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Ecology quiz 2 (lectures 7-11)
Terms in this set (142)
an ecological process acting on
A group of individuals of the same species living in the
A group of organisms that naturally interbreed with each
other and produce fertile offspring.
What is "the same location"?
Species boundaries and spatial limits of a population are directly
connected, and may be hard to define in some cases
Differential survival and reproduction of individual
organisms dictated by the interactions between phenotype and the
Change in a population's gene pool over time.
Natural selection connection with evolution
Natural selection within a population leads to evolution - the process
that is unique to populations.
Natural selection is the primary non-random mechanism of evolution
within populations, but not the only mechanism.
Three key steps in adaptive evolution by natural selection:
1. heritable variation in phenotype among individuals.
2. difference in reproductive success among individuals dictated
by particular aspects (i.e. traits) of the heritable phenotypic
3. heritable phenotype of more reproductively successful
individuals is more prevalent in the following generation.
sources of heritable genetic variation (4)
Any change in the DNA that codes for a gene or the
expression of a gene.
• Most changes come from nucleotide substitutions, deletions, or
insertions during copying events.
• Some changes can cause fatal phenotypic changes, some are
neutral or "silent", some can result in beneficial changes.
Single genetic change, multiple phenotypic effects.
Hierarchical control of the expression of one gene by
Populations are integrated units:
Populations members reproduce,
defining a distinct gene pool where a high level of mixing occurs
What population characteristics always influence the gene pool? (3)
1. Suitable habitat (location) can divide populations into subpopulations or isolated non-interbreeding populations.
2.Dispersal to available habitat can influence the geographic range of populations.
3.Population structure (number, density, and spacing of individuals) can alter ecological processes.
Populations and suitable habitat
Suitable habitat might be patchily distributed within the larger area
where it is found, creating sub-populations with distinct spatial structure
The range of conditions populations of a species can tolerate, which also defines its functional role within the environment it occupies.
The full range of habitat conditions that a population of organisms can tolerate and persist in
Predators, competitors, and pathogens might further limit a population to a smaller __________
The movement of individuals from one area of suitable habitat to another
Suitable habitat ultimately determines geographic range, but only if...
populations can reach all suitable habitat.
The absence of a population from suitable habitat because of barriers to movement
Natural founding populations that reach new suitable habitat tend to be _______ and represent a ________
small, rare chance event
Human trade and travel intentionally and unintentionally move
______ in ______ and with ______
organisms, large numbers, high frequency.
• Human-mediated dispersal facilitates..
larger founding populations
and multiple founding events in a short period of time.
A non-native species in the ecological system under consideration that is likely to cause:
or harm to human health.
Distributions need to be known for:
• Land management
• Reintroduction efforts
• Tracking and preventing negative consequences of invasions
Dispersal of populations to track suitable habitat.
Migration and geographic range
1. Seasonal changes in the population's needs - e.g. feeding vs.
mating in Salmon migrations.
2. Seasonal shifts in location of suitable habitat - e.g. Seasonal shifts in food distribution tracked by locusts.
Locust migrations (swarms)
• Increased density switches life-stage (phenotypic plasticity).
• Associated shifts in behavior facilitate swarming.
• Massive economic impacts result from this shift.
Total number of individuals within a defined area.
Number of individuals per unit area or volume.
The spacing of individuals within the geographic range of a population - can be different under the same abundance and density conditions.
Changes/differences in abundance, density, and dispersion can be indicative of ________
different population-level interactions
Three classes of dispersion patterns along a continuum:
• Random: No influence of biotic or abiotic interactions on dispersion - unlikely and usually a null hypothesis in studies of dispersion within a population.
Clustered dispersion can result from (3)
• Social interactions.
• Clustered resources.
• Limited dispersal of offspring.
Even dispersion may most often result from ______
among individuals, and especially _______
direct interactions, competitive interactions.
Individual phenotypic responses and fitness
The individual does not benefit from evolution - evolution is a
population-level process. Individuals develop, populations evolve.
Genotype of an individual is fixed, but its phenotype may not be,
potentially improving fitness.
**look at graph of NBA player height
Where does selection act?
Environment can "select" (create differential survival) at any stage
before and during reproduction - selection is widespread and powerful!
Form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve
Where does selection act: before mating
Tolerance of environment
• Resource acquisition
• Finding shelter
Random processes that result in evolution
genetic drift, bottleneck effects, founder effects
chance loss of genetic variation followed by
What does selection acts on?: Phenotype vs. genotype
Natural selection acts on the phenotype, which directly represents
the genotype to varying degrees
• Only genotypic aspects of the phenotype will evolve.
is the implementation of the genetic instructions, which
can then interact with forces of natural selection.
is influenced by the environment, but the genotype sets
the limits on how an organism looks.
• Phenotypic plasticity
The capacity of an individual's phenotype to
respond to environmental change within its lifetime.
chance loss of genetic variation due to
severe reduction in population size
Producing a plastic phenotype: Reaction norms
The observed relationship between individual
phenotype and the environment - the observable pattern of phenotypic
plasticity within a population.
Adaptive phenotypic plasticity:
Selection has favored flexible
responses to environmental change that maximize fitness under a
range of conditions potentially experienced by an organism
is the change over time within a population - our
focus so far.
is evolutionary change that results in the production
of new species.
• Two contrasting modes of speciation
The evolution of new species within a
population, without any geographic isolation.
• Allopatric speciation:
The evolution of new species via
geographic isolation of subpopulations
Example of reciprocal transplant experiment and reaction norms
Eastern fence lizards transplanted between nutrient-poor pine
barrens of New Jersey and nutrient-rich prairie of Nebraska.
Evolution documented - crickets & parasitoids
Observations: Males of an introduced cricket on Kauai (Hawaii) had
become increasingly quieter over two decades of research. The same
crickets suffered mortality from a recently introduced parasitoid fly.
• Hypothesis: Mortality from fly attacks has driven selection for quieter
• Hypothesis suggests that flies are the new selection pressure on
cricket traits for calling.
• But how do quiet males still meet mates?
Alt. definition of adaptive phenotypic plasticity:
reaction norm that
maximizes fitness across an environmental gradient
• Reciprocal transplant experiments
help address why populations
from different environments show different phenotypes.
**look at graphs of genetic and environmental factors
Acclimatization - Flexible adaptive phenotypic plasticity
Acclimatization: Dynamic phenotypic plasticity in response to
repeated (especially seasonal) environmental shifts.
Development - Irreversible phenotypic plasticity
Developmental responses: Permanent phenotypic plasticity that
tracks persistent environmental characteristics
Producing a plastic phenotype:
All phenotypic expression of the genotype is affected by the
Simplest reaction norms are seen in the influence of environment on the
is a set of genetic instructions for building an organism.
• Founder effects:
random differences in genetic variation in
small populations that occupy a new area.
where does selection act: mating process
Finding a mate
• Investing in offspring
• Caring for offspring
trait-environment interaction determines
how evolution is shaped.
form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle
Natural selection that favors intermediate variants by acting against extreme phenotypes
types of selection
stabilizing, directional, disruptive
from phenotypic variation, to
performance, to selection and fitness
• Phenotype dictates performance in ecologically relevant tasks.
Performance interacts with environment to determine selection.
• Strength of selection is measured in lifetime reproductive success.
• Lifetime reproductive success is also know as evolutionary fitness.
• Fitness is determined by which traits are selected by the
The capabilities conferred by phenotypic traits.
Complex interactions among many genes, resulting
in continuously varying phenotypic traits.
individual offspring production vs. their own death
ex) Population growth via births and deaths
Total population growth
the individual reproductive rate multiplied
by the population size.
greater if the population size is bigger
discrete time steps
USED TO VIEW GROWTH
When taking counts,
take at the same time each time step, to be sure
that the same birth and death cycles are included
Growth via discrete time steps
Nt = N0λ^t
• N = Number of individuals
• λ (lambda) = Geometric growth factor (a multiplier - ratio of
population size/population size the previous year).
• t = Number of discrete time steps.
a function of starting population size, per capita
growth factor, and number of time steps
reproduce and die at a relatively steady rate at all times: use exponential growth
• Exponential growth:
Growth (positive or negative) at a continuous
rate that is a proportion of the total number of individuals at any
Nt = N0e^rt
= Exponential growth rate. "e" is the exponential constant, and er
is simply replaces λ, to describe that all individuals have a chance
of reproducing at any time, not just at a discrete time step.
• N = Number of individuals
• t = Time elapsed.
Calculating continuous growth
Some proportion of the individual are reproducing at any given
moment = exponential growth.
Population size is a function of starting population _____, the ____
rate, and the time that has _______
size, growth, elapsed
Comparing exponential and geometric growth
Same pattern, but exponential is continuous growth and geometric is
achieved via discrete bursts or reproduction.
Decreasing population size 0 < λ < 1
Constant population size λ = 1
Increasing population size λ > 1
Decreasing population size r < 0
Constant population size r = 0
Increasing population size r > 0
When birth and death rates vary with age
we have to account for the
growth factor/rate of each age class to get accurate calculations
The proportion of individuals in each age class within
Populations with the _______ but ____________ will _____________
same birth and death rates, different age structures, grow at different rates.
used to organize the information for age structured
populations and to calculate growth
Data typically tracks females, and number of female offspring per
reproductive female - contribution of individual males hard to track.
Cohort tracking approach:
follows a group of individuals from birth
through to death.
• Requires that all individuals can be marked and tracked for their whole
• Provides rich data, but no replication for strange years - age
confounded by time.
Static age structure approach:
Quantifies the survival and fecundity of
all individuals of all ages in a population at a single time interval.
• Requires a way to assess survival and fecundity within a single time
• All age classes face the same environment at the time of census, so
age not confounded by time, BUT unclear if generalizable across years
General patterns of survivorship
I. High initial survival, followed by age-specific mortality in later age
classes. e.g. Big mammals - like us.
• II. Constant survival - organisms of all ages face the same likelihood
of dying. e.g. Small mammals
• III. High mortality early in life then escape major sources of mortality.
e.g. Plants and invertebrates
Env. change X overfishing
Environmental change in ocean
temperatures reduced survivorship,
especially of younger age classes.
• Conspicuous mating aggregations of
older, reproductively mature age classes
• Over fishing heavily impacted older age
classes, reducing reproduction.
• Environmental change continued to have
an impact of survivorship of younger age
• Environmental impact x over fishing led
to unnoticed, apparently sudden
To fully understand growth, we need to identify
and fecundity patterns.
typically follows one of three distinct patterns.
almost always age structured.
**ability to be fertile and produce offspring
• Cultural shifts that can slow population growth:
Fewer children - lower fecundity rate better reflecting very high
• Later reproduction - slower generation time reduces per capita
growth rate per year, similar to later age of reproductive maturity.
• Three layers to understand with life tables
Age-specific survival and fecundity.
• Number of offspring per age class and overall.
• Total population size.
Limits on population growth
Density independent factors:
Negative density dependent factors
Density independent factors:
Factors affecting population growth
that are unrelated to population size (e.g. droughts, storms, flooding).
Negative density dependent factors:
Factors negatively affecting
population growth that have increasing strength with increasing
• Decreased resource availability for existing adults
• Reduced offspring production
• Reduced offspring quality and lower per capita survival
• Increased target for predators
Slow growth is a common response to competition, resulting in
smaller size at higher density, and reduced survival and fecundity.
Formalizes the relationship between increasing
population size and decreasing growth rate, as the carrying capacity
• Carrying capacity:
The maximum number of organisms the
environment can support - the point where growth falls to zero in the
logistic growth curve
• Inflection point:
Separates early accelerating phase from the later
Negative effects of high density cause some
individuals to die, allowing remaining plants to increase in average
size - Consistent negative relationship established between plant
density and average plant size.
Positive density dependence:
Increasing population size has a
positive influence of growth rate (up to a point!).
Causes of positive density dependence:
Allee effect: Beneficial social interactions are larger group sizes
increases individual fitness - mating, group foraging, etc.
• Larger populations are more genetically diverse (deleterious
mutations are less likely to be expressed).
Beneficial social interactions are larger group sizes
increases individual fitness - mating, group foraging, etc.
Allee effect explains rapid decline of human impacted species,
driving them further towards extinction
causes of flucuations in density dependence
Birth and death rates follow environmental changes.
• Biology of the organism may favor instability in population size.
Fluctuations are the norm, but the magnitude and frequency of the
fluctuations can vary dramatically.
Biology favoring intrinsic population stability
Large body size.
• Homeostasis (ability to resist external environmental fluctuations).
• Long life.
• Significant overlap of generations.
Biology favoring intrinsic fluctuations/instability
Minute size and no homeostasis.
• Very short lived.
• High turnover - high mortality rate, so organisms at any time are
mostly those from last reproductive event.
• Periodic population cycling:
Repeated, regular fluctuations in
Temporal variation and age structure
Signature of population fluctuations can be carried through the
population age structure.
• Sizes of age classes provides a history of population changes.
Population cycling and delayed responses to density
• Populations have an equilibrium carrying capacity, but they are easily
displaced from it, creating back and forth cycling.
Momentum from high birth rates and death rates generates
overshooting of the carrying capacity and subsequent die-off.
More individuals are produced than can be sustained
at adulthood - e.g. starvation in rapidly expanded populations.
Strong effects of overpopulation cause population decline
that drives population well below carrying capacity - population crash
following density dependent effects.
Time delays and oscillations
Population oscillations are amplified by an increased time delay until
population growth responds to the approach of the carrying capacity
Increasing time delay in population
response to carrying capacity
drives increased oscillations around
the carrying capacity.
spatially explicit models
study the dynamics of population growth and structure.
• Three modeling approaches with increasing layers of complexity:
Describe a set of subpopulations
occupying patches of habitat, between which individuals move.
Measures "patch occupation" of equal quality patches.
• Source-sink model:
Adds information on habitat quality in
Adds patch quality and directional movement data
• Landscape model:
Adds information on the differences in habitat
within the habitat matrix - how surrounding habitat improves
Adds data on habitat and barriers that alter movement.
support fewer individuals and are more likely go
• e.g. Island bird populations tracked over 80 years - recorded local
extinction and recolonizations.
Combining spatial and temporal dynamics
Most populations are spread across habitat patches of different sizes
capable of sustaining sub-populations of different sizes.
• Spatially separated patches are increasing as human activity
fragments larger areas of habitat
• Movement determines how the overall meta-population behaves.
Metapopulation dynamics have two main sets of processes:
Growth and regulation of subpopulations - each subpopulation
may have its own birth and death rates and growth dynamics.
• Colonization of empty patches and the extinction of existing
• Movement determines how the overall meta-population behaves.
Factors influencing subpopulation dynamics (3)
1. Local catastrophes and chance fluctuations in the number of
individuals - Density-independent events have greater impact on small
2. Density-dependent factors.
3. Movement between subpopulations as a buffer
Movement between subpopulations as a buffer:
The more individual movement between subpopulations, the more
subpopulation dynamics mirror the dynamics of the full population.
• Zero or very little movement means each subpopulation has
• At intermediate movement, subpopulations go extinct but are then
recolonized, creating a shifting mosaic of patch occupation.
Calculating and predicting metapopulation equilibrium
pe = 1 - (e/c)
• pe is equilibrium proportion of occupied patches.
• e is the extinction rate.
• c is the colonization rate.
Dynamics can be influenced significantly by (incorporated into e & c
1. Different patch size within a metapopulation.
2. Different rates of colonization for each patch.
3. Different dispersal from each patch.
4. Interdependent patch colonization and extinction rates
• Rescue effect
The extent to which migration from large, productive
patches can prevent small, unproductive patches from going extinct
Patch size and distance in metapopulations
population dynamics meet species interactions:
Dynamics of Consumer-Resource Populations
So far we have focused on population dynamics with respect to
environmental and intra-specific interactions.
• Being eaten can have a big impact on population dynamics!
• Consumer-resource interactions:
***The consumer can limit the resource population.
When one organism feeds on another organism
Time delays and predator-prey cycles: lynx-hare
Lynx-hare cycling has a cycle length of about 9-10 years, consistent
with a time delay of about 1-2 years.
• Cycling is driven by combination of time delays, overshooting, and
density-dependent effects in both predator and prey.
• Approximate single prey interactions are rare in nature,
• More prey species tend to stabilize cycling.
• The more closely 1:1 predator-prey interaction is approximated, the more regular the cycling.
predator-prey population cycling in the lab
With adjusted patch (oranges) number and spatial arrangement, plus
a dispersal advantage to the prey (posts), cycling was established.
• Predator population lagged due to time delay in dispersal to new
patches and reproduction on new patches.
**look at graph
used to predict the oscillations in the size of
predator and prey populations.
Calculates the rate of change of predator and prey populations as
each is reciprocally influenced by the other
• Tracks the dynamic interaction of growth rates
Lotka-Volterra model cont.
A model of predator-prey interactions that incorporates oscillations in the abundances of predator and prey populations and shows predator numbers lagging behind those of their prey
Joint equilibrium point Lotka-Volterra model
The point where equilibrium isoclines cross
- point at which populations will not change over time
Factors stabilizing Lotka-Volterra cycling
Predator inefficiency - prevents prey from being driven down so
• Density-dependent limitation that is independent of the predatorprey
relationship (disease, prey's resource availability, etc.)
• Alternative food sources for the predator - prevents continued
driving down of prey population and crash of predator population.
• Refuges for the prey at low densities - availability of predator-free space for the population to recover.
• Reduced time-delays in predator responses to changes in prey
abundance - flattens high peaks and low troughs.
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