Ecology Flashcards
Ecology
the study of relationships between living organisms, and their physical environment.
*highly interdisciplinary- genetics, evolutionary bio, physics, and chem, geography, ethnology, demography, sociology
Individuals
metabolism, behavior, life-history
Populations
con specifics living in the same habitat
Meta populations
populations connected by migration/dispersal
Communities
interacting populations of different species
Ecosystems
including their physical and chemical characteristics
Complex
describing something that is dynamic; composed of many interacting agents; network structure; nonlinear interactions
Adaptive
respond to change; adapt to new conditions; evolve
First Law of Ecology
If left unchecked, populations will grow/ decay very fast (aka exponential growth or decay)
Limiting factors of Population Growth (as defined by Malthus)
Food resources, war, famine, abortion, economic factors, and delayed marriage
Carrying capacity
the maximum population size an environment can sustain indefinitely
Intra-specific competition
a special case of density-dependent growth: the per-capita growth rate depends on the density of the population
Second Law of Ecology
No population is left unchecked for a long time (but it could be long enough to cause great damage)
Bistable dynamic system
a dynamical system that has two stable equilibrium states
Allee effect
The idea that populations could grow faster when in groups than in isolation
Formula: rate of the populations’ change over the change in time = r(N)(N/A-1)(1-N/K)
Possible processes leading to Allee effect:
- finding a mate can be hard when the population is at low abundance.
- social cooperation could help escaping predators.
- social hunting could be beneficial.
- inbreeding depression.
- demographic stochasticity
Critical population size:
A
Catastrophic bifurcation (critical transition)
small changes in conditions trigger extreme, discontinuous
responses that might be difficult to reverse
Critcal slowing down
When N is close to A, making (N/A-1) = ~0 [the rate of change in the population slows]. Or, A is increasing, the perturbations will slow down.
Summary of Week 7 notes
• Dynamical systems can have different attractors.
• Stochastic fluctuations can move the system between states.
• Allee effect is sufficient to create bi-stable systems.
• Bistable systems can be re-created in the laboratory, and the approaching of a critical transition can be
measured.
• In natural systems, we observe similar dynamics.
• This is especially worrisome in the case of fisheries—many cases of collapse in the past 20 years.
• We need more holistic approaches for determining what can be harvested.
Summary of Week 6 notes:
• Human population has grown rapidly (1800, 1B; 1927, 2B; 1960, 3B; 1974, 4B; 1987, 5B; 1999, 6B;
2011, 7B).
• Humans have strong impact on the environment.
• Natural populations will initially growth very rapidly if unchecked (geometric, exponential).
• However, soon they will reach an asymptote (logistic).
• Humans were able to keep moving the asymptote by changing the environment and through technological
developments.
• Human populations follow a demographic transition, going from high mortality and high natality, to
low mortality and low natality.
• The stage in which mortality is low and birth rates are still high yields a rapid rise in population
numbers.
Hysteresis
Multiple states may persist under equal environmental condition
Global equilibrium
only one point of equilibrium
Demographic stochasticity
math ratios that lead to extinction
Continuous population growth models are more appropriate for human populations. WHY?
Humans give birth with roughly equal probability on all days of any given year. Discrere population growth models are appropriate for populaions with varied probabilities of birth at certain times.
Are carrying capacity and growth rate always constant?
NO!! They can be changed as seen with the human population. This means that the human population cannot be fitted to a logistic model.
On a dX(t)/dt v. X(t), what does a point @ y=0 represent?
An equilibrium population density predicted by the model
Locally, asymptotically stable means?
The population will eventually (not necessarily quickly) return to the equilibrium after a small perturbation
What’s the difference b/t exponential and logistic growth?
Per capita growth rate of the population (1/X dX/dt) is equal to the intrinsic growth rate (r) at all population sizes fr exponential growth but not for logistic growth.
For a population growing according to a static life table, then…
The number in each age class will increase and the proportion in each age class will eventually stabilize
dX(t)/dt = rX(t) is the model for…
Continuous growth of a population
Long period and higher amplitudes in a population versus time graph is caused by…
with a long time lag…the growth rate depends on the population size a long time in the past, so that it continues to undershoot and overshoot K
The equation is N(t+1) = (1+x)N(t)
How do you find the x?
You are given the equation N(t) = N-naught(exp(-0.0001216t)), how do you find t?
ln(N(t)/N-naught) divided by -0.0001216 = time
Signs of density dependence in a population:
- Direct density dependence occurs when the population growth rate varies as a causative inverse function of population size or density.
- The ecological mechanisms of density dependence are competition, and in some circumstances, predation (including parasitism and disease).
- Density dependence is most commonly tested by examining the relationship between the population growth rate (or individual demographic rates) and population density, either observationally or experimentally.
How to calculate net reproductive rate:
The net reproductive rate is the lifetime
reproductive potential of the average female, adjusted for survival. We can
calculate it by multiplying the standardized survivorship of each age (lx) by its
fecundity (bx), and summing these products.
- “The sum of lx times bx as x goes from 0 to k.”
if R0 > 1, then the population
will grow exponentially, if R0 < 1, the population will shrink exponentially, and
if R0 = 1, the population size will not change over time.
An example of demographic stochasticity is: “In the dusky seaside sparrow, loss of habitat led the population to plummet to 6, all of which happened to be males”
-sex ration imbalance would lead to the extinction of the species…SAD
if the population densities are close to 0 (X<
EXPONENTIALLY EXPLODES, soorry no, grows
Allee effect is caused by…
- finding mate can be hard when the population is at low abundance
- social cooperation culd help escaping predators
- social hunting could be lethal
- inbreeding depression
- demographic stochasticity
(N/A - 1)(1 - N/K)
Why has the maximum sustainable yield concept frequently failed?
- natural flutuations in populations are not taken into account
- the models are difficult to parameterize
- age structure matters, and is not incorporated in the model
Attractor
a state that a system will naturally tend towards, from many starting points
The greatest long term harvest is achieved
at the point below its equilibrium, intermediate value
Critical slowing down
slower return to the ecosystem state from which it was perturbed
Size of basin of attraction
resilience
Bifurcation
tipping point
Bottom of basin of attraction
line of stability
Evolution in ecological interactions
- viruses have high mutation rates
- viruses have short generation times
- viruses potentially have a large selective impact on the host
in serial passage experiments
the pathogen increase in virulence
Why would a disease evolve to intermediate virulence?
high virulence kills too fast to be tansmitted, low virulence doesn’t produce enough propagules to be picked up by vectors
Where the predator and prey isoclines cross in a predator-prey phase portrait of the Lotka-Volterra equations is a point of stability:
is it unstable; small deviations will lead to regular oscillatons and no return to the point
If you were to effect the benefit resources of the prey/predator population, would the that population reap the rewards in effect or the latter.
The latter
In the SIR model
individuals can leave but not re-enter the susceptible class
How do you calculate minimum fraction of vaccination for a populagton given the R-naught of the disease?
p(i.e. the critical vaccination fraction) > [1 - (1/R-naught)]
under the SI model of infectious disease, the number of infected individuals grows
logistically until I=N
R-naught, in the SIR model, means
the number of infections spread by the first infected individual in a population of susceptible
We assume that there are no births in te populations when modeling an infectious disease epidemic because…
the time over which we are modleing the epidemic is assumed to be short enough that we can discount births
We need to include birth and death rates in an endemic disease model because
an endemic disease persists in a population over a long enough time period that we can’t ignore the effects of births and deaths on the numbers of individuals in certain classes; a epidemic disease spreads and then goes away over a short time
Isocline
a line along which a species’ growth rate is 0
According to the L-V model, the outcome of an interaction may depend on
- the initial population sizes of the two species
- each species’ carrying capacity
- the effect that the two species have on each other
Assumption not included int the L-V model
- the prey compete with themselves
Mathematically evaluation of the generality of the principle of competitive exclusion
setting the competition coefficients very close to one and observing that the range of coexistence is very narrow
In models with more than two competing species
we can get chaotic dynamics over time and stable limit cyckes
Person-to-person transmissin
Direct contact (i.e. exchange of blood or other bodlily fluids); vertical (mother to child)
Indirect disease transmission
Airborne, vector-borne, food-borne
Types of interactions b/t species
- Competition (-,-)
- Antagonism (+,-); e.g. consumption, parasitism
- Mutualism (+,+); e.g. pollination, seed-dispersal, symbiosis
- Amensalism (-,0)
- Commensalism (+,0)
Ecological Network Structure
- Food webs (who eats whom?)
- Pollination networks (plant-animal; bipartite)
- Herbivory (bipartite)
- Parasitism (parasite/ parasitoid-host; bipartite)
Cooperation
Within cells- is the origin of eukaryotic organelles endosymbiotic
b/t cells- multicellular
b/t individuals- group hunting and defense
b/t species- mutualism, symbiosis
Difference b/t deterministic and stochastic strategies
Deterministic- no randomness
Stochastic- random choice
Difference b/t reactive and non-reactive strategies
Reactive: reacts to the previous move
Non-reactive: doesn’t react to the previous move
Differences of memories
the strategy uses no information on the previous move (Memory
0)
information on the previous move of the opponent (Memory 1/2)
information on the previous move
of both player (Memory 1)
Direct reciprocity
I scratch your back, you scratch my back
Indirect reciprocity
Golden rule — I scratch your back, somebody will
scratch mine
Values of 0 equlas the growth rates of the predator or prey population
dP/ dt = 0 @ d/ ac or beta
dV/ dt = 0 @ r/ beta or c
Interspecific competition
is a form of competition in which individuals of different species compete for the same resources in an ecosystem (e.g. food or living space)
Intraspecific competition
an interaction in population ecology, whereby members of the same species compete for limited resources. This leads to a reduction in fitness for both individuals. By contrast, interspecific competition occurs when members of different species compete for a shared resource.
The Prisoner’s Dilemma is a dilemma because
the only rational strategy in a single round of the game is to play “Defect” even though the payoff
for mutual cooperation is greater than the payoff for mutual defection.
Under the assumptions of the Lotka-Volterra predator-prey model,
predator and prey densities oscillate over the long term, with peaks in predator density occurring
after peaks in prey density.
Joint equilibrium point
The point population at which the equilibrium isoclines for predator and prey populations cross
Neutral stability
The system stays where it is, either at the joint equilibrium point or cycling around it, until it is pertubed
The relationship b/t the per capita growth rate, r, and per gen. growth rate (R-naught)
r = (Ln(R-naught)/T)
