unbiased=random mortality, unselective for favourable traits, severe storms
Density-dependence logistic model: What factors influence population growth in crowded populations?
a) Intraspecific competition increases
b) Predator density increases (higher risk of predation)
* at the population level!
* at the individual level, there is a lower risk of predation use to safety in numbers
c) Parasite density (higher risk of parasitism)
d) Disease (higher rate of disease perpetuation)
How does density-dependence (logistic model) affect population?
Density-dependence (Logistic model) may reduce growth, survival and reproduction of individuals in a population, thereby affecting population growth through births and deaths (r) with increased crowding
What is the primary underlying assumption of the logistic model of population growth?
-factors limiting population growth exert stronger effects on births and deaths as a population grows (population growth is density-dependent)
What is the difference between the logistic model and exponential model in terms of r?
Due to density-dependence, we should expect r (=b-d) to vary with N… (2nd assumption of Exponential Model is that r is constant)
In the logistic model, what happens to competition, births and deaths in terms or r and N?
- r is highest at N ≈ 0 (low competition: b is high, d is low)
- r decreases as N increases (competition increases: b decreases, d increases)
- r is lowest at high N (competition increases: b≈d) when N=K, r=0 (b=d)
Carrying capacity (K)
- N that the environment can carry or support
- is a stable equilibrium in the graph and population size stabilizes around K
- no population growth occurs here
Logistic model equation
dN/dt = r N (1 - N/K)
(1-N/K) = density-dependent term
Logistic model in a graph N vs t
1) N grows slowly (few individuals reproduce)
2) N grows exponentially (more individuals reproducing)
3) N grows slower as N approaches K (carrying capacity, r is declining)
4) N levels off at N=K (b=d, r=0)
5) *population may fluctuate over and under K (populations increase when N is below K and r>0) and (population decreases when N is above K and r<0)
Inflection point
the point that is half way to the carrying capacity
In the logistic model graph where Rate of change of N (dN/dt) vs populations size (N), what does this look like?
- 0 is in the middle of the y axis
- population increases (dN/dt>0) and peaks at k/2 (half way to carrying capacity=inflection point)
- population begins to decrease (rate of increase in population size decreases)
- reaches K where b=d and dN/dt=0, then it continues to decrease in the rate under the carrying capacity where dN/dt<0
In the logistic model equation, r is constant theoretically, but in reality is this still true?
no it is not
What does the logistic model not represent? What does it represent well? *on exam
DOES NOT:
- does not represent the quantitative dynamics of natural populations
- K changes with varying environmental conditions and seasons→ K constantly changes
DOES:
- does represent the qualitative dynamics of natural populations
- Population sizes below K increase towards K
- Populations sizes above K decrease towards K
Why is the simplicity of the logistic model an advantage?
- logistic model has played a central role in the development of population ecology
- This model is the basis of many other models in population ecology
Density-dependent factors of the logistic model
- factors tend to bring populations under control and maintain their size close to K
- Caused by biotic factors (eg. competition, predator-prey interactions)
- Example) Paramecium population in lab
Density-independent factors of the logistic model
-factors tend to reduce populations far below K and initiate periods of population recovery
-Caused by abiotic factors (eg. temperature fluctuations, seasons, low K in winter)
-Density-independent example → Thrips
Example) Song sparrow population in lab (never actually reaching carrying capacity
How are thrips a good example of density-independence in the logistic model?
- Spring=large population increase, due to high resource abundance, increased reproduction/survival
- Summer=large population decrease due to high adult mortality in heat and dry conditions
- Winter=population is stable since low reproduction due to cold and rainy conditions, lower carrying capacity for the environment
- Population size mirrors seasonal changes in weather
- Population size never became ‘over-crowded’ …resources were unlimited (plant pollen as energy source)
The relative importance of Density-dependent and Density-independent factors will depend on?
- Intensity and frequency of environmental fluctuations
- Life history characteristics of the population in question
- Infrequent and mild environmental fluctuations (K-selected, Mechanism of regulation: density-dependent)
- Frequent and extreme environmental fluctuations (R-selected, Mechanism of regulation: density-independent )
- both interact in a complex way to cause variable patterns in population size
_______ assumes that density-dependent factors limit exponential rates of growth (r is not constant).
Logistic growth
________ factors include any factors whose effects become stronger as crowding within a population increases.
Density-dependent
Population size is limited at the _________ of the environment.
Carrying capacity (K)
__________ is a stable equilibrium around which population size (N) will stabilize.
Carrying capacity (K)
_________ changes with varying environmental conditions and is rarely constant.
Carrying capacity (K)
The ________ is an oversimplification of the natural world, but this simplicity has lead to its central role in the development of population ecology.
logistic equation
All natural populations exhibit population regulation…. The relative importance of Density-dependent and Density-independent regulations will depend on the ______ of the species and the _____ and _______ of environmental variation.
life history
intensity
frequency
Conservation practices
- Conservation practices are based on a thorough understanding of the principles of ecology
- must integrate ecology with social, political and economic systems
Sustainability
- matching quantities of harvest rate to the rate of population growth (supply rate = demand rate)
- Want to harvest the maximum number of individuals from a population without diminishing the ability of the population to regenerate over the long-term
Yield
number of individuals of a species harvested per unit time
Sustainable yield
ensure a similar yield at each harvest
What assumption is made with species and resources?
is renewable, resupplied or regenerated
What does it mean for a resource to be nonrenewable vs renewable?
If nonrenewable:
- harvest is never sustainable
- eg. Mineral resources – aluminum, nickel, copper
- But can be recycled, effectively reduces harvest rate (demand)
If renewable at a slow rate -harvest is not sustainable
- eg. Fossil fuels – coal, oil, natural gas – (millions of years to regenerate)
- supply rate is ~ zero at the rate of human consumption
If renewable at a fast rate
-to be sustainable, the demand rate should not exceed the supply rate
otherwise the population will decline
Maximum sustainable yield
- largest average harvest (or yield) that can be continuously taken from a population without causing a population decline
- supply>harvest/yield
What is the goal of maximum sustainable yield?
- maximize economic gains
- maintain maximum population growth rate (or replacement rate) of the harvested population
- harvest rate = replacement rate
- Wants to keep N where r is highest (exponential growth)
How can we quantify maximum sustainable yield?
- using the logistic growth model, the rate of change of a population (dN/dt) is maximum at K/2
- so we would be able to keep a higher demand rate
- Intermediate population sizes have the greatest growth rate (or ability to produce the maximum number of harvestable individuals)
- Optimize harvest (economic gains) by harvesting enough individuals to keep the population at intermediate sizes (~ K/2
- Keep N @ K/2 to supply the maximum number of harvestable individuals (yield)
- Basis of forestry and fisheries science
What are the problems with maximum sustainable yield?
*on exam
a. Hard to quantify N at any given time
b. Environmental conditions constantly change K, making it difficult to quantify K/2 (or MSY)
c. Density-independent factors can be unpredictable, causing high mortality and reducing N
d. Age structure of populations change
e. Failure to incorporate economics
- Strong pressure to maintain harvest at previous levels to maintain payments on infrastructure
What is an example of failure to incorporate economics in maximum sustainable yield?
- Strong pressure to maintain harvest at previous levels to maintain payments on infrastructure
- E.g. Fisheries, fishers invest in boats, nets, etc.
- If reduce harvest…Fishers cannot maintain payments, wages of crew (→ unemployment → industry collapses)
- Politicians will lose votes as fishers lose livelihood
- Reducing harvest rates meets strong opposition!!
__________ refers to matching _____ rate with ______ rate.
Sustainability (sustainable yield)
supply
demand
Optimize harvest ____ (economic gains) by harvesting enough individuals to keep the population at an _______ size where population growth rates are highest (Maximum sustainable yield =______)
yield
intermediate
K/2
Five main problems with Maximum Sustainable Yield concept: 1. 2. 3. 4. 5.
- hard to quantify N at any given time
- environmental conditions constantly change K
- density-independent factors can be unpredictable
- age structure of populations change
- failure to incorporate economics
Facts about Atlantic Cod
- Potential to reach 2 meters long and up to 96 kilograms (200+ pounds)
- 25 years life span
- Maturity around 2-4 years old (higher the longevity means a later maturity age, k-selected species)
- Apex predator at top of the food chain
- Female lays millions of eggs (can be k and r selected)
- Canadian Cod Fishery mostly centered around the Grand Banks of Newfoundland
500 years ago, John Cabot discovered Cod. What was the Cod population like during his time? What happened after this discovery?
- The population was so abundant you could “walk across their backs”
- Thought to be infinite; became a commodity
- No resource is truly unlimited
- Declines in cod across their range including Baltic Sea and especially coast of Newfoundland/Labrador
What happened to Atlantic Cod fisheries throughout the year and why did these happen?
- 1950s:↑ in cod landings, factory freezer trawlers (store fish in freezer vessels, so can bring back a lot more fish)
- ↓ 1977 200 mile limit EEZ (noticing reduction in Cod population, bans other nations fishing for them, only Canadian fishermen can fish there, EEZ= Economic Exclusion Zone)
- ↓ 1991 Cold year (not fishing)
- ↓ 1992 Fishing moratorium (no longer aloud to fish for Cod)
- these are the only REPORTED captures of Cod
Why did the Cod population dramatically decrease to such low levels?
- Technology
- 1950s, technology allowed fishermen to fish by trawling a large area, to a deep depth and for longer times
- Uses huge nets to capture more fish at once
- Uses freezer trawlers to store more fish and keep fishing
- 1960s, powerful trawlers equipped with radar, electronic navigation systems and sonar allowed crews to catch fish with unparalleled success
Since 1977, the 200 mile limit Exclusive Economic Zone EEZ was implemented why and by whom?
- excluded foreign nations from fishing in Canadian waters
- Canadian Government set the annual harvest rate (no. caught per year) based on information from scientists…*off of reported captures!
Why did WWII scientists overestimate the high N-set annual harvest rate for capturing cod?
- Estimates of N were based on commercial catch rates (assumed: high catches = high N)
- Aggregated (dispersion) during spawning allowed high catches while population was declining fast
- Underestimated mortality from fishery
- catches were misreported by fishers
- large discarding in by-catch when harvesting other species (Cod thrown back into ocean live or dead by fishermen targeting other fish species and not being reported so scientists misreported too high)
In 1980s the annual harvest rates were higher than scientists recommended. Why is this?
- Fishers lobbied hard for higher harvest rates
- Attitude was that cod was a super-abundant resource
- Government maintained annual harvest rates higher than recommended to avoid political suicide…
In 1992, the Cod population had declined to 99% of its original level. What was put into place to allow the population to recover? Then 1995, there was a slight increase in population size. What happened?
- fishing moratorium of 1992
- Government re-opened a small inshore fishery despite strong opposition from scientists
In 2003, why did the fishery close again?
- population had declined to 99.9% of its original level
- Recommended to be listed as an Endangered species under Canada’s Species At Risk Act (SARA)
The fishing moratorium in 1992 closed the cod fishery to allow populations to recover. What happened to the workers of the fishery?
- 19,000 fishers and plant workers became unemployed
- 20,000 other jobs were lost (In 100s of small communities – the cod fishery was the only employer)
- TAGS program for social assistance
- Retraining programs
- Emigration of people out of Newfoundland to find work
- Fishers shifted to harvest other species…
By-catch
- unused catch discarded at sea
- contains target and non-target species
What is an example of by-catch?
- e.g. Shrimp Trawl Fishery (33% of global by-catch)
- 3:1 to 20:1 (by-catch:landed)
- For every shrimp you catch, you’re catching 3 non-target species
- Shrimp are at the bottom of the food chain so you are also catching their predators
What are still the issues with Cod populations being so low?
- Misreported and illegal catch and by-catch
- Hard to estimate population declines
- Cod killed by nets or die when brought to surface
- Returned to the ocean dead
- Trawling also wrecks coral reefs
Demersal fish
-Cod are demersal fish meaning that they live along the ocean floor (“groundfish”)
Removing this apex predator, the cod, does what to other species in the food web?
- food web is complex!
- Need to know more about how species interact to understand how adding/removing a species will influence community structure and to conserve marine biodiversity!!
Population resilience
rate at which a population returns to equilibrium size (k) after a population crash
What is the population resilience in terms of r-selected and k-selected populations?
i. r-selected
- Invest heavily into reproduction (high r)
- shorter potential time to return to K again if population is reduced
- quick recovery, high resilience
ii. K-selected (e.g. cod)
- Invest heavily into growth/survival (low r)
- longer potential time to return to K again if the population is reduced
- slow recovery, low resilience
In 2015 the Fishery Improvement Project (FIP) is implemented. However, after 25 years after the moratorium, what is the cod’s population situation like?
cod populations still exist in the critical zone (~ 300,000 tonnes)
According to Rose and Rowe in 2016, the Northern Cod is making a comeback. What are the statistics?
- 10,000s to >200,000 tonnes in a decade
- Growth rates approaching 34% per annum
- Recommended to allow population to grow to 900,000 tonnes to bring back sustainable historical yields (should take another decade)
Although they were showing a comeback in 2016, what happened once the government found out, even after the recommendations to give the population a couple of decades to recover?
- Small-scale commercial fisheries being opened by Newfoundland & Labrador Groundfish Industry Development Council (NL-GIDC)
- Never learn! Going for irreversible demise of cod
- Growth rates already decreased to single digits
- Plans to expand fishing license and length of season
Do predators reduce prey populations?
General pattern: prey N is lower in the presence vs absence of predators
Do predator-prey interactions cause populations to oscillate? Use the Hudson’s Bay fur trapping of lynx and hares as an example.
- yearly data collected on the number of lynx and hare furs harvested
- large regular cycles (10 years)
- N of predator and prey species are highly synchronized
- trend: predator N trails prey N by 1-2 years (Spikes in population of hare followed by subsequent spike in predator population)
What is the relationship between the reproduction of prey and predators?
As prey populations decrease, predator populations decrease as well
Lotka Volterra Models
- foundation for understanding predator-prey population oscillations
- an elaboration of the logistic equation, but P=predator population size and H=prey population size
What is the underlying principle of the Lotka Volterra Model? *on exam
- population sizes of predators and prey are linked through density-dependent influences each species has on the other’s birth and death rates
- Prey=death rates influenced by the size of the predator population
- Predator=birth rates influenced by the size of the prey population
Functional response
the relationship between prey density and predator consumption rate
What are the three types of functional responses?
- Type I (Rarely observed) *linear graph (consumption rates vs density)
- search time varies with prey density
- handling time is constant but near zero
- Eg. passive predators (spiders, filter feeders, herbivores)
- occurs if prey densities do not become high enough for satiation
- As prey density increases, encounter rates increase, search time decreases
- Consumption rates do not level off
- *s>h - Type II (Most common) *graph increases fast and plateaus
- search time varies with prey density
- handling time is constant
- Predator consumption rate levels off at high prey densities
- As prey density increases, search time decreases because easier to find prey (s»_space; h)
- As prey density increases *2, search time is zero but handling remains constant (h»_space; s)
* h>s - Type III (Rarely observed) *graph starts to slowly increase, then increases rapidly, then plateaus = exponential
- search time and handling time vary with prey density
- Predator consumption rate is lower at low prey densities
- At low prey density, search time ↑ and handling time ↑ (=pursue, subdue & ingest prey)
Numerical response
increasing the prey consumption rate by the predator causes an increase in the offspring production rate by the predator
Lotka Volterra Model: Prey population equation
dH/dt = rH-pHP
Lotka Volterra Model-Prey Population: variables of the equation
dH/dt=rH-pHP
- H=prey population size
- P=predator population size
- p=efficiency of the predator to capture prey (or proportion of encounters resulting in removal of a prey individual)
- pHP=mortality by predator, growth of prey population will decline faster as p, H and P increase
What assumption can be made regarding Lotka Volterra Model: prey population?
functional response
Lotka Volterra Model-prey population: Relationship between H and P variables?
-as H and P increase, encounter rates of predators and prey increase, search time decreases
Lotka Volterra Model-predator population: equation
dP/dt=apHP-dP
Lotka Volterra Model-predator population: variables of the equation dP/dt=apHP-dP
p=the efficiency of the predator to capture prey
a=energy consumed that is converted to predator offspring
apHP=predator population will increase by this
pHP=number of prey captured
dP=predators die at this constant rate (independent of number of prey in population, dependent on number of predators/density-dependent/intraspecific competition)
Lotka Volterra Model-predator population: What assumption can be made regarding the calculations?
- birth of predators is positively related to number of prey captured
- predators do not utilize 100% of energy consumed
- predator-prey interactions result in a stabilization of population growth for both populations
Instead of K (carrying capacity), the predator and prey population size in Lotka Volterra are regulated around the equilibrium by what?
- the prey population size will be regulated around an equilibrium predator population size, predators are keeping them in check (where dH/dt=0)
- the predator population size will be regulated around an equilibrium prey population size (where dP/dt=0)
Isocline
- the line of no growth of prey or predator population where dH/dt=0 or dP/dt=0
- these dynamics create oscillating predator-prey populations
A graph with predator population vs prey population in Lotka Volterra Model has what trends in each quadrant (predator population vs prey population axes)?
1st quadrant (top left): predator low, prey low
2nd quadrant (top right): predator high, prey low
3rd (bottom left): predator low, prey high
4th (bottom right): predator high, prey high
Co-evolution
- predators act as a selective pressure on prey species and vice-versa
- prey traits that reduce chances of being detected and captured by predators will increase fitness
- natural selection will result in smarter more evasive prey
- failure to capture prey results in reduced fitness of predators
- predator traits that increase the chances of capturing prey will increase fitness
- natural selection will result in smarter more skilled predators
- predator and prey populations are in an arms race
- predators and prey co-evolve with the prey one step ahead of the predators to avoid going extinct
Explain the evolutionary arms race between prey and predators.
Prey: 1) detect predators 2) avoid being seen 3) prevent attack 4) escape once attacked Predator: 1) response to better hide from prey (cryptic colouration, mimicry, stalking/ambush) 2) prey detection 3) poison resistance, social hunting groups
What is the Red Queen Hypothesis?
- Co-evolutionary arms race
- The prey faces an ever-adapting predator
- The predator faces an ever-adapting prey
- Have to run (evolve) in order to stay in the same place
- Example) Alice in Wonderland
Name some examples of co-evolution.
- Garter scale that tolerates tetrodotoxin produced by the rough-skinned newt
- Beetles that disarm explosive capabilities of some tropical plants
- Eat away at the leaf that contains toxin of plant and then can eat the rest
Predators can _____ prey populations and predator-prey interactions cause both populations to oscillate.
reduce
__________ are an extension of the ______ equation and are the basis for understanding predator-prey population oscillations.
Lotka-Voleterra Models
Logistic
Population sizes of predators and prey are linked through the ______ influences each species has on the other’s _______ and _____ rates.
density-dependent
birth
death
Predator-prey interactions act as selective pressures, resulting in the _______ of predator and prey species through _________.
coevolution
natural selection
Intraspecific competiton vs interspecific competiton
intraspecific competition: an interaction between individuals of the same species brought about by a shared requirement for a resource in limited supply
interspecific competition: an interaction between individuals of different species brought about by a shared requirement for a resource in limited supply
What effect does interspecific competition have on populations?
- negative effect on both species
- each species contributes to the regulation of the other population as well as its own
- less obvious effects than predation, reduction in growth, reproduction and survival
- can fight for territory, space or food
Fundamental niche
- full range of conditions/resources used by a species to survive/reproduced
- competition restricts a species to a portion of its fundamental niche
Realized niche
- the portion of the fundamental niche a species actually exploits as a result of competition
- species may occupy the portion of their fundamental niche that does not allow the highest growth and reproduction (fitness)
Niche overlap
- when two or more species use a portion of the same resource (food or habitat) simultaneously
- amount of overlap is the degree of potential competition for that resource
- no overlap=no competition
- Minor overlap=minor competition
- High overlap=high competition
What are the three possible outcomes when one species is introduced to an area where another species exists?
1) coexistence without competition (not limited)
2) coexistence with competition (moderately limited) results in reduction in one or both populations
3) one species is eliminated (resource extremely limited)
Asymmetrical competition
one species is more strongly affected than the other
Competitively dominant
species least affected by competition
Resource partitioning
- each species uses a portion of the same resource
- can reduce competition among co-occurring species (niche specialization, niche breadth)
Competitive exclusion principle *on exam
two species that have the same resource requirements and cannot coexist when those resources are scarce
Is there evidence of competition in plants?
- plants compete with neighbouring plants of the same or different species and results in changes of growth rates (plant size, shape), reproduction
- root competition for water and nutrients
- shoot competition for light
A greenhouse experiment was done to observe two growing plant species, the broad leaf and small leaf in different competitions for growth. What was the results from this experiment?
- a control experiment was done for no competition
- root competition where one pot was used but both plants were far apart
- shoot competition where plants were placed in separate pots but close together
- root and shoot competition where both plants were placed in the same pot and close together
- result: both plants experienced reduction in growth rates, but asymmetrical competition where one species is more strongly affected than the other (one is a stronger competitor)
Is there evidence of competition in animals?
- evidence in contraction of a fundamental niche in the presence of another competing species
- expansion of a realized niche in the absence of another competing species
- competitively dominant where one species will be least affected by the competition
Competitive release *on exam
If you remove a competitive species, and there is expansion of a realized niche, then the removed competitor was causing contraction of the realized niche for that species.
True or false? One species has a growth rate higher than another species, this means that competition is the cause.
False. Does not mean that competition is the cause. Must do it experimentally by removing one to see if the other species’ growth rates will be different.
If interspecific competition is often asymmetrical, how are less competitive species able to persist?
a) environmental gradients: abiotic conditions exist along a continuum where ideal conditions for different species may shift over the range and alter competitive ability
b) temporal variations: competing species may evolve to maximize their resource utilization at different time periods to avoid competition;
Peak temperature for germination changes from species to species, so less competition at different times of the season to prepare for the winter
c) multiple resources: species are often competing over multiple resources with multiple different species; adaptations that make them competitively dominant for one resource may not aid or even hinder their competitive ability for others
What is an example of a species where less competitive ones are still able to persist and be the top competitors in another environment?
Ex) one chipmunk species will outcompete another species depending on where they are located on the mountain
Why is the Lotka-Volterra Model used in comparing competition? What assumption is made?
- to help understand the theoretical limits of the responses of competing populations
- assumes stabilization of population growth for both populations or elimination of one of the populations from the system
Lotka-Volterra Model for Interspecific Competition: What is it?
- an extension of the logistic equation
- differential equations (dN/dt) express the rate of growth of populations of competing species
Lotka-Volterra Model for Interspecific Competition: equation for two competing species i and j
dNi = ri Ni (1 - Ni/Ki) - (aij*Nj / Ki)
Lotka-Volterra Model for Intraspecific Competition: equation for species i
dNi = ri Ni (1 - Ni/Ki)
Lotka-Volterra Model for Interspecific Competition: variables for the equation for two competing species i and j
dNi = ri Ni (1 - Ni/Ki) - (aij*Nj / Ki)
- species j will have a negative effect on population growth rate of species i
- aij=coefficient of competition; effect of an individual of species j on the exponential growth of species i; a dimensionless constant; degree that individuals of species j utilize resources of species i; converts individuals of species i into species j and vice-versa
- aij Nj=converts population of j into units of species i
- aij Nj / Ki=interspecific competition (j on i), proportion of Ki that is used by equivalent units of species i
- Ni/Ki=intraspecific competition (i on i)
- K: amount of space available for species i to live (limited by this), is fixed
- when sum of intraspecific component and interspecific component is smaller than 1, population will decline
- when N is near K, slight changes in aij Nj/Ki will alter population growth from + to -
Lotka-Volterra Model for Intraspecific Competition: variables for the equation for species i
dNi = ri Ni (1 - Ni/Ki)
Ni/Ki: intraspecific competition
-K: amount of space available for species i to live (limited by this), is fixed
If an individual of species j takes up half the space of an individual of species i, how can this be applied in the Lotka-Volterra Model equation (interspecific competition)?
aij=0.5 and aji=2
100 j = 50 i (1000.5)
100 i = 200 j (1002)
What is a key point about interspecific competition’s effect on population growth?
Even very low levels of interspecific competition can have a strong effect on population growth of either species
What are the realities regarding competition?
a) competitive abilities can shift as abiotic factors change
b) competition involves multiple resources and multiple species
c) competition acts as a selective pressure for individuals to maximize access to essential resources (increase fitness)
“Ghosts of competition past”
- resource partitioning observed in nature is often thought to be due to competition among species in the past
- hard to prove
- no information if species coexisted in the past
- species may have responded to natural selection differently and are simply different (no competition, current or past)
- species may have been competitively excluded leaving those that were different enough (no competition, current or past)
_______ competition is an interaction between individuals of different species brought about by a shared requirement for a limited resource.
Interspecific
The _____ niche is the portion of the ______ niche a species actually exploits as a result of competition.
realized
fundamental
Possible outcomes of interspecific interactions are _______, ________, and _________.
coexistence without competition
coexistence with competition
competitive exclusion
There is evidence of interspecific competition in plants and animals, where one species is competitively dominant over the other, called __________.
asymmetric competition
When a competitively dominant species is removed, this may result in __________ of the less dominant species.
competitive release
_____________ are an extension of the logistic equation, whereby interspecific competition effectively ______ K for competing species.
Lotka-Volterra models
decreases
In nature, many species compete over multiple ________ and competitive interactions are modified by ______ and ______ variation.
resources
abiotic
biotic
Extinction
Give some common examples.
disappearance of ALL individuals of a species (elimination of a species)
ex) Dodo bird, carrier pigeon, caused by humans
Extirpation
- the disappearance of a population of a particular species from a local area (elimination of a population)
- *a population may be extirpated but NOT extinct
- a natural process that expresses the failure of a species to adapt to changing environmental conditions
- can be an extinction if the population that is removed is the only population left of that species
Why might a species be unable to adapt to changing environmental conditions?
- environmental conditions may change too quickly for adaptation to occur
- deaths>births, so population declines (r<0)
- unless the population can reverse the trend, it may become so low that it declines towards extinction
What are the three types of extinction?
1) background extinction
2) mass extinction
3) anthropogenic mass extinction
Background extinction
- species disappear and others take their place as environmental conditions change
- natural process
Mass extinction
- dying off of large numbers of species as a result of natural catastrophes
- natural process
Anthropogenic mass extinction
-dying off of large numbers of species as a result of human activities
What did information from the fossil records tell us about the normal background rate of extinction? What is the present anthropogenic extinction rate?
*on exam
- background rate: 1 species/year
- present anthropogenic extinction: 1000X background rate (similar to other mass extinctions where 50% of Earth’s species disappeared like the dinosaurs)
What is the ultimate factor causing this mass anthropogenic extinction?
due to an increase in human population size and increased per capita use of resources
What other factors are causing the mass anthropogenic extinction?
1) habitat loss
2) global warming
3) introduced species
4) exploitation-harvesting
Anthropogenic extinction: habitat loss
- 60% of Earth is used for cropland, forestry, rangeland
- clearcutting in marine environment by trawling (destroys coral reefs, the homes of many fish at bottom floor of ocean)
- its not where we are living that is taking up so much space (only 2%), but the resources that we are exploiting
Anthropogenic extinction: Global warming
- each species lives or tolerates a certain range of environmental conditions
- if there is a shift in conditions outside this range, the species may cease to exist in that location (limits to phenotypic plasticity)
- “climate change”
- increasing average temperature of the Earth
- equivalent to warming since last glaciation only 50X faster
- human induced due to increase of burning fossil fuels, so higher CO2 in atmosphere
- if species can’t adapt fast enough, it could cause worldwide extinction of many species
Anthropogenic extinction: Introduced species
- ex) zebra mussels introduced into St. Lawrence lake, caused foul shells of freshwater clams
- competition for food with native clams and fish
- have eliminated native species from lakes and rivers=competitive exclusion since better competitor
- introduced species can become invasive
What are some examples of invasive species?
Verola mite: -Feeds on honey bees -Causes diseases -Huge decrease in population of the bees Australian species that are not native to the continent: -Toads -Cactus -Mice came on shipping vessels, outcompeted and overpopulated -Horses -Water buffalo *all introduced, not native from there
Anthropogenic extinction: Exploitation-Harvesting
- 52% of global fish stocks are fully exploited (maximum sustainable yield)
- 28% of global fish stocks are over-exploited (waiting for recovery)
- 22% of global fish stocks are under-exploited (no decline yet)
What do we need to consider when determining if a species is at risk of extinction?
-life history and population structure that influence a species’ vulnerability to human activities and natural catastrophes
What are the general patterns when determining if a species is at risk of extinction? * on exam
1) smaller populations have a greater risk of extinction than larger ones
2) larger the geographic range of a species, the lower the risk of extinction
3) the more age and spatial structure of a species, the lower the risk of extinction
4) large endothermic animals have a lower risk of extinction than smaller endothermic animals
5) ectothermic animals have a higher risk of extinction than endothermic animals
6) k-selected are at higher risk of extinction than r-selected
Allee effect: pattern?
- a small N (population size) can result in a further decline in reproduction and survival
- typical pattern: N declines, r increases, n increases
- Allee effect: N declines below critical threshold level, r decreases, N declines
Allee affect: Causes?
- decrease risk of predation by living in a group
- increase foraging efficiency by searching for prey in a group
- increase success of finding mates by spawning in a group
Ubiquitous vs endemic geographical ranges
Ubiquitous: widespread over a large area
Endemic: only occur in a small area *can lead to exerpation where loss of habitat in one region leads to loss of species (extinction)
In the example of marine gastropods and bivalves in the fossil record, what could be said about the relationship between geographical range and extinction?
-small ranges had higher rates of extinction
Using the example of the European shag, what helped buffer their extinction?
- colonial nesters, eat fish
- have limited geographical range since nest sites are limited
- have delayed maturity
- *age and spatial structure buffered extinction
- spatial: not all colonies were affected (high dispersal rates allowed recolonization
- age: nonbreeding birds nested the next year (weren’t using up energy for reproduction that year since not mature yet)
What can be explained why large endothermic animals have a lower risk of extinction than smaller endothermic animals?
smaller animals have a shorter period to starvation (high surface area/volume ratio) so more susceptible to changes in environmental conditions that result in reduced food
Why are ectothermic animals more at risk of extinction than endothermic animals?
- ectotherms have a higher mortality risk when temperature conditions fluctuate a lot
- growth, reproduction and survival depend on external conditions for ectotherms
Population resilience
rate at which a population returns to equilibrium size (K) after a population crash
Why are K-selected populations at higher risk of extinction than r-selected?
- k-selected have low resilience
- they put more energy into growth before reproduction
- r-selected reproduce a lot
International Union for the Conservation of Nature (IUCN)
-created a quantitative classification system based on a species’ risk of extinction
What are the three levels of risk of extinction in the quantitative classification system created by IUCN?
1) critically endangered: >50% chance of extinction within 10 years (3 gens)
2) endangered: 20% chance within 20 years (5 gens)
3) vulnerable: >10% chance of extinction within 100 years
What information is required to classify species in the correct level of risk of extinction?
- geographic range and metapopulation strcture
- total N, number of individuals breeding (effective population size)
- expected decline in population size if current and projected trends in population decline or habitat destruction continues (minimum viable population)
- probability of the species going extinct in a certain number of years or generations (population viability analysis)
What is an advantage of the IUCN classification system?
-provides a standard, quantifiable method of classifying species
What is a problem in the IUCN classification system?
-often do not have complete information
Precautionary principle
-in the absence of complete scientific data, uncertainty will not be used as a reason to postpone conservation efforts of species when the species is faced with the threat of serious or irreversible harm
Presently, the Earth is undergoing ______ caused by human activities (_____________) at ________ rates. *on exam
mass extinction
Anthropogenic Mass extinction
1000X background
Causes of Anthropogenic Extinction include ________, _________, __________, _________
habitat loss/destruction
global climate change
introduced species
harvesting/exploitation
Quantitavely classifying the extinction risk of species is important for conservation on a global scale and depends on both ecological knowledge and the _________. * on exam
Precautionary principle
