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an interspecific interaction in which the net benefits to both partners are usually positive
Mutualism
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an intimate interspecific association usually lasting the lifetime of the participants. May be mutualistic, neutral or antagonisitic
Symbiosis
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Interaction in which partners depend on each other in order to reproduce
Obligate mutualism
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Interaction type in which mutualist partners can survive in the absence of the mutualism. Multiple species may be involved.
Facultative mutualism
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usually describes cases where one species benefits; the
other experiences little to no benefit.
Facilitation
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Mutualisms (+/+) and host-parasite interactions (+/-) sometimes form _____________
A continuum
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Mutualisms should be viewed as instances of ________________
Mutual exploitation
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Examples of obligate mutualisms (3)
1) Lichens (symbiotic association between a photoautotroph that provides fixed Carbon and a fungus that provides structure/UV and herbivore protection)
2) Yucca and its sole pollinator, tegiticula (moth)
3) Figs and fig wasps (figs get pollinated; females colonize, lay eggs in fruit; larvae develop inside fig, mating occurs in figs)
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Types of facultative mutualisms (4)
- a. plant - pollinator interactions (many)
- b. protection mutualisms
- c. plants and N-fixing bacteria
- d. plants and mycorrhizal fungi
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transfer of male gametophyte of seed plants (pollen) from anthers to the female organs (stigma) for fertilization of ovule
Pollination
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Bees that feed on nectar and pollen of just a few plant species are known as _________; usually _________
Oligolectic; Solitary
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__________ bees are mostly ____________, meaning they feed on nectar & pollen of many plant species
Eusocial; polylectic
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Examples of cheating in mutualisms (2)
Orchids and wasps, orchid looks like a female wasp
Nectar robbing--drilling holes in flowers to obtain nectar but avoid pollen
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Example of a protection mutualism
Ants and plants
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Humans have __________ population growth; many organisms in contrast have ____________ population growth
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dN/dt refers to ___________
The growth rate of a population
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The value of r expresses population change on a _______________ basis
Per capita
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With exponential growth, per-capita growth rate is ______________ with population size
Constant
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Exponential growth is a __________ feedback
Positive (destabilizing)
-
A continuously accelerating curve of increase
Exponential growth
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N(t) = N(0) ert is used to predict ________________, assuming the population is experiencing ___________
- The number of individuals at a particular point in time;
- Exponential growth
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Exponential population growth rate __________________ with population size
Increases linearly
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Exponential per-capita population growth rate _______________ with population size
Does not change
-
t = (ln 2) refers to ___________
r
Doubling time in an exponentially growing population
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Typically, the __________ a species' body size, the __________ its doubling time
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As per-capita growth rate increases, doubling time __________
Decreases
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The logistic growth model must be modified to include ________
Carrying capacity (K)
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Population size when dN/dt becomes zero
Carrying capacity
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In logistic growth, population growth rate __________
Reaches its maximum at K/2 (hump-shaped curve)
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In logistic growth, the per-capita rate of increase ___________________
Decreases linearly with N
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Interaction strength refers to ______________
The impact that one species has on the abundance of another
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If interaction strength is greater than 1, ______________________
There is a NEGATIVE effect of the focal species on the target species (target species goes up when focal is removed)
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Hypotheses for the evolution of semelparity
- 1) Environmental uncertainty
- 2) Predator satiation
- 3) Unproductive environments and/or slow growing organisms
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Why might complex life cycles evolve?
Break down/prevention of disease transmission
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3 common life history tradeoffs and examples
- Survival vs time to maturity (cod fishing)
- Number vs size of offspring (fish)
- Survival vs reproduction (rotifers)
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What is discrete time? What do we use it to model?
A way of modeling populations with discrete reproductive periods, rather than continuous.
Geometric population growth
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Survivorship vs survival
- Survivorship = probability of living from birth to a particular year, lx
- Survival = probability of living from one year to the next, sx
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What do we use survivorship and fecundity to calculate?
Net reproductive rate of a population (R0)
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When R0 > 1, ___________
When R0 < 1, ___________
When R0 = 1, ___________
- The population is growing
- The population is declining
- The population is stable
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Advantages of life tables (2)
Works well for organisms that can be resampled easily, plants and sessile animals
Can be useful for conservation planning when you know the species' sensitivity to population growth at different life stages
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Disadvantages of life tables (2)
- Hard to apply to mobile animals
- Does not account for changes due to environmental variation
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3 reasons it is hard to define communities
- Interactions are cryptic
- Boundaries are porous
- Species ranges vary hugely
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Holistic view of communities sees them as _______ units of _______ species, with ________ boundaries. Known as "_________ communities"
- Discrete
- Highly interacting, co-evolving
- Recognizable
- Closed
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Individualistic view of communities sees them as __________ of species with __________ boundaries. Known as "_________ communities"
- Random associations
- Unrecognizable
- Open
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What is an ecotone (3)
- Area of rapid replacement of species between 2 environments
- Often defined by abrupt change in the environment, giving it a sharp boundary
- More species here than in adjacent communities
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What are trophic subsidies
Linkages between communities that occur when nutrients or resources move across boundaries and affect the new community
Exemplify the problem of leaky borders in communities
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Depicts paths of energy flow through populations in a community, acknolwedging that each species shares resources and consumers with other populations
Food web
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Depicts the passage of energy from a primary producer through a series of consumers at progressively higher levels
Food chain
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Position in the food chain, determined by the number of energy transfer steps it takes to get there
Trophic level
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What 2 processes result in indirect interactions?
- Trophic cascade
- Trophic facilitation
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Two hypotheses of why food chains are usually short
- Energetic hypothesis (E runs out before chain gets long)
- Dynamic instability (low-level fluctuations lead to extinction of top levels)
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Formula of trophic position and what the variables mean
- n = # of prey species
- TPprey = trophic position of prey
-
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How do you test for bottom-up control?
Add limiting resource to the primary producer. If it is bottom-up control, everything will increase
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How do you test for top-down control?
Remove predator. If you see more herbivores and fewer primary producers, it is top-down.
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What are trophic cascades?
Changes in the rate of consumption at one trophic level that affects abundance or composition of lower trophic levels
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Example of trophic cascade
More bees near ponds with fish that eat bee predators (dragonfly larvae)
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Benefits of plants in plant-pollinator mutualisms (2)
- More efficient, direct pollen transfer (than wind dispersal)
- Outbreeding made possible
- Spacing out of pollen that reduces intraspecific competition and pest outbreaks
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Effects of fishing (4)
- 1) Decrease total fish biomass
- 2) Mainly affects top predators, who can't recover quickly enough
- 3) Communities dominated by smaller fish
- 4) Meso-predator release, and thus no herbivore explosion
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Ways of defining communities (5)
- Physical environment
- Biological/what species are in a given area
- Taxonomically
- Guild
- Functional group
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How do we estimate K?
Set dN/dt to 0 and solve for K when the population is no longer growing
-
Aquatic systems have inverted pyramids because __________________, while terrestrial systems do not, because _______________
High turnover rate in primary producers --> sustains a large top predator population
Low turnover rate of primary producers --> bottom of trophic pyramid will always be large
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Example of positive density dependence
California abalone -- need high density to grow
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Example of negative density dependence
Mountain lions -- low growth at high populations
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Specialists have ______ trophic positions than generalists because they have __________ numbers of prey
-
World is green because __________
Plants produce more biomass than can be eaten, as predators limit herbivores
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If removal of predators results in effects of a trophic cascade, then the population is experiencing ____________ control
Top-down
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Red curve is _____________, i.e. that of __________
-
Purple curve is ______________, i.e. that of _______
-
In population dynamics, regulation refers to __________________
Leading the population to a stable equilibirum, i.e. bringing it down when it is above K, and bringing it up when it is below K
-
Example of negative density dependence
Song sparrows raise fewer babies when there are more female birds on the island
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__________ Density Dependence
Negative
-
__________ Density Dependence
Positive
-
Mechanisms of positive density dependence (3)
- Allee effect
- Overwhelm predators
- Affect the structure of the environment
-
Intrinsic variation causes populations to cycle periodically when ________________, and aperiodically when __________________
- The populations show lag density dependence
- Population dynamics are complex/chaotic
-
Extrinsic variation causes populations to cycle periodically when __________, and aperiodically when _________
- The environment is predictable, ie seasonal
- The environment varies irregularly
-
Small populations are at risk of extinction because of (4):
- Allee effects/Positive density dependent growth
- Inbreeding depression
- Environmental stochasticity
- Demographic stochasticity
-
(1/N) (dN/dt) refers to _______
Per capita growth
-
High risk factors of extinction (3)
- Small population size
- High growth rate ("cranking up r0"), can lead to chaos
- Environmental stochasticity
-
Humans have a _________ survivorship curve
Convex
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In the Discrete Time /geometric population growth model, N(t) = N(0) * (lambda)t , What do t and lambda stand for?
t = # of time steps
lambda = Nt+1 / Nt
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Random variation in survival and reproduction
Demographic stochasticity
-
Higher levels of stochasticity lead to more variability, and thus a larger __________ of lambda
standard deviation
-
2 factors that increase variability of lambda
- More variable environment
- More demographic stochasticity
-
Delayed density dependence can occur in (3)
- Predator/prey cycles
- Complex life cycles
- Discrete generations
-
Stable limit cycle refers to ______________ oscillations above and below K. This happens with a large _______
- Regularly fluctuating
- Time lag (weird T)
-
Species example of delayed density dependence
Blowflies
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In delayed density dependence, cycles can result from _______ in the response of populations to _____________
- Time lags
- Their own densities
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A metapopulation is ______________
A population divided into subpopulations among which individuals migrate
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In metapopulation models, "p" refers to ________. When p = 0, _____________
When p = 1, _____________
- Fraction of sites occupied
- All sites are unoccupied, metapopulation is extinct
- All sites are occupied, landscape is saturated
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In metapopulation dynamics, "I" refers to __________, or _____________, and "E" refers to _________, or _______________
- Immigration rate, proportion of sites colonized per unit time
- Extinction rate, proportion of sites that go extinct per unit time
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To find "I" in metapopulation dynamics, you use the equation c*p(1-p). What does c refer to, and what does (1-p) refer to?
- c = colonization rate
- 1-p = proportion of vacant patches
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To find "E" in metapopulation dynamics, you use the equation ep. What does "e" stand for?
e = probability that an occupied patch will go extinct
-
In metapopulation dynamics, dp/dt refers to _______, and is calculated as _________
Change in # of occupied patches per unit of time
I-E
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At equilibrium in metapopulation dynamics, dp/dt = __
0
-
By using the metapopulation equilibrium equation of the change in occupied patches over time,
Pequil = 1 - (e/c), if e = 0, _______; if e = c, _______, and if e is between 0 and c, __________
- All sites are occupied, Pequil = 1
- Metapopulation heads towards extinction, Pequil = 0
- There is a shifting mosaic of occupied and empty sites
-
Model assumptions of metapopulation dynamics (3)
- All sites are equal
- Rates of extinction and colonization don't change
- No spatial structure--E and I are not affected by spatial arrangement of sites
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What do the results of the metapopulation colonization model, Pequil = 1 - (e/c), show us the importance of?
- Preventing habitat patches from becoming too isolated
- --> Can do this by maintaining corridors between patches
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Advantages of increased connectivity (2)? Disadvantages (3)?
Can increase movement, shown to work in birds
Costly and possibly harmful, can increase edges/ecotones, often compromised bc of development
-
How can a plant be a predator?
- By relying on invertebrates and bacteria to "digest" prey, by decomposing it and respiring nutrients
- More like a mutualism
-
Scavenging predators, like ________, combine _______ and ___________
- Hyenas, coyotes
- Predation and scavenging
-
Intermediate between predators and parasites, develop on or in their hosts and usually kill or consume it
Parasitoids
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Parasitoids are ________ of their prey than parasites
Much choosier
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Who supports more scavenging, humans or wolves? Why?
Wolves, more consistent in space and time
-
Develop on or in hosts, forming an intimiate association
Parasites
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Herbivores, who eat ____, can function like _________, and like ____________
Example?
- Plants
- Predators, when they eat whole plants/seeds
- Parasites, when they eat parts of a plant
- Deer
-
Example of a non-lethal effect of a predator on its prey?
Moose hanging out near roads when there are lots of bears
-
Predators can regulate their prey populations in both ______ and _______
-
When prey abundance affects predators, but predators don't affect prey, this is known as ___________
Donor control
-
When can donor control happen? (2)
When predators only have access to a small part of the prey population, like sea birds on fish populations
When predator populations are controlled by something other than prey availability
-
On a graph, donor control is a __________ correlation between the predators and prey,
predators ________ populations of prey
-
On a graph, predator regulation of its prey is a ________ correlation, in which the predator has a strong __________ effect on the prey population
-
You expect predators to have a big effect on prey when their population growth rate is _________,
When they have a ______ dispersal ability, and when they are resource _________
- Similar to that of their prey
- High
- Generalists
-
Lynx and hares exhibit _______, hares peak ~_____ the lynx population
- Synchronized cycles
- 1 year before
-
Hares in predator-prey cycle have the highest reproduction rate when their density is ____
Low
-
Protozoan experiments of predator-prey cycles illustrated the importance of __________
Prey refuges
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In predator-prey cycle experiments of paramecium, When prey had no refuge, _________,
When prey had refuge, ____________,
When predators were restocked, _________
- Both went extinct
- Predator went extinct
- Predator-prey cycles occurred predictably
-
Predator-prey cycles occur when (2), but not when (2)
- Predators have strong regulating impact on prey
- Prey allow predator population to grow fast
- Prey have refuge
- Prey have defenses
-
The mites predator-prey experiment found that they could co-exist without restocking predators, but that it required _____ dispersal of predators, and _____ dispersal of prey
-
In the mathematical model of predator-prey interactions, we start with the __________ Model, but can omit the _____ part of it
- Logistic growth
- 1 - N/K (Carrying capacity)
-
Amount of prey taken by predators (for the pred-prey interaction model) depends on (3)
- Predator density
- Prey density
- Attack rate of predator
-
To find predation rate (prey losses), we use the equation dN/dt = rN - aNP , with rN referring to ________ and aNP referring to _______
- Exponential growth of prey
- Rate of predation (attack rate x prey density x predator density)
-
Rate at which predators convert prey into new "predators", ie, how many offspring a predator is able to produce for every prey eaten
Conversion efficiency
-
In predator population models, e ______ with the value of individual prey items
Increases
-
In predator-prey models, N refers to ________, and P refers to _______
- Prey population size
- Predator population size
-
in the predator population model, we use the formula dP/dt = aeNP - dP , where aeNP refers to ______, and d refers to ________
- Predation rate x conversion efficiency
- Death rate of predators
-
Equilibrium predator-prey equation becomes
Pequil = r/a , (Prey equilibrium, in terms of predator population), where r = ______ and a = ________
- growth rate of prey population
- attack rate of predation
-
In the prey equilibrium model, an increase in r (growth rate of prey) and/or a decrease in a (attack rate of predation) lead to a(n) ___________ in predator density
Increase
-
In the predator equilibrium model, an increase in d (death rate of predators) leads to a(n) __________ in prey population
An increase in a (attack rate) or e (conversion efficiency) lead to a(n) _________ in prey density
-
Point where the predator and prey isoclines cross, at which neither population is changing
Joint equilibrium
-
Name 3 stabilizing factors of the inherently unstable predator-prey cycle.
- Reduced time delay in predator’s response to changes in prey abundance
- Prey phenotypic plasticity--behaviorally, they can hide in refuge, for instance
- Low predator attack rate
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