Exam 2 Flashcards
fundamental niche
the range of abiotic conditions (ex: temperature, humidity, salinity) under which a species can persist
Where a species is able to live
realized niche
the range of abiotic and biotic conditions under which a species can persist
Where a species is actually found
- changes frequently
niche
range of abiotic and biotic conditions an organism can tolerate
habitat
place/physical setting in which an organism lives
- A habitat is NOT a niche–> habitat is a place, niche is a set of conditions
- more suitable the habitat, the larger a population can grow within that habitat
geographic range
a measure of the total area covered by a population
- includes all the areas its members occupy during their life
- small-scale variation in the environment create geographic ranges that are composed of small patches of suitable habitat (individuals of a species/population do not occupy every location within their geographic range–> differing climate, topography, soil, vegetation…etc.)
conservation impacts of realized niches and population distributions
understanding the realized niche of a species aids in species conservation and can help to limit the spread of invasive species
ecological niche modeling
the process of determining the suitable habitat conditions (ecological envelope) for a species
ecological envelope
range of ecological conditions that are predicted to be suitable for a species
realized niche vs ecological envelope
- realized niche= conditions species currently lives in
- ecological envelope= prediction of where a species could potentially live
endemic
species that live in a single, often isolated, location
cosmopolitan
species with very large geographic ranges that can span several continents
- populations with larger geographic ranges are less vulnerable because their population would remain unaffected
abundance
total number of individuals in a defined area
- provides a measure of whether the population is thriving or on the brink of extinction
census
counting every individual in the population
- possible, but tricky
survey
count subset of population–> estimate abundance, density, geographic range, distribution
- more common than census
area- and volume-based surveys
surveys that define the boundaries of an area or volume and then count all of the individuals in the space
- size of defined space is related to the abundance and density of the population
- by taking multiple samples, it is possible to determine how many individuals are in an average sample (depending on how variable the environment is, determines how many subsamples should be taken)
line-transect survey
surveys that count the number of individuals observed as one moves along a line
- this data can be converted into area estimates of a population
when are area and volume and line-transect studies useful
for organisms that do not move or that aren’t easily disturbed
mark-recapture survey
a method of population estimation in which researchers capture and mark a subset of a population from an are, return it to the area, and capture a second sample of the population after time has passed
when are mark-recapture surveys useful
- many animals are sensitive to the presence of researchers and will leave the area when surveyed
- some species are camoflaged and hard to find
- can cause us to underestimate number of individuals in a population when use another type of survey
assumptions about mark-recapture surveys
- animals that are captured are equally likely to be recaptured vs leave
- animals that live in tight groups (wolves = territorial)
- marking can’t lead to predators getting to species easier
- time interval can’t be too long
- not a lot of immigration/ emigration
density
number of individuals in unit area or volume
abundance/area
what does density tell ecologists
how many individuals are packed into an area
- tells if population can continue to grow in area or if individuals need to leave or population will have lower growth ro survival
where does largest density of individuals occur
near the center of a population’s geographic range
- near the edges of the range, population densities decrease
- this is because biotic/abiotic conditions become less ideal and support fewer individuals
dispersion
spacing of individuals with respect to one another withing geographic range of a population
clustered dispersion
when individuals are aggregated in discrete groups
- sometimes results from individuals living in groups, staying near resources, offspring staying close to parents… etc.
evenly spaced dispersion
when each individual maintains a uniform distance between itself and its neighbors
- ex: crops, direct interactions between individuals (defending territory)
random dispersion
when the position of each individual is independent of other individuals
- not common in nature because abiotic conditions, resources, interactions… etc. are not evenly distributed
why do individuals choose to position themselves in the ways they do
- when habitats differ in quality and individuals can move easily among habitat patches, natural selection should favor individuals that can choose habitat that provides them with the most energy
- once there are too many competitors in the “high quality” habitat, it pays off to occupy the lower quality habitat, where you have fewer competitors (too many competitors= resources must be divided)
- follow the ideal free distribution
per capita benefit
resources available to each individual
- can fall so low that an individual would benefit by moving to the low-quality habitat
ideal free distribution
when individuals distribute themselves among different habitats in a way that allows them to have the same per capita benefit; assumes perfect knowledge of habitat variation
- tells how individuals should distribute themselves among habitats of differing quality
requirements of ideal free distribution
1) when all animals know where the resources are
2) they can travel to where the resources are
3) they evenly distribute the resources
4) they are equal competitors, no predation risks
- individuals in nature rarely match ideal expectations–> often used as null model
- fitness is not solely determined by maximizing resources; other factors may influence distribution
ideal despotic distribution
- example of a situation that violates the ideal free distribution–> territorial animals
- better competitors = better territory = more fitness
dispersal
movement of individuals from one area to another
- involves individuals leaving habitat of origin and typically not returning
- mechanism that individuals can move to better suitable habitats/colonize suitable habitats not already inhabited
- can help avoid areas of high competition or predation
what is NOT dispersal
dispersion and migration
migration
seasonal movement of individuals back and forth between habitats
quantifying dispersal
- dispersal can be quantified by measuring how far individuals travel from a single source location
- need to ensure that there is only one possible source of individuals and then determine how far individuals disperse from this single location
- in other cases, individuals are marked and then observed or recaptured at some later time to determine how far they moved from the location when they were marked
- track with GPS, ear tags, radio transmitters, wing bands, leg bands
lifetime dispersal distance
the average distance an individual moves from where it was born to where it reproduces
- provides an estimate for how fast a population can increase its geographic range
dispersal limitation
the absence of a population from suitable habitat because of barriers to dispersal
common dispersal limitation
presence of a large expanse of inhospitable land that organism can’t cross
habitat corridor
a strip of favorable habitat located between two large patches of habitat that facilitates dispersal (ex: narrow band of trees that connects forests)
coefficient of determination (R2)
statistic showing how strongly 2 variables are related
population growth
under ideal conditions, populations can grow rapidly
- under ideal conditions (abundant resources, mates, favorable abiotic conditions) individuals can reach max reproductive rates and minimum death rates which leads to intrinsic growth rate
demography
the study of populations
growth rate
in a population, the number of individuals that are produced per unit of time minus the number of individuals that die
intrinsic growth rate (r)
the highest possible per capita growth rate for a population (maximum birth rate, minimum death rate)
exponential growth model
a model of population growth in which the population increases continuously at an exponential rate
- estimates how population will grow over time under ideal conditions
- applies to species that reproduce throughout the year
J-shaped curve
the shape of exponential growth when plotted
exponential population growth assumptions
- populations will initially grow slowly because there is a small number of reproductive individuals’ growth rate increases with the number of reproductive individuals–> dN/dt increases over time
assumptions are very unrealistic–> most species have discrete breeding seasons
geometric growth model
a model of population growth that compares population sizzes at regular time intervals
- expressed as a ratio of a population’s size in one year to its size in the preceding year(𝜆)
𝜆 cannot be negative
population decrease
𝜆<1, r<0
population constant
𝜆=1, r=0
population increase
𝜆>1, r>0
difference between exponential and geometric models
- exponential has continuous data points that form a curve
- geometric model has discrete data points for each breeding season
show same pattern
density independent factors
limit population size regardless of the population’s density
common density independent factors
climactic events (ex: tornadoes, floods, extreme temperatures, and droughts)
density dependent factors
affect population size in relation to the population’s density
negative density dependence
when the rate of population growth decreases as population density increases
what are some factors that cause negative density dependence
- limited supply of resources (food, nesting sites, physical space)
- as population increases-> resources must be divided among more individuals–> per capita amount of resources decrease and eventually reaches level where individual can’t grow, reproduce, and survive
self thinning curves
decrease in population density over time leads to increase in mass of each individual in population
positive density dependence
when the rate of population growth increases as population density increases
Allee effect
when does positive density dependence occur
when population densities are low, which make it hard to find mates or pollen, particularly when sex ratios are uneven (and male-biased)
- low densities increase risk of inbreeding
- dilution effect
difference between negative and positive density dependence
negative density dependence causes slow population growth due to overcrowding, positive density dependence causes slow population growth due to undercrowding
Allee effect
problems associated with “undercrowding”
real populations are moderated by BOTH positive and negative effects
- increased densities provide more individuals for breeding
- but above some density, resources become limiting and negative density dependence begins to play a role
carrying capacity(K)
the maximum population size that can be supported by the environment
logistic growth model
a growth model that describes slowing growth of populations at high densities
inflection point
the point on a sigmoidal growth curve at which the population has its highest growth rate
- above this point, population growth begins to slow
- the point of fastest growth after which growth begins to slow because reproductive individuals are each obtaining fewer resources
- as population increases from a very small size, the rate of increase grows until reaching 1/2 the carrying capacity (inflection point)
=1/2K
breakdown of logistic growth model
logistic growth curve shows initial rapid increase in growth due to increasing number of individuals in population, followed by slowing rate of growth as per capita resources become limited
how do we make better population models
- individuals within a population DO NOT all have the same intrinsic growth rate (r)
- fecundity (per capita growth rate) and survival (per capita death rate) of individuals varies greatly with age, size, life history
(individual cannot reproduce until reaches reproductive maturity, individual with greater mass = higher fecundity, different fecundity rates during each life stage)
age structure
the proportion of individuals that occurs in different age classes
survival curves
most populations exhibit a survivorship curve that combines features of type I and III curves
- survivorship changes ‘r’ at different life stages
Type I curve
low mortality early, high mortality late
Type II curve
relatively constant mortality throughout life
Type III curve
high mortality early, high survival later
life tables
tables that contain class-specific survival and fecundity data
- typically based on the number of female offspring per female
- helps determine how age, size, life history classes affect growth of a population
x
age class
nx
the number of individuals in each age class immediately after the population has produces offspring
sx
the survival rate from one age class to the next age class
bx
the fecundity of each age class
number surviving to next age class
(nx) x (sx)
number of new offspring produced
(nx) x (sx) x (bx)
what happens to 𝜆 given stable age distribution
given a stable age distribution (when the proportion, survival, and fecundity or each age class does not change over time), 𝜆 will stabilize over time
stable age distributions rarely occur in nature
- all models assume stable age distribution-> rarely occurs
- environment varies from year to year-> can affect survival/fecundity
- ex: disease, drought, natural disasters… etc.
Net reproductive rate (R0)
the total number of female offspring that we expect an average female to produce over the course of her life
- populations grow when R0>1, populations decline when R0<1
Generation time (T)
the average time between the birth of an individual and the birth of its offspring
age distributions fluctuate…
due to environmental conditions, so any approximation of 𝜆 or r is restricted to the environmental conditions that the population experiences at the time of measurement
survivorship (lx)
what is it
the probability of surviving from birth to any later age class
- survivorship in the first age class is always set at 1
l2
l1s1
R0
sum of (lx) x (bx)
- if R0>1 then each female has “replaced” herself in the population, and the population will grow
when intrinsic rate of increase is estimated from a life table, we assume…
the life table has a stable age distribution-> stable age distributions rarely occur in nature-> approximate 𝜆 or r is limited to environmental conditions the population experiences
cohort life tables
- marked individuals continuously tracked over their lives
- doesn’t work well for very mobile or long-lived species–> used for plants/sessile animals that can be tracked over their lifetime
- age can be confounded with random environmental changes–> change in environment can affect survival/fecundity of cohort that year
- follows group of individuals born at the same time and quantifies their survival and fecundity until death of the last individual
static life tables
- considers survival and fecundity of all ages in a single time period
- must be able to tell ages of individuals
- ideally need to sample over multiple years–> construct life tables for multiple time intervals to look at how much environmental variation affects predicted population growth
- quantifies survival and fecundity of all individuals in a population (all ages) during a single time interval–> can look at highly mobile/long lifespan species
population dynamics
variation in population size over time/space
populations fluctuate
changes in availability of food and resting sites, predation, competition, disease, parasites, weather, climate
- can be driven by predators (boom/bust cycle follows predator boom/bust cycle
fluctuation is the rule…
K, small vs large population
density dependence affects population size
- populations tend to increase or decrease toward equilibrium numbers around their carrying capacities (K)
- small, short-lived organisms may fluctuate wildly
- long-lived populations of species include individuals born over a long time period–> even out effects of short-term fluctuations
when certain age group contains unusually high/low number of individuals, it suggests that…
the population experienced unusually high birth/death rates in the past
periodic cycles
regular oscillations between highs and lows in the population
- often related to the periodic cycles of other species
- drivers of natural population cycles can occur over large areas
overshoot
grow beyond their carrying capacity
- can occur when carrying capacity of a habitat decreases from one year to the next
die-off
substantial decline in population density that typically goes well below carrying capacity
delayed density dependece
when density dependence occurs, but it is based on the population density at some time in the past
𝜏
the time difference between now and “some time in the past”
- as time delay increases, the population is more likely to over/undershoot its carrying capacity
- as intrinsic rate of growth increases, the population grows more rapidly and is also more likely to over/undershoot
what causes delayed density dependence
because of predation, disease, or density-independent event-> population grows–> population growth is sufficiently rapid, population can grow beyond K (delay between initiation of breeding and time offspring are added to the population)–> population overshoots K–> die-off–> population swings back toward K (when population experiences large reduction in size during die-off, can undershoot K)
momentum and population growth and decline
- rapid growth can push a population past its carrying capacity
- rapid decline can cause a population to slip below its carrying capacity
examples of delayed density dependence
- animal can live for time after carrying capacity is reached (can use resources in body, may even reproduce)
- gestation (conditions could be great but takes time to see growth)
- takes time to use those resources (energy taken from new resources, takes time to be converted into new individuals)
ex: predators experience increase in prey–> K increases but it may take time for predators to convert abundant prey into increased numbers of offspring-> prey may no longer be abundant - takes time to reach sexual maturity
when is there a greater chance of oscillations around K
as 𝜏 (time delay) increases and as intrinsic rate of frowth (r) increases
𝜏r= small
fewer oscillations
𝜏r= medium
damped oscillations
𝜏r= big
stable limit cycle
density dependent factors effects on small vs large populations
- large population= density dependent factors cause slow growth
- small population= density dependent factors cause faster growth
deterministic model
a model that is designed to predict a result without accounting for random variation in population growth rate (birth and death rates)
stochastic models
incorporate random variation in population growth rate
demographic stochasticity
r randomly varies among individuals in a population (inherent variation)
- random variations in birth/death rates is due to differences among individuals and not due to changes in environment
environmental stochasticity
r randomly varies due to the environment
- random variations in birth/death rates is due to changes in environmental conditions
why are small populations more likely to go extinct
- chance events exert their influence more forcefully in small populations
all populations, doomed?
no matter what the population size is, chance fluctuations in r cause “bad years”. Given enough time, a string of “bad years” will occur and cause any population to go extinct
subpopulations
when a large population is broken up into smaller groups that live in isolated patches
- this happens because preferred habitat is not continuous–> occurs as patches of suitable habitat surrounding a matrix of unsuitable habitat
are subpopulation fluctuations more synchronous when dispersal among subpopulations is common or rare
- more synchronous when greater dispersal (less isolated with greater dispersal)
- what’s happening in one population influences others
source subpopulations
in high-quality habitats, subpopulations that serve as a source of dispersers
sink subpopulation
in low-quality habitats, subpopulations that rely on outside dispersers to maintain the subpopulation
habitat fragmentation
small habitats represent only a fraction of original habitat
interconnected small populations
- small habitat = small population (more prone to extinction) BUT a group of small populations that is interconnected by dispersal has a dynamic where dispersers can create new subpopulations-> balances extinction/colonization
metapopulation
a system composed of multiple subpopulations geographically separated but functionally connected through dispersal
- generally discussed when each subpopulation has a reasonably high chance of extinction but also of recolonization
- can occur naturally when habitat is patchy
- can also occur because of human activity (clearing forest, draining wetlands, constructing roads, housing, properties)
trends in metapopulations
1) good quality habitat patches tend to be sources, poor quality habitats are sinks (low quality habitats rarely produce enough offspring to produce dispersers-> depend on outside dispersers to maintain subpopulation)
2) small patches are less likely to be occupied than large patches
3) the less isolated an unoccupied patch or declining subpopulation is, the more likely it will be colonized or rescued, respectively
rescue effect
when dispersers supplement a declining subpopulation that is headed toward extinction
SLOSS debate
“Single Large or Several Small”
- Should we conserve species in “megareserves” or many smaller reserves of the same total area?
competition
(-/-)
- a negative interaction between two species that depend on the same limiting resource to survive, grow, and reproduce
Resource
anything an organism consumes or uses that causes an increase in population growth rate when it becomes more available
- ecological factors that cannot be consumed are not considered resources
resources for plants
sunlight, water, gametes, soil nutrients
resources for animals
food, water, mates, and space
renewable resources
resources that are constantly regenerated
- can originate from inside or outside the ecosystem in which competitors live
nonrenewable resources
resources that are not regenerated
intraspecific competition
competition among individuals of the same species
interspecific competition
competition among individuals of different species
exploitative competition
competition in which individuals consume or acquire a resource and thus deprive others of using it (indirect competition)
interference competition
when individuals prevent access to a resource through aggressive or exclusionary methods (direct competition)
allelopathy
a type of interference competition that occurs when organisms use chemicals to harm their competitors
apparent competition
when two species have a negative effect on each other through an enemy (including a predator, parasite, or herbivore)
- Species A experiences more intense predation/parasitism because of the presence of the alternative prey-host (Species B)
- result of change in predator/parasite abundance or behaviors
Leibig’s Law of the Minimum
law stating that a population increases until the supply of the most limiting resource prevents it from increasing further
- when two species compete for a single limiting resource, the species that persists is the one that can drive down the abundance of that resource to the lowest level
competitive exclusion principle
two species that are limited by the same resources cannot coexist indefinitely in the same community
- one species is either better at obtaining that resource or better able to survive when the resource is scarce
character displacement
the evolutionary process through which closely related species diverge in traits, and consequently take advantage of different niches
community
an assemblage of species found together in a specific habitat at a certain time, interacting with each other in that area
how might the competitive exclusion principle affect community assembly
2 hypotheses
1) related species, which should compete strongly, should be found in different habitats (communities)
2) Related species might have similar traits that promote success in a particular environment; these might be found in similar habitats(communities)
to include a second species to the logistic growth equation we add
1) the number of individuals of the second species
2) How much each individual of the second species affects the carrying capacity of the first species
𝛼
competition coefficient for species 1, which converts individuals of species 2 into the equivalent number of individuals of species 1
𝛽
competition coefficient for species 2, which converts individuals of species 1 into the equivalent number of individuals of species 2
zero population growth isocline
population sizes at which a population experiences zero growth
predation/parasitoidism, parasitism, herbivory
(+/-)
introduced, exotic, or non-native species
species that are introduced to a region of the world where they have not historically existed
invasive species
introduced species that spread rapidly and negatively affect other species
mesopredators
relatively small carnivores that consume herbivores
top predators
predators that typically consume both herbivores and predators
active hunting strategies
spend most of their time moving around looking for prey
ambush
(sit-and-wait)
- lie in wait for prey to pass by
hunting can be thought of as a series of events including…
detecting, pursuing, catching, handling, and consuming prey
antipredator adaptations
traits that increase an organism’s avoidance or survival following encounters with predators
activity reduction
- antipredator strategy
- reduce activity to avoid being detected by a predator
activity increase
- antipredator strategy
- increase certain activities that will reduce risk
- ex: alarm calling
crypsis
camouflage that either allows an individual to match its environment or breaks up the outline of an individual to blend in better with the background
- antipredator adaptation
aposematism
- antipredator strategy
- warning coloration
- a strategy where distastefulness (or being “dangerous”) evolves in association with very conspicuous colors and patterns
- predators have innate aversions to aposematic colors; others learn to avoid certain colors and markings through experience
batesian mimicry
when palatable species evolve warning coloration that resembles unpalatable species
mullerian mimicry
when several unpalatable species evolve a similar pattern of warning coloration
structural defense
- antipredator strategy
- reduce a predator’s ability to capture, attack, or handle prey
structural anti-herbivore adaptations
- selective pressure from herbivores has caused the evolution of plant defenses
- some have phenotypically plastic defenses induced by attack, wherease others have fixed defenses
- structural defenses (ex: sharp spines, hair) deter herbivores from consuming leaves, stems, flowers, and fruits
- chemical defenses include sticky resins and latex compounds that are hard to consume, and alkaloids that have a wide range of toxic effects
plant chemical defenses against herbivory are VERY important to humans
most spices, seasonings, condiments, and perfumes are made using plant substances that actually function as toxins to insects or other herbivores
